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+The Project Gutenberg EBook of ASCE 1193: The Water-Works and Sewerage of
+Monterrey, N. L., Mexico, by George Robert Graham Conway
+
+This eBook is for the use of anyone anywhere at no cost and with
+almost no restrictions whatsoever.  You may copy it, give it away or
+re-use it under the terms of the Project Gutenberg License included
+with this eBook or online at www.gutenberg.org
+
+
+Title: ASCE 1193: The Water-Works and Sewerage of Monterrey, N. L., Mexico
+       The 4th article from the June, 1911, Volume LXXII,
+       Transactions of the American Society of Civil Engineers.
+       Paper No. 1193, Feb. 1, 1911.
+
+Author: George Robert Graham Conway
+
+Release Date: December 31, 2011 [EBook #38455]
+
+Language: English
+
+Character set encoding: ISO-8859-1
+
+*** START OF THIS PROJECT GUTENBERG EBOOK ASCE 1193: THE WATER-WORKS ***
+
+
+
+
+Produced by Juliet Sutherland, Henry Gardiner and the
+Online Distributed Proofreading Team at http://www.pgdp.net
+
+
+
+
+
+
+       *       *       *       *       *
+
+Transcriber's Note: Words in italics are indicated like _this_. Subscripts
+are indicated like this: H_{2}O. The original publication has been
+replicated faithfully except as listed at the end of the text.
+
+       *       *       *       *       *
+
+
+
+
+                           TABLE OF CONTENTS
+
+
+          INTRODUCTORY.                                    475
+          THE CONCESSION.                                  476
+          GEOLOGY AND TOPOGRAPHY.                          476
+          POPULATION, AREA, AND MORTALITY.                 479
+          RAINFALL AND TEMPERATURE.                        480
+          AVAILABLE SOURCES OF SUPPLY.                     484
+          MATERIALS FOR CONCRETE.                          491
+          ESTANZUELA SUPPLY.                               494
+          SOUTH DISTRIBUTING RESERVOIR.                    506
+          SAN GERONIMO GRAVITY SUPPLY.                     514
+          DISTRIBUTING RESERVOIR AT OBISPADO.              525
+          COMPARISON OF SOUTH AND OBISPADO RESERVOIRS.     530
+          ANALYSES OF ESTANZUELA AND SAN GERONIMO WATERS.  532
+          CITY WATER DISTRIBUTION SYSTEM.                  532
+          MAIN SEWERAGE SYSTEM.                            539
+          MAIN OUTFALL SEWER.                              542
+          SEWAGE DISPOSAL WORKS AND IRRIGATION LANDS.      545
+          QUALITY OF AND RATES FOR LABOR.                  552
+          COST OF WORKS.                                   552
+          TARIFFS AND SANITARY REGULATIONS.                553
+          ENGINEERS, ETC.                                  556
+          DISCUSSION.                                      557
+          JAMES D. SCHUYLER.                               557
+          DAVID T. PITKETHLY.                              559
+          V. SAUCEDO.                                      563
+          GEORGE T. HAMMOND.                               567
+          RUDOLF MEYER.                                    576
+          GEORGE ROBERT GRAHAM CONWAY.                     580
+
+
+
+
+                   AMERICAN SOCIETY OF CIVIL ENGINEERS
+
+                           INSTITUTED 1852
+
+                             TRANSACTIONS
+
+                            Paper No. 1193
+
+                    THE WATER-WORKS AND SEWERAGE OF
+                       MONTERREY, N. L., MEXICO.[1]
+
+            BY GEORGE ROBERT GRAHAM CONWAY, M. AM. SOC. C. E.
+
+     WITH DISCUSSION BY MESSRS. JAMES D. SCHUYLER, DAVID T. PITKETHLY,
+         GEORGE S. BINCKLEY, VICENTE SAUCEDO, GEORGE T. HAMMOND,
+             RUDOLF MEYER, AND GEORGE ROBERT GRAHAM CONWAY.
+
+
+
+
+                              INTRODUCTORY.
+
+
+[1] Presented at the meeting of February 1st, 1911.
+
+Monterrey, the Capital of the State of Nuevo León, Mexico, is built on
+the site of the old village of Santa Lucía de León, which was
+established in 1583 by the Governor of the Kingdom of León, Don Luis
+Carabajal. Four years later Carabajal was imprisoned by the Inquisition,
+and the village of Santa Lucía was abandoned by its few inhabitants.
+
+In 1596, Captain Diego Montemayor, a resident of Saltillo, in the
+adjoining State, wishing to render a service to his king, Philip II of
+Spain, assembled his friends, and on September 20th of that year,
+proceeded to establish a town on the site of the old village on the
+northern side of the principal spring at the place. The town was named
+"Nuestra Señora de Monterrey" (Our Lady of Monterrey), after the Count
+of Monterrey (Ojos de Santa Lucía y Valle de Extremadura), the ruling
+Governor of New Spain, as Mexico was then called.
+
+Monterrey is approximately in the center of the State of Nuevo León, 1°
+12´ west of Mexico City, and in latitude 26° 40´ N. It is a distributing
+railway center on the main line of the National Railroad, 270 km. from
+the Rio Grande at Laredo, 1,022 km. from Mexico, and 520 km. from
+Tampico by the Mexican Central Railway. It is the center of many large
+industries, and is the second largest manufacturing city in the
+Republic.
+
+
+
+
+                            THE CONCESSION.
+
+
+The works described in this paper were carried out under a guaranteed
+concession granted by His Excellency, General Bernardo Reyes, Governor
+of the State of Nuevo León, to Messrs. James D. Stocker and William
+Walker, of Scranton, Pa. The concession is dated October 19th, 1904, and
+is for 99 years from that date; the works for a complete water and
+drainage system were to be finished in 3 years from the time of their
+commencement. Before the works were designed and begun, the concession
+was acquired by Mr. William Mackenzie, of the firm of Mackenzie, Mann
+and Company, Limited, of Toronto, Ont., Canada, who, on May 4th, 1906,
+organized the Monterrey Water-Works and Sewerage Company, Limited
+(Compañía de Servicio de Agua y Drenaje de Monterrey, S. A.), under the
+laws of the Dominion of Canada, of which company he is President. Mr.
+Mackenzie is also President of the Monterrey Railway, Light, and Power
+Company, Limited, which was constructing the street railways of
+Monterrey concurrently with the water-works. Under the provisions of the
+concession, the Government appointed a Financial Interventor, who had
+authority to examine and check the company's expenditures, and also a
+Technical Inspector to examine and report on the construction. The
+duties of these officials also apply to the operation of the system when
+the construction is finished. The Government has the right, after the
+system has been operated 40 years, to purchase the entire property,
+subject to 6 months' notice, for a sum equal to 16-2/3 times the average
+annual net proceeds during the 3 preceding years. This right may be
+exercised at the end of 40 years, or at the end of any 10-year period
+thereafter, up to 99 years from the commencement of operations.
+
+
+
+
+                         GEOLOGY AND TOPOGRAPHY.
+
+
+Monterrey lies in a plain at the foot of the Eastern Sierra Madre
+Mountains which constitute the eastern margin of the Mexican Cordilleran
+Plateau, and is surrounded by the magnificent mountains of that group,
+among the most notable of which are the beautiful Mitra and Silla
+Mountains. In the neighborhood of Monterrey these mountains attain
+heights of from 2,000 to 2,400 m., and are noted for their broken and
+jagged sky-lines. The leading geological characteristics of the district
+are the uplifted limestones of the older cretaceous age which form the
+main mass of the mountains.
+
+Primarily, the mountains are compressional folds which, in the Sierra
+Madre, near Monterrey, are close and vertically compressed.[2] The
+drainage areas of the Santa Catarina River, which flows through
+Monterrey, and of the Estanzuela and Silla Rivers, its tributaries, are
+of limestone and shale; originally the shales were above the limestone,
+but the convulsion which formed the Sierra Madre as an anticlinal fold,
+left the originally horizontal strata standing nearly upright, and
+subsequent erosion in the upper part of the anticline has exposed nearly
+vertical strata in many places. The limestone being hard and resisting
+erosion, there is generally, along the line of contact, an abrupt drop
+vertically on the face of the limestone to the shale below. In many
+places this abrupt drop is broken by a limestone talus, but the line of
+contact can generally be traced. Mining operations in these mountains
+have revealed the presence of large caves at a considerable elevation,
+many of which contain large reservoirs of water, delivered to them
+through numerous faults. The river valleys are formed of masses of
+limestone conglomerate and coarse gravels, re-cemented in many cases by
+the lime deposits of the flowing waters. One of the chief
+characteristics of the subsoil of Monterrey itself is a local rock
+called "sillar," which is a superficial deposit of carbonate of lime
+from the evaporated waters. In some places the "sillar" is largely mixed
+with a conglomerate called "tepetate," or "impure sillar."
+
+[2] _Transactions_, Am. Inst. Min. Engrs., Vol. XXXII (1902), pp.
+163-178.
+
+[Illustration: PLATE II.--GENERAL PLAN OF THE WATER SUPPLY AND DRAINAGE
+WORKS FOR MONTERREY, N. L., MEXICO.]
+
+Topographically, the region around Monterrey is distinguished by the
+drainage area of the River Santa Catarina, which rises in the Sierra
+Madre near the Laguna de Sanchez, at an elevation of 1,850 m., as shown
+on Plate II. From this Laguna it follows a tortuous course between
+precipitous mountains through the Boca of Santa Catarina to Monterrey,
+for a distance of 90 km., eventually finding its way to the San Juan
+River, a tributary of the Rio Grande. Throughout its course it
+disappears, flows underground, and again appears; and, except in flood
+time, it has a subsurface flow for a distance of 16 km. above the city.
+In the Cañon of Santa Catarina it appears at the surface, having a
+normal flow of about 1,415 liters (50 cu. ft.) per sec., and its waters
+at that point are divided into two parts and carried into irrigation
+canals. The drainage area of the river above Monterrey is 1,410 sq. km.,
+and its bed at Monterrey is between 518 and 545 m. above sea level.
+
+Southward from Monterrey the country rises along the valley of the Silla
+for a distance of 19 km., where the Silla is separated from the San Juan
+by a low divide, the former flowing northward to Monterrey and the
+latter southeastward toward Allende. The Silla Valley is bounded on the
+east and west by the steep ranges of the Silla and Sierra Madre
+Mountains. The floor of this valley is gently rolling, but is cut by
+many arroyos which carry little or no water during the greater part of
+the year. The chief feeder of the Silla River is the Estanzuela, a
+stream which derives its waters from several springs coming to the
+surface near the line of contact between the limestone and the shale, at
+elevations of about 800 and 900 m.[3] above datum. The water-shed of
+this stream is rich with abundant vegetation due to the precipitation
+being greater than on the Santa Catarina water-shed. To the south of the
+divide the country is well wooded, and El Porvenir, 35 km. from
+Monterrey, is the garden spot of the State of Nuevo León. Here the
+rainfall is much greater than at any other point near Monterrey, and
+there are many streams which are used for irrigation purposes. Monterrey
+is built on a plain, chiefly on the north side of the Santa Catarina
+River. This plain has a general fall toward the northeast, and beyond
+the city it slopes gently northward for several miles toward the Topo
+Grande River, and then southeastward to join the great coastal plain of
+the Gulf of Mexico. The general elevation of the city lies between the
+519- and 550-m. contours. The Plaza Zaragoza, in the center of the city,
+is 533.90 m. above sea level; the elevation of the highest part of the
+city, at the western boundary, is 550.05 m., and of the lowest part, at
+the northeastern boundary, 518.0 m. above sea level.
+
+[3] Throughout this paper datum refers to the height in meters above the
+mean sea level of the Gulf of Mexico at the Port of Tampico.
+
+[Illustration: PLATE III, FIG. 1.--GENERAL VIEW OF LINE, ESTANZUELA
+AQUEDUCT.]
+
+
+
+
+                    POPULATION, AREA, AND MORTALITY.
+
+
+The population of Monterrey has increased as follows:
+
+                  Census of   1851      14,621
+                    "  "      1861      26,000
+                    "  "      1871      33,811
+                    "  "      1881      39,456
+                    "  "      1891      41,154
+                    "  "      1901      73,508
+                  (Estimated) 1909      86,000 to 90,000
+
+The greatest progress, it will be noted, was between 1891-1901, with an
+increase of more than 22,000 in 10 years. In designing the new works,
+provision has been made for the future requirements of a city of 200,000
+persons.
+
+The actual area within the city limits proper is 960.5 hectares (2,374
+acres), forming the area to be provided with water and drainage, but the
+municipal district extends to many surrounding suburbs, and covers an
+area of 33,758 hectares (83,426 acres).
+
+        TABLE 1.--POPULATION AND DEATH RATE OF MONTERREY, N. L.,
+                  MEXICO, FROM 1901 TO 1909, INCLUSIVE.
+
+  ============+========+=========+========+=========================|
+              |        |         |        |DEATHS FROM TYPHOID FEVER|
+              | Popu-  | Deaths  | Rate   +----+----+----+----+-----+
+     Year.    |lation. |from all |  per   |    |    |    |    |     |
+              |        | causes. | 1,000. |Jan.|Feb.|Mar.|Apr.|May. |
+              |        |         |        |    |    |    |    |     |
+  ------------+--------+---------+--------+----+----+----+----+-----+
+  Census 1901 | 73,508 |   2,965 |  40.3  |  0 |  2 |  1 |  3 |  4  |
+  Estim. 1902 | 74,500 |   3,338 |  44.8  |  1 |  4 |  2 |  3 |  6  |
+     "   1903 | 76,000 |   3,825 |  50.3  |  3 |  2 |  4 |  1 |  0  |
+     "   1904 | 77,500 |   2,905 |  37.4  |  0 |  1 |  1 |  5 |  3  |
+     "   1905 | 79,000 |   2,951 |  37.4  |  2 |  0 |  0 |  3 |  3  |
+     "   1906 | 80,000 |   2,935 |  36.7  |  1 |  2 |  1 |  3 |  3  |
+     "   1907 | 82,500 |   3,269 |  39.6  |  4 |  6 |  3 |  3 |  5  |
+     "   1908 | 84,000 |   3,188 |  37.9  |  5 |  2 |  5 |  3 |  8  |
+     "   1909 | 86,000 |[4]3,477 |  40.4  |  5 |  1 |  4 |  5 | 13  |
+  ============+========+=========+========+====+====+====+====+=====+
+
+  ============+=========================================+==============+
+              |  DEATHS FROM TYPHOID FEVER. (Continued) | Deaths from  |
+              |----+----+----+----+----+----+----+------+ Typhoid fever|
+  Year.       |    |    |    |    |    |    |    |Total | per year per |
+              |Jne.|Jly.|Aug.|Sep.|Oct.|Nov.|Dec.|for   | 100,000      |
+              |    |    |    |    |    |    |    |year. | population.  |
+  ------------+----+----+----+----+----+----+----+------+--------------+
+  Census 1901 |  3 |  6 |  6 |  3 |  6 |  4 |  2 |   40 |     54       |
+  Estim. 1902 |  5 |  3 |  1 |  1 |  2 |  3 |  5 |   36 |     48       |
+     "   1903 |  5 |  3 |  5 |  6 | 16 |  3 |  1 |   49 |     64       |
+     "   1904 |  3 |  3 |  4 |  1 |  5 |  1 |  0 |   27 |     35       |
+     "   1905 |  7 |  6 |  3 |  2 |  7 |  2 |  2 |   37 |     47       |
+     "   1906 |  6 |  5 |  3 |  2 |  1 |  2 |  3 |   32 |     40       |
+     "   1907 |  6 |  4 |  4 |  9 |  3 |  0 |  3 |   50 |     61       |
+     "   1908 |  5 |  9 |  7 |  2 |  7 |  4 |  0 |   57 |     68       |
+     "   1909 | 11 | 15 | 12 |  6 |  8 |  3 |  4 |   87 |    101       |
+  ============+====+====+====+====+====+====+====+======+==============+
+
+[4] Excluding deaths due to drowning in the great flood of August 27th
+and 28th.
+
+Table 1 gives particulars of the death rate for 1901 to 1909, inclusive,
+and data relative to the mortality due to typhoid fever. The high death
+rate is caused by the excessive infantile mortality, which is so
+prevalent throughout the whole of Mexico. The climatic condition of
+Monterrey, with its exceptionally healthy subsoil, ought to make it one
+of the healthiest of cities, if proper care were taken to enforce
+sanitary laws. The data regarding typhoid mortality are probably
+understated, as they were compiled by the writer, in the absence of any
+official publications, from the actual death certificates, but no
+special care is taken by the authorities to insure accuracy in such
+certificates. Attention is called to the typhoid rate in May, June,
+July, and August, 1909; this high rate coincides with a scarcity of
+rainfall and the greatest period of drought experienced in 30 years, and
+immediately precedes the great flood of August 27th. It was probably due
+to the lowering of the ground-water throughout the city and the
+consequent contamination of the private wells, which were largely in use
+during that time. Throughout the city the wells are sunk to a depth of
+about 12 or 15 m., in order to reach the subterranean waters, and the
+cesspools are often in dangerous proximity to them and at a much higher
+level. The nature of the subsoil, which is often much fissured and open
+in the conglomerate and sillar strata, would make the passage of
+contamination an easy matter, and this alone would account for a high
+mortality due to water-borne diseases.
+
+
+
+
+                       RAINFALL AND TEMPERATURE.
+
+
+The precipitation records of Monterrey and its neighborhood are very
+meager, and cannot be relied on for a longer period than from 1894 to
+1909, inclusive. The records are available from 1886, but in the early
+years there are many apparent discrepancies, and they are probably
+inaccurate. The average rainfall for the 15 years (1894-1908) is 21.94
+in.; the driest years for this period are as follows: 1894, 14.14 in.;
+1902, 15.29 in.; 1907, 15.23 in.; 1908, 15.11 in. Assuming the early
+records to be correct, the average rainfall for the period, 1886-1908,
+would be 19.86 in.
+
+At Saltillo, which is 50 miles due southwest, at an elevation of about
+1,520 m. above sea level, the average rainfall for the 23 years,
+1884-1908, inclusive, is given as 21 in. The maximum year was 1889, with
+33-1/2 in., and the minimum 1903, with 7-1/2 in.
+
+At Carmen, in the State of Tamaulipas, 144 km. southwest of Monterrey,
+at an elevation of about 310 m. above sea level, the average fall for 12
+years is 24.70 in., the maximum year being 1897, with a fall of 34.09
+in., and the minimum year, 1905, with 13.41 in.
+
+[Illustration: FIG. 1.--ANNUAL RAINFALL IN MONTERREY COVERING THE PERIOD
+FROM 1894 TO 1909.]
+
+Fig. 1 shows the annual variation of rainfall at Monterrey for
+1894-1909. Fig. 2 shows the monthly variation during the same period,
+and gives the minimum, average, and maximum for each month.
+
+From these diagrams it will be seen that the months of least rainfall
+are December, January, February, and March, with averages of 0.66, 0.59,
+0.79, and 0.93 in., respectively. The months of greatest rainfall are
+August, with an average of 4.39 in., and September with 4.87 in. The
+maximum in any month prior to 1909 was 16.75 in., during September,
+1904.
+
+_Rainfall in 1909._--The rainfall in 1909 was unprecedented, causing the
+disastrous flood in the Santa Catarina River, which will be referred to
+when describing the works. Fig. 3 shows the monthly rainfall for 1906 to
+1909, inclusive, and has been plotted to show the variation of rainfall
+prior to the great precipitation of August, 1909. In that month there
+were two heavy falls, one beginning at midnight on August 9th, and
+during the following 42 hours a fall of 13.28 in. was recorded by the
+gauge at the Water-Works Company's general offices, 10.20 in. of which
+fell, during the first 24 hours. From 6 P. M. to 11 P. M., on August
+10th, 5.019 in. were recorded, or an average of 1 in. per hour.
+
+[Illustration: FIG. 2.--MONTHLY RAINFALL IN MONTERREY COVERING THE
+PERIOD FROM 1894 TO 1909 INCLUSIVE.]
+
+[Illustration: FIG. 3.--MONTHLY VARIATION OF RAINFALL AT MONTERREY
+1906-1907-1908-1909.]
+
+After 13 dry days, another rainstorm began, at 4 P. M., on August 25th,
+and continued more or less intermittently until August 29th. During this
+98-hour period there was an additional fall of 21.61 in., 11.27 in.
+falling in 24 hours.
+
+The total precipitation during the month amounted to 36.00 in. The
+highest previous record for the month of August was in 1895, with a fall
+of 6.61 in. Fig. 4 gives the details of the two heavy precipitations in
+August. As no automatic recording gauge was available, the maximum
+intensity could only be computed approximately, owing to the
+intermittent character of the readings taken from the ordinary rain
+gauge on the roof of the Water-Works Company's office in the city. From
+the readings thus obtained, it was shown that the maximum intensity
+occurred early on the morning of the 28th, and was nearly 2 in. per
+hour. Above Monterrey, in the Santa Catarina water-shed, it is believed
+that the precipitation was considerably greater, but no gauges were
+accessible during the month.
+
+[Illustration: FIG. 4.--CURVE OF RAINFALL AT MONTERREY DURING AUGUST
+10TH & 11TH AND FROM AUGUST 25TH TO 29TH - 1909.]
+
+The total rainfall for 1909 amounted to 47.46 in., of which 75% fell in
+August. This is 50% greater than the previous highest annual record
+(31.65 in. in 1900) for Monterrey.
+
+_Temperature._--Fig. 6 gives a record of the temperature at Monterrey
+from 1901 to 1909, inclusive. These records were taken at an altitude of
+520 m. It will be noted that the lowest recorded temperatures are in
+January and February. The lowest during these years was 24° Fahr., in
+January, 1905. The monthly maxima vary between 80 and 110° Fahr. The
+mean annual temperature is 72.65° Fahr. (The mean annual barometer is
+28.2 in.)
+
+[Illustration: FIG. 6.--DIAGRAM OF TEMPERATURE VARIATION AT MONTERREY,
+1901-09.]
+
+
+
+
+                       AVAILABLE SOURCES OF SUPPLY.
+
+
+The question of the best sources from which Monterrey should be supplied
+with potable water was one that had been long under discussion, and was
+the subject of many investigations prior to the granting of the present
+concession. Several of the original schemes called for an impounding
+reservoir in the Cañon of Santa Catarina and it was on the assumption
+that a dam would be built that a clause was inserted in the concession
+for the purpose of making its construction obligatory. The general
+character of the physical and geological conditions surrounding
+Monterrey has already been referred to. A thorough study of these
+conditions proved that no suitable site for impounding the Santa
+Catarina River could be found, apart from the fact that periodically
+this river is subject to enormous floods which tear through the steep
+cañon with tremendous velocity.
+
+At the site originally proposed for the dam, a considerable underflow
+was found, and later investigations, carried out under the present
+concession, proved that, although borings were carried to a depth of 54
+m., bed-rock could not be found, the strata being composed of gravels,
+conglomerate and sand. Assuming that such a dam could have been built,
+the quality of the water draining from a comparatively barren
+water-shed, on which many thousands of goats are pastured, would have
+made its filtration an absolute necessity before it could be delivered
+to the consumers.
+
+The various available sources from which water could be delivered to the
+city by gravity were investigated by Mr. F. S. Hyde, in the autumn of
+1905, and also by J. D. Schuyler, M. Am. Soc. C. E., who was afterward
+retained as Consulting Engineer for the Company. The various
+investigations made from time to time showed that the question of a
+satisfactory supply was one of extreme difficulty, requiring prolonged
+observation and study, more particularly into the character of the
+underground sources of supply.
+
+One of the chief characteristics of many of the streams in the State of
+Nuevo León, is their disappearance and reappearance at different points
+along their routes, and the Santa Catarina River, under normal
+conditions, as already remarked, is a very notable example of a river
+which is very dry at the surface for many kilometers of its length. In
+the writer's opinion, the waters of this and similar rivers in the State
+pass through many open caverns underground, so that experience gained in
+the investigation of underflow waters in other places would be
+insufficient to determine the quantity passing at any point along the
+river if ascertained by merely computing it from the velocity of the
+underflow and the area of the water-bearing gravels. The rainfall on the
+water-shed of the Santa Catarina River is probably 25% greater than at
+Monterrey, and all ordinary rains sink rapidly into the limestone soils
+and quickly disappear. In another water-shed of a very similar
+character, namely, that of the Rio Blanco, in the southern part of the
+State, the underflow waters appear at the surface at a place called
+Mezquital, where a metamorphosed sandstone barrier prevents them from
+disappearing underground. At this point the normal quantity of water is
+about 5,660 liters (200 cu. ft.) per sec., but it gradually disappears,
+and a few kilometers below it has sunk to an insignificant stream,
+finally disappearing altogether for about 20 km. In the neighborhood of
+Monterrey similar conditions exist with regard to the surface-water
+supplies, and investigations, therefore, were directed toward obtaining
+unpolluted supplies from springs and underground sources.
+
+_Santa Catarina Sources._--The chief points from which it was thought
+desirable to obtain underflow supplies were (1) at the barrier of San
+Geronimo, and (2) at the Cañon of Santa Catarina, both shown on Plate
+II.
+
+Conditions at San Geronimo, which is only 6-1/2 km. west of Monterrey,
+were investigated by the State Government in 1892, to determine the
+depth of bed-rock, the rock on either side of the valley being shale,
+with its original bedding planes standing almost vertical. To determine
+this depth, borings were made by driving 2-in. tubes until it was
+assumed that bed-rock had been reached, a method which, in strata
+containing so many boulders, was obviously unreliable. These borings
+indicated that bed-rock was from 12 to 15 m. below the surface. If these
+had proved to be correct, there is no doubt that a development of the
+underground water at this point, by constructing a submerged dam
+combined with an infiltration gallery, would have yielded a large
+supply.
+
+In March, 1906, the Company commenced operations at San Geronimo by
+sinking a well a few meters north of the then dry bed of the river.
+Water was found in considerable quantities a few meters below the
+surface, practically at the level of the river, that is, 570 m. above
+datum. This supply was used for provisional purposes, and will be
+referred to later in describing the San Geronimo gravity supply works.
+
+Between August, 1906, and January, 1907, 4-in. bore-holes were sunk in
+the river bed and on the high ground to the north with a "Keystone"
+driller outfit. These borings showed bed-rock immediately under the
+river bed, at a depth of from 15 to 45 m., but dipping gradually as the
+borings were carried northward.
+
+Boring operations were also carried on at Santa Catarina, during
+November and December, 1906, and in January, 1907, to determine the
+geological conditions, and the results are shown on Fig. 7. From the
+area of water-bearing gravels found, it was proposed to tap the
+underflow water at the 630-m. level by an infiltration gallery. This
+would have necessitated a gravitation tunnel 3,000 m. long, and an
+aqueduct of 14 km., which it was proposed to carry to one of two
+distributing reservoirs at Guadalupe, on the south side of the river,
+opposite Monterrey. In May, 1907, the writer, after making a study of
+all the available data which had been accumulated, had additional
+borings sunk farther across the valley to the north, and these revealed
+a considerable area of water-bearing gravels, and proved that, in former
+geological times, the Santa Catarina flowed about 500 m. north of its
+present position, and to the back of Obispado Mountain, instead of
+through the city. This aspect of the subject was discussed with Mr.
+Schuyler, who agreed with the writer that, in the interest of economy,
+it was better to tap this supply by an infiltration gallery at the
+560-m. level, and bring the water thus obtained to a reservoir to be
+placed at the western limits of the city, dividing the city, for
+distribution purposes, into two interchangeable systems, a high- and a
+low-pressure, the high-pressure system being supplied from Estanzuela,
+18 km. south of the city. One advantage to be gained from this change
+was that the scheme was capable of considerable extension, and any
+future developments at Santa Catarina Cañon would form part of the works
+to be constructed for both high- and low-pressure districts.
+
+[Illustration: FIG. 7.--CROSS-SECTION OF SANTA CATARINA RIVER AT SANTA
+CATARINA.]
+
+The future extension of the Santa Catarina sources, the writer believes,
+can be developed best by driving an infiltration gallery 10 m. below the
+surface of the Santa Catarina River, a little west of the village of the
+same name, and then conveying the water through a comparatively short
+gravitation tunnel and pressure conduit to a main reservoir near San
+Geronimo having a top water level at an elevation of about 590 m. above
+datum.
+
+_Southern Sources of Supply._--The available sources of supply southward
+from Monterrey include a number of springs at various points in a
+distance of 40 km. Many of these springs are of uncertain quantity, and
+some are quite dry during periods of drought. The chief perennial
+springs near Monterrey are those which contribute to form the Estanzuela
+and Diente Rivers, both tributaries of the Silla, while farther south,
+at the Potrero Cerna, near El Porvenir, there are excellent springs, at
+a considerable elevation, with a minimum flow of from 170 to 200 liters
+(from 6 to 7 cu. ft.) per sec. The total quantity of water available
+from all these springs during the driest season would probably not be
+less than about 560 or 700 liters (from 20 to 25 cu. ft.) per sec.
+
+The Estanzuela springs issue at the foot of the Sierra Madre Mountains,
+and have a normal flow of from 56 to 85 liters (2 to 3 cu. ft.) per sec.
+in an ordinary dry year; they probably derive their water, through the
+limestone formation, from the neighboring water-shed of Santa Catarina,
+as the catchment area of the stream is only 910 hectares, and the stream
+has never been known to fail, even in the driest periods of prolonged
+drought. The rainfall on the area is about 30 in. per annum, and the
+catchment area is well wooded and covered with abundant vegetation. The
+El Diente springs have an ordinary dry-weather flow of about 28-1/2
+liters (1 cu. ft.) per sec.; but part of the water is carried
+underground, and the real quantity is much greater and could be
+developed by a small submerged dam carried down to bed-rock.
+
+The elevation and the extreme purity of the water of the Estanzuela
+River made its acquisition very desirable, and the Company, therefore,
+purchased the Federal water rights owned by various members of the
+Estanzuela community, amounting to 91 liters per sec., and has since
+acquired a Federal concession to all the flood-waters of that river. It
+was decided, therefore, to adopt the Estanzuela River as the first step
+toward developing the water to the south of Monterrey for a
+high-pressure supply, the advantage of the scheme being that from time
+to time extensions could be made to tap other sources by gravity, as the
+demands of the city required. The Estanzuela scheme, therefore, is a
+preliminary step toward future extensions which will be necessary in
+this direction as the city grows. The springs near El Porvenir, and
+others which contribute to the San Juan River, can be tapped at a
+sufficiently high level to convey them by a gravity pressure line to the
+Estanzuela Aqueduct near Mederos.
+
+The two sources definitely decided on in July, 1907, were those from
+Estanzuela and San Geronimo. The works were designed to supply
+40,000,000 liters daily, which it was assumed would be sufficient for
+all future developments for a population of 200,000 at a per capita
+consumption of 200 liters per day. The present requirements of the
+city's population, assuming that all the water was supplied by the
+Company, would be, at that rate, which is a very liberal one, only
+18,000,000 liters daily. This, it was thought, would be easily met by
+the San Geronimo source alone, as it was estimated that it would provide
+not less than 20,000,000 liters, if the infiltration gallery was driven
+far enough into the water-bearing gravels.
+
+The question of a high-pressure water supply for domestic use in a city
+like Monterrey is not a serious one, as practically nine-tenths of the
+houses are of one story. The increase in the number of large commercial
+buildings, however, will make the demand greater in the future, and this
+point has been kept in mind in arranging the division of the
+distribution systems.
+
+
+
+
+                         MATERIALS FOR CONCRETE.
+
+
+_Cement._--In the early stages of construction the cement for the work
+was obtained from the Associated Portland Cement Manufacturers, Limited,
+of London, which supplied the "Pyramid" brand, from the Knight, Bevan,
+and Sturges Works, but later the supply was obtained from a new factory
+at Hidalgo, near Monterrey. The total quantity of Portland cement used
+was 42,500 bbl. of "Pyramid" and 32,500 bbl. of "Hidalgo." The English
+cement was tested for the Water-Works Company in London before shipment
+and again at Monterrey, to conform to the British Standard
+Specifications; the "Hidalgo" cement was required to pass the Standard
+Specifications advocated by the Special Committee of the American
+Society of Civil Engineers. The quality in each case was of the very
+highest, no difficulties being experienced at any time.
+
+_Sand and Rock._--One of the chief difficulties in connection with the
+construction work in its initial stages was in procuring satisfactory
+sand for the concrete. An investigation of the quality of all the
+available sands in the neighborhood of Monterrey resulted in the
+decision to use a manufactured sand obtained from the calcareous shales
+in the foot-hills opposite the city, on the south side, and near the
+site of one of the proposed reservoirs. A quarry was opened, and the raw
+material was delivered by a gravity plane to a crushing plant, 230 m.
+from the quarry and at a level about 50 m. lower.
+
+The plant consisted of a No. 5 Austin gyratory rock-crusher, fitted with
+elevators and revolving screens of various dimensions, driven by a
+150-h.p. Erie steam engine; two sets of Traylor's heavy-duty crushing
+rolls, one having 30 by 16-in. and the other 18 by 12-in. rolls; and a
+Niagara sand disintegrator. This plant, except during a short period
+when the requirements were beyond its capacity, was able to produce all
+the sand and rock required for construction purposes. More than 40,000
+tons of rock were quarried, the greater part of which was converted into
+crushed stone and sand.
+
+Table 2 gives the chemical analysis of the chief constituents of the
+various sands examined.
+
+   TABLE 2.--ANALYSIS OF SANDS IN THE NEIGHBORHOOD OF MONTERREY.
+
+              KEY:
+
+              A: Percentage of silica (absolute), SiO_{2}
+              B: Percentage of alumina, Al_{2}O_{3}
+              C: Percentage of sesquioxide, Fe_{2}O_{3}
+              D: Percentage of lime carbonate, CaCO_{3}
+
+  ===+============================+=======+=======+=======+=======+
+  No.| Location.                  |   A   |   B   |   C   |   D   |
+  ---+----------------------------+-------+-------+-------+-------+
+   1.| Arroyo Seco, near          |       |       |       |       |
+     |   brickyard at Monterrey   | 60.10 |17.95  |  2.89 |  8.01 |
+   2.| Arroyo Seco, near          |       |       |       |       |
+     |   brickyard at Monterrey,  |       |       |       |       |
+     |   No. 2                    | 42.92 |14.26  |  4.66 | 34.58 |
+   3.| Near Garcia Station,       |       |       |       |       |
+     |   Mexican National R. R.,  |       |       |       |       |
+     |   Chiquito River, No. 1    | 50.22 | 9.72  |  1.44 | 34.62 |
+   4.| Near Garcia Station.       |       |       |       |       |
+     |   Mexican National R. R.,  |       |       |       |       |
+     |   Chiquito River, No. 2    | 48.7  | 4.92  |  8.28 | 35.43 |
+   5.| San Luis Potosí            | 85.02 | 5.00  |  7.38 |  2.21 |
+   6.| Topo Grande, Pesquería     |       |       |       |       |
+     |   River                    | 40.20 | 5.15  |  4.25 | 46.50 |
+   7.| Hornos, near Torreón       | 77.9  | 13.1  |  2.4  |  4.9  |
+   8.| Salinas River, at Salinas  | 41.5  |  5.7  |  1.4  | 48.2  |
+   9.| Pits near Caballeros, on   |       |       |       |       |
+     |   Tampico Branch of        |       |       |       |       |
+     |   Mexican Central R. R.    | 73.4  |  5.6  |  4.4  | 10.1  |
+  10.| Santa Catarina River,      |       |       |       |       |
+     |   near San Geronimo        |       |       |       |       |
+     |   (washed sand)            | 12.40 |  2.06 |  1.14 | 81.70 |
+  11.| Santa Catarina River,      |       |       |       |       |
+     |   at Monterrey             | 17.4  |  2.50 |  2.00 | 77.00 |
+  12.| Composition of rock, quarry|       |       |       |       |
+     |   in foot-hills opposite   |       |       |       |       |
+     |   Monterrey, Monterrey     |       |       |       |       |
+     |   Water-Works and Sewer    |       |       |       |       |
+     |   Company's property       | 40.44 | 15.70 |  2.20 | 34.30 |
+  13.| Manufactured sand from     |       |       |       |       |
+     |   above quarry             |       |       |       |       |
+     |   (run of crusher)         | 51.80 | 12.14 |  8.7  | 32.6  |
+     |                            |       |       |       |       |
+  ===+============================+=======+=======+=======+=======+
+
+The chief sands used for ordinary building purposes in Monterrey are
+Nos. 10 and 11, which are procured from the bed of the Santa Catarina
+River. As these sands contain large proportions of lime carbonates,
+which make them very undesirable for important structures, their use was
+limited to relatively unimportant work. The best sands procurable were
+Nos. 5 and 9, but the long distance of the pits from Monterrey, and
+consequently the heavy freight rate, made their use prohibitive on
+economical grounds. The best of the available sands, although it was
+very fine, was No. 7, from Hornos, near Torreon, as it could be depended
+on for uniformity and could be obtained f. o. b. cars at Monterrey for
+3.18[5] pesos per ton.
+
+[5] All costs given in this paper are in Mexican pesos, one peso being
+equivalent to 50 cents in U. S. currency.
+
+The bulk of the sand and crushed rock used was similar to Nos. 12 and
+13, and reference to the cement sand tests in Table 3, will show that
+the manufactured sands gave very satisfactory results.
+
+Table 3 gives the average tests made with the "Hidalgo" cement and
+various sands, alone and in combination, for the purpose of obtaining
+comparative results; the mixtures tested were composed of 3 parts of
+sand to 1 of cement.
+
+        TABLE 3.--TESTS OF "HIDALGO" CEMENT WITH VARIOUS SANDS.
+
+      =====================================+============+============
+                     Sand.                 | At 7 days. | At 28 days.
+      -------------------------------------+------------+------------
+      Ottawa (Standard)                    |  305 lb.   |  414 lb.
+      Monterrey, 1-1/2 parts, }            |            |
+      Hornos, 1-1/2 parts     }            |  188  "    |  313  "
+      Monterrey                            |  253  "    |  365  "
+      Hornos                               |  202  "    |  301  "
+      Manufactured sand, Company's crusher |  372  "    |  566  "
+      Hornos, 2 parts,     }               |            |
+      Crusher sand, 1 part }               |  231  "    |  352  "
+      Hornos, 1-1/2 parts,      }          |            |
+      Crusher sand, 1-1/2 parts }          |  265  "    |  346  "
+      Hornos, 1 part,        }             |            |
+      Crusher sand, 2 parts  }             |  248  "    |  328  "
+      =====================================+============+============
+
+The Hornos sand was used during a few weeks in the latter part of 1908,
+when the crusher was unable to produce all that was required. Its use
+was restricted to thick walls which were required to be water-tight, and
+it was always used in equal proportions with the crusher dust.
+
+
+
+
+                           ESTANZUELA SUPPLY.
+
+
+[Illustration: FIG. 8.--LOCATION PLAN OF ESTANZUELA DAM.]
+
+_Intake Works._--The intake (Fig. 8) is about 1 km. below the lowest
+spring and at a point where the maximum flow of the stream was observed.
+The works consist of a small monolithic concrete dam, placed obliquely
+across the stream at an angle selected for the purpose of obtaining a
+foundation running parallel to the direction of the strata, which at
+this point were lying almost vertically across the bed of the stream.
+Above these strata the stream bed was formed chiefly of large cemented
+limestone blocks and smaller conglomerate. No storage being possible in
+this valley, which has a very precipitous fall, the height of the dam
+was fixed merely to obtain a small settling basin for sand and débris
+brought down in time of flood. The dam foundation was excavated to
+bed-rock, from which the upper disintegrated portions were carefully
+removed; the rock was then stepped, and dovetailed recesses were left
+for properly bonding the concrete.
+
+The dam is carried well into the banks. Its extreme length is 52 m., its
+maximum height 4.50 m., and its greatest thickness 2 m. The up-stream
+face has a batter of 1 in 12, and the down-stream face, 1 in 8. The top
+of the wall is 1 m. thick. For the discharge of flood-water there is a
+weir 10 m. long, and it was calculated that with a depth of 1 m. it
+would discharge about 400 times the ordinary flow, or about 23,000
+liters per sec., but, in addition, the whole length of the dam
+(excluding that occupied by the gate-house) was arranged for the
+discharge of abnormal floods, one of which, on August 27th, reached the
+enormous quantity of 82,070 liters (2,900 cu. ft.) per sec., or 825 cu.
+ft. per sec. per sq. mile of drainage area, a remarkable run-off from so
+small an area as 910 hectares. The concrete forming the dam is a 1:3:5
+mixture. The overflow sill is 692 m. above sea level. When the dam was
+completed it was filled to the overflow level, in order to test the
+water-tightness of the basin, which, when cleared, was found to be
+slightly fissured on the north side. The leakage was sufficient to cause
+a serious loss during periods of drought, and it was then decided to
+line the basin with concrete, so that the stream would enter it without
+being under a head greater than its own depth. The length of the basin,
+measured along the center line of the original stream surface, is 85 m.,
+and its area is 1,100 sq. m. At its upper end it is merely a lined
+channel, 5 m. wide at the entrance. The floor of the basin has a fall of
+4 m. The lining was formed in two thicknesses totaling 30.5 cm. (12
+in.) of 1:2-1/2:3-1/2 concrete, laid in panels approximately 3 m.
+square, the upper panels breaking joint with those immediately below; in
+this way a very satisfactory and water-tight lining was obtained. A
+parapet wall, 45.7 cm. high, surrounds the basin. For scouring out the
+basin a 30.5-cm. (12-in.) cast-iron pipe was taken through the dam at
+the lowest point, this pipe being provided with a gate-valve encased in
+concrete on the down-stream face.
+
+The gate-house was built in connection with the dam at the north end of
+the overflow weir, its inner dimensions being 4.34 by 2.80 m. The
+substructure, to the level of the dam, is of concrete founded on the
+solid rock, and the superstructure is of brick rendered with cement
+plaster. The roof is of framed timber with red French tiles.
+
+The intake pipe is of cast iron. 40.6 cm. (16 in.) in internal diameter,
+fitted outside with a movable copper screen which is further protected
+by a wrought-iron hinged screen to prevent damage from stones, floating
+timber, etc., during times of flood. Inside the gate-house the outlet
+pipe is provided with a 40.6-cm. (16-in.) sluice-valve, operated from
+the floor level by a vertical head-stock with worm-gearing. The
+gate-house has a scour-out pipe (also operated by a head-stock) and
+duplicate copper screens fitted to iron frames. From this house the
+water is conveyed to the upper portion of the conduit, which is a
+45.7-cm. (18-in.) cast-iron pipe.
+
+Of the total area of land, 885 hectares (2,187 acres), owned by the
+company, 392 hectares (970 acres) have been fenced in, to prevent any
+contamination of the springs. This fence is formed of five lines of
+barbed wire protected with stout hog netting at the bottom, in order to
+prevent more particularly the entrance of goats, many thousands of which
+pasture in the adjoining mountains.
+
+On the high ground immediately below the intake, a 3-roomed stone house
+has been constructed for the inspector in charge of the intake works,
+who also keeps in daily touch with the general office and records the
+condition of the stream, particulars of rainfall, etc.
+
+_Aqueduct._--The total length of the aqueduct, from the intake dam to
+the South Reservoir, is 18,700 m., made up as shown in Table 4.
+
+                      TABLE 4.--ESTANZUELA AQUEDUCT.
+
+  +===========================================================+==========+
+  |              Description.                                 |Length,   |
+  |                                                           |in meters |
+  +-----------------------------------------------------------+----------+
+  |                                                           |          |
+  |Cast-iron pipes, 45.7 cm. (18 in.) in diameter, along      |          |
+  |                   the stream bed of the Estanzuela River  |   110    |
+  |                                                           |          |
+  |Concrete tubes, 55.9 cm. (22 in.) in diameter,             |          |
+  |                  to Mederos (including 281 m. of tunnel)  | 4,473.81 |
+  |                                                           |          |
+  |Cast-iron siphons, 45.7 cm. (18 in.)                       |          |
+  |                          in diameter:  Calabozos    239 m |          |
+  |                                        South Virgen 124 " |          |
+  |                                        North Virgen 177 " |          |
+  |                                        Mederos      426 " |          |
+  |                                                     ----- |   966    |
+  |                                                           |          |
+  |Concrete tubes, 63.5 cm. (25 in.) in diameter,             |          |
+  |                               Mederos to South Reservoir. |12,039.19 |
+  |                                                           |          |
+  |Cast-iron siphons, 50.8 cm. (20 in.) in diameter:          |          |
+  |                                        Necaxa       315 m.|          |
+  |                                        San Augustin 796 " |          |
+  |                                                     ----- | 1,111    |
+  |                                                           |          |
+  +-----------------------------------------------------------+----------+
+  |              Total                                        |18,700    |
+  +===========================================================+==========+
+
+The gradient of the concrete pipes is 0.43% from Estanzuela to Mederos,
+and 0.53% from Mederos to the South Reservoir. The calculated
+discharging capacity of the conduit when running full is 364 liters (13
+cu. ft.) per sec. for the upper, and 465 liters (16.4 cu. ft.) per sec.
+for the lower section. For these pipes, the coefficient, _n_, in
+Kutter's formula, was taken at 0.013. At present the line has been
+limited by overflows to discharge three-quarters full.
+
+The increase in the size of the pipes from Mederos is for the purpose of
+receiving the waters of the Mederos River and other springs in the San
+Pablo and Aqua Verde catchment areas, as shown on Plate II.
+
+The invert of the concrete conduit where it leaves the Estanzuela River
+is 684.25 m. above datum, and at the valve-house of the South Reservoir
+it is 589.00 m.
+
+The concrete pipes were manufactured and laid under contract with Mr.
+Arthur S. Bent, of Los Angeles, Cal., the Company providing all
+materials, labor, etc. The contractor was paid 10 cents per lin. ft. of
+pipe manufactured and 10 cents per lin. ft. laid. He was also
+responsible for the satisfactory completion of the work.
+
+[Illustration: FIG. 9.--ESTANZUELA PIPE LINE STEEL FORMS FOR THE
+MANUFACTURE OF CONCRETE PIPE.]
+
+Fig. 9 shows the details of the joint recommended by Mr. Schuyler and
+adopted for these pipes. The 63.5-cm. (25-in.) pipes were 61 cm. long
+and 76 mm. (3 in.) thick. The 55.9-cm. (22-in.) pipes were of the same
+length, but 70 mm. (2-3/4 in.) thick. For the purpose of strengthening
+these pipes while hauling them over very rough roads they were
+reinforced with four rings of No. 6 galvanized-iron wire.
+
+_Manufacture of Pipes._--The pipes were manufactured under the
+Supervision of Mr. H. Stanley Bent, at a pipe yard established below
+the crushing plant, from which the crushed rock and sand were delivered
+by gravity in bogies run on narrow-gauge rails. The area of the pipe
+yard was approximately 1-1/4 hectares, and it was laid out with parallel
+lines of 76-mm. (3-in.) galvanized-iron piping with hose couplings for
+sprinkling purposes. After trials with aggregates of various sizes, the
+concrete for the pipes was proportioned by volume as follows:
+
+  Crushed rock broken to pass through a 19-mm. screen   0.136 cu. m.
+  Manufactured sand (run of rolls)                      0.119  "  "
+  Portland cement                                       0.090  "  "
+                                                        ------------
+  Total                                                 0.345 cu. m.=
+                                                       (12.2 cu. ft.)
+
+
+[Illustration: PLATE III, FIG. 2.--STEEL FORMS FOR MOULDING CONCRETE
+TUBES, ESTANZUELA AQUEDUCT.]
+
+The above quantity manufactured two 63.5-cm. pipes; a 55.9-cm. pipe
+required 0.1415 cu. m. (5 cu. ft.) of the material, in the same
+proportions. Fig. 9 shows the forms for these pipes, and Fig. 2, Plate
+III, illustrates the process of moulding. The forms consist of cast-iron
+bottom rings, to the proper section of the joint, and inner and outer
+steel forms of 3-mm. plate, provided with inner and outer locking
+arrangements. The concrete was poured through a cast-iron hopper which
+fitted to the top of the outer form.
+
+The concrete, which was mixed very dry, in a 1/2-cu. yd. batch, "Smith"
+mixer, was thoroughly tamped with a 22-lb. tamper, and worked until it
+was of a stiff jelly-like consistency, the wire rings being added as the
+concrete was placed. The best results were obtained with the minimum
+quantity of water. The upper joint was moulded with a heavy cast-iron
+ring. The jacket and core forms were loosened immediately, and placed
+over other rings, a sufficient number of bottom rings being used for a
+day's work. For the pipes required for curves, special forms were used
+to give the necessary bevel to the joint. After 24 hours the finished
+pipes were lifted from the bottom ring with a special lifter, and ranged
+in position for coating internally with a Portland cement grout to which
+a little freshly slaked lime was added. The pipes were all numbered, and
+were kept moist for 10 days by constant sprinkling. They were not hauled
+to the work until 28 days after they were moulded, although this rule
+was sometimes broken, to the detriment of the pipes. More than 32,000
+pipes were manufactured, but some were used for purposes other than the
+Estanzuela Aqueduct.
+
+_Cost of Pipes._--The contractor brought with him experienced concrete
+pipe makers from California, and these were afterward assisted by
+Mexican labor. In a day two tampers could manufacture from 45 to 50
+pipes of the larger (63.5-cm,), and from 55 to 60 of the smaller
+(55.9-cm.) size.
+
+The cost varied from 2.75 to 3.25 pesos per pipe for the smaller, and
+from 3.50 to 4.00 pesos for the larger size.
+
+The approximate cost of manufacturing is as follows: Taking, as a fair
+example, one week's work during March, 1908, the wages paid to the 74
+men comprising the total pay-roll (though part of this labor was
+intermittent) amounted to 981 pesos. This includes a general foreman at
+10 pesos per day, four American tampers at 7.50 pesos, and Mexican labor
+varying from 4 to 1 peso, and all labor necessary to handle and finish
+the pipes, including coating the interiors. During this week there were
+made 1,126 of the 63.5-cm. and 1,095 of the 55.9-cm. size. The pay-roll
+includes 520 pesos for the larger pipes (46 cents each) and 461 pesos
+for the smaller pipe (42 cents each). Table 5 shows the quantities and
+cost of the materials used in the manufacture of these pipes.
+
+                    TABLE 5.--COST OF CONCRETE PIPE.
+
+  ========================================+===============================
+                                          | FOR 1,126 PIPES 63.5 CM.
+                                          | IN DIAMETER.
+            Materials.                    +-------------+-----------------
+                                          | Quantities. |  Cost.
+  ----------------------------------------+-------------+-----------------
+  Portland cement, at 8.00 pesos per      |             |
+    bbl., delivered at pipe-making yard.  |   401 bbl.  | 3,208.00 pesos.
+  Sand, at 2.65 pesos per cu. m.          |    85 cu. m.|   225.25  "
+  Crushed rock, 19-mm. (3/4-in.), at 2.65 |             |
+    pesos per cu. m.                      |    62 cu. m.|   164.30  "
+  No. 6 galvanized-wire hoops. 4 rings    |             |
+    to each pipe.                         | 4,504       |   203.00  "
+  ----------------------------------------+-------------+-----------------
+            Totals.                       |   ...       | 3,800.55 pesos.
+  ----------------------------------------+-------------+-----------------
+            Cost per pipe.                |   ...       |     3.37 pesos.
+  ========================================+=============+=================
+
+  ========================================+==============================
+                                          | FOR 1,095 PIPES 55.9 CM.
+                                          | IN DIAMETER.
+            Materials.                    +-------------+----------------
+                                          | Quantities. |  Cost.
+  ----------------------------------------+-------------+----------------
+  Portland cement, at 8.00 pesos per      |             |
+    bbl., delivered at pipe-making yard.  |   303 bbl.  | 2,424.00 pesos.
+  Sand, at 2.65 pesos per cu. m.          |    68 cu. m.|   180.20  "
+  Crushed rock, 19-mm. (3/4-in.), at 2.65 |             |
+    pesos per cu. m.                      |    50 cu. m.|   132.15  "
+  No. 6 galvanized-wire hoops. 4 rings    |             |
+    to each pipe.                         | 4,380       |   183.00  "
+  ----------------------------------------+-------------+----------------
+            Totals.                       |   ...       | 2,919.45 pesos.
+  ----------------------------------------+-------------+----------------
+            Cost per pipe.                |   ...       |     2.66 pesos.
+  ========================================+=============+================
+
+From Table 5 it is seen that the cost of the 63.5-cm. pipes was 3.37
+pesos for material plus 0.46 peso for labor = 3.83 pesos per pipe, or
+6.26 pesos per lin. m. (1.91 pesos per lin. ft.).
+
+The cost of the 55.9-cm. pipes amounted to 2.66 pesos for material plus
+0.42 peso for labor = 3.08 pesos per pipe, or 5.05 pesos per lin. m.
+(1.54 pesos per lin. ft.).
+
+The cost of cement included hauling from the bodega to the yard, a
+distance of about 5 km. At a later date, after the Company had commenced
+using the "Hidalgo" cement, some additional 55.9-cm. pipes were
+manufactured, so as to have them on hand as a reserve in case of
+emergency. In this work only Mexican labor was used, as the previous
+gang had been dispersed, but the tampers had previous experience. Taking
+the cost of 418 pipes made during one period of 9 days, the detailed
+cost was as given in Table 6.
+
+                  TABLE 6.--COST OF 55.9-CM. CONCRETE PIPES.
+
+  ========================================+===============================
+                                          | FOR 1,126 PIPES 63.5 CM.
+                                          | IN DIAMETER.
+            Materials.                    +-------------+-----------------
+                                          | Quantities. |  Cost.
+  ----------------------------------------+-------------+-----------------
+  Portland cement, at 8.00 pesos per      |             |
+    bbl., delivered at pipe-making yard.  |   401 bbl.  | 3,208.00 pesos.
+  Sand, at 2.65 pesos per cu. m.          |    85 cu. m.|   225.25  "
+  Crushed rock, 19-mm. (3/4-in.), at 2.65 |             |
+    pesos per cu. m.                      |    62 cu. m.|   164.30  "
+  No. 6 galvanized-wire hoops. 4 rings    |             |
+    to each pipe.                         | 4,504       |   203.00  "
+  ----------------------------------------+-------------+-----------------
+            Totals.                       |   ...       | 3,800.55 pesos.
+  ----------------------------------------+-------------+-----------------
+            Cost per pipe.                |   ...       |     3.37 pesos.
+  ========================================+=============+=================
+
+  ========================================+==============================
+                                          | FOR 1,095 PIPES 55.9 CM.
+                                          | IN DIAMETER.
+            Materials.                    +-------------+----------------
+                                          | Quantities. |  Cost.
+  ----------------------------------------+-------------+----------------
+  Portland cement, at 8.00 pesos per      |             |
+    bbl., delivered at pipe-making yard.  |   303 bbl.  | 2,424.00 pesos.
+  Sand, at 2.65 pesos per cu. m.          |    68 cu. m.|   180.20  "
+  Crushed rock, 19-mm. (3/4-in.), at 2.65 |             |
+    pesos per cu. m.                      |    50 cu. m.|   132.15  "
+  No. 6 galvanized-wire hoops. 4 rings    |             |
+    to each pipe.                         | 4,380       |   183.00  "
+  ----------------------------------------+-------------+----------------
+            Totals.                       |   ...       | 2,919.45 pesos.
+  ----------------------------------------+-------------+----------------
+            Cost per pipe.                |   ...       |     2.66 pesos.
+  ========================================+=============+================
+
+_Excavation for Pipe Line and Siphons._--The excavation for the pipe
+line and for bridge works, etc., was let by contract to Messrs. Scott
+and Lee, of Monterrey, under three classifications:
+
+      (1) "All material which in the judgment of the Engineer can
+      be economically loosened with picks and handled with
+      shovels."
+
+      (2) "Indurated earth or gravel, shale or rock which can be
+      loosened without blasting, and 'sillar', locally so-called,
+      whether pure or mixed with other substances, and whether it
+      requires blasting or not."
+
+      (3) "All rock not included in the above which requires
+      drilling or blasting."
+
+Locally, this classification is well understood, particularly No. 2, as
+it covers the sillar soils which are common in the neighborhood of
+Monterrey. The contract prices were: No. 1, 50 cents; No. 2, 1.50
+pesos; and No. 3, 2.50 pesos per cu. m. These prices were over and above
+the clearing and grubbing of the line, which was paid for at the rate of
+100 pesos per hectare.
+
+The route of the pipe line being along broken country, at some points
+difficult of access, service roadways, about 3 m. wide, for hauling
+material were constructed, and, for about 7 km., a roadway was made
+along the line of the trench.
+
+The prices for the roadway, under the above classification, were: For
+No. 1, 35 cents; No. 2, 1.50 pesos; and No. 3, 2.50 pesos per cu. m.
+
+The trenches were excavated 5 cm. below the required finishing depth, to
+allow for grading the pipes in selected material, and were taken out to
+an average width of 40 cm. greater than the outside diameter of the
+pipe, to allow for their proper jointing, and also to give sufficient
+room to roll the pipes in the trenches.
+
+The final quantities of excavation were:
+
+          TRENCH:   No. 1             11,115 cu. m.
+                    No. 2             18,096  "  "
+                    No. 3              6,650  "  "
+                                    --------------
+                    Total             35,861 cu. m.
+
+          ROADWAYS: No. 1             4,165 cu. m.
+                    No. 2             1,999  " "
+                    No. 3                30  " "
+                                     -------------
+                    Total             6,194 cu. m.
+
+The route of the pipe line was laid out so as to obtain an average fill
+of not more than 1 m. over the tops of the pipes, but in some cases the
+cuts, for short lengths, were 3 m. deep. The excavation for this work
+began in June, 1907.
+
+_Hauling Pipes._--The pipes were hauled to the site of the work with
+ox-carts and mule teams. The cost of hauling varied from 25 cents per
+pipe at the lower end, to 1 peso per pipe at the upper and,
+comparatively speaking, inaccessible portion of the line. The weight of
+each 55.9-cm. pipe was about 182 kg.; that of each 63.5-cm. pipe was
+about 216 kg.
+
+The breakages in all the pipes cast at the pipe yard amounted to about
+1%, due chiefly to unloading them carelessly near the pipe line.
+
+_Pipe Laying._--The pipe-laying gang was composed of 7 Mexicans under
+the direction of an American foreman, who was in charge of several
+gangs. One gang could lay daily from 60 to 73 m. (from 100 to 120
+pipes). The following was the ordinary pay-roll for one gang:
+
+       1 Foreman at 8 pesos (proportion).         2.00 pesos.
+       1 Pipe layer at 3 pesos.                   3.00  "
+       1 Pipe layer's assistant at 2 pesos.       2.00  "
+       1 Cement mixer at 2 pesos.                 2.00  "
+       2 Outside plasterers at 2.50 pesos.        5.00  "
+       2 Inside plasterers at 2.25 pesos.         4.50  "
+       1 Water boy at 0.50 peso.                  0.50  "
+                                                  -----------
+       Total.                                    20.00 pesos.
+
+This brings the average cost of laying the pipes to 32.8 cents per lin.
+m.
+
+The pipes were jointed with 1:2 cement mortar, the outer joint being
+rounded over both pipes for a width of 12-1/2 cm. (5 in.) and a height
+of about 19 mm. (3/4 in.). In making these joints the pipe layers wore
+rubber gloves. The joints were kept moist, and the trench was
+back-filled with fine, screened material to a depth of 10 cm. above the
+top of the pipe. Inside, the joints were carefully caulked with cement
+and rendered smooth, the plasterers working continuously along with the
+pipe layers, doing from 20 to 35 m. at a time. Water had to be conveyed
+to the trenches by barrels on burros, and during the dry season it was
+sometimes carried 5 or 6 km.
+
+[Illustration: PLATE IV, FIG. 1.--TYPICAL REINFORCED CONCRETE GIRDER
+BRIDGE, ESTANZUELA AQUEDUCT.]
+
+[Illustration: PLATE IV, FIG. 2.--ELLIPTICAL ARCH BRIDGE CARRYING
+ESTANZUELA AQUEDUCT.]
+
+_Bridges._--The line as laid out passed over many gulches and dry
+arroyos, and these were crossed with reinforced concrete bridges of
+varying spans and heights, two being shown on Plate IV.
+
+These bridges were formed of continuous horizontal girders, 1.10 m. deep
+and 1 m. wide, with a cantilever overhang at the abutments, varying in
+length from 1 to 2 m., so as to avoid settlement between the pipes and
+the bridges. The bottom reinforcement consisted of from 2 to 6 twisted
+bars of mild steel, varying in different spans from 12.7 to 19 mm. (1/2
+to 3/4 in.) in diameter. The turned up bars were 28-1/2 mm. (1-1/8 in.)
+in diameter; they were placed on either side, carried over the upper
+part of the beams, and continued along the end for the overhanging part
+of the girder. These bars, when not obtainable of the full length, were
+spliced with a lap of 1.2 m. with No. 6 galvanized-steel wire. The
+vertical stirrups were 4.7 by 25.4 mm. (3/16 by 1 in.), of mild steel;
+they were equally spaced 30.5 cm. (12 in.) apart, and carried all around
+the girders, lapping at the center about 15 cm. (6 in.), all the steel
+being carefully wired together before placing the concrete.
+
+The general type of the piers and abutments is shown by Fig. 1, Plate
+IV, and varies in height with practically every bridge, the foundations
+in every case resting on hard rock. The concrete for the girders was a
+1:2-1/2:3-1/2 mixture, the crushed stone used having all passed a mesh
+of 19 mm. (3/4 in.). The piers were of 1:3-1/2:5-1/2 concrete, and heavy
+"displacers" were embedded within them.
+
+The concrete was placed after the pipes had been laid through the form
+by the pipe contractor, the joints being kept clear of the bottom to the
+required distance by small moulded concrete blocks. The tops of the
+girders were moulded to a slightly segmental form. The bridges were all
+kept watered for about 15 days, and the forms were not struck for 28
+days after placing. At Station 13.4 the pipes were carried over a
+picturesque arroyo on an elliptical arched bridge (Fig. 2, Plate IV) of
+11 m. clear span.
+
+The abutments of all bridges were protected by rubble walls in cement
+mortar carried up 60 cm. above the tops of the girders.
+
+The contract price for the concrete work of these bridges, the Company
+furnishing the steel and cement, was 14 pesos per cu. m., and for
+placing reinforcing steel 35 pesos per metric ton (2,204 lb.).
+
+There are 49 single-span bridges, the larger spans being 9.10 m.; 8
+two-span, and 11 three-span bridges, their total length, including the
+overhang, amounting to 870.50 m., or 4-1/2% of the whole length of
+aqueduct.
+
+_Concrete Aprons._--At 76 points there were small depressions which did
+not necessitate the construction of bridges, and at these places the
+pipes were encased in blocks of concrete carried up the hillside in the
+form of an apron having small abutment walls from 1 to 2 m. apart. This
+also served to protect the pipes from scouring action during rainstorms.
+At the upper end of the line, near the intake, the pipe had to be
+protected by concrete continuously for a distance of about 300 m., in
+order to prevent damage from falling rocks.
+
+[Illustration: PLATE V, FIG. 1.--VENTILATING COLUMN AND ENTRANCE
+MANHOLE, ESTANZUELA AQUEDUCT.]
+
+_Ventilators and Manholes._--Along the route of the concrete pipe there
+are 27 ventilators, one of which, together with an entrance manhole, is
+shown by Fig. 1, Plate V. They consisted of simple concrete columns,
+3.35 m. high, above the ground line, the interior of the shafts being
+formed of fire-clay pipes, 15 cm. (6 in.) in diameter. At each
+ventilator the pipe was cut and a block of concrete, the width of the
+trench, filled in as a foundation. Entrance manholes were also placed at
+49 points, at 27 of which they immediately adjoined the ventilating
+columns.
+
+_Estanzuela Tunnel._--At 1,560 m. from the intake at Estanzuela, the
+conduit is laid through a tunnel 281 m. long. The tunnel was driven
+through hard calcareous strata from the open cuttings at each end. The
+inner dimensions were trimmed to approximately 2 m. high and 1-1/2 m.
+wide. At the ends of the tunnel the rock was moderately easy to take
+out, but the inner section was very hard and difficult to blast.
+Ordinary hand drilling was adopted, and the actual cost of driving
+varied from 28 pesos per lin. m. at the ends to 50 pesos in the center.
+
+The pipes were laid through the tunnel in the ordinary way, and
+back-filled from the center, so as to give a cover of about 45 cm. above
+to protect them from falling pieces of shale.
+
+[Illustration: PLATE V, FIG. 2.--PLACING CONCRETE PIPES IN FORMS FOR
+BRIDGE CROSSING AT NORTH END OF TUNNEL, ESTANZUELA AQUEDUCT.]
+
+_Siphons._--It has already been mentioned that there are 6 cast-iron
+pipe siphons. The head on these varies between 10 and 38 m. All are
+provided with special inlets and outlets, forming combined overflow and
+ventilating chambers, and have wooden hand-sluices to divert the water
+when necessary. The bottoms of all siphons are provided with 20-cm.
+cast-iron scour-out pipes, fitted with valves, and carried down to a
+lower point to obtain a free outlet. The valve-boxes are protected by
+being placed in heavy concrete chambers carried up above the level of
+ordinary floods.
+
+The siphons are formed of cast-iron socket pipes, 3.65 m. (12 ft.) long,
+caulked in the ordinary way with lead joints. The thickness of the
+45.7-cm. (18-in.) pipes is 19 mm.; that of the 50.8-cm. pipes is 21 mm.
+On the steep hillsides the pipes are anchored securely to the rock in
+concrete blocks reinforced with heavy iron chains. In some cases these
+siphons were difficult of access, but ox-teams hauled the pipes in a
+very efficient and satisfactory manner.
+
+_Overflow Chambers._--The ordinary overflows, of which there are 14, are
+similar in design to the siphon inlets.
+
+_Testing, etc._--When the line was completed it was tested for
+water-tightness, and the loss was found to be about 5%, part of which
+was probably due to absorption. At a later date it was found that the
+waters of the Estanzuela River, which contain 150 parts of calcium
+carbonate (CaCO_{3}) per million, deposited a very fine film of lime on the
+interior of the pipes, completely filling any pores there might have
+been. At the present time there is no measurable leakage, thus proving
+that the character of the work is very satisfactory.
+
+The water was turned into the conduit on June 11th, 1908, and delivered
+to the city on the following day through a by-pass, before the reservoir
+was completed.
+
+The pipe line is patrolled daily by an inspector with the authority of a
+gendarme, so as to prevent the unlawful abstraction of water, a very
+necessary precaution in so dry a country.
+
+
+
+
+                       SOUTH DISTRIBUTING RESERVOIR.
+
+
+The distributing reservoir for the Estanzuela supply is at Guadalupe, on
+the foot-hills to the south of the Santa Catarina River, about 2 km.
+from the center of the city. The reservoir is a covered one, of
+reinforced concrete, and its capacity is 38,000,000 liters (10,000,000
+U. S. gal.).
+
+[Illustration: PLATE VIII, FIG. 1.--GENERAL VIEW OF EXCAVATION AND
+EMBANKMENT FOR SOUTH RESERVOIR BEFORE LINING.]
+
+_Excavation and Embankment._--The heavy slope of the ground at the
+selected site made the circular form the most desirable. On the low side
+the ground was excavated about 2 m. below the original ground line,
+while the excavation at the upper part of the slope was about 12 m.
+deep. The excavated material consisted chiefly of sillar and limestone
+conglomerate, which when broken up forms a calcareous clay of an
+excellent character for the formation of embankments, when proper care
+is taken. The dimensions fixed for the internal diameter of the finished
+concrete work of the reservoir were: 81 m. (265.68 ft.) at the top, and
+a depth of water of 9 m., with sides sloping 55 in 100.
+
+[Illustration: FIG. 10.--SOUTH RESERVOIR PLAN OF EXCAVATION.]
+
+Fig. 10 is a plan of the reservoir, with a cross-section of the
+excavation and embankment. On the lower side the original ground line
+was cut down in steps, and all loose earth, roots, etc., were carefully
+removed. The floor of the reservoir was chiefly sillar conglomerate, a
+hard material that required a considerable amount of blasting for its
+removal. The embankments were formed in 10-cm. layers of sillar and
+conglomerate broken into small fragments and then rolled with 3-ton
+sectional rollers drawn by teams of 4 and 6 mules, which assisted in
+disintegrating the mass thoroughly, and produced by constant wetting a
+homogeneous and compact clay. The excavation and embankment were left so
+that 15 cm. of trimming could be done at a later date, immediately prior
+to the lining of the reservoir. The excavated material amounted to about
+34,000 cu. m., and, of this quantity, 31,500 cu. m. were used to form
+the embankment; the remainder was taken to a spoil bank immediately
+adjoining, the black earth stripping being separated and reserved for
+covering the reservoir, etc. The contract prices for the excavated
+material placed in the embankment were:
+
+                                                                     Pesos
+                                                                     per
+                                                                     cubic
+                                                                     meter
+
+  Class 1.--Material which could be removed by plows and scrapers    0.60
+  Class 2.--This consisted chiefly of "sillar"                       1.09
+  Class 3.--Limestone conglomerate (requiring blasting)              1.65
+
+The prices (for the same classification) for material taken to the spoil
+bank, were 0.40, 0.80, and 1.40 pesos, respectively. Of the material
+taken out, 15% came under No. 1 classification, 80% under No. 2, and 5%
+under No. 3.
+
+The excavation was begun at the end of May, 1907, and completed in
+January, 1908, by Scott and Lee, the contractors. The embankments were
+then allowed to stand until the beginning of July, 1908, to permit the
+whole to become thoroughly settled and consolidated prior to beginning
+the lining. In July the work of trimming the embankments and excavating
+for the foundations of the reservoir columns was commenced, under the
+Company's own administration, which completed the entire work.
+
+[Illustration: PLATE VI.--DETAILS OF BEAMS AND COLUMNS FOR SOUTH
+RESERVOIR.]
+
+[Illustration: PLATE VIII, FIG. 1.--DETAILS OF FORMS FOR SOUTH
+RESERVOIR.]
+
+[Illustration: PLATE VIII, FIG. 2.--VIEW OF WESTERN HALF OF SOUTH
+RESERVOIR, SHOWING FINAL SETTING UP OF DERRICK ON CENTRAL COLUMNS.]
+
+_Concrete Lining and Roof._--The general arrangement and details of the
+side-walls, columns, and roof are shown on Plates VI, VII, VIII and IX.
+The principal feature consists in dividing the reservoir into radial
+sections and supporting the roof on 135 primary and 670 secondary beams,
+from 135 columns, spaced as follows:
+
+           Outer ring, at 34.25 m. from center    40 columns.
+            2d    "    "  27.88 "   "             40  "
+            3d    "    "  21.51 "   "             20  "
+           4th    "    "  15.41 "   "             20  "
+           5th    "    "   8.77 "   "             10  "
+           6th    "    "   2.40 "   "              5  "
+                                                 ---
+               Total                             135 columns.
+
+The inner bottom diameter of the reservoir is 70.32 m. (230.64 ft.); the
+upper inside diameter is 81 m. (265.68 ft.); the water depth at the
+overflow level is 9 m. (29-1/2 ft).
+
+The roof was designed to carry a dead load (the earth cover) of 150 lb.
+per sq. ft., and a live load of 100 lb. The maximum compressive fiber
+stress in the concrete was assumed at 550 lb. per sq. in. for the beams,
+and at 350 lb. for the columns, a low figure, because of their eccentric
+loading. The tensile strength of the steel was taken at 14,500 and
+16,000 lb. per sq. in. The twisted steel used for the column
+reinforcement was made at the local steel plant, but for the beams,
+etc., a twisted lug bar, of higher quality and greater permissible
+tensile stress, was used. The total quantity of steel used was 178 tons.
+It was calculated that the load on the column foundations would not
+exceed 1-1/4 tons per sq. ft. With the exception of the side-wall and
+floor, all the concrete was reinforced with steel, of the sizes and
+spacing shown on Plate VI.
+
+_General Construction and Erection Scheme._--The question of ordinary
+forms, requiring very heavy timber work, was a serious one, as suitable
+lumber is very expensive in Mexico; and the necessity of finishing this
+reservoir before the end of the first term allowed under the concession,
+which expired on December 31st, 1908, led to the adoption of what the
+writer believes is an original scheme for so large a structure. This
+scheme was to cast the columns in short sections, mould the radial and
+secondary beams as separate members, and then place them in position
+with derricks. At the same time, in the case of the beams, it was
+important not to sacrifice either the benefit of that part of the slab
+which is ordinarily assumed to act as a part of the beam, or the
+additional strength due to continuity; and, in case of the columns, the
+strength due to the reinforcement extending from the foundation to the
+beams.
+
+The T-beam section was secured by notching the tops of the moulded
+members, with notches 10 cm. deep, throughout the lengths of the beams,
+as shown on Plate VI. A computation of the maximum flange increment
+shows that these notches are sufficient to transfer the flange stresses
+to the stem, but, for additional security, flat steel bars were bent to
+a Z-shape and embedded in the top of the beam, about 60 cm. apart.
+Continuity in the beams was secured by carrying the steel to the tops of
+the beams over all supports, and, after erection, concreting them into
+the roof slab. The secondary beams, after casting, were dropped into
+recesses left in the radial beams for the purpose.
+
+_Concreting, Mixing, etc._--The radial beams and column sections were
+cast as nearly as possible under their ultimate positions; the secondary
+beams were cast outside and immediately adjoining the reservoir.
+
+The rock and sand was brought from the Company's crushing plant, in
+3-cu. yd., side-dump cars, running on a 30-in. track by gravity a
+distance of 1 km., the last 150 m. requiring hauling with 6 mules. The
+cars returned all the way to the crusher by gravity. These cars dumped
+the material into bins on the high ground above the reservoir; from
+there it was hoppered into cars which carried to the mixer all the
+material for one batch of concrete. Two No. 1 Smith mixers were used,
+and from 25 to 30 batches per hour could be handled in each machine.
+
+The concrete was transported from the mixers to place in 1/2-cu. yd.,
+18-in. gauge, swivel, steel dump-cars pushed by two men. All the
+concrete used in the bottom of the reservoir, for the main beams,
+columns, and floor, amounting to about 2,460 cu. m., was dumped through
+a chute into smaller cars. The chute had so many baffle-plates and bolts
+that it resembled a gravity mixer, but, although it was 12 m. long, it
+effectively prevented the separation of the materials.
+
+_Concrete Placing and Moulding._--The square foundations for the columns
+were deposited _in situ_, a recess being left for the reception of the
+pedestals, which were moulded in place afterward. The capitals and
+pedestals were cast in one piece, and the columns in 1.21-m. (48-in.)
+sections, eight 5-cm. holes being left in them by using wrought-iron
+pipes, held in place by templates and removed when the castings were
+about 3 hours old. The columns were erected by threading them on the
+15.8-mm. (5/8-in.) reinforcing rods, which extended from the pedestals
+up through the capitals. The rods were in two lengths, arranged to lap
+alternately at one-fourth, the center, and three-fourths of the height
+of the columns. In erection, a light timber frame was used in
+conjunction with the derrick, and, as the columns were placed, the
+reinforcing steel was grouted solid with 1:2 cement mortar.
+
+All the erection was done with a combined stiff-leg or guy derrick,
+having an 80-ft. boom and a 50-ft. mast, and fitted with a 30-h.p.
+Lambert hoisting engine. The derrick was erected seven times at the
+circumference, and its final position was on top of the center columns.
+The moving of the derrick a distance of about 45 m. and its subsequent
+erection occupied usually about 48 hours. The erection work was carried
+on continuously, day and night, the placing of the whole of the radial
+and secondary beams and columns occupying 2-1/2 months.
+
+_Forms._--As the erection scheme was designed to reduce the cost of
+forms, economical construction was of considerable importance. The wall
+was formed in 40 panels, about 6 m. wide and 11.27 m. high. The chief
+object in arranging them in this manner was to permit an expansion
+joint, 30 cm. wide, at each panel; this joint was not filled until after
+the completion of the roof, when the temperature inside the reservoir
+was uniform and not subjected to such great fluctuations as if exposed
+alternately to the hot sun and comparatively cool nights. The range of
+temperature during the construction period sometimes amounted to 80°
+Fahr. in 24 hours.
+
+The expansion joints were left to the last, when a uniform temperature
+of about 70° inside permitted the filling of the joints, thus avoiding
+all trouble from expansion cracks.
+
+The forms are shown in detail on Plate VII. They consisted of shutters
+stiffened with four trapezoidal trusses. The bottom posts of the trusses
+were fixed in holes formed in the foundation block; they were propped
+back from the embankment at the top, and secured to anchorages by iron
+rods.
+
+Six sets of these forms were used to construct the whole wall. The
+concrete was placed in position through stove-pipe chutes, 20 cm. in
+diameter, in continuous layers, the workmen treading and spading it well
+as it was deposited. The forms were allowed to remain 4 or 5 days, and
+were then struck and removed to another section. The pedestals and
+capital forms were of lumber, and five of each were used to cast the
+total number required. In the column sections the outer steel forms used
+in the manufacture of the Estanzuela pipes were adapted for this
+purpose. The radial beam forms, shown on Plate VII, were arranged with
+internal wedge-shaped blocks to mould accurately the recess for the
+secondary beams. The bottom forms were left attached to the beams for 28
+days, but the sides and ends were removed after 24 hours. Eight forms
+were sufficient for the whole 135 beams.
+
+For the secondary beams, 29 forms were used for the 670 beams, the
+bottom lumber also being left until they were mature for handling.
+
+By referring to the cross-section of the secondary beam, it will be
+noticed that it is jug-shaped, shelves being left on either side for the
+support of the roof forms, which were placed after the secondary beams
+had been properly grouted to the radial ones. The lagging was laid
+diagonally, so that the short diameter was slightly greater than the
+distance between the beams. This greatly facilitated the removal of the
+lagging, as it was merely necessary to strike the wedge-shaped fillets
+beneath, and turn them clockwise, after tearing out the end lagging.
+
+[Illustration: PLATE IX, FIG. 1.--VIEW OF SEPARATELY MOULDED SECONDARY
+BEAMS IN YARD BELOW SOUTH RESERVOIR.]
+
+[Illustration: PLATE IX, FIG. 2.--SETTING PRIMARY BEAMS, SOUTH
+RESERVOIR.]
+
+The writer believes that the adoption of forms of this type, rather than
+the ordinary kind, led to a saving of lumber of about 400,000 ft. b. m.
+During the erection and placing of the concrete, all the joining
+surfaces were carefully picked and cleaned, particular care being taken
+at the junction of the secondary with the radial beams, and the upper
+surfaces of all beams before laying the roof slab.
+
+After the greater part of the roof was completed, the floor was laid in
+those sections where it was protected from the sun's rays. The concrete
+was placed in two 15-cm. thicknesses, and the work was carried on night
+and day, without any joints. The laying of the floor occupied 8 days, or
+an average of nearly 100 cu. m. daily.
+
+[Illustration: PLATE X, FIG. 1.--VIEW OF COMPLETED SECTION OF SOUTH
+RESERVOIR. EXPANSION JOINTS IN SIDE-WALL NOT YET FILLED.]
+
+_Proportions of Concrete._--All the concrete work was brought to a
+smooth face by careful spading, no plastering being used throughout the
+reservoir, except in the superstructures. The work was kept well watered
+in every case for about 15 days. The whole of the concrete work in
+connection with the reservoir was completed in 5-1/2 months. The
+concrete for the columns and foundations was a 1:3:5 mixture, the
+aggregate consisting of equal parts of 19-mm. (3/4-in.) and 38-mm.
+(1-1/2-in.) crushed stone. The remainder of the concrete, except that
+for the roof, was a 1:2:4 mixture, the aggregate also consisting of
+equal parts of 19-and 38-mm. stone. With the exception of a short length
+of the side-walls, the sand used was that manufactured by the Company.
+When the crushing plant was unable to produce all the sand required, the
+Hornos sand (see Table 3) was used in the side-walls in equal
+proportions with the crusher sand.
+
+_Reservoir Outlet and Entrance Tower._--The outlet, 61 cm. (24 in.) in
+diameter, leads from a well in the center of the reservoir and passes
+under the floor and embankment to an outside valve-pit, 89 m. from the
+center. This pipe was laid in a trench in a solid cutting before the
+construction of the embankment, and was encased in 1:4:8 concrete.
+Where it passes under the embankment a 1:2:4 concrete cut-off wall, 3.6
+m. wide, 2.5 m. high, and 1 m. thick, was placed across it at right
+angles. The cast-iron pipe is curved upward in the central well, and has
+a bellmouth on which rests a movable circular copper screen.
+
+Above the outlet well, and on the roof of the reservoir, there is a
+central tower, giving access to the interior by a steel stairway. This
+tower also serves as a main ventilating shaft, and in it are arranged
+the guide-screens and gearing for raising them for cleaning purposes. In
+addition to the ventilation provided in the tower, 20 circular openings,
+30 cm. in diameter, are carried through the roof of the reservoir at the
+circumference and into the parapet walls.
+
+_Inlet Gate-House, etc._--The inlet gate-house is above the reservoir
+and about 54-1/2 m. from its center. The conduit enters at 589.00 m.
+above datum, and the gate-house contains the valves for controlling the
+inlet pipe to the reservoir, the by-pass, overflow, scour-out pipe, and
+the copper screens. The inlet, which is 45.7 cm. (18 in.) in diameter,
+is of cast-iron flanged pipes, carried on iron hangers on the side-wall
+of the reservoir, and, at a point 90 cm. above the floor level, it is
+turned at right angles to the side-wall and carried on concrete piers to
+the center of the first row of columns. The end of the pipe is closed by
+a blank flange, and the water is deflected at right angles through two
+30-cm. (12-in.) branches, for the purpose of setting up a slight
+circular motion as it enters the reservoir.
+
+The valve-pit is clear of the embankment, and in it are brought together
+the main supply and by-pass pipes on which are placed two 61-cm.
+(24-in.) sluice-valves; and between them there is a 20-cm. (8-in.)
+scour-out pipe, for emptying the reservoir into an adjoining arroyo. The
+arrangement of the valves gives complete control over the contents of
+the reservoir.
+
+_Venturi Meter-House._--Fig. 11 shows the arrangement of the Venturi
+meter and its automatic register in a house over the main supply pipe.
+This house is designed to form a feature of the entrance gateway of the
+reservoir grounds, which cover an area of 12 hectares.
+
+[Illustration: FIG. 11.--VENTURI METER-HOUSE.]
+
+_General._--The roof of the reservoir has been laid out as a garden, and
+the embankments are turfed. The intention is to develop the Company's
+land as a public park, as it commands fine views of the city and the
+surrounding mountains. An inspector's house has been built, and a
+private telephone line provides for communication with the Estanzuela
+intake and also with the general offices in the city.
+
+[Illustration: PLATE XVIII, FIG. 1.--VIEW OF SOUTH RESERVOIR, LOOKING
+TOWARD THE CITY.]
+
+
+
+
+                       SAN GERONIMO GRAVITY SUPPLY.
+
+
+_Provisional Supply._--It has already been stated that the Company began
+operations at San Geronimo in March, 1906, by sinking a well on the
+north bank of the Santa Catarina River at San Geronimo. At this point, a
+little later, a small steam pumping plant, sufficient to handle about
+8,000 liters per min., was installed. The lowest depth to which this
+well was ultimately sunk in water-bearing strata, was 7 m., the normal
+level of the water during 1906 and 1907 never falling lower than 569 m.
+above datum. Tests made from time to time during 1907-08, showed that
+this well was capable of supplying nearly 10,000,000 liters (264,000
+gal.) of water daily.
+
+The excellent supply yielded by this well made it desirable to adopt it
+immediately as a provisional measure, pending the completion of the
+larger works forming the western source of supply. To utilize the well
+to its fullest extent, a reinforced concrete reservoir, of 3,000,000
+liters capacity, was constructed on the south bank of the river, the top
+water level being 585 m. above datum, that is, at the same elevation as
+the proposed reservoir for the Estanzuela supply. The reservoir is 53.80
+m. long, 21 m. wide, and has a water depth of 3.25 m. at the overflow
+level. It is excavated on a steep hill slope, and has an earth
+embankment on the lower side. The lining is of concrete, 20 cm. thick,
+and the roof is of reinforced concrete composed of flat arches springing
+from beams carried on 46 by 35-cm. reinforced columns. There are 68 of
+these columns, and they are 3 m. apart longitudinally and 5 m. apart
+transversely. The roof was not constructed until October and November,
+1907, and prior to that time the necessity of covering the reservoir was
+amply demonstrated by the growth, during hot weather, of considerable
+quantities of green algæ, which had to be skimmed from the surface of
+the reservoir every few days.
+
+The delivery pipe from the pumping plant was originally of riveted steel
+and was asphalted. It was 30 cm. in diameter, 2 mm. in thickness, with
+slip joints, and where it crossed the river it was encased in concrete.
+This pipe was afterward replaced by a cast-iron pipe of the same
+diameter. The supply pipe to the city was also of sheet steel, 30 cm. in
+diameter. For a part of its length it was laid in the high ground of the
+south bank of the river, which it crossed near the western limits of the
+city, and was then connected to a 30-cm, cast-iron pipe in the
+distribution system. The total length of the pipe from the reservoir to
+the city distribution system was 2,850 m.
+
+This provisional pipe continued in service from October, 1906, until
+August 27th, 1909, when the river portion was completely swept away,
+together with the provisional pump-house at San Geronimo, during the
+great flood in the Santa Catarina River. Fortunately, the permanent
+supply works were completed at the time, so that the destruction of this
+pipe line, which had already served its original purpose, had no effect
+on the supply of water to the city.
+
+[Illustration: PLATE XI.--SECTION OF INFILTRATION GALLERY, SAN GERONIMO
+GRAVITY SUPPLY.]
+
+_Infiltration Gallery._--The chief feature of the San Geronimo gravity
+supply is the infiltration gallery. By referring to the profile on Plate
+XI it will be seen that at this place there is a considerable area of
+what is undoubtedly water-bearing gravel. The main conditions were
+revealed by the borings previously carried across the valley, but the
+profile has been corrected to show the actual conditions as established
+at a subsequent date by shafts. Practically, the water-bearing strata
+are not limited merely to the sand and coarse gravels, as the clay
+formation lying above and below them is full of small gravel deposits
+containing considerable volumes of water. The main direction of the
+underflow is toward the east, and the hydraulic gradient, which was
+established from wells sunk farther west, was found to be approximately
+1%, or practically the same as the average surface of the bed of the
+river above the line of the infiltration gallery.
+
+The general scheme for tapping this underflow was to drive a main
+gallery at the 560-m. level on a grade of 0.05%, which was sufficiently
+high to take the supply by gravity to the western reservoir, having a
+top water level at 558.75 m. above datum. This elevation is sufficient
+to give an excellent pressure over about 60% of the city, and a fair
+pressure to reach the upper stories of the highest houses, if required,
+over the whole supply district. From this gallery it was proposed to
+sink shafts at frequent intervals, for a total distance of 300 m.,
+carrying them below the gallery level, to tap any water-bearing gravels
+there might be in the clay formation underlying the gravels and sands.
+From the main gallery it was proposed to construct branch galleries up
+stream on a flat gradient, so as to obtain the advantage of an increased
+head due to the steep hydraulic gradient of the underflow water.
+
+[Illustration: FIG. 12.--DIAGRAM SHOWING VARIATION IN WATER PLANE 1905
+TO MARCH 1910 AT SAN GERONIMO.]
+
+In investigations of this kind, it is of first importance to have a
+continuous record of the level of the water plane, and Fig. 12 has been
+plotted to show its variation at San Geronimo from the beginning of
+1905 to March, 1910. From January, 1909, to March 31st, 1910, these
+levels are averages of daily readings taken in 9 shafts sunk along the
+proposed line of the infiltration gallery. In 1902 the water plane was
+standing at 570.18 m. above datum, but from that date until 1905 the
+writer has been unable to find any records. This diagram should be
+examined together with the rainfall diagram, Fig. 3, and it will be
+noticed that the fall in the water plane drops with the general scarcity
+of the rainfall during 1907-08, and until July, 1909. The year previous
+to July, 1909, is regarded, by many competent local observers to have
+been the longest period of extreme drought in 30 years in Nuevo León,
+and the evidence which the writer has been able to gather regarding
+stream flow in the neighborhood of Monterrey supports this view. The
+total rainfall at Monterrey for the year prior to July 1st, 1909,
+amounted to 9.98 in., or 4.16 in. less than the lowest record for any
+calender year since 1894, or, in other words, about 45% of the average
+annual rainfall.
+
+The lowest point to which the water plane dropped was during June and
+July, 1909, when the levels stood slightly above 565.00 m., or 5 m.
+above the level of the floor of the infiltration gallery. During this
+period pumping tests were made in the various wells, and from these it
+was quite clear that the infiltration gallery, if carried far enough to
+meet them all, would yield a supply of from 25,000,000 to 40,000,000
+liters daily. During the great rainfall of August, 1909, the water
+levels rose very rapidly; the heavy precipitation between August 9th and
+10th caused the level to rise to 568.00 m. in about 4 days, and 6 days
+after the great flood of August 27th, the water level, which had
+continued rising gradually, reached 571.40 m., and then fell gradually
+until at the end of March, 1910, it was practically the same as it had
+been from 1902 to 1905.
+
+[Illustration: PLATE XII.--SAN GERONIMO GRAVITY SUPPLY.]
+
+It should be noticed that the readings were taken in the shafts on the
+high ground to the west of the present river bed, and were independent
+of any flow there might be in the river. During times of ordinary floods
+in the river, it was very noticeable that, notwithstanding the fact that
+the river water might be turbid to an extreme degree, the well even in
+immediate proximity to the river bed did not show the least sign of
+discoloration.
+
+_Design of Works._--Plate XII shows the general design of the gravity
+scheme, which consists of a main tunnel 550 m. long and a concrete
+aqueduct, 1.06 m. (42 in.) in internal diameter and 2,311 m. in length,
+discharging into a low-service distributing reservoir at the extreme
+western limits of the city. The tunnel and aqueduct were laid on a
+gradient of 0.05%, and the latter was designed to discharge 55,000,000
+liters per day (22.8 cu. ft. per sec.) if flowing to its full capacity.
+
+_Gravitation Tunnel._--This tunnel, shown on Plate XII and Fig. 13, was
+completed prior to driving the infiltration gallery into the
+water-bearing gravel, so that the water encountered in the gallery could
+be easily drained off by gravity, thus avoiding a heavy outlay for
+pumping. The tunnel passes through various strata, the principal ones
+being calcareous shale, conglomerate, and gravels. The tunneling
+operations were carried on from 5 shafts, No. 1 being 23 m. deep, and
+the others varying from 20 to 10 m. The shafts in loose ground were
+timbered in the usual way, having clear inside dimensions of 2 m. Shaft
+No. 1, which was entirely in shale, was taken out approximately to 3.35
+m. in diameter, so as to permit it to be lined with concrete having a
+finished internal diameter of 2.43 m.
+
+[Illustration: FIG. 13.--GENERAL DETAILS SAN GERONIMO GRAVITY PIPE LINE.]
+
+Fig. 13 shows the details of the tunnel, which was lined with concrete,
+the bottom and sides being approximately 23 cm. (9 in.) thick. The
+interior dimension is 0.91 m. at the invert level and 1.016 m. at a
+height of 1.22 m., the corners between the side-walls and the floor
+being slightly curved. The arch is formed of two rings of brickwork in
+cement mortar, this thickness being increased in some lengths to three
+rings. Where the rock was in good condition, and not likely to
+disintegrate easily, the arch, for a distance of 90 m., was left
+unlined. Of the total distance of 550 m., careful timbering was required
+for 300 m. In lining the timbered portion of the tunnel with concrete,
+all the timber was removed, except in loose ground, where the laggings
+were left in position.
+
+While the tunnel was being driven, a start was made to drive the north
+end of the infiltration gallery, which was in rock for a distance of 44
+m. Water appeared at about 35 m., and then the work was temporarily
+suspended until the gravitation tunnel was completed and a length of the
+aqueduct had been constructed far enough down stream on the north bank
+of the river to permit of draining direct to the river. This point was
+reached at 1,170 m. from Shaft No. 1, and there a temporary overflow
+chamber was constructed.
+
+When the tunnel was completed, the two intermediate shafts were filled
+up, the remaining three being retained permanently. Shafts Nos. 2 and 3
+were lined with concrete, 76 cm. (30 in.) in internal diameter, and 23
+cm. thick. They were domed at the top to form circular openings to
+receive cast-iron covers. Progress on this tunnel was slow, taking from
+December, 1907, to November, 1908, to complete, owing chiefly to
+difficulties with an incompetent contractor. The contract was
+subsequently transferred to Mr. John Phillips, of Mexico City (who was
+also the contractor for the aqueduct), who completed it satisfactorily.
+
+_Continuation of the Infiltration Gallery._--When the aqueduct (to be
+referred to again) was completed as far as 1,170 m. from Shaft No. 1,
+the driving of the infiltration gallery, which was 2 m. high and 1-1/2
+m. wide, was continued until gravel was encountered in the roof, at 44
+m. from the shaft. At this point the rock dipped at an angle of 45°,
+and the gravels contained quantities of large boulders mixed with fine
+sand; immediately after encountering the gravel, a flow of about 90
+liters per sec. was met, evidently coming through from a pot-hole in the
+shale. This quantity diminished in about 10 days to about one-fourth,
+but gradually increased again as the driving proceeded. The operations
+of driving the tunnel from 44 m. forward were begun in the dry season,
+in February, 1909, and the gravel was encountered for a distance of 24
+m., or up to 68 m. from the shaft. The center of this gravel bed was
+about 30 m. south of the old river channel, which had been continuously
+dry at the surface for several years. Up to 68 m. the work was very
+difficult, owing to the upper part being of loose gravel and the lower
+in very contorted shale. The timbering of the tunnel in the full gravel
+section consisted of heavy square settings, 1 m. apart. At 68 m. the
+clay and gravel formation was met, and the rate of progress then was
+about 4 or 5 m. a week. A short branch gallery was also driven about 7
+m. up stream near Shaft No. 2. The total distance the infiltration
+gallery was carried from Shaft No. 1, was 100 m., when the floods of
+August, 1909, caused its suspension.
+
+During the progress of the gallery, attempts were made to sink a 3-1/2
+by 2-m. shaft at a point along the line of the infiltration gallery,
+about 130 m. from Shaft No. 1, but water in such abundance was
+encountered that it was practically impossible to sink it in the
+ordinary way more than about 6 m. deep, the quantity of water to be
+dealt with amounting to about 20,000,000 liters daily. Seven shafts were
+then sunk in the high ground to the north of the river, five of these
+being on the line of the gallery and two 30 m. westward. They were sunk
+during the dry season prior to July, 1909. These were ordinary timbered
+shafts, 2 m. square between the walings, and were carried to the depths
+shown on Plate XI. In Shafts Nos. 5, 6, and 7 the water was flowing with
+considerable velocity, while Shaft No. 9 seemed to have penetrated a
+different water plane and one which was probably independent of that
+showing in any of the other shafts, in which the water was practically
+at a uniform level. The evidence obtained showed that if the gallery
+could be carried to Shafts Nos. 6 or 7 a great abundance of water would
+be intercepted. Owing to the difficulties of sinking ordinary shafts in
+the wide river channel, circular shafts were put down. These were 1.37
+m. in internal diameter and 23 cm. thick, and were of concrete
+reinforced with No. 10 vertical rods, 19 mm. in diameter, tied together
+with No. 6 wire. These shafts were provided with steel cutting edges.
+
+Shaft No. 2 was sunk to a depth of 1 m. below the infiltration gallery
+level, No. 3 within 2 m., and No. 4 within 4 m., before August, 1909.
+The shafts were sunk by digging them out and loading them at the top,
+the top of the shafts being kept generally 3 m. out of the ground. Shaft
+No. 3 encountered great volumes of water, and, in order to enable
+sinking operations to proceed, a pumping shaft, 2-1/4 m. square, was
+sunk a little west of it to draw off the water. Notwithstanding the fact
+that the prolonged period of drought had lowered the general water plane
+in all the shafts to 565.00 m. above datum, the difficulties of handling
+the water even at that level were considerable. At the beginning of
+August the work was progressing very satisfactorily, but the
+extraordinary rainfall of that month caused the work to be shut down
+temporarily.
+
+_Effect of the Floods in the Santa Catarina River._--The area of the
+water-shed of the Santa Catarina River above Monterrey is about 1,410
+sq. km. (544 sq. miles), and its area at San Geronimo, owing to its
+configuration, is practically the same. Its general character has
+already been referred to. On the night of August 10th and early on the
+morning of August 11th, a big flood came down the river, flowing at its
+maximum about 1,130 cu. m. (40,000 cu. ft.) per sec., due to the heavy
+rainfall (Fig. 4). This flood carried away all the temporary staging
+around the shafts, seriously wrecking the temporary pumping station, as
+well as destroying the 30-cm. cast-iron pipe, notwithstanding the fact
+that it had been encased in a block of concrete 3 m. wide and 1-1/2 m.
+thick right across the river; but no damage was done to the infiltration
+gallery or to the shafts in the river channel. The effect of the flood
+on this pipe is shown by Fig. 2, Plate XXXI.
+
+[Illustration: PLATE XXXI, FIG. 2.--PROFILE SKETCH, LOOKING UP STREAM ON
+LINE OF 24-INCH MAIN SUPPLY PIPE.]
+
+Following this flood, which had caused the loss of 14 lives in the city,
+3 miles below San Geronimo, there was practically no rain for 13 days.
+Then, on August 25th the second heavy precipitation began and continued
+until August 29th, the details being shown on Fig. 4.
+
+This precipitation, therefore, fell on a water-shed which was completely
+saturated, as it had already absorbed a large proportion of the 13.38
+in. of rain which fell during August 10th and 11th; and at every point
+along the river, prior to August 25th, springs were issuing forth, and
+there had been very little evaporation during the intervening dry spell.
+
+The writer has calculated that at Monterrey this flood reached the
+enormous quantity of 6,650 cu. m. (235,000 cu. ft.) per sec., a rate
+equal to 432 cu. ft. per sec. per sq. mile of water-shed.[6] The effect
+of this flood was to demolish completely about 1,200 "sillar" houses
+(without taking into consideration the numerous wooden houses) at
+Monterrey, and to cause a fearful loss of life, variously estimated
+between 3,000 and 5,000 persons; the lower figure the writer believes is
+approximately correct. At San Geronimo the original pumping station was
+carried away entirely, leaving practically no trace whatever.
+
+[6] The writer, in a brief article contributed to _Engineering News_
+soon after the flood (September 23d, 1909), gave this figure as 271,500,
+or approximately equal to a run-off of 500 cu. ft. per sec. per sq.
+mile; but, from a later and more complete study of the conditions for
+many miles above Monterrey, he believes the above quantity to be
+approximately correct.
+
+Shaft No. 2 was apparently destroyed, while No. 3 was turned at an angle
+of about 50° down stream and filled up completely with sand. The
+infiltration gallery, near Shaft No. 2, was completely blocked with fine
+sand and gravel, and access could only be obtained as far as 54 m. The
+profile, Plate XI, shows the change which had taken place in the river
+bed. The original course of the stream was changed to the north bank, 50
+m. distant, the effect of the scouring action of the flood being to
+lower the general level at this point about 3.65 m., while the southern
+portion of the channel was slightly raised. At present (April, 1910),
+the end of the driven portion of the infiltration gallery is about 35 m.
+from the center of the stream, which is still carrying about 2,270
+liters (80 cu. ft.) per sec.
+
+Immediately after the flood the flow in the gallery was 450 liters (16
+cu. ft.) per sec., and this quantity has remained constant since that
+time. The probable effect of the flood was to disturb the whole
+subsurface above the infiltration gallery and put it in motion,
+completely cleaning the gravels of their surrounding clay, which would
+account for the large infiltration of water in so limited a distance.
+The water has always been limpid and pure, but its hardness remains the
+same as it was prior to the flood.
+
+With the copious supply of water from this source, due of course to
+abnormal conditions and not likely to be permanent, the operations of
+tunneling have been suspended temporarily; but it is proposed to
+continue the driving of the gallery, from a new shaft west of No. 3.
+The water encountered will be drained off by pumping until the main
+water-bearing gravels, in the neighborhood of Shaft No. 5, are reached.
+It is also proposed to reconstruct the 30-cm. high-level pipe line, from
+San Geronimo along the high road on the north bank of the river, so that
+by pumping water can be delivered to the city system from Shafts Nos. 5,
+6, and 7, in the event of a shortness of supply from the Estanzuela
+River.
+
+_Shaft No. 1._--Shaft No. 1 is designed to connect the infiltration
+gallery with the gravitation tunnel. This shaft has an inner diameter of
+2.43 m. (8 ft.) and is fitted with a special gate-valve. In the bottom
+of the door of this valve there is a smaller valve, 30 cm. in diameter,
+so that, when the infiltration gallery is closed for cleaning out the
+sump, the smaller door, which is operated through the same spindle by a
+bevel-geared head-stock at the top of the shaft, can be opened first.
+Space is also left for screens if these should be found necessary.
+Access to this shaft is gained by a reinforced concrete stairway in nine
+stages. The superstructure is to be supported on reinforced concrete
+column foundations carried to the firm rock, owing to the loose
+condition of the strata at the top of the shaft.
+
+_Aqueduct._--The construction of the concrete conduit was begun in
+April, 1908. Fig. 13 shows the general types. Type _A_ was adopted in
+gravel and conglomerate formation, and Type _B_ where the excavation was
+in "sillar," the soft nature of this rock permitting it to be excavated
+exactly to the required external diameter of the concrete lining.
+
+The concrete which was without steel reinforcement was a 1:2-1/2:3-1/2
+mixture, the sand being from the crusher and the aggregate from the
+river bed, screened to pass a 25-mm. mesh. Where the conduit crossed the
+river obliquely, immediately below the gravitation tunnel, it was
+strengthened with mass boulder concrete of Type _C_. During the great
+flood this heavy section withstood its effects without damage of any
+kind, but beyond this point, where the conduit had been laid in compact
+cemented gravels, the scouring action of the flood on the north bank
+lowered the level of the gravels from 2 to 3 m.; the only damage,
+however, was the scouring away of the gravels at the south side of the
+conduit. To prevent such an occurrence in the future, the conduit at
+that point was strengthened with additional concrete for a distance of
+195 m., as shown on Fig. 13. The extra concrete, amounting to 733 cu.
+m., was a 1:3:5 mixture, in which was embedded 20% of heavy boulders.
+The top of this special length now forms a weir for the present river
+flow. Where the conduit enters the bluff on the north side of the river,
+at 1,200 m., there is an overflow chamber which has a sluice-gate 76 cm.
+wide, arranged so that the conduit can overflow at the present time when
+running 76 cm. deep. To deflect the flow in the conduit, a wrought-iron
+plate, provided with a balance weight, is dropped into a groove on the
+lower side. The outlet is a 61 cm. concrete tube, having its invert
+above ordinary flood level, and arranged to be closed by a gate.
+
+At 1,963 m. the conduit is carried over an arroyo on a segmental arch of
+8 m. clear span, as shown on Fig. 13. There are 5 ventilating columns
+and 5 manholes on the aqueduct.
+
+[Illustration: PLATE X, FIG. 2.--SETTING FORMS FOR SAN GERONIMO
+CULVERT.]
+
+The aqueduct terminates in the Obispado distributing reservoir
+valve-house, at a level of 558.50 m. The work in connection with this
+aqueduct was completed by December, 1908.
+
+
+
+
+                   DISTRIBUTING RESERVOIR AT OBISPADO.
+
+
+The main distributing reservoir for the San Geronimo gravity supply is
+immediately below the historic Obispado (Bishop's Palace), at the western
+limits of the city. The general arrangement and lay-out is shown on Plate
+XIII.
+
+[Illustration: PLATE XIII.--GENERAL PLAN AND SECTIONS, OBISPADO
+RESERVOIR.]
+
+_Valve-House._--The invert of the conduit from San Geronimo, where it
+enters the valve-house, is 558.50 m. above datum. The valve-house, which
+is built in the center of the reservoir, is shown on Fig. 2, Plate XVIII.
+One of its special features is the provision of the main overflow at this
+point instead of within the reservoir proper. The inlet, main supply
+tunnel, independent by-pass overflow, scour-out pipes, gate-valves, and
+screens, are all controlled within the valve-house.
+
+[Illustration: PLATE XVIII, FIG. 2.--VIEW OF ROOF OF OBISPADO RESERVOIR,
+LOOKING NORTH.]
+
+_Reservoir._--The reservoir is rectangular, 126 by 81 m. (413.28 by
+265.68 ft.) at the top, and has a water depth of 4 m. (13.1 ft.). In the
+design it was necessary to limit it to the lowest economical depth, so
+as to increase the static pressure over the low-pressure district as
+much as possible.
+
+_Excavation and Embankment._--The excavation, except for a depth of
+about 1 m. which was in black soil, was chiefly in a disintegrated
+"sillar" stratum of a heavy clayey nature, the greater part of which
+could be handled conveniently with plows and scrapers; the actual
+foundation on the eastern half required blasting for the final depths.
+
+The total excavation amounted to 56,479 cu. m., of which 7,255 cu. m.
+were placed in the embankment, the remainder being deposited in the
+immediate neighborhood of the reservoir. The final trimming of the
+banks, which were left 30 cm. full, was not undertaken until the lining
+was begun. The work was done under contract with Mr. J. S. Nickerson, of
+Monterrey. The excavation had only one classification, and the contract
+prices were 0.50 peso per cu. m. for material carried to spoil banks,
+and 1.00 peso for material placed in the embankment. The excavation was
+begun in December, 1907, and completed in April, 1908. The work was then
+left standing until the end of 1908 to allow the banks to consolidate
+thoroughly prior to lining, which was begun on January 4th, 1909.
+
+_Concrete Lining and Roof._--Plate XIII shows the general plan and
+sections, the main feature being the simple division of the reservoir
+into 24 rows of columns longitudinally and 15 rows transversely, making
+a total of 360 columns, less the four left out at the central tower. All
+the columns are 5 m. apart both ways. The roof was designed for a live
+load of 100 lb. and a dead load of 150 lb., the same as at the South
+Reservoir. With the exception of the floor, all the concrete work was
+reinforced with twisted steel lug bars. The foundation load on the
+columns for the eastern half of the reservoir is 0.9 ton per sq. ft.;
+that on the columns for the western half, where the foundation is of
+very hard sillar and conglomerate, is 1.95 tons per sq. ft.
+
+_Under-drainage of the Floor._--To provide for proper drainage in case
+of seepage, the floor was underdrained with rubble drains, 30 cm. wide
+and 23 cm. deep, filled with large round gravel carted from the bed of
+the Santa Catarina River. The total length of these underdrains is 1,160
+m. In order to facilitate the detection of any seepage, they were
+conducted to a permanent inspection pit outside of the reservoir.
+
+_Main Distributing Conduit._--The main distributing conduit is laid
+along the inside of the reservoir, at the inlet end, and carried on
+elliptical arches of 2 m. span to a height of 71 cm. above the finished
+floor level. This conduit is 76 cm. high and 45.7 cm. wide, and it
+branches in two directions from the inlet tunnel to each side of the
+reservoir, its total length being 69 m. In order to prevent any
+stagnation and to give a continuous circulation, the water is delivered
+at eight points, in the length of the distributing pipe, through square
+openings with semicircular tops, the areas of the openings increasing
+toward the ends. These inlets are placed so that the current will not
+strike the roof columns.
+
+_Outlet Tunnel and Valve-House._--The outlet tunnel is at the north end
+of the reservoir, and was excavated in hard sillar rock. The tunnel is
+lined with concrete 30 cm. thick, the finished internal dimensions being
+1.52 by 0.91 m. The length of the tunnel is 22.5 m. to the point where
+it enters the outlet-house. This house is divided by a wall 45 cm.
+thick, which supports a 76-cm. (30-in.) penstock-valve. The supply pipe
+to the city leaves this chamber in the west wall, and is also fitted
+with a 76-cm. penstock-valve. The supply pipe has a copper screen of the
+same design and dimensions as those in the inlet-house. A 30-cm.
+(12-in.) scour-out pipe in this chamber provides for draining the
+contents of the reservoir to a neighboring irrigation ditch, when
+necessary.
+
+The superstructure of the valve-house is of concrete, and at the floor
+level there are bevel-geared head-stocks to raise the valves, etc.
+
+_By-Pass and Supply Pipes._--The by-pass and supply pipes are carried
+below the reservoir embankment to join the main 76-cm. (30-in.)
+cast-iron distributing pipe to the city. For this short distance they
+were constructed of concrete, 76 cm. in internal diameter, 10 cm. (4
+in.) thick, reinforced with 6-1/2-mm. square steel longitudinal rods, 30
+cm. from center to center in the circumference, and hooped with
+6-1/2-mm. square steel rods spaced 30 cm. apart. The concrete forming
+these pipes was a 1:1-1/2:2-1/2 mixture.
+
+_Parapet Walls._--The parapet walls have 12 piers at each side and 8 at
+each end. In these piers there are ventilating openings branching at the
+top to each side of the parapet, with outlets provided with cast-iron
+screens. This arrangement gives 4 sq. m. of ventilating space (exclusive
+of that provided in the central tower), equally distributed at 40 points
+around the walls of the reservoir.
+
+_General Construction Scheme._--The concrete mixing plant, which
+consisted of two No. 1 Smith mixers, was arranged in connection with the
+bins and hoppers for the rock and sand on the high ground to the west,
+and from there the material was conveyed on a framed timber gangway
+carried right across the center of the reservoir, as shown by Fig. 1,
+Plate XVII. From this central platform the concrete for the columns was
+filled from stages placed on the top of traveling towers, 5 m. high,
+which were run between two rows of columns on standard-gauge rails laid
+on the floor of the reservoir. By this arrangement 24 columns could be
+filled from each length of track. A main narrow track was also laid
+right around the reservoir, with the necessary turn-outs.
+
+[Illustration: PLATE XVII, FIG. 1.--FILLING PRIMARY BEAMS FROM TRAVELING
+TOWER, OBISPADO RESERVOIR.]
+
+[Illustration: PLATE XV, FIG. 1.--CONSTRUCTION OF WEST SIDE-WALL OF
+OBISPADO RESERVOIR.]
+
+[Illustration: PLATE XV, FIG. 2.--PRIMARY BEAMS AND COLUMNS, OBISPADO
+RESERVOIR.]
+
+[Illustration: PLATE XIV.--DETAILS OF FORMS FOR CONCRETE WORK, OBISPADO
+RESERVOIR.]
+
+The forms for the columns, primary and secondary beams, are shown on
+Plate XIV. The side forms for the primary beams were struck in 24 hours,
+so as to economize lumber; but the bottom lumber was left in position
+for 28 days. To avoid much unnecessary timber, the secondary beam forms
+were supported at the ends on reinforced concrete corbels cast on the
+primary beams.
+
+For placing the side-walls, a special traveling form was used, the
+details of which are shown clearly on Plate XIV. At the end of each form
+an expansion joint of 25 cm. was left to be filled after the roof was
+placed in position. The concrete was delivered to the wall through
+stove-pipe chutes, and carefully spaded by workmen in the limited space
+between the forms and the embankment. The wall form was removed after 36
+hours, by loosening the jacks and pulling forward the hooked tie-rods.
+This form is also shown on Fig. 2, Plate XVI.
+
+[Illustration: PLATE XVI, FIG. 2.--TRAVELING SIDE-WALL FORM, OBISPADO
+RESERVOIR.]
+
+[Illustration: PLATE XVI, FIG. 1.--PREPARING FLOOR FOR CONCRETING,
+OBISPADO RESERVOIR.]
+
+The concreting of the roof slab was carried on continuously, and, when
+partly completed, the floor was laid in the shade. The bottom layer of
+the floor, 13 cm. thick, was laid in continuous panels between the
+columns, and brought to a fairly smooth surface. On this surface, after
+keeping it wet for 10 days and then allowing it to dry thoroughly, a
+layer of asphaltum, supplied by the American Asphaltum and Rubber
+Company, of Chicago, was placed. The work was done by ordinary Mexican
+laborers after they had received a few days' instruction from one of the
+Asphaltum Company's superintendents. The surface of the lower layer was
+kept perfectly clean, and then received one coat of "Pioneer" paint. The
+asphaltum, heated in a boiler inside the reservoir to a temperature of
+approximately 425° Fahr., was then poured over the floor from buckets,
+in a layer approximately 4 mm. thick. Where the floor joined the column
+pedestals, and at each new panel section, a double thickness was used.
+The labor cost of water-proofing, including superintendence, etc.,
+amounted to 3.3 cents (Mexican) per sq. m. for painting with "Pioneer"
+paint, and 5.4 cents for the asphaltum coating, or a total labor cost of
+8.7 cents per sq. m. for the complete water-proofing. This cost is based
+on a rate of 8.00 pesos per day for a foreman, and 1.00 peso for each
+laborer. It required 50 U. S. gal. of the paint to cover 265.2 sq. m.,
+and an average of about 6 lb. of asphaltum for 1 sq. m.
+
+The upper concrete layer of the floor, 10 cm. thick, was placed so as to
+break joint with the lower, and was brought to a smooth surface with
+wooden floats sheathed with steel and reaching across the panels. In
+this way a perfectly smooth surface was obtained without any plastering.
+
+[Illustration: PLATE XVII, FIG. 2.--CENTRAL TOWER AND STAIRWAY, OBISPADO
+RESERVOIR.]
+
+The concrete for the beams, columns, side-walls, and floor, was a
+1:2-1/2:4 mixture, crushed sand and stone being used throughout. In the
+roof slab the mixture was 1:2:3.
+
+The whole of the concrete work of the reservoir was completed in 6
+months, by the Company's own administration, and the reservoir was first
+put into service a few days after the great flood of August 27th, when
+the Estanzuela supply main, crossing the Santa Catarina River, was
+partly destroyed. Since that time frequent examinations of the
+inspection pit, which is connected by a pipe to the rubble drains under
+the floor, have never revealed the slightest leakage.
+
+_Lay-Out of the Reservoir Roof and Grounds._--The Company owns about
+11-1/2 hectares of land, which includes that occupied by the reservoir
+and its surroundings, and as this property is in an attractive
+situation, commanding fine views of the Sierra Madre Mountains, the
+whole of the works have been given a pleasing architectural character,
+and the grounds laid out to form a public park for the citizens of
+Monterrey.
+
+[Illustration: FIG. 14.--SKETCH PLAN OF LAY OUT AT OBISPADO RESERVOIR.]
+
+The general plan of the scheme is shown by Fig. 14 and Fig. 2, Plate
+XVIII. The roof, which has an area of 1 hectare, has been laid out with
+walks and grass plots, and the surrounding embankments have been
+converted into driveways. Above the reservoir a small plazuela of 1/2
+hectare has been laid out with a space above it for a band-stand. The
+whole of the ground has been encircled with carriage drives, on which it
+is the intention to plant shade trees. The lay-out of this land also
+embraced the scheme for protecting the reservoir by draining the
+surface-water away to the irrigation ditches.
+
+
+
+
+               COMPARISON OF SOUTH AND OBISPADO RESERVOIRS.
+
+
+The two reservoirs are practically of the same capacity, the only
+difference being the level of the overflows in their relationship to the
+roof, which gives the Obispado Reservoir a slightly greater capacity.
+Some comparative figures may be of interest, owing to the differences in
+type and construction. Table 7 gives the comparative quantities of
+material in each reservoir proper, that is to say, exclusive of the
+valve-houses, lay-out of grounds, etc.
+
+  TABLE 7.--COMPARISON OF MATERIALS IN SOUTH AND OBISPADO RESERVOIRS.
+
+  ==========================+===============================+============
+                            |    SOUTH RESERVOIR.  | _OBISPADO RESERVOIR._
+                            +--------+-------------+--------+------------
+                            |        | Quantities, |        | Quantities,
+                            |   No.  | in cubic    |   No.  | in cubic
+                            |        | meters.     |        | meters.
+  --------------------------+--------+-------------+--------+------------
+  _Earthwork:_              |        |             |        |
+      Total excavation      |  ...   |   34,000    |   ...  |   56,479
+      Placed in embankment  |  ...   |   31,500    |   ...  |    7,255
+      Placed in spoil banks |  ...   |    2,500    |   ...  |   49,224
+                            +--------+-------------+--------+------------
+  _Concrete:_               |        |             |        |
+      Columns (including    |        |             |        |
+               foundations) |  135   |    1,240    |   356  |      543
+      Primary beams         |  135   |      440    |   374  |      462
+      Secondary beams       |  670   |      515    | 1,252  |      576
+      Side-walls            |  ...   |    1,255    |   ...  |      710
+                            |        |             |        |
+                            | Square |             | Square |
+                            | meters.|             | meters.|
+      Roof slab             | 5,140  |      520    | 10,206 |    1,020
+      Floor                 | 4,070  |      780    |  9,200 |    2,120
+      Parapet walls         |  ...   |       90    |   ...  |      165
+                            +--------+-------------+--------+------------
+           Total concrete   |  ...   |    4,840    |   ...  |    5,596
+                            +--------+-------------+--------+------------
+                            |        |  Pounds.    |        |  Pounds.
+  Reinforcing steel bars    |  ...   |  387,000    |   ...  |  380,000
+                            |        |             |        |
+                            |        |  Square     |        |  Square
+                            |        |  meters.    |        |  meters.
+  Expanded metal in roofs,  |        |             |        |
+                slabs, etc. |  ...   |    5,691    |   ...  |   10,490
+  ==========================+========+=============+========+============
+
+The total cost of these reservoirs, including valve-houses, by-passes,
+and the length of supply pipe where the by-pass joins, and including all
+engineering expenses, etc., but exclusive of the cost of lands,
+planting, fencing, and special work in connection with the formation of
+parks, was as follows:
+
+South Reservoir: 394,000 pesos, or 10,368 pesos per million liters.
+
+Obispado Reservoir: 375,000 pesos, or 9,375 pesos[7] per million liters.
+
+[7] Mexican currency.
+
+These rates may be regarded as reasonable when taking into consideration
+the special difficulties of construction in Mexico, and the high cost of
+all imported material, on which heavy duties are levied.
+
+The value of the materials alone in these reservoirs amounted to more
+than 70% of their total cost.
+
+
+
+
+              ANALYSES OF ESTANZUELA AND SAN GERONIMO WATERS.
+
+
+Table 8 shows analyses of the Estanzuela and San Geronimo waters, made
+in February, 1910, by Messrs. Ledoux, of New York City. The Estanzuela
+sample was taken at the valve-house of the South Reservoir, while that
+of San Geronimo was taken in Shaft No. 1 of the infiltration gallery
+when flowing at the rate of about 450 liters per sec. Both waters are
+absolutely free from turbidity.
+
+         TABLE 8.--ANALYSES OF ESTANZUELA AND SAN GERONIMO WATERS.
+                          In Parts per Million.
+
+  ==================================+================+===============
+                                    |                | San Geronimo
+                                    | Estanzuela.    | Infiltration
+                                    |                | Gallery.
+  ----------------------------------+----------------+---------------
+  Total solid matter in solution    |     209.00     |    305.00
+  Organic and volatile matter       | Not weighable. | Not weighable.
+                                    |                |
+  ANALYSIS OF SOLIDS:               |                |
+      Silica                        |      10.5      |     12.0
+      Iron and Alumina              |    Traces.     |   Traces.
+      Lime                          |      85.4      |    112.6
+      Magnesia                      |       3.8      |     22.6
+      Soda (Na_{2}O)                |      13.3      |     20.2
+      Potash (K_{2}O)               |       2.0      |      1.9
+      Sulphuric Acid                |      24.4      |     11.5
+      Chlorine                      |       2.0      |      2.8
+                                    +----------------+---------------
+  PROBABLE COMBINATION OF BASES &   |                |
+    ACID RADICALS IN THE SOLIDS:    |                |
+      Silica                        |      10.5      |     12.0
+      Iron and Alumina              |    Traces.     |   Traces.
+      Sodium Chloride               |       3.3      |      4.6
+      Potassium Sulphate            |       3.7      |      3.5
+      Sodium Sulphate               |      26.3      |     40.8
+      Calcium Sulphate              |      13.3      |     22.1
+      Calcium Carbonate             |     142.7      |    184.8
+      Magnesium Carbonate           |       8.4      |     49.8
+                                    +----------------+---------------
+                                    |     208.2      |    317.6
+                                    |                |
+  Nitrogen as Free Ammonia          |       0.004    |      0.032
+  Nitrogen as Albuminoid Ammonia    |       0.006    |      0.022
+  Nitrogen as Nitrites (N_{2}O_{3}) |       0.002    |      0.002
+  Nitrogen as Nitrates (N_{2}O_{3}) |       0.100    |      1.85
+  Total Hardness (as CaCO_{3})      |     155.0      |    220.0
+  Alkalinity (as CaCO_{3})          |     121.0      |    180.0
+  ==================================+================+===============
+
+
+
+
+                     CITY WATER DISTRIBUTION SYSTEM.
+
+
+[Illustration: PLATE XIX.--DIAGRAM OF THE MAIN WATER PIPES OF MONTERREY.]
+
+The distribution system was begun in September, 1906, but the general
+lay-out of the mains was modified in July, 1907, in view of the division
+of the system into two services, for high and low pressure. Plate XIX
+shows in skeleton form the lines of the cast-iron mains. These are laid
+at the present time along routes containing houses (excluding wooden
+shacks) which can be served immediately. The distribution system is
+arranged to serve as follows:
+
+               Estanzuela supply              4,150 houses.
+               San Geronimo supply            8,600   "
+                                             --------------
+                   Total                     12,750 houses.
+
+This represents, at the present time, a division of the city of 32-1/2%
+for the Estanzuela, and 67-1/2% for the San Geronimo supply. Of the area
+of the supply district north of Santa Catarina River, 57% will be
+supplied from San Geronimo and 43% from Estanzuela. The real development
+of the city, however, is northward in the area of the low-pressure
+supply.
+
+The static pressure over the city in the two sections varies as follows:
+
+                Estanzuela supply             85 to 50 lb.
+                San Geronimo supply           55 to 29 lb.
+
+The main supply pipe from the South Reservoir is 61 cm. (24 in.) in
+internal diameter, and this size allows ample provision for future
+extensions. The supply pipe from the Obispado Reservoir is 76 cm. (30
+in.) in internal diameter. On this main, in Calle de Cinco de Mayo, at a
+distance of 320 m. from the reservoir, has been placed a 76-cm. (30-in.)
+Venturi meter, the recording apparatus being in the house on the side of
+the road. Both these supply pipes are carried well into the city, and
+from them the distribution mains are laid; these are 45.7 and 30 cm. (18
+and 12 in.) in internal diameter, with intermediate sections of 15 and
+10 cm. (6 in. and 4 in.). Along Calle de Cinco de Mayo, where the
+division between the two services takes place, two lines are laid, a
+30-cm. for high pressure and a 38-cm. (15-in.) for the low pressure. A
+duplicate pipe, 30 cm. (12 in.) in diameter, is also laid in Calle de
+Dr. Coss. On Calle de Alvarez the low-pressure pipe is 61 cm. (24 in.),
+and the high-pressure, 45.7 cm. (18 in.) in diameter. Provision is also
+made for extending the range of the two services to other districts.
+Practically every block is provided with gate-valves to cut off the
+supply in any direction. On the 76-cm. main, 61-cm. (24-in.) valves are
+used, and are connected by tapers to the pipe. On the 61-cm. mains,
+45.7-cm. (18-in.) valves are used. The actual frictional loss by
+reducing the valve being small, this method permitted the use of valves
+of a more convenient size. On all the larger valves there are 15-cm.
+by-passes fitted with independent gate-valves.
+
+[Illustration: FIG. 15.--CONNECTION BETWEEN HIGH-AND LOW-PRESSURE AREAS
+AND THE INTERSECTION OF CINCO DE MAYO AND ALVAREZ STREETS.]
+
+Scour-out pipes, 10 cm. (4 in.) and 15 cm. (6 in.) in diameter, are
+placed in various parts of the system, draining to the sewers.
+Air-valves, both double and single, are also placed at high points in
+different parts of the system.
+
+_Reducing Valves._--At four points in the system the mains are arranged
+so that the supply can be interchangeable. Fig. 15 shows the arrangement
+of the mains at the junction of Cinco de Mayo and Alvarez Streets, and
+is typical of the arrangement at the other points.
+
+Each reducing valve is placed on a 30-cm. (12-in.) branch main between
+the two services. These valves adjust themselves automatically to the
+pressure required, after they have been properly regulated to the
+different pressures on either side. To allow repairs to be easily made,
+there are ordinary gate-valves at each end enclosed in the same pit. If
+necessary, as in case of fire, any part of the system can be changed
+into high pressure temporarily by closing the valves against the San
+Geronimo supply.
+
+Table 9 gives the length of the mains as laid, and the number of valves.
+
+                    TABLE 9.--LENGTH OF WATER MAINS.
+
+      =========================+=====================+=============
+            DIAMETER:          |                     |
+      --------------+----------+ Length, in meters.  | Number of
+       Centimeters. |  Inches. |                     | gate-valves.
+      --------------+----------+---------------------+-------------
+           10.2     |     4    |     49,831.68       |    677
+           15.2     |     6    |     31,918.31       |    306
+           30.5     |    12    |     14,461.31       |    117
+           38.1     |    15    |      1,661.98       |     11
+           45.7     |    18    |      4,522.61       |      5
+           61.0     |    24    |      2,826.54       |     10
+           76.2     |    30    |      1,454.40       |
+      --------------+----------+---------------------+-------------
+                 Totals        |    106,676.83       |  1,126
+      =========================+=====================+=============
+
+The pipes were all cast according to the British Standard Specification,
+in 3.65-m. (12-ft.) lengths, and were supplied by Messrs. D. Y. Stewart
+and Company, and Messrs. Dick, Kerr and Company, of Kilmarnock and
+London. The valves were all of standard design, faced with gun-metal,
+and were supplied by Messrs. Glenfield and Kennedy, Limited, of
+Kilmarnock, Scotland.
+
+In the distribution system it is proposed to provide 200 fire-hydrants,
+by arrangement with the municipality, but only a few of these have been
+placed. The general type is a double hydrant for two 63.5-mm.
+(2-1/2-in.) streams. These are to be placed at the corner of every block
+in the business portion of the city; single-way hydrants will be used in
+the residential districts.
+
+_Laying Cast-iron Pipes._--Table 10 has been prepared to show what can
+be accomplished with Mexican labor in laying pipes. In this kind of work
+the labor was particularly efficient; after the gangs were once drilled
+into shape, the work proceeded systematically, and at very good speed.
+All the pipes, after being laid, were tested to 150 lb. per sq. in. in
+the presence of the Technical Inspector.
+
+Table 11 gives the details of the excavation, the material, and the
+average cost, of laying about 106.6 km. of pipes.
+
+_House Connections._--The ordinary house connections, which are of
+19-mm. (3/4-in.) galvanized-steel pipe, are connected to the mains by
+lead goosenecks and brass corporation cocks. The Company's obligation
+under the concession extended to the edge of the sidewalk, and at this
+point curb-boxes, chiefly of the Hays pattern, were placed; but,
+subsequently, owing to the metering of every house service in the city,
+the control of the Company extended to the meter, which, as a rule, is
+placed immediately inside of the house. Owing to the rapid deterioration
+of the house service pipes in some districts of the northern part of the
+city, where the soil is formed of decaying organic matter, it has been
+decided to use lead pipe entirely from the main to the meter.
+
+_Damage Due to Floods._--During the night of August 27th, the main
+61-cm. pipe, under the river bed of Santa Catarina, at the point where
+the main entered the city, was destroyed for a distance of 130 m., due
+to the scouring away of a whole block of city property. The Venturi
+meter register chart at the South Reservoir showed that the break
+occurred a few minutes before midnight. The location of this pipe is
+shown by Fig. 5; its broken end was in proximity to an old bridge pier.
+Fortunately, at the time of the flood, the Obispado Reservoir works were
+completed, and the whole city was supplied with water from San Geronimo
+within 48 hours. As only about 1,500 services had then been connected,
+this delay was not serious; in fact, in the lower part of the city, the
+water in the mains was sufficient until the San Geronimo supply could be
+connected. To make a temporary connection to conduct the high-pressure
+water to the city, a 15-cm. steel pipe was placed above ground, on the
+line of the main, for a distance of 100 m. This pipe was supported by a
+cable, 30 mm. in diameter, and by timber trestles. By limiting the
+supply district, this pipe was of sufficient capacity to serve until the
+large main could be safely restored.
+
+   TABLE 10.--COST OF LAYING AND JOINTING CAST-IRON PIPES, EXCLUDING
+   LOWERING AND TESTING.
+
+  +--------------+----------+----------------------------------------+
+  |              |          | 76 CM. (30 IN.)                        |
+  |              |          +-------+------------+--------+----------+
+  | Employees.   | Rate for | Total | Total cost | No. of | Cost per |
+  |              | 10-hour  | No.   | of labor.  | pipes  | linear   |
+  |              | day.     | men.  | Pesos.     | laid.  | meter.   |
+  |              | Pesos.   |       |            |        | Pesos.   |
+  +--------------+----------+-------+------------+--------+----------+
+  | Foreman      | 4.50     |  1    |  4.50      | ...    |   ...    |
+  | Caulkers     | 3.00     |  4    | 12.00      | ...    |   ...    |
+  | Lead pourers | 2.00     |  2    |  4.00      | ...    |   ...    |
+  | Lead melter  | 1.50     |  1    |  1.50      |  20    | 0.498    |
+  | Pipe cutter  | 2.00     |  1    |  2.00      | ...    |   ...    |
+  | Peons        | 1.00     | 12    | 12.00      | ...    |   ...    |
+  | Water boy    | 0.50     |  1    |  0.50      | ...    |   ...    |
+  |              |          |       |            |        |          |
+  |              | ...      | 22    | 36.50      | ...    |   ...    |
+  +--------------+----------+-------+------------+--------+----------+
+  |              |          | 61 CM. (24 IN.)                        |
+  |              |          +-------+------------+--------+----------+
+  | Employees.   | Rate for | Total | Total cost | No. of | Cost per |
+  |              | 10-hour  | No.   | of labor.  | pipes  | linear   |
+  |              | day.     | men.  | Pesos.     | laid.  | meter.   |
+  |              | Pesos.   |       |            |        | Pesos.   |
+  +--------------+----------+-------+------------+--------+----------+
+  | Foreman      | 4.50     |  1    |   4.50     | ...    |   ...    |
+  | Caulkers     | 3.00     |  5    |  15.00     | ...    |   ...    |
+  | Lead pourers | 2.00     |  2    |   4.00     | ...    |   ...    |
+  | Lead melter  | 1.50     |  1    |   1.50     |  25    | 0.410    |
+  | Pipe cutter  | 2.00     |  1    |   2.00     | ...    |   ...    |
+  | Peons        | 1.00     | 10    |  10.00     | ...    |   ...    |
+  | Water boy    | 0.50     |  1    |   0.50     | ...    |   ...    |
+  |              |          |       |            |        |          |
+  |              | ...      | 21    |  37.50     | ...    |   ...    |
+  +--------------+----------+-------+------------+--------+----------+
+  |              |          | 50 CM. (20 IN.)                        |
+  |              |          +-------+------------+--------+----------+
+  |              | Rate for | Total | Total cost | No. of | Cost per |
+  | Employees.   | 10-hour  | No.   | of labor.  | pipes  | linear   |
+  |              | day.     | men.  | Pesos.     | laid.  | meter.   |
+  |              | Pesos.   |       |            |        | Pesos.   |
+  +--------------+----------+-------+------------+--------+----------+
+  | Foreman      | 4.50     |  1    |  4.50      | ...    |   ...    |
+  | Caulkers     | 3.00     |  4    | 12.00      | ...    |   ...    |
+  | Lead pourers | 2.00     |  2    |  4.00      | ...    |   ...    |
+  | Lead melter  | 1.50     |  1    |  1.50      |  35    | 0.287    |
+  | Pipe cutter  | 2.00     |  1    |  2.00      | ...    |   ...    |
+  | Peons        | 1.00     | 12    | 12.00      | ...    |   ...    |
+  | Water boy    | 0.50     |  1    |  0.50      | ...    |   ...    |
+  |              |          |       |            |        |          |
+  |              |          | 22    | 36.50      | ...    |   ...    |
+  +--------------+----------+-------+------------+--------+----------+
+  |              |          | 45.7 CM. (18 IN.)                      |
+  |              |          +-------+------------+--------+----------+
+  |              | Rate for | Total | Total cost | No. of | Cost per |
+  | Employees.   | 10-hour  | No.   | of labor.  | pipes  | linear   |
+  |              | day.     | men.  | Pesos.     | laid.  | meter.   |
+  |              | Pesos.   |       |            |        | Pesos.   |
+  +--------------+----------+-------+------------+--------+----------+
+  | Foreman      | 4.50     |  1    |   4.50     | ...    |   ...    |
+  | Caulkers     | 3.00     |  4    |  12.00     | ...    |   ...    |
+  | Lead pourers | 2.00     |  2    |   4.00     | ...    |   ...    |
+  | Lead melter  | 1.50     |  1    |   1.50     |  40    | 0.221    |
+  | Pipe cutter  | 2.00     |  1    |   2.00     | ...    |   ...    |
+  | Peons        | 1.00     |  8    |   8.00     | ...    |   ...    |
+  | Water boy    | 0.50     |  1    |   0.50     | ...    |   ...    |
+  |              |          |       |            |        |          |
+  |              |          | 18    |  32.50     | ...    |   ...    |
+  +--------------+----------+-------+------------+--------+----------+
+  |              |          | 38 CM. (15 IN.)                        |
+  |              |          +-------+------------+--------+----------+
+  |              | Rate for | Total | Total cost | No. of | Cost per |
+  | Employees.   | 10-hour  | No.   | of labor.  | pipes  | linear   |
+  |              | day.     | men.  | Pesos.     | laid.  | meter.   |
+  |              | Pesos.   |       |            |        | Pesos.   |
+  +--------------+----------+-------+------------+--------+----------+
+  | Foreman      | 4.50     |  1    |  4.50      | ...    |   ...    |
+  | Caulkers     | 3.00     |  4    | 12.00      | ...    |   ...    |
+  | Lead pourers | 2.00     |  2    |  4.00      | ...    |   ...    |
+  | Lead melter  | 1.50     |  1    |  1.50      |  45    | 0.196    |
+  | Pipe cutter  | 2.00     |  1    |  2.00      | ...    |   ...    |
+  | Peons        | 1.00     |  8    |  8.00      | ...    |   ...    |
+  | Water boy    | 0.50     |  1    |  0.50      | ...    |   ...    |
+  |              |          |       |            |        |          |
+  |              |          | 18    | 32.50      | ...    |   ...    |
+  +--------------+----------+-------+------------+-------------------+
+  |              |          | 30.5 CM. (12 IN.)                      |
+  |              |          +-------+------------+--------+----------+
+  |              | Rate for | Total | Total cost | No. of | Cost per |
+  | Employees.   | 10-hour  | No.   | of labor.  | pipes  | linear   |
+  |              | day.     | men.  | Pesos.     | laid.  | meter.   |
+  |              | Pesos.   |       |            |        | Pesos.   |
+  +--------------+----------+-------+------------+--------+----------+
+  | Foreman      | 4.50     |  1    |   4.50     | ...    |   ...    |
+  | Caulkers     | 3.00     |  4    |  12.00     | ...    |   ...    |
+  | Lead pourers | 2.00     |  2    |   4.00     | ...    |   ...    |
+  | Lead melter  | 1.50     |  1    |   1.50     |  60    | 0.147    |
+  | Pipe cutter  | 2.00     |  1    |   2.00     | ...    |   ...    |
+  | Peons        | 1.00     |  8    |   8.00     | ...    |   ...    |
+  | Water boy    | 0.50     |  1    |   0.50     | ...    |   ...    |
+  |              |          |       |            |        |          |
+  |              |          | 18    |  32.50     | ...    |   ...    |
+  +--------------+----------+-------+------------+--------+----------+
+  |              |          | 15 CM. (6 IN.)                         |
+  |              |          +-------+------------+--------+----------+
+  | Employees.   | Rate for | Total | Total cost | No. of | Cost per |
+  |              | 10-hour  | No.   | of labor.  | pipes  | linear   |
+  |              | day.     | men.  | Pesos.     | laid.  | meter.   |
+  |              | Pesos.   |       |            |        | Pesos.   |
+  +--------------+----------+-------+------------+--------+----------+
+  | Foreman      | 4.50     |  1    |  4.50      | ...    |   ...    |
+  | Caulkers     | 3.00     |  4    | 12.00      | ...    |   ...    |
+  | Lead pourers | 2.00     |  2    |  4.00      | ...    |   ...    |
+  | Lead melter  | 1.50     |  1    |  1.50      | 100    | 0.082    |
+  | Pipe cutter  | 2.00     |  1    |  2.00      | ...    |   ...    |
+  | Peons        | 1.00     |  6    |  6.00      | ...    |   ...    |
+  | Water boy    | 0.50     |  1    |  0.50      | ...    |   ...    |
+  |              |          |       |            |        |          |
+  |              |          | 16    | 30.50      | ...    |   ...    |
+  +--------------+----------+-------+------------+--------+----------+
+  |              |          | 10 CM.  (4 IN.)                        |
+  |              |          +-------+------------+--------+----------+
+  | Employees.   | Rate for | Total | Total cost | No. of | Cost per |
+  |              | 10-hour  | No.   | of labor.  | pipes  | linear   |
+  |              | day.     | men.  | Pesos.     | laid.  | meter.   |
+  |              | Pesos.   |       |            |        | Pesos.   |
+  +--------------+----------+-------+------------+--------+----------+
+  | Foreman      | 4.50     |  1    |   4.50     | ...    |   ...    |
+  | Caulkers     | 3.00     |  4    |  12.00     | ...    |   ...    |
+  | Lead pourers | 2.00     |  2    |   4.00     | ...    |   ...    |
+  | Lead melter  | 1.50     |  1    |   1.50     | 150    | 0.0574   |
+  | Pipe cutter  | 2.00     |  1    |   2.00     | ...    |   ...    |
+  | Peons        | 1.00     |  6    |   6.00     | ...    |   ...    |
+  | Water boy    | 0.50     |  1    |   0.50     | ...    |   ...    |
+  |              |          |       |            |        |          |
+  |              |          | 16    |  30.50     | ...    |   ...    |
+  +--------------+----------+-------+------------+--------+----------+
+
+                TABLE 11.--CAST-IRON WATER PIPES.--COST
+                 OF MATERIALS AND LAYING AT MONTERREY.
+
+                 MATERIALS PER STANDARD LENGTH OF PIPE .
+
+ Key: cm = centimeter in = inch mm = millimeter kg = kilogram m = linear meter
+ +-----------+------+-------+--------+-------------+--------+--------+-------+
+ |   PIPE    |      |Weight |Cost/   |    LEAD     |  OAKUM |CHARCOAL| Total |
+ | DIAMETER  |Thick-|  of   |piece   +------+------+--------+--------+ Ma-   |
+ +------+----+ ness | Pipe  |fob Mon-|Weight| Cost |  Cost  | Cost   |terial |
+ |      |    |      |       |terrey  |      |      |        |        | Cost  |
+ |  cm  | in |  mm  |  kg   | pesos  |  kg  |pesos | pesos  | pesos  | per m |
+ +------+----+------+-------+--------+------+------+--------+--------+-------+
+ | 10   |  4 | 10.3 |   109 |  11.65 |  2.0 | 0.37 | 0.025  | 0.0525 |  3.30 |
+ | 15   |  6 | 11.1 |   163 |  15.74 |  3.7 | 0.67 | 0.0675 | 0.065  |  4.51 |
+ | 30.5 | 12 | 15.8 |   463 |  76.50 |  7.9 | 1.44 | 0.1225 | 0.1    | 21.35 |
+ | 38   | 15 | 17.4 |   680 |  79.36 | 10.6 | 1.94 | 0.175  | 0.12   | 22.30 |
+ | 45.7 | 18 | 19.0 |   871 |  90.28 | 13.4 | 2.42 | 0.2375 | 0.1375 | 25.42 |
+ | 61   | 24 | 22.2 | 1,261 | 117.60 | 18.8 | 3.42 | 0.335  | 0.175  | 33.20 |
+ | 76   | 30 | 25.4 | 1,946 | 199.05 | 24.5 | 4.42 | 0.44   | 0.2125 | 55.77 |
+ +------+----+------+-------+--------+------+------+--------+--------+-------+
+
+                           LABOR.
+
+  Key: cm = centimeter, in = inch, m = meter
+  +-----------+------+------+------+------+-------+-------+----
+  |           |      |      |      |      |       |Total  |
+  | DIAMETER  |      |      | Cubic| Cost |Back-  |cost,  |
+  | OF PIPE:  | Width|Depth |meters| of   |filling|exca-  |
+  |           |  of  |      | per  |exca- |and re-|vation |
+  +------+----+trench|      |linear|vation|moving |back-  | Continues
+  |      |    |      |      | meter| per  |surplus|filling|
+  |  cm  | in |  m   |  m   |      |lin. m|Pesos  |etc.   |
+  |      |    |      |      |      |      |       |Pesos  |
+  +------+----+------+------+------+------+-------+-------+----
+  | 10   |  4 | 0.55 | 0.90 | 0.50 | 0.60 | 0.18  | 0.78  |
+  | 15   |  6 | 0.60 | 1.00 | 0.60 | 0.72 | 0.22  | 0.94  |
+  | 30.5 | 12 | 0.65 | 1.20 | 0.78 | 0.94 | 0.29  | 1.23  |
+  | 38   | 15 | 0.70 | 1.30 | 0.91 | 1.10 | 0.34  | 1.44  | Below
+  | 45.7 | 18 | 0.80 | 1.40 | 1.12 | 1.34 | 0.41  | 1.75  |
+  | 61   | 24 | 1.00 | 1.50 | 1.50 | 1.80 | 0.55  | 2.35  |
+  | 76   | 30 | 1.10 | 1.60 | 1.76 | 2.11 | 0.65  | 2.76  |
+  +------+----+------+------+------+------+-------+-------+----
+
+  --+----------------+--------+--------+--------+
+    |  HAULING PER   |  Cost  | Total  | Total  |
+    |                |  of    |hauling |excava- |
+    |  LINEAR METER  | laying | and    |tion and|
+    |                |  per   |laying  |laying, |
+    +--------+-------+ linear | per    |labor,  |
+    | Haul-  | Misc. | meter  |linear  |complete|
+    |  ing   | Pesos |        | meter  |        |
+    | Pesos  |       | Pesos  | Pesos  | Pesos  |
+  --+--------+-------+--------+--------+--------+
+    | 0.0275 | 0.005 | 0.06   | 0.0925 | 0.8725 |
+    | 0.45   | 0.005 | 0.825  | 0.1325 | 1.0725 |
+    | 0.18   | 0.0075| 0.1475 | 0.335  | 1.565  |
+    | 0.2725 | 0.01  | 0.19   | 0.4775 | 1.9125 |
+    | 0.2725 | 0.01  | 0.245  | 0.5275 | 2.2775 |
+    | 0.825  | 0.08  | 0.41   | 1.315  | 3.665  |
+    | 0.83   | 0.10  | 0.53   | 1.46   | 4.22   |
+  --+--------+-------+--------+--------+--------+
+
+NOTE.--The above costs of earthwork are based on the following rates and
+percentages over the whole city:
+
+              Earth, per cubic meter      | 0.35 pesos | 50%
+              Soft sillar                 | 0.75   "   | 20%
+              Hard sillar                 | 1.50   "   | 20%
+              Rock (chiefly conglomerate) | 4.00   "   | 10%
+
+                          SUMMARY OF TABLE 11.
+
+   +------------------------+-------------+------------+------------+
+   | DIAMETER               | Total labor | Materials. | Total cost |
+   | OF PIPE :              | cost.       | Pesos.     | per linear |
+   +--------------+---------+ In pesos.   |            | meter, in  |
+   | Centimeters. | Inches. |             |            | pesos.     |
+   +--------------+---------+-------------+------------+------------+
+   | 10           |  4      | 0.8725      |  3.30      |  4.1725    |
+   | 15           |  6      | 1.0725      |  4.51      |  5.5825    |
+   | 30.5         | 12      | 1.565       | 21.35      | 22.915     |
+   | 38           | 15      | 1.9125      | 22.30      | 24.2125    |
+   | 45.7         | 18      | 2.2775      | 25.42      | 27.6975    |
+   | 61           | 24      | 3.665       | 33.20      | 36.865     |
+   | 76           | 30      | 4.22        | 55.77      | 59.99      |
+   +--------------+---------+-------------+------------+------------+
+
+The flood destroyed about 1,200 houses in the neighborhood of the river.
+In a number of blocks the smaller mains were scoured away, but
+considerable salvage was done afterward, and, as it is the intention of
+the authorities not to permit rebuilding along the flood-path of the
+river, these mains do not require reconstruction.
+
+
+
+
+                          MAIN SEWERAGE SYSTEM.
+
+
+The Company's obligations, as far as drainage is concerned, were limited
+to the removal and disposal of sewage, no provision being required for
+storm-water, which is allowed to find its way to the natural
+watercourses. Apart from that fact, however, the best system for a city
+like Monterrey, where rainfall for many months at a time is very scarce,
+is the strictly "separate system." In the design advantage was taken of
+the natural topography of the drainage district, which is almost an
+ideal one for a gravitation system of sewers, the general fall in all
+directions being northeast; it was also in this direction that the best
+available land could be obtained for disposal purposes.
+
+[Illustration: PLATE XX.--DIAGRAM OF THE MAIN SEWERS OF MONTERREY.]
+
+Plate XX shows in skeleton form the general lay-out of the sewers. Two
+drainage districts are arranged, divided by Calle de Washington, which may
+be regarded as practically the center of the city, and each of these
+districts has an independent main collector connecting to the outfall
+sewer at the northeast extremity of the city.
+
+The system has been designed so that extensions may be made and may cover
+any part within the city limits; the main collectors are large enough for
+the whole area when fully built up.
+
+The sewers are designed on a very liberal basis, namely, on the assumption
+that when flowing half full the quantity to be dealt with will be 380
+liters per capita per day, with a maximum rate of flow of 200 per cent. It
+was assumed that each house would be occupied by 7 persons and have a
+frontage of 12-1/2 m. The minimum velocities in the sewers, when running
+full, vary between 0.91 and 1.5 m. per sec., with the exception of a few
+blocks.
+
+The minimum size adopted was 24.3 cm. (8 in.) in internal diameter. The
+sewers of diameters between 24.3 and 50 cm., are 0.91 m. (36 in.) long,
+and are of salt-glazed vitrified clay, imported from San Antonio, Tex.
+
+Table 12 gives the details of the length of the various sewers laid.
+
+                      TABLE 12.--LENGTH OF SEWERS.
+
+   +----------+------------------------------------------+-----------+
+   |DIAMETER: |                                          |           |
+   +-----+----+        Kind.                             | Length,   |
+   |  cm | in.|                                          | in meters.|
+   +-----+----+------------------------------------------+-----------+
+   |24.3 |  8 |    Fire-clay                             | 38,332.85 |
+   |25.4 | 10 |       "                                  | 16,400.69 |
+   |30.5 | 12 |       "                                  |  7,953.15 |
+   |38.1 | 15 |       "                                  |  4,850.56 |
+   |45.7 | 18 |       "                                  |  2,023.40 |
+   |50.8 | 20 |       "                                  |  1,450.53 |
+   |55.9 | 22 | Reinforced concrete tubes, 6.9 cm. thick |  3,134.20 |
+   |61.0 | 25 |     "         "       "    7.6 "     "   |    357.40 |
+   |68.6 | 27 |       Brick and concrete                 |    484.05 |
+   |76.2 | 30 |         "    "     "                     |    662.69 |
+   |     |    |                                          |           |
+   |     |    |                                 Total    | 75,649.15 |
+   +-----+----+------------------------------------------+-----------+
+
+The greater number of the manholes are of brickwork, 23 cm. thick, and
+have concrete inverts. They have a diameter of 1.2 m., which is reduced to
+0.61 m. at the top, and each is provided with a heavy cast-iron frame and
+closed cover weighing about 190 kg. There are 521 manholes, and they are
+placed at every block and on long lines about 80 m. apart.
+
+[Illustration: FIG. 16.--STANDARD 300-GAL. FLUSH TANKS.]
+
+The sewers are flushed with 15-cm. (6-in.) automatic flushing siphons of
+the Miller pattern with 20-cm. (8-in.) discharge pipes. There are 278 of
+these siphons, and they are placed in flush-tanks (Fig. 16) built of
+brickwork and plastered with 1:1 cement mortar. Their capacity varies from
+800 to 1,200 liters, and they discharge from 22-1/2 to 28-1/2 liters per
+sec. They are timed to flush once in 24 hours.
+
+The system is at present ventilated by 23-cm. (9-in.) steel ventilating
+columns (Fig. 16), with ornamental cast-iron bases. There are 220 of these
+columns. Most of them are 7.85 m. above the level of the edge of the
+sidewalk, and are connected to special 15-cm. branch pipes leading from
+the sewer on the outside of the flush-tanks. In the center of the city
+they are provided with extension lengths, giving a total height of 12 m.
+
+Table 13 gives the particulars of the average distributed cost of laying
+the 75.6 km. of sewers.
+
+        TABLE 13.--AVERAGE COST, PER LINEAR METER, FOR 75.6 KM.
+            OF SEWERS, FOR MATERIALS AND LABOR COMPLETE.
+
+  +----------+-----------+--------+-----------------------------+--------+
+  |          | INTERNAL  |Cost of |    EARTHWORK AND LABOR:     | Total  |
+  |          | DIAMETER  | mater- |-------+------------+--------| cost of|
+  |          |   OF      | ials   |       | Cost of    |Cost of | sewer  |
+  |          |  SEWERS.  |includ- |Average| excavation,|labor   |complete|
+  |Kind of   +------+----+ ing    | depth | including  |  in    |  per   |
+  |  Sewer.  |      |    |10-cm.  |  of   | back-      |laying  | linear |
+  |          |      |    |(4-in.) | sewer | filling,   |(includ-| meter. |
+  |          |  cm. | in.|branches|       | removing   | ing    |        |
+  |          |      |    |every   |   m.  | surplus,   |hauling,|        |
+  |          |      |    |4-1/2 m.|       | etc.       | etc.). |        |
+  |          |      |    |Pesos.  |       | Pesos.     | Pesos. |        |
+  +----------+------+----+--------+-------+------------+--------+--------+
+  |Fire-clay | 24.3 |  8 |  2.00  |  2.10 |    3.46    | 0.21   | 5.67   |
+  |    "     | 25.4 | 10 |  2.78  |  2.25 |    3.97    | 0.2625 | 7.0125 |
+  |    "     | 30.5 | 12 |  3.64  |  2.50 |    4.705   | 0.305  | 8.65   |
+  |    "     | 38.1 | 15 |  6.14  |  2.75 |    5.50    | 0.4375 |12.0775 |
+  |    "     | 45.7 | 18 |  8.80  |  3.00 |    6.745   | 0.645  |16.19   |
+  |    "     | 50.8 | 20 | 11.30  |  3.50 |    8.275   | 0.815  |20.39   |
+  |Concrete  | 55.9 | 22 |  5.93  |  3.50 |    9.19    | 1.325  |16.445  |
+  |    "     | 61.0 | 25 |  7.30  |  3.75 |   11.245   | 1.685  |20.23   |
+  |One brick}|      |    |        |       |            |        |        |
+  |thick on }| 68.6 | 27 |  7.17  |  3.75 |   11.735   | 3.93   |22.835  |
+  |concrete }| 76.2 | 30 |  7.925 |  4.00 |    14.53   | 4.515  |26.97   |
+  |founda-  }|      |    |        |       |            |        |        |
+  |tions    }|      |    |        |       |            |        |        |
+  +----------+------+----+--------+-------+------------+--------+--------+
+
+[Illustration: FIG. 17.--SKETCH SHOWING DISCONNECTING TRAP ON HOUSE
+DRAIN.]
+
+The house connections are chiefly of 10-cm. (4-in.) pipes, laid on a
+minimum gradient of 2-1/2%, from oblique branches on the sewer to siphon
+intercepting traps near the house, as shown by Fig. 17. From this trap a
+10-cm. fire-clay inspection pipe is carried up and capped at the sidewalk
+level with a cast-iron box having a locked cover. From this inspection
+pipe a branch is connected to a cast-iron fresh-air inlet, in most cases
+set in the wall of the house, the inlet being 30 cm. above the level of
+the pavement.
+
+_Effect of the Flood on Sewers._--The flood of August 27th and 28th, 1909,
+partly destroyed one of the main collectors, which was laid along the
+banks of the river and encased in concrete. This has now been relaid
+farther north, and out of the way of any future floods. The total length
+of the new sewers replacing those damaged amounts to 1200 m., and they
+vary in internal diameter from 20 to 55.9 cm. (8 to 22 in.).
+
+
+
+
+                          MAIN OUTFALL SEWER.
+
+
+The direction of the main outfall sewer was determined after a thorough
+study of all the available land lying to the north and northeast of the
+city, as it was the intention of the Company to utilize for irrigation
+purposes the sewage and any surplus waters that might be developed. The
+best available site was found to be about 12 km. north of the city, a
+little northwest of the village of San Nicolas de los Garzas, as shown on
+Plate II. The long length of outfall required was justified by the cheap
+cost of the land and its excellent character for sewage irrigation. The
+sewer was designed for a capacity of 90,000,000 liters a day (36.76 cu.
+ft. per sec.) in order to allow for conveying surplus waters as well as
+sewage.
+
+[Illustration: PLATE XXII.--OUTFALL SEWER: PLAN OF GROUND SHOWING SEWER;
+ALSO DETAILS OF VARIOUS SECTIONS.]
+
+The outfall intercepts the two main branches of the city sewers at Calle
+de Allende and Calle de Tapia, and its total length is approximately
+11,900 m. The chief type adopted is shown on Plate XXII. It is formed
+with an invert of radial bricks laid in 1:2 cement mortar, on a foundation
+of 1:3:5 concrete approximately 7 cm. thick. As the ground was chiefly in
+hard sillar, only a little concrete was required to mould the bottom to
+the correct shape. The arch was formed of special radial bricks, 15 cm. (6
+in.) deep, laid in cement mortar. These bricks were adopted in preference
+to concrete, owing to the heavy cost of sand and rock, due to the long
+haul, and for the purpose of obtaining rapid work. Plate XXI shows the
+sewer arch, and one of the ventilating columns and manholes. The bricks
+were obtained from the local brick plant, and form a very satisfactory
+material for sewers, being well burnt, thoroughly hard, and absorbing not
+more than 7-1/2% of their weight of water. The contract prices for the
+labor on the brickwork were 1.25 pesos per sq. m., and 1.38 pesos for the
+arch.
+
+[Illustration: PLATE XXI, FIG. 1.--VIEW OF ARCH, OUTFALL SEWER.]
+
+[Illustration: PLATE XXI, FIG. 2.--VENTILATING COLUMN AND MANHOLE, OUTFALL
+SEWER.]
+
+The general route of the sewer is very direct, long straight lines of
+several kilometers being possible, and these were joined by curves of
+approximately 30 m. radius. The gradient of the sewer invert is 0.2% (1 in
+500) which is approximately the general fall of the ground northward from
+Monterrey.
+
+The total quantity of excavation was as follows:
+
+                 No. 1, soft earth          8,960 cu. m.
+                 No. 2, sillar             18,492  "  "
+                 No. 3, conglomerate rock   9,822  "  "
+                                           ------
+                 Total                     37,274 cu. m.
+
+The contract prices for this excavation were: for No. 1, 32 cents; No. 2,
+85 cents; and No. 3, 2.17 pesos per cu. m.
+
+All the excavation was in perfectly dry ground. Where the sewer was partly
+out of the ground it had a foundation of concrete, 1.75 m. wide, from 15
+to 23 cm. thick, below the bottom of the brickwork, and carried up to the
+springing of the arch, and a well-tamped embankment, with slopes of 1-1/2
+to 1, to protect the sewer to a height of 30 cm. (12 in.) above the arch.
+For 342 m. at the Monterrey end of the line, the sewer was constructed in
+tunnel, from, the open end and from two intermediate shafts. The tunnel
+throughout was in sillar, and the contract price for excavation was 24.50
+pesos per lin. m. This work was done without timbering of any kind, except
+at the shaft lengths. Plate XXII shows the lining of the tunnel, which
+was of concrete with a brick invert. At four places the sewer passes under
+main railway tracks, which at these points were carried on steel girders
+supported on concrete abutments, the sewer being carried under the tracks
+in the ordinary way.
+
+_Bridges._--At three points the sewer was carried over arroyos on
+reinforced concrete girders. No. 1, at Station 5,600, consisted of four
+10-m. spans; No. 2, at Station 8,365, over the Estanscia Arroyo, consisted
+of nine 10-m. spans; and No. 3, at Station 8,960, over the Topo Chico
+Arroyo, consisted of three 10-m. spans. One of these bridges is shown on
+Plate XXIII. They were designed as two parallel continuous girders with
+connecting top and bottom slabs. The concrete for the girders was a
+1:2-1/2:3-1/2 mixture, the sand being from the crusher and the rock gauged
+to pass a 19-mm. (3/4-in.) screen. The inside was rendered with a coat of
+1:1 cement mortar, 7 mm. thick, for water-tightness.
+
+[Illustration: PLATE XXIII, FIG. 1.--FORMS FOR MAIN GIRDERS, ESTANSCIA
+BRIDGE, OUTFALL SEWER.]
+
+[Illustration: PLATE XXIII, FIG. 2.--VIEW OF ESTANSCIA BRIDGE, COMPLETED.]
+
+The piers of the Estanscia Bridge (Plate XXIII) were carried down through
+soft earth to a stiff clay from 4-1/2 to 6 m. below the surface, and the
+foundations were spread so that the pressure would not exceed 1 ton per
+sq. ft. The ends of the bridges were protected by rubble wing-walls
+supporting the embankment over the sewer. A 1:3:5 concrete was used for
+the upper part of the piers, and the lower part was of the same mixture
+with 30% of large boulders. There are 70 manholes (Fig. 19) along the line
+of the sewer, and they vary from 150 to 230 m. apart. The sewer is
+ventilated with 30 concrete towers (Fig. 18, and Fig. 2, Plate XXI), 2.9
+m. high, having 20-cm. (8-in.) shafts.
+
+[Illustration: FIG. 18.--DETAILS OF VENTILATORS ON OUTFALL SEWER.]
+
+[Illustration: FIG. 19.--DETAILS OF MANHOLES ON OUTFALL SEWER.]
+
+The works for the outfall sewer were carried out satisfactorily under a
+contract with Mr. John Phillips, of Mexico City, the Company supplying the
+greater part of the materials. The work was begun on March 16th, and
+finished on November 12th, 1908.
+
+
+
+
+                SEWAGE DISPOSAL WORKS AND IRRIGATION LANDS.
+
+
+For the purpose of disposing of the sewage and using it profitably, the
+Company purchased 909 hectares (2,246 acres) of land from the Community of
+San Nicolas de los Garzas, the outfall sewer being carried to the
+southwestern boundary of the land acquired. This area has a general fall
+in all directions to the northeastern boundary, with a gradual fall of
+about 25 m. across the diagonal of the land. The area purchased was
+practically virgin land, only small portions having been cultivated. The
+greater part was covered with a growth of mezquite trees and small shrubs.
+The quality of the land is excellent, if properly irrigated, and capable
+of yielding abundant crops of every description. The limits of this land
+are shown on Plate II.
+
+_Sewage Purification Tanks._--For the purpose of obtaining a satisfactory
+effluent to discharge on the land without causing nuisance, the Company
+built a system of detritus chambers and liquefying tanks at the end of the
+outfall sewer. One difficulty to be faced, in designing these works, was
+the fact that there were no data regarding the probable quantity of
+dry-weather sewage, nor any particulars as to its general character;
+there was also the probability that the outfall sewer would have to carry
+large quantities of surplus water. Therefore, the system was designed so
+as to be capable of extension if necessary, and the sizes of the various
+tanks were limited at present, because of the septic processes which would
+be set up in the long length of outfall sewer. The tanks were designed to
+deal with 10,000,000 liters of sewage proper per day, and the channels,
+etc., were proportioned to take the full flow of the sewer if necessary.
+Provision was also made for discharging large volumes of surplus water
+directly on the land, independent of the tanks. To do this a by-pass was
+taken from the sewer a short distance before reaching the site of the
+tanks. By properly timing the flow, arrangements could be made to
+discharge these waters in the early hours of the morning, by allowing the
+scour-pipes in the distribution system to be opened at night when the
+domestic sewage flow was at its minimum. As the area of land available is
+very great, the degree of purification in the tanks was relatively
+unimportant; the object to be obtained consisted chiefly in distributing
+on the land an effluent which would be innocuous and clear.
+
+The general design of the works is shown on Plate XXIV, and they consist
+essentially of a screen chamber, duplicate detritus tanks, and three
+liquefying tanks. There is also a sludge-pit 629 m. from the tanks.
+
+[Illustration: PLATE XXIV.--SEWAGE DISPOSAL WORKS AT SAN NICOLAS DE LOS
+GARZAS; GENERAL PLAN OF DETRITUS AND LIQUEFYING TANKS, WITH DETAILS OF THE
+LATTER.]
+
+_Screen Chamber and Detritus Tanks._--Enlarged details of the screen
+chamber are shown on Plate XXV. The invert, where the sewer enters the
+screen chamber, is 489.45 m. above datum. This chamber has duplicate
+screens which are fully detailed on Plate XXX. For cleaning purposes the
+screens are raised by a steel-framed head-gear, which is arranged so that
+they may be lowered to a small traveling bogie, out of the way of the
+screen chamber.
+
+[Illustration: PLATE XXV.--SEWAGE DISPOSAL WORKS AT SAN NICOLAS DE LOS
+GARZAS. DETAILS OF DETRITUS CHAMBERS AND INLET CHANNELS.]
+
+[Illustration: PLATE XXVI.--SEWAGE DISPOSAL WORKS AT SAN NICOLAS DE LOS
+GARZAS DETRITUS AND LIQUEFYING TANKS; DETAILS OF DISTRIBUTING CHANNELS.]
+
+[Illustration: PLATE XXX.--SEWAGE DISPOSAL WORKS AT SAN NICOLAS DE LOS
+GARZAS. DETAILS OF SCREENING APPARATUS.]
+
+From the screen chamber there are two main channels, 1.22 m. wide,
+branching to the two concrete detritus chambers. Each channel has a square
+penstock, so that the sewage can be diverted into either chamber when
+necessary.
+
+The detritus chambers are octagonal in plan, 4 m. in diameter, and each is
+provided with an outlet weir 1.50 m. wide. At the weir level the chambers
+have a depth of 1.75 m., with drainage channels below that level. The
+coping is 1 m. above the outlet weir of the detritus tanks. To drain off
+these chambers, each has a scour-out pipe, 30 cm. in diameter, controlled
+from valves with spindles carried above the coping level. Each of these
+pipes is connected to a central chamber, and leads to a 56-cm. (22-in.)
+sludge-pipe. The chambers as designed are of smaller capacity than those
+usually provided, but, as all surface water is strictly excluded from the
+sewerage system, the quantity of detritus reaching the chambers may be
+small. The velocity through them when both are in use will be
+approximately 0.082 m. (0.27 ft.) per sec.
+
+From these chambers the sewage is carried to the three liquefying tanks by
+a main channel, 11.5 m. long and 1.50 m. wide.
+
+[Illustration: PLATE XXVII, FIG. 1.--CAST CONCRETE BEAMS BEING PLACED IN
+POSITION, LIQUEFYING TANKS.]
+
+[Illustration: PLATE XXVII, FIG. 2.--INLET WEIRS TO LIQUEFYING TANKS,
+DURING CONSTRUCTION.]
+
+[Illustration: PLATE XXVIII, FIG. 1.--VIEW OF LIQUEFYING TANKS, FROM INLET
+END.]
+
+The tanks are of concrete and have reinforced concrete roofs. Each is 66
+m. long and 6 m. wide; the minimum depth for the sewage is 1.50 m. at the
+outlet end, and 2.25 m. at the inlet, increasing to a maximum depth of
+2.75 m. at the lowest depth at the scour-out channel. Their combined
+capacity is 2,500,000 liters, which is equivalent to 6 hours' flow of the
+quantity of sewage for which they were designed. The sewage passes from
+the main channel, through penstock-valves which control the flow, into one
+or the other of the tanks. From these valve openings it flows over
+concrete weirs, 5 m. long, and is deflected to the bottom of the tank by a
+reinforced concrete scum-plate, extending across each tank, with a
+clearance of 15 cm. at each end. This scum-plate is 1.5 m. deep and 10 cm.
+thick, and is placed 40 cm. from the end walls.
+
+[Illustration: PLATE XXIX.--SEWAGE DISPOSAL WORKS AT SAN NICOLAS DE LOS
+GARZAS; DETAILS OF OUTLET CHANNELS AND WEIR BOX.]
+
+The details of the concrete division and outside walls are shown on Plate
+XXIX. The floor was constructed in two layers, and its surface is divided
+into 6 channels formed by small walls, 20 cm. wide and 15 cm. deep, the
+object of these channels being to facilitate the cleaning of the floor by
+scouring it out to a specially arranged channel at the deepest point of
+the tank, near the inlet end. Each scour-out channel has a 30-cm. (12-in.)
+gate-valve, controlled from the roof of the tank, the three scour-pipes
+meeting in a concrete chamber outside of the tanks, from which a 56-cm.
+(22-in.) concrete pipe discharges the contents of the tanks to the
+sludge-pit during cleaning operations. The velocity through the tanks,
+when they are used in combination, is 0.0253 m. (0.083 ft.) per sec., the
+tanks being made as long as economically possible, in order to obtain this
+low velocity and thus permit the proper sedimentation of the suspended
+matters. The roof of each tank is 1 m. above the weir level. Each tank has
+four ventilating columns, 3.7 m. high and 30 cm. in diameter, vitrified
+clay pipes, with an exterior casing of contrete, being used for the
+shafts. The roof is enclosed within parapet walls, and is covered with a
+layer of earth 25 cm. thick.
+
+The outlet channel from the tanks leads to a measuring chamber, 3 m.
+square, as shown on Plate XXIX. This chamber is fitted with penstocks,
+1.83 m. wide, and measuring weirs. From this chamber the sewage is
+delivered to two main irrigation ditches, which distribute the sewage in
+two directions, one northward and the other to the western extremity of
+the lands.
+
+_Construction of Tanks._--The excavation for the tanks was in soft earth
+for a depth of 1-1/2 m.; the lower depths were in a firm foundation of
+sillar and calcareous clay. The total excavation in the tanks, channels,
+etc., was 8,335 cu. m., and the actual cost was 45-3/4 cents per cu. m. To
+facilitate the construction, about six-tenths of the concrete beams were
+cast as single monoliths and placed in position by sliding them across the
+tanks on temporary timbers. The remainder of the beams, the roof, and the
+slab were placed in position in the ordinary way with timber forms. The
+total quantity of concrete placed was 1,360 cu. m. A 1:2-1/2:4-1/2
+concrete was used for the walls, channels, etc., and a 1:2:3 mixture for
+the roof slab and beams.
+
+Table 14 gives the average cost per cubic meter for all the concrete work.
+
+    TABLE 14.--AVERAGE COST PER CUBIC METER FOR CONCRETE IN TANKS.
+
+   +-----------------------------------------+-----------+-----------+
+   |                                         | Pesos per | Pesos per |
+   |                                         | cubic     | cubic     |
+   |                                         | meter.    | meter.    |
+   +-----------------------------------------+-----------+-----------+
+   | LABOR :                                 |           |           |
+   |  Mixing and placing                     |  5.20     |           |
+   |  Carpenter work in forms, framing, etc. |  4.20     |           |
+   |                                         |  _____    |           |
+   | Total labor cost                        |           |  9.40     |
+   |                                         |           |           |
+   | MATERIALS :                             |           |           |
+   | Screened gravel                         |  4.04     |           |
+   | Sand (from neighboring arroyo)          |  4.98     |           |
+   | Cement (including hauling)              | 15.19     |           |
+   | Lumber, nails, and other supplies       |  1.90     | 26.11     |
+   +-----------------------------------------+-----------+-----------+
+   | Total cost of concrete per cubic meter                35.51     |
+   +-----------------------------------------------------------------+
+
+_Sludge-pit._--The sludge-pit, used when cleaning out the tanks, is
+carried 639 m. northward, far enough to get the available fall to drain
+the bottom of the detritus chambers and liquefying tanks. The drainage
+pipe was formed of 56-cm. (22-in.) concrete tubes. The sludge-pit is
+merely an excavation in the earth 20 m. square and 2 m. deep, the sides
+having a slope of 1-1/2 to 1. An overflow drains the pit to an irrigation
+ditch, the solid matter being allowed to settle and the liquid to drain
+off. From time to time it is proposed to dig out the solids and plow them
+into the land.
+
+_General._--To the east of the tanks a 3-roomed house has been built for
+the inspector.
+
+In order to provide a good supply of water for cleaning operations, a well
+22 m. deep has been sunk and is fitted with pumps operated by an Eclipse
+windmill, 4 m. in diameter, on a tower 22 m. high, which delivers the pump
+water to a circular wooden tank of 20,000 liters capacity.
+
+The work in connection with the purification tanks was carried out by the
+Company's own staff; it was begun on September 10th, 1908, and practically
+completed by the first week in January, 1909.
+
+At the time of writing, the tanks have to deal with the sewage from a
+population of only 10,000 persons, as only from 15 to 20% of the
+connections have been made. The sewage, therefore, has been diluted with
+several times its volume of surplus water, and the necessary scum on the
+top of the sewage in the tanks has not yet assumed the usual thick matty
+condition observed in most systems. As there are no available means in
+Monterrey of having proper determinations made of the degree of
+purification which takes place in the passage of the sewage through the
+liquefying tanks, a few simple tests have been made. These tests were
+limited to the determination of the amount of oxygen absorbed in 4 hours,
+and show a purification of 50% in passing from the detritus chambers to
+the outlet. The sewage, although very black and full of suspended matter
+as it enters the tanks, leaves them in a very clarified condition.
+
+Of the total area of land acquired by the Company, 904 hectares (2,234
+acres) have been leased to the Monterrey Railway, Light, and Power
+Company, for 99 years, the Water-Works Company reserving 5 hectares (12
+acres) absolutely for future extensions of the sewage works. By giving 12
+months' notice, the Company also reserves the right to utilize any part of
+145 hectares (358 acres) near the tanks, should it be required at any time
+in the future for sewage purification purposes.
+
+
+
+
+                    QUALITY OF AND RATES FOR LABOR.
+
+
+All the work was practically under the direction of English-speaking
+superintendents and general foremen. For the ordinary skilled and
+low-skilled labor, Mexicans were employed exclusively, and, on the work,
+which was quite new to them, they proved entirely efficient and
+satisfactory; throughout the work, on which at some periods between 2,000
+and 3,000 men were employed, chiefly under the Company's direct
+administration, they were very tractable and willing to do their best, and
+no trouble was experienced at any time. The Mexican "peon," and also the
+ordinary skilled workman in the north of Mexico, is intelligent, and is
+excellent for purely routine work, but he is not adaptable or resourceful
+in cases of emergency. Under intelligent and careful supervision, however,
+it is quite possible to get as good results as could be obtained anywhere.
+
+The daily rates of wages for a 10-hour day were approximately as given in
+Table 15, these rates being varied in special cases.
+
+                       TABLE 15.--RATES OF WAGES
+
+      +-----------------------------------+-------------------+
+      |                                   | Pesos per day.    |
+      +-----------------------------------+-------------------+
+      | General foreman                   |  8.00  to 10.00   |
+      | Foreman                           |  6.00  "   8.00   |
+      | Cabos                             |  2.00  "   4.00   |
+      | Masons                            |  3.00  "   4.00   |
+      | Bricklayers                       |  3.00  "   4.00   |
+      | Masons and bricklayers helpers    |       1.50        |
+      | Cast-iron pipe jointers (foreman) |       4.50        |
+      |  "   " caulkers                   |       3.00        |
+      |  "   " helpers                    |  1.50  to  2.00   |
+      | Fire-clay pipe layers             |       1.75        |
+      |  "   " helpers                    |  1.25  to  1.50   |
+      | Drillers                          |  1.25  "   1.50   |
+      | Carpenters                        |  2.00  "   2.50   |
+      | Blacksmiths                       |       2.50        |
+      | Crane men                         |       6.00        |
+      | Peons (laborers)                  |  1.00  to  1.25   |
+      | Boys (watering concrete)          |  0.37-1/2 to 0.50 |
+      | Watchman                          |       1.00        |
+      | Timekeepers                       |  22.00 per week.  |
+      +-----------------------------------+-------------------+
+
+
+
+
+                             COST OF WORKS.
+
+
+Table 16 gives the main items of the approximate expenditure. These
+include all expenses for preliminary location, engineering,
+superintendence, purchase of lands, water rights, etc., but do not include
+other heavy expenditures chargeable to the concession, such, for example,
+as general expenses, interest at the rate of 6% during the construction
+period, preliminary expenses for investigations, etc., items which would
+increase the total by nearly 25 per cent.
+
+              TABLE 16.--PRINCIPAL ITEMS OF EXPENDITURE.
+
+  +---------------------------------------------+--------------------+
+  |                                             | Pesos,             |
+  |                                             | Mexican currency.  |
+  +---------------------------------------------+--------------------+
+  | ESTANZUELA SUPPLY :                         |                    |
+  |  Aqueduct and dam                           | 502,000            |
+  |  South Reservoir                            | 429,000            |
+  |                                             | -------    931,000 |
+  |                                             |                    |
+  | SAN GERONIMO GRAVITY SUPPLY :               |                    |
+  |  Aqueduct, tunnel, and infiltration gallery | 223,000            |
+  |  Obispado Reservoir                         | 436,000            |
+  |                                             | -------    659,000 |
+  |                                             |                    |
+  | SAN GERONIMO PROVISIONAL SUPPLY ,           |                    |
+  |  including boring operations, etc.          |            130,000 |
+  |                                             |                    |
+  | CITY WATER DISTRIBUTION SYSTEM              |          1,195,700 |
+  |                                             |                    |
+  | CITY SEWER SYSTEM                           |          1,036,000 |
+  |                                             |                    |
+  | OUTFALL :                                   |                    |
+  |  Main outfall sewer                         | 425,000            |
+  |  Sewage purification works                  |  75,000            |
+  |                                             | -------    500,000 |
+  +---------------------------------------------+--------------------+
+  | Total                                                  4,451,700 |
+  +---------------------------------------------+--------------------+
+
+As a general statement, the actual cost of labor is about 33-1/3% of the
+total cost of the construction work, including materials. Fig. 20 shows in
+graphic form the amount of the labor pay-rolls and the progress of the
+work during the whole construction period from 1906 to 1909, inclusive,
+comprising also that done under contract.
+
+[Illustration: FIG. 20.--PROGRESS DIAGRAM SHOWING MONTHLY LABOR PAY-ROLLS
+DURING THE CONSTRUCTION PERIOD.]
+
+
+
+
+                    TARIFFS AND SANITARY REGULATIONS.
+
+
+_Tariffs._--The tariffs charged for the water and drainage service (Table
+17) were approved by the State Government (which accepts the
+responsibility for their collection), under a compulsory State law which
+came into force on March 1st, 1910, for the southern portion of the city,
+and on July 1st, for the northern half, the penalty for non-compliance
+being a tax of 10% on the monthly rental value of the property, as
+assessed by the State officials.
+
+The basis of the tariffs (which were published on February 22d, 1909) is a
+charge for water varying between 12 and 16 cents (Mexican) per 1,000
+liters, with a minimum monthly rate for each different class of property
+connected to the system. The rate for house drainage is fixed at 80% of
+the minimum water rate levied on the consumer. The minimum rates have been
+fixed so that the poorer classes of the community will not be overtaxed,
+while at the same time the rate is actually levied on the quantity of
+water used, as indicated by the meter. All the services at the present
+time are metered, and the meter system will be used throughout.
+
+                        TABLE 17.--THE TARIFFS.
+
+  +-----+------------+---------+-----------+---------+----------+--------+
+  |     | Monthly    | Liters  | Price for | Minimum | Rate for | Total  |
+  |Class| property   |   of    | 1,000     | monthly | drainage | rate   |
+  |     | rental.    |  water  | liters.   | rate.   | service. |payable.|
+  |     | Pesos.     | allowed.| Cents.    | Pesos.  | Pesos.   | Pesos. |
+  +-----+------------+---------+-----------+---------+----------+--------+
+  |   I | Up to 20   |  7,800  |   16      | 1.25    |   1.09   |  2.25  |
+  |  II | 21 to 40   | 12,500  |   16      | 2.00    |   1.60   |  3.60  |
+  | III | 41 to 60   | 18,750  |   16      | 3.00    |   2.40   |  5.40  |
+  |  IV | 61 to 120  | 23,350  |   15      | 3.50    |   2.80   |  6.30  |
+  |   V | 121 to 300 | 30,000  |   15      | 4.50    |   3.60   |  8.10  |
+  |  VI | 301 upward | 33,350  |   15      | 5.00    |   4.00   |  9.00  |
+  +-----+------------+---------+-----------+---------+----------+--------+
+
+    "Notes: (1st) The rental for the water meters 5/8-in. size
+    (15-1/2 mm.), which shall always be considered the property
+    of the Company, will be 20 cents per month. Houses of the
+    first and second classes shall be exempt from paying such
+    rental for one year's time, counting from this date.
+
+    "(2d) All excess consumption of water over that allowed by the
+    tariff will be charged for at 2 cents less than the price
+    shown in the tariff per thousand liters.
+
+    "(3d) Extra large houses, large establishments, such as
+    colleges, hotels, etc., etc., having a consumption of 50,000
+    to 60,000 liters of water per month, will pay at the rate of
+    14 cents per thousand liters. The drainage rate for such
+    buildings will be arranged in proportion to the water tariff,
+    or 80% of the value of the water.
+
+    "(4th) The laundry establishments, bath-houses, etc., when
+    using 50,000 liters or upward, can arrive at some agreement so
+    as to pay 12 cents per 1,000 liters.
+
+    "(5th) Groups can be formed of two or more small houses so as
+    to obtain a joint service under the proportion shown in the
+    tariff.
+
+    "(6th) Any other combination that cannot be entered into under
+    the basis of this tariff, will be arranged by specially agreed
+    upon prices, such agreement being as much as possible subject
+    to the basis mentioned."
+
+_Sanitary Regulations._--The State Government, on March 1st, 1909,
+published regulations for the proper installation of the water and
+drainage services within the houses.
+
+At the Government's request, a draft of the proposed regulations was
+submitted by the writer, who prepared it, after a study of American and
+British sanitary by-laws, to suit the special conditions of Monterrey.
+These regulations were afterward modified by him in collaboration with the
+Government Technical Inspector and Financial Interventor, and, in their
+final form, though not as stringent as those adopted in many northern
+cities, are probably more complete than those in any other Mexican city.
+Under these regulations only registered plumbers can undertake plumbing
+installations, and they have to execute a bond to the satisfaction of the
+_Alcalde Primero_ (City Mayor) for the sum of 2,000 pesos as a guaranty of
+responsibility. For defective workmanship or any infraction of the
+plumbing regulations, they are liable to heavy fines, and can be called on
+to make good all defects in workmanship, without extra charge to the owner
+of the property. The provisions of the regulations are carried out under
+the supervision of the Government Technical Inspector, the Company's
+obligations extending only to the sidewalk and to the meters placed within
+the houses.
+
+
+
+
+                             ENGINEERS, ETC.
+
+
+G. S. Binckley, M. Am. Soc. C. E., was Chief Engineer of the Company from
+February to December, 1906. The writer was Chief Engineer from May
+1st, 1907, until April, 1910, and is responsible for the design and
+construction of the works carried out during that period. Mr. J. D.
+Schuyler advised the Company throughout all preliminary studies and
+investigations, and acted as Consulting Engineer until February, 1908. The
+Technical Inspector, on behalf of the Government, throughout the whole
+progress of the works, has been Rudolf Meyer, M. Am. Soc. C. E., and the
+writer wishes to record the valuable assistance the Company has received
+from him.
+
+In conclusion the writer may be permitted to pay a tribute to the devoted
+public spirit shown by his Excellency, General Bernardo Reyes, the
+Governor of the State of Nuevo León from 1885 to February, 1910, and who,
+untiring in his devotion to the interests of the city, was primarily
+responsible for the inception of the works and their successful
+completion.
+
+
+
+
+                               DISCUSSION.
+
+
+JAMES D. SCHUYLER, M. AM. SOC. C. E. (by letter).--For completeness of
+detail and wide range of subjects of general interest to engineers, this
+paper is certainly one of the notable contributions to recent engineering
+literature. It is a minute and painstaking record of the successful
+accomplishment of construction work under unusual climatic conditions and
+difficult circumstances, and reflects credit on the author, not only in
+his capacity as an engineer, but as a faithful recorder of facts. It was
+particularly fortunate that he was an eyewitness of the disastrous and
+extraordinary flood which swept through Monterrey, destroying many lives
+and much property, and has thus been able to give an intelligent estimate
+of the maximum discharge of the river during the height of the flood wave
+of August 27th-28th, 1909, when the rate of run-off per unit of area of
+water-shed drained reached an amount which has seldom been equalled or
+exceeded, as far as reliable records extend. It is worthy of note that
+works deriving their water supply from the source of such torrential
+floods should have survived with so little actual damage, and with
+scarcely any interruption of service. The repair of all damages to the
+system was estimated to have cost not more than $20,000.
+
+As Mr. Conway did not assume charge of construction until May, 1907, he
+was spared the responsibility of deciding on the general plan of securing
+an abundant supply of pure water from sources permitting of delivery by
+gravity under adequate pressure for fire protection--a responsibility
+which devolved on the writer, assisted by G. S. Binckley, M. Am. Soc. C.
+E., Mr. Conway's predecessor, as Chief Engineer. Not only the water-works,
+but the system of sewerage and sewage disposal by broad irrigation were
+subsequently carried out on the plans submitted to the State Government by
+the writer in 1906, and given provisional acquiescence at that time.
+
+There was no lack of water at hand for the supply of a city of that size,
+as there are large perennial springs which flow out of the travertine of
+the plain, and are used for irrigation in the valley below the city. One
+of the largest of these, near the civic center, has a normal flow of
+nearly 30 cu. ft. per sec.; another nearby, also within the city limits,
+flows some 10 or 12 sec-ft., while both the Estanscia and Robalar springs,
+but a few miles below (shown on Plate II), discharge more than 20 sec-ft.,
+as nearly as memory serves. Besides this supply, the water to be developed
+by sinking shafts in certain parts of the plain, as demonstrated at the
+brewery and elsewhere, was apparently a reliable source of large volume.
+
+To utilize these sources, however, would have involved condemnation of the
+water-rights in the case of the springs, depriving present owners of the
+use of the water, and this Governor Reyes wished to avoid. Besides, it
+would have necessitated pumping the water for the city in perpetuity, an
+expense which the Governor was equally anxious to save; hence a gravity
+supply was made the prime requisite of the plans.
+
+Until the concession was granted, and for a year or more afterward, it was
+assumed that an adequate supply could only be obtained by the storage of
+the flood-water of the Santa Catarina River in a large reservoir; and the
+earlier plans of the concessionaires were based on the construction of a
+high masonry storage dam at the upper end of the "narrows," where the
+river turns from a western direction to a course almost due east, between
+high vertical cliffs of limestone. The concession distinctly provided for
+such a dam, and among the plans on file in the State Capitol is one
+prepared by the late E. Sherman Gould, M. Am. Soc. C. E., for a masonry
+weir across the gorge. Samuel M. Gray, M. Am. Soc. C. E., also filed a
+plan and report proposing a capacious, shallow, storage reservoir near the
+city, to be filled by a large flood-water canal from the Santa Catarina
+Cañon.
+
+Although the writer could not have anticipated the occurrence of floods of
+the magnitude of the one of August, 1909, which would surely have
+destroyed any reservoir built in the Cañon, he was unable to endorse the
+storage plan of water development, chiefly because of the uncertainty of
+the water-tightness of the reservoir in a cavernous limestone formation,
+and also because of the probable impurity of water draining from such
+extensive goat pastures. He, therefore, urged the development of the
+underflow of the river, which was manifesting itself in the springs
+referred to. Mr. Binckley secured two Keystone drilling machines and
+proceeded to profile the bed-rock at Santa Catarina Cañon and at San
+Geronimo, the two places on the stream where the river flows between walls
+of rock _in situ_. At both sites the strata were standing nearly vertical
+across the channel, and, by careful sampling and testing, it was found
+that in both locations there were thick strata of limestone so highly
+silicious as to be insoluble, and hence free from caverns. From this
+determination it was concluded that all the water which appeared in the
+valley below must pass through the sections where the borings were made.
+The results of this drilling, however, proved conclusively that the depth
+to bed-rock at either place was too great to permit of a masonry dam being
+considered as practical, and demonstrated the inadequacy of methods which
+had been used in the earlier investigations when dams were regarded as
+feasible.
+
+The results have also shown that the subterranean supply at the lower
+cross-section of the river, at San Geronimo, is abundant, and can probably
+be increased to an indefinite degree by continuing the filtration gallery;
+while at Santa Catarina the same type of development can be made for a
+high-source supply, although requiring a long and expensive tunnel and
+conduit.
+
+
+DAVID T. PITKETHLY, ASSOC. M. AM. SOC. C. E. (by letter).--Having been
+engaged on the design of sewerage systems for some years, the writer finds
+this paper of peculiar interest, particularly the sewerage portion. There
+are some points in the design, however, which do not appear to be clear.
+
+The system is described as "strictly separate," and yet the sewers are
+designed to run half-full, providing a capacity of 200%, the 100% basis,
+or 380 liters per capita, being 90%, or 180 liters, in excess of the
+calculated water supply of 200 liters per capita.
+
+It has been the writer's practice to design sanitary sewer systems on the
+basis of the water consumption, and to assume the whole daily amount to
+reach the sewer in 16 hours, thus providing capacity sufficient to care
+for the maximum or wash-day flow without causing the sewers to run above
+the calculated hydraulic gradient, which should be placed within the pipe
+so as to provide air space for ventilation under all circumstances.
+
+The practice of calculating sanitary sewers to run half-full is a good one
+when ground-water is expected in sufficient amount to fill the remaining
+portion of the sewer, but when no ground-water, or roof-, or surface-water
+is allowed to enter the system, or all precautions are taken to exclude
+such, then the system may be designed so that the expected maximum, or
+wash-day flow, will fill the sewer to the desired hydraulic gradient.
+
+The method of ventilating the sewers does not seem practicable. The houses
+are principally of one story, and yet the stand-pipes on the sewers have
+openings 25 ft. 9 in. above the sidewalk. Are the ventilating or vent
+pipes of the house plumbing carried to a height to balance this, or will
+these chimneys draw the air from the house drains and fresh-air pipes,
+breaking the seal in the so-called disconnecting traps, thus causing the
+circulation of air in the house piping to be downward through the sewers
+instead of upward through the fresh-air inlets and vents, as designed?
+
+It is interesting to note that crude sewage, as well as the liquefying
+(septic) tank effluent, is to be applied to land for irrigation purposes,
+but the application of crude sewage without any attempt at removing the
+suspended matter, or the effluent from the septic tanks where only a
+partial removal occurs, seems to be bad practice.
+
+The author states that:
+
+"The degree of purification in the tanks was relatively unimportant; the
+object to be obtained consisted chiefly in distributing on the land an
+effluent which would be innocuous and clear."
+
+How he expects to obtain such an effluent by passage through screens,
+detritus tanks, and septic tanks only, is more than the writer can
+understand.
+
+The removal of suspended matter in a septic tank depends on the strength
+of the sewage, the time of retention, the time elapsing between cleaning,
+the presence of trade wastes, etc., and seldom exceeds 38 per cent.
+
+The subject of septic tanks and their effect on sewage is discussed in the
+"Fifth Report of the Royal Commission on Sewage Disposal" (England, 1908),
+and the following extracts, relative to the application of crude sewage to
+land and the effect of septic tanks on sewage, seem apropos:
+
+    "23. * * * There are also many cases in which crude sewage has
+    been passed over land, but the evidence shows that land treatment
+    of crude sewage is liable to give rise to nuisance by the
+    accumulation of solids on the surface of the land. Moreover, in
+    some cases these solids are apt to form an impervious layer,
+    which interferes with the aeration of the soil, and so impairs
+    the efficiency of the treatment."
+
+    "31. * * * At that time it was claimed that the septic tank
+    possessed the following, among other, advantages:
+
+    "That it solved the sludge difficulty, inasmuch as practically all
+    the organic solid matter was digested in the tank.
+
+    "That it destroyed any pathogenic organisms which there might be
+    in the sewage."
+
+    "32. As regards the first of these claims, it is now clearly
+    established that, in practice, all the organic solids are not
+    digested by septic tanks, and that the actual amount of digestion
+    varies to some extent with the character of the sewage, the size
+    of the tanks relative to the volume treated, and the frequency of
+    cleansing."
+
+    "At Huddersfield, Mr. Campbell estimated that about 38 per cent.
+    of the solids were converted into gas or digested; * * * while at
+    Birmingham, Messrs. Watson and O'Shaughnessy say that the figures
+    available indicated a digestion of not more than 10 per cent. of
+    the suspended matter entering the tanks."
+
+    "33. As regards the second claim, we find as a result of a very
+    large number of observations that the sewage issuing from the
+    septic tanks is, bacteriologically, almost as impure as the sewage
+    entering the tanks."
+
+Messrs. Winslow and Phelps, in their interesting paper, "Investigations on
+the Purification of Boston Sewage,"[8] quote a suggestion made by
+Stoddart (1905):
+
+[8] Water Supply and Irrigation Paper No. 185, p. 125.
+
+    "He finds, in a septic tank of several compartments, a
+    considerable deposit of sludge in the first compartment, giving
+    a fairly clear supernatant liquid, which in the last chamber of
+    all undergoes a secondary decomposition, leading to the
+    throwing down of an additional precipitate of offensive
+    sludge."
+
+What took place in the case referred to by Stoddart corresponds to the
+author's observations of the liquid leaving the tanks in a clarified
+condition, but the secondary decomposition must take place in some manner,
+and, when it does, a nuisance seems to be unavoidable where no provision
+is made to care for it.
+
+In view of the experience of others, some further treatment seems to be
+necessary. Such treatment should include disinfection, as no method of
+disposal yet devised has succeeded in reducing materially the pathogenic
+germs usually to be found in sewage and tank effluents.
+
+If the crops to be irrigated are to be eaten, uncooked, by mankind, then
+disinfection at least is imperative.
+
+
+GEORGE S. BINCKLEY, M. AM. SOC. C. E. (by letter).--Mr. Conway's admirable
+paper is of special interest to the writer, as the entire general design
+of the system, as well as the extensive hydrological studies and final
+selection of the sources of water supply, was completed during 1906
+through the joint labors of the writer, as Chief Engineer, and James D.
+Schuyler, M. Am. Soc. C. E., as Consulting Engineer.
+
+In this work, Mr. Schuyler and the writer had the rare privilege of
+dealing from its inception with the problem of designing a complete and
+somewhat extensive system of municipal water supply and drainage,
+unhampered by any existing works to which the new systems would have to be
+adapted. It would probably be difficult to find in the United States a
+city of 85,000 inhabitants, previously totally lacking either a water
+supply or sewerage system, which, under a consistent and harmonious
+design, has been provided with both in the degree of completeness and
+structural excellence exemplified in the works at Monterrey.
+
+The few important changes or amplifications made in the original design,
+and the manner in which its detail has been executed is naturally most
+interesting to the writer, and this excellent paper should be of very
+substantial value, particularly to engineers engaged on similar work in
+Mexico or Spanish America.
+
+The very novel construction method adopted by Mr. Conway in the roofing of
+the South or Guadalupe Reservoir, seems to the writer rather to invite
+criticism, and the fact that in the subsequent construction of the roof
+over the rectangular Obispado Reservoir the customary monolithic concrete
+construction was apparently reverted to after experience with the
+separate-unit plan previously used, would indicate that Mr. Conway reached
+the same conclusion.
+
+The original design of the circular Guadalupe Reservoir contemplated just
+about the same arrangement of columns and roof support as that actually
+used, but the writer had expected that the columns would be cast in place,
+and that the system of primary and secondary beams would be filled at the
+same time as, and integral with, the roof slab, the reinforcement being
+placed in accordance with what may be described as conventional practice.
+The writer believes that the efficiency of the concrete and steel placed
+in this manner would be notably higher than under the system actually
+adopted, which, in effect, is pretty much the same as constructing the
+supporting system of units of cut stone. If, with all the elements of
+structural weakness involved in the multiplicity of mortised joints,
+discontinuous reinforcement, etc., this construction is strong enough, it
+would seem that an important reduction in the dimensions of the members
+could have been effected by monolithic construction and continuous
+reinforcement, without sacrifice of strength.
+
+The comparison, in Table 7, of the costs of these two reservoirs, is
+interesting, but very moderately illuminating, as the comparative unit
+cost of the most important element in their construction--the concrete--is
+not given. The total excavation cost for each reservoir is practically the
+same, and the general expense, engineering, and cost of fittings and
+accessories presumably so, but the total cost of the Guadalupe Reservoir
+as given is $19,000 (pesos) in excess of that of the Obispado Reservoir,
+while, in the latter, there were 756 cu. m. more concrete. This certainly
+indicates a much higher cost of concrete per unit as laid in the South
+(Guadalupe) Reservoir. An actual comparison of the cost per unit of
+concrete laid under the two systems would be instructive.
+
+The writer is interested to observe that the same system of sub-drainage
+used by him in the construction of the reservoir for the provisional
+supply of water from San Geronimo, has been used by the author in the
+Obispado Reservoir. This arrangement of drains under the floor of the
+reservoir at San Geronimo was devised as a safeguard against damage to the
+lining through the accumulation of water inside the impervious bank
+against its back.
+
+It was realized that, in such a climate as that of Monterrey, perfect
+water-tightness of the lining might be difficult to secure or maintain,
+and, if leaks existed, a sudden draft on the contents of the reservoir
+might result in serious damage through the static pressure exerted against
+the lining of the sides or upward thrust against the floor. In the
+writer's opinion, such a system of drains is an important element, as not
+alone the fact but the quantity of leakage may be determined, and danger
+of saturation of the supporting bank avoided--a matter of importance
+where, as is sometimes the case, the material of such a bank is unfit to
+resist the effects of saturation. The author does not state whether or not
+this safeguard was omitted in the Guadalupe Reservoir. Incidentally,
+however, the matter of saturation of the bank is not important in either
+reservoir, as the material of which these banks are constructed is such
+that settlement or failure through saturation is out of the question. It
+may be remarked, however, that in fixing the angle of the sides of the
+Guadalupe Reservoir at 60° the writer contemplated the same system of
+constructing the bank as he used in that of the San Geronimo Reservoir. In
+this case, the bank was built up by spreading the material in thin layers,
+wetting down, and rolling and puddling by the passage of the ox-carts used
+for the transportation of the material, the wheels of the carts, and
+especially the cloven hoofs of the animals, producing a most excellent
+effect. The inside slope was built up in this fashion to a much lower
+angle, and with a top width considerably in excess of the finished
+dimensions. The excess material was then picked off to the line, and
+exactly to the slope. Thus the finished slope presented a surface which
+was compacted to a degree impossible to attain at or near the surface of
+the bank as built, and presenting a support of the best possible character
+for the concrete lining and coping.
+
+
+V. SAUCEDO, ASSOC. M. AM. SOC. C. E. (by letter).--The author's
+description of the water-works and sewerage of Monterrey, one of the most
+extensive schemes in Mexico, will be of general interest to engineers,
+especially those engaged in hydraulic and sanitary problems. The writer,
+having been connected with the works for four years, knows the local
+conditions well, and presents herewith some complementary data on what he
+considers an important feature, the subject of floods, mentioned by the
+author on different occasions, especially as certain developments in the
+works show the importance of such occurrences as a factor in designing.
+
+Abnormal rainfalls of long duration and high intensity are common in the
+semi-arid region of Mexico. They come at irregular intervals, though
+tending to coincide with the early fall. The floods of August, 1909, were
+a repetition of similar occurrences in the past; and, though there are no
+numerical records of previous cases, local traditions and historical state
+documents describe them as having occurred since the foundation of the
+city, at intervals of from 15 to 40 years. The graphic descriptions of the
+places flooded are in accord with the character of the floods of August,
+1909, and September, 1910.
+
+The diagram, Fig. 21, is a record of the rainfall during the latter flood,
+and was plotted from intermittent readings of standard gauges. It
+demonstrates that the intensity increased toward the mountains on the
+south, which form the tributary water-shed of the Santa Catarina River,
+showing a difference of 10.54 in. between the city and the Estanzuela Dam,
+which is not quite 12 miles to the southeast.
+
+[Illustration: FIG. 21.--RAINFALL DURING FLOODS OF SEPTEMBER 14TH-16TH,
+1910, IN MONTERREY.]
+
+An estimate of the volume of discharge of the river at the time of maximum
+flood is only a reasonable conjecture which (without special reference to
+accuracy) aims to impress those who have not witnessed such occurrences
+with the tremendous volume coming from barren steep surfaces previously
+saturated.
+
+The original computation, referred to by the author, was obtained from the
+average of two different methods which gave results close to each other.
+In one method the extent and nature of the water-shed were considered,
+together with the maximum period of precipitation that occurred,
+sufficient to gather a maximum volume of water in the river. In the other
+method the volume was derived from a cross-section of the wetted perimeter
+of the river at the time of maximum flow, in combination with velocity
+approximations obtained by using rough floats. This gave 271,500 cu. ft.
+per sec. The figure submitted by the author, 235,000 cu, ft. per sec., is
+in accord with the proposed formula[9] for impervious surfaces by C. E.
+Gregory, M. Am. Soc. C. E. In the first and last methods, the intensity, a
+governing factor, is more or less of an assumption, and the
+cross-sectional method is also unreliable, as the river-bed was greatly
+disturbed, due to the high velocity of the water, which deepens the
+channel to a considerable extent at times of maximum flood, the gravels
+being redeposited during the period of subsidence. Such was the case
+during the flood of September, 1910, when the depth of gravel above the
+roof of the San Geronimo Infiltration Gallery was diminished to such an
+extent that it was so inefficient as a filter for the flood as to permit
+the percolation of turbid water into the underground supply.
+
+[9] _Transactions_. Am. Soc. C. E., Vol. LVIII. p. 458.
+
+During the floods of August, 1909, Shafts Nos. 2 and 3 were damaged beyond
+repair, and sand and gravel, entering through them, blocked up the
+gallery to within about 150 ft. of Shaft No. 1. The interior timbering
+probably collapsed, due to cavings and disturbance in the river-bed during
+the period of maximum flood, but no explorations have been possible on
+account of the great quantity of water still coming through (at present
+more than 650 liters per sec.). For this reason the work of driving the
+gallery, as well as lining Shaft No. 1, has been suspended.
+
+[Illustration: PLATE XXVIII, FIG. 2.--VIEW OF SANTA CATARINA RIVER IN
+FLOOD, ON AUGUST 28TH, 1909.]
+
+[Illustration: PLATE XXXI, FIG. 1.--FLUSH-TANK CARRIED DOWN BY FLOOD OF
+AUGUST 27TH-28TH, 1909.]
+
+[Illustration: PLATE XXXI, FIG. 2.--VIEW SHOWING SCOURING EFFECT OF FLOOD
+ON SAN GERONIMO AQUEDUCT.]
+
+[Illustration: PLATE XXXII, FIG. 1.--VIEW OF SANTA CATARINA RIVER AFTER
+THE FLOOD.]
+
+[Illustration: PLATE XXXII, FIG. 2.--VIEW OF SANTA CATARINA RIVER FLOWING
+THROUGH LOW-LYING STREETS, 8 DAYS AFTER THE FLOOD.]
+
+On reaching the city, the flood of August, 1909, swept away two streets
+adjoining the river. These streets had been built on made ground, in what
+was originally the river-bed. The sewers and water mains laid in them were
+destroyed entirely, and some 460 ft. of the 24-in. cast-iron pipe, buried
+under the river-bed at a depth of 8 ft., were carried away. In relaying
+this portion of the main, and for protecting the remainder of it across
+the river, it is now proposed to encase it in a solid rubble concrete
+block, 8 ft. square, which will impart weight and stability against the
+scouring effect of floods.
+
+The South Reservoir is circular in shape, with an interior diameter of
+165.68 ft. at the top, and is partly excavated in the ground and partly
+completed by an embankment of vast proportions (Fig. 10). Right after the
+flood of August, 1909, a wet spot appeared on the northeastern toe of the
+embankment, and it was supposed for some time that it was the effect of
+the saturation produced by the preceding rains, but, as it persisted for
+several months, it was obvious that its origin was in the interior of the
+reservoir, which was emptied when the writer took charge of the work. The
+first inspection revealed a horizontal crack in the concrete lining, about
+310 ft. long and extending about 153° around the circumference on the
+north side. Throughout its length it coincided with the line of cut and
+fill. Vertical cracks, coinciding with the panel points in the lining, had
+also developed, and extended from the main horizontal crack to the roof.
+The circumstances originating this development can be conjectured by
+considering the position of the main crack, its characteristic features,
+and the conditions that preceded its formation. The coincidence of the
+crack with the joint of cut and fill, points to this line as a source of
+danger. An examination showed, besides, that the fracture was clean and
+sharp, ranging in thickness from a hair line at the ends to 3/16 in. at
+the center, and that its upper border projected over the lower one
+perceptibly, a proof that horizontal motion had taken place. The vertical
+cracks were a secondary effect, the consequence of the displacement
+immediately after it was scoured. A fracture was discovered in the floor
+of the reservoir. It started at the center and branched out into two
+diverging lines in a radial direction.
+
+The circumstance of two abnormal rainfalls, giving 35 in. in 9 days, the
+precipitation being concentrated in two periods, not far apart, of 42
+hours and 98 hours, respectively (Fig. 4), together with lack of provision
+for shedding the water from the roof of the reservoir and from the
+surrounding embankment, lead to the inference that the latter became
+saturated, increasing thereby in weight and decreasing in stability,
+especially in its steep inner face. A settlement and the consequent
+horizontal displacement, under these conditions, was natural. The concrete
+lining, only 16 in. thick at that height, was not sufficient to sustain
+the resulting strain, and the main fracture developed, permitting the
+stored-up water to leak into the bank. In time this seepage found its way
+under the bottom of the reservoir, softening the ground and producing a
+slight settlement which caused the crack in the floor. Had under-drainage
+been provided, as at the Obispado Reservoir, the actual conditions would
+have been noticed earlier. However, as the embankment is of vast
+proportions, stable in itself to sustain with a large margin of safety the
+weight of the stored-up water, there was no actual danger of failure,
+except for the fact that the material forming the structure, on account of
+its calcareous nature, is dissolved by water. Long exposure to this
+condition would, in time, open passages in the embankment, and it is
+certain that there would be cavings in its interior.
+
+The necessary grouting has been done, and provision is being made for
+water-proofing the interior of the reservoir and shedding the water from
+the roof and from the embankment, thus relieving the structure of the
+consequent strain.
+
+Another place in the works where floods have had a damaging effect is the
+Estanzuela intake basin, which, when the dam was completed, was filled to
+the overflow level in order to test its water-tightness. As this basin,
+when cleaned, was found to be slightly fissured on the north side, it was
+decided to line it with concrete. As shown in Fig. 8, the lining does not
+cover its entire area, but only the central portion, leaving a strip on
+either side without protection. The flood of September, 1910, coming in
+greater volume than the previous ones of August, 1909, in passing through
+the narrow gorge at the entrance, undermined the lining in those places
+where it was not founded on solid rock. Figs. 1, 2, and 3, Plate XXXIII,
+show some of the damage caused by this flood. The buoyant effect of the
+water and the impact of large rolling boulders caused fractures all over
+the surface, and lifted the concrete lining bodily; but the dam proper,
+being founded on rock bottom, did not suffer any injury. In the future, in
+order to avoid the seepage of the ordinary supply, alluded to by the
+author, the water will be carried to the valve-house in an open rubble
+concrete channel, lined with cement mortar and built high up against the
+western hillside. The remainder of the basin will be paved with large
+boulders.
+
+[Illustration: PLATE XXXIII, FIG. 1.--ESTANZUELA DAM: BROKEN CONCRETE
+BASIN LINING.]
+
+[Illustration: PLATE XXXIII, FIG. 2.--ESTANZUELA DAM: BROKEN CONCRETE
+BASIN LINING, EAST SIDE.]
+
+[Illustration: PLATE XXXIII, FIG. 3.--ESTANZUELA DAM SEPT. 26, 1910: VIEW
+OF SHEARING FRACTURES OF WALL AND LINING AFTER FLOOD SEPT. 14-17, 1910.]
+
+In conclusion, the writer wishes to emphasize the point that,
+notwithstanding the severity of the test, relatively small damage was
+inflicted on the extensive works carried out under the author's design and
+direction. A test so severe that it caused serious damage and immense
+losses in the entire region, washing away kilometers of railroad track and
+destroying practically all the bridges within reach of the flood, is an
+occurrence of paramount importance, and should be remembered as a leading
+factor in the design of engineering works.
+
+
+GEORGE T. HAMMOND, M. AM. SOC. C. E. (by letter).--In a country, such as
+that described in this paper, where water is valuable, and a shortage is
+at times possible, where the majority of the population is very poor, and
+water and sewage discharge are both to be paid for on a basis of volume,
+the question of the expected quantity of daily water supply and sewage
+flow per capita is of primary importance. This question, notwithstanding
+its difficulty, should be given a first place in the studies for
+water-works and sewerage projects, and should never be lost sight of in
+the design, which should be such that, while proper for the expected
+future flow for a reasonable time, should also be proper and economical
+for conditions which at present obtain and may change but slowly.
+
+It is desirable, of course, to get as much capacity in works as one can
+for the outlay, but there are instances where one can get too much for the
+money, as where a larger pipe than is necessary is used for a sewer,
+merely because it costs about the same as a smaller one, and as a result
+the cost of maintenance is permanently increased.
+
+The water-works were designed to supply 40,000,000 liters (10,582,000
+gal.) daily, which it was assumed would be sufficient for all future
+developments in Monterrey for a population of 200,000 at a per capita
+consumption of 200 liters (about 53 gal.) per day. The present population
+of the city is given as less than 90,000, there having been an increase of
+22,000 in ten years (1891-1901), but it is evident that in the last ten
+years (1901-1911) this rate of increase has not continued. Taking into
+account all the data known to the writer, it does not seem that the city
+will attain a population of 200,000 in a great many years, if it ever
+does; but this is a matter of personal opinion, and is only stated as
+such.
+
+The present requirements of the city's population, assuming that each
+person uses 200 liters (53 gal.) per day, would be, at that rate, which is
+a very liberal one, only 18,000,000 liters (4,762,000 gal.) per day, or
+less than half the amount which may be provided.
+
+If the water were not to be metered and the sewage discharge paid for by
+measure, it is possible that the free use of water might lead to the usual
+waste with which all are fairly familiar; but the use of meters, and the
+rates charged, will reduce the water consumption to a minimum. This end
+will especially result from Section 5 of the Tariffs which provides that:
+
+"Groups can be formed of two or more small houses so as to obtain a joint
+service under the proportion shown in the tariff."
+
+This provision will keep down the per capita supply, among the majority of
+the people, to about 37-1/2 liters (10 gal.) per day. A similar provision
+led to abuse in Santiago de Cuba, as well as in other Cuban cities, where
+one householder, taking water, frequently delivers it to adjoining houses
+and tenements through rubber hose. As many as ten or twelve families are
+sometimes found to be supplied from one tap in this manner. Indeed, it may
+be stated as a rule, having but few exceptions, that where water is paid
+for by meter its use is always restricted.
+
+The water mains and distribution system, however, are so well laid out,
+and the whole design is so good, that the writer would not anticipate much
+difficulty because it is on rather too liberal lines for the present or
+probable future. It may, perhaps, be argued that it may cost more to keep
+the mains in such a system clean; but this extra cost will scarcely be of
+much moment, and will be offset by the greater lasting quality of the
+larger pipes. There is another feature of the problem, however, which is
+not affected favorably by a too liberal forecast of the per capita water
+supply, namely, the sewerage system.
+
+If it is assumed that, using 200 liters per capita per day, the total
+water supply of the city for the present population will be 18,000,000
+liters, and that this may double in fifty years, or even amount to
+40,000,000 liters in that time, it would seem that a rather liberal
+provision has been made for the water supply, and that this will scarcely
+be exceeded by the sewage, for the latter must come from the water supply,
+there being little or no ground-water and no storm-water taken into the
+sewers. Designing the sewers to flow half full for all diameters less than
+18 in., and seven-tenths full for all larger sizes, it would seem that
+this would give ample capacity for all time to come in such a city, and
+that good practice would not exceed these figures, it being more desirable
+that the sewers should not be too large to work well, than that they
+should be large enough in all places to meet every possible contingency.
+If all the sewers of a system are too large, the condition is incurably
+bad; while, if a few miles prove to be too small, on account of growth and
+prosperity not anticipated by the designer, it will be easy enough to
+relay such parts when this becomes necessary.
+
+Mr. Conway states that:
+
+"The sewers are designed on a very liberal basis, namely, on the
+assumption that when flowing half full the quantity to be dealt with will
+be 380 liters [100 gal.] per capita per day, with a maximum rate of flow
+of 200 per cent."
+
+If the writer understands this statement correctly, it means that the
+sewers, flowing half full, will carry 380 liters per capita in 12 hours,
+or are designed with 200% of the capacity required to take the assumed
+flow in 24 hours.
+
+It was assumed that each house would be occupied by 7 persons and have a
+frontage of 12-1/2 m. (about 41 ft.), that is, about 700 gal. per day per
+house, the maximum flow rate being 200%, or at the rate of 700 gal. per
+house in 12 hours.
+
+It is to be remembered that nearly all the houses are of one story, and
+that, as a rule in tropical and sub-tropical countries, the per capita use
+of water diminishes with some function of the increasing number of
+inhabitants in one house. Most of the water is used in the kitchen, and
+where there are 7 persons instead of 5, the quantity used by the smaller
+number will generally serve the larger.
+
+The writer is unable to understand how this quantity of sewage will be
+produced, especially as the author states that, as far as the company is
+concerned, it is limited to the removal and disposal of the sewage, and is
+not required to provide for storm-water. He also states that:
+
+"Apart from that fact, however, the best system for a city like Monterrey,
+where rainfall for many months at a time is very scarce, is the strictly
+'separate system'."
+
+The minimum velocities in the sewers, when running full, vary between 0.91
+and 1.5 m. (from 3 to 5 ft.) per sec., and will be the same flowing half
+full.
+
+From the foregoing data it will be observed that:
+
+    (1) The water supply is the only source from which sewage flow
+    is anticipated;
+
+    (2) The water supply is very liberally estimated at 200 liters
+    (53 gal.) per capita daily;
+
+    (3) For purposes of sewer design, the daily flow of sewage
+    expected (all of which is derived from the water supply of 200
+    liters per capita) is estimated at 380 liters per capita, with a
+    maximum rate of flow of 200% (or at the rate of 760 liters per
+    capita), and with this quantity the sewers are designed to flow
+    only half full;
+
+    (4) The gradients are such that a velocity of from 3 to 5 ft.
+    (0.91 to 1.5 m.) per sec. will be secured in the sewers flowing
+    half full with the above quantity of flow per capita.
+
+The writer does not agree with this method of computation, as he feels
+sure that it will give sewers which are too large, with grades too steep
+for the best obtainable results. His experience, extending over more than
+twenty years in sewer design and hydraulic work, convinces him that the
+method pursued is wrong in principle.
+
+The principles involved in sewer design are first of all hydraulic. The
+quantity of flow, in the nature of things, cannot be forecasted
+accurately; success depends on getting the nearest possible approximation
+to average conditions. If 200 liters per capita per day is a liberal
+allowance, and 40,000,000 liters per day is a liberal expectation at this
+rate for double the present population, and the sewers are designed to
+flow half full only, why should this again be doubled?
+
+The design of a sewer system for a city such as Monterrey is, in fact, a
+very difficult problem, especially as the quantity of sewage will be very
+limited, flush-water will have to be used in considerable quantities, and
+water in that part of the world is precious at all times and often scarce.
+Under these circumstances, the size or shape of the pipes selected for the
+lateral sewers, should have been such as would more nearly agree with the
+requirements than does the 8-in. circular.
+
+A. P. Folwell, M. Am. Soc. C. E., writing of the 8-in. circular size,
+states:[10]
+
+[10] "Sewerage," by A. P. Folwell, M. Am, Soc. C. E.
+
+    "To secure a flow in this pipe having an average depth of 4
+    inches would require the sewage from a population of 6,500. In
+    general it may be said that the ordinary depth of flow in any
+    sewer should not be less than 2 inches, nor should it be less
+    than 1/2 the radius of the invert, since if it is so there is
+    much more danger of deposits forming along the edges and even in
+    the center of the stream. It will sometimes be impossible to
+    meet this requirement fully, but it should be kept in mind as
+    extremely desirable."
+
+Sewers of small size should be proportioned throughout the system so that
+the depth of the minimum daily flow in the invert, and the velocity of
+flow, will be the best possible to prevent deposits. The transporting
+power of water is dependent mainly on the depth of flow, a minimum
+velocity being selected rather than a minimum depth of flow. To those who
+have had charge of the maintenance of sewers, as well as of their design
+and construction, this principle seems so obvious that it is always a
+surprise to see it disregarded by designers, who in these days seem
+inclined to consider sewerage as a system of grades and sizes of pipes
+installed for ideal, rather than for actual, conditions. Messrs. Staley
+and Pierson have well stated the principle involved as follows:
+
+"A stream having a depth of flow sufficient to immerse solid matter held
+in suspension, to a certain extent lifts it and carries it forward. The
+entire surface is also exposed to the action of the current. A stream
+having an equal velocity but a less depth in proportion to the diameter of
+the solid matters to be transported, evidently has less transporting
+power. * * * An amount of sewage which can be properly transported by a
+circular sewer of a given size, cannot be as efficiently transported by
+one of larger diameter."
+
+From some strange idea, which is apparently without foundation in logic or
+based on any actual justification from experience, it has of late years
+become the practice of designing engineers to make the 8-in. circular
+pipe the smallest size for sewers; and it is not improbable that the
+designer of the Monterrey system has merely followed this example. It has
+also become the frequent practice of designers to give every length of
+sewer all the grade possible, regardless of the fact, taught both by
+hydraulics and experience, that the best grade is that which will give as
+much depth of flow as is consistent with a scouring velocity.
+
+Some years ago it was the standard practice, in the "strictly separate
+system" of sewers, to use the 6-in. pipe as the minimum size, and, as far
+as the writer has been able to discover, after giving the matter a rather
+extensive investigation, the 6-in. size has given excellent results
+wherever its use was proper. In places where it has not succeeded there
+were excellent reasons why it should not have been selected, and these
+could easily have been observed at the time the designs were made. The
+best sizes for the sewers in a given system is always a matter to be
+determined by local conditions; but there seems to be no reason why the
+6-in. size should not be used where the flow is so slight that the 8-in.
+will not work well; or where the velocity must of necessity be so great
+that a flotation depth of flow cannot be maintained in the larger size. As
+to likelihood of clogging and stoppage, the writer's opinion, based on the
+maintenance of three rather extensive systems in different parts of the
+United States, in each of which the 6-in. size comprises more than 75% of
+the whole length of pipe, and of three other systems, one having 12-in.
+and two having 8-in. as the minimum sizes, is that the 6-in. size, where
+properly used, is less likely to become clogged than either of the others
+used improperly. The cost of maintaining the 6-in. pipe lateral, under
+these circumstances, is much less than that of maintaining the 8-in.
+lateral.
+
+The 6-in. pipe is not being used now as much as the 8-in., and in most
+cases this is probably because the capacity of the latter is nearly double
+that of the 6-in., and costs only a few cents more per foot. If there is a
+sufficient population per acre, or if, within 30 or 40 years, such a
+population is anticipated as will fill the 8-in. pipe half full, its use,
+of course, is justified and necessary; but where it is quite evident that
+this will never occur, its use is counter-indicated.
+
+In Monterrey, where the building lots have a frontage of 41 ft., where the
+houses, as a rule, are only one story high, where the water service is
+metered and paid for, and the sewage flow is also paid for, there seems to
+be no reason to justify the use of 8-in. pipe for the upper reaches of the
+smallest sewers. The sewage flow to be anticipated will probably never be
+sufficient to keep an 8-in. pipe sewer in a good clean condition at the
+upper ends of the lines of sewers without excessive flushing; and the
+sharper or steeper the grade on which it is placed, the worse will be the
+result, because the sharper the grade, the thinner the flowing thread of
+sewage will be drawn out in the invert; on the other hand, if the grades
+are flat, the slight quantity of sewage flow will be spread out in a
+sluggish stream, without sufficient depth, on the bottom of the 8-in.
+pipe.
+
+Where a wide surface is given to a small quantity of flowing sewage, it
+stagnates slowly along the bottom of the sewer, leaving frequent deposits
+to undergo decomposition and create foul air, if not to choke the sewer, a
+result often produced; and where a circular sewer which is too large for
+the ordinary flow is given a strong velocity by using steep grades, the
+stream, though flowing rapidly, is drawn out to such a thin thread that it
+will not effect the flotation of the solid masses in the sewage brought in
+at house connections, and the shallow and thin stream simply flows around
+such masses until a dam or obstruction forms and the sewage is backed up
+sufficiently to force the obstruction farther down, to form another
+obstruction in a larger pipe below. Flushing may possibly keep such a
+sewer fairly clean; but, as usually practiced, it is effective only for a
+few hundred feet from the flush-tank; and the quantity of flush-water
+required by an 8-in. pipe is more than twice as much as that required to
+keep the 6-in. pipe clean. Ventilation is better in the smaller sewer than
+in the larger, as there is less air to move; but the elaborate ventilating
+stacks provided at Monterrey may take care of this; and it is evidently a
+place where ventilation will be needed.
+
+The ideal size and shape of cross-section for a sewer is such as will give
+the best flotation to moving solids which are being carried along by the
+flow; and this means the sewer that, with the expected ordinary or average
+flow, will give the best depth in the invert, when the velocity of flow is
+sufficient to keep suspended solids, grit, etc., moving at a rate of from
+2 to 3 ft. per sec. The size, however, is limited by practical
+considerations. The circular pipes cannot well be less than 6 in. in
+diameter, because the house connections cannot well be less than 4-in.
+pipe, and the sewer should be larger than the house connections, for
+various practical reasons; but, in order to secure flotation and a
+scouring flow, the smallest pipe, or the pipe having the smallest invert
+radius, that practical considerations permit, should be selected. The
+grade should be such, and the collecting system so laid out, that the flow
+may be conserved as far as possible, and the sewage flow should be kept of
+as great a depth in the invert, or bottom of the sewer, as safety in
+self-cleansing velocity will permit. This will save flush-water and
+prevent stoppages, and thus reduce the cost of maintenance to a minimum.
+For good sanitary practice, the sewers should be designed, first of all,
+to comply with the requirements of the present, or immediately expected,
+ordinary flow, with some reasonable allowance for the future. They should
+be neither too large nor too small, and the grade should neither be too
+great nor too little, to secure the best flotation and scouring effects
+and the best flush-wave action under all circumstances.
+
+The use of cement concrete pipe for sewers seems to be growing in favor;
+nor is this surprising, in view of the many improvements made in their
+design and manufacture. The excellence of the concrete pipe used in
+Monterrey and its success, suggest the query: Why was it not used still
+more extensively?
+
+Table 13 shows that the cement pipe cost much less than the vitrified
+tile, or "fire-clay" pipe. Thus, the 38.1 cm. (15-in.) fire-clay cost 6.14
+pesos per lin. m., the 45.7 cm. (18-in.) cost 8.80 pesos, and the 50.8 cm.
+(20-in.) cost 11.30 pesos. Compared with this, the concrete pipe was much
+the cheaper; the 55.9 cm. (22-in.) cost 5.93 pesos, which is less than the
+cost of the 38.1 cm. (15-in.) fire-clay; and the 61.0 cm. (25-in.)
+concrete pipe cost 7.30 pesos, which is less than the 45.7 cm. (18-in.)
+fire-clay.
+
+The writer's experience with concrete pipe, derived mainly from a long
+service in sewer design and construction in Brooklyn, N. Y., leads him to
+believe that at Monterrey the whole sewer system might, with advantage,
+have been built of concrete pipe, using an egg-shaped pipe with an area
+slightly larger than an 8-in. circle, designed for a discharge equal to an
+8-in. pipe for all the smaller sewers. The invert of such an egg-shaped
+pipe would fulfill the present requirements in carrying a very small flow
+with good flotation depth, better than would a 6-in. circular pipe, and
+the reserve capacity of the 8-in. pipe would be secured without
+interfering with good present service. Egg-shaped pipes, similar to those
+used in Brooklyn, the writer believes, would have given far better
+satisfaction throughout the Monterrey sewerage system than circular
+fire-clay pipe, and would have cost no more, but probably less. The
+egg-shaped pipe referred to is made with a flat base and a self-centering
+joint, thus insuring perfect alignment, and a smoother interior surface
+than can be obtained with fire-clay pipes.
+
+Brooklyn has about 450 miles of concrete pipe sewers, of all sizes less
+than 24 in., the greater part of which is egg-shaped. There are also about
+250 miles of vitrified stoneware circular pipe sewers of similar sizes,
+and the cost of repairs and replacing pipe, over a period of years is
+about the same per mile for each kind. Incidentally, it may be stated that
+the annual cost of repairs per mile on both kinds of pipe is very small,
+and is only about one-fifth of the cost of repairs per mile on the brick
+sewers, of which there are about 200 miles.
+
+The principal advantages and disadvantages of cement concrete pipe sewers
+may be summed up as follows:
+
+                      ADVANTAGES OF CONCRETE PIPE.
+
+  (a) Cement concrete pipe is usually less costly than vitrified
+      pipe.
+
+  (b) It can be formed in any shape desired.
+
+  (c) It is not cracked by vibration, and resists impact better than
+      vitrified pipe, for which reason it is a better material to
+      lay near the surface of a street in which there is heavy
+      traffic.
+
+  (d) It is not affected by ordinary sewage.
+
+  (e) The cost of repairing and maintaining is about the same as for
+      a vitrified pipe sewer.
+
+  (f) It can be made in the city or town where it is to be
+      installed, thus giving the locality the advantage of having
+      some of the money paid for labor in its manufacture spent in
+      the place where the sewers are being put in, where it is
+      raised as a tax, etc.; also saving freight charges, etc.
+
+  (g) It can be made under the most careful local supervision and
+      inspection, of selected material, by the engineer who is
+      responsible for the success of the work. Vitrified pipe can
+      seldom be made in this way.
+
+                      DISADVANTAGES OF CONCRETE PIPE.
+
+  (a) If not carefully made and of the best of materials, it is
+      subject to failure by disintegration, etc.
+
+  (b) It will not stand strong chemical action, and therefore the
+      smaller sizes should not be used where they are likely to be
+      exposed to trade wastes containing strong acids. In the larger
+      sizes the quantity of flow mixes so quickly with the trade
+      wastes that this danger is minimized, and it is very seldom
+      that even the smaller sizes become affected; but vitrified
+      pipe may be used in places where chemical action is
+      anticipated.
+
+  (c) If not properly made, it will be attacked by steam and hot
+      vapor, and by animal fats in the sewage; but, if properly
+      made, it is not affected by these.
+
+  (d) Unless reinforced or made very thick, it will not stand as
+      great a crushing load as the best vitrified stoneware pipe;
+      but, as sewers are not intended to be used under very heavy
+      pressure, this is not so very important. It is amply strong to
+      withstand any internal pressure or any external crushing load
+      to which it probably will be submitted.
+
+  (e) Under a considerable head of ground-water, it may permit water
+      to infiltrate through its walls for a considerable time after
+      it is laid, thereby temporarily increasing the flow, which, if
+      the sewage is to be pumped, will increase the cost of pumping.
+      This difficulty can be met by using a carefully selected mix
+      of materials in making the pipe, and by making the joints
+      carefully. Infiltration through concrete diminishes rapidly
+      after the sewer is in use; it occurs in vitrified pipe, also,
+      to some extent.
+
+The house connection drain adopted in Monterrey, with the disconnecting
+trap, is very much like one which the writer has seen introduced with very
+bad result. These are being removed as rapidly as possible by one of his
+clients, a sewerage company, in the Southern States. It has been a
+fruitful cause of stoppages and bad smells; the ordinary method now in
+general use is much better. In the design shown, it would seem that there
+may even be some danger that the ventilation of the sewer by the
+stand-pipes in the streets may force the traps.
+
+One is rather surprised to learn that the main outfall sewer is designed
+with a capacity of 90,000,000 liters per day, the present sewage being
+estimated as not more than 18,000,000 liters, and the far future being
+thought to require only 40,000,000 liters. Why this excessive size?
+Possibly the surplus water which it is to carry is to be discharged into
+the sewers from the water supply system direct, and is intended for
+irrigating the land at the disposal area, when the sewage is insufficient
+for this purpose. The author states that all surface water is strictly
+excluded.
+
+The method of sewage disposal gives rise to several questions. It is
+proposed to use an extensive area for growing crops, which are to be
+irrigated with sewage. The paper states that the underlying strata at
+Monterrey contain numerous caverns, and the first question is: What will
+be the effect on the water supply of other towns lower down the valley?
+The writer recollects a serious outbreak of typhoid fever in Bluefield, W.
+Va., caused by the pollution of the water in similar strata finding its
+way through unknown underground caverns and channels to the city's water
+supply.
+
+The next question is: What crops will be grown? It is a well-known fact
+that vegetables grown by the use of sewage as a fertilizer, are unsafe in
+a raw state for human consumption. This is well-known to European
+travelers in China and Japan, where the use of fecal matter as fertilizer
+renders the various water supplies (where not filtered and disinfected)
+and all green vegetables, unsafe, on account of typhoid germs. Moreover,
+crops not intended for human consumption, which are grown on lands
+irrigated by sewage bearing typhoid germs, etc., are unsafe for men to
+handle; even to store them may cause a dissemination of disease. It is
+evident, therefore, that the whole sewage flow should be in some manner
+disinfected at least, if not filtered, before it is used.
+
+The method of sewage disposal and the use of merely settled septic sewage
+for irrigation seem to be open to objection. The disposal plant is not
+sufficiently effective to meet the present requirements of sanitary
+science; and the sludge-pit will be certain to breed a pest of flies, if
+it is not also an intolerable nuisance on account of foul smells.
+Monterrey would seem to be a proper place for the introduction of the
+Imhoff tank, with percolating filters, and a final settling tank, the
+effluent being disinfected, before entering the latter tank. The flow
+might then be used safely for irrigation purposes for crops not to be
+eaten uncooked by man. The writer does not see how the method provided can
+possibly fulfill the object stated, to distribute on the land an effluent
+which will be "innocuous and clear," or how any consequential degree of
+purification can be obtained in the tanks provided.
+
+While there are described in this paper many things to find fault with,
+there are also many things to commend. The water supply system, with its
+reservoirs, etc., seems to be admirable; and the methods of construction
+by which the expense for forms was reduced is very interesting. The
+parking and ornamentation of the grounds over the reservoir roofs cannot
+fail to benefit the people and popularize the work.
+
+
+RUDOLF MEYER, M. AM. SOC. C. E. (by letter).--The writer, as Engineer for
+the Government (guaranteeing the concessionaires a gross return of 10% per
+annum on the capital invested), and as inspector of the various works has
+had exceptional opportunities to become acquainted, not only with their
+construction, but also with events leading up to the granting of the final
+concession under which they were built and will be extended. In order to
+judge of the extent to which the different engineers, in their turn
+contributed toward the design of these works, the writer has thought it
+desirable to submit a complete statement of all matters relating to the
+inception, investigations, surveys, tests, etc., previous to the adoption
+of the present plans.
+
+Data regarding former investigations, plans, and concessions which have
+since lapsed, have been obtained from the Government archives. These refer
+to periods prior to Mr. Conway's engagement, and anterior to the retaining
+of Mr. Schuyler by the concessionaires, and Mr. Binckley's connection with
+the scheme, and they are presented here as complementary to the
+information in the paper.
+
+Samuel M. Gray, M. Am. Soc. C. E., acting in the interest of some American
+capitalists (who had been induced by Col. J. A. Robertson, of Monterrey,
+to look into the merits of a concession acquired by him, for building
+these works), being guided by the Government's proposition to supply the
+city with water by damming the flood-waters of the Santa Catarina River in
+the narrow gorge through which the stream emerges from the Sierras, some
+eight miles from the city, had several soundings made and reservoir sites
+surveyed in the first two box cañons up the river, and prepared and
+presented to the Government several alternative projects, besides the one
+mentioned by Mr. Schuyler. Several different dam sites were designated by
+Mr. Gray, whose investigations extended over some two years, and were
+finally abandoned after he had designed the general outlay for a complete
+network of water mains and sewers for the city, on account of the
+unwillingness of the Government at that time, about 1897, to grant any
+guaranties as to bonds or income to the concessionaire or his assigns. Mr.
+Gray did not favor the general scheme of storing flood-waters as a water
+supply, but strongly recommended to the attention of the Government the
+greater advantages of deriving the supply from subterranean flow in the
+river, by an infiltration gallery driven into the water-bearing gravels in
+the Santa Catarina Cañon (only a short distance above the place where Mr.
+Binckley afterward established his bore-holes across the river). He
+proposed to take advantage of the steep slope of the river at a turn in
+the cañon, and from the lower end drive a tunnel through a projecting rock
+spur, which tunnel, though starting well above the ordinary reach of
+floods, would terminate in water-bearing gravel, at a sufficient depth
+below the surface of the river-bed to intercept part of the underflow. Mr.
+Gray, through investigations made under his direction, by Nathaniel
+Turner, M. Am. Soc. C. E., had ascertained that there was an abundant
+subterranean flow, and work had actually been started on the proposed
+tunnel.
+
+The results of Mr. Gray's investigations were put at the disposal of
+Messrs. Mackenzie, Mann & Co. by Mr. Robertson, at whose offices Mr.
+Binckley prepared the first plans submitted by him for the approval of the
+Government.
+
+After Mr. Gray's investigations, Messrs. Mackin and Dillon (F. H. Dillon,
+Assoc. M. Am. Soc. C. E.), under contract with the Government, prepared
+the following plans: For a dam in the Santa Catarina Cañon; for a pipe
+line, similar to the one proposed by Mr. Gray, to a reservoir and settling
+basin on the left bank of the river (a short distance above where the
+provisional pumping station was established afterward by Mr. Binckley),
+but on the flat above the bluff skirting the river, practically at the
+same elevation as the present high-pressure reservoirs; for a complete
+network of water mains and sewers in the city, indicating the approximate
+direction in which the sewage would be disposed of, either by turning it
+into the river or by spreading it over suitable lands, the location of
+which was to be determined later; and also a complete set of
+specifications.
+
+On these data bids were invited by publication, and inquiries were
+received from several parties. Finally, Messrs. Stocker and Walker, of
+Scranton, Pa., entered into negotiations with the Government, and the
+present concession was agreed upon and granted.
+
+Messrs. Stocker and Walker engaged the late E. Sherman Gould, M. Am. Soc.
+C. E., to prepare a plan for a storage dam in the Santa Catarina Cañon,
+and submitted plans for water distribution and sewers in the city,
+slightly modifying the original plans of Messrs. Mackin and Dillon.
+
+In the fall of 1905, the concession was acquired by Messrs. Mackenzie,
+Mann & Co., of Toronto, Canada, together with all plans, etc.,
+presented by the original concessionaires. The new concessionaires stated
+that they would examine the whole situation again, for the purpose of
+presenting modified plans for works.
+
+Mr. Schuyler, in the interest of the new owners, had paid one flying visit
+to Monterrey when Mr. Gray's projects were brought to his notice, and the
+writer had an opportunity to show him the tunnel which had been started.
+Mr. Schuyler left for Brazil and did not return until February, 1906, when
+he was accompanied by the Chief Engineer appointed by the concessionaires.
+Messrs. Schuyler and Binckley then prepared plans for the water
+distribution and sewer systems in the city and for a provisional water
+supply to be pumped at San Geronimo, some two miles up the river. The new
+plans for the city work followed closely the general disposition by Mr.
+Gray, the principal difference being that the main reservoirs for the
+permanent water supply were located to the south instead of to the west.
+This change was due to the results of an investigation, made during Mr.
+Schuyler's absence in Brazil, by Mr. F. S. Hyde, late Hydraulic Engineer
+of the Necaxa Water Power plant, who, accompanied by the writer, visited
+the whole water-shed of the Santa Catarina River in October, 1905, in
+search of suitable dam sites and prospects of power development. Mr. Hyde
+extended his studies to the Santiago Cañon, southeast of the city,
+recommending finally that the water be brought from that cañon, and that
+wells be dug in different points of the Santa Catarina River between San
+Geronimo and the entrance of the cañon, and tested by pumping, for the
+purpose of establishing levels and ascertaining the available amount of
+underflow, with a view of determining the location for an infiltration
+gallery high enough up the river to permit of a gravity delivery and under
+good pressure in the city.
+
+In view of Mr. Hyde's report, and as the result of a visit to the Santiago
+Cañon, Mr. Schuyler decided to locate the reservoirs south of the town,
+intending to bring in water from the southeast, from springs in the
+Santiago Cañon, and also by infiltration from Santa Catarina, his and Mr.
+Binckley's scheme of water supply being for the same pressure throughout
+the city.
+
+To supply water during construction, and partly meet the demands of the
+city, Mr. Binckley, on his arrival, decided to establish a provisional
+pumping station at the well in the river nearest to town, started by
+direction of Mr. Hyde at San Geronimo. This well was situated within the
+bed of inundation of high floods, on a low bank, at the foot of a
+conglomerate bluff some 20 ft. high, limiting a flat which was above the
+reach of any flood. It was on the same side of the river as the city, and
+there was plenty of good ground on the flat above for the establishment of
+a reservoir.
+
+A slightly shorter pipe line was secured by crossing the river, building
+the reservoir (a substantial concrete-lined and vaulted-over structure) on
+the opposite bank, laying out the pipe line to follow that bank nearly to
+the city, and finally crossing back again; but the result has been that
+since the flood of August, 1909, in which the river crossings were
+destroyed, the reservoir remains isolated on the other side of the river
+from town, though intended to form part of the permanent works and act as
+a compensating reservoir for equalizing the pressure of the high-pressure
+system. Fortunately, the pumping station, the larger pumps, and the
+boilers, had been moved up the bank (after a rapid rise in the river on
+August 10th, 1909) to the new wells established by Mr. Conway on the line
+of the proposed prolongation of the infiltration gallery. The reservoir,
+however, is left to stand alone on the other side of the river, and its
+usefulness will not be restored until a new line is laid across the river,
+re-establishing its connection with the new pump line and the new and
+permanent pipe line to be laid along the north bank from the pumping
+station to the city. This will free Monterrey from the constant menace of
+a water famine. At present its two main water supplies may be cut off by
+unexpected floods like those of 1909 and 1910, as both supplies are
+carried across the river, and though only the cast-iron pipe connecting
+with the water supply from Estanzuela was carried away by the flood, the
+concrete conduit of the San Geronimo low-pressure supply was seriously
+threatened. Such risks are too great to be carried for any length of time;
+besides, a succession of dry years would cause such a reduction in the
+Estanzuela supply as to require an additional reserve in the way of
+pumping stations drawing on the under-flow of the river, such as already
+exists in San Geronimo.
+
+Afterward, Messrs. Schuyler and Binckley submitted preliminary plans and
+profiles for the projected concrete gravity conduit from Estanzuela to the
+reservoir south of the city, and Mr. Binckley submitted excavation plans
+for two reservoirs, only one of which was built, and from designs by Mr.
+Conway.
+
+Stephen E. Kieffer, M. Am. Soc. C. E., was intrusted by Mr. Binckley with
+the revision of the plans of the water distribution and sewers. The
+southern half was approved by the Government and executed according to his
+plans; the northern part was afterward revised by Mr. Conway and has been
+partly built.
+
+The final maturing of the project of an infiltration gallery in San
+Geronimo as a low-pressure gravity supply, the division of the city into
+high- and low-pressure districts corresponding to the two supplies, with
+one reservoir, instead of two to the south of the city, and the other to
+the west at the Obispado, the entire details of both these gravity
+schemes, and of the whole sewage disposal scheme, as well as the
+modification introduced into the city work for the northern half, are
+unquestionably due to Mr. Conway, independently of the general views which
+may have been held on those points by other engineers.
+
+In March, 1910, Mr. Conway left Monterrey, all the principal works being
+finished. Since that time Vicente Saucedo, Assoc. M. Am. Soc. C. E., has
+put in many additional water mains and sewers in the northern part of the
+city, and is finishing the _force majeure_ work caused by the destruction
+wrought in the districts along the river banks by the extraordinary
+floods.
+
+The writer, having had an opportunity to watch the earnest efforts of the
+several engineers connected with these works, in the course of their
+design and construction, resulting without doubt in being the first of
+their kind built in Mexico, has been induced to contribute this discussion
+in order to bring out clearly the share of each.
+
+Mr. Pitkethly's apprehensions as to the adequacy of the system of
+ventilation adopted have not been realized, in part perhaps because the
+houses, though generally of only one story, have such high ceilings that
+the tops of their vent pipes are generally higher than the ventilating
+columns at the heads of the branch sewers.
+
+
+GEORGE ROBERT GRAHAM CONWAY, M. AM. SOC. C. E. (by letter).--The writer
+regrets that some features of the works described in this paper have
+failed to call forth the many useful criticisms which he expected, and his
+remarks, therefore, are limited to the few points which have been raised.
+He is particularly indebted to Messrs. Schuyler, Meyer, and Saucedo for
+adding supplementary information of value to the paper, but regrets that
+he cannot support Mr. Binckley in his claim that "the entire general
+design of the system, as well as the extensive hydrological studies and
+final selection of the sources of water supply, was completed in 1906,"
+etc. On May 1st, 1907, when the writer assumed responsibility as Chief
+Engineer, he was unfortunately confronted with the fact that very little
+data and only a few preliminary and incomplete plans were available. His
+first duty was to report upon the final sources of supply, and the
+recommendations made in his report (dated July 12th), received Mr. (now
+Sir William) Mackenzie's approval during the same month. The final plans,
+upon which the approval of the State Government was definitely obtained,
+were prepared by the writer during the summer of 1907, were submitted to
+the Governor of the State, Gen. Bernard Reyes, on October 19th, and
+received his approval on December 12th, 1907. No works, with a long
+preliminary history, such as those at Monterrey, can rightly be said to be
+due to any one individual; many engineers contributed to the final result,
+and the writer willingly acknowledges his indebtedness to the able men,
+who, for ten years prior to the construction of the works, investigated
+the particular problems which were met--problems which were not only of an
+engineering and physical nature, but racial and financial. The
+responsibility of constructing the works in their present form, and
+leaving them practically complete, did, however, fall on the writer's
+shoulders.
+
+Messrs. Pitkethly and Hammond have criticized the basis of the
+calculations upon which the sewer system was laid down. In considering
+this problem, it is necessary to remember that, in designing this system,
+there was practically no information upon which to base the calculations;
+and the writer believed that the wisest course was to anticipate a liberal
+growth, and provide a large margin of safety. In designing a sewer system
+in older and well-established communities, the engineer is generally able
+to compile considerable information regarding the probable sewage flow for
+which it is necessary to provide. In Monterrey this quantity was
+absolutely unknown. The writer's practice in other places has been to
+assume that about 8% of the total daily discharge of sewage will flow off
+in one hour; and, from many curves which he has plotted regarding sewage
+flow in British towns, this rate appears to him to be approximately
+correct. In Monterrey, however, the old Mexican traditions are rapidly
+changing, and the city is now becoming one of the most Americanized in
+Mexico; the old one-story houses will give way in time to buildings of
+several stories--a change, already noticeable, which has occurred during
+the past few years, particularly in the business portion of the city.
+Taking these facts into consideration, it is believed that it would be,
+not only bad engineering, but bad business, for a company whose concession
+lasts 99 years, to provide sewers as small as 6 in., as Mr. Hammond would
+recommend, and then be called upon, under the terms of the concession, to
+relay larger sewers at a future date, thus incurring further capital
+expenditure upon which no Government guaranty would apply, and no further
+revenue be obtained. In matters of this kind, not only the engineering,
+but the commercial, aspect of the question must be kept in view, and this
+point, the writer must frankly admit, he has always seriously considered.
+
+The writer's experience with reference to the method of ventilating sewers
+by tall columns extends over many years, and he still maintains that no
+other system gives such satisfactory results. In this view he finds
+considerable support in a recent paper on "Salisbury Drainage," by Mr. W.
+J. E. Binnie,[11] written since the system at Monterrey was installed, in
+which the result of a series of experiments carried on during 1906-07 are
+given. At Salisbury, England, 68 ventilators, 6 in. in internal diameter,
+30 ft. high, were connected to the main sewer by 6-in. stoneware pipes.
+They were placed about 540 ft. apart, and, from careful anemometer
+readings, the following conclusions were reached:
+
+[11] _Minutes of Proceedings_, Inst. C. E., Vol. CLXXXI, p. 317.
+
+  "(1) That four ventilators all lying in the lower portion of the
+       town acted sometimes as air-inlets and sometimes as
+       air-outlets, and that the other sixty-four acted as
+       air-outlets.
+
+  "(2) That the average velocity of the air escaping up these
+       columns was 3.2 feet per second, representing the circulation
+       of 3,600,000 cubic feet of air per diem, or sufficient to
+       change the air in the sewers every 10 minutes.
+
+  "(3) That the average velocity of the current of air in the
+       ventilating-column increases with the size of the sewer to
+       which it is connected, averaging 2.4 feet per second with the
+       7-inch sewer, 3.6 feet per second with the 9-inch sewer, 3.7
+       feet per second with the 12-inch sewer, and 4.1 feet per
+       second with the 15-inch sewer in these experiments.
+
+  "(4) That the draught in the column is very largely dependent on
+       the wind, being at its minimum on a still day, and could
+       therefore be readily increased by the use of a suitable cowl.
+
+  "(5) That the draught is very little affected by the
+       sewer-gradients. It was expected that, in ventilating-columns
+       placed in connection with the upper end of a sewer laid at a
+       steep gradient, a strong draught would have been obtained. No
+       direct connection, however, was traceable."
+
+As the result of these experiments, Mr. Binnie rightly came to the
+conclusion that this system of ventilation was efficient.
+
+Mr. Hammond anticipates that the house connection trap system at Monterrey
+will lead to bad results, but the writer has seen the system at work in
+many widely different cities with excellent results. He believes that it
+is in accord with the best practice of the most eminent sanitarians during
+the last 20 years, and has no apology to make for introducing that system
+in Monterrey.
+
+Regarding Mr. Hammond's summary of the advantages of concrete pipes for
+sewer construction, the writer is in entire agreement, and would willingly
+have introduced them throughout the whole of the Monterrey system, but for
+the fact that it was an exceedingly difficult matter to obtain suitable
+sand for their manufacture during the early days of construction, and
+considerable delays would have arisen if a complete network of such pipes
+had been used. His later experience at Monterrey, when the sand difficulty
+had been solved, clearly showed that concrete pipe could be laid down at
+much less expense than fire clay.
+
+Both Mr. Pitkethly and Mr. Hammond refer to the system of liquefying tanks
+used at Monterrey preparatory to turning the sewage on the irrigation
+lands, and both express doubts as to their efficiency. The writer is now
+separated from his library and notes by many thousands of miles, and
+cannot quote "chapter and verse" as accurately as he would like, in order
+to support his views that the system adopted was adequate for dealing
+with a system such as that at Monterrey. It must be pointed out that not
+only was it intended to prevent the sewage from becoming a nuisance, but
+that the sewage flow plus a large quantity of surplus water was intended
+to be used profitably for irrigation purposes. With that object, the
+Company--or rather its allied Company, the Monterrey Railway, Light, and
+Power Company--obtained the control of 2,246 acres of the very finest
+arable land, with almost perfect natural drainage conditions, so that this
+land could be utilized to create a profitable revenue from the use of the
+sewage. The outfall sewer was accordingly designed to carry sufficient
+water and sewage to irrigate about 2,500 acres of land, which area could
+be considerably extended if necessary at any future time.
+
+Most authorities now agree that before turning sewage upon land, a
+preliminary treatment is required to remove as much as possible of the
+suspended matter, and then reduce the latter by subsidence in liquefying
+or septic tanks, so that the quantity remaining in the effluent is so
+small and finely divided that it may be readily decomposed and oxidized by
+bacterial action without risk of clogging the surface or interstices of
+the land upon which it may discharge.[12]
+
+[12] See Raikes, "Sewage Disposal Works," pages 97-98.
+
+Mr. Pitkethly quotes Messrs. Watson and O'Shaughnessy as saying, in their
+evidence before the Royal Commission on Sewage Disposal, that not more
+than 10% of the solids are digested in septic tanks, but it must be
+remembered that in many other places evidence was given before the same
+Commission showing that from 25 to 30% was actually obtained.
+
+Mr. J. D. Watson, in his paper, "Birmingham Sewage-Disposal Works,"[13]
+read in March, 1910, points out that:
+
+[13] _Minutes of Proceedings_, Inst. C. E., Vol. CLXXXI, p. 259.
+
+    "The much-maligned sewage-farm still may be allowed (where the
+    conditions are favourable) to rank as one of the best methods
+    of sewage-disposal. Diverse opinions may be held as to what are
+    favourable conditions, particularly as conditions are sure to
+    vary widely with locality; but it may be assumed that where
+    there is 1 acre of suitable land per 100 persons, as in Berlin
+    and several other important cities, the efficiently-worked
+    sewage-farm, when judged solely by the standard of the effluent
+    produced, is still in the front rank. Effluents from such a
+    farm are remarkable for their paucity of micro-organisms, their
+    low albuminoid ammonia, and their unvarying character."
+
+Assuming that not more than 2,000 acres of the irrigated land at Monterrey
+were available for sewage purposes, this area would represent the sewage
+treatment of the present population of not more than 45 persons per acre,
+and on the basis of the design, that is, for a population of 200,000
+persons, this represents not more than 100 persons per acre. In many
+sewage farms on the continent of Europe, the number treated per acre
+varies between 80 and 200 persons; for example, at Breslau it is 187, at
+Berlin 105, at Brunswick 88, and at Steglitz 185.
+
+Regarding the crops to be grown on the land, very satisfactory results
+were obtained from growing Indian corn, and two excellent crops per annum
+were taken from an area of 500 acres during the period in which the writer
+was responsible for the works. It was also his intention to grow alfalfa,
+and turn a part of the land into a pecan grove, and, although he does not
+share the apprehensions of danger of either Mr. Pitkethly or Mr. Hammond
+as to growing root crops, he believes the growth of alfalfa, Indian corn,
+oats, barley, and pecan and fruit trees is eminently suitable for the
+land, which is a deep rich loam, from 4 to 8 ft. deep, overlying the
+"sillar" formation referred to in the paper. The writer has seen many
+sewage farms during the last 18 years, upon which root crops of excellent
+quality have been grown, and not the least suspicion has ever been raised
+regarding their use.
+
+In reference to the adoption of the monolithic form for constructing the
+South Reservoir, the writer is so convinced as to its economy that had he
+to build this reservoir again, he would adopt the same method. Mr.
+Binckley, in drawing attention to the method of construction, has
+overlooked the fact that the cost of forms for a reservoir 30 ft. deep was
+a very serious item, and warranted the adoption of this new method, not
+only on account of economy but because of rapidity of construction; while,
+in the case of the Obispado Reservoir, which is very much shallower,
+simpler forms could be and were adopted.
+
+Mr. Saucedo's remarks regarding the repetition of the extraordinary floods
+of August, 1909, in September, 1910, are particularly interesting, and
+show how abnormal conditions are in so dry a section of Mexico as the
+State of Nuevo León. These two floods, the writer believes, are among the
+most instructive in North America, particularly when one remembers that
+prior to 1909 the average rainfall during a period of 15 years, was less
+than 22 in. per annum.
+
+             TABLE 18.--COMPARISON OF VOLUME OF FLOODS, ETC.
+
+  +------------------------------+-----------+----------+-------+--------+
+  |                              |           | Maximum  |Cu. ft.| Annual |
+  |                              | Drainage  | recorded | /sec. | amount |
+  | River.                       | area, in  | flow, in | per   |   of   |
+  |                              | square    |  cu. ft. |square |  rain- |
+  |                              | miles.    | per sec. | mile. |  fall. |
+  +------------------------------+-----------+----------+-------+--------+
+  | Santa Catarina, Monterrey,   |           |          |       |        |
+  |   August 27th, 1907          |      544  | 235,000  | 432   |  22    |
+  | Estanzuela, near Monterrey,  |           |          |       |        |
+  |   August 28th, 1909          |       3.5 |   2,900  | 825   |  25    |
+  | Tansa, India                 |      52.5 |  35,000  | 666.7 | 101    |
+  | Krishna, India               |     345   | 118,000  | 342.6 | 258    |
+  | Coquitlam River, Vancouver   |     100   |  12,000  | 120   |147-189 |
+  | Sweetwater, Cal.             |     186   |  18,150  |  99   |  ...   |
+  | Delaware, Lambertville, N. J.|   6,820   | 250,000  |  36.5 |  45    |
+  | Colorado, Austin, Tex.       |  37,000   | 123,000  |   3.3 |  24.5  |
+  | Ohio, Cairo, Ill.            | 214,000   | 700,000  |   3.3 |  54.9  |
+  +------------------------------+-----------+----------+-------+--------+
+
+Table 18, compiled by the writer, shows how very extreme the floods of
+1909 were compared with those on other rivers, while those of 1910,
+referred to by Mr. Saucedo, although not so great, would appear to have
+reached a rate of flow of about 300 cu. ft. per sec. per sq. mile of the
+drainage area.
+
+The writer agrees with Mr. Saucedo that in the semi-arid regions of Mexico
+and the Southern States, and also in India, the possibility of these
+abnormal floods is an important consideration in the design of hydraulic
+works.
+
+       *       *       *       *       *
+
+                       Changes To This Document
+
+Transcriber's Note: The table of contents has been added. Blank pages
+have been deleted. Illustrations may have been moved. Discovered
+publisher's punctuation errors have been corrected. Some wide tables
+have been re-formatted to narrower equivalents with some words replaced
+with commonly known abbreviations and possibly a key. Some ditto marks
+have been replaced with the words represented. In addition, the
+following changes or corrections were made:
+
+ p. 501: but the tampers had had[del 2nd had] previous experience
+ p. 508: shown on Plates VI to IX[VI, VII, VIII, IX[to accomodate links]]
+ p. 516: at this place there is a considererable[considerable] area
+ p. 538: based on the following rates and and[del 2nd and] percentages
+ p. 579: by crossing the river, build-the[building the] reservoir
+ p. 550: [For Table 14: added "Total materials cost"]
+ p. 566: respectively (Fig. 5)[(Fig. 4)], together with lack of
+ p. 584: [Table 17 renamed to Table 18 to avoid duplication.]
+ p. 584: Table 17[18], compiled by the writer, shows how very extreme
+
+       *       *       *       *       *
+
+
+
+
+
+End of the Project Gutenberg EBook of ASCE 1193: The Water-Works and
+Sewerage of Monterrey, N. L., Mexico, by George Robert Graham Conway
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+      The Project Gutenberg eBook of ASCE 1193 The Water-Works and Sewerage of Monterrey, N. L., Mexico, by George Robert Graham Conway.
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+<pre>
+
+The Project Gutenberg EBook of ASCE 1193: The Water-Works and Sewerage of
+Monterrey, N. L., Mexico, by George Robert Graham Conway
+
+This eBook is for the use of anyone anywhere at no cost and with
+almost no restrictions whatsoever.  You may copy it, give it away or
+re-use it under the terms of the Project Gutenberg License included
+with this eBook or online at www.gutenberg.org
+
+
+Title: ASCE 1193: The Water-Works and Sewerage of Monterrey, N. L., Mexico
+       The 4th article from the June, 1911, Volume LXXII,
+              Transactions of the American Society of Civil Engineers.
+              Paper No. 1193, Feb. 1, 1911.
+
+Author: George Robert Graham Conway
+
+Release Date: December 31, 2011 [EBook #38455]
+
+Language: English
+
+Character set encoding: ISO-8859-1
+
+*** START OF THIS PROJECT GUTENBERG EBOOK ASCE 1193: THE WATER-WORKS ***
+
+
+
+
+Produced by Juliet Sutherland, Henry Gardiner and the
+Online Distributed Proofreading Team at http://www.pgdp.net
+
+
+
+
+
+
+</pre>
+
+
+<hr class="RuleChapter" />
+
+<div class="center" style="width: 25em; margin: auto; border: solid 1px; padding: 1em;">
+Transcriber's Note: The original publication has been replicated faithfully except as listed
+<a href="#Changes" name="Start" id="Start">here</a>.
+<br />
+The text conforms to changes in window size.
+</div>
+
+<hr class="RuleChapter" />
+
+<h2>TABLE OF CONTENTS</h2>
+
+<table summary="Table of Contents">
+  <tr>
+    <td class="tocdsc">
+    <a href="#Introductory">INTRODUCTORY.</a>
+    </td>
+    <td class="tocpge">
+      <a href="#Page_475">475</a>
+    </td>
+  </tr>
+  <tr>
+    <td class="tocdsc">
+      <a href="#The_Concession">THE CONCESSION.</a>
+    </td>
+    <td class="tocpge">
+      <a href="#Page_476">476</a>
+    </td>
+  </tr>
+  <tr>
+    <td class="tocdsc">
+    <a href="#Geology_and_Topography">GEOLOGY AND TOPOGRAPHY.</a>
+    </td>
+    <td class="tocpge">
+      <a href="#Page_476">476</a>
+    </td>
+  </tr>
+  <tr>
+    <td class="tocdsc">
+      <a href="#Population_Area_and_Mortality">POPULATION, AREA, AND MORTALITY.</a>
+    </td>
+    <td class="tocpge">
+      <a href="#Page_479">479</a>
+    </td>
+  </tr>
+  <tr>
+    <td class="tocdsc">
+      <a href="#Rainfall_and_Temperature">RAINFALL AND TEMPERATURE.</a>
+    </td>
+    <td class="tocpge">
+      <a href="#Page_480">480</a>
+    </td>
+  </tr>
+  <tr>
+    <td class="tocdsc">
+      <a href="#Available_Sources_of_Supply">AVAILABLE SOURCES OF SUPPLY.</a>
+    </td>
+    <td class="tocpge">
+      <a href="#Page_484">484</a>
+    </td>
+  </tr>
+  <tr>
+    <td class="tocdsc">
+      <a href="#Materials_for_Concrete">MATERIALS FOR CONCRETE.</a>
+    </td>
+    <td class="tocpge">
+      <a href="#Page_491">491</a>
+    </td>
+  </tr>
+  <tr>
+    <td class="tocdsc">
+      <a href="#Estanzuela_Supply">ESTANZUELA SUPPLY.</a>
+    </td>
+    <td class="tocpge">
+      <a href="#Page_494">494</a>
+    </td>
+  </tr>
+  <tr>
+    <td class="tocdsc">
+      <a href="#South_Distributing_Reservoir">SOUTH DISTRIBUTING RESERVOIR.</a>
+    </td>
+    <td class="tocpge">
+      <a href="#Page_506">506</a>
+    </td>
+  </tr>
+  <tr>
+    <td class="tocdsc">
+      <a href="#San_Geronimo_Gravity_Supply">SAN GERONIMO GRAVITY SUPPLY.</a>
+    </td>
+    <td class="tocpge">
+      <a href="#Page_514">514</a>
+    </td>
+  </tr>
+  <tr>
+    <td class="tocdsc">
+      <a href="#Distributing_Reservoir_at_Obispado">DISTRIBUTING RESERVOIR AT OBISPADO.</a>
+    </td>
+    <td class="tocpge">
+      <a href="#Page_525">525</a>
+    </td>
+  </tr>
+  <tr>
+    <td class="tocdsc">
+      <a href="#Comparison_of_South_and_Obispado_Reservoirs">COMPARISON OF SOUTH AND OBISPADO RESERVOIRS.</a>
+    </td>
+    <td class="tocpge">
+      <a href="#Page_530">530</a>
+    </td>
+  </tr>
+  <tr>
+    <td class="tocdsc">
+      <a href="#Analyses_of_Estanzuela_and_San_Geronimo_Waters">ANALYSES OF ESTANZUELA AND SAN GERONIMO WATERS.</a>
+    </td>
+    <td class="tocpge">
+      <a href="#Page_532">532</a>
+    </td>
+  </tr>
+  <tr>
+    <td class="tocdsc">
+      <a href="#City_Water_Distribution_System">CITY WATER DISTRIBUTION SYSTEM.</a>
+    </td>
+    <td class="tocpge">
+      <a href="#Page_532">532</a>
+    </td>
+  </tr>
+  <tr>
+    <td class="tocdsc">
+      <a href="#Main_Sewerage_System">MAIN SEWERAGE SYSTEM.</a>
+    </td>
+    <td class="tocpge">
+      <a href="#Page_539">539</a>
+    </td>
+  </tr>
+  <tr>
+    <td class="tocdsc">
+      <a href="#Main_Outfall_Sewer">MAIN OUTFALL SEWER.</a>
+    </td>
+    <td class="tocpge">
+      <a href="#Page_542">542</a>
+    </td>
+  </tr>
+  <tr>
+    <td class="tocdsc">
+      <a href="#Sewage_Disposal_Works_and_Irrigation_Lands">SEWAGE DISPOSAL WORKS AND IRRIGATION LANDS.</a>
+    </td>
+    <td class="tocpge">
+      <a href="#Page_545">545</a>
+    </td>
+  </tr>
+  <tr>
+    <td class="tocdsc">
+      <a href="#Quality_of_and_Rates_for_Labor">QUALITY OF AND RATES FOR LABOR.</a>
+    </td>
+    <td class="tocpge">
+      <a href="#Page_552">552</a>
+    </td>
+  </tr>
+  <tr>
+    <td class="tocdsc">
+      <a href="#Cost_of_Works">COST OF WORKS.</a>
+    </td>
+    <td class="tocpge">
+      <a href="#Page_552">552</a>
+    </td>
+  </tr>
+  <tr>
+    <td class="tocdsc">
+      <a href="#Tariffs_and_Sanitary_Regulations">TARIFFS AND SANITARY REGULATIONS.</a>
+    </td>
+    <td class="tocpge">
+      <a href="#Page_553">553</a>
+    </td>
+  </tr>
+  <tr>
+    <td class="tocdsc">
+      <a href="#Engineers_etc">ENGINEERS, ETC.</a>
+    </td>
+    <td class="tocpge">
+      <a href="#Page_556">556</a>
+    </td>
+  </tr>
+  <tr>
+    <td class="tocdsc">
+      <a href="#DISCUSSION">DISCUSSION.</a>
+    </td>
+    <td class="tocpge">
+      <a href="#Page_557">557</a>
+    </td>
+  </tr>
+  <tr>
+    <td class="tocdsc">
+      <a href="#James_D_Schuyler">JAMES D. SCHUYLER.</a>
+    </td>
+    <td class="tocpge">
+      <a href="#Page_557">557</a>
+    </td>
+  </tr>
+  <tr>
+    <td class="tocdsc">
+      <a href="#David_T_Pitkethly">DAVID T. PITKETHLY.</a>
+    </td>
+    <td class="tocpge">
+      <a href="#Page_559">559</a>
+    </td>
+  </tr>
+  <tr>
+    <td class="tocdsc">
+      <a href="#V_Saucedo">V. SAUCEDO.</a>
+    </td>
+    <td class="tocpge">
+      <a href="#Page_563">563</a>
+    </td>
+  </tr>
+  <tr>
+    <td class="tocdsc">
+      <a href="#George_T_Hammond">GEORGE T. HAMMOND.</a>
+    </td>
+    <td class="tocpge">
+      <a href="#Page_567">567</a>
+    </td>
+  </tr>
+  <tr>
+    <td class="tocdsc">
+      <a href="#Rudolf_Meyer">RUDOLF MEYER.</a>
+    </td>
+    <td class="tocpge">
+      <a href="#Page_576">576</a>
+    </td>
+  </tr>
+  <tr>
+    <td class="tocdsc">
+      <a href="#George_Robert_Graham_Conway">GEORGE ROBERT GRAHAM CONWAY.</a>
+    </td>
+    <td class="tocpge">
+      <a href="#Page_580">580</a>
+    </td>
+  </tr>
+</table>
+
+<hr class="RuleChapter" />
+<!--475.png--><p><span class="pagenum"><a name="Page_475" id="Page_475"></a></span></p>
+
+
+
+
+<div class="c2">AMERICAN SOCIETY OF CIVIL ENGINEERS</div>
+
+<div class="c4">INSTITUTED 1852</div>
+
+<div class="c2">TRANSACTIONS</div>
+
+<div class="c3">Paper No. 1193</div>
+
+<h1>THE WATER-WORKS AND SEWERAGE OF<br />
+MONTERREY, N. L., MEXICO.<a name="FNanchor_1_1" id="FNanchor_1_1"></a>
+<a href="#Footnote_1_1" class="fnanchor">[1]</a></h1>
+
+<div class="c4"><span class="smcap">By George Robert Graham Conway, M. Am. Soc. C. E.</span></div>
+
+<hr class="RuleHeaderDivider" />
+
+<div class="c4"><span class="smcap">With Discussion by Messrs. James D. Schuyler, David T. Pitkethly,
+George S. Binckley, Vicente Saucedo, George T. Hammond,
+Rudolf Meyer, and George Robert Graham Conway.</span></div>
+
+<hr class="RuleHeaderDivider" />
+
+<h1><a name="Introductory" id="Introductory"></a><span class="smcap">Introductory.</span></h1>
+
+<div class="footnote"><a name="Footnote_1_1" id="Footnote_1_1"></a><a href="#FNanchor_1_1"><span class="label">[1]</span></a> Presented at the meeting of February 1st, 1911.</div>
+
+<p>Monterrey, the Capital of the State of Nuevo León, Mexico, is built on
+the site of the old village of Santa Lucía de León, which was
+established in 1583 by the Governor of the Kingdom of León, Don Luis
+Carabajal. Four years later Carabajal was imprisoned by the Inquisition,
+and the village of Santa Lucía was abandoned by its few inhabitants.</p>
+
+<p>In 1596, Captain Diego Montemayor, a resident of Saltillo, in the
+adjoining State, wishing to render a service to his king, Philip II of
+Spain, assembled his friends, and on September 20th of that year,
+proceeded to establish a town on the site of the old village on the
+northern side of the principal spring at the place. The town was named
+"Nuestra Señora de Monterrey" (Our Lady of Monterrey), after the Count
+of Monterrey (Ojos de Santa Lucía y Valle de Extremadura), the ruling
+Governor of New Spain, as Mexico was then called.</p>
+<!--476.png--><p><span class="pagenum"><a name="Page_476" id="Page_476">476</a></span></p>
+<p>Monterrey is approximately in the center of the State of Nuevo León, 1°
+12´ west of Mexico City, and in latitude 26° 40´ N. It is a distributing
+railway center on the main line of the National Railroad, 270 km. from
+the Rio Grande at Laredo, 1,022 km. from Mexico, and 520 km. from
+Tampico by the Mexican Central Railway. It is the center of many large
+industries, and is the second largest manufacturing city in the
+Republic.</p>
+
+
+<h2><span class="smcap"><a name="The_Concession" id="The_Concession"></a>The Concession.</span></h2>
+
+<p>The works described in this paper were carried out under a guaranteed
+concession granted by His Excellency, General Bernardo Reyes, Governor
+of the State of Nuevo León, to Messrs. James D. Stocker and William
+Walker, of Scranton, Pa. The concession is dated October 19th, 1904, and
+is for 99 years from that date; the works for a complete water and
+drainage system were to be finished in 3 years from the time of their
+commencement. Before the works were designed and begun, the concession
+was acquired by Mr. William Mackenzie, of the firm of Mackenzie, Mann
+and Company, Limited, of Toronto, Ont., Canada, who, on May 4th, 1906,
+organized the Monterrey Water-Works and Sewerage Company, Limited
+(Compañía de Servicio de Agua y Drenaje de Monterrey, S. A.), under the
+laws of the Dominion of Canada, of which company he is President. Mr.
+Mackenzie is also President of the Monterrey Railway, Light, and Power
+Company, Limited, which was constructing the street railways of
+Monterrey concurrently with the water-works. Under the provisions of the
+concession, the Government appointed a Financial Interventor, who had
+authority to examine and check the company's expenditures, and also a
+Technical Inspector to examine and report on the construction. The
+duties of these officials also apply to the operation of the system when
+the construction is finished. The Government has the right, after the
+system has been operated 40 years, to purchase the entire property,
+subject to 6 months' notice, for a sum equal to 16<sup>2</sup>&frasl;<sub>3</sub> times the average
+annual net proceeds during the 3 preceding years. This right may be
+exercised at the end of 40 years, or at the end of any 10-year period
+thereafter, up to 99 years from the commencement of operations.</p>
+
+
+<h2><span class="smcap"><a name="Geology_and_Topography" id="Geology_and_Topography"></a>Geology and Topography.</span></h2>
+
+<p>Monterrey lies in a plain at the foot of the Eastern Sierra Madre
+Mountains which constitute the eastern margin of the Mexican Cordilleran
+<!--477.png--><span class="pagenum">477</span>Plateau,
+and is surrounded by the magnificent mountains of that group,
+among the most notable of which are the beautiful Mitra and Silla
+Mountains. In the neighborhood of Monterrey these mountains attain
+heights of from 2,000 to 2,400 m., and are noted for their broken and
+jagged sky-lines. The leading geological characteristics of the district
+are the uplifted limestones of the older cretaceous age which form the
+main mass of the mountains.</p>
+
+<p>Primarily, the mountains are compressional folds which, in the Sierra
+Madre, near Monterrey, are close and vertically compressed.<a name="FNanchor_2_2" id="FNanchor_2_2"></a><a href="#Footnote_2_2" class="fnanchor">[2]</a> The
+drainage areas of the Santa Catarina River, which flows through
+Monterrey, and of the Estanzuela and Silla Rivers, its tributaries, are
+of limestone and shale; originally the shales were above the limestone,
+but the convulsion which formed the Sierra Madre as an anticlinal fold,
+left the originally horizontal strata standing nearly upright, and
+subsequent erosion in the upper part of the anticline has exposed nearly
+vertical strata in many places. The limestone being hard and resisting
+erosion, there is generally, along the line of contact, an abrupt drop
+vertically on the face of the limestone to the shale below. In many
+places this abrupt drop is broken by a limestone talus, but the line of
+contact can generally be traced. Mining operations in these mountains
+have revealed the presence of large caves at a considerable elevation,
+many of which contain large reservoirs of water, delivered to them
+through numerous faults. The river valleys are formed of masses of
+limestone conglomerate and coarse gravels, re-cemented in many cases by
+the lime deposits of the flowing waters. One of the chief
+characteristics of the subsoil of Monterrey itself is a local rock
+called "sillar," which is a superficial deposit of carbonate of lime
+from the evaporated waters. In some places the "sillar" is largely mixed
+with a conglomerate called "tepetate," or "impure sillar."</p>
+
+<div class="footnote"><a name="Footnote_2_2" id="Footnote_2_2"></a><a href="#FNanchor_2_2"><span class="label">[2]</span></a> <i>Transactions</i>, Am. Inst. Min. Engrs., Vol. XXXII (1902),
+pp. 163-178.</div>
+
+<div class="figright" style="width: 300px;"><a name="p02"></a>
+<img src="images/p02t.jpg" width="300" height="238" alt="Plate II." title="" />
+<span class="caption"><span class="smcap">Plate II.&mdash;General Plan Of The Water Supply And Drainage Works For
+Monterrey, N. L., Mexico.</span></span><br />
+<a href="images/p02.png" target="_blank">Larger.</a>
+</div>
+
+<p>Topographically, the region around Monterrey is distinguished by the
+drainage area of the River Santa Catarina, which rises in the Sierra
+Madre near the Laguna de Sanchez, at an elevation of 1,850 m., as shown
+on <a href="#p02">Plate II</a>. From this Laguna it follows a tortuous
+course between precipitous mountains through the Boca of Santa Catarina
+to Monterrey, for a distance of 90 km., eventually finding
+<!--478.png--><span class="pagenum">478</span>its way to
+the San Juan River, a tributary of the Rio Grande. Throughout its course
+it disappears, flows underground, and again appears; and, except in
+flood time, it has a subsurface flow for a distance of 16 km. above the
+city. In the Cañon of Santa Catarina it appears at the surface, having a
+normal flow of about 1,415 liters (50 cu. ft.) per sec., and its waters
+at that point are divided into two parts and carried into irrigation
+canals. The drainage area of the river above Monterrey is 1,410 sq. km.,
+and its bed at Monterrey is between 518 and 545 m. above sea level.</p>
+
+<p>Southward from Monterrey the country rises along the valley of the Silla
+for a distance of 19 km., where the Silla is separated from the San Juan
+by a low divide, the former flowing northward to Monterrey and the
+latter southeastward toward Allende. The Silla Valley is bounded on the
+east and west by the steep ranges of the Silla and Sierra Madre
+Mountains. The floor of this valley is gently rolling, but is cut by
+many arroyos which carry little or no water during the greater part of
+the year. The chief feeder of the Silla River is the Estanzuela, a
+stream which derives its waters from several springs coming to the
+surface near the line of contact between the limestone and the shale, at
+elevations of about 800 and 900 m.<a name="FNanchor_3_3" id="FNanchor_3_3"></a><a href="#Footnote_3_3" class="fnanchor">[3]</a> above datum. The water-shed of
+this stream is rich with abundant vegetation due to the precipitation
+being greater than on the Santa Catarina water-shed. To the south of the
+divide the country is well wooded, and El Porvenir, 35 km. from
+Monterrey, is the garden spot of the State of Nuevo León. Here the
+rainfall is much greater than at any other point near Monterrey, and
+there are many streams which are used for irrigation purposes. Monterrey
+is built on a plain, chiefly on the north side of the Santa Catarina
+River. This plain has a general fall toward the northeast, and beyond
+the city it slopes gently northward for several miles toward the Topo
+Grande River, and then southeastward to join the great coastal plain of
+the Gulf of Mexico. The general elevation of the city lies between the
+519- and 550-m. contours. The Plaza Zaragoza, in the center of the city,
+is 533.90 m. above sea level; the elevation of the highest part of the
+city, at the western boundary, is 550.05 m., and of the lowest part, at
+the northeastern boundary, 518.0 m. above sea level.</p>
+
+<div class="footnote"><a name="Footnote_3_3" id="Footnote_3_3"></a><a href="#FNanchor_3_3"><span class="label">[3]</span></a>
+Throughout this paper datum refers to the height in meters
+above the mean sea level of the Gulf of Mexico at the Port of Tampico.</div>
+<!--479.png-->
+<div class="figcenter" style="width: 600px;">
+<img src="images/i01.jpg" width="600" height="399" alt="Fig. 1." title="" />
+<span class="caption"><span class="smcap">Plate III, Fig. 1.&mdash;General View of Line, Estanzuela
+Aqueduct.</span></span>
+</div>
+
+<!--481.png--><p><span class="pagenum"><a name="Page_479" id="Page_479">479</a></span></p>
+
+
+<h2><span class="smcap"><a name="Population_Area_and_Mortality" id="Population_Area_and_Mortality"></a>Population, Area, and Mortality.</span></h2>
+
+<p>The population of Monterrey has increased as follows:</p>
+
+<div class="center">
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td></td><td>Census</td><td>of</td><td>1851</td><td>14,621</td></tr>
+<tr><td></td><td>"</td><td>"</td><td>1861</td><td>26,000</td></tr>
+<tr><td></td><td>"</td><td>"</td><td>1871</td><td>33,811</td></tr>
+<tr><td></td><td>"</td><td>"</td><td>1881</td><td>39,456</td></tr>
+<tr><td></td><td>"</td><td>"</td><td>1891</td><td>41,154</td></tr>
+<tr><td></td><td>"</td><td>"</td><td>1901</td><td>73,508</td></tr>
+<tr><td></td><td>&nbsp;</td><td>(Estimated)</td><td>1909</td><td>86,000 to 90,000</td></tr>
+</table></div>
+
+<p>The greatest progress, it will be noted, was between 1891-1901, with an
+increase of more than 22,000 in 10 years. In designing the new works,
+provision has been made for the future requirements of a city of 200,000
+persons.</p>
+
+<p>The actual area within the city limits proper is 960.5 hectares (2,374
+acres), forming the area to be provided with water and drainage, but the
+municipal district extends to many surrounding suburbs, and covers an
+area of 33,758 hectares (83,426 acres).</p>
+
+<div class="TableHeader">
+TABLE 1.&mdash;<span class="smcap">Population And Death Rate Of Monterrey, N. L.,<br />
+Mexico, From 1901 To 1909, Inclusive.</span></div>
+
+<div class="center">
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr align="center"><td rowspan="2">Year.</td><td rowspan="2">Population.<br />(Census Est.)</td><td rowspan="2">Deaths from all causes.</td><td rowspan="2">Rate per 1,000.</td><td colspan="13"><span class="smcap">Deaths From Typhoid Fever.</span></td><td rowspan="2">Deaths from Typhoid fever per year per 100,000 population.</td></tr>
+<tr align="center"><td>Jan.</td><td>Feb.</td><td>Mar.</td><td>Apr.</td><td>May.</td><td>Jne.</td><td>Jly.</td><td>Aug.</td><td>Sep.</td><td>Oct.</td><td>Nov.</td><td>Dec.</td><td>Total for year.</td></tr>
+<tr align="center"><td>1901</td><td>73,508</td><td>2,965</td><td>40.3</td><td>0</td><td>2</td><td>1</td><td>3</td><td>4</td><td>3</td><td>6</td><td>6</td><td>3</td><td>6</td><td>4</td><td>2</td><td>40</td><td>54</td></tr>
+<tr align="center"><td>1902</td><td>74,500</td><td>3,338</td><td>44.8</td><td>1</td><td>4</td><td>2</td><td>3</td><td>6</td><td>5</td><td>3</td><td>1</td><td>1</td><td>2</td><td>3</td><td>5</td><td>36</td><td>48</td></tr>
+<tr align="center"><td>1903</td><td>76,000</td><td>3,825</td><td>50.3</td><td>3</td><td>2</td><td>4</td><td>1</td><td>0</td><td>5</td><td>3</td><td>5</td><td>6</td><td>16</td><td>3</td><td>1</td><td>49</td><td>64</td></tr>
+<tr align="center"><td>1904</td><td>77,500</td><td>2,905</td><td>37.4</td><td>0</td><td>1</td><td>1</td><td>5</td><td>3</td><td>3</td><td>3</td><td>4</td><td>1</td><td>5</td><td>1</td><td>0</td><td>27</td><td>35</td></tr>
+<tr align="center"><td>1905</td><td>79,000</td><td>2,951</td><td>37.4</td><td>2</td><td>0</td><td>0</td><td>3</td><td>3</td><td>7</td><td>6</td><td>3</td><td>2</td><td>7</td><td>2</td><td>2</td><td>37</td><td>47</td></tr>
+<tr align="center"><td>1906</td><td>80,000</td><td>2,935</td><td>36.7</td><td>1</td><td>2</td><td>1</td><td>3</td><td>3</td><td>6</td><td>5</td><td>3</td><td>2</td><td>1</td><td>2</td><td>3</td><td>32</td><td>40</td></tr>
+<tr align="center"><td>1907</td><td>82,500</td><td>3,269</td><td>39.6</td><td>4</td><td>6</td><td>3</td><td>3</td><td>5</td><td>6</td><td>4</td><td>4</td><td>9</td><td>3</td><td>0</td><td>3</td><td>50</td><td>61</td></tr>
+<tr align="center"><td>1908</td><td>84,000</td><td>3,188</td><td>37.9</td><td>5</td><td>2</td><td>5</td><td>3</td><td>8</td><td>5</td><td>9</td><td>7</td><td>2</td><td>7</td><td>4</td><td>0</td><td>57</td><td>68</td></tr>
+<tr align="center"><td>1909</td><td>86,000</td><td>[4]3,477</td><td>40.4</td><td>5</td><td>1</td><td>4</td><td>5</td><td>13</td><td>11</td><td>15</td><td>12</td><td>6</td><td>8</td><td>3</td><td>4</td><td>87</td><td>101</td></tr>
+</table></div>
+
+<div class="footnote"><span class="label">[4]</span> Excluding deaths due to drowning in the great flood of
+August 27th and 28th.</div>
+
+<p>Table 1 gives particulars of the death rate for 1901 to 1909, inclusive,
+and data relative to the mortality due to typhoid fever. The high death
+rate is caused by the excessive infantile mortality, which is so
+prevalent throughout the whole of Mexico. The climatic condition of
+Monterrey, with its exceptionally healthy subsoil, ought to make it one
+of the healthiest of cities, if proper care were taken to enforce
+sanitary laws. The data regarding typhoid mortality are probably
+<!--482.png--><span class="pagenum"><a name="Page_480" id="Page_480">480</a></span>
+understated, as they were compiled by the writer, in the absence of any
+official publications, from the actual death certificates, but no
+special care is taken by the authorities to insure accuracy in such
+certificates. Attention is called to the typhoid rate in May, June,
+July, and August, 1909; this high rate coincides with a scarcity of
+rainfall and the greatest period of drought experienced in 30 years, and
+immediately precedes the great flood of August 27th. It was probably due
+to the lowering of the ground-water throughout the city and the
+consequent contamination of the private wells, which were largely in use
+during that time. Throughout the city the wells are sunk to a depth of
+about 12 or 15 m., in order to reach the subterranean waters, and the
+cesspools are often in dangerous proximity to them and at a much higher
+level. The nature of the subsoil, which is often much fissured and open
+in the conglomerate and sillar strata, would make the passage of
+contamination an easy matter, and this alone would account for a high
+mortality due to water-borne diseases.</p>
+
+
+<h2><span class="smcap"><a name="Rainfall_and_Temperature" id="Rainfall_and_Temperature"></a>Rainfall and Temperature.</span></h2>
+
+<p>The precipitation records of Monterrey and its neighborhood are very
+meager, and cannot be relied on for a longer period than from 1894 to
+1909, inclusive. The records are available from 1886, but in the early
+years there are many apparent discrepancies, and they are probably
+inaccurate. The average rainfall for the 15 years (1894-1908) is 21.94
+in.; the driest years for this period are as follows: 1894, 14.14 in.;
+1902, 15.29 in.; 1907, 15.23 in.; 1908, 15.11 in. Assuming the early
+records to be correct, the average rainfall for the period, 1886-1908,
+would be 19.86 in.</p>
+
+<p>At Saltillo, which is 50 miles due southwest, at an elevation of about
+1,520 m. above sea level, the average rainfall for the 23 years,
+1884-1908, inclusive, is given as 21 in. The maximum year was 1889, with
+33<sup>1</sup>&frasl;<sub>2</sub> in., and the minimum 1903, with
+7<sup>1</sup>&frasl;<sub>2</sub> in.</p>
+
+<p>At Carmen, in the State of Tamaulipas, 144 km. southwest of Monterrey,
+at an elevation of about 310 m. above sea level, the average fall for 12
+years is 24.70 in., the maximum year being 1897, with a fall of 34.09
+in., and the minimum year, 1905, with 13.41 in.</p>
+
+<div class="figcenter" style="width: 700px;">
+<img src="images/i481.jpg" width="700" height="539" alt="Fig. 1." title="" />
+<span class="caption"><span class="smcap">Fig. 1.&mdash;Annual Rainfall In Monterrey<br />
+Covering The Period From 1894 To 1909.</span></span>
+</div>
+
+<p>Fig. 1 shows the annual variation of rainfall at Monterrey for
+1894-1909. Fig. 2 shows the monthly variation during the same period,
+and gives the minimum, average, and maximum for each month.
+<!--485.png--><span class="pagenum">481</span>
+From these
+diagrams it will be seen that the months of least rainfall are December,
+January, February, and March, with averages of 0.66, 0.59, 0.79, and
+0.93 in., respectively. The months of greatest rainfall are August, with
+an average of 4.39 in., and September with 4.87 in. The maximum in any
+month prior to 1909 was 16.75 in., during September, 1904.</p>
+
+<p><i>Rainfall in 1909.</i>&mdash;The rainfall in 1909 was unprecedented, causing the
+disastrous flood in the Santa Catarina River, which will be referred to
+when describing the works. Fig. 3 shows the monthly rainfall for 1906 to
+1909, inclusive, and has been plotted to show the variation of rainfall
+prior to the great precipitation of August, 1909. In that month there
+were two heavy falls, one beginning at midnight on August 9th, and
+during the following 42 hours a fall of 13.28 in. was recorded by the
+gauge at the Water-Works Company's general offices, 10.20 in. of which
+fell, during the first 24 hours. From 6 <span class="smcap">P. M.</span> to 11 <span class="smcap">P. M.</span>, on August
+10th, 5.019 in. were recorded, or an average of 1 in. per hour.</p>
+
+<div class="figcenter" style="width: 542px;">
+<img src="images/i482.jpg" width="542" height="700" alt="Fig. 2." title="" />
+<span class="caption"><span class="smcap">Fig. 2.&mdash;Monthly Rainfall in Monterrey Covering
+The Period From 1894 To 1909 Inclusive.</span></span>
+</div>
+
+<div class="figcenter" style="width: 700px;">
+<img src="images/i483.jpg" width="700" height="344" alt="Fig. 3." title="" />
+<span class="caption"><span class="smcap">Fig. 3.&mdash;Monthly Variation Of Rainfall At Monterrey 1906-1907-1908-1909.</span></span>
+</div>
+
+<p>After 13 dry days, another rainstorm began, at 4 <span class="smcap">P. M.</span>, on August
+<!--486.png--><span class="pagenum">482</span>25th,
+and continued more or less intermittently until August 29th. During this
+98-hour period there was an additional fall of 21.61 in., 11.27 in.
+falling in 24 hours.</p>
+
+<p>The total precipitation during the month amounted to 36.00 in. The
+highest previous record for the month of August was in 1895, with a fall
+of 6.61 in. Fig. 4 gives the details of the two heavy precipitations in
+August. As no automatic recording gauge was available,
+<!--488.png--><span class="pagenum"><a name="Page_484" id="Page_484">484</a></span>
+the maximum
+intensity could only be computed approximately, owing to the
+intermittent character of the readings taken from the ordinary rain
+gauge on the roof of the Water-Works Company's office in the city. From
+the readings thus obtained, it was shown that the maximum intensity
+occurred early on the morning of the 28th, and was nearly 2 in. per
+hour. Above Monterrey, in the Santa Catarina water-shed, it is believed
+that the precipitation was considerably greater, but no gauges were
+accessible during the month.</p>
+
+<div class="figcenter" style="width: 300px;"><a name="i485a" id="i485a"></a>
+<img src="images/i485at.jpg" width="300" height="102" alt="Fig. 4." title="" />
+<span class="caption"><span class="smcap">Fig. 4.&mdash;Curve Of Rainfall At Monterrey During
+August 10th &amp; 11th And From August 25th To 29th - 1909.</span></span><br />
+<a href="images/i485a.jpg" target="_blank">Larger.</a>
+</div>
+
+<p>The total rainfall for 1909 amounted to 47.46 in., of which 75% fell in
+August. This is 50% greater than the previous highest annual record
+(31.65 in. in 1900) for Monterrey.</p>
+
+<p><i>Temperature.</i>&mdash;Fig. 6 gives a record of the temperature at Monterrey
+from 1901 to 1909, inclusive. These records were taken at an altitude of
+520 m. It will be noted that the lowest recorded temperatures are in
+January and February. The lowest during these years was 24° Fahr., in
+January, 1905. The monthly maxima vary between 80 and 110° Fahr. The
+mean annual temperature is 72.65° Fahr. (The mean annual barometer is
+28.2 in.)</p>
+
+<div class="figcenter" style="width: 476px;">
+<img src="images/i487.jpg" width="476" height="700" alt="Fig. 6." title="" />
+<span class="caption"><span class="smcap">Fig. 6.&mdash;Diagram Of Temperature Variation At Monterrey,
+1901-09.</span></span>
+</div>
+
+
+<h2><span class="smcap"><a name="Available_Sources_of_Supply" id="Available_Sources_of_Supply"></a>Available Sources of Supply.</span></h2>
+
+<p>The question of the best sources from which Monterrey should be supplied
+with potable water was one that had been long under discussion, and was
+the subject of many investigations prior to the granting of the present
+concession. Several of the original schemes called for an impounding
+reservoir in the Cañon of Santa Catarina and it was on the assumption
+that a dam would be built that a clause was inserted in the concession
+for the purpose of making its construction obligatory. The general
+character of the physical and geological conditions surrounding
+Monterrey has already been referred to. A thorough study of these
+conditions proved that no suitable site for impounding the Santa
+Catarina River could be found, apart from the fact that periodically
+this river is subject to enormous floods which tear through the steep
+cañon with tremendous velocity.</p>
+
+<p>At the site originally proposed for the dam, a considerable underflow
+was found, and later investigations, carried out under the present
+concession, proved that, although borings were carried to a depth of 54
+m., bed-rock could not be found, the strata being composed of gravels,
+conglomerate and sand. Assuming that such a dam could
+<!--490.png--><span class="pagenum">486</span>
+have been built,
+the quality of the water draining from a comparatively barren
+water-shed, on which many thousands of goats are pastured, would have
+made its filtration an absolute necessity before it could be delivered
+to the consumers.</p>
+
+<p>The various available sources from which water could be delivered to the
+city by gravity were investigated by Mr. F. S. Hyde, in the autumn of
+1905, and also by J. D. Schuyler, M. Am. Soc. C. E., who was afterward
+retained as Consulting Engineer for the Company. The various
+investigations made from time to time showed that the question of a
+satisfactory supply was one of extreme difficulty, requiring prolonged
+observation and study, more particularly into the character of the
+underground sources of supply.</p>
+
+<p>One of the chief characteristics of many of the streams in the State of
+Nuevo León, is their disappearance and reappearance at different points
+along their routes, and the Santa Catarina River, under normal
+conditions, as already remarked, is a very notable example of a river
+which is very dry at the surface for many kilometers of its length. In
+the writer's opinion, the waters of this and similar rivers in the State
+pass through many open caverns underground, so that experience gained in
+the investigation of underflow waters in other places would be
+insufficient to determine the quantity passing at any point along the
+river if ascertained by merely computing it from the velocity of the
+underflow and the area of the water-bearing gravels. The rainfall on the
+water-shed of the Santa Catarina River is probably 25% greater than at
+Monterrey, and all ordinary rains sink rapidly into the limestone soils
+and quickly disappear. In another water-shed of a very similar
+character, namely, that of the Rio Blanco, in the southern part of the
+State, the underflow waters appear at the surface at a place called
+Mezquital, where a metamorphosed sandstone barrier prevents them from
+disappearing underground. At this point the normal quantity of water is
+about 5,660 liters (200 cu. ft.) per sec., but it gradually disappears,
+and a few kilometers below it has sunk to an insignificant stream,
+finally disappearing altogether for about 20 km. In the neighborhood of
+Monterrey similar conditions exist with regard to the surface-water
+supplies, and investigations, therefore, were directed toward obtaining
+unpolluted supplies from springs and underground sources.</p>
+
+<p><i>Santa Catarina Sources.</i>&mdash;The chief points from which it was
+<!--494.png--><span class="pagenum">488</span>
+thought
+desirable to obtain underflow supplies were (1) at the barrier of San
+Geronimo, and (2) at the Cañon of Santa Catarina, both shown on
+<a href="#p02">Plate II</a>.</p>
+
+<p>Conditions at San Geronimo, which is only 6<sup>1</sup>&frasl;<sub>2</sub> km. west of Monterrey,
+were investigated by the State Government in 1892, to determine the
+depth of bed-rock, the rock on either side of the valley being shale,
+with its original bedding planes standing almost vertical. To determine
+this depth, borings were made by driving 2-in. tubes until it was
+assumed that bed-rock had been reached, a method which, in strata
+containing so many boulders, was obviously unreliable. These borings
+indicated that bed-rock was from 12 to 15 m. below the surface. If these
+had proved to be correct, there is no doubt that a development of the
+underground water at this point, by constructing a submerged dam
+combined with an infiltration gallery, would have yielded a large
+supply.</p>
+
+<p>In March, 1906, the Company commenced operations at San Geronimo by
+sinking a well a few meters north of the then dry bed of the river.
+Water was found in considerable quantities a few meters below the
+surface, practically at the level of the river, that is, 570 m. above
+datum. This supply was used for provisional purposes, and will be
+referred to later in describing the San Geronimo gravity supply works.</p>
+
+<p>Between August, 1906, and January, 1907, 4-in. bore-holes were sunk in
+the river bed and on the high ground to the north with a "Keystone"
+driller outfit. These borings showed bed-rock immediately under the
+river bed, at a depth of from 15 to 45 m., but dipping gradually as the
+borings were carried northward.</p>
+
+<p>Boring operations were also carried on at Santa Catarina, during
+November and December, 1906, and in January, 1907, to determine the
+geological conditions, and the results are shown on <a href="#i489">Fig. 7</a>. From the
+area of water-bearing gravels found, it was proposed to tap the
+underflow water at the 630-m. level by an infiltration gallery. This
+would have necessitated a gravitation tunnel 3,000 m. long, and an
+aqueduct of 14 km., which it was proposed to carry to one of two
+distributing reservoirs at Guadalupe, on the south side of the river,
+opposite Monterrey. In May, 1907, the writer, after making a study of
+all the available data which had been accumulated, had additional
+borings sunk farther across the valley to the north, and these revealed
+a considerable area of water-bearing gravels, and proved that, in former
+<!--495.png--><span class="pagenum">489</span>
+geological times, the Santa Catarina flowed about 500 m. north of its
+present position, and to the back of Obispado Mountain, instead of
+through the city. This aspect of the subject was discussed with Mr.
+Schuyler, who agreed with the writer that, in the interest of economy,
+it was better to tap this supply by an infiltration gallery at the
+560-m. level, and bring the water thus obtained to a reservoir to be
+placed at the western limits of the city, dividing the city, for
+distribution purposes, into two interchangeable systems, a high- and a
+low-pressure, the high-pressure system being supplied from Estanzuela,
+18 km. south of the city. One advantage to be gained from this change
+was that the scheme was capable of considerable extension, and any
+future developments at Santa Catarina Cañon would form part of the works
+to be constructed for both high- and low-pressure districts.</p>
+
+<div class="figcenter" style="width: 700px;"><a name="i489" id="i489"></a>
+<img src="images/i489.jpg" width="700" height="594" alt="Fig. 7." title="" />
+<span class="caption"><span class="smcap">Fig. 7.&mdash;Cross-section Of Santa Catarina River At
+Santa Catarina.</span></span>
+</div>
+
+<p>The future extension of the Santa Catarina sources, the writer believes,
+can be developed best by driving an infiltration gallery 10 m. below the
+surface of the Santa Catarina River, a little west of the village of the
+same name, and then conveying the water through a comparatively
+<!--496.png--><span class="pagenum">490</span>short
+gravitation tunnel and pressure conduit to a main reservoir near San
+Geronimo having a top water level at an elevation of about 590 m. above
+datum.</p>
+
+<p><i>Southern Sources of Supply.</i>&mdash;The available sources of supply southward
+from Monterrey include a number of springs at various points in a
+distance of 40 km. Many of these springs are of uncertain quantity, and
+some are quite dry during periods of drought. The chief perennial
+springs near Monterrey are those which contribute to form the Estanzuela
+and Diente Rivers, both tributaries of the Silla, while farther south,
+at the Potrero Cerna, near El Porvenir, there are excellent springs, at
+a considerable elevation, with a minimum flow of from 170 to 200 liters
+(from 6 to 7 cu. ft.) per sec. The total quantity of water available
+from all these springs during the driest season would probably not be
+less than about 560 or 700 liters (from 20 to 25 cu. ft.) per sec.</p>
+
+<p>The Estanzuela springs issue at the foot of the Sierra Madre Mountains,
+and have a normal flow of from 56 to 85 liters (2 to 3 cu. ft.) per sec.
+in an ordinary dry year; they probably derive their water, through the
+limestone formation, from the neighboring water-shed of Santa Catarina,
+as the catchment area of the stream is only 910 hectares, and the stream
+has never been known to fail, even in the driest periods of prolonged
+drought. The rainfall on the area is about 30 in. per annum, and the
+catchment area is well wooded and covered with abundant vegetation. The
+El Diente springs have an ordinary dry-weather flow of about 28<sup>1</sup>&frasl;<sub>2</sub>
+liters (1 cu. ft.) per sec.; but part of the water is carried
+underground, and the real quantity is much greater and could be
+developed by a small submerged dam carried down to bed-rock.</p>
+
+<p>The elevation and the extreme purity of the water of the Estanzuela
+River made its acquisition very desirable, and the Company, therefore,
+purchased the Federal water rights owned by various members of the
+Estanzuela community, amounting to 91 liters per sec., and has since
+acquired a Federal concession to all the flood-waters of that river. It
+was decided, therefore, to adopt the Estanzuela River as the first step
+toward developing the water to the south of Monterrey for a
+high-pressure supply, the advantage of the scheme being that from time
+to time extensions could be made to tap other sources by gravity, as the
+demands of the city required. The Estanzuela scheme, therefore,
+<!--497.png--><span class="pagenum"><a name="Page_491" id="Page_491">491</a></span>
+is a
+preliminary step toward future extensions which will be necessary in
+this direction as the city grows. The springs near El Porvenir, and
+others which contribute to the San Juan River, can be tapped at a
+sufficiently high level to convey them by a gravity pressure line to the
+Estanzuela Aqueduct near Mederos.</p>
+
+<p>The two sources definitely decided on in July, 1907, were those from
+Estanzuela and San Geronimo. The works were designed to supply
+40,000,000 liters daily, which it was assumed would be sufficient for
+all future developments for a population of 200,000 at a per capita
+consumption of 200 liters per day. The present requirements of the
+city's population, assuming that all the water was supplied by the
+Company, would be, at that rate, which is a very liberal one, only
+18,000,000 liters daily. This, it was thought, would be easily met by
+the San Geronimo source alone, as it was estimated that it would provide
+not less than 20,000,000 liters, if the infiltration gallery was driven
+far enough into the water-bearing gravels.</p>
+
+<p>The question of a high-pressure water supply for domestic use in a city
+like Monterrey is not a serious one, as practically nine-tenths of the
+houses are of one story. The increase in the number of large commercial
+buildings, however, will make the demand greater in the future, and this
+point has been kept in mind in arranging the division of the
+distribution systems.</p>
+
+
+<h2><span class="smcap"><a name="Materials_for_Concrete" id="Materials_for_Concrete"></a>Materials for Concrete.</span></h2>
+
+<p><i>Cement.</i>&mdash;In the early stages of construction the cement for the work
+was obtained from the Associated Portland Cement Manufacturers, Limited,
+of London, which supplied the "Pyramid" brand, from the Knight, Bevan,
+and Sturges Works, but later the supply was obtained from a new factory
+at Hidalgo, near Monterrey. The total quantity of Portland cement used
+was 42,500 bbl. of "Pyramid" and 32,500 bbl. of "Hidalgo." The English
+cement was tested for the Water-Works Company in London before shipment
+and again at Monterrey, to conform to the British Standard
+Specifications; the "Hidalgo" cement was required to pass the Standard
+Specifications advocated by the Special Committee of the American
+Society of Civil Engineers. The quality in each case was of the very
+highest, no difficulties being experienced at any time.</p>
+<!--498.png--><p><span class="pagenum">492</span></p>
+
+<p><i>Sand and Rock.</i>&mdash;One of the chief difficulties in connection with the
+construction work in its initial stages was in procuring satisfactory
+sand for the concrete. An investigation of the quality of all the
+available sands in the neighborhood of Monterrey resulted in the
+decision to use a manufactured sand obtained from the calcareous shales
+in the foot-hills opposite the city, on the south side, and near the
+site of one of the proposed reservoirs. A quarry was opened, and the raw
+material was delivered by a gravity plane to a crushing plant, 230 m.
+from the quarry and at a level about 50 m. lower.</p>
+
+<p>The plant consisted of a No. 5 Austin gyratory rock-crusher, fitted with
+elevators and revolving screens of various dimensions, driven by a
+150-h.p. Erie steam engine; two sets of Traylor's heavy-duty crushing
+rolls, one having 30 by 16-in. and the other 18 by 12-in. rolls; and a
+Niagara sand disintegrator. This plant, except during a short period
+when the requirements were beyond its capacity, was able to produce all
+the sand and rock required for construction purposes. More than 40,000
+tons of rock were quarried, the greater part of which was converted into
+crushed stone and sand.</p>
+
+<p>Table 2 gives the chemical analysis of the chief constituents of the
+various sands examined.</p>
+
+<div class="TableHeader">
+TABLE 2.&mdash;<span class="smcap">Analysis Of Sands In The Neighborhood Of Monterrey.</span></div>
+<table border="0" cellspacing="0" cellpadding="4" summary="Sand Compositions">
+<tr>
+<td>No.</td>
+<td>Location.</td>
+<td align="center">Percentage of silica (absolute), SiO<sub>2</sub></td>
+<td align="center">Percentage of alumina, Al<sub>2</sub>O<sub>3</sub></td>
+<td align="center">Percentage of sesquioxide, Fe<sub>2</sub>O<sub>3</sub></td>
+<td align="center">Percentage of lime carbonate, CaCO<sub>3</sub></td>
+</tr>
+<tr>
+<td>1.</td>
+<td>Arroyo Seco, near<br />
+brickyard at Monterrey</td>
+<td align="center">60.10</td>
+<td align="center">17.95</td>
+<td align="center">2.89</td>
+<td align="center">8.01</td>
+</tr>
+<tr>
+<td>2.</td>
+<td>Arroyo Seco, near<br />
+brickyard at Monterrey, No. 2</td>
+<td align="center">42.92</td>
+<td align="center">14.26</td>
+<td align="center">4.66</td>
+<td align="center">34.58</td>
+</tr>
+<tr>
+<td>3.</td>
+<td>Near Garcia Station,
+Mexican National R.&nbsp;R.,
+Chiquito River, No. 1</td>
+<td align="center">50.22</td>
+<td align="center">9.72</td>
+<td align="center">1.44</td>
+<td align="center">34.62</td>
+</tr>
+<tr>
+<td>4.</td>
+<td>Near Garcia Station.
+Mexican National R.&nbsp;R.,
+Chiquito River, No. 2</td>
+<td align="center">48.7</td>
+<td align="center">4.92</td>
+<td align="center">8.28</td>
+<td align="center">35.43</td>
+</tr>
+<tr>
+<td>5.</td>
+<td>San Luis Potos&iacute;</td>
+<td align="center">85.02</td>
+<td align="center">5.00</td>
+<td align="center">7.38</td>
+<td align="center">2.21</td>
+</tr>
+<tr>
+<td>6.</td>
+<td>Topo Grande, Pesquer&iacute;a<br />
+River</td>
+<td align="center">40.20</td>
+<td align="center">5.15</td>
+<td align="center">4.25</td>
+<td align="center">46.50</td>
+</tr>
+<tr>
+<td>7.</td>
+<td>Hornos, near Torre&oacute;n</td>
+<td align="center">77.9</td>
+<td align="center">13.1</td>
+<td align="center">2.4</td>
+<td align="center">4.9</td>
+</tr>
+<tr>
+<td>8.</td>
+<td>Salinas River, at Salinas</td>
+<td align="center">41.5</td>
+<td align="center">5.7</td>
+<td align="center">1.4</td>
+<td align="center">48.2</td>
+</tr>
+<tr>
+<td>9.</td>
+<td>Pits near Caballeros, on<br />
+Tampico Branch of<br />
+Mexican Central R.&nbsp;R.</td>
+<td align="center">73.4</td>
+<td align="center">5.6</td>
+<td align="center">4.4</td>
+<td align="center">10.1</td>
+</tr>
+<tr>
+<td>10.</td>
+<td>Santa Catarina River,
+near San Geronimo<br />
+(washed sand)</td>
+<td align="center">12.40</td>
+<td align="center">2.06</td>
+<td align="center">1.14</td>
+<td align="center">81.70</td>
+</tr>
+<tr>
+<td>11.</td>
+<td>Santa Catarina River,
+at Monterrey</td>
+<td align="center">17.4</td>
+<td align="center">2.50</td>
+<td align="center">2.00</td>
+<td align="center">77.00</td>
+</tr>
+<tr>
+<td>12.</td>
+<td>Composition of rock, quarry<br />
+in foot-hills opposite<br />
+Monterrey, Monterrey<br />
+Water-Works and Sewer<br />
+Company's property</td>
+<td align="center">40.44</td>
+<td align="center">15.70</td>
+<td align="center">2.20</td>
+<td align="center">34.30</td>
+</tr>
+<tr>
+<td>13.</td>
+<td>Manufactured sand from<br />
+above quarry<br />
+(run of crusher)</td>
+<td align="center">51.80</td>
+<td align="center">12.14</td>
+<td align="center">8.7</td>
+<td align="center">32.6</td>
+</tr>
+</table>
+
+<!--501.png--><p><span class="pagenum">493</span></p>
+<p>The chief sands used for ordinary building purposes in Monterrey are
+Nos. 10 and 11, which are procured from the bed of the Santa Catarina
+River. As these sands contain large proportions of lime carbonates,
+which make them very undesirable for important structures, their use was
+limited to relatively unimportant work. The best sands procurable were
+Nos. 5 and 9, but the long distance of the pits from Monterrey, and
+consequently the heavy freight rate, made their use prohibitive on
+economical grounds. The best of the available sands, although it was
+very fine, was No. 7, from Hornos, near Torreon, as it could be depended
+on for uniformity and could be obtained f. o. b. cars at Monterrey for
+3.18<a name="FNanchor_5_5" id="FNanchor_5_5"></a><a href="#Footnote_5_5" class="fnanchor">[5]</a> pesos per ton.</p>
+
+<div class="footnote"><a name="Footnote_5_5" id="Footnote_5_5"></a><a href="#FNanchor_5_5"><span class="label">[5]</span></a> All costs given in this paper are in Mexican pesos, one
+peso being equivalent to 50 cents in U. S. currency.</div>
+
+<p>The bulk of the sand and crushed rock used was similar to Nos. 12 and
+13, and reference to the cement sand tests in Table 3, will show that
+the manufactured sands gave very satisfactory results.</p>
+
+<p>Table 3 gives the average tests made with the "Hidalgo" cement and
+various sands, alone and in combination, for the purpose of obtaining
+comparative results; the mixtures tested were composed of 3 parts of
+sand to 1 of cement.</p>
+
+<div class="TableHeader">
+TABLE 3.&mdash;<span class="smcap">Tests Of "Hidalgo" Cement With Various Sands.</span>
+</div>
+
+<table border="0" cellspacing="0" cellpadding="2" summary="Tests of Cement">
+<tr>
+<td align="center">Sand.</td>
+<td colspan="2" align="center">At 7 days.</td>
+<td colspan="2" align="center">At 28 days.</td>
+</tr>
+<tr><td>&nbsp;</td></tr>
+<tr>
+<td>Ottawa (Standard)</td>
+<td align="center">305</td>
+<td>lb.</td>
+<td align="center">414</td>
+<td>lb.</td>
+</tr>
+<tr>
+<td>Monterrey, 1<sup>1</sup>&frasl;<sub>2</sub> parts,
+Hornos, 1<sup>1</sup>&frasl;<sub>2</sub> parts</td>
+<td align="center">188</td>
+<td>"</td>
+<td align="center">313</td>
+<td>"</td>
+</tr>
+<tr>
+<td>Monterrey</td>
+<td align="center">253</td>
+<td>"</td>
+<td align="center">365</td>
+<td>"</td>
+</tr>
+<tr>
+<td>Hornos</td>
+<td align="center">202</td>
+<td>"</td>
+<td align="center">301</td>
+<td>"</td>
+</tr>
+<tr>
+<td>Manufactured sand, Company's crusher</td>
+<td align="center">372</td>
+<td>"</td>
+<td align="center">566</td>
+<td>"</td>
+</tr>
+<tr>
+<td>Hornos, 2 parts,
+Crusher sand, 1 part</td>
+<td align="center">231</td>
+<td>"</td>
+<td align="center">352</td><td>"</td>
+</tr>
+<tr>
+<td>Hornos, 1<sup>1</sup>&frasl;<sub>2</sub> parts,
+Crusher sand, 1<sup>1</sup>&frasl;<sub>2</sub> parts</td>
+<td align="center">265</td>
+<td>"</td>
+<td align="center">346</td>
+<td>"</td>
+</tr>
+<tr>
+<td>Hornos, 1 part,
+Crusher sand, 2 parts</td>
+<td align="center">248</td>
+<td>"</td>
+<td align="center">328</td>
+<td>"</td>
+</tr>
+</table>
+
+<p>The Hornos sand was used during a few weeks in the latter part of 1908,
+when the crusher was unable to produce all that was required. Its use
+was restricted to thick walls which were required to be water-tight, and
+it was always used in equal proportions with the crusher dust.</p>
+<!--502.png--><p><span class="pagenum"><a name="Page_494" id="Page_494">494</a></span></p>
+
+
+<h2><span class="smcap"><a name="Estanzuela_Supply" id="Estanzuela_Supply"></a>Estanzuela Supply.</span></h2>
+
+<div class="figright" style="width: 300px;"><a name="i495" id="i495"></a>
+<img src="images/i495t.jpg" width="300" height="205" alt="Fig. 8." title="" />
+<span class="caption"><span class="smcap">Fig. 8.&mdash;Location Plan of Estanzuela Dam.</span></span><br />
+<a href="images/i495.png" target="_blank">Larger.</a>
+</div>
+
+<p><i>Intake Works.</i>&mdash;The intake (Fig. 8) is about 1 km. below the lowest
+spring and at a point where the maximum flow of the stream was observed.
+The works consist of a small monolithic concrete dam, placed obliquely
+across the stream at an angle selected for the purpose of obtaining a
+foundation running parallel to the direction of the strata, which at
+this point were lying almost vertically across the bed of the stream.
+Above these strata the stream bed was formed chiefly of large cemented
+limestone blocks and smaller conglomerate. No storage being possible in
+this valley, which has a very precipitous fall, the height of the dam
+was fixed merely to obtain a small settling basin for sand and débris
+brought down in time of flood. The dam foundation was excavated to
+bed-rock, from which the upper disintegrated portions were carefully
+removed; the rock was then stepped, and dovetailed recesses were left
+for properly bonding the concrete.</p>
+
+<p>The dam is carried well into the banks. Its extreme length is 52 m., its
+maximum height 4.50 m., and its greatest thickness 2 m. The up-stream
+face has a batter of 1 in 12, and the down-stream face, 1 in 8. The top
+of the wall is 1 m. thick. For the discharge of flood-water there is a
+weir 10 m. long, and it was calculated that with a depth of 1 m. it
+would discharge about 400 times the ordinary flow, or about 23,000
+liters per sec., but, in addition, the whole length of the dam
+(excluding that occupied by the gate-house) was arranged for the
+discharge of abnormal floods, one of which, on August 27th, reached the
+enormous quantity of 82,070 liters (2,900 cu. ft.) per sec., or 825 cu.
+ft. per sec. per sq. mile of drainage area, a remarkable run-off from so
+small an area as 910 hectares. The concrete forming the dam is a 1:3:5
+mixture. The overflow sill is 692 m. above sea level. When the dam was
+completed it was filled to the overflow level, in order to test the
+water-tightness of the basin, which, when cleared, was found to be
+slightly fissured on the north side. The leakage was sufficient to cause
+a serious loss during periods of drought, and it was then decided to
+line the basin with concrete, so that the stream would enter it without
+being under a head greater than its own depth. The length of the basin,
+measured along the center line of the original stream surface, is 85 m.,
+and its area is 1,100 sq. m. At its upper end it is merely a lined
+channel, 5 m. wide at the entrance. The floor of the basin has a fall of
+4 m. The lining was formed in
+<!--504.png--><span class="pagenum">496</span>two
+thicknesses totaling 30.5 cm. (12
+in.) of 1:2<sup>1</sup>&frasl;<sub>2</sub>:3<sup>1</sup>&frasl;<sub>2</sub>
+concrete, laid in panels approximately 3 m.
+square, the upper panels breaking joint with those immediately below; in
+this way a very satisfactory and water-tight lining was obtained. A
+parapet wall, 45.7 cm. high, surrounds the basin. For scouring out the
+basin a 30.5-cm. (12-in.) cast-iron pipe was taken through the dam at
+the lowest point, this pipe being provided with a gate-valve encased in
+concrete on the down-stream face.</p>
+
+<p>The gate-house was built in connection with the dam at the north end of
+the overflow weir, its inner dimensions being 4.34 by 2.80 m. The
+substructure, to the level of the dam, is of concrete founded on the
+solid rock, and the superstructure is of brick rendered with cement
+plaster. The roof is of framed timber with red French tiles.</p>
+
+<p>The intake pipe is of cast iron. 40.6 cm. (16 in.) in internal diameter,
+fitted outside with a movable copper screen which is further protected
+by a wrought-iron hinged screen to prevent damage from stones, floating
+timber, etc., during times of flood. Inside the gate-house the outlet
+pipe is provided with a 40.6-cm. (16-in.) sluice-valve, operated from
+the floor level by a vertical head-stock with worm-gearing. The
+gate-house has a scour-out pipe (also operated by a head-stock) and
+duplicate copper screens fitted to iron frames. From this house the
+water is conveyed to the upper portion of the conduit, which is a
+45.7-cm. (18-in.) cast-iron pipe.</p>
+
+<p>Of the total area of land, 885 hectares (2,187 acres), owned by the
+company, 392 hectares (970 acres) have been fenced in, to prevent any
+contamination of the springs. This fence is formed of five lines of
+barbed wire protected with stout hog netting at the bottom, in order to
+prevent more particularly the entrance of goats, many thousands of which
+pasture in the adjoining mountains.</p>
+
+<p>On the high ground immediately below the intake, a 3-roomed stone house
+has been constructed for the inspector in charge of the intake works,
+who also keeps in daily touch with the general office and records the
+condition of the stream, particulars of rainfall, etc.</p>
+
+<p><i>Aqueduct.</i>&mdash;The total length
+of the aqueduct, from the intake dam to
+the South Reservoir, is 18,700 m., made up as shown in Table 4.</p>
+
+<div class="TableHeader">
+TABLE 4.&mdash;<span class="smcap">Estanzuela Aqueduct.</span>
+</div>
+
+<table border="0" cellspacing="0" cellpadding="4" summary="Estanzuela Aqueduct">
+<tr>
+<td>&nbsp;</td>
+</tr>
+<tr valign="top">
+<td align="center">Description.</td>
+<td>&nbsp;</td>
+<td>&nbsp;</td>
+<td align="right">Length,
+in meters</td>
+</tr>
+<tr>
+<td>&nbsp;</td>
+</tr>
+<tr valign="top">
+<td>Cast-iron pipes, 45.7 cm. (18 in.) in diameter, along the stream bed of the Estanzuela River</td>
+<td>&nbsp;</td>
+<td>&nbsp;</td>
+<td align="right" valign="bottom">110</td>
+</tr>
+<tr valign="top">
+<td>Concrete tubes, 55.9 cm. (22 in.) in diameter, to Mederos (including 281 m. of tunnel)</td>
+<td>&nbsp;</td>
+<td>&nbsp;</td>
+<td align="right" valign="bottom">4,473.81</td>
+</tr>
+<tr valign="top">
+<td>Cast-iron siphons, 45.7 cm. (18 in.) in diameter:</td>
+<td>Calabozos</td>
+<td valign="bottom">239&nbsp;m</td>
+<td>&nbsp;</td>
+</tr>
+<tr>
+<td>&nbsp;</td>
+<td>South Virgen</td>
+<td valign="bottom">124 "</td>
+<td>&nbsp;</td>
+</tr>
+<tr>
+<td>&nbsp;</td>
+<td>North Virgen</td>
+<td valign="bottom">177 "</td>
+<td>&nbsp;</td>
+</tr>
+<tr>
+<td>&nbsp;</td>
+<td>Mederos</td>
+<td valign="bottom">426 "</td>
+<td>&nbsp;</td>
+</tr>
+<tr>
+<td>&nbsp;</td>
+<td>&nbsp;</td>
+<td>&mdash;&mdash;</td>
+<td align="right" valign="bottom">966</td>
+</tr>
+<tr valign="top">
+<td>Concrete tubes, 63.5 cm. (25 in.) in diameter, Mederos to South Reservoir.</td>
+<td>&nbsp;</td>
+<td>&nbsp;</td>
+<td align="right" valign="bottom">12,039.19</td>
+</tr>
+<tr valign="top">
+<td>Cast-iron siphons, 50.8 cm. (20 in.) in diameter:</td>
+<td></td>
+<td></td>
+<td></td>
+</tr>
+<tr>
+<td>&nbsp;</td>
+<td>Necaxa</td>
+<td valign="bottom">315 m.</td>
+<td>&nbsp;</td>
+</tr>
+<tr>
+<td>&nbsp;</td>
+<td>San Augustin</td>
+<td valign="bottom">796 "</td>
+<td>&nbsp;</td>
+</tr>
+<tr>
+<td>&nbsp;</td>
+<td>&nbsp;</td>
+<td>&mdash;&mdash;</td>
+<td align="right" valign="bottom">1,111</td>
+</tr>
+<tr>
+<td>&nbsp;</td>
+<td>&nbsp;</td>
+<td>&nbsp;</td>
+<td align="right">&mdash;&mdash;&mdash;</td>
+</tr>
+<tr>
+<td>&nbsp;</td>
+<td>&nbsp;</td>
+<td>Total</td>
+<td align="right" valign="bottom">18,700</td>
+</tr>
+<tr>
+<td>&nbsp;</td>
+</tr>
+</table>
+
+<p>The gradient of the concrete pipes is 0.43% from Estanzuela to Mederos,
+and 0.53% from Mederos to the South Reservoir. The calculated
+discharging capacity of the conduit when running full is 364
+<!--507.png--><span class="pagenum">497</span>liters
+(13 cu. ft.) per sec. for the upper, and 465 liters (16.4 cu. ft.) per sec.
+for the lower section. For these pipes, the coefficient, <i>n</i>, in
+Kutter's formula, was taken at 0.013. At present the line has been
+limited by overflows to discharge three-quarters full.</p>
+
+<p>The increase in the size of the pipes from Mederos is for the purpose of
+receiving the waters of the Mederos River and other springs in the San
+Pablo and Aqua Verde catchment areas, as shown on <a href="#p02">Plate
+II</a>.</p>
+
+<p>The invert of the concrete conduit where it leaves the Estanzuela River
+is 684.25 m. above datum, and at the valve-house of the South Reservoir
+it is 589.00 m.</p>
+
+<p>The concrete pipes were manufactured and laid under contract with Mr.
+Arthur S. Bent, of Los Angeles, Cal., the Company providing all
+materials, labor, etc. The contractor was paid 10 cents per lin. ft. of
+pipe manufactured and 10 cents per lin. ft. laid. He was also
+responsible for the satisfactory completion of the work.</p>
+
+<div class="figright" style="width: 300px;">
+<img src="images/i499t.jpg" width="300" height="202" alt="Fig. 9." title="" />
+<span class="caption"><span class="smcap">Fig. 9.&mdash;Estanzuela Pipe Line Steel Forms For The
+Manufacture Of Concrete Pipe.</span></span><br />
+<a href="images/i499.png" target="_blank">Larger.</a>
+</div>
+
+<p>Fig. 9 shows the details of the joint recommended by Mr. Schuyler and
+adopted for these pipes. The 63.5-cm. (25-in.) pipes were 61 cm. long
+and 76 mm. (3 in.) thick. The 55.9-cm. (22-in.) pipes were of the same
+length, but 70 mm. (2<sup>3</sup>&frasl;<sub>4</sub> in.) thick. For the purpose of strengthening
+these pipes while hauling them over very rough roads they were
+reinforced with four rings of No. 6 galvanized-iron wire.</p>
+
+<p><i>Manufacture of Pipes.</i>&mdash;The pipes were manufactured under the
+Supervision of Mr. H. Stanley Bent, at a pipe yard established below
+<!--508.png--><span class="pagenum">498</span>the
+crushing plant, from which the crushed rock and sand were delivered
+by gravity in bogies run on narrow-gauge rails. The area of the pipe
+yard was approximately 1<sup>1</sup>&frasl;<sub>4</sub> hectares, and it was laid out with parallel
+lines of 76-mm. (3-in.) galvanized-iron piping with hose couplings for
+sprinkling purposes. After trials with aggregates of various sizes, the
+concrete for the pipes was proportioned by volume as follows:</p>
+
+<div class="center">
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align="left"> Crushed rock broken to pass through a 19-mm. screen</td><td >0.136</td><td>cu.</td><td>m.</td></tr>
+<tr><td align="left"> Manufactured sand (run of rolls)</td><td >0.119</td><td >"</td><td >"</td></tr>
+<tr><td align="left"> Portland cement</td><td >0.090</td><td >"</td><td >"</td></tr>
+<tr><td align="left"></td><td>&mdash;&mdash;&mdash;&mdash;&mdash;</td></tr>
+<tr><td align="right">Total</td><td >0.345 cu. m.</td></tr>
+<tr><td align="left"></td><td>= (12.2 cu. ft.)</td></tr>
+</table></div>
+
+<div class="figcenter" style="width: 600px;">
+<img src="images/i02.jpg" width="600" height="425" alt="Fig. 2." title="" />
+<span class="caption"><span class="smcap">Plate III, Fig. 2.&mdash;Steel Forms for Moulding Concrete Tubes,
+Estanzuela Aqueduct.</span></span>
+</div>
+
+<p>The above quantity manufactured two 63.5-cm. pipes; a 55.9-cm. pipe
+required 0.1415 cu. m. (5 cu. ft.) of the material, in the same
+proportions. Fig. 9 shows the forms for these pipes, and Fig. 2, Plate
+III, illustrates the process of moulding. The forms
+consist of cast-iron bottom rings, to the proper section of the joint,
+and inner and outer steel forms of 3-mm. plate, provided with inner and
+outer locking arrangements. The concrete was poured through a cast-iron
+hopper which fitted to the top of the outer form.</p>
+
+<p>The concrete, which was mixed very dry, in a <sup>1</sup>&frasl;<sub>2</sub>-cu. yd. batch, "Smith"
+mixer, was thoroughly tamped with a 22-lb. tamper, and worked until it
+was of a stiff jelly-like consistency, the wire rings being added as the
+concrete was placed. The best results were obtained with the minimum
+quantity of water. The upper joint was moulded with a heavy cast-iron
+ring. The jacket and core forms were loosened immediately, and placed
+over other rings, a sufficient number of bottom rings being used for a
+day's work. For the pipes required for curves, special forms were used
+to give the necessary bevel to the joint. After 24 hours the finished
+pipes were lifted from the bottom ring with a special lifter, and ranged
+in position for coating internally with a Portland cement grout to which
+a little freshly slaked lime was added. The pipes were all numbered, and
+were kept moist for 10 days by constant sprinkling. They were not hauled
+to the work until 28 days after they were moulded, although this rule
+was sometimes broken, to the detriment of the pipes. More than 32,000
+pipes were
+<!--510.png--><span class="pagenum">500</span>manufactured,
+but some were used for purposes other than the
+Estanzuela Aqueduct.</p>
+
+<p><i>Cost of Pipes.</i>&mdash;The contractor brought with him experienced concrete
+pipe makers from California, and these were afterward assisted by
+Mexican labor. In a day two tampers could manufacture from 45 to 50
+pipes of the larger (63.5-cm,), and from 55 to 60 of the smaller
+(55.9-cm.) size.</p>
+
+<p>The cost varied from 2.75 to 3.25 pesos per pipe for the smaller, and
+from 3.50 to 4.00 pesos for the larger size.</p>
+
+<p>The approximate cost of manufacturing is as follows: Taking, as a fair
+example, one week's work during March, 1908, the wages paid to the 74
+men comprising the total pay-roll (though part of this labor was
+intermittent) amounted to 981 pesos. This includes a general foreman at
+10 pesos per day, four American tampers at 7.50 pesos, and Mexican labor
+varying from 4 to 1 peso, and all labor necessary to handle and finish
+the pipes, including coating the interiors. During this week there were
+made 1,126 of the 63.5-cm. and 1,095 of the 55.9-cm. size. The pay-roll
+includes 520 pesos for the larger pipes (46 cents each) and 461 pesos
+for the smaller pipe (42 cents each). Table 5 shows the quantities and
+cost of the materials used in the manufacture of these pipes.</p>
+
+<div class="TableHeader">
+TABLE 5.&mdash;<span class="smcap">Cost of Concrete Pipe.</span></div>
+
+<table border="0" cellspacing="0" cellpadding="4" summary="Table 5.">
+<tr>
+<td>&nbsp;</td>
+<td>&nbsp;</td>
+<td colspan="4" align="center"><span class="smcap">For 1,126 pipes 63.5 cm. in diameter.</span></td>
+<td>&nbsp;</td>
+<td colspan="4" align="center"><span class="smcap">For 1,095 pipes 55.9 cm. in diameter.</span></td>
+</tr>
+<tr>
+<td align="center">Materials.</td>
+<td>&nbsp;</td>
+</tr>
+<tr>
+<td>&nbsp;</td>
+<td>&nbsp;</td>
+<td colspan="2" align="center">Quantities.</td>
+<td colspan="2" align="center">Cost.</td>
+<td>&nbsp;</td>
+<td colspan="2" align="center">Quantities.</td>
+<td colspan="2" align="center">Cost.</td>
+</tr>
+<tr valign="top">
+<td>Portland cement, at 8.00 pesos per bbl., delivered at pipe-making yard.</td>
+<td></td>
+<td align="right">401</td>
+<td>bbl.</td>
+<td align="right">3,208.00</td>
+<td>pesos.</td>
+<td></td>
+<td align="right">303</td>
+<td>bbl.</td>
+<td align="right">2,424.00</td>
+<td>pesos.</td>
+</tr>
+<tr>
+<td>Sand, at 2.65 pesos per cu.&nbsp;m.</td>
+<td>&nbsp;</td>
+<td align="right">85</td>
+<td>cu.&nbsp;m.</td>
+<td align="right">225.25</td>
+<td align="center">"</td>
+<td>&nbsp;</td>
+<td align="right">68</td>
+<td>cu.&nbsp;m.</td>
+<td align="right">180.20</td>
+<td align="center">"</td>
+</tr>
+<tr>
+<td>Crushed rock, 19-mm. (<sup>3</sup>&frasl;<sub>4</sub>-in.), at 2.65 pesos per cu.&nbsp;m.</td>
+<td>&nbsp;</td>
+<td align="right">62</td>
+<td>cu.&nbsp;m.</td>
+<td align="right">164.30</td>
+<td align="center">"</td>
+<td>&nbsp;</td>
+<td align="right">50</td>
+<td>cu.&nbsp;m.</td>
+<td align="right">132.15</td>
+<td align="center">"</td>
+</tr>
+<tr>
+<td>No. 6 galvanized-wire hoops. 4 rings to each pipe.</td>
+<td>&nbsp;</td>
+<td align="right">4,504</td>
+<td>&nbsp;</td>
+<td align="right">203.00</td>
+<td align="center">"</td>
+<td>&nbsp;</td>
+<td align="right">4,380</td>
+<td>&nbsp;</td>
+<td align="right">183.00</td>
+<td align="center">"</td>
+</tr>
+<tr>
+<td>Totals.</td>
+<td>&nbsp;</td>
+<td align="right">...</td>
+<td>&nbsp;</td>
+<td align="right">3,800.55</td>
+<td>pesos.</td>
+<td>&nbsp;</td>
+<td align="right">...</td>
+<td>&nbsp;</td>
+<td align="right">2,919.45</td>
+<td>pesos.</td>
+</tr>
+<tr>
+<td>Cost per pipe.</td>
+<td>&nbsp;</td>
+<td align="right">...</td>
+<td>&nbsp;</td>
+<td align="right">3.37</td>
+<td>pesos.</td>
+<td>&nbsp;</td>
+<td align="right">...</td>
+<td>&nbsp;</td>
+<td align="right">2.66</td>
+<td>pesos.</td>
+</tr>
+</table>
+
+<p>From Table 5 it is seen that the cost of the 63.5-cm. pipes was 3.37
+pesos for material plus 0.46 peso for labor = 3.83 pesos per pipe, or
+6.26 pesos per lin. m. (1.91 pesos per lin. ft.).</p>
+
+<!--513.png--><p><span class="pagenum">501</span></p>
+
+<p>The cost of the 55.9-cm. pipes amounted to 2.66 pesos for material plus
+0.42 peso for labor = 3.08 pesos per pipe, or 5.05 pesos per lin. m.
+(1.54 pesos per lin. ft.).</p>
+
+<p>The cost of cement included hauling from the bodega to the yard, a
+distance of about 5 km. At a later date, after the Company had commenced
+using the "Hidalgo" cement, some additional 55.9-cm. pipes were
+manufactured, so as to have them on hand as a reserve in case of
+emergency. In this work only Mexican labor was used, as the previous
+gang had been dispersed, but the tampers had previous experience. Taking
+the cost of 418 pipes made during one period of 9 days, the detailed
+cost was as given in Table 6.</p>
+
+<div class="TableHeader">
+TABLE 6.&mdash;<span class="smcap">Cost of 55.9-Cm. Concrete Pipes.</span></div>
+
+<table border="0" cellspacing="0" cellpadding="1" summary="Concrete Pipe Cost">
+<tr>
+<td>&nbsp;</td>
+</tr>
+<tr valign="top">
+<td><span class="smcap">Labor For 9 Days.</span></td>
+<td>&nbsp;</td>
+<td>&nbsp;</td>
+</tr>
+<tr>
+<td>&nbsp;</td>
+</tr>
+<tr>
+<td>Tampers, 2 at 4 pesos.</td>
+<td align="right">72.00</td>
+<td>Pesos.</td>
+</tr>
+<tr>
+<td>Cement mixers (hand-mixing) and helpers, 6 at 1 peso.</td>
+<td align="right">54.00</td>
+<td align="center">"</td>
+</tr>
+<tr>
+<td>Water boy.</td>
+<td align="right">4.50</td>
+<td align="center">"</td>
+</tr>
+<tr>
+<td>Proportion of time of crusher foreman, one-third  of 6 pesos, 2 pesos.</td>
+<td align="right">18.00</td>
+<td align="center">"</td>
+</tr>
+<tr>
+<td>Making 1,672 wire hoops, at 5 pesos per thousand.</td>
+<td align="right">8.36</td>
+<td align="center">"</td>
+</tr>
+<tr>
+<td>Man coating pipe, at 1 peso per day.</td>
+<td align="right">5.00</td>
+<td align="center">"</td>
+</tr>
+<tr>
+<td>&nbsp;</td>
+<td>&mdash;&mdash;&mdash;</td>
+</tr>
+<tr>
+<td style="padding-left: 5em;">Cost of labor making 418 pipes.</td>
+<td align="right">161.86</td>
+<td>Pesos.</td>
+</tr>
+<tr>
+<td style="padding-left: 5em;">Cost of labor per pipe.</td>
+<td align="right">0.38</td>
+<td>Peso.</td>
+</tr>
+<tr>
+<td>&nbsp;</td>
+</tr>
+<tr valign="top">
+<td><span class="smcap">Material.</span></td>
+<td>&nbsp;</td>
+<td>&nbsp;</td>
+</tr>
+<tr>
+<td>&nbsp;</td>
+</tr>
+<tr>
+<td>Cement, 118<sup>1</sup>&frasl;<sub>2</sub> bbl., at 6.40 pesos per bbl., at pipe-making yard.</td>
+<td align="right">758.40</td>
+<td>Pesos.</td>
+</tr>
+<tr>
+<td>Sand, 24.6 cu.&nbsp;m., at 2.50 pesos per cu.&nbsp;m.</td>
+<td align="right">61.50</td>
+<td align="center">"</td>
+</tr>
+<tr>
+<td>Rock, 21.6 cu.&nbsp;m., at 2.00 pesos per cu.&nbsp;m.</td>
+<td align="right">43.20</td>
+<td align="center">"</td>
+</tr>
+<tr>
+<td>No. 6 wire, 3,362 lin. m.</td>
+<td align="right">55.56</td>
+<td align="center">"</td>
+</tr>
+<tr>
+<td>Lime.</td>
+<td align="right">1.50</td>
+<td align="center">"</td>
+</tr>
+<tr>
+<td>&nbsp;</td>
+<td>&mdash;&mdash;&mdash;</td>
+</tr>
+<tr>
+<td style="padding-left: 5em;">Cost of material for 418 pipes.</td>
+<td align="right">920.16</td>
+<td>Pesos.</td>
+</tr>
+<tr>
+<td>&nbsp;</td>
+</tr>
+<tr>
+<td style="padding-left: 5em;">Cost of material per pipe.</td>
+<td align="right">2.20</td>
+<td align="center">"</td>
+</tr>
+<tr>
+<td style="padding-left: 5em;">Add cost of labor.</td>
+<td align="right">0.38</td>
+<td align="center">"</td>
+</tr>
+<tr>
+<td>&nbsp;</td>
+</tr>
+<tr>
+<td style="padding-left: 5em;">Total cost per pipe for labor and material.</td>
+<td align="right">2.58</td>
+<td>Pesos.</td>
+</tr>
+<tr>
+<td style="padding-left: 5em;">Equivalent to 4.23 pesos per lin. m., or 1.29 pesos per lin. ft.</td>
+</tr>
+</table>
+
+<p><i>Excavation for Pipe Line and Siphons.</i>&mdash;The excavation for the pipe
+line and for bridge works, etc., was let by contract to Messrs. Scott
+and Lee, of Monterrey, under three classifications:</p>
+
+<p class="blockquot" style="text-indent: -1.5em; padding-left: 1.5em">(1) "All material which in the judgment of the Engineer can be
+economically loosened with picks and handled with shovels."</p>
+
+<p class="blockquot" style="text-indent: -1.5em; padding-left: 1.5em">(2) "Indurated earth or gravel, shale or rock which can be loosened
+without blasting, and 'sillar', locally so-called, whether pure or
+mixed with other substances, and whether it requires blasting or
+not."</p>
+
+<p class="blockquot" style="text-indent: -1.5em; padding-left: 1.5em">(3) "All rock not included in the above which requires drilling or
+blasting."</p>
+
+<p>Locally, this classification is well understood, particularly No. 2, as
+it covers the sillar soils which are common in the neighborhood of
+<!--514.png--><span class="pagenum">502</span>Monterrey.
+The contract prices were: No. 1, 50 cents; No. 2, 1.50
+pesos; and No. 3, 2.50 pesos per cu. m. These prices were over and above
+the clearing and grubbing of the line, which was paid for at the rate of
+100 pesos per hectare.</p>
+
+<p>The route of the pipe line being along broken country, at some points
+difficult of access, service roadways, about 3 m. wide, for hauling
+material were constructed, and, for about 7 km., a roadway was made
+along the line of the trench.</p>
+
+<p>The prices for the roadway, under the above classification, were: For
+No. 1, 35 cents; No. 2, 1.50 pesos; and No. 3, 2.50 pesos per cu. m.</p>
+
+<p>The trenches were excavated 5 cm. below the required finishing depth, to
+allow for grading the pipes in selected material, and were taken out to
+an average width of 40 cm. greater than the outside diameter of the
+pipe, to allow for their proper jointing, and also to give sufficient
+room to roll the pipes in the trenches.</p>
+
+<p>The final quantities of excavation were:</p>
+
+<div class="center">
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align="left"><span class="smcap">Trench:</span></td><td align="left">No. 1</td><td align="right">11,115</td><td align="left">cu. m.</td></tr>
+<tr><td align="left"></td><td align="left">No. 2</td><td align="right">18,096</td><td align="center">"</td></tr>
+<tr><td align="left"></td><td align="left">No. 3</td><td align="right">6,650</td><td align="center">"</td></tr>
+<tr><td align="left"></td><td align="left"></td><td align="right">&mdash;&mdash;&mdash;</td></tr>
+<tr><td align="left"></td><td align="left">Total</td><td align="right">35,861</td><td align="left">cu. m.</td></tr>
+<tr><td>&nbsp;</td></tr>
+<tr><td align="left"><span class="smcap">Roadways:</span></td><td>No. 1</td><td align="right">4,165</td><td align="left">cu. m.</td></tr>
+<tr><td align="left"></td><td align="left">No. 2</td><td align="right">1,999</td><td align="center">"</td></tr>
+<tr><td align="left"></td><td align="left">No. 3</td><td align="right">30</td><td align="center">"</td></tr>
+<tr><td align="left"></td><td align="left"></td><td align="right">&mdash;&mdash;&mdash;</td></tr>
+<tr><td align="left"></td><td align="left">Total</td><td align="right">6,194</td><td align="left">cu. m.</td></tr>
+</table></div>
+
+<p>The route of the pipe line was laid out so as to obtain an average fill
+of not more than 1 m. over the tops of the pipes, but in some cases the
+cuts, for short lengths, were 3 m. deep. The excavation for this work
+began in June, 1907.</p>
+
+<p><i>Hauling Pipes.</i>&mdash;The pipes were hauled to the site of the work with
+ox-carts and mule teams. The cost of hauling varied from 25 cents per
+pipe at the lower end, to 1 peso per pipe at the upper and,
+comparatively speaking, inaccessible portion of the line. The weight of
+each 55.9-cm. pipe was about 182 kg.; that of each 63.5-cm. pipe was
+about 216 kg.</p>
+
+<p>The breakages in all the pipes cast at the pipe yard amounted to about
+1%, due chiefly to unloading them carelessly near the pipe line.</p>
+<!--515.png--><p><span class="pagenum">503</span></p>
+<p><i>Pipe Laying.</i>&mdash;The pipe-laying gang was composed of 7 Mexicans under
+the direction of an American foreman, who was in charge of several
+gangs. One gang could lay daily from 60 to 73 m. (from 100 to 120
+pipes). The following was the ordinary pay-roll for one gang:</p>
+
+<div class="center">
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align="left">1 Foreman at 8 pesos (proportion).</td><td align="left">2.00</td><td align="left">pesos.</td></tr>
+<tr><td align="left">1 Pipe layer at 3 pesos.</td><td align="left">3.00</td><td align="left">"</td></tr>
+<tr><td align="left">1 Pipe layer's assistant at 2 pesos.</td><td align="left">2.00</td><td align="left">"</td></tr>
+<tr><td align="left">1 Cement mixer at 2 pesos.</td><td align="left">2.00</td><td align="left">"</td></tr>
+<tr><td align="left">2 Outside plasterers at 2.50 pesos.</td><td align="left">5.00</td><td align="left">"</td></tr>
+<tr><td align="left">2 Inside plasterers at 2.25 pesos.</td><td align="left">4.50</td><td align="left">"</td></tr>
+<tr><td align="left">1 Water boy at 0.50 peso.</td><td align="left">0.50</td><td align="left">"</td></tr>
+<tr><td></td><td align="left">&mdash;&mdash;&mdash;</td></tr>
+<tr><td align="right">Total.</td><td align="left">20.00</td><td align="left">pesos.</td></tr>
+</table></div>
+
+<p>This brings the average cost of laying the pipes to 32.8 cents per lin.
+m.</p>
+
+<p>The pipes were jointed with 1:2 cement mortar, the outer joint being
+rounded over both pipes for a width of 12<sup>1</sup>&frasl;<sub>2</sub> cm. (5 in.) and a height
+of about 19 mm. (<sup>3</sup>&frasl;<sub>4</sub> in.). In making these joints the pipe layers wore
+rubber gloves. The joints were kept moist, and the trench was
+back-filled with fine, screened material to a depth of 10 cm. above the
+top of the pipe. Inside, the joints were carefully caulked with cement
+and rendered smooth, the plasterers working continuously along with the
+pipe layers, doing from 20 to 35 m. at a time. Water had to be conveyed
+to the trenches by barrels on burros, and during the dry season it was
+sometimes carried 5 or 6 km.</p>
+
+<div class="figcenter" style="width: 592px;">
+<img src="images/i03.jpg" width="592" height="345" alt="Fig. 1." title="" />
+<span class="caption"><span class="smcap">Plate IV, Fig. 1.&mdash;Typical Reinforced Concrete Girder Bridge,
+Estanzuela Aqueduct.</span></span>
+</div>
+
+<div class="figcenter" style="width: 600px;">
+<img src="images/i04.jpg" width="600" height="346" alt="Fig. 2." title="" />
+<span class="caption"><span class="smcap">Plate IV, Fig. 2.&mdash;Elliptical Arch Bridge Carrying Estanzuela
+Aqueduct.</span></span>
+</div>
+
+<p><i>Bridges.</i>&mdash;The line as laid out passed over many gulches and dry
+arroyos, and these were crossed with reinforced concrete bridges of
+varying spans and heights, two being shown on Plate IV.</p>
+
+<p>These bridges were formed of continuous horizontal girders, 1.10 m. deep
+and 1 m. wide, with a cantilever overhang at the abutments, varying in
+length from 1 to 2 m., so as to avoid settlement between the pipes and
+the bridges. The bottom reinforcement consisted of from 2 to 6 twisted
+bars of mild steel, varying in different spans from 12.7 to 19 mm. (<sup>1</sup>&frasl;<sub>2</sub>
+to <sup>3</sup>&frasl;<sub>4</sub> in.) in diameter. The turned up bars were 28<sup>1</sup>&frasl;<sub>2</sub> mm.
+(1<sup>1</sup>&frasl;<sub>8</sub> in.)
+in diameter; they were placed on either side, carried over the upper
+part of the beams, and continued along the end for the
+<!--516.png--><span class="pagenum">504</span>overhanging part
+of the girder. These bars, when not obtainable of the full length, were
+spliced with a lap of 1.2 m. with No. 6 galvanized-steel wire. The
+vertical stirrups were 4.7 by 25.4 mm. (<sup>3</sup>&frasl;<sub>16</sub> by 1 in.), of mild steel;
+they were equally spaced 30.5 cm. (12 in.) apart, and carried all around
+the girders, lapping at the center about 15 cm. (6 in.), all the steel
+being carefully wired together before placing the concrete.</p>
+
+<p>The general type of the piers and abutments is shown by Fig. 1, Plate
+IV, and varies in height with practically every bridge,
+the foundations in every case resting on hard rock. The concrete for the
+girders was a 1:2<sup>1</sup>&frasl;<sub>2</sub>:3<sup>1</sup>&frasl;<sub>2</sub> mixture, the crushed stone used having all
+passed a mesh of 19 mm. (<sup>3</sup>&frasl;<sub>4</sub> in.). The piers were of 1:3<sup>1</sup>&frasl;<sub>2</sub>:5<sup>1</sup>&frasl;<sub>2</sub>
+concrete, and heavy "displacers" were embedded within them.</p>
+
+<p>The concrete was placed after the pipes had been laid through the form
+by the pipe contractor, the joints being kept clear of the bottom to the
+required distance by small moulded concrete blocks. The tops of the
+girders were moulded to a slightly segmental form. The bridges were all
+kept watered for about 15 days, and the forms were not struck for 28
+days after placing. At Station 13.4 the pipes were carried over a
+picturesque arroyo on an elliptical arched bridge (Fig. 2, Plate
+IV) of 11 m. clear span.</p>
+
+<p>The abutments of all bridges were protected by rubble walls in cement
+mortar carried up 60 cm. above the tops of the girders.</p>
+
+<p>The contract price for the concrete work of these bridges, the Company
+furnishing the steel and cement, was 14 pesos per cu. m., and for
+placing reinforcing steel 35 pesos per metric ton (2,204 lb.).</p>
+
+<p>There are 49 single-span bridges, the larger spans being 9.10 m.; 8
+two-span, and 11 three-span bridges, their total length, including the
+overhang, amounting to 870.50 m., or 4<sup>1</sup>&frasl;<sub>2</sub>% of the whole length of
+aqueduct.</p>
+
+<p><i>Concrete Aprons.</i>&mdash;At 76 points there were small depressions which did
+not necessitate the construction of bridges, and at these places the
+pipes were encased in blocks of concrete carried up the hillside in the
+form of an apron having small abutment walls from 1 to 2 m. apart. This
+also served to protect the pipes from scouring action during rainstorms.
+At the upper end of the line, near the intake, the pipe had to be
+protected by concrete continuously for a distance of about 300 m., in
+order to prevent damage from falling rocks.</p>
+<!--517.png--><p><span class="pagenum">505</span></p>
+
+<div class="figcenter" style="width: 352px;">
+<img src="images/i05.jpg" width="352" height="600" alt="Fig. 1." title="" />
+<span class="caption"><span class="smcap">Plate V, Fig. 1.&mdash;Ventilating Column and Entrance Manhole,
+Estanzuela Aqueduct.</span></span>
+</div>
+
+<p><i>Ventilators and Manholes.</i>&mdash;Along the route of the concrete pipe there
+are 27 ventilators, one of which, together with an entrance manhole, is
+shown by Fig. 1, Plate V. They consisted of simple
+concrete columns, 3.35 m. high, above the ground line, the interior of
+the shafts being formed of fire-clay pipes, 15 cm. (6 in.) in diameter.
+At each ventilator the pipe was cut and a block of concrete, the width
+of the trench, filled in as a foundation. Entrance manholes were also
+placed at 49 points, at 27 of which they immediately adjoined the
+ventilating columns.</p>
+
+<p><i>Estanzuela Tunnel.</i>&mdash;At 1,560 m. from the intake at Estanzuela, the
+conduit is laid through a tunnel 281 m. long. The tunnel was driven
+through hard calcareous strata from the open cuttings at each end. The
+inner dimensions were trimmed to approximately 2 m. high and 1<sup>1</sup>&frasl;<sub>2</sub> m.
+wide. At the ends of the tunnel the rock was moderately easy to take
+out, but the inner section was very hard and difficult to blast.
+Ordinary hand drilling was adopted, and the actual cost of driving
+varied from 28 pesos per lin. m. at the ends to 50 pesos in the center.</p>
+
+<p>The pipes were laid through the tunnel in the ordinary way, and
+back-filled from the center, so as to give a cover of about 45 cm. above
+to protect them from falling pieces of shale.</p>
+
+<div class="figcenter" style="width: 399px;">
+<img src="images/i06.jpg" width="399" height="600" alt="Fig. 2" title="" />
+<span class="caption"><span class="smcap">Plate V, Fig. 2.&mdash;Placing Concrete Pipes in Forms for Bridge
+Crossing at North End of Tunnel, Estanzuela Aqueduct.</span></span>
+</div>
+
+<p><i>Siphons.</i>&mdash;It has already been mentioned that there are 6 cast-iron
+pipe siphons. The head on these varies between 10 and 38 m. All are
+provided with special inlets and outlets, forming combined overflow and
+ventilating chambers, and have wooden hand-sluices to divert the water
+when necessary. The bottoms of all siphons are provided with 20-cm.
+cast-iron scour-out pipes, fitted with valves, and carried down to a
+lower point to obtain a free outlet. The valve-boxes are protected by
+being placed in heavy concrete chambers carried up above the level of
+ordinary floods.</p>
+
+<p>The siphons are formed of cast-iron socket pipes, 3.65 m. (12 ft.) long,
+caulked in the ordinary way with lead joints. The thickness of the
+45.7-cm. (18-in.) pipes is 19 mm.; that of the 50.8-cm. pipes is 21 mm.
+On the steep hillsides the pipes are anchored securely to the rock in
+concrete blocks reinforced with heavy iron chains. In some cases these
+siphons were difficult of access, but ox-teams hauled the pipes in a
+very efficient and satisfactory manner.</p>
+
+<p><i>Overflow Chambers.</i>&mdash;The ordinary overflows, of which there are 14, are
+similar in design to the siphon inlets.</p>
+<!--518.png--><p><span class="pagenum"><a name="Page_506" id="Page_506">506</a></span></p>
+<p><i>Testing, etc.</i>&mdash;When the line was completed it was tested for
+water-tightness, and the loss was found to be about 5%, part of which
+was probably due to absorption. At a later date it was found that the
+waters of the Estanzuela River, which contain 150 parts of calcium
+carbonate (CaCO<sub>3</sub>) per million, deposited a very fine film of lime on
+the interior of the pipes, completely filling any pores there might have
+been. At the present time there is no measurable leakage, thus proving
+that the character of the work is very satisfactory.</p>
+
+<p>The water was turned into the conduit on June 11th, 1908, and delivered
+to the city on the following day through a by-pass, before the reservoir
+was completed.</p>
+
+<p>The pipe line is patrolled daily by an inspector with the authority of a
+gendarme, so as to prevent the unlawful abstraction of water, a very
+necessary precaution in so dry a country.</p>
+
+
+<h2><span class="smcap"><a name="South_Distributing_Reservoir" id="South_Distributing_Reservoir"></a>South Distributing Reservoir.</span></h2>
+
+<p>The distributing reservoir for the Estanzuela supply is at Guadalupe, on
+the foot-hills to the south of the Santa Catarina River, about 2 km.
+from the center of the city. The reservoir is a covered one, of
+reinforced concrete, and its capacity is 38,000,000 liters (10,000,000
+U. S. gal.).</p>
+
+<div class="figcenter" style="width: 600px;">
+<img src="images/i07.jpg" width="600" height="358" alt="Fig. 1." title="" />
+<span class="caption"><span class="smcap">Plate VIII, Fig. 1.&mdash;General View of Excavation and Embankment for
+South Reservoir Before Lining.</span></span>
+</div>
+
+<p><i>Excavation and Embankment.</i>&mdash;The heavy slope of the ground at the
+selected site made the circular form the most desirable. On the low side
+the ground was excavated about 2 m. below the original ground line,
+while the excavation at the upper part of the slope was about 12 m.
+deep. The excavated material consisted chiefly of sillar and limestone
+conglomerate, which when broken up forms a calcareous clay of an
+excellent character for the formation of embankments, when proper care
+is taken. The dimensions fixed for the internal diameter of the finished
+concrete work of the reservoir were: 81 m. (265.68 ft.) at the top, and
+a depth of water of 9 m., with sides sloping 55 in 100.</p>
+
+<div class="figright" style="width: 259px;"><a name="i507" id="i507"></a>
+<img src="images/i507t.jpg" width="259" height="300" alt="Fig. 10." title="" />
+<span class="caption"><span class="smcap">Fig. 10.&mdash;South Reservoir Plan Of
+Excavation.</span></span><br />
+<a href="images/i507.jpg" target="_blank">Larger.</a>
+</div>
+
+<p>Fig. 10 is a plan of the reservoir, with a cross-section of the
+excavation and embankment. On the lower side the original ground line
+was cut down in steps, and all loose earth, roots, etc., were carefully
+removed. The floor of the reservoir was chiefly sillar conglomerate, a
+hard material that required a considerable amount of blasting for its
+removal. The embankments were formed in 10-cm. layers
+<!--519.png--><span class="pagenum">507</span>of sillar and
+conglomerate broken into small fragments and then rolled with 3-ton
+sectional rollers drawn by teams of 4 and 6 mules, which assisted in
+disintegrating the mass thoroughly, and produced by constant wetting a
+homogeneous and compact clay. The excavation and embankment were left so
+that 15 cm. of trimming could be done at a later date, immediately prior
+to the lining of the reservoir. The excavated material amounted to about
+34,000 cu. m., and, of this quantity, 31,500 cu. m. were used to form
+the embankment; the
+<!--520.png--><span class="pagenum">508</span>remainder
+was taken to a spoil bank immediately
+adjoining, the black earth stripping being separated and reserved for
+covering the reservoir, etc. The contract prices for the excavated
+material placed in the embankment were:</p>
+
+<div class="center">
+<table border="0" cellpadding="3" cellspacing="0" summary="">
+<tr><td align="left"></td><td align="right">Pesos per<br />cubic meter</td></tr>
+<tr><td align="left">Class 1.&mdash;Material which could be removed by plows and scrapers</td><td align="right">0.60</td></tr>
+<tr><td align="left">Class 2.&mdash;This consisted chiefly of "sillar"</td><td align="right">1.09</td></tr>
+<tr><td align="left">Class 3.&mdash;Limestone conglomerate (requiring blasting)</td><td align="right">1.65</td></tr>
+</table></div>
+
+<p>The prices (for the same classification) for material taken to the spoil
+bank, were 0.40, 0.80, and 1.40 pesos, respectively. Of the material
+taken out, 15% came under No. 1 classification, 80% under No. 2, and 5%
+under No. 3.</p>
+
+<p>The excavation was begun at the end of May, 1907, and completed in
+January, 1908, by Scott and Lee, the contractors. The embankments were
+then allowed to stand until the beginning of July, 1908, to permit the
+whole to become thoroughly settled and consolidated prior to beginning
+the lining. In July the work of trimming the embankments and excavating
+for the foundations of the reservoir columns was commenced, under the
+Company's own administration, which completed the entire work.</p>
+
+<div class="figcenter" style="width: 300px;"><a name="p06" id="p06"></a>
+<img src="images/p06t.jpg" width="300" height="222" alt="Plate VI." title="" />
+<span class="caption"><span class="smcap">Plate VI.&mdash;Details Of Beams And Columns For South Reservoir.</span></span><br />
+<a href="images/p06.png" target="_blank">Larger.</a>
+</div>
+
+<div class="figcenter" style="width: 300px;"><a name="p07" id="p07"></a>
+<img src="images/p07t.jpg" width="300" height="222" alt="Plate VIII" title="" />
+<span class="caption"><span class="smcap">Plate VIII, Fig. 1.&mdash;Details Of Forms For South Reservoir.</span></span><br />
+<a href="images/p07.png" target="_blank">Larger.</a>
+</div>
+
+<div class="figcenter" style="width: 700px;">
+<img src="images/i08.jpg" width="700" height="476" alt="Fig. 2" title="" />
+<span class="caption"><span class="smcap">Plate VIII, Fig. 2.&mdash;View of Western Half of South Reservoir, Showing
+Final Setting Up of Derrick on Central Columns.</span></span>
+</div>
+
+<p><i>Concrete Lining and Roof.</i>&mdash;The general arrangement and details of the
+side-walls, columns, and roof are shown on Plates VI, VII, VIII and <a href="#i09">IX</a>. The
+principal feature consists in dividing the reservoir into radial
+sections and supporting the roof on 135 primary and 670 secondary beams,
+from 135 columns, spaced as follows:</p>
+
+<div class="center">
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td>Outer</td><td>ring,</td><td>at</td><td>34.25</td><td>m.</td><td>from center</td><td>40</td><td>columns.</td></tr>
+<tr><td> 2d</td><td>"</td><td>"</td><td>27.88</td><td>"</td><td>"</td><td>40</td><td>"</td></tr>
+<tr><td> 3d</td><td>"</td><td>"</td><td>21.51</td><td>"</td><td>"</td><td>20</td><td>"</td></tr>
+<tr><td> 4th</td><td>"</td><td>"</td><td>15.41</td><td>"</td><td>"</td><td>20</td><td>"</td></tr>
+<tr><td> 5th</td><td>"</td><td>"</td><td>8.77</td><td>"</td><td>"</td><td>10</td><td>"</td></tr>
+<tr><td> 6th</td><td>"</td><td>"</td><td>2.40</td><td>"</td><td>"</td><td>5</td><td>"</td></tr>
+<tr><td></td><td></td><td></td><td></td><td></td><td></td><td>&mdash;&mdash;</td></tr>
+<tr><td></td><td></td><td></td><td></td><td></td><td>Total</td><td>135</td><td>columns.</td></tr>
+</table></div>
+
+<p>The inner bottom diameter of the reservoir is 70.32 m. (230.64 ft.); the
+upper inside diameter is 81 m. (265.68 ft.); the water depth at the
+overflow level is 9 m. (29<sup>1</sup>&frasl;<sub>2</sub> ft).</p>
+<!--521.png--><p><span class="pagenum">509</span></p>
+<p>The roof was designed to carry a dead load (the earth cover) of 150 lb.
+per sq. ft., and a live load of 100 lb. The maximum compressive fiber
+stress in the concrete was assumed at 550 lb. per sq. in. for the beams,
+and at 350 lb. for the columns, a low figure, because of their eccentric
+loading. The tensile strength of the steel was taken at 14,500 and
+16,000 lb. per sq. in. The twisted steel used for the column
+reinforcement was made at the local steel plant, but for the beams,
+etc., a twisted lug bar, of higher quality and greater permissible
+tensile stress, was used. The total quantity of steel used was 178 tons.
+It was calculated that the load on the column foundations would not
+exceed 1<sup>1</sup>&frasl;<sub>4</sub> tons per sq. ft. With
+the exception of the side-wall and
+floor, all the concrete was reinforced with steel, of the sizes and
+spacing shown on <a href="#p06">Plate VI</a>.</p>
+
+<p><i>General Construction and Erection Scheme.</i>&mdash;The question of ordinary
+forms, requiring very heavy timber work, was a serious one, as suitable
+lumber is very expensive in Mexico; and the necessity of finishing this
+reservoir before the end of the first term allowed under the concession,
+which expired on December 31st, 1908, led to the adoption of what the
+writer believes is an original scheme for so large a structure. This
+scheme was to cast the columns in short sections, mould the radial and
+secondary beams as separate members, and then place them in position
+with derricks. At the same time, in the case of the beams, it was
+important not to sacrifice either the benefit of that part of the slab
+which is ordinarily assumed to act as a part of the beam, or the
+additional strength due to continuity; and, in case of the columns, the
+strength due to the reinforcement extending from the foundation to the
+beams.</p>
+
+<p>The T-beam section was secured by notching the tops of the moulded
+members, with notches 10 cm. deep, throughout the lengths of the beams,
+as shown on <a href="#p06">Plate VI</a>. A computation of the maximum flange
+increment shows that these notches are sufficient to transfer the flange
+stresses to the stem, but, for additional security, flat steel bars were
+bent to a Z-shape and embedded in the top of the beam, about 60 cm.
+apart. Continuity in the beams was secured by carrying the steel to the
+tops of the beams over all supports, and, after erection, concreting
+them into the roof slab. The secondary beams, after casting, were
+dropped into recesses left in the radial beams for the purpose.</p>
+
+<!--522.png--><p><span class="pagenum">510</span></p>
+
+<p><i>Concreting, Mixing, etc.</i>&mdash;The radial beams and column sections were
+cast as nearly as possible under their ultimate positions; the secondary
+beams were cast outside and immediately adjoining the reservoir.</p>
+
+<p>The rock and sand was brought from the Company's crushing plant, in
+3-cu. yd., side-dump cars, running on a 30-in. track by gravity a
+distance of 1 km., the last 150 m. requiring hauling with 6 mules. The
+cars returned all the way to the crusher by gravity. These cars dumped
+the material into bins on the high ground above the reservoir; from
+there it was hoppered into cars which carried to the mixer all the
+material for one batch of concrete. Two No. 1 Smith mixers were used,
+and from 25 to 30 batches per hour could be handled in each machine.</p>
+
+<p>The concrete was transported from the mixers to place in <sup>1</sup>&frasl;<sub>2</sub>-cu. yd.,
+18-in. gauge, swivel, steel dump-cars pushed by two men. All the
+concrete used in the bottom of the reservoir, for the main beams,
+columns, and floor, amounting to about 2,460 cu. m., was dumped through
+a chute into smaller cars. The chute had so many baffle-plates and bolts
+that it resembled a gravity mixer, but, although it was 12 m. long, it
+effectively prevented the separation of the materials.</p>
+
+<p><i>Concrete Placing and Moulding.</i>&mdash;The square foundations for the columns
+were deposited <i>in situ</i>, a recess being left for the reception of the
+pedestals, which were moulded in place afterward. The capitals and
+pedestals were cast in one piece, and the columns in 1.21-m. (48-in.)
+sections, eight 5-cm. holes being left in them by using wrought-iron
+pipes, held in place by templates and removed when the castings were
+about 3 hours old. The columns were erected by threading them on the
+15.8-mm. (<sup>5</sup>&frasl;<sub>8</sub>-in.) reinforcing rods, which extended from the pedestals
+up through the capitals. The rods were in two lengths, arranged to lap
+alternately at one-fourth, the center, and three-fourths of the height
+of the columns. In erection, a light timber frame was used in
+conjunction with the derrick, and, as the columns were placed, the
+reinforcing steel was grouted solid with 1:2 cement mortar.</p>
+
+<p>All the erection was done with a combined stiff-leg or guy derrick,
+having an 80-ft. boom and a 50-ft. mast, and fitted with a 30-h.p.
+Lambert hoisting engine. The derrick was erected seven times at the
+circumference, and its final position was on top of the center columns.
+The moving of the derrick a distance of about 45 m. and its subsequent
+<!--525.png--><span class="pagenum">511</span>erection
+occupied usually about 48 hours. The erection work was carried
+on continuously, day and night, the placing of the whole of the radial
+and secondary beams and columns occupying 2<sup>1</sup>&frasl;<sub>2</sub> months.</p>
+
+<p><i>Forms.</i>&mdash;As the erection scheme was designed to reduce the cost of
+forms, economical construction was of considerable importance. The wall
+was formed in 40 panels, about 6 m. wide and 11.27 m. high. The chief
+object in arranging them in this manner was to permit an expansion
+joint, 30 cm. wide, at each panel; this joint was not filled until after
+the completion of the roof, when the temperature inside the reservoir
+was uniform and not subjected to such great fluctuations as if exposed
+alternately to the hot sun and comparatively cool nights. The range of
+temperature during the construction period sometimes amounted to 80°
+Fahr. in 24 hours.</p>
+
+<p>The expansion joints were left to the last, when a uniform temperature
+of about 70° inside permitted the filling of the joints, thus avoiding
+all trouble from expansion cracks.</p>
+
+<p>The forms are shown in detail on <a href="#p07">Plate VII</a>. They
+consisted of shutters stiffened with four trapezoidal trusses. The
+bottom posts of the trusses were fixed in holes formed in the foundation
+block; they were propped back from the embankment at the top, and
+secured to anchorages by iron rods.</p>
+
+<p>Six sets of these forms were used to construct the whole wall. The
+concrete was placed in position through stove-pipe chutes, 20 cm. in
+diameter, in continuous layers, the workmen treading and spading it well
+as it was deposited. The forms were allowed to remain 4 or 5 days, and
+were then struck and removed to another section. The pedestals and
+capital forms were of lumber, and five of each were used to cast the
+total number required. In the column sections the outer steel forms used
+in the manufacture of the Estanzuela pipes were adapted for this
+purpose. The radial beam forms, shown on <a href="#p07">Plate VII</a>, were
+arranged with internal wedge-shaped blocks to mould accurately the
+recess for the secondary beams. The bottom forms were left attached to
+the beams for 28 days, but the sides and ends were removed after 24
+hours. Eight forms were sufficient for the whole 135 beams.</p>
+
+<p>For the secondary beams, 29 forms were used for the 670 beams, the
+bottom lumber also being left until they were mature for handling.</p>
+
+<p>By referring to the cross-section of the secondary beam, it will
+<!--526.png--><span class="pagenum">512</span>be
+noticed that it is jug-shaped, shelves being left on either side for the
+support of the roof forms, which were placed after the secondary beams
+had been properly grouted to the radial ones. The lagging was laid
+diagonally, so that the short diameter was slightly greater than the
+distance between the beams. This greatly facilitated the removal of the
+lagging, as it was merely necessary to strike the wedge-shaped fillets
+beneath, and turn them clockwise, after tearing out the end lagging.</p>
+
+<div class="figcenter" style="width: 600px;"><a name="i09" id="i09"></a>
+<img src="images/i09.jpg" width="600" height="352" alt="Fig. 1." title="" />
+<span class="caption"><span class="smcap">Plate IX, Fig. 1.&mdash;View of Separately Moulded Secondary Beams in
+Yard Below South Reservoir.</span></span>
+</div>
+
+<div class="figcenter" style="width: 576px;">
+<img src="images/i10.jpg" width="576" height="410" alt="Fig. 2." title="" />
+<span class="caption"><span class="smcap">Plate IX, Fig. 2.&mdash;Setting Primary Beams, South
+Reservoir.</span></span>
+</div>
+
+<p>The writer believes that the adoption of forms of this type, rather than
+the ordinary kind, led to a saving of lumber of about 400,000 ft. b. m.
+During the erection and placing of the concrete, all the joining
+surfaces were carefully picked and cleaned, particular care being taken
+at the junction of the secondary with the radial beams, and the upper
+surfaces of all beams before laying the roof slab.</p>
+
+<p>After the greater part of the roof was completed, the floor was laid in
+those sections where it was protected from the sun's rays. The concrete
+was placed in two 15-cm. thicknesses, and the work was carried on night
+and day, without any joints. The laying of the floor occupied 8 days, or
+an average of nearly 100 cu. m. daily.</p>
+
+<div class="figcenter" style="width: 375px;">
+<img src="images/i11.jpg" width="375" height="600" alt="Fig. 1." title="" />
+<span class="caption"><span class="smcap">Plate X, Fig. 1.&mdash;View of Completed Section of South Reservoir.
+Expansion Joints in Side-Wall Not Yet Filled.</span></span>
+</div>
+
+<p><i>Proportions of Concrete.</i>&mdash;All the concrete work was brought to a
+smooth face by careful spading, no plastering being used throughout the
+reservoir, except in the superstructures. The work was kept well watered
+in every case for about 15 days. The whole of the concrete work in
+connection with the reservoir was completed in 5<sup>1</sup>&frasl;<sub>2</sub> months. The
+concrete for the columns and foundations was a 1:3:5 mixture, the
+aggregate consisting of equal parts of 19-mm. (<sup>3</sup>&frasl;<sub>4</sub>-in.) and 38-mm.
+(1<sup>1</sup>&frasl;<sub>2</sub>-in.) crushed stone. The remainder of the concrete, except that
+for the roof, was a 1:2:4 mixture, the aggregate also consisting of
+equal parts of 19-and 38-mm. stone. With the exception of a short length
+of the side-walls, the sand used was that manufactured by the Company.
+When the crushing plant was unable to produce all the sand required, the
+Hornos sand (see Table 3) was used in the side-walls in equal
+proportions with the crusher sand.</p>
+
+<p><i>Reservoir Outlet and Entrance Tower.</i>&mdash;The outlet, 61 cm. (24 in.) in
+diameter, leads from a well in the center of the reservoir and passes
+under the floor and embankment to an outside valve-pit, 89 m. from the
+center. This pipe was laid in a trench in a solid cutting before the
+construction of the embankment, and was encased in 1:4:8 concrete.
+<!--529.png--><span class="pagenum">513</span>Where
+it passes under the embankment a 1:2:4 concrete cut-off wall, 3.6
+m. wide, 2.5 m. high, and 1 m. thick, was placed across it at right
+angles. The cast-iron pipe is curved upward in the central well, and has
+a bellmouth on which rests a movable circular copper screen.</p>
+
+<p>Above the outlet well, and on the roof of the reservoir, there is a
+central tower, giving access to the interior by a steel stairway. This
+tower also serves as a main ventilating shaft, and in it are arranged
+the guide-screens and gearing for raising them for cleaning purposes. In
+addition to the ventilation provided in the tower, 20 circular openings,
+30 cm. in diameter, are carried through the roof of the reservoir at the
+circumference and into the parapet walls.</p>
+
+<p><i>Inlet Gate-House, etc.</i>&mdash;The inlet gate-house is above the reservoir
+and about 54<sup>1</sup>&frasl;<sub>2</sub> m. from its center. The conduit enters at 589.00 m.
+above datum, and the gate-house contains the valves for controlling the
+inlet pipe to the reservoir, the by-pass, overflow, scour-out pipe, and
+the copper screens. The inlet, which is 45.7 cm. (18 in.) in diameter,
+is of cast-iron flanged pipes, carried on iron hangers on the side-wall
+of the reservoir, and, at a point 90 cm. above the floor level, it is
+turned at right angles to the side-wall and carried on concrete piers to
+the center of the first row of columns. The end of the pipe is closed by
+a blank flange, and the water is deflected at right angles through two
+30-cm. (12-in.) branches, for the purpose of setting up a slight
+circular motion as it enters the reservoir.</p>
+
+<p>The valve-pit is clear of the embankment, and in it are brought together
+the main supply and by-pass pipes on which are placed two 61-cm.
+(24-in.) sluice-valves; and between them there is a 20-cm. (8-in.)
+scour-out pipe, for emptying the reservoir into an adjoining arroyo. The
+arrangement of the valves gives complete control over the contents of
+the reservoir.</p>
+
+<p><i>Venturi Meter-House.</i>&mdash;Fig. 11 shows the arrangement of the Venturi
+meter and its automatic register in a house over the main supply pipe.
+This house is designed to form a feature of the entrance gateway of the
+reservoir grounds, which cover an area of 12 hectares.</p>
+
+<div class="figright" style="width: 198px;">
+<img src="images/i515t.jpg" width="198" height="300" alt="Fig. 11." title="" />
+<span class="caption"><span class="smcap">Fig. 11.&mdash;Venturi Meter-House.</span></span><br />
+<a href="images/i515.png" target="_blank">Larger.</a>
+</div>
+
+<p><i>General.</i>&mdash;The roof of the reservoir has been laid out as a garden, and
+the embankments are turfed. The intention is to develop the Company's
+land as a public park, as it commands fine views of the city and the
+surrounding mountains. An inspector's house has been built, and a
+private telephone line provides for communication with the Estanzuela
+intake and also with the general offices in the city.</p>
+
+<div class="figcenter" style="width: 700px;">
+<img src="images/i19.jpg" width="700" height="204" alt="Fig. 1." title="" />
+<span class="caption"><span class="smcap">Plate XVIII, Fig. 1.&mdash;View of South Reservoir, Looking Toward the
+City.</span></span>
+</div>
+
+<!--530.png--><p><span class="pagenum"><a name="Page_514" id="Page_514">514</a></span></p>
+
+
+<h2><span class="smcap"><a name="San_Geronimo_Gravity_Supply" id="San_Geronimo_Gravity_Supply"></a>San Geronimo Gravity Supply.</span></h2>
+
+<p><i>Provisional Supply.</i>&mdash;It has already been stated that the Company began
+operations at San Geronimo in March, 1906, by sinking a well on the
+north bank of the Santa Catarina River at San Geronimo. At this point, a
+little later, a small steam pumping plant, sufficient to handle about
+8,000 liters per min., was installed. The lowest depth to which this
+well was ultimately sunk in water-bearing strata, was 7 m., the normal
+level of the water during 1906 and 1907 never falling lower than 569 m.
+above datum. Tests made from time to time during 1907-08, showed that
+this well was capable of supplying nearly 10,000,000 liters (264,000
+gal.) of water daily.</p>
+
+<p>The excellent supply yielded by this well made it desirable to adopt it
+immediately as a provisional measure, pending the completion of the
+larger works forming the western source of supply. To utilize the well
+to its fullest extent, a reinforced concrete reservoir, of 3,000,000
+liters capacity, was constructed on the south bank of the river, the top
+water level being 585 m. above datum, that is, at the same elevation as
+the proposed reservoir for the Estanzuela supply. The reservoir is 53.80
+m. long, 21 m. wide, and has a water depth of 3.25 m. at the overflow
+level. It is excavated on a steep hill slope, and has an earth
+embankment on the lower side. The lining is of concrete, 20 cm. thick,
+and the roof is of reinforced concrete composed of flat arches springing
+from beams carried on 46 by 35-cm. reinforced columns. There are 68 of
+these columns, and they are 3 m. apart longitudinally and 5 m. apart
+transversely. The roof was not constructed until October and November,
+1907, and prior to that time the necessity of covering the reservoir was
+amply demonstrated by the growth, during hot weather, of considerable
+quantities of green algæ, which had to be skimmed from the surface of
+the reservoir every few days.</p>
+
+<p>The delivery pipe from the pumping plant was originally of riveted steel
+and was asphalted. It was 30 cm. in diameter, 2 mm. in thickness, with
+slip joints, and where it crossed the river it was encased in concrete.
+This pipe was afterward replaced by a cast-iron pipe of the same
+diameter. The supply pipe to the city was also of sheet steel, 30 cm. in
+diameter. For a part of its length it was laid in the high ground of the
+south bank of the river, which it crossed near the western limits of the
+city, and was then connected to a 30-cm, cast-iron pipe in the
+<!--534.png--><span class="pagenum">516</span>distribution
+system. The total length of the pipe from the reservoir to
+the city distribution system was 2,850 m.</p>
+
+<p>This provisional pipe continued in service from October, 1906, until
+August 27th, 1909, when the river portion was completely swept away,
+together with the provisional pump-house at San Geronimo, during the
+great flood in the Santa Catarina River. Fortunately, the permanent
+supply works were completed at the time, so that the destruction of this
+pipe line, which had already served its original purpose, had no effect
+on the supply of water to the city.</p>
+
+<div class="figright" style="width: 300px;"><a name="p11" id="p11"></a>
+<img src="images/p11t.jpg" width="300" height="223" alt="Plate XI" title="" />
+<span class="caption"><span class="smcap">Plate XI.&mdash;Section of Infiltration Gallery,
+San Geronimo Gravity Supply.</span></span><br />
+<a href="images/p11.png" target="_blank">Larger.</a>
+</div>
+
+<p><i>Infiltration Gallery.</i>&mdash;The chief feature of the San Geronimo gravity
+supply is the infiltration gallery. By referring to the profile on Plate
+XI it will be seen that at this place there is a
+considerable area of what is undoubtedly water-bearing gravel. The main
+conditions were revealed by the borings previously carried across the
+valley, but the profile has been corrected to show the actual conditions
+as established at a subsequent date by shafts. Practically, the
+water-bearing strata are not limited merely to the sand and coarse
+gravels, as the clay formation lying above and below them is full of
+small gravel deposits containing considerable volumes of water. The main
+direction of the underflow is toward the east, and the hydraulic
+gradient, which was established from wells sunk farther west, was found
+to be approximately 1%, or practically the same as the average surface
+of the bed of the river above the line of the infiltration gallery.</p>
+
+<p>The general scheme for tapping this underflow was to drive a main
+gallery at the 560-m. level on a grade of 0.05%, which was sufficiently
+high to take the supply by gravity to the western reservoir, having a
+top water level at 558.75 m. above datum. This elevation is sufficient
+to give an excellent pressure over about 60% of the city, and a fair
+pressure to reach the upper stories of the highest houses, if required,
+over the whole supply district. From this gallery it was proposed to
+sink shafts at frequent intervals, for a total distance of 300 m.,
+carrying them below the gallery level, to tap any water-bearing gravels
+there might be in the clay formation underlying the gravels and sands.
+From the main gallery it was proposed to construct branch galleries up
+stream on a flat gradient, so as to obtain the advantage of an increased
+head due to the steep hydraulic gradient of the underflow water.</p>
+
+<div class="figright" style="width: 300px;">
+<img src="images/i517t.jpg" width="300" height="274" alt="Fig. 12." title="" />
+<span class="caption"><span class="smcap">Fig. 12.&mdash;Diagram Showing Variation In Water Plane 1905
+To March 1910 At San Geronimo.</span></span><br />
+<a href="images/i517.jpg" target="_blank">Larger.</a>
+</div>
+
+<p>In investigations of this kind, it is of first importance to have a
+continuous record of the level of the water plane, and Fig. 12 has been
+<!--537.png--><span class="pagenum">517</span>plotted
+to show its variation at San Geronimo from the beginning of
+1905 to March, 1910. From January, 1909, to March 31st, 1910, these
+levels are averages of daily readings taken in 9 shafts sunk along the
+proposed line of the infiltration gallery. In 1902 the water plane was
+standing at 570.18 m. above datum, but from that date until 1905 the
+writer has been unable to find any records. This diagram should be
+examined together with the rainfall diagram, Fig. 3, and it will be
+noticed that the fall in the water plane drops with the general scarcity
+of the rainfall during 1907-08, and until July, 1909. The year previous
+to July, 1909, is regarded, by many competent local observers to have
+been the longest period of extreme drought in 30 years in Nuevo León,
+and the evidence which the writer has been able to gather regarding
+stream flow in the neighborhood of Monterrey supports this view. The
+total rainfall at Monterrey for the year prior to July 1st, 1909,
+amounted to 9.98 in., or 4.16 in. less than the lowest record for any
+<!--538.png--><span class="pagenum">518</span>calender
+year since 1894, or, in other words, about 45% of the average
+annual rainfall.</p>
+
+<p>The lowest point to which the water plane dropped was during June and
+July, 1909, when the levels stood slightly above 565.00 m., or 5 m.
+above the level of the floor of the infiltration gallery. During this
+period pumping tests were made in the various wells, and from these it
+was quite clear that the infiltration gallery, if carried far enough to
+meet them all, would yield a supply of from 25,000,000 to 40,000,000
+liters daily. During the great rainfall of August, 1909, the water
+levels rose very rapidly; the heavy precipitation between August 9th and
+10th caused the level to rise to 568.00 m. in about 4 days, and 6 days
+after the great flood of August 27th, the water level, which had
+continued rising gradually, reached 571.40 m., and then fell gradually
+until at the end of March, 1910, it was practically the same as it had
+been from 1902 to 1905.</p>
+
+<div class="figright" style="width: 300px;">
+<img src="images/p12t.jpg" width="300" height="164" alt="Plate XII" title="" />
+<span class="caption"><span class="smcap">Plate XII.&mdash;San Geronimo Gravity Supply.</span></span><br />
+<a href="images/p12.png" target="_blank">Larger.</a>
+</div>
+
+<p>It should be noticed that the readings were taken in the shafts on the
+high ground to the west of the present river bed, and were independent
+of any flow there might be in the river. During times of ordinary floods
+in the river, it was very noticeable that, notwithstanding the fact that
+the river water might be turbid to an extreme degree, the well even in
+immediate proximity to the river bed did not show the least sign of
+discoloration.</p>
+
+<p><i>Design of Works.</i>&mdash;Plate XII shows the general design of
+the gravity scheme, which consists of a main tunnel 550 m. long and a
+concrete aqueduct, 1.06 m. (42 in.) in internal diameter and 2,311 m. in
+length, discharging into a low-service distributing reservoir at the
+extreme western limits of the city. The tunnel and aqueduct were laid on
+a gradient of 0.05%, and the latter was designed to discharge 55,000,000
+liters per day (22.8 cu. ft. per sec.) if flowing to its full capacity.</p>
+
+<p><i>Gravitation Tunnel.</i>&mdash;This tunnel, shown on Plate XII
+and Fig. 13, was completed prior to driving the
+infiltration gallery into the water-bearing gravel, so that the water
+encountered in the gallery could be easily drained off by gravity, thus
+avoiding a heavy outlay for pumping. The tunnel passes through various
+strata, the principal ones being calcareous shale, conglomerate, and
+gravels. The tunneling operations were carried on from 5 shafts, No. 1
+being 23 m. deep, and the others varying from 20 to 10 m. The shafts in
+loose ground were
+<!--540.png--><span class="pagenum">520</span>timbered
+in the usual way, having clear inside
+dimensions of 2 m. Shaft No. 1, which was entirely in shale, was taken
+out approximately to 3.35 m. in diameter, so as to permit it to be lined
+with concrete having a finished internal diameter of 2.43 m.</p>
+
+<div class="figright" style="width: 184px;"><a name="i519" id="i519"></a>
+<img src="images/i519t.jpg" width="184" height="300" alt="Fig. 13." title="" />
+<span class="caption"><span class="smcap">Fig. 13.&mdash;
+General Details San Geronimo Gravity Pipe Line.</span></span><br />
+<a href="images/i519.jpg" target="_blank">Larger.</a>
+</div>
+
+<p>Fig. 13 shows the details of the tunnel, which was lined with concrete,
+the bottom and sides being approximately 23 cm. (9 in.) thick. The
+interior dimension is 0.91 m. at the invert level and 1.016 m. at a
+height of 1.22 m., the corners between the side-walls and the floor
+being slightly curved. The arch is formed of two rings of brickwork in
+cement mortar, this thickness being increased in some lengths to three
+rings. Where the rock was in good condition, and not likely to
+disintegrate easily, the arch, for a distance of 90 m., was left
+unlined. Of the total distance of 550 m., careful timbering was required
+for 300 m. In lining the timbered portion of the tunnel with concrete,
+all the timber was removed, except in loose ground, where the laggings
+were left in position.</p>
+
+<p>While the tunnel was being driven, a start was made to drive the north
+end of the infiltration gallery, which was in rock for a distance of 44
+m. Water appeared at about 35 m., and then the work was temporarily
+suspended until the gravitation tunnel was completed and a length of the
+aqueduct had been constructed far enough down stream on the north bank
+of the river to permit of draining direct to the river. This point was
+reached at 1,170 m. from Shaft No. 1, and there a temporary overflow
+chamber was constructed.</p>
+
+<p>When the tunnel was completed, the two intermediate shafts were filled
+up, the remaining three being retained permanently. Shafts Nos. 2 and 3
+were lined with concrete, 76 cm. (30 in.) in internal diameter, and 23
+cm. thick. They were domed at the top to form circular openings to
+receive cast-iron covers. Progress on this tunnel was slow, taking from
+December, 1907, to November, 1908, to complete, owing chiefly to
+difficulties with an incompetent contractor. The contract was
+subsequently transferred to Mr. John Phillips, of Mexico City (who was
+also the contractor for the aqueduct), who completed it satisfactorily.</p>
+
+<p><i>Continuation of the Infiltration Gallery.</i>&mdash;When the aqueduct (to be
+referred to again) was completed as far as 1,170 m. from Shaft No. 1,
+the driving of the infiltration gallery, which was 2 m. high and 1<sup>1</sup>&frasl;<sub>2</sub>
+m. wide, was continued until gravel was encountered in the roof, at 44
+m.
+<!--541.png--><span class="pagenum">521</span>from
+the shaft. At this point the rock dipped at an angle of 45°,
+and the gravels contained quantities of large boulders mixed with fine
+sand; immediately after encountering the gravel, a flow of about 90
+liters per sec. was met, evidently coming through from a pot-hole in the
+shale. This quantity diminished in about 10 days to about one-fourth,
+but gradually increased again as the driving proceeded. The operations
+of driving the tunnel from 44 m. forward were begun in the dry season,
+in February, 1909, and the gravel was encountered for a distance of 24
+m., or up to 68 m. from the shaft. The center of this gravel bed was
+about 30 m. south of the old river channel, which had been continuously
+dry at the surface for several years. Up to 68 m. the work was very
+difficult, owing to the upper part being of loose gravel and the lower
+in very contorted shale. The timbering of the tunnel in the full gravel
+section consisted of heavy square settings, 1 m. apart. At 68 m. the
+clay and gravel formation was met, and the rate of progress then was
+about 4 or 5 m. a week. A short branch gallery was also driven about 7
+m. up stream near Shaft No. 2. The total distance the infiltration
+gallery was carried from Shaft No. 1, was 100 m., when the floods of
+August, 1909, caused its suspension.</p>
+
+<p>During the progress of the gallery, attempts were made to sink a 3<sup>1</sup>&frasl;<sub>2</sub>
+by 2-m. shaft at a point along the line of the infiltration gallery,
+about 130 m. from Shaft No. 1, but water in such abundance was
+encountered that it was practically impossible to sink it in the
+ordinary way more than about 6 m. deep, the quantity of water to be
+dealt with amounting to about 20,000,000 liters daily. Seven shafts were
+then sunk in the high ground to the north of the river, five of these
+being on the line of the gallery and two 30 m. westward. They were sunk
+during the dry season prior to July, 1909. These were ordinary timbered
+shafts, 2 m. square between the walings, and were carried to the depths
+shown on <a href="#p11">Plate XI</a>. In Shafts Nos. 5, 6, and 7 the water
+was flowing with considerable velocity, while Shaft No. 9 seemed to have
+penetrated a different water plane and one which was probably
+independent of that showing in any of the other shafts, in which the
+water was practically at a uniform level. The evidence obtained showed
+that if the gallery could be carried to Shafts Nos. 6 or 7 a great
+abundance of water would be intercepted. Owing to the difficulties of
+sinking ordinary shafts in the wide river channel, circular shafts were
+put down. These were 1.37 m. in internal diameter and 23 cm.
+<!--542.png--><span class="pagenum">522</span>thick, and
+were of concrete reinforced with No. 10 vertical rods, 19 mm. in
+diameter, tied together with No. 6 wire. These shafts were provided with
+steel cutting edges.</p>
+
+<p>Shaft No. 2 was sunk to a depth of 1 m. below the infiltration gallery
+level, No. 3 within 2 m., and No. 4 within 4 m., before August, 1909.
+The shafts were sunk by digging them out and loading them at the top,
+the top of the shafts being kept generally 3 m. out of the ground. Shaft
+No. 3 encountered great volumes of water, and, in order to enable
+sinking operations to proceed, a pumping shaft, 2<sup>1</sup>&frasl;<sub>4</sub> m. square, was
+sunk a little west of it to draw off the water. Notwithstanding the fact
+that the prolonged period of drought had lowered the general water plane
+in all the shafts to 565.00 m. above datum, the difficulties of handling
+the water even at that level were considerable. At the beginning of
+August the work was progressing very satisfactorily, but the
+extraordinary rainfall of that month caused the work to be shut down
+temporarily.</p>
+
+<p><i>Effect of the Floods in the Santa Catarina River.</i>&mdash;The area of the
+water-shed of the Santa Catarina River above Monterrey is about 1,410
+sq. km. (544 sq. miles), and its area at San Geronimo, owing to its
+configuration, is practically the same. Its general character has
+already been referred to. On the night of August 10th and early on the
+morning of August 11th, a big flood came down the river, flowing at its
+maximum about 1,130 cu. m. (40,000 cu. ft.) per sec., due to the heavy
+rainfall <a href="#i485a">(Fig. 4)</a>. This flood carried away all the temporary staging
+around the shafts, seriously wrecking the temporary pumping station, as
+well as destroying the 30-cm. cast-iron pipe, notwithstanding the fact
+that it had been encased in a block of concrete 3 m. wide and 1<sup>1</sup>&frasl;<sub>2</sub> m.
+thick right across the river; but no damage was done to the infiltration
+gallery or to the shafts in the river channel. The effect of the flood
+on this pipe is shown by Fig. 2, Plate XXXI.</p>
+
+<div class="figcenter" style="width: 300px;"><a name="i485b" id="i485b"></a>
+<img src="images/i485bt.jpg" width="300" height="80" alt="Plate XXXI, Fig. 2." title="" />
+<span class="caption"><span class="smcap">Plate XXXI, Fig. 2.&mdash;Profile Sketch, Looking Up Stream On Line Of
+24-inch Main Supply Pipe.</span></span><br />
+<a href="images/i485b.jpg" target="_blank">Larger.</a>
+</div>
+
+<p>Following this flood, which had caused the loss of 14 lives in the city,
+3 miles below San Geronimo, there was practically no rain for 13 days.
+Then, on August 25th the second heavy precipitation began and continued
+until August 29th, the details being shown on <a href="#i485a">Fig. 4</a>.</p>
+
+<p>This precipitation, therefore, fell on a water-shed which was completely
+saturated, as it had already absorbed a large proportion of the 13.38
+in. of rain which fell during August 10th and 11th; and at every point
+along the river, prior to August 25th, springs were issuing forth,
+<!--543.png--><span class="pagenum">523</span>and
+there had been very little evaporation during the intervening dry spell.</p>
+
+<p>The writer has calculated that at Monterrey this flood reached the
+enormous quantity of 6,650 cu. m. (235,000 cu. ft.) per sec., a rate
+equal to 432 cu. ft. per sec. per sq. mile of
+water-shed.<a name="FNanchor_6_6" id="FNanchor_6_6"></a><a href="#Footnote_6_6" class="fnanchor">[6]</a> The effect
+of this flood was to demolish completely about 1,200 "sillar" houses
+(without taking into consideration the numerous wooden houses) at
+Monterrey, and to cause a fearful loss of life, variously estimated
+between 3,000 and 5,000 persons; the lower figure the writer believes is
+approximately correct. At San Geronimo the original pumping station was
+carried away entirely, leaving practically no trace whatever.</p>
+
+<div class="footnote"><a name="Footnote_6_6" id="Footnote_6_6"></a><a href="#FNanchor_6_6"><span class="label">[6]</span></a> The
+writer, in a brief article contributed to <i>Engineering
+News</i> soon after the flood (September 23d, 1909), gave this figure as
+271,500, or approximately equal to a run-off of 500 cu. ft. per sec. per
+sq. mile; but, from a later and more complete study of the conditions
+for many miles above Monterrey, he believes the above quantity to be
+approximately correct.</div>
+
+<p>Shaft No. 2 was apparently destroyed, while No. 3 was turned at an angle
+of about 50° down stream and filled up completely with sand. The
+infiltration gallery, near Shaft No. 2, was completely blocked with fine
+sand and gravel, and access could only be obtained as far as 54 m. The
+profile,<a href="#p11"> Plate XI</a>, shows the change which had taken place
+in the river bed. The original course of the stream was changed to the
+north bank, 50 m. distant, the effect of the scouring action of the
+flood being to lower the general level at this point about 3.65 m.,
+while the southern portion of the channel was slightly raised. At
+present (April, 1910), the end of the driven portion of the infiltration
+gallery is about 35 m. from the center of the stream, which is still
+carrying about 2,270 liters (80 cu. ft.) per sec.</p>
+
+<p>Immediately after the flood the flow in the gallery was 450 liters (16
+cu. ft.) per sec., and this quantity has remained constant since that
+time. The probable effect of the flood was to disturb the whole
+subsurface above the infiltration gallery and put it in motion,
+completely cleaning the gravels of their surrounding clay, which would
+account for the large infiltration of water in so limited a distance.
+The water has always been limpid and pure, but its hardness remains the
+same as it was prior to the flood.</p>
+
+<p>With the copious supply of water from this source, due of course to
+abnormal conditions and not likely to be permanent, the operations of
+tunneling have been suspended temporarily; but it is proposed to
+<!--544.png--><span class="pagenum">524</span>continue
+the driving of the gallery, from a new shaft west of No. 3.
+The water encountered will be drained off by pumping until the main
+water-bearing gravels, in the neighborhood of Shaft No. 5, are reached.
+It is also proposed to reconstruct the 30-cm. high-level pipe line, from
+San Geronimo along the high road on the north bank of the river, so that
+by pumping water can be delivered to the city system from Shafts Nos. 5,
+6, and 7, in the event of a shortness of supply from the Estanzuela
+River.</p>
+
+<p><i>Shaft No. 1.</i>&mdash;Shaft No. 1 is designed to connect the infiltration
+gallery with the gravitation tunnel. This shaft has an inner diameter of
+2.43 m. (8 ft.) and is fitted with a special gate-valve. In the bottom
+of the door of this valve there is a smaller valve, 30 cm. in diameter,
+so that, when the infiltration gallery is closed for cleaning out the
+sump, the smaller door, which is operated through the same spindle by a
+bevel-geared head-stock at the top of the shaft, can be opened first.
+Space is also left for screens if these should be found necessary.
+Access to this shaft is gained by a reinforced concrete stairway in nine
+stages. The superstructure is to be supported on reinforced concrete
+column foundations carried to the firm rock, owing to the loose
+condition of the strata at the top of the shaft.</p>
+
+<p><i>Aqueduct.</i>&mdash;The construction of the concrete conduit was begun in
+April, 1908. <a href="#i519">Fig. 13</a> shows the general types. Type <i>A</i> was adopted in
+gravel and conglomerate formation, and Type <i>B</i> where the excavation was
+in "sillar," the soft nature of this rock permitting it to be excavated
+exactly to the required external diameter of the concrete lining.</p>
+
+<p>The concrete which was without steel reinforcement was a
+1:2<sup>1</sup>&frasl;<sub>2</sub>:3<sup>1</sup>&frasl;<sub>2</sub>
+mixture, the sand being from the crusher and the aggregate from the
+river bed, screened to pass a 25-mm. mesh. Where the conduit crossed the
+river obliquely, immediately below the gravitation tunnel, it was
+strengthened with mass boulder concrete of Type <i>C</i>. During the great
+flood this heavy section withstood its effects without damage of any
+kind, but beyond this point, where the conduit had been laid in compact
+cemented gravels, the scouring action of the flood on the north bank
+lowered the level of the gravels from 2 to 3 m.; the only damage,
+however, was the scouring away of the gravels at the south side of the
+conduit. To prevent such an occurrence in the future, the conduit at
+that point was strengthened with additional concrete for a distance of
+<!--547.png--><span class="pagenum"><a name="Page_525" id="Page_525">525</a></span>195 m.,
+as shown on <a href="#i519">Fig. 13</a>. The extra concrete, amounting to 733 cu.
+m., was a 1:3:5 mixture, in which was embedded 20% of heavy boulders.
+The top of this special length now forms a weir for the present river
+flow. Where the conduit enters the bluff on the north side of the river,
+at 1,200 m., there is an overflow chamber which has a sluice-gate 76 cm.
+wide, arranged so that the conduit can overflow at the present time when
+running 76 cm. deep. To deflect the flow in the conduit, a wrought-iron
+plate, provided with a balance weight, is dropped into a groove on the
+lower side. The outlet is a 61 cm. concrete tube, having its invert
+above ordinary flood level, and arranged to be closed by a gate.</p>
+
+<p>At 1,963 m. the conduit is carried over an arroyo on a segmental arch of
+8 m. clear span, as shown on <a href="#i519">Fig. 13</a>. There are 5 ventilating columns
+and 5 manholes on the aqueduct.</p>
+
+<div class="figcenter" style="width: 449px;">
+<img src="images/i12.jpg" width="449" height="600" alt="Fig. 2." title="" />
+<span class="caption"><span class="smcap">Plate X, Fig. 2.&mdash;Setting Forms for San Geronimo
+Culvert.</span></span></div>
+
+<p>The aqueduct terminates in the Obispado distributing reservoir
+valve-house, at a level of 558.50 m. The work in connection with this
+aqueduct was completed by December, 1908.</p>
+
+
+<h2><span class="smcap"><a name="Distributing_Reservoir_at_Obispado" id="Distributing_Reservoir_at_Obispado"></a>Distributing Reservoir at Obispado.</span></h2>
+
+<p>The main distributing reservoir for the San Geronimo gravity supply is
+immediately below the historic Obispado (Bishop's Palace), at the
+western limits of the city. The general arrangement and lay-out is shown
+on Plate XIII.</p>
+
+<div class="figcenter" style="width: 300px;"><a name="p13" id="p13"></a>
+<img src="images/p13t.jpg" width="300" height="223" alt="Plate XIII" title="" />
+<span class="caption"><span class="smcap">Plate XIII.&mdash;General Plan and Sections,
+Obispado Reservoir.</span></span><br />
+<a href="images/p13.png" target="_blank">Larger.</a>
+</div>
+
+<p><i>Valve-House.</i>&mdash;The invert of the conduit from San Geronimo, where it
+enters the valve-house, is 558.50 m. above datum. The valve-house, which
+is built in the center of the reservoir, is shown on <a href="#i20">Fig. 2, Plate
+XVIII</a>. One of its special features is the provision of
+the main overflow at this point instead of within the reservoir proper.
+The inlet, main supply tunnel, independent by-pass overflow, scour-out
+pipes, gate-valves, and screens, are all controlled within the
+valve-house.</p>
+
+<div class="figcenter" style="width: 700px;"><a name="i20" id="i20"></a>
+<img src="images/i20.jpg" width="700" height="183" alt="Fig. 2." title="" />
+<span class="caption"><span class="smcap">Plate XVIII, Fig. 2.&mdash;View of Roof of Obispado Reservoir, Looking
+North.</span></span>
+</div>
+
+<p><i>Reservoir.</i>&mdash;The reservoir is rectangular, 126 by 81 m. (413.28 by
+265.68 ft.) at the top, and has a water depth of 4 m. (13.1 ft.). In the
+design it was necessary to limit it to the lowest economical depth, so
+as to increase the static pressure over the low-pressure district as
+much as possible.</p>
+
+<p><i>Excavation and Embankment.</i>&mdash;The excavation, except for a depth of
+about 1 m. which was in black soil, was chiefly in a disintegrated
+<!--548.png--><span class="pagenum">526</span>"sillar"
+stratum of a heavy clayey nature, the greater part of which
+could be handled conveniently with plows and scrapers; the actual
+foundation on the eastern half required blasting for the final depths.</p>
+
+<p>The total excavation amounted to 56,479 cu. m., of which 7,255 cu. m.
+were placed in the embankment, the remainder being deposited in the
+immediate neighborhood of the reservoir. The final trimming of the
+banks, which were left 30 cm. full, was not undertaken until the lining
+was begun. The work was done under contract with Mr. J. S. Nickerson, of
+Monterrey. The excavation had only one classification, and the contract
+prices were 0.50 peso per cu. m. for material carried to spoil banks,
+and 1.00 peso for material placed in the embankment. The excavation was
+begun in December, 1907, and completed in April, 1908. The work was then
+left standing until the end of 1908 to allow the banks to consolidate
+thoroughly prior to lining, which was begun on January 4th, 1909.</p>
+
+<p><i>Concrete Lining and Roof.</i>&mdash;<a href="#p13">Plate XIII</a> shows the general
+plan and sections, the main feature being the simple division of the
+reservoir into 24 rows of columns longitudinally and 15 rows
+transversely, making a total of 360 columns, less the four left out at
+the central tower. All the columns are 5 m. apart both ways. The roof
+was designed for a live load of 100 lb. and a dead load of 150 lb., the
+same as at the South Reservoir. With the exception of the floor, all the
+concrete work was reinforced with twisted steel lug bars. The foundation
+load on the columns for the eastern half of the reservoir is 0.9 ton per
+sq. ft.; that on the columns for the western half, where the foundation
+is of very hard sillar and conglomerate, is 1.95 tons per sq. ft.</p>
+
+<p><i>Under-drainage of the Floor.</i>&mdash;To provide for proper drainage in case
+of seepage, the floor was underdrained with rubble drains, 30 cm. wide
+and 23 cm. deep, filled with large round gravel carted from the bed of
+the Santa Catarina River. The total length of these underdrains is 1,160
+m. In order to facilitate the detection of any seepage, they were
+conducted to a permanent inspection pit outside of the reservoir.</p>
+
+<p><i>Main Distributing Conduit.</i>&mdash;The main distributing conduit is laid
+along the inside of the reservoir, at the inlet end, and carried on
+elliptical arches of 2 m. span to a height of 71 cm. above the finished
+floor level. This conduit is 76 cm. high and 45.7 cm. wide, and it
+branches in two directions from the inlet tunnel to each side of the
+<!--549.png--><span class="pagenum">527</span>reservoir,
+its total length being 69 m. In order to prevent any
+stagnation and to give a continuous circulation, the water is delivered
+at eight points, in the length of the distributing pipe, through square
+openings with semicircular tops, the areas of the openings increasing
+toward the ends. These inlets are placed so that the current will not
+strike the roof columns.</p>
+
+<p><i>Outlet Tunnel and Valve-House.</i>&mdash;The outlet tunnel is at the north end
+of the reservoir, and was excavated in hard sillar rock. The tunnel is
+lined with concrete 30 cm. thick, the finished internal dimensions being
+1.52 by 0.91 m. The length of the tunnel is 22.5 m. to the point where
+it enters the outlet-house. This house is divided by a wall 45 cm.
+thick, which supports a 76-cm. (30-in.) penstock-valve. The supply pipe
+to the city leaves this chamber in the west wall, and is also fitted
+with a 76-cm. penstock-valve. The supply pipe has a copper screen of the
+same design and dimensions as those in the inlet-house. A 30-cm.
+(12-in.) scour-out pipe in this chamber provides for draining the
+contents of the reservoir to a neighboring irrigation ditch, when
+necessary.</p>
+
+<p>The superstructure of the valve-house is of concrete, and at the floor
+level there are bevel-geared head-stocks to raise the valves, etc.</p>
+
+<p><i>By-Pass and Supply Pipes.</i>&mdash;The by-pass and supply pipes are carried
+below the reservoir embankment to join the main 76-cm. (30-in.)
+cast-iron distributing pipe to the city. For this short distance they
+were constructed of concrete, 76 cm. in internal diameter, 10 cm. (4
+in.) thick, reinforced with 6<sup>1</sup>&frasl;<sub>2</sub>-mm. square steel longitudinal rods, 30
+cm. from center to center in the circumference, and hooped with
+6<sup>1</sup>&frasl;<sub>2</sub>-mm. square steel rods spaced 30 cm. apart. The concrete forming
+these pipes was a 1:1<sup>1</sup>&frasl;<sub>2</sub>:2<sup>1</sup>&frasl;<sub>2</sub> mixture.</p>
+
+<p><i>Parapet Walls.</i>&mdash;The parapet walls have 12 piers at each side and 8 at
+each end. In these piers there are ventilating openings branching at the
+top to each side of the parapet, with outlets provided with cast-iron
+screens. This arrangement gives 4 sq. m. of ventilating space (exclusive
+of that provided in the central tower), equally distributed at 40 points
+around the walls of the reservoir.</p>
+
+<p><i>General Construction Scheme.</i>&mdash;The concrete mixing plant, which
+consisted of two No. 1 Smith mixers, was arranged in connection with the
+bins and hoppers for the rock and sand on the high ground to the west,
+and from there the material was conveyed on a framed timber
+<!--550.png--><span class="pagenum">528</span>gangway
+carried right across the center of the reservoir, as shown by Fig. 1,
+Plate XVII. From this central platform the concrete for
+the columns was filled from stages placed on the top of traveling
+towers, 5 m. high, which were run between two rows of columns on
+standard-gauge rails laid on the floor of the reservoir. By this
+arrangement 24 columns could be filled from each length of track. A main
+narrow track was also laid right around the reservoir, with the
+necessary turn-outs.</p>
+
+<div class="figcenter" style="width: 496px;">
+<img src="images/i17.jpg" width="496" height="700" alt="Fig. 1." title="" />
+<span class="caption"><span class="smcap">Plate XVII, Fig. 1.&mdash;Filling Primary Beams from Traveling Tower,
+Obispado Reservoir.</span></span>
+</div>
+
+<div class="figcenter" style="width: 700px;">
+<img src="images/i13.jpg" width="700" height="501" alt="Fig. 1." title="" />
+<span class="caption"><span class="smcap">Plate XV, Fig. 1.&mdash;Construction of West Side-Wall of Obispado
+Reservoir.</span></span>
+</div>
+
+<div class="figcenter" style="width: 700px;">
+<img src="images/i14.jpg" width="700" height="481" alt="Fig. 2." title="" />
+<span class="caption"><span class="smcap">Plate XV, Fig. 2.&mdash;Primary Beams and Columns, Obispado
+Reservoir.</span></span>
+</div>
+
+<div class="figcenter" style="width: 300px;">
+<img src="images/p14t.jpg" width="300" height="222" alt="Plate XIV" title="" />
+<span class="caption"><span class="smcap">Plate XIV.&mdash;Details Of Forms For Concrete Work, Obispado Reservoir.</span></span><br />
+<a href="images/p14.png" target="_blank">Larger.</a>
+</div>
+
+<p>The forms for the columns, primary and secondary beams, are shown on
+Plate XIV. The side forms for the primary beams were
+struck in 24 hours, so as to economize lumber; but the bottom lumber was
+left in position for 28 days. To avoid much unnecessary timber, the
+secondary beam forms were supported at the ends on reinforced concrete
+corbels cast on the primary beams.</p>
+
+<p>For placing the side-walls, a special traveling form was used, the
+details of which are shown clearly on Plate XIV. At the
+end of each form an expansion joint of 25 cm. was left to be filled
+after the roof was placed in position. The concrete was delivered to the
+wall through stove-pipe chutes, and carefully spaded by workmen in the
+limited space between the forms and the embankment. The wall form was
+removed after 36 hours, by loosening the jacks and pulling forward the
+hooked tie-rods. This form is also shown on Fig. 2, Plate
+XVI.</p>
+
+<div class="figcenter" style="width: 700px;">
+<img src="images/i16.jpg" width="700" height="410" alt="Fig. 2." title="" />
+<span class="caption"><span class="smcap">Plate XVI, Fig. 2.&mdash;Traveling Side-Wall Form, Obispado
+Reservoir.</span></span>
+</div>
+
+<div class="figcenter" style="width: 700px;">
+<img src="images/i15.jpg" width="700" height="504" alt="Fig. 1." title="" />
+<span class="caption"><span class="smcap">Plate XVI, Fig. 1.&mdash;Preparing Floor for Concreting, Obispado
+Reservoir.</span></span>
+</div>
+
+<p>The concreting of the roof slab was carried on continuously, and, when
+partly completed, the floor was laid in the shade. The bottom layer of
+the floor, 13 cm. thick, was laid in continuous panels between the
+columns, and brought to a fairly smooth surface. On this surface, after
+keeping it wet for 10 days and then allowing it to dry thoroughly, a
+layer of asphaltum, supplied by the American Asphaltum and Rubber
+Company, of Chicago, was placed. The work was done by ordinary Mexican
+laborers after they had received a few days' instruction from one of the
+Asphaltum Company's superintendents. The surface of the lower layer was
+kept perfectly clean, and then received one coat of "Pioneer" paint. The
+asphaltum, heated in a boiler inside the reservoir to a temperature of
+approximately 425° Fahr., was then poured over the floor from buckets,
+in a layer approximately 4 mm. thick. Where the floor joined the column
+pedestals, and at each new panel section, a double thickness was used.
+The labor cost of water-proofing, including superintendence, etc.,
+amounted to
+<!--553.png--><span class="pagenum">529</span>3.3
+cents (Mexican) per sq. m. for painting with "Pioneer"
+paint, and 5.4 cents for the asphaltum coating, or a total labor cost of
+8.7 cents per sq. m. for the complete water-proofing. This cost is based
+on a rate of 8.00 pesos per day for a foreman, and 1.00 peso for each
+laborer. It required 50 U. S. gal. of the paint to cover 265.2 sq. m.,
+and an average of about 6 lb. of asphaltum for 1 sq. m.</p>
+
+<p>The upper concrete layer of the floor, 10 cm. thick, was placed so as to
+break joint with the lower, and was brought to a smooth surface with
+wooden floats sheathed with steel and reaching across the panels. In
+this way a perfectly smooth surface was obtained without any plastering.</p>
+
+<div class="figcenter" style="width: 426px;">
+<img src="images/i18.jpg" width="426" height="700" alt="Fig. 2." title="" />
+<span class="caption"><span class="smcap">Plate XVII, Fig. 2.&mdash;Central Tower and Stairway, Obispado
+Reservoir.</span></span>
+</div>
+
+<p>The concrete for the beams, columns, side-walls, and floor, was a
+1:2<sup>1</sup>&frasl;<sub>2</sub>:4 mixture, crushed sand and stone being used throughout. In the
+roof slab the mixture was 1:2:3.</p>
+
+<p>The whole of the concrete work of the reservoir was completed in 6
+months, by the Company's own administration, and the reservoir was first
+put into service a few days after the great flood of August 27th, when
+the Estanzuela supply main, crossing the Santa Catarina River, was
+partly destroyed. Since that time frequent examinations of the
+inspection pit, which is connected by a pipe to the rubble drains under
+the floor, have never revealed the slightest leakage.</p>
+
+<p><i>Lay-Out of the Reservoir Roof and Grounds.</i>&mdash;The Company owns about
+11<sup>1</sup>&frasl;<sub>2</sub> hectares of land, which includes that occupied by the reservoir
+and its surroundings, and as this property is in an attractive
+situation, commanding fine views of the Sierra Madre Mountains, the
+whole of the works have been given a pleasing architectural character,
+and the grounds laid out to form a public park for the citizens of
+Monterrey.</p>
+
+<div class="figcenter" style="width: 239px;">
+<img src="images/i530t.jpg" width="239" height="300" alt="Fig. 14." title="" />
+<span class="caption"><span class="smcap">Fig. 14.&mdash;Sketch Plan Of Lay Out At Obispado
+Reservoir.</span></span><br />
+<a href="images/i530.jpg" target="_blank">Larger.</a>
+</div>
+
+<p>The general plan of the scheme is shown by Fig. 14 and
+<a href="#i20">Fig. 2, Plate XVIII</a>. The roof, which has an area of 1
+hectare, has been laid out with walks and grass plots, and the
+surrounding embankments have been converted into driveways. Above the
+reservoir a small plazuela of <sup>1</sup>&frasl;<sub>2</sub> hectare has been laid out with a space
+above it for a band-stand. The whole of the ground has been encircled
+with carriage drives, on which it is the intention to plant shade trees.
+The lay-out of this land also embraced the scheme for protecting the
+reservoir by draining the surface-water away to the irrigation ditches.</p>
+
+<!--554.png--><p><span class="pagenum"><a name="Page_530" id="Page_530">530</a></span></p>
+
+
+<h2><span class="smcap"><a name="Comparison_of_South_and_Obispado_Reservoirs"
+id="Comparison_of_South_and_Obispado_Reservoirs"></a>Comparison of South and Obispado Reservoirs.</span></h2>
+
+<p>The two reservoirs are practically of the same capacity, the only
+difference being the level of the overflows in their relationship to the
+roof, which gives the Obispado Reservoir a slightly greater capacity.
+Some comparative figures may be of interest, owing to the differences in
+type and construction. Table 7 gives the comparative quantities of
+material in each reservoir proper, that is to say, exclusive of the
+valve-houses, lay-out of grounds, etc.</p>
+<!--555.png--><p><span class="pagenum">531</span></p>
+
+<div class="TableHeader"><a name="TABLE_7" id="TABLE_7"></a>
+TABLE 7.&mdash;<span class="smcap">Comparison of Materials in South and
+Obispado Reservoirs.</span>
+</div>
+
+<div class="center">
+<table border="0" cellpadding="0" summary="&nbsp;">
+<tr><td align="left">&nbsp;</td><td align="left">&nbsp;</td><td align="center" colspan="2"><span class="smcap">South Reservoir.</span></td><td align="center" colspan="2"><span class="smcap">Obispado Reservoir.</span></td></tr>
+<tr><td align="left">&nbsp;</td><td align="left">&nbsp;</td><td align="center">No.</td><td align="center">Quantities,<br />in cubic meters:</td><td align="center">No.</td><td align="center">Quantities,<br />in cubic meters:</td></tr>
+<tr><td align="left"><i>Earthwork:</i></td></tr>
+<tr><td align="left">&nbsp;</td><td align="left">Total excavation</td><td align="center">...</td><td align="center">34,000</td><td align="center">...</td><td align="center">56,479</td></tr>
+<tr><td align="left">&nbsp;</td><td align="left">Placed in embankment</td><td align="center">...</td><td align="center">31,500</td><td align="center">...</td><td align="center">7,255</td></tr>
+<tr><td align="left">&nbsp;</td><td align="left">Placed in spoil banks</td><td align="center">...</td><td align="center">2,500</td><td align="center">...</td><td align="center">49,224</td></tr>
+<tr><td align="left"><i>Concrete:</i></td></tr>
+<tr><td align="left">&nbsp;</td><td align="left">Columns (including foundations)</td><td align="center">135</td><td align="center">1,240</td><td align="center">356</td><td align="center">543</td></tr>
+<tr><td align="left">&nbsp;</td><td align="left">Primary beams</td><td align="center">135</td><td align="center">440</td><td align="center">374</td><td align="center">462</td></tr>
+<tr><td align="left">&nbsp;</td><td align="left">Secondary beams</td><td align="center">670</td><td align="center">515</td><td align="center">1,252</td><td align="center">576</td></tr>
+<tr><td align="left">&nbsp;</td><td align="left">Side-walls</td><td align="center">...</td><td align="center">1,255</td><td align="center">...</td><td align="center">710</td></tr>
+<tr><td align="left">&nbsp;</td><td align="left">Roof slab</td><td align="center">Square<br />meters:<br />5,140</td><td align="center">520</td><td align="center">Square<br />meters:<br />10,206</td><td align="center">1,020</td></tr>
+<tr><td align="left">&nbsp;</td><td align="left">Floor</td><td align="center">4,070</td><td align="center">780</td><td align="center">9,200</td><td align="center">2,120</td></tr>
+<tr><td align="left">&nbsp;</td><td align="left">Parapet walls</td><td align="center">...</td><td align="center">90</td><td align="center">...</td><td align="center">165</td></tr>
+<tr><td align="left">&nbsp;</td><td align="left" style="padding-left: 5em;">Total concrete</td><td align="center">...</td><td align="center">4,840</td><td align="center">...</td><td align="center">5,596</td></tr>
+<tr><td align="left"></td><td align="left">Reinforcing steel bars</td><td align="center">...</td><td align="center">Pounds:<br />387,000</td><td align="center">...</td><td align="center">Pounds:<br />380,000</td></tr>
+<tr><td align="left"></td><td align="left">Expanded metal in roofs, slabs, etc.</td><td align="center">...</td><td align="center">Square<br />meters:<br />5,691</td><td align="center">...</td><td align="center">Square<br />meters:<br />10,490</td></tr>
+</table>
+</div>
+
+<p>The total cost of these reservoirs, including valve-houses, by-passes,
+and the length of supply pipe where the by-pass joins, and including all
+engineering expenses, etc., but exclusive of the cost of lands,
+planting, fencing, and special work in connection with the formation of
+parks, was as follows:</p>
+
+<p class="blockquot" style="text-indent: -3em; padding-left: 3em">South Reservoir: 394,000 pesos, or 10,368 pesos per million
+liters.</p>
+
+<p class="blockquot" style="text-indent: -3em; padding-left: 3em">Obispado Reservoir: 375,000 pesos, or 9,375 pesos<a name="FNanchor_7_7" id="FNanchor_7_7"></a><a href="#Footnote_7_7" class="fnanchor">[7]</a> per
+million liters.</p>
+
+<div class="footnote"><a name="Footnote_7_7" id="Footnote_7_7"></a><a href="#FNanchor_7_7"><span class="label">[7]</span></a> Mexican currency.</div>
+
+<p>These rates may be regarded as reasonable when taking into consideration
+the special difficulties of construction in Mexico, and the high cost of
+all imported material, on which heavy duties are levied.</p>
+
+<p>The value of the materials alone in these reservoirs amounted to more
+than 70% of their total cost.</p>
+<!--556.png--><p><span class="pagenum"><a name="Page_532" id="Page_532">532</a></span></p>
+
+<h2><span class="smcap"><a name="Analyses_of_Estanzuela_and_San_Geronimo_Waters"
+id="Analyses_of_Estanzuela_and_San_Geronimo_Waters"></a>Analyses of Estanzuela and San Geronimo Waters.</span></h2>
+
+<p>Table 8 shows analyses of the Estanzuela and San Geronimo waters, made
+in February, 1910, by Messrs. Ledoux, of New York City. The Estanzuela
+sample was taken at the valve-house of the South Reservoir, while that
+of San Geronimo was taken in Shaft No. 1 of the infiltration gallery
+when flowing at the rate of about 450 liters per sec. Both waters are
+absolutely free from turbidity.</p>
+
+<div class="TableHeader">
+TABLE 8.&mdash;<span class="smcap">Analyses
+of Estanzuela and San Geronimo Waters.</span><br />
+<span style="font-variant: normal;">In Parts per Million.</span>
+</div>
+
+<div class="center">
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align="left"></td><td align="center">Estanzuela.</td><td align="center">San Geronimo<br />Infiltration Gallery.</td></tr>
+<tr><td>&nbsp;</td></tr>
+<tr><td align="left">Total solid matter in solution</td><td align="center">209.00</td><td align="center">305.00</td></tr>
+<tr><td align="left">Organic and volatile matter</td><td align="center">Not weighable.</td><td align="center">Not weighable.</td></tr>
+<tr><td>&nbsp;</td></tr>
+<tr><td align="left" class="smcap">Analysis of Solids:</td></tr>
+<tr><td align="left" style="padding-left: 2em">Silica</td><td align="center">10.5</td><td align="center">12.0</td></tr>
+<tr><td align="left" style="padding-left: 2em">Iron and Alumina</td><td align="center">Traces.</td><td align="center">Traces.</td></tr>
+<tr><td align="left" style="padding-left: 2em">Lime</td><td align="center">85.4</td><td align="center">112.6</td></tr>
+<tr><td align="left" style="padding-left: 2em">Magnesia</td><td align="center">3.8</td><td align="center">22.6</td></tr>
+<tr><td align="left" style="padding-left: 2em">Soda (Na<sub>2</sub>O)</td><td align="center">13.3</td><td align="center">20.2</td></tr>
+<tr><td align="left" style="padding-left: 2em">Potash (K<sub>2</sub>O)</td><td align="center">2.0</td><td align="center">1.9</td></tr>
+<tr><td align="left" style="padding-left: 2em">Sulphuric Acid</td><td align="center">24.4</td><td align="center">11.5</td></tr>
+<tr><td align="left" style="padding-left: 2em">Chlorine</td><td align="center">2.0</td><td align="center">2.8</td></tr>
+<tr><td>&nbsp;</td></tr>
+<tr><td align="left" class="smcap">Probable Combination of Bases &amp;<br />Acid Radicals in the Solids:</td></tr>
+<tr><td align="left" style="padding-left: 2em">Silica</td><td align="center">10.5</td><td align="center">12.0</td></tr>
+<tr><td align="left" style="padding-left: 2em">Iron and Alumina</td><td align="center">Traces.</td><td align="center">Traces.</td></tr>
+<tr><td align="left" style="padding-left: 2em">Sodium Chloride</td><td align="center">3.3</td><td align="center">4.6</td></tr>
+<tr><td align="left" style="padding-left: 2em">Potassium Sulphate</td><td align="center">3.7</td><td align="center">3.5</td></tr>
+<tr><td align="left" style="padding-left: 2em">Sodium Sulphate</td><td align="center">26.3</td><td align="center">40.8</td></tr>
+<tr><td align="left" style="padding-left: 2em">Calcium Sulphate</td><td align="center">13.3</td><td align="center">22.1</td></tr>
+<tr><td align="left" style="padding-left: 2em">Calcium Carbonate</td><td align="center">142.7</td><td align="center">184.8</td></tr>
+<tr><td align="left" style="padding-left: 2em">Magnesium Carbonate</td><td align="center">8.4</td><td align="center">49.8</td></tr>
+<tr><td>&nbsp;</td><td align="center">&mdash;&mdash;</td><td align="center">&mdash;&mdash;</td></tr>
+<tr><td align="left"></td><td align="center">208.2</td><td align="center">317.6</td></tr>
+<tr><td>&nbsp;</td></tr>
+<tr><td align="left">Nitrogen as Free Ammonia</td><td align="center">0.004</td><td align="center">0.032</td></tr>
+<tr><td align="left">Nitrogen as Albuminoid Ammonia</td><td align="center">0.006</td><td align="center">0.022</td></tr>
+<tr><td align="left">Nitrogen as Nitrites (N<sub>2</sub>O<sub>3</sub>)</td><td align="center">0.002</td><td align="center">0.002</td></tr>
+<tr><td align="left">Nitrogen as Nitrates (N<sub>2</sub>O<sub>3</sub>)</td><td align="center">0.100</td><td align="center">1.85</td></tr>
+<tr><td align="left">Total Hardness (as CaCO<sub>3</sub>)</td><td align="center">155.0</td><td align="center">220.0</td></tr>
+<tr><td align="left">Alkalinity (as CaCO<sub>3</sub>)</td><td align="center">121.0</td><td align="center">180.0</td></tr>
+</table></div>
+
+
+<h2><span class="smcap"><a name="City_Water_Distribution_System"
+id="City_Water_Distribution_System"></a>City Water Distribution System.</span></h2>
+
+<div class="figcenter" style="width: 300px;">
+<img src="images/p19t.jpg" width="300" height="233" alt="Plate XIX" title="" />
+<span class="caption"><span class="smcap">Plate XIX.&mdash;Diagram Of The Main Water Pipes Of Monterrey.</span></span><br />
+<a href="images/p19.png" target="_blank">Larger.</a>
+</div>
+
+<p>The distribution system was begun in September, 1906, but the general
+lay-out of the mains was modified in July, 1907, in view of the division
+of the system into two services, for high and low pressure. Plate
+XIX shows in skeleton form the lines of the cast-iron
+mains. These are laid at the present time along routes containing houses
+<!--557.png--><span class="pagenum">533</span>
+(excluding wooden shacks) which
+can be served immediately. The
+distribution system is arranged to serve as follows:</p>
+
+<div class="center">
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align="left">Estanzuela supply</td><td align="right">4,150</td><td align="left">houses.</td></tr>
+<tr><td align="left">San Geronimo supply</td><td align="right">8,600</td><td align="center">"</td></tr>
+<tr><td align="left"></td><td align="right">&mdash;&mdash;&mdash;</td></tr>
+<tr><td align="right">Total</td><td align="right">12,750</td><td align="center">houses.</td></tr>
+</table></div>
+
+<p>This represents, at the present time, a division of the city of 32<sup>1</sup>&frasl;<sub>2</sub>%
+for the Estanzuela, and 67<sup>1</sup>&frasl;<sub>2</sub>% for the San Geronimo supply. Of the area
+of the supply district north of Santa Catarina River, 57% will be
+supplied from San Geronimo and 43% from Estanzuela. The real development
+of the city, however, is northward in the area of the low-pressure
+supply.</p>
+
+<p>The static pressure over the city in the two sections varies as follows:</p>
+
+<div class="center">
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align="left">Estanzuela supply</td><td align="center">85 to 50 lb.</td></tr>
+<tr><td align="left">San Geronimo supply</td><td align="center">55 to 29 lb.</td></tr>
+</table></div>
+
+<p>The main supply pipe from the South Reservoir is 61 cm. (24 in.) in
+internal diameter, and this size allows ample provision for future
+extensions. The supply pipe from the Obispado Reservoir is 76 cm. (30
+in.) in internal diameter. On this main, in Calle de Cinco de Mayo, at a
+distance of 320 m. from the reservoir, has been placed a 76-cm. (30-in.)
+Venturi meter, the recording apparatus being in the house on the side of
+the road. Both these supply pipes are carried well into the city, and
+from them the distribution mains are laid; these are 45.7 and 30 cm. (18
+and 12 in.) in internal diameter, with intermediate sections of 15 and
+10 cm. (6 in. and 4 in.). Along Calle de Cinco de Mayo, where the
+division between the two services takes place, two lines are laid, a
+30-cm. for high pressure and a 38-cm. (15-in.) for the low pressure. A
+duplicate pipe, 30 cm. (12 in.) in diameter, is also laid in Calle de
+Dr. Coss. On Calle de Alvarez the low-pressure pipe is 61 cm. (24 in.),
+and the high-pressure, 45.7 cm. (18 in.) in diameter. Provision is also
+made for extending the range of the two services to other districts.
+Practically every block is provided with gate-valves to cut off the
+supply in any direction. On the 76-cm. main, 61-cm. (24-in.) valves are
+used, and are connected by tapers to the pipe. On the 61-cm. mains,
+45.7-cm. (18-in.) valves are used. The actual frictional loss by
+reducing the valve
+<!--558.png--><span class="pagenum">534</span>being
+small, this method permitted the use of valves
+of a more convenient size. On all the larger valves there are 15-cm.
+by-passes fitted with independent gate-valves.</p>
+
+<div class="figright" style="width: 400px;">
+<img src="images/i535t.jpg" width="400" height="283" alt="Fig. 15." title="" />
+<span class="caption"><span class="smcap">Fig. 15.&mdash;Connection Between High-and Low-pressure Areas
+And The Intersection Of Cinco De Mayo And Alvarez
+Streets.</span></span><br /><br />
+<a href="images/i535.png" target="_blank">Larger.</a>
+</div>
+
+<p>Scour-out pipes, 10 cm. (4 in.) and 15 cm. (6 in.) in diameter, are
+placed in various parts of the system, draining to the sewers.
+Air-valves, both double and single, are also placed at high points in
+different parts of the system.</p>
+
+<p><i>Reducing Valves.</i>&mdash;At four points in the system the mains are arranged
+so that the supply can be interchangeable. Fig. 15 shows the arrangement
+of the mains at the junction of Cinco de Mayo and Alvarez Streets, and
+is typical of the arrangement at the other points.</p>
+
+<p>Each reducing valve is placed on a 30-cm. (12-in.) branch main between
+the two services. These valves adjust themselves automatically to the
+pressure required, after they have been properly regulated to the
+different pressures on either side. To allow repairs to be easily made,
+there are ordinary gate-valves at each end enclosed in the same pit. If
+necessary, as in case of fire, any part of the system can be changed
+into high pressure temporarily by closing the valves against the San
+Geronimo supply.</p>
+
+<p>Table 9 gives the length of the mains as laid, and the number of valves.</p>
+
+<div class="TableHeader">
+TABLE 9.&mdash;<span class="smcap">Length of Water Mains.</span></div>
+
+<div class="center">
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align="center" colspan="2"><span class="smcap">Diameter:</span></td><td align="center">Length,<br />in meters.</td><td align="center">Number of<br />gate-valves.</td></tr>
+<tr><td align="center">Centimeters.</td><td align="center">Inches.</td></tr>
+<tr><td align="center">10.2</td><td align="center">4</td><td align="center">49,831.68</td><td align="center">677</td></tr>
+<tr><td align="center">15.2</td><td align="center">6</td><td align="center">31,918.31</td><td align="center">306</td></tr>
+<tr><td align="center">30.5</td><td align="center">12</td><td align="center">14,461.31</td><td align="center">117</td></tr>
+<tr><td align="center">38.1</td><td align="center">15</td><td align="center">1,661.98</td><td align="center">11</td></tr>
+<tr><td align="center">45.7</td><td align="center">18</td><td align="center">4,522.61</td><td align="center">5</td></tr>
+<tr><td align="center">61.0</td><td align="center">24</td><td align="center">2,826.54</td><td align="center">10</td></tr>
+<tr><td align="center">76.2</td><td align="center">30</td><td align="center">1,454.40</td></tr>
+<tr><td align="center"></td><td align="center"></td><td align="center">&mdash;&mdash;&mdash;&mdash;</td><td align="center">&mdash;&mdash;&mdash;</td></tr>
+<tr><td align="center"></td><td align="center">Totals</td><td align="center">106,676.83</td><td align="center">1,126</td></tr>
+</table></div>
+
+<p>The pipes were all cast according to the British Standard Specification,
+in 3.65-m. (12-ft.) lengths, and were supplied by Messrs. D. Y. Stewart
+and Company, and Messrs. Dick, Kerr and Company, of Kilmarnock and
+London. The valves were all of standard design, faced with gun-metal,
+and were supplied by Messrs. Glenfield and Kennedy, Limited, of
+Kilmarnock, Scotland.</p>
+
+<!--560.png--><p><span class="pagenum">536</span></p>
+
+<p>In the distribution system it is proposed to provide 200 fire-hydrants,
+by arrangement with the municipality, but only a few of these have been
+placed. The general type is a double hydrant for two 63.5-mm.
+(2<sup>1</sup>&frasl;<sub>2</sub>-in.) streams. These are to be placed at the corner of every block
+in the business portion of the city; single-way hydrants will be used in
+the residential districts.</p>
+
+<p><i>Laying Cast-iron Pipes.</i>&mdash;Table 10 has been prepared to show what can
+be accomplished with Mexican labor in laying pipes. In this kind of work
+the labor was particularly efficient; after the gangs were once drilled
+into shape, the work proceeded systematically, and at very good speed.
+All the pipes, after being laid, were tested to 150 lb. per sq. in. in
+the presence of the Technical Inspector.</p>
+
+<p>Table 11 gives the details of the excavation, the material, and the
+average cost, of laying about 106.6 km. of pipes.</p>
+
+<p><i>House Connections.</i>&mdash;The ordinary house connections, which are of
+19-mm. (<sup>3</sup>&frasl;<sub>4</sub>-in.) galvanized-steel pipe, are connected to the mains by
+lead goosenecks and brass corporation cocks. The Company's obligation
+under the concession extended to the edge of the sidewalk, and at this
+point curb-boxes, chiefly of the Hays pattern, were placed; but,
+subsequently, owing to the metering of every house service in the city,
+the control of the Company extended to the meter, which, as a rule, is
+placed immediately inside of the house. Owing to the rapid deterioration
+of the house service pipes in some districts of the northern part of the
+city, where the soil is formed of decaying organic matter, it has been
+decided to use lead pipe entirely from the main to the meter.</p>
+
+<p><i>Damage Due to Floods.</i>&mdash;During the night of August 27th, the main
+61-cm. pipe, under the river bed of Santa Catarina, at the point where
+the main entered the city, was destroyed for a distance of 130 m., due
+to the scouring away of a whole block of city property. The Venturi
+meter register chart at the South Reservoir showed that the break
+occurred a few minutes before midnight. The location of this pipe is
+shown by <a href="#i485b">Fig. 5</a>; its broken end was in proximity to an old bridge pier.
+Fortunately, at the time of the flood, the Obispado Reservoir works were
+completed, and the whole city was supplied with water from San Geronimo
+within 48 hours. As only about 1,500 services had then been connected,
+this delay was not serious; in fact, in the lower part of the city, the
+water in the mains was sufficient until the San Geronimo supply could be
+connected. To make a temporary connection
+<!--561.png--><span class="pagenum">537</span>to conduct the high-pressure
+water to the city, a 15-cm. steel pipe was placed above ground, on the
+line of the main, for a distance of 100 m. This pipe was supported by a
+cable, 30 mm. in diameter, and by timber trestles. By limiting the
+supply district, this pipe was of sufficient capacity to serve until the
+large main could be safely restored.</p>
+
+<div class="TableHeader">
+
+TABLE 10.&mdash;<span class="smcap">Cost of Laying and Jointing Cast-Iron Pipes,<br />
+Excluding Lowering and Testing.</span>
+</div>
+
+<div class="center">
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<caption><span class="smcap">76 Cm. (30 in.)</span></caption>
+<colgroup align="center" width="50"><col align="left" width="none" /><col span="5" /></colgroup>
+<tr><td>Employees.</td><td>Rate for 10 hour day. Pesos.</td><td>Total No. men.</td><td>Total cost of labor. Pesos.</td><td>No. of pipes laid..</td><td>Cost per linear meter. Pesos.</td></tr>
+<tr><td>Foreman</td><td>4.50</td><td>1</td><td>4.50</td><td>...</td><td>...</td></tr>
+<tr><td>Caulkers</td><td>3.00</td><td>4</td><td>12.00</td><td>...</td><td>...</td></tr>
+<tr><td>Lead pourers</td><td>2.00</td><td>2</td><td>4.00</td><td>...</td><td>...</td></tr>
+<tr><td>Lead melter</td><td>1.50</td><td>1</td><td>1.50</td><td>20</td><td>0.498</td></tr>
+<tr><td>Pipe cutter</td><td>2.00</td><td>1</td><td>2.00</td><td>...</td><td>...</td></tr>
+<tr><td>Peons</td><td>1.00</td><td>12</td><td>12.00</td><td>...</td><td>...</td></tr>
+<tr><td>Water boy</td><td>0.50</td><td>1</td><td>0.50</td><td>...</td><td>...</td></tr>
+<tr><td></td><td></td><td>&mdash;&mdash;</td><td>&mdash;&mdash;&mdash;</td></tr>
+<tr><td></td><td>...</td><td>22</td><td>36.50</td><td>...</td><td>...</td></tr>
+</table>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<caption><span class="smcap">61 Cm. (24 in.)</span></caption>
+<colgroup align="center" width="50"><col align="left" width="none" /><col span="5" /></colgroup>
+<tr><td>Employees.</td><td>Rate for 10 hour day. Pesos.</td><td>Total No. men.</td><td>Total cost of labor. Pesos.</td><td>No. of pipes laid..</td><td>Cost per linear meter. Pesos.</td></tr>
+<tr><td>Foreman</td><td>4.50</td><td>1</td><td>4.50</td><td>...</td><td>...</td></tr>
+<tr><td>Caulkers</td><td>3.00</td><td>5</td><td>15.00</td><td>...</td><td>...</td></tr>
+<tr><td>Lead pourers</td><td>2.00</td><td>2</td><td>4.00</td><td>...</td><td>...</td></tr>
+<tr><td>Lead melter</td><td>1.50</td><td>1</td><td>1.50</td><td>25</td><td>0.410</td></tr>
+<tr><td>Pipe cutter</td><td>2.00</td><td>1</td><td>2.00</td><td>...</td><td>...</td></tr>
+<tr><td>Peons</td><td>1.00</td><td>10</td><td>10.00</td><td>...</td><td>...</td></tr>
+<tr><td>Water boy</td><td>0.50</td><td>1</td><td>0.50</td><td>...</td><td>...</td></tr>
+<tr><td></td><td></td><td>&mdash;&mdash;</td><td>&mdash;&mdash;&mdash;</td></tr>
+<tr><td></td><td>...</td><td>21</td><td>37.50</td><td>...</td><td>...</td></tr>
+</table>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<caption><span class="smcap">50 Cm. (20 in.)</span></caption>
+<colgroup align="center" width="50"><col align="left" width="none" /><col span="5" /></colgroup>
+<tr><td>Employees.</td><td>Rate for 10 hour day. Pesos.</td><td>Total No. men.</td><td>Total cost of labor. Pesos.</td><td>No. of pipes laid..</td><td>Cost per linear meter. Pesos.</td></tr>
+<tr><td>Foreman</td><td>4.50</td><td>1</td><td>4.50</td><td>...</td><td>...</td></tr>
+<tr><td>Caulkers</td><td>3.00</td><td>4</td><td>12.00</td><td>...</td><td>...</td></tr>
+<tr><td>Lead pourers</td><td>2.00</td><td>2</td><td>4.00</td><td>...</td><td>...</td></tr>
+<tr><td>Lead melter</td><td>1.50</td><td>1</td><td>1.50</td><td>35</td><td>0.287</td></tr>
+<tr><td>Pipe cutter</td><td>2.00</td><td>1</td><td>2.00</td><td>...</td><td>...</td></tr>
+<tr><td>Peons</td><td>1.00</td><td>12</td><td>12.00</td><td>...</td><td>...</td></tr>
+<tr><td>Water boy</td><td>0.50</td><td>1</td><td>0.50</td><td>...</td><td>...</td></tr>
+<tr><td></td><td></td><td>&mdash;&mdash;</td><td>&mdash;&mdash;&mdash;</td></tr>
+<tr><td></td><td>...</td><td>22</td><td>36.50</td><td>...</td><td>...</td></tr>
+</table>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<caption><span class="smcap">45.7 Cm. (18 in.)</span></caption>
+<colgroup align="center" width="50"><col align="left" width="none" /><col span="5" /></colgroup>
+<tr><td>Employees.</td><td>Rate for 10 hour day. Pesos.</td><td>Total No. men.</td><td>Total cost of labor. Pesos.</td><td>No. of pipes laid..</td><td>Cost per linear meter. Pesos.</td></tr>
+<tr><td>Foreman</td><td>4.50</td><td>1</td><td>4.50</td><td>...</td><td>...</td></tr>
+<tr><td>Caulkers</td><td>3.00</td><td>4</td><td>12.00</td><td>...</td><td>...</td></tr>
+<tr><td>Lead pourers</td><td>2.00</td><td>2</td><td>4.00</td><td>...</td><td>...</td></tr>
+<tr><td>Lead melter</td><td>1.50</td><td>1</td><td>1.50</td><td>40</td><td>0.221</td></tr>
+<tr><td>Pipe cutter</td><td>2.00</td><td>1</td><td>2.00</td><td>...</td><td>...</td></tr>
+<tr><td>Peons</td><td>1.00</td><td>8</td><td>8.00</td><td>...</td><td>...</td></tr>
+<tr><td>Water boy</td><td>0.50</td><td>1</td><td>0.50</td><td>...</td><td>...</td></tr>
+<tr><td></td><td></td><td>&mdash;&mdash;</td><td>&mdash;&mdash;&mdash;</td></tr>
+<tr><td></td><td>...</td><td>18</td><td>32.50</td><td>...</td><td>...</td></tr>
+</table>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<caption><span class="smcap">38 Cm. (15 in.)</span></caption>
+<colgroup align="center" width="50"><col align="left" width="none" /><col span="5" /></colgroup>
+<tr><td>Employees.</td><td>Rate for 10 hour day. Pesos.</td><td>Total No. men.</td><td>Total cost of labor. Pesos.</td><td>No. of pipes laid..</td><td>Cost per linear meter. Pesos.</td></tr>
+<tr><td>Foreman</td><td>4.50</td><td>1</td><td>4.50</td><td>...</td><td>...</td></tr>
+<tr><td>Caulkers</td><td>3.00</td><td>4</td><td>12.00</td><td>...</td><td>...</td></tr>
+<tr><td>Lead pourers</td><td>2.00</td><td>2</td><td>4.00</td><td>...</td><td>...</td></tr>
+<tr><td>Lead melter</td><td>1.50</td><td>1</td><td>1.50</td><td>45</td><td>0.196</td></tr>
+<tr><td>Pipe cutter</td><td>2.00</td><td>1</td><td>2.00</td><td>...</td><td>...</td></tr>
+<tr><td>Peons</td><td>1.00</td><td>8</td><td>8.00</td><td>...</td><td>...</td></tr>
+<tr><td>Water boy</td><td>0.50</td><td>1</td><td>0.50</td><td>...</td><td>...</td></tr>
+<tr><td></td><td></td><td>&mdash;&mdash;</td><td>&mdash;&mdash;&mdash;</td></tr>
+<tr><td></td><td>...</td><td>18</td><td>32.50</td><td>...</td><td>...</td></tr>
+</table>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<caption><span class="smcap">30.5 Cm. (12 in.)</span></caption>
+<colgroup align="center" width="50"><col align="left" width="none" /><col span="5" /></colgroup>
+<tr><td>Employees.</td><td>Rate for 10 hour day. Pesos.</td><td>Total No. men.</td><td>Total cost of labor. Pesos.</td><td>No. of pipes laid..</td><td>Cost per linear meter. Pesos.</td></tr>
+<tr><td>Foreman</td><td>4.50</td><td>1</td><td>4.50</td><td>...</td><td>...</td></tr>
+<tr><td>Caulkers</td><td>3.00</td><td>4</td><td>12.00</td><td>...</td><td>...</td></tr>
+<tr><td>Lead pourers</td><td>2.00</td><td>2</td><td>4.00</td><td>...</td><td>...</td></tr>
+<tr><td>Lead melter</td><td>1.50</td><td>1</td><td>1.50</td><td>60</td><td>0.147</td></tr>
+<tr><td>Pipe cutter</td><td>2.00</td><td>1</td><td>2.00</td><td>...</td><td>...</td></tr>
+<tr><td>Peons</td><td>1.00</td><td>8</td><td>8.00</td><td>...</td><td>...</td></tr>
+<tr><td>Water boy</td><td>0.50</td><td>1</td><td>0.50</td><td>...</td><td>...</td></tr>
+<tr><td></td><td></td><td>&mdash;&mdash;</td><td>&mdash;&mdash;&mdash;</td></tr>
+<tr><td></td><td>...</td><td>18</td><td>32.50</td><td>...</td><td>...</td></tr>
+</table>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<caption><span class="smcap">15 Cm. (6 in.)</span></caption>
+<colgroup align="center" width="50"><col align="left" width="none" /><col span="5" /></colgroup>
+<tr><td>Employees.</td><td>Rate for 10 hour day. Pesos.</td><td>Total No. men.</td><td>Total cost of labor. Pesos.</td><td>No. of pipes laid..</td><td>Cost per linear meter. Pesos.</td></tr>
+<tr><td>Foreman</td><td>4.50</td><td>1</td><td>4.50</td><td>...</td><td>...</td></tr>
+<tr><td>Caulkers</td><td>3.00</td><td>4</td><td>12.00</td><td>...</td><td>...</td></tr>
+<tr><td>Lead pourers</td><td>2.00</td><td>2</td><td>4.00</td><td>...</td><td>...</td></tr>
+<tr><td>Lead melter</td><td>1.50</td><td>1</td><td>1.50</td><td>100</td><td>0.082</td></tr>
+<tr><td>Pipe cutter</td><td>2.00</td><td>1</td><td>2.00</td><td>...</td><td>...</td></tr>
+<tr><td>Peons</td><td>1.00</td><td>6</td><td>6.00</td><td>...</td><td>...</td></tr>
+<tr><td>Water boy</td><td>0.50</td><td>1</td><td>0.50</td><td>...</td><td>...</td></tr>
+<tr><td></td><td></td><td>&mdash;&mdash;</td><td>&mdash;&mdash;&mdash;</td></tr>
+<tr><td></td><td>...</td><td>16</td><td>30.50</td><td>...</td><td>...</td></tr>
+</table>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<caption><span class="smcap">10 Cm. (4 in.)</span></caption>
+<colgroup align="center" width="50"><col align="left" width="none" /><col span="5" /></colgroup>
+<tr><td>Employees.</td><td>Rate for 10 hour day. Pesos.</td><td>Total No. men.</td><td>Total cost of labor. Pesos.</td><td>No. of pipes laid..</td><td>Cost per linear meter. Pesos.</td></tr>
+<tr><td>Foreman</td><td>4.50</td><td>1</td><td>4.50</td><td>...</td><td>...</td></tr>
+<tr><td>Caulkers</td><td>3.00</td><td>4</td><td>12.00</td><td>...</td><td>...</td></tr>
+<tr><td>Lead pourers</td><td>2.00</td><td>2</td><td>4.00</td><td>...</td><td>...</td></tr>
+<tr><td>Lead melter</td><td>1.50</td><td>1</td><td>1.50</td><td>150</td><td>0.0574</td></tr>
+<tr><td>Pipe cutter</td><td>2.00</td><td>1</td><td>2.00</td><td>...</td><td>...</td></tr>
+<tr><td>Peons</td><td>1.00</td><td>6</td><td>6.00</td><td>...</td><td>...</td></tr>
+<tr><td>Water boy</td><td>0.50</td><td>1</td><td>0.50</td><td>...</td><td>...</td></tr>
+<tr><td></td><td></td><td>&mdash;&mdash;</td><td>&mdash;&mdash;&mdash;</td></tr>
+<tr><td></td><td></td><td>16</td><td>30.50</td><td>...</td><td>...</td></tr>
+</table></div>
+
+<!--562.png--><p><span class="pagenum">538</span></p>
+
+<div class="TableHeader">
+
+TABLE 11.&mdash;<span class="smcap">Cast-Iron Water Pipes.&mdash;Cost
+of Materials and Laying at Monterrey.</span></div>
+
+<div class="center">
+<table border="0" cellpadding="5" cellspacing="0" summary="">
+<caption><span class="smcap">Materials per Standard Length of Pipe.</span><br />
+Key: cm = centimeter in = inch mm = millimeter kg = kilogram m = linear meter</caption>
+<colgroup align="center" width="50"><col span="10" /></colgroup>
+<tr><td colspan="2"><span class="smcap">Pipe Diameter</span></td><td>Thickness</td><td>Weight of Pipe</td><td>Cost/piece fob Monterrey</td><td colspan="2"><span class="smcap">Lead</span></td><td><span class="smcap">Oakum</span></td><td><span class="smcap">Charcoal</span></td><td>Total Material Cost per m</td></tr>
+<tr><td>cm</td><td>in</td><td>mm</td><td>kg</td><td>pesos</td><td>Weight kg</td><td>Cost pesos</td><td>Cost pesos</td><td>Cost pesos</td><td>pesos</td></tr>
+<tr><td>&nbsp;</td></tr>
+<tr><td>10</td><td>4</td><td>10.3</td><td>109</td><td>11.65</td><td>2.0</td><td>0.37</td><td>0.025</td><td>0.0525</td><td>3.30</td></tr>
+<tr><td>15</td><td>6</td><td>11.1</td><td>163</td><td>15.74</td><td>3.7</td><td>0.67</td><td>0.0675</td><td>0.065</td><td>4.51</td></tr>
+<tr><td>30.5</td><td>12</td><td>15.8</td><td>463</td><td>76.50</td><td>7.9</td><td>1.44</td><td>0.1225</td><td>0.1</td><td>21.35</td></tr>
+<tr><td>38</td><td>15</td><td>17.4</td><td>680</td><td>79.36</td><td>10.6</td><td>1.94</td><td>0.175</td><td>0.12</td><td>22.30</td></tr>
+<tr><td>45.7</td><td>18</td><td>19.0</td><td>871</td><td>90.28</td><td>13.4</td><td>2.42</td><td>0.2375</td><td>0.1375</td><td>25.42</td></tr>
+<tr><td>61</td><td>24</td><td>22.2</td><td>1,261</td><td>117.60</td><td>18.8</td><td>3.42</td><td>0.335</td><td>0.175</td><td>33.20</td></tr>
+<tr><td>76</td><td>30</td><td>25.4</td><td>1,946</td><td>199.05</td><td>24.5</td><td>4.42</td><td>0.44</td><td>0.2125</td><td>55.77</td></tr>
+</table>
+</div>
+
+<div class="center">
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<caption><span class="smcap">Labor.</span><br />Key: cm = centimeter, in = inch, m = meter</caption>
+<colgroup><col span="13" align="center" width="50" /></colgroup>
+<tr><td colspan="2"><span class="smcap">Diameter of pipe:</span></td><td>Width of trench</td><td>Depth</td><td>Cubic meters per linear meter</td><td>Cost of excavation per lin. m</td><td>Back-filling and removing surplus</td><td>Total cost, excavation back filling etc.</td><td colspan="2"><span class="smcap">Hauling per linear meter</span></td><td>Cost of laying per linear meter</td><td>Total hauling and laying per linear meter</td><td>Total excavation and laying, labor, complete</td></tr>
+<tr><td>cm</td><td>in</td><td>m</td><td>m</td><td></td><td>Pesos</td><td>Pesos</td><td>Pesos</td><td>Hauling</td><td>Misc.</td><td>Pesos</td><td>Pesos</td><td>Pesos</td></tr>
+<tr><td>&nbsp;</td></tr>
+<tr><td>10</td><td>4</td><td>0.55</td><td>0.90</td><td>0.50</td><td>0.60</td><td>0.18</td><td>0.78</td><td>0.0275</td><td>0.005</td><td>0.06</td><td>0.0925</td><td>0.8725</td></tr>
+<tr><td>15</td><td>6</td><td>0.60</td><td>1.00</td><td>0.60</td><td>0.72</td><td>0.22</td><td>0.94</td><td>0.45</td><td>0.005</td><td>0.825</td><td>0.1325</td><td>1.0725</td></tr>
+<tr><td>30.5</td><td>12</td><td>0.65</td><td>1.20</td><td>0.78</td><td>0.94</td><td>0.29</td><td>1.23</td><td>0.18</td><td>0.0075</td><td>0.1475</td><td>0.335</td><td>1.565</td></tr>
+<tr><td>38</td><td>15</td><td>0.70</td><td>1.30</td><td>0.91</td><td>1.10</td><td>0.34</td><td>1.44</td><td>0.2725</td><td>0.01</td><td>0.19</td><td>0.4775</td><td>1.9125</td></tr>
+<tr><td>45.7</td><td>18</td><td>0.80</td><td>1.40</td><td>1.12</td><td>1.34</td><td>0.41</td><td>1.75</td><td>0.2725</td><td>0.01</td><td>0.245</td><td>0.5275</td><td>2.2775</td></tr>
+<tr><td>61</td><td>24</td><td>1.00</td><td>1.50</td><td>1.50</td><td>1.80</td><td>0.55</td><td>2.35</td><td>0.825</td><td>0.08</td><td>0.41</td><td>1.315</td><td>3.665</td></tr>
+<tr><td>76</td><td>30</td><td>1.10</td><td>1.60</td><td>1.76</td><td>2.11</td><td>0.65</td><td>2.76</td><td>0.83</td><td>0.10</td><td>0.53</td><td>1.46</td><td>4.22</td></tr>
+</table></div>
+
+<p><span class="smcap">Note.</span>&mdash;The above costs of earthwork are based on the following rates and
+percentages over the whole city:</p>
+
+<div class="center">
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align="left">Earth, per cubic meter</td><td align="left">0.35</td><td align="left">pesos</td><td align="left">50%</td></tr>
+<tr><td align="left">Soft sillar</td><td align="left">0.75</td><td align="center">"</td><td align="left">20%</td></tr>
+<tr><td align="left">Hard sillar</td><td align="left">1.50</td><td align="center">"</td><td align="left">20%</td></tr>
+<tr><td align="left">Rock (chiefly conglomerate)</td><td align="left">4.00</td><td align="center">"</td><td align="left">10%</td></tr>
+</table></div>
+
+<div class="center" style="padding-bottom: 1em;"><span class="smcap">Summary of Table 11.</span></div>
+
+<div class="center">
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<colgroup><col span="5" align="center" width="50" /></colgroup>
+<tr><td colspan="2"><span class="smcap">Diameter of pipe:</span></td><td>Total labor cost.</td><td>Materials.</td><td>Total cost per linear meter.</td></tr>
+<tr><td>Centimeters.</td><td>Inches.</td><td>Pesos.</td><td>Pesos.</td><td>Pesos.</td></tr>
+<tr><td>&nbsp;</td></tr>
+<tr><td>10</td><td>4</td><td>0.8725</td><td>3.30</td><td>4.1725</td></tr>
+<tr><td>15</td><td>6</td><td>1.0725</td><td>4.51</td><td>5.5825</td></tr>
+<tr><td>30.5</td><td>12</td><td>1.565</td><td>21.35</td><td>22.915</td></tr>
+<tr><td>38</td><td>15</td><td>1.9125</td><td>22.30</td><td>24.2125</td></tr>
+<tr><td>45.7</td><td>18</td><td>2.2775</td><td>25.42</td><td>27.6975</td></tr>
+<tr><td>61</td><td>24</td><td>3.665</td><td>33.20</td><td>36.865</td></tr>
+<tr><td>76</td><td>30</td><td>4.22</td><td>55.77</td><td>59.99</td></tr>
+</table></div>
+<!--565.png--><p><span class="pagenum"><a name="Page_539" id="Page_539">539</a></span></p>
+
+<p>The flood destroyed about 1,200 houses in the neighborhood of the river.
+In a number of blocks the smaller mains were scoured away, but
+considerable salvage was done afterward, and, as it is the intention of
+the authorities not to permit rebuilding along the flood-path of the
+river, these mains do not require reconstruction.</p>
+
+
+<h2><span class="smcap"><a name="Main_Sewerage_System"
+id="Main_Sewerage_System"></a>Main Sewerage System.</span></h2>
+
+<p>The Company's obligations, as far as drainage is concerned, were limited
+to the removal and disposal of sewage, no provision being required for
+storm-water, which is allowed to find its way to the natural
+watercourses. Apart from that fact, however, the best system for a city
+like Monterrey, where rainfall for many months at a time is very scarce,
+is the strictly "separate system." In the design advantage was taken of
+the natural topography of the drainage district, which is almost an
+ideal one for a gravitation system of sewers, the general fall in all
+directions being northeast; it was also in this direction that the best
+available land could be obtained for disposal purposes.</p>
+
+<div class="figcenter" style="width: 300px;">
+<img src="images/p20t.jpg" width="300" height="237" alt="Plate XX" title="" />
+<span class="caption"><span class="smcap">Plate XX.&mdash;Diagram Of The Main Sewers Of Monterrey.</span></span><br />
+<a href="images/p20.png" target="_blank">Larger.</a>
+</div>
+
+<p>Plate XX shows in skeleton form the general lay-out of
+the sewers. Two drainage districts are arranged, divided by Calle de
+Washington, which may be regarded as practically the center of the city,
+and each of these districts has an independent main collector connecting
+to the outfall sewer at the northeast extremity of the city.</p>
+
+<p>The system has been designed so that extensions may be made and may
+cover any part within the city limits; the main collectors are large
+enough for the whole area when fully built up.</p>
+
+<p>The sewers are designed on a very liberal basis, namely, on the
+assumption that when flowing half full the quantity to be dealt with
+will be 380 liters per capita per day, with a maximum rate of flow of
+200 per cent. It was assumed that each house would be occupied by 7
+persons and have a frontage of 12<sup>1</sup>&frasl;<sub>2</sub> m. The minimum velocities in the
+sewers, when running full, vary between 0.91 and 1.5 m. per sec., with
+the exception of a few blocks.</p>
+<!--566.png--><p><span class="pagenum">540</span></p>
+<p>The minimum size adopted was 24.3 cm. (8 in.) in internal diameter. The
+sewers of diameters between 24.3 and 50 cm., are 0.91 m. (36 in.) long,
+and are of salt-glazed vitrified clay, imported from San Antonio, Tex.</p>
+
+<p>Table 12 gives the details of the length of the various sewers laid.</p>
+
+<div class="TableHeader">
+TABLE 12.&mdash;<span class="smcap">Length of Sewers.</span>
+</div>
+
+<div class="center">
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align="left" colspan="2"><span class="smcap">Diameter:</span></td><td align="left" style="padding-left: 2em;">Kind.</td><td align="right">Length, in meters.</td></tr>
+<tr><td align="right">cm</td><td align="right">in.</td></tr>
+<tr><td align="right">24.3</td><td align="right">8</td><td align="left">Fire clay</td><td align="right">38,332.85</td></tr>
+<tr><td align="right">25.4</td><td align="right">10</td><td align="left" style="padding-left: 1.5em;">"</td><td align="right">16,400.69</td></tr>
+<tr><td align="right">30.5</td><td align="right">12</td><td align="left" style="padding-left: 1.5em;">"</td><td align="right">7,953.15</td></tr>
+<tr><td align="right">38.1</td><td align="right">15</td><td align="left" style="padding-left: 1.5em;">"</td><td align="right">4,850.56</td></tr>
+<tr><td align="right">45.7</td><td align="right">18</td><td align="left" style="padding-left: 1.5em;">"</td><td align="right">2,023.40</td></tr>
+<tr><td align="right">50.8</td><td align="right">20</td><td align="left" style="padding-left: 1.5em;">"</td><td align="right">1,450.53</td></tr>
+<tr><td align="right">55.9</td><td align="right">22</td><td align="left">Reinforced concrete tubes, 6.9 cm. thick</td><td align="right">3,134.20</td></tr>
+<tr><td align="right">61.0</td><td align="right">25</td><td align="left">Reinforced concrete tubes, 7.6 cm. thick</td><td align="right">357.40</td></tr>
+<tr><td align="right">68.6</td><td align="right">27</td><td align="left">Brick and concrete</td><td align="right">484.05</td></tr>
+<tr><td align="right">76.2</td><td align="right">30</td><td align="left">Brick and concrete</td><td align="right">662.69</td></tr>
+<tr><td align="right"></td><td align="right"></td><td align="left"></td><td align="right">&mdash;&mdash;&mdash;</td></tr>
+<tr><td align="left"></td><td align="left"></td><td align="right">Total</td><td align="right">75,649.15</td></tr>
+</table></div>
+
+<p>The greater number of the manholes are of brickwork, 23 cm. thick, and
+have concrete inverts. They have a diameter of 1.2 m., which is reduced
+to 0.61 m. at the top, and each is provided with a heavy cast-iron frame
+and closed cover weighing about 190 kg. There are 521 manholes, and they
+are placed at every block and on long lines about 80 m. apart.</p>
+
+<div class="figright" style="width: 300px;">
+<img src="images/i541t.jpg" width="300" height="213" alt="Fig. 16." title="" />
+<span class="caption"><span class="smcap">Fig. 16.&mdash;Standard 300-gal. Flush Tanks.</span></span><br />
+<a href="images/i541.png" target="_blank">Larger.</a>
+</div>
+
+<p>The sewers are flushed with 15-cm. (6-in.) automatic flushing siphons of
+the Miller pattern with 20-cm. (8-in.) discharge pipes. There are 278 of
+these siphons, and they are placed in flush-tanks (Fig. 16) built of
+brickwork and plastered with 1:1 cement mortar. Their capacity varies
+from 800 to 1,200 liters, and they discharge from 22<sup>1</sup>&frasl;<sub>2</sub> to 28<sup>1</sup>&frasl;<sub>2</sub>
+liters per sec. They are timed to flush once in 24 hours.</p>
+
+<p>The system is at present ventilated by 23-cm. (9-in.) steel ventilating
+columns (Fig. 16), with ornamental cast-iron bases. There are 220 of
+these columns. Most of them are 7.85 m. above the level of the edge of
+the sidewalk, and are connected to special 15-cm. branch pipes leading
+from the sewer on the outside of the flush-tanks. In the center of the
+city they are provided with extension lengths, giving a total height of
+12 m.</p>
+<!--568.png--><p><span class="pagenum"><a name="Page_542" id="Page_542">542</a></span></p>
+<p>Table 13 gives the particulars of the average distributed cost of laying
+the 75.6 km. of sewers.</p>
+
+<div class="TableHeader"><a name="TABLE_13" id="TABLE_13"></a>
+TABLE 13.&mdash;<span class="smcap">Average Cost, Per Linear Meter, for 75.6 Km. of Sewers,<br />
+for Materials and Labor Complete.</span>
+</div>
+
+<div class="center">
+<table border="0" cellpadding="4" cellspacing="0" summary="x">
+<colgroup><col span="8" align="center" width="80" /></colgroup>
+<tr><td rowspan="2">Kind of Sewer.</td><td colspan="2"><span class="smcap">Internal Diameter of Sewers.</span></td><td rowspan="2"> Cost of materials including 10 cm. (4 in.) branches every 4<sup>1</sup>&frasl;<sub>2</sub> m. Pesos.</td><td colspan="3"><span class="smcap">Earthwork and Labor:</span></td><td rowspan="2"> Total cost of sewer complete per linear meter.</td></tr>
+<tr><td>cm.</td><td>in.</td><td>Average depth of sewer<br />m.</td><td>Cost of excavation, including back filling, removing surplus, etc. Pesos.</td><td>Cost of labor in laying (including hauling, etc.). Pesos.</td></tr>
+<tr><td>Fire clay</td><td> 24.3</td><td> 8</td><td> 2.00</td><td> 2.10</td><td> 3.46</td><td> 0.21</td><td> 5.67</td></tr>
+<tr><td>"</td><td> 25.4</td><td> 10</td><td> 2.78</td><td> 2.25</td><td> 3.97</td><td> 0.2625</td><td> 7.0125</td></tr>
+<tr><td>"</td><td> 30.5</td><td> 12</td><td> 3.64</td><td> 2.50</td><td> 4.705</td><td> 0.305</td><td> 8.65</td></tr>
+<tr><td>"</td><td> 38.1</td><td> 15</td><td> 6.14</td><td> 2.75</td><td> 5.50</td><td> 0.4375</td><td> 12.0775</td></tr>
+<tr><td>"</td><td> 45.7</td><td> 18</td><td> 8.80</td><td> 3.00</td><td> 6.745</td><td> 0.645</td><td> 16.19</td></tr>
+<tr><td>"</td><td> 50.8</td><td> 20</td><td> 11.30</td><td> 3.50</td><td> 8.275</td><td> 0.815</td><td> 20.39</td></tr>
+<tr><td>Concrete</td><td> 55.9</td><td> 22</td><td> 5.93</td><td> 3.50</td><td> 9.19</td><td> 1.325</td><td> 16.445</td></tr>
+<tr><td>"</td><td> 61.0</td><td> 25</td><td> 7.30</td><td> 3.75</td><td> 11.245</td><td> 1.685</td><td> 20.23</td></tr>
+<tr><td rowspan="2">One brick thick on concrete foundations</td><td> 68.6</td><td> 27</td><td> 7.17</td><td> 3.75</td><td> 11.735</td><td> 3.93</td><td> 22.835</td></tr>
+<tr><td> 76.2</td><td> 30</td><td> 7.925</td><td> 4.00</td><td> 14.53</td><td> 4.515</td><td> 26.97</td></tr>
+</table></div>
+
+<div class="figcenter" style="width: 511px;">
+<img src="images/i543.jpg" width="511" height="600" alt="Fig. 17." title="" />
+<span class="caption"><span class="smcap">Fig. 17.&mdash;Sketch Showing Disconnecting Trap On House
+Drain.</span></span>
+</div>
+
+<p>The house connections are chiefly of 10-cm. (4-in.) pipes, laid on a
+minimum gradient of 2<sup>1</sup>&frasl;<sub>2</sub>%, from oblique branches on the sewer to siphon
+intercepting traps near the house, as shown by Fig. 17. From this trap a
+10-cm. fire-clay inspection pipe is carried up and capped at the
+sidewalk level with a cast-iron box having a locked cover. From this
+inspection pipe a branch is connected to a cast-iron fresh-air inlet, in
+most cases set in the wall of the house, the inlet being 30 cm. above
+the level of the pavement.</p>
+
+<p><i>Effect of the Flood on Sewers.</i>&mdash;The flood of August 27th and 28th,
+1909, partly destroyed one of the main collectors, which was laid along
+the banks of the river and encased in concrete. This has now been relaid
+farther north, and out of the way of any future floods. The total length
+of the new sewers replacing those damaged amounts to 1200 m., and they
+vary in internal diameter from 20 to 55.9 cm. (8 to 22 in.).</p>
+
+
+<h2><span class="smcap"><a name="Main_Outfall_Sewer"
+id="Main_Outfall_Sewer"></a>Main Outfall Sewer.</span></h2>
+
+<p>The direction of the main outfall sewer was determined after a thorough
+study of all the available land lying to the north and northeast of the
+city, as it was the intention of the Company to utilize
+<!--571.png--><span class="pagenum">543</span>for
+irrigation purposes the sewage and any surplus waters that might be developed. The
+best available site was found to be about 12 km. north of the city, a
+little northwest of the village of San Nicolas de los Garzas, as shown
+on <a href="#p02">Plate II</a>. The long length of outfall required was
+justified by the cheap cost of the land and its excellent character for
+sewage irrigation. The sewer was designed for a capacity of 90,000,000
+liters a day (36.76 cu. ft. per sec.) in order to allow for conveying
+surplus waters as well as sewage.</p>
+
+<div class="figcenter" style="width: 300px;"><a name="p22" id="p22"></a>
+<img src="images/p22t.jpg" width="300" height="229" alt="Plate XXII" title="" />
+<span class="caption"><span class="smcap">Plate XXII.&mdash;Outfall Sewer: Plan Of Ground Showing Sewer;
+Also Details Of Various Sections.</span></span><br />
+<a href="images/p22.png" target="_blank">Larger.</a>
+</div>
+
+<p>The outfall intercepts the two main branches of the city sewers at Calle
+de Allende and Calle de Tapia, and its total length is approximately
+<!--572.png--><span class="pagenum">544</span>11,900 m.
+The chief type adopted is shown on Plate XXII.
+It is formed with an invert of radial bricks laid in 1:2 cement mortar,
+on a foundation of 1:3:5 concrete approximately 7 cm. thick. As the
+ground was chiefly in hard sillar, only a little concrete was required
+to mould the bottom to the correct shape. The arch was formed of special
+radial bricks, 15 cm. (6 in.) deep, laid in cement mortar. These bricks
+were adopted in preference to concrete, owing to the heavy cost of sand
+and rock, due to the long haul, and for the purpose of obtaining rapid
+work. <a href="#i21">Plate XXI</a> shows the sewer arch, and one of the
+ventilating columns and manholes. The bricks were obtained from the
+local brick plant, and form a very satisfactory material for sewers,
+being well burnt, thoroughly hard, and absorbing not more than 7<sup>1</sup>&frasl;<sub>2</sub>% of
+their weight of water. The contract prices for the labor on the
+brickwork were 1.25 pesos per sq. m., and 1.38 pesos for the arch.</p>
+
+<div class="figcenter" style="width: 495px;"><a name="i21" id="i21"></a>
+<img src="images/i21.jpg" width="495" height="700" alt="Fig. 1." title="" />
+<span class="caption"><span class="smcap">Plate XXI, Fig. 1.&mdash;View of Arch, Outfall Sewer.</span></span>
+</div>
+
+<div class="figright" style="width: 207px;"><a name="i22" id="i22"></a>
+<img src="images/i22.jpg" width="207" height="400" alt="Fig. 2." title="" />
+<span class="caption"><span class="smcap">Plate XXI, Fig. 2.&mdash;Ventilating Column and Manhole, Outfall
+Sewer.</span></span>
+</div>
+
+<p>The general route of the sewer is very direct, long straight lines of
+several kilometers being possible, and these were joined by curves of
+approximately 30 m. radius. The gradient of the sewer invert is 0.2% (1
+in 500) which is approximately the general fall of the ground northward
+from Monterrey.</p>
+
+<p>The total quantity of excavation was as follows:</p>
+
+<div class="center">
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align="left">No. 1, soft earth</td><td align="right">8,960</td><td align="left">cu. m.</td></tr>
+<tr><td align="left">No. 2, sillar</td><td align="right">18,492</td><td align="center">"</td></tr>
+<tr><td align="left">No. 3, conglomerate rock</td><td align="right">9,822</td><td align="center">"</td></tr>
+<tr><td align="left"></td><td align="right">&mdash;&mdash;&mdash;</td></tr>
+<tr><td align="left">Total</td><td align="right">37,274</td><td align="left">cu. m.</td></tr>
+</table></div>
+
+<p>The contract prices for this excavation were: for No. 1, 32 cents; No.
+2, 85 cents; and No. 3, 2.17 pesos per cu. m.</p>
+
+<p>All the excavation was in perfectly dry ground. Where the sewer was
+partly out of the ground it had a foundation of concrete, 1.75 m. wide,
+from 15 to 23 cm. thick, below the bottom of the brickwork, and carried
+up to the springing of the arch, and a well-tamped embankment, with
+slopes of 1<sup>1</sup>&frasl;<sub>2</sub> to 1, to protect the sewer to a height of 30 cm. (12
+in.) above the arch. For 342 m. at the Monterrey end of the line, the
+sewer was constructed in tunnel, from, the open end and from two
+intermediate shafts. The tunnel throughout was in sillar, and the
+contract price for excavation was 24.50 pesos per lin. m. This work was
+done without timbering of any kind, except at the shaft lengths. <a href="#p22">Plate
+XXII</a> shows
+<!--573.png--><span class="pagenum"><a name="Page_545" id="Page_545">545</a></span>the
+lining of the tunnel, which was of
+concrete with a brick invert. At four places the sewer passes under main
+railway tracks, which at these points were carried on steel girders
+supported on concrete abutments, the sewer being carried under the
+tracks in the ordinary way.</p>
+
+<p><i>Bridges.</i>&mdash;At three points the sewer was carried over arroyos on
+reinforced concrete girders. No. 1, at Station 5,600, consisted of four
+10-m. spans; No. 2, at Station 8,365, over the Estanscia Arroyo,
+consisted of nine 10-m. spans; and No. 3, at Station 8,960, over the
+Topo Chico Arroyo, consisted of three 10-m. spans. One of these bridges
+is shown on Plate XXIII. They were designed as two
+parallel continuous girders with connecting top and bottom slabs. The
+concrete for the girders was a 1:2<sup>1</sup>&frasl;<sub>2</sub>:3<sup>1</sup>&frasl;<sub>2</sub> mixture, the sand being
+from the crusher and the rock gauged to pass a 19-mm. (<sup>3</sup>&frasl;<sub>4</sub>-in.) screen.
+The inside was rendered with a coat of 1:1 cement mortar, 7 mm. thick,
+for water-tightness.</p>
+
+<div class="figcenter" style="width: 700px;">
+<img src="images/i23.jpg" width="700" height="404" alt="Fig. 1." title="" />
+<span class="caption"><span class="smcap">Plate XXIII, Fig. 1.&mdash;Forms for Main Girders, Estanscia Bridge,
+Outfall Sewer.</span></span>
+</div>
+
+<div class="figcenter" style="width: 700px;">
+<img src="images/i24.jpg" width="700" height="398" alt="Fig. 2." title="" />
+<span class="caption"><span class="smcap">Plate XXIII, Fig. 2.&mdash;View of Estanscia Bridge,
+Completed.</span></span>
+</div>
+
+<p>The piers of the Estanscia Bridge (Plate XXIII) were
+carried down through soft earth to a stiff clay from 4<sup>1</sup>&frasl;<sub>2</sub> to 6 m. below
+the surface, and the foundations were spread so that the pressure would
+not exceed 1 ton per sq. ft. The ends of the bridges were protected by
+rubble wing-walls supporting the embankment over the sewer. A 1:3:5
+concrete was used for the upper part of the piers, and the lower part
+was of the same mixture with 30% of large boulders. There are 70
+manholes (Fig. 19) along the line of the sewer, and they vary from 150
+to 230 m. apart. The sewer is ventilated with 30 concrete towers (Fig.
+18, and <a href="#i22">Fig. 2, Plate XXI</a>), 2.9 m. high,
+having 20-cm. (8-in.) shafts.</p>
+
+<div class="figcenter" style="width: 264px;">
+<img src="images/i546t.jpg" width="264" height="300" alt="Fig. 18." title="" />
+<span class="caption"><span class="smcap">Fig. 18.&mdash;Details Of Ventilators On Outfall
+Sewer.</span></span><br />
+<a href="images/i546.png" target="_blank">Larger.</a>
+</div>
+
+<div class="figcenter" style="width: 221px;">
+<img src="images/i547t.jpg" width="221" height="300" alt="Fig. 19." title="" />
+<span class="caption"><span class="smcap">Fig. 19.&mdash;Details Of Manholes On Outfall
+Sewer.</span></span><br />
+<a href="images/i547.jpg" target="_blank">Larger.</a>
+</div>
+
+<p>The works for the outfall sewer were carried out satisfactorily under a
+contract with Mr. John Phillips, of Mexico City, the Company supplying
+the greater part of the materials. The work was begun on March 16th, and
+finished on November 12th, 1908.</p>
+
+
+<h2><span class="smcap"><a name="Sewage_Disposal_Works_and_Irrigation_Lands"
+id="Sewage_Disposal_Works_and_Irrigation_Lands"></a>Sewage Disposal Works and Irrigation Lands.</span></h2>
+
+<p>For the purpose of disposing of the sewage and using it profitably, the
+Company purchased 909 hectares (2,246 acres) of land from the Community
+of San Nicolas de los Garzas, the outfall sewer being carried to the
+southwestern boundary of the land acquired. This area has a general fall
+in all directions to the northeastern boundary, with a gradual fall of
+about 25 m. across the diagonal of the land. The area purchased was
+practically virgin land, only small portions having
+<!--574.png--><span class="pagenum">546</span>been cultivated.
+The greater part was covered with a growth of mezquite trees and small
+shrubs. The quality of the land is excellent, if properly irrigated, and
+capable of yielding abundant crops of every description. The limits of
+this land are shown on <a href="#p02">Plate II</a>.</p>
+
+<p><i>Sewage Purification Tanks.</i>&mdash;For the purpose of obtaining a
+satisfactory effluent to discharge on the land without causing nuisance,
+the Company built a system of detritus chambers and liquefying tanks at
+the end of the outfall sewer. One difficulty to be faced, in designing
+these works, was the fact that there were no data regarding the probable
+quantity of dry-weather sewage, nor any particulars as to its general
+<!--576.png--><span class="pagenum">548</span>character;
+there was also the probability that the outfall sewer would
+have to carry large quantities of surplus water. Therefore, the system
+was designed so as to be capable of extension if necessary, and the
+sizes of the various tanks were limited at present, because of the
+septic processes which would be set up in the long length of outfall
+sewer. The tanks were designed to deal with 10,000,000 liters of sewage
+proper per day, and the channels, etc., were proportioned to take the
+full flow of the sewer if necessary. Provision was also made for
+discharging large volumes of surplus water directly on the land,
+independent of the tanks. To do this a by-pass was taken from the sewer
+a short distance before reaching the site of the tanks. By properly
+timing the flow, arrangements could be made to discharge these waters in
+the early hours of the morning, by allowing the scour-pipes in the
+distribution system to be opened at night when the domestic sewage flow
+was at its minimum. As the area of land available is very great, the
+degree of purification in the tanks was relatively unimportant; the
+object to be obtained consisted chiefly in distributing on the land an
+effluent which would be innocuous and clear.</p>
+
+<p>The general design of the works is shown on Plate XXIV,
+and they consist essentially of a screen chamber, duplicate detritus
+tanks, and three liquefying tanks. There is also a sludge-pit 629 m.
+from the tanks.</p>
+
+<div class="figcenter" style="width: 300px;">
+<img src="images/p24t.jpg" width="300" height="217" alt="Plate XXIV" title="" />
+<span class="caption"><span class="smcap">Plate XXIV.&mdash;Sewage Disposal Works At San
+Nicolas De Los Garzas<br />General Plan Of Detritus And Liquefying
+Tanks; With Details Of The Latter.<br /></span></span>
+<a href="images/p24.png" target="_blank">Larger.</a>
+</div>
+
+<p><i>Screen Chamber and Detritus Tanks.</i>&mdash;Enlarged details of the screen
+chamber are shown on Plate XXV. The invert, where the
+sewer enters the screen chamber, is 489.45 m. above datum. This chamber
+has duplicate screens which are fully detailed on Plate
+XXX. For cleaning purposes the screens are raised by a
+steel-framed head-gear, which is arranged so that they may be lowered to
+a small traveling bogie, out of the way of the screen chamber.</p>
+
+<div class="figcenter" style="width: 300px;">
+<img src="images/p25t.jpg" width="300" height="251" alt="Plate XXV" title="" />
+<span class="caption"><span class="smcap">Plate XXV.&mdash;Sewage Disposal Works At San
+Nicolas De Los Garzas.<br />Details Of Detritus Chambers And Inlet Channels.</span></span><br />
+<a href="images/p25.png" target="_blank">Larger.</a>
+</div>
+
+<div class="figcenter" style="width: 300px;">
+<img src="images/p26t.jpg" width="300" height="169" alt="Plate XXVI" title="" />
+<span class="caption"><span class="smcap">Plate XXVI.&mdash;Sewage Disposal Works At San Nicolas De Los
+Garzas<br />Detritus And Liquefying Tanks; Details Of Distributing Channels.</span></span><br />
+<a href="images/p26.png" target="_blank">Larger.</a>
+</div>
+
+<div class="figcenter" style="width: 300px;">
+<img src="images/p30t.jpg" width="300" height="168" alt="Plate XXX" title="" />
+<span class="caption"><span class="smcap">Plate XXX.&mdash;Sewage Disposal Works At San Nicolas De Los
+Garzas.<br />Details Of Screening Apparatus.</span></span><br />
+<a href="images/p30.png" target="_blank">Larger.</a>
+</div>
+
+<p>From the screen chamber there are two main channels, 1.22 m. wide,
+branching to the two concrete detritus chambers. Each channel has a
+square penstock, so that the sewage can be diverted into either chamber
+when necessary.</p>
+
+<p>The detritus chambers are octagonal in plan, 4 m. in diameter, and each
+is provided with an outlet weir 1.50 m. wide. At the weir level the
+chambers have a depth of 1.75 m., with drainage channels below that
+level. The coping is 1 m. above the outlet weir of the detritus tanks.
+To drain off these chambers, each has a scour-out pipe, 30 cm. in
+<!--577.png--><span class="pagenum">549</span>diameter,
+controlled from valves with spindles carried above the coping
+level. Each of these pipes is connected to a central chamber, and leads
+to a 56-cm. (22-in.) sludge-pipe. The chambers as designed are of
+smaller capacity than those usually provided, but, as all surface water
+is strictly excluded from the sewerage system, the quantity of detritus
+reaching the chambers may be small. The velocity through them when both
+are in use will be approximately 0.082 m. (0.27 ft.) per sec.</p>
+
+<p>From these chambers the sewage is carried to the three liquefying tanks
+by a main channel, 11.5 m. long and 1.50 m. wide.</p>
+
+<div class="figcenter" style="width: 700px;">
+<img src="images/i25.jpg" width="700" height="411" alt="Fig. 1." title="" />
+<span class="caption"><span class="smcap">Plate XXVII, Fig. 1.&mdash;Cast Concrete Beams Being Placed in Position,
+Liquefying Tanks.</span></span>
+</div>
+
+<div class="figcenter" style="width: 700px;">
+<img src="images/i26.jpg" width="700" height="416" alt="Fig. 2." title="" />
+<span class="caption"><span class="smcap">Plate XXVII, Fig. 2.&mdash;Inlet Weirs to Liquefying Tanks, During
+Construction.</span></span>
+</div>
+
+<div class="figcenter" style="width: 700px;">
+<img src="images/i27.jpg" width="700" height="410" alt="Fig. 1." title="" />
+<span class="caption"><span class="smcap">Plate XXVIII, Fig. 1.&mdash;View of Liquefying Tanks, from Inlet
+End.</span></span>
+</div>
+
+<p>The tanks are of concrete and have reinforced concrete roofs. Each is 66
+m. long and 6 m. wide; the minimum depth for the sewage is 1.50 m. at
+the outlet end, and 2.25 m. at the inlet, increasing to a maximum depth
+of 2.75 m. at the lowest depth at the scour-out channel. Their combined
+capacity is 2,500,000 liters, which is equivalent to 6 hours' flow of
+the quantity of sewage for which they were designed. The sewage passes
+from the main channel, through penstock-valves which control the flow,
+into one or the other of the tanks. From these valve openings it flows
+over concrete weirs, 5 m. long, and is deflected to the bottom of the
+tank by a reinforced concrete scum-plate, extending across each tank,
+with a clearance of 15 cm. at each end. This scum-plate is 1.5 m. deep
+and 10 cm. thick, and is placed 40 cm. from the end walls.</p>
+
+<div class="figcenter" style="width: 300px;"><a name="p29" id="p29"></a>
+<img src="images/p29t.jpg" width="300" height="264" alt="Plate XXIX" title="" />
+<span class="caption"><span class="smcap">Plate XXIX.&mdash;Sewage Disposal Works At San Nicolas De Los
+Garzas;<br />Details Of Outlet Channels And Weir Box.</span></span><br />
+<a href="images/p29.png" target="_blank">Larger.</a>
+</div>
+
+<p>The details of the concrete division and outside walls are shown on
+Plate XXIX. The floor was constructed in two layers, and
+its surface is divided into 6 channels formed by small walls, 20 cm.
+wide and 15 cm. deep, the object of these channels being to facilitate
+the cleaning of the floor by scouring it out to a specially arranged
+channel at the deepest point of the tank, near the inlet end. Each
+scour-out channel has a 30-cm. (12-in.) gate-valve, controlled from the
+roof of the tank, the three scour-pipes meeting in a concrete chamber
+outside of the tanks, from which a 56-cm. (22-in.) concrete pipe
+discharges the contents of the tanks to the sludge-pit during cleaning
+operations. The velocity through the tanks, when they are used in
+combination, is 0.0253 m. (0.083 ft.) per sec., the tanks being made as
+long as economically possible, in order to obtain this low velocity and
+thus permit the proper sedimentation of the suspended matters. The roof
+of each tank is 1 m. above the weir level. Each tank has four
+ventilating columns, 3.7 m. high and 30 cm. in diameter, vitrified clay
+pipes, with an exterior
+<!--578.png--><span class="pagenum">550</span>casing
+of contrete, being used for the shafts. The roof is enclosed within
+parapet walls, and is covered with a
+layer of earth 25 cm. thick.</p>
+
+<p>The outlet channel from the tanks leads to a measuring chamber, 3 m.
+square, as shown on <a href="#p29">Plate XXIX</a>. This chamber is fitted
+with penstocks, 1.83 m. wide, and measuring weirs. From this chamber the
+sewage is delivered to two main irrigation ditches, which distribute the
+sewage in two directions, one northward and the other to the western
+extremity of the lands.</p>
+
+<p><i>Construction of Tanks.</i>&mdash;The excavation for the tanks was in soft earth
+for a depth of 1<sup>1</sup>&frasl;<sub>2</sub> m.; the lower depths were in a firm foundation of
+sillar and calcareous clay. The total excavation in the tanks, channels,
+etc., was 8,335 cu. m., and the actual cost was 45<sup>3</sup>&frasl;<sub>4</sub> cents per cu. m.
+To facilitate the construction, about six-tenths of the concrete beams
+were cast as single monoliths and placed in position by sliding them
+across the tanks on temporary timbers. The remainder of the beams, the
+roof, and the slab were placed in position in the ordinary way with
+timber forms. The total quantity of concrete placed was 1,360 cu. m. A
+1:2<sup>1</sup>&frasl;<sub>2</sub>:4<sup>1</sup>&frasl;<sub>2</sub> concrete was used for
+the walls, channels, etc., and a
+1:2:3 mixture for the roof slab and beams.</p>
+
+<p>Table 14 gives the average cost per cubic meter for all the concrete
+work.</p>
+
+<div class="TableHeader">
+TABLE 14.&mdash;<span class="smcap">Average Cost per Cubic Meter for Concrete in Tanks</span>.</div>
+
+<div class="center">
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td></td><td align="left"> Pesos per<br />cubic meter.</td><td align="center"> Pesos per<br />cubic meter.</td></tr>
+<tr><td>&nbsp;</td></tr>
+<tr><td align="left"><span class="smcap">Labor</span>:</td><td align="center"></td><td align="center"></td></tr>
+<tr><td align="left"> Mixing and placing</td><td align="center"> 5.20</td><td align="center"></td></tr>
+<tr><td align="left"> Carpenter work in forms, framing, etc.</td><td align="center"> 4.20</td><td align="center"></td></tr>
+<tr><td align="left"></td><td align="center">&mdash;&mdash;&mdash;</td><td align="center"></td></tr>
+<tr><td align="center"> Total labor cost</td><td></td><td align="center"> 9.40</td></tr>
+<tr><td>&nbsp;</td></tr>
+<tr><td align="left"><span class="smcap">Materials</span>:</td><td align="center"></td><td align="center"></td></tr>
+<tr><td align="left"> Screened gravel</td><td align="center"> 4.04</td><td align="center"></td></tr>
+<tr><td align="left"> Sand (from neighboring arroyo)</td><td align="center"> 4.98</td><td align="center"></td></tr>
+<tr><td align="left"> Cement (including hauling)</td><td align="center"> 15.19</td><td align="center"></td></tr>
+<tr><td align="left"> Lumber, nails, and other supplies</td><td align="center"> 1.90</td><td align="center"></td></tr>
+<tr><td align="left"></td><td align="center">&mdash;&mdash;&mdash;</td></tr>
+<tr><td align="center">Total materials cost</td><td></td><td align="center">26.11</td></tr>
+<tr><td>&nbsp;</td></tr>
+<tr><td align="center"> Total cost of concrete per cubic meter</td><td align="center"></td><td align="center"> 35.51</td></tr>
+</table></div>
+
+<p><i>Sludge-pit.</i>&mdash;The sludge-pit, used when cleaning out the tanks, is
+carried 639 m. northward, far enough to get the available fall to drain
+the bottom of the detritus chambers and liquefying tanks. The drainage
+<!--581.png--><span class="pagenum">551</span>pipe
+was formed of 56-cm. (22-in.) concrete tubes. The sludge-pit is
+merely an excavation in the earth 20 m. square and 2 m. deep, the sides
+having a slope of 1<sup>1</sup>&frasl;<sub>2</sub> to 1. An overflow drains the pit to an
+irrigation ditch, the solid matter being allowed to settle and the
+liquid to drain off. From time to time it is proposed to dig out the
+solids and plow them into the land.</p>
+
+<p><i>General.</i>&mdash;To the east of the tanks a 3-roomed house has been built for
+the inspector.</p>
+
+<p>In order to provide a good supply of water for cleaning operations, a
+well 22 m. deep has been sunk and is fitted with pumps operated by an
+Eclipse windmill, 4 m. in diameter, on a tower 22 m. high, which
+delivers the pump water to a circular wooden tank of 20,000 liters
+capacity.</p>
+
+<p>The work in connection with the purification tanks was carried out by
+the Company's own staff; it was begun on September 10th, 1908, and
+practically completed by the first week in January, 1909.</p>
+
+<p>At the time of writing, the tanks have to deal with the sewage from a
+population of only 10,000 persons, as only from 15 to 20% of the
+connections have been made. The sewage, therefore, has been diluted with
+several times its volume of surplus water, and the necessary scum on the
+top of the sewage in the tanks has not yet assumed the usual thick matty
+condition observed in most systems. As there are no available means in
+Monterrey of having proper determinations made of the degree of
+purification which takes place in the passage of the sewage through the
+liquefying tanks, a few simple tests have been made. These tests were
+limited to the determination of the amount of oxygen absorbed in 4
+hours, and show a purification of 50% in passing from the detritus
+chambers to the outlet. The sewage, although very black and full of
+suspended matter as it enters the tanks, leaves them in a very clarified
+condition.</p>
+
+<p>Of the total area of land acquired by the Company, 904 hectares (2,234
+acres) have been leased to the Monterrey Railway, Light, and Power
+Company, for 99 years, the Water-Works Company reserving 5 hectares (12
+acres) absolutely for future extensions of the sewage works. By giving
+12 months' notice, the Company also reserves the right to utilize any
+part of 145 hectares (358 acres) near the tanks, should it be required
+at any time in the future for sewage purification purposes.</p>
+<!--582.png--><p><span class="pagenum"><a name="Page_552" id="Page_552">552</a></span></p>
+
+
+<h2><span class="smcap"><a name="Quality_of_and_Rates_for_Labor"
+id="Quality_of_and_Rates_for_Labor"></a>Quality of and Rates for Labor.</span></h2>
+
+<p>All the work was practically under the direction of English-speaking
+superintendents and general foremen. For the ordinary skilled and
+low-skilled labor, Mexicans were employed exclusively, and, on the work,
+which was quite new to them, they proved entirely efficient and
+satisfactory; throughout the work, on which at some periods between
+2,000 and 3,000 men were employed, chiefly under the Company's direct
+administration, they were very tractable and willing to do their best,
+and no trouble was experienced at any time. The Mexican "peon," and also
+the ordinary skilled workman in the north of Mexico, is intelligent, and
+is excellent for purely routine work, but he is not adaptable or
+resourceful in cases of emergency. Under intelligent and careful
+supervision, however, it is quite possible to get as good results as
+could be obtained anywhere.</p>
+
+<p>The daily rates of wages for a 10-hour day were approximately as given
+in Table 15, these rates being varied in special cases.</p>
+
+<div class="TableHeader">
+TABLE 15.&mdash;<span class="smcap">Rates of Wages</span></div>
+
+<div class="center">
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align="left"></td><td align="center">Pesos per day.</td></tr>
+<tr><td align="left">General foreman</td><td align="center">8.00 to 10.00</td></tr>
+<tr><td align="left">Foreman</td><td align="center">6.00 to 8.00</td></tr>
+<tr><td align="left">Cabos</td><td align="center">2.00 to 4.00</td></tr>
+<tr><td align="left">Masons</td><td align="center">3.00 to 4.00</td></tr>
+<tr><td align="left">Bricklayers</td><td align="center">3.00 to 4.00</td></tr>
+<tr><td align="left">Masons and bricklayers helpers</td><td align="center">1.50</td></tr>
+<tr><td align="left">Cast-iron pipe jointers (foreman)</td><td align="center">4.50</td></tr>
+<tr><td align="left">Cast-iron pipe caulkers</td><td align="center">3.00</td></tr>
+<tr><td align="left">Cast-iron pipe helpers</td><td align="center">1.50 to 2.00</td></tr>
+<tr><td align="left">Fire-clay pipe layers</td><td align="center">1.75</td></tr>
+<tr><td align="left">Fire-clay pipe helpers</td><td align="center">1.25 to 1.50</td></tr>
+<tr><td align="left">Drillers</td><td align="center">1.25 to 1.50</td></tr>
+<tr><td align="left">Carpenters</td><td align="center">2.00 to 2.50</td></tr>
+<tr><td align="left">Blacksmiths</td><td align="center">2.50</td></tr>
+<tr><td align="left">Crane men</td><td align="center">6.00</td></tr>
+<tr><td align="left">Peons (laborers)</td><td align="center">1.00 to 1.25</td></tr>
+<tr><td align="left">Boys (watering concrete)</td><td align="center">0.37<sup>1</sup>&frasl;<sub>2</sub> to 0.50</td></tr>
+<tr><td align="left">Watchman</td><td align="center">1.00</td></tr>
+<tr><td align="left">Timekeepers</td><td align="center">22.00 per week.</td></tr>
+</table></div>
+
+
+<h2><span class="smcap"><a name="Cost_of_Works"
+id="Cost_of_Works"></a>Cost of Works.</span></h2>
+
+<p>Table 16 gives the main items of the approximate expenditure. These
+include all expenses for preliminary location, engineering,
+superintendence, purchase of lands, water rights, etc., but do not
+include other heavy expenditures chargeable to the concession, such, for
+example, as general expenses, interest at the rate of 6% during the
+construction period,
+<!--585.png--><span class="pagenum"><a name="Page_553" id="Page_553">553</a></span>preliminary
+expenses for investigations, etc.,
+items which would increase the total by nearly 25 per cent.</p>
+
+<div class="TableHeader">
+TABLE 16.&mdash;<span class="smcap">Principal Items of Expenditure</span>.</div>
+
+<div class="center">
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align="left">&nbsp;</td><td align="center">Pesos, Mexican currency.</td></tr>
+<tr><td align="left"><span class="smcap">Estanzuela Supply:</span></td></tr>
+<tr><td align="left" style="padding-left: 3em">Aqueduct and dam</td><td align="center">502,000</td></tr>
+<tr><td align="left" style="padding-left: 3em">South Reservoir</td><td align="center">429,000</td></tr>
+<tr><td align="left">&nbsp;</td><td align="center">&mdash;&mdash;&mdash;</td><td align="center">931,000</td></tr>
+<tr><td align="left"><span class="smcap">San Geronimo Gravity Supply:</span></td></tr>
+<tr><td align="left" style="padding-left: 3em">Aqueduct, tunnel, and infiltration gallery</td><td align="center">223,000</td></tr>
+<tr><td align="left" style="padding-left: 3em">Obispado Reservoir</td><td align="center">436,000</td></tr>
+<tr><td align="left">&nbsp;</td><td align="center">&mdash;&mdash;&mdash;</td><td align="center">659,000</td></tr>
+<tr><td align="left"><span class="smcap">San Geronimo Provisional Supply</span>,</td></tr>
+<tr><td align="left" style="padding-left: 3em">including boring operations, etc.</td><td align="center">130,000</td></tr>
+<tr><td align="left"><span class="smcap">City Water Distribution System</span></td><td align="center">1,195,700</td></tr>
+<tr><td>&nbsp;</td></tr>
+<tr><td align="left"><span class="smcap">City Sewer System</span></td><td align="center">1,036,000</td></tr>
+<tr><td>&nbsp;</td></tr>
+<tr><td align="left"><span class="smcap">Outfall</span>:</td></tr>
+<tr><td align="left" style="padding-left: 3em">Main outfall sewer</td><td align="center">425,000</td></tr>
+<tr><td align="left" style="padding-left: 3em">Sewage purification works</td><td align="center">75,000</td></tr>
+<tr><td align="left">&nbsp;</td><td align="center">&mdash;&mdash;&mdash;</td><td align="center">500,000</td></tr>
+<tr><td>&nbsp;</td><td></td><td>&mdash;&mdash;&mdash;&mdash;&mdash;</td></tr>
+<tr><td align="left" style="padding-left: 6em">Total</td><td align="center">&nbsp;</td><td align="center">4,451,700</td></tr>
+</table></div>
+
+<p>As a general statement, the actual cost of labor is about 33<sup>1</sup>&frasl;<sub>3</sub>% of the
+total cost of the construction work, including materials. Fig. 20 shows
+in graphic form the amount of the labor pay-rolls and the progress of
+the work during the whole construction period from 1906 to 1909,
+inclusive, comprising also that done under contract.</p>
+
+<div class="figcenter" style="width: 700px;">
+<img src="images/i555.jpg" width="700" height="358" alt="Fig. 20." title="" />
+<span class="caption"><span class="smcap">Fig. 20.&mdash;Progress diagram showing monthly
+labor pay-rolls during the construction period.</span></span>
+</div>
+
+
+<h2><span class="smcap"><a name="Tariffs_and_Sanitary_Regulations"
+id="Tariffs_and_Sanitary_Regulations"></a>Tariffs and Sanitary Regulations.</span></h2>
+
+<p><i>Tariffs.</i>&mdash;The tariffs charged for the water and drainage service
+(Table 17) were approved by the State Government (which accepts the
+responsibility for their collection), under a compulsory State law which
+came into force on March 1st, 1910, for the southern portion of the
+city, and on July 1st, for the northern half, the penalty for
+non-compliance being a tax of 10% on the monthly rental value of the
+property, as assessed by the State officials.</p>
+
+<p>The basis of the tariffs (which were published on February 22d, 1909) is
+a charge for water varying between 12 and 16 cents (Mexican) per 1,000
+liters, with a minimum monthly rate for each different class of property
+connected to the system. The rate for house drainage is fixed at 80% of
+the minimum water rate levied on the consumer. The minimum rates have
+been fixed so that the poorer classes of the community
+<!--586.png--><span class="pagenum">554</span>will not be
+overtaxed, while at the same time the rate is actually levied on the
+quantity of water used, as indicated by the meter. All the services at
+the present time are metered, and the meter system will be used
+throughout.</p>
+
+<div class="TableHeader">
+TABLE 17.&mdash;<span class="smcap">The Tariffs</span>.
+</div>
+
+<div class="center">
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr align="center"><td></td><td> Class</td><td>Monthly property rental. Pesos.</td><td>Liters of water allowed.</td><td>Price for 1,000 liters. Cents.</td><td>Minimum monthly rate. Pesos.</td><td>Rate for drainage service. Pesos.</td><td>Total rate payable. Pesos.</td></tr>
+<tr align="center"><td>&nbsp;</td></tr>
+<tr align="center"><td></td><td>I</td><td>Up to 20</td><td>7,800</td><td>16</td><td>1.25</td><td>1.09</td><td>2.25</td></tr>
+<tr align="center"><td></td><td>II</td><td>21 to 40</td><td>12,500</td><td>16</td><td>2.00</td><td>1.60</td><td>3.60</td></tr>
+<tr align="center"><td></td><td>III</td><td>41 to 60</td><td>18,750</td><td>16</td><td>3.00</td><td>2.40</td><td>5.40</td></tr>
+<tr align="center"><td></td><td>IV</td><td>61 to 120</td><td>23,350</td><td>15</td><td>3.50</td><td>2.80</td><td>6.30</td></tr>
+<tr align="center"><td></td><td>V</td><td>121 to 300</td><td>30,000</td><td>15</td><td>4.50</td><td>3.60</td><td>8.10</td></tr>
+<tr align="center"><td></td><td>VI</td><td>301 upward</td><td>33,350</td><td align="center">15</td><td>5.00</td><td>4.00</td><td>9.00</td></tr>
+</table></div>
+
+<p class="blockquot">"Notes: (1st) The rental for the water meters
+<sup>5</sup>&frasl;<sub>8</sub>-in. size (15<sup>1</sup>&frasl;<sub>2</sub> mm.),
+which shall always be considered the property of the Company, will be 20
+cents per month. Houses of the first and second classes shall be exempt
+from paying such rental for one year's time, counting from this date.</p>
+
+<p class="blockquot">"(2d) All excess consumption of water over that allowed by the tariff
+will be charged for at 2 cents less than the price shown in the tariff
+per thousand liters.</p>
+
+<p class="blockquot">"(3d) Extra large houses, large establishments, such as colleges,
+hotels, etc., etc., having a consumption of 50,000 to 60,000 liters of
+water per month, will pay at the rate of 14 cents per thousand liters.
+The drainage rate for such buildings will be arranged in proportion to
+the water tariff, or 80% of the value of the water.</p>
+
+<p class="blockquot">"(4th) The laundry establishments, bath-houses, etc., when using 50,000
+liters or upward, can arrive at some agreement so as to pay 12 cents per
+1,000 liters.</p>
+
+<p class="blockquot">"(5th) Groups can be formed of two or more small houses so as to obtain
+a joint service under the proportion shown in the tariff.</p>
+
+<p class="blockquot">"(6th) Any other combination that cannot be entered into under the basis
+of this tariff, will be arranged by specially agreed upon prices, such
+agreement being as much as possible subject to the basis mentioned."</p>
+
+<p><i>Sanitary Regulations.</i>&mdash;The State Government, on March 1st, 1909,
+published regulations for the proper installation of the water and
+drainage services within the houses.</p>
+
+<p>At the Government's request, a draft of the proposed regulations was
+submitted by the writer, who prepared it, after a study of American
+<!--588.png--><span class="pagenum"><a name="Page_556" id="Page_556">556</a></span>and
+British sanitary by-laws, to suit the special conditions of Monterrey.
+These regulations were afterward modified by him in collaboration with
+the Government Technical Inspector and Financial Interventor, and, in
+their final form, though not as stringent as those adopted in many
+northern cities, are probably more complete than those in any other
+Mexican city. Under these regulations only registered plumbers can
+undertake plumbing installations, and they have to execute a bond to the
+satisfaction of the <i>Alcalde Primero</i> (City Mayor) for the sum of 2,000
+pesos as a guaranty of responsibility. For defective workmanship or any
+infraction of the plumbing regulations, they are liable to heavy fines,
+and can be called on to make good all defects in workmanship, without
+extra charge to the owner of the property. The provisions of the
+regulations are carried out under the supervision of the Government
+Technical Inspector, the Company's obligations extending only to the
+sidewalk and to the meters placed within the houses.</p>
+
+
+<h2><span class="smcap"><a name="Engineers_etc"
+id="Engineers_etc"></a>Engineers, etc.</span></h2>
+
+<p>G. S. Binckley, M. Am. Soc. C. E., was Chief Engineer of the Company
+from February to December, 1906. The writer was Chief Engineer from May
+1st, 1907, until April, 1910, and is responsible for the design and
+construction of the works carried out during that period. Mr. J. D.
+Schuyler advised the Company throughout all preliminary studies and
+investigations, and acted as Consulting Engineer until February, 1908.
+The Technical Inspector, on behalf of the Government, throughout the
+whole progress of the works, has been Rudolf Meyer, M. Am. Soc. C. E.,
+and the writer wishes to record the valuable assistance the Company has
+received from him.</p>
+
+<p>In conclusion the writer may be permitted to pay a tribute to the
+devoted public spirit shown by his Excellency, General Bernardo Reyes,
+the Governor of the State of Nuevo León from 1885 to February, 1910, and
+who, untiring in his devotion to the interests of the city, was
+primarily responsible for the inception of the works and their
+successful completion.</p>
+<!--589.png--><p><span class="pagenum"><a name="Page_557" id="Page_557">557</a></span></p>
+
+
+
+
+<hr class="RuleChapter" />
+<h2 style="padding-top: 3em; padding-bottom: 2em;"><a name="DISCUSSION" id="DISCUSSION"></a>DISCUSSION.</h2>
+
+
+<p><span class="smcap"><a name="James_D_Schuyler" id="James_D_Schuyler"></a>James D. Schuyler, M. Am. Soc</span>. C. E. (by letter).&mdash;For completeness of
+detail and wide range of subjects of general interest to engineers, this
+paper is certainly one of the notable contributions to recent
+engineering literature. It is a minute and painstaking record of the
+successful accomplishment of construction work under unusual climatic
+conditions and difficult circumstances, and reflects credit on the
+author, not only in his capacity as an engineer, but as a faithful
+recorder of facts. It was particularly fortunate that he was an
+eyewitness of the disastrous and extraordinary flood which swept through
+Monterrey, destroying many lives and much property, and has thus been
+able to give an intelligent estimate of the maximum discharge of the
+river during the height of the flood wave of August 27th-28th, 1909,
+when the rate of run-off per unit of area of water-shed drained reached
+an amount which has seldom been equalled or exceeded, as far as reliable
+records extend. It is worthy of note that works deriving their water
+supply from the source of such torrential floods should have survived
+with so little actual damage, and with scarcely any interruption of
+service. The repair of all damages to the system was estimated to have
+cost not more than $20,000.</p>
+
+<p>As Mr. Conway did not assume charge of construction until May, 1907, he
+was spared the responsibility of deciding on the general plan of
+securing an abundant supply of pure water from sources permitting of
+delivery by gravity under adequate pressure for fire protection&mdash;a
+responsibility which devolved on the writer, assisted by G. S. Binckley,
+M. Am. Soc. C. E., Mr. Conway's predecessor, as Chief Engineer. Not only
+the water-works, but the system of sewerage and sewage disposal by broad
+irrigation were subsequently carried out on the plans submitted to the
+State Government by the writer in 1906, and given provisional
+acquiescence at that time.</p>
+
+<p>There was no lack of water at hand for the supply of a city of that
+size, as there are large perennial springs which flow out of the
+travertine of the plain, and are used for irrigation in the valley below
+the city. One of the largest of these, near the civic center, has a
+normal flow of nearly 30 cu. ft. per sec.; another nearby, also within
+the city limits, flows some 10 or 12 sec-ft., while both the Estanscia
+and Robalar springs, but a few miles below (shown on <a href="#p02">Plate
+II</a>), discharge more than 20 sec-ft., as nearly as memory
+serves. Besides this supply, the water to be developed by sinking shafts
+in certain parts of the plain, as demonstrated at the brewery and
+elsewhere, was apparently a reliable source of large volume.</p>
+
+<p>To utilize these sources, however, would have involved condemnation of
+the water-rights in the case of the springs, depriving present owners of
+the use of the water, and this Governor Reyes wished to
+<!--590.png--><span class="pagenum">558</span>avoid. Besides,
+it would have necessitated pumping the water for the city in perpetuity,
+an expense which the Governor was equally anxious to save; hence a
+gravity supply was made the prime requisite of the plans.</p>
+
+<p>Until the concession was granted, and for a year or more afterward, it
+was assumed that an adequate supply could only be obtained by the
+storage of the flood-water of the Santa Catarina River in a large
+reservoir; and the earlier plans of the concessionaires were based on
+the construction of a high masonry storage dam at the upper end of the
+"narrows," where the river turns from a western direction to a course
+almost due east, between high vertical cliffs of limestone. The
+concession distinctly provided for such a dam, and among the plans on
+file in the State Capitol is one prepared by the late E. Sherman Gould,
+M. Am. Soc. C. E., for a masonry weir across the gorge. Samuel M. Gray,
+M. Am. Soc. C. E., also filed a plan and report proposing a capacious,
+shallow, storage reservoir near the city, to be filled by a large
+flood-water canal from the Santa Catarina Cañon.</p>
+
+<p>Although the writer could not have anticipated the occurrence of floods
+of the magnitude of the one of August, 1909, which would surely have
+destroyed any reservoir built in the Cañon, he was unable to endorse the
+storage plan of water development, chiefly because of the uncertainty of
+the water-tightness of the reservoir in a cavernous limestone formation,
+and also because of the probable impurity of water draining from such
+extensive goat pastures. He, therefore, urged the development of the
+underflow of the river, which was manifesting itself in the springs
+referred to. Mr. Binckley secured two Keystone drilling machines and
+proceeded to profile the bed-rock at Santa Catarina Cañon and at San
+Geronimo, the two places on the stream where the river flows between
+walls of rock <i>in situ</i>. At both sites the strata were standing nearly
+vertical across the channel, and, by careful sampling and testing, it
+was found that in both locations there were thick strata of limestone so
+highly silicious as to be insoluble, and hence free from caverns. From
+this determination it was concluded that all the water which appeared in
+the valley below must pass through the sections where the borings were
+made. The results of this drilling, however, proved conclusively that
+the depth to bed-rock at either place was too great to permit of a
+masonry dam being considered as practical, and demonstrated the
+inadequacy of methods which had been used in the earlier investigations
+when dams were regarded as feasible.</p>
+
+<p>The results have also shown that the subterranean supply at the lower
+cross-section of the river, at San Geronimo, is abundant, and can
+probably be increased to an indefinite degree by continuing the
+filtration gallery; while at Santa Catarina the same type of development
+can be made for a high-source supply, although requiring a long and
+expensive tunnel and conduit.</p>
+<!--591.png--><p><span class="pagenum"><a name="Page_559" id="Page_559">559</a></span></p>
+
+<div class="tb"></div>
+
+
+<p><span class="smcap"><a name="David_T_Pitkethly" id="David_T_Pitkethly"></a>David T. Pitkethly, Assoc. M. Am. Soc.</span> C. E. (by letter).&mdash;Having been
+engaged on the design of sewerage systems for some years, the writer
+finds this paper of peculiar interest, particularly the sewerage
+portion. There are some points in the design, however, which do not
+appear to be clear.</p>
+
+<p>The system is described as "strictly separate," and yet the sewers are
+designed to run half-full, providing a capacity of 200%, the 100% basis,
+or 380 liters per capita, being 90%, or 180 liters, in excess of the
+calculated water supply of 200 liters per capita.</p>
+
+<p>It has been the writer's practice to design sanitary sewer systems on
+the basis of the water consumption, and to assume the whole daily amount
+to reach the sewer in 16 hours, thus providing capacity sufficient to
+care for the maximum or wash-day flow without causing the sewers to run
+above the calculated hydraulic gradient, which should be placed within
+the pipe so as to provide air space for ventilation under all
+circumstances.</p>
+
+<p>The practice of calculating sanitary sewers to run half-full is a good
+one when ground-water is expected in sufficient amount to fill the
+remaining portion of the sewer, but when no ground-water, or roof-, or
+surface-water is allowed to enter the system, or all precautions are
+taken to exclude such, then the system may be designed so that the
+expected maximum, or wash-day flow, will fill the sewer to the desired
+hydraulic gradient.</p>
+
+<p>The method of ventilating the sewers does not seem practicable. The
+houses are principally of one story, and yet the stand-pipes on the
+sewers have openings 25 ft. 9 in. above the sidewalk. Are the
+ventilating or vent pipes of the house plumbing carried to a height to
+balance this, or will these chimneys draw the air from the house drains
+and fresh-air pipes, breaking the seal in the so-called disconnecting
+traps, thus causing the circulation of air in the house piping to be
+downward through the sewers instead of upward through the fresh-air
+inlets and vents, as designed?</p>
+
+<p>It is interesting to note that crude sewage, as well as the liquefying
+(septic) tank effluent, is to be applied to land for irrigation
+purposes, but the application of crude sewage without any attempt at
+removing the suspended matter, or the effluent from the septic tanks
+where only a partial removal occurs, seems to be bad practice.</p>
+
+<p>The author states that:</p>
+
+<p class="blockquot">"The degree of purification in the tanks was relatively unimportant; the
+object to be obtained consisted chiefly in distributing on the land an
+effluent which would be innocuous and clear."</p>
+
+<p>How he expects to obtain such an effluent by passage through screens,
+detritus tanks, and septic tanks only, is more than the writer can
+understand.</p>
+
+<p>The removal of suspended matter in a septic tank depends on the
+<!--592.png--><span class="pagenum">560</span>strength
+of the sewage, the time of retention, the time elapsing
+between cleaning, the presence of trade wastes, etc., and seldom exceeds
+38 per cent.</p>
+
+<p>The subject of septic tanks and their effect on sewage is discussed in
+the "Fifth Report of the Royal Commission on Sewage Disposal" (England,
+1908), and the following extracts, relative to the application of crude
+sewage to land and the effect of septic tanks on sewage, seem apropos:</p>
+
+<p class="blockquot">"23. * * * There are also many cases in which crude sewage has been
+passed over land, but the evidence shows that land treatment of
+crude sewage is liable to give rise to nuisance by the accumulation
+of solids on the surface of the land. Moreover, in some cases these
+solids are apt to form an impervious layer, which interferes with
+the aeration of the soil, and so impairs the efficiency of the
+treatment."</p>
+
+<p class="blockquot">"31. * * * At that time it was claimed that the septic tank
+possessed the following, among other, advantages:</p>
+
+<p class="blockquot">"That it solved the sludge difficulty, inasmuch as practically all
+the organic solid matter was digested in the tank.</p>
+
+<p class="blockquot">"That it destroyed any pathogenic organisms which there might be in
+the sewage."</p>
+
+<p class="blockquot">"32. As regards the first of these claims, it is now clearly
+established that, in practice, all the organic solids are not
+digested by septic tanks, and that the actual amount of digestion
+varies to some extent with the character of the sewage, the size of
+the tanks relative to the volume treated, and the frequency of
+cleansing."</p>
+
+<p class="blockquot">"At Huddersfield, Mr. Campbell estimated that about 38 per cent. of
+the solids were converted into gas or digested; * * * while at
+Birmingham, Messrs. Watson and O'Shaughnessy say that the figures
+available indicated a digestion of not more than 10 per cent. of
+the suspended matter entering the tanks."</p>
+
+<p class="blockquot">"33. As regards the second claim, we find as a result of a very
+large number of observations that the sewage issuing from the
+septic tanks is, bacteriologically, almost as impure as the sewage
+entering the tanks."</p>
+
+<p>Messrs. Winslow and Phelps, in their interesting paper, "Investigations
+on the Purification of Boston Sewage,"
+<a name="FNanchor_8_8" id="FNanchor_8_8"></a><a href="#Footnote_8_8" class="fnanchor">[8]</a> quote
+a suggestion made by
+Stoddart (1905):</p>
+
+<div class="footnote"><a name="Footnote_8_8" id="Footnote_8_8"></a><a href="#FNanchor_8_8"><span class="label">[8]</span></a> Water
+Supply and Irrigation Paper No. 185, p. 125.</div>
+
+<p class="blockquot">"He finds, in a septic tank of several compartments, a considerable
+deposit of sludge in the first compartment, giving a fairly clear
+supernatant liquid, which in the last chamber of all undergoes a
+secondary decomposition, leading to the throwing down of an
+additional precipitate of offensive sludge."</p>
+
+<p>What took place in the case referred to by Stoddart corresponds to the
+author's observations of the liquid leaving the tanks in a clarified
+condition, but the secondary decomposition must take place in some
+manner, and, when it does, a nuisance seems to be unavoidable where no
+provision is made to care for it.</p>
+<!--593.png--><p><span class="pagenum">561</span></p>
+
+<p>In view of the experience of others, some further treatment seems to be
+necessary. Such treatment should include disinfection, as no method of
+disposal yet devised has succeeded in reducing materially the pathogenic
+germs usually to be found in sewage and tank effluents.</p>
+
+<p>If the crops to be irrigated are to be eaten, uncooked, by mankind, then
+disinfection at least is imperative.</p>
+
+<div class="tb"></div>
+
+
+<p><span class="smcap">George S. Binckley, M. Am. Soc.</span> C. E. (by letter).&mdash;Mr. Conway's
+admirable paper is of special interest to the writer, as the entire
+general design of the system, as well as the extensive hydrological
+studies and final selection of the sources of water supply, was
+completed during 1906 through the joint labors of the writer, as Chief
+Engineer, and James D. Schuyler, M. Am. Soc. C. E., as Consulting
+Engineer.</p>
+
+<p>In this work, Mr. Schuyler and the writer had the rare privilege of
+dealing from its inception with the problem of designing a complete and
+somewhat extensive system of municipal water supply and drainage,
+unhampered by any existing works to which the new systems would have to
+be adapted. It would probably be difficult to find in the United States
+a city of 85,000 inhabitants, previously totally lacking either a water
+supply or sewerage system, which, under a consistent and harmonious
+design, has been provided with both in the degree of completeness and
+structural excellence exemplified in the works at Monterrey.</p>
+
+<p>The few important changes or amplifications made in the original design,
+and the manner in which its detail has been executed is naturally most
+interesting to the writer, and this excellent paper should be of very
+substantial value, particularly to engineers engaged on similar work in
+Mexico or Spanish America.</p>
+
+<p>The very novel construction method adopted by Mr. Conway in the roofing
+of the South or Guadalupe Reservoir, seems to the writer rather to
+invite criticism, and the fact that in the subsequent construction of
+the roof over the rectangular Obispado Reservoir the customary
+monolithic concrete construction was apparently reverted to after
+experience with the separate-unit plan previously used, would indicate
+that Mr. Conway reached the same conclusion.</p>
+
+<p>The original design of the circular Guadalupe Reservoir contemplated
+just about the same arrangement of columns and roof support as that
+actually used, but the writer had expected that the columns would be
+cast in place, and that the system of primary and secondary beams would
+be filled at the same time as, and integral with, the roof slab, the
+reinforcement being placed in accordance with what may be described as
+conventional practice. The writer believes that the efficiency of the
+concrete and steel placed in this manner would be notably higher than
+under the system actually adopted, which, in effect, is pretty much the
+same as constructing the supporting system of units of cut stone. If,
+with all the elements of structural weakness involved in the
+multiplicity of mortised joints, discontinuous reinforcement,
+<!--594.png--><span class="pagenum">562</span>etc.,
+this construction is strong enough, it would seem that an important
+reduction in the dimensions of the members could have been effected by
+monolithic construction and continuous reinforcement, without sacrifice
+of strength.</p>
+
+<p>The comparison, in <a href="#TABLE_7">Table 7</a>, of the costs of these two reservoirs, is
+interesting, but very moderately illuminating, as the comparative unit
+cost of the most important element in their construction&mdash;the
+concrete&mdash;is not given. The total excavation cost for each reservoir is
+practically the same, and the general expense, engineering, and cost of
+fittings and accessories presumably so, but the total cost of the
+Guadalupe Reservoir as given is $19,000 (pesos) in excess of that of the
+Obispado Reservoir, while, in the latter, there were 756 cu. m. more
+concrete. This certainly indicates a much higher cost of concrete per
+unit as laid in the South (Guadalupe) Reservoir. An actual comparison of
+the cost per unit of concrete laid under the two systems would be
+instructive.</p>
+
+<p>The writer is interested to observe that the same system of sub-drainage
+used by him in the construction of the reservoir for the provisional
+supply of water from San Geronimo, has been used by the author in the
+Obispado Reservoir. This arrangement of drains under the floor of the
+reservoir at San Geronimo was devised as a safeguard against damage to
+the lining through the accumulation of water inside the impervious bank
+against its back.</p>
+
+<p>It was realized that, in such a climate as that of Monterrey, perfect
+water-tightness of the lining might be difficult to secure or maintain,
+and, if leaks existed, a sudden draft on the contents of the reservoir
+might result in serious damage through the static pressure exerted
+against the lining of the sides or upward thrust against the floor. In
+the writer's opinion, such a system of drains is an important element,
+as not alone the fact but the quantity of leakage may be determined, and
+danger of saturation of the supporting bank avoided&mdash;a matter of
+importance where, as is sometimes the case, the material of such a bank
+is unfit to resist the effects of saturation. The author does not state
+whether or not this safeguard was omitted in the Guadalupe Reservoir.
+Incidentally, however, the matter of saturation of the bank is not
+important in either reservoir, as the material of which these banks are
+constructed is such that settlement or failure through saturation is out
+of the question. It may be remarked, however, that in fixing the angle
+of the sides of the Guadalupe Reservoir at 60° the writer contemplated
+the same system of constructing the bank as he used in that of the San
+Geronimo Reservoir. In this case, the bank was built up by spreading the
+material in thin layers, wetting down, and rolling and puddling by the
+passage of the ox-carts used for the transportation of the material, the
+wheels of the carts, and especially the cloven hoofs of the animals,
+producing a most excellent effect. The inside slope
+<!--595.png--><span class="pagenum"><a name="Page_563" id="Page_563">563</a></span>was built up in
+this fashion to a much lower angle, and with a top width considerably in
+excess of the finished dimensions. The excess material was then picked
+off to the line, and exactly to the slope. Thus the finished slope
+presented a surface which was compacted to a degree impossible to attain
+at or near the surface of the bank as built, and presenting a support of
+the best possible character for the concrete lining and coping.</p>
+
+<div class="tb"></div>
+
+
+<p><span class="smcap"><a name="V_Saucedo" id="V_Saucedo"></a>V. Saucedo, Assoc. M. AM. Soc.</span> C. E. (by letter).&mdash;The author's
+description of the water-works and sewerage of Monterrey, one of the
+most extensive schemes in Mexico, will be of general interest to
+engineers, especially those engaged in hydraulic and sanitary problems.
+The writer, having been connected with the works for four years, knows
+the local conditions well, and presents herewith some complementary data
+on what he considers an important feature, the subject of floods,
+mentioned by the author on different occasions, especially as certain
+developments in the works show the importance of such occurrences as a
+factor in designing.</p>
+
+<p>Abnormal rainfalls of long duration and high intensity are common in the
+semi-arid region of Mexico. They come at irregular intervals, though
+tending to coincide with the early fall. The floods of August, 1909,
+were a repetition of similar occurrences in the past; and, though there
+are no numerical records of previous cases, local traditions and
+historical state documents describe them as having occurred since the
+foundation of the city, at intervals of from 15 to 40 years. The graphic
+descriptions of the places flooded are in accord with the character of
+the floods of August, 1909, and September, 1910.</p>
+
+<p>The diagram, Fig. 21, is a record of the rainfall during the latter
+flood, and was plotted from intermittent readings of standard gauges. It
+demonstrates that the intensity increased toward the mountains on the
+south, which form the tributary water-shed of the Santa Catarina River,
+showing a difference of 10.54 in. between the city and the Estanzuela
+Dam, which is not quite 12 miles to the southeast.</p>
+
+<div class="figcenter" style="width: 700px;">
+<img src="images/i564.jpg" width="700" height="679" alt="Fig. 21." title="" />
+<span class="caption"><span class="smcap">Fig. 21.&mdash;Rainfall during floods of
+September 14th-16th, 1910, in Monterrey.</span></span>
+</div>
+
+<p>An estimate of the volume of discharge of the river at the time of
+maximum flood is only a reasonable conjecture which (without special
+reference to accuracy) aims to impress those who have not witnessed such
+occurrences with the tremendous volume coming from barren steep surfaces
+previously saturated.</p>
+
+<p>The original computation, referred to by the author, was obtained from
+the average of two different methods which gave results close to each
+other. In one method the extent and nature of the water-shed were
+considered, together with the maximum period of precipitation that
+occurred, sufficient to gather a maximum volume of water in the river.
+In the other method the volume was derived from a cross-section of the
+wetted perimeter of the river at the time of maximum flow, in
+combination with velocity approximations obtained by using
+<!--596.png--><span class="pagenum">564</span>rough
+floats. This gave 271,500 cu. ft. per sec. The figure submitted by the
+author, 235,000 cu, ft. per sec., is in accord with the proposed
+formula<a name="FNanchor_9_9" id="FNanchor_9_9"></a><a href="#Footnote_9_9" class="fnanchor">[9]</a> for
+impervious surfaces by C. E. Gregory, M. Am. Soc. C. E.
+In the first and last methods, the intensity, a governing factor, is
+more or less of an assumption, and the cross-sectional method is also
+unreliable, as the river-bed was greatly disturbed, due to the high
+velocity of the water, which deepens the channel to a considerable
+extent at times of maximum flood, the gravels being redeposited during
+the period of subsidence. Such was the case during the flood of
+September, 1910, when the depth of gravel above the roof of the San
+Geronimo Infiltration Gallery was diminished to such an extent that it
+was so inefficient as a filter for the flood as to permit the
+percolation of turbid water into the underground supply.</p>
+
+<div class="footnote"><a name="Footnote_9_9" id="Footnote_9_9"></a><a href="#FNanchor_9_9">
+<span class="label">[9]</span></a> <i>Transactions</i>. Am. Soc. C. E., Vol. LVIII. p. 458.</div>
+
+<p>During the floods of August, 1909, Shafts Nos. 2 and 3 were damaged
+beyond repair, and sand and gravel, entering through them,
+<!--597.png--><span class="pagenum">565</span>blocked up
+the gallery to within about 150 ft. of Shaft No. 1. The interior
+timbering probably collapsed, due to cavings and disturbance in the
+river-bed during the period of maximum flood, but no explorations have
+been possible on account of the great quantity of water still coming
+through (at present more than 650 liters per sec.). For this reason the
+work of driving the gallery, as well as lining Shaft No. 1, has been
+suspended.</p>
+
+<div class="figcenter" style="width: 700px;">
+<img src="images/i28.jpg" width="700" height="409" alt="Fig. 2." title="" />
+<span class="caption"><span class="smcap">Plate XXVIII, Fig. 2.&mdash;View of Santa Catarina River in Flood, on August
+28th, 1909.</span></span>
+</div>
+
+<div class="figcenter" style="width: 600px;">
+<img src="images/i29.jpg" width="600" height="339" alt="Fig. 1." title="" />
+<span class="caption"><span class="smcap">Plate XXXI, Fig. 1.&mdash;Flush-Tank Carried Down by Flood of August
+27th-28th, 1909.</span></span>
+</div>
+
+<div class="figcenter" style="width: 600px;">
+<img src="images/i30.jpg" width="600" height="339" alt="Fig. 2." title="" />
+<span class="caption"><span class="smcap">Plate XXXI, Fig. 2.&mdash;View Showing Scouring Effect Of Flood
+On San Geronimo Aqueduct.</span></span>
+</div>
+
+<div class="figcenter" style="width: 700px;">
+<img src="images/i31.jpg" width="700" height="182" alt="Fig. 1." title="" />
+<span class="caption"><span class="smcap">Plate XXXII, Fig. 1.&mdash;View of Santa Catarina River After the
+Flood.</span></span>
+</div>
+
+<div class="figcenter" style="width: 700px;">
+<img src="images/i32.jpg" width="700" height="181" alt="Fig. 2." title="" />
+<span class="caption"><span class="smcap">Plate XXXII, Fig. 2.&mdash;View of Santa Catarina River Flowing Through
+Low-Lying Streets, 8 Days After the Flood.</span></span>
+</div>
+
+<p>On reaching the city, the flood of August, 1909, swept away two streets
+adjoining the river. These streets had been built on made ground, in
+what was originally the river-bed. The sewers and water mains laid in
+them were destroyed entirely, and some 460 ft. of the 24-in. cast-iron
+pipe, buried under the river-bed at a depth of 8 ft., were carried away.
+In relaying this portion of the main, and for protecting the remainder
+of it across the river, it is now proposed to encase it in a solid
+rubble concrete block, 8 ft. square, which will impart weight and
+stability against the scouring effect of floods.</p>
+
+<p>The South Reservoir is circular in shape, with an interior diameter of
+165.68 ft. at the top, and is partly excavated in the ground and partly
+completed by an embankment of vast proportions (<a href="#i507">Fig. 10</a>). Right after
+the flood of August, 1909, a wet spot appeared on the northeastern toe
+of the embankment, and it was supposed for some time that it was the
+effect of the saturation produced by the preceding rains, but, as it
+persisted for several months, it was obvious that its origin was in the
+interior of the reservoir, which was emptied when the writer took charge
+of the work. The first inspection revealed a horizontal crack in the
+concrete lining, about 310 ft. long and extending about 153° around the
+circumference on the north side. Throughout its length it coincided with
+the line of cut and fill. Vertical cracks, coinciding with the panel
+points in the lining, had also developed, and extended from the main
+horizontal crack to the roof. The circumstances originating this
+development can be conjectured by considering the position of the main
+crack, its characteristic features, and the conditions that preceded its
+formation. The coincidence of the crack with the joint of cut and fill,
+points to this line as a source of danger. An examination showed,
+besides, that the fracture was clean and sharp, ranging in thickness
+from a hair line at the ends to <sup>3</sup>&frasl;<sub>16</sub> in. at the center, and that its
+upper border projected over the lower one perceptibly, a proof that
+horizontal motion had taken place. The vertical cracks were a secondary
+effect, the consequence of the displacement immediately after it was
+scoured. A fracture was discovered in the floor of the reservoir. It
+started at the center and branched out into two diverging lines in a
+radial direction.</p>
+
+<p>The circumstance of two abnormal rainfalls, giving 35 in. in 9 days, the
+precipitation being concentrated in two periods, not far
+<!--598.png--><span class="pagenum">566</span>apart, of 42
+hours and 98 hours, respectively (<a href="#i485a">Fig. 4</a>), together with lack of
+provision for shedding the water from the roof of the reservoir and from
+the surrounding embankment, lead to the inference that the latter became
+saturated, increasing thereby in weight and decreasing in stability,
+especially in its steep inner face. A settlement and the consequent
+horizontal displacement, under these conditions, was natural. The
+concrete lining, only 16 in. thick at that height, was not sufficient to
+sustain the resulting strain, and the main fracture developed,
+permitting the stored-up water to leak into the bank. In time this
+seepage found its way under the bottom of the reservoir, softening the
+ground and producing a slight settlement which caused the crack in the
+floor. Had under-drainage been provided, as at the Obispado Reservoir,
+the actual conditions would have been noticed earlier. However, as the
+embankment is of vast proportions, stable in itself to sustain with a
+large margin of safety the weight of the stored-up water, there was no
+actual danger of failure, except for the fact that the material forming
+the structure, on account of its calcareous nature, is dissolved by
+water. Long exposure to this condition would, in time, open passages in
+the embankment, and it is certain that there would be cavings in its
+interior.</p>
+
+<p>The necessary grouting has been done, and provision is being made for
+water-proofing the interior of the reservoir and shedding the water from
+the roof and from the embankment, thus relieving the structure of the
+consequent strain.</p>
+
+<p>Another place in the works where floods have had a damaging effect is
+the Estanzuela intake basin, which, when the dam was completed, was
+filled to the overflow level in order to test its water-tightness. As
+this basin, when cleaned, was found to be slightly fissured on the north
+side, it was decided to line it with concrete. As shown in <a href="#i495">Fig. 8</a>, the
+lining does not cover its entire area, but only the central portion,
+leaving a strip on either side without protection. The flood of
+September, 1910, coming in greater volume than the previous ones of
+August, 1909, in passing through the narrow gorge at the entrance,
+undermined the lining in those places where it was not founded on solid
+rock. Figs. 1, 2, and 3,
+Plate XXXIII, show some of the damage caused by this flood. The buoyant
+effect of the water and the impact of large rolling boulders caused
+fractures all over the surface, and lifted the concrete lining bodily;
+but the dam proper, being founded on rock bottom, did not suffer any
+injury. In the future, in order to avoid the seepage of the ordinary
+supply, alluded to by the author, the water will be carried to the
+valve-house in an open rubble concrete channel, lined with cement mortar
+and built high up against the western hillside. The remainder of the
+basin will be paved with large boulders.</p>
+
+<div class="figcenter" style="width: 700px;">
+<img src="images/i33.jpg" width="700" height="362" alt="Fig. 1." title="" />
+<span class="caption"><span class="smcap">Plate XXXIII, Fig. 1.&mdash;Estanzuela Dam: Broken Concrete Basin
+Lining.</span></span>
+</div>
+
+<div class="figcenter" style="width: 700px;">
+<img src="images/i34.jpg" width="700" height="352" alt="Fig. 2." title="" />
+<span class="caption"><span class="smcap">Plate XXXIII, Fig. 2.&mdash;Estanzuela Dam: Broken Concrete
+Basin Lining, East Side.</span></span>
+</div>
+
+<div class="figcenter" style="width: 700px;">
+<img src="images/i35.jpg" width="700" height="354" alt="Fig. 3." title="" />
+<span class="caption"><span class="smcap">Plate XXXIII, Fig. 3.&mdash;Estanzuela Dam Sept. 26, 1910:
+View of Shearing Fractures of Wall and Lining After Flood Sept. 14-17, 1910.</span></span>
+</div>
+
+<p>In conclusion, the writer wishes to emphasize the point that,
+notwithstanding
+<!--601.png--><span class="pagenum"><a name="Page_567" id="Page_567">567</a></span>the
+severity of the test, relatively small damage was
+inflicted on the extensive works carried out under the author's design
+and direction. A test so severe that it caused serious damage and
+immense losses in the entire region, washing away kilometers of railroad
+track and destroying practically all the bridges within reach of the
+flood, is an occurrence of paramount importance, and should be
+remembered as a leading factor in the design of engineering works.</p>
+
+<div class="tb"></div>
+
+
+<p><span class="smcap"><a name="George_T_Hammond" id="George_T_Hammond"></a>George T. Hammond, M. AM. Soc.</span> C. E. (by letter).&mdash;In a country, such as
+that described in this paper, where water is valuable, and a shortage is
+at times possible, where the majority of the population is very poor,
+and water and sewage discharge are both to be paid for on a basis of
+volume, the question of the expected quantity of daily water supply and
+sewage flow per capita is of primary importance. This question,
+notwithstanding its difficulty, should be given a first place in the
+studies for water-works and sewerage projects, and should never be lost
+sight of in the design, which should be such that, while proper for the
+expected future flow for a reasonable time, should also be proper and
+economical for conditions which at present obtain and may change but
+slowly.</p>
+
+<p>It is desirable, of course, to get as much capacity in works as one can
+for the outlay, but there are instances where one can get too much for
+the money, as where a larger pipe than is necessary is used for a sewer,
+merely because it costs about the same as a smaller one, and as a result
+the cost of maintenance is permanently increased.</p>
+
+<p>The water-works were designed to supply 40,000,000 liters (10,582,000
+gal.) daily, which it was assumed would be sufficient for all future
+developments in Monterrey for a population of 200,000 at a per capita
+consumption of 200 liters (about 53 gal.) per day. The present
+population of the city is given as less than 90,000, there having been
+an increase of 22,000 in ten years (1891-1901), but it is evident that
+in the last ten years (1901-1911) this rate of increase has not
+continued. Taking into account all the data known to the writer, it does
+not seem that the city will attain a population of 200,000 in a great
+many years, if it ever does; but this is a matter of personal opinion,
+and is only stated as such.</p>
+
+<p>The present requirements of the city's population, assuming that each
+person uses 200 liters (53 gal.) per day, would be, at that rate, which
+is a very liberal one, only 18,000,000 liters (4,762,000 gal.) per day,
+or less than half the amount which may be provided.</p>
+
+<p>If the water were not to be metered and the sewage discharge paid for by
+measure, it is possible that the free use of water might lead to the
+usual waste with which all are fairly familiar; but the use of meters,
+and the rates charged, will reduce the water consumption
+<!--602.png--><span class="pagenum">568</span>to a minimum.
+This end will especially result from Section 5 of the Tariffs which
+provides that:</p>
+
+<p class="blockquot">"Groups can be formed of two or more small houses so as to obtain a
+joint service under the proportion shown in the tariff."</p>
+
+<p>This provision will keep down the per capita supply, among the majority
+of the people, to about 37<sup>1</sup>&frasl;<sub>2</sub> liters (10 gal.) per day. A similar
+provision led to abuse in Santiago de Cuba, as well as in other Cuban
+cities, where one householder, taking water, frequently delivers it to
+adjoining houses and tenements through rubber hose. As many as ten or
+twelve families are sometimes found to be supplied from one tap in this
+manner. Indeed, it may be stated as a rule, having but few exceptions,
+that where water is paid for by meter its use is always restricted.</p>
+
+<p>The water mains and distribution system, however, are so well laid out,
+and the whole design is so good, that the writer would not anticipate
+much difficulty because it is on rather too liberal lines for the
+present or probable future. It may, perhaps, be argued that it may cost
+more to keep the mains in such a system clean; but this extra cost will
+scarcely be of much moment, and will be offset by the greater lasting
+quality of the larger pipes. There is another feature of the problem,
+however, which is not affected favorably by a too liberal forecast of
+the per capita water supply, namely, the sewerage system.</p>
+
+<p>If it is assumed that, using 200 liters per capita per day, the total
+water supply of the city for the present population will be 18,000,000
+liters, and that this may double in fifty years, or even amount to
+40,000,000 liters in that time, it would seem that a rather liberal
+provision has been made for the water supply, and that this will
+scarcely be exceeded by the sewage, for the latter must come from the
+water supply, there being little or no ground-water and no storm-water
+taken into the sewers. Designing the sewers to flow half full for all
+diameters less than 18 in., and seven-tenths full for all larger sizes,
+it would seem that this would give ample capacity for all time to come
+in such a city, and that good practice would not exceed these figures,
+it being more desirable that the sewers should not be too large to work
+well, than that they should be large enough in all places to meet every
+possible contingency. If all the sewers of a system are too large, the
+condition is incurably bad; while, if a few miles prove to be too small,
+on account of growth and prosperity not anticipated by the designer, it
+will be easy enough to relay such parts when this becomes necessary.</p>
+
+<p>Mr. Conway states that:</p>
+
+<p class="blockquot">"The sewers are designed on a very liberal basis, namely, on the
+assumption that when flowing half full the quantity to be dealt with
+will be 380 liters [100 gal.] per capita per day, with a maximum rate of
+flow of 200 per cent."</p>
+<!--603.png--><p><span class="pagenum">569</span></p>
+
+<p>If the writer understands this statement correctly, it means that the
+sewers, flowing half full, will carry 380 liters per capita in 12 hours,
+or are designed with 200% of the capacity required to take the assumed
+flow in 24 hours.</p>
+
+<p>It was assumed that each house would be occupied by 7 persons and have a
+frontage of 12<sup>1</sup>&frasl;<sub>2</sub> m. (about 41 ft.), that is, about 700 gal. per day
+per house, the maximum flow rate being 200%, or at the rate of 700 gal.
+per house in 12 hours.</p>
+
+<p>It is to be remembered that nearly all the houses are of one story, and
+that, as a rule in tropical and sub-tropical countries, the per capita
+use of water diminishes with some function of the increasing number of
+inhabitants in one house. Most of the water is used in the kitchen, and
+where there are 7 persons instead of 5, the quantity used by the smaller
+number will generally serve the larger.</p>
+
+<p>The writer is unable to understand how this quantity of sewage will be
+produced, especially as the author states that, as far as the company is
+concerned, it is limited to the removal and disposal of the sewage, and
+is not required to provide for storm-water. He also states that:</p>
+
+<p class="blockquot">"Apart from that fact, however, the best system for a city like
+Monterrey, where rainfall for many months at a time is very scarce, is
+the strictly 'separate system'."</p>
+
+<p>The minimum velocities in the sewers, when running full, vary between
+0.91 and 1.5 m. (from 3 to 5 ft.) per sec., and will be the same flowing
+half full.</p>
+
+<p>From the foregoing data it will be observed that:</p>
+
+<p class="blockquot" style="text-indent: -1.5em; padding-left: 1.5em;">(1) The water supply is the only source from which sewage flow is
+anticipated;</p>
+
+<p class="blockquot" style="text-indent: -1.5em; padding-left: 1.5em;">(2) The water supply is very liberally estimated at 200 liters (53
+gal.) per capita daily;</p>
+
+<p class="blockquot" style="text-indent: -1.5em; padding-left: 1.5em;">(3) For purposes of sewer design, the daily flow of sewage expected
+(all of which is derived from the water supply of 200 liters per
+capita) is estimated at 380 liters per capita, with a maximum rate
+of flow of 200% (or at the rate of 760 liters per capita), and
+with this quantity the sewers are designed to flow only half full;</p>
+
+<p class="blockquot" style="text-indent: -1.5em; padding-left: 1.5em;">(4) The gradients are such that a velocity of from 3 to 5 ft. (0.91 to
+1.5 m.) per sec. will be secured in the sewers flowing half full
+with the above quantity of flow per capita.
+</p>
+
+<p>The writer does not agree with this method of computation, as he feels
+sure that it will give sewers which are too large, with grades too steep
+for the best obtainable results. His experience, extending over more
+than twenty years in sewer design and hydraulic work, convinces him that
+the method pursued is wrong in principle.</p>
+
+<p>The principles involved in sewer design are first of all hydraulic. The
+quantity of flow, in the nature of things, cannot be forecasted
+<!--604.png--><span class="pagenum">570</span>accurately;
+success depends on getting the nearest possible
+approximation to average conditions. If 200 liters per capita per day is
+a liberal allowance, and 40,000,000 liters per day is a liberal
+expectation at this rate for double the present population, and the
+sewers are designed to flow half full only, why should this again be
+doubled?</p>
+
+<p>The design of a sewer system for a city such as Monterrey is, in fact, a
+very difficult problem, especially as the quantity of sewage will be
+very limited, flush-water will have to be used in considerable
+quantities, and water in that part of the world is precious at all times
+and often scarce. Under these circumstances, the size or shape of the
+pipes selected for the lateral sewers, should have been such as would
+more nearly agree with the requirements than does the 8-in. circular.</p>
+
+<p>A. P. Folwell, M. Am. Soc. C. E., writing of the 8-in. circular size,
+states:<a name="FNanchor_10_10" id="FNanchor_10_10"></a><a href="#Footnote_10_10" class="fnanchor">[10]</a></p>
+
+<div class="footnote"><a name="Footnote_10_10" id="Footnote_10_10"></a><a href="#FNanchor_10_10"><span class="label">[10]</span></a> "Sewerage," by A. P. Folwell, M. Am, Soc. C. E.</div>
+
+<p class="blockquot">"To secure a flow in this pipe having an average depth of 4 inches would
+require the sewage from a population of 6,500. In general it may be said
+that the ordinary depth of flow in any sewer should not be less than 2
+inches, nor should it be less than <sup>1</sup>&frasl;<sub>2</sub> the radius of the invert, since
+if it is so there is much more danger of deposits forming along the
+edges and even in the center of the stream. It will sometimes be
+impossible to meet this requirement fully, but it should be kept in mind
+as extremely desirable."</p>
+
+<p>Sewers of small size should be proportioned throughout the system so
+that the depth of the minimum daily flow in the invert, and the velocity
+of flow, will be the best possible to prevent deposits. The transporting
+power of water is dependent mainly on the depth of flow, a minimum
+velocity being selected rather than a minimum depth of flow. To those
+who have had charge of the maintenance of sewers, as well as of their
+design and construction, this principle seems so obvious that it is
+always a surprise to see it disregarded by designers, who in these days
+seem inclined to consider sewerage as a system of grades and sizes of
+pipes installed for ideal, rather than for actual, conditions. Messrs.
+Staley and Pierson have well stated the principle involved as follows:</p>
+
+<p class="blockquot">"A stream having a depth of flow sufficient to immerse solid matter held
+in suspension, to a certain extent lifts it and carries it forward. The
+entire surface is also exposed to the action of the current. A stream
+having an equal velocity but a less depth in proportion to the diameter
+of the solid matters to be transported, evidently has less transporting
+power. * * * An amount of sewage which can be properly transported by a
+circular sewer of a given size, cannot be as efficiently transported by
+one of larger diameter."</p>
+
+<p>From some strange idea, which is apparently without foundation in logic
+or based on any actual justification from experience, it has of late
+years become the practice of designing engineers to make the
+<!--605.png--><span class="pagenum">571</span>8-in.
+circular pipe the smallest size for sewers; and it is not improbable
+that the designer of the Monterrey system has merely followed this
+example. It has also become the frequent practice of designers to give
+every length of sewer all the grade possible, regardless of the fact,
+taught both by hydraulics and experience, that the best grade is that
+which will give as much depth of flow as is consistent with a scouring
+velocity.</p>
+
+<p>Some years ago it was the standard practice, in the "strictly separate
+system" of sewers, to use the 6-in. pipe as the minimum size, and, as
+far as the writer has been able to discover, after giving the matter a
+rather extensive investigation, the 6-in. size has given excellent
+results wherever its use was proper. In places where it has not
+succeeded there were excellent reasons why it should not have been
+selected, and these could easily have been observed at the time the
+designs were made. The best sizes for the sewers in a given system is
+always a matter to be determined by local conditions; but there seems to
+be no reason why the 6-in. size should not be used where the flow is so
+slight that the 8-in. will not work well; or where the velocity must of
+necessity be so great that a flotation depth of flow cannot be
+maintained in the larger size. As to likelihood of clogging and
+stoppage, the writer's opinion, based on the maintenance of three rather
+extensive systems in different parts of the United States, in each of
+which the 6-in. size comprises more than 75% of the whole length of
+pipe, and of three other systems, one having 12-in. and two having 8-in.
+as the minimum sizes, is that the 6-in. size, where properly used, is
+less likely to become clogged than either of the others used improperly.
+The cost of maintaining the 6-in. pipe lateral, under these
+circumstances, is much less than that of maintaining the 8-in. lateral.</p>
+
+<p>The 6-in. pipe is not being used now as much as the 8-in., and in most
+cases this is probably because the capacity of the latter is nearly
+double that of the 6-in., and costs only a few cents more per foot. If
+there is a sufficient population per acre, or if, within 30 or 40 years,
+such a population is anticipated as will fill the 8-in. pipe half full,
+its use, of course, is justified and necessary; but where it is quite
+evident that this will never occur, its use is counter-indicated.</p>
+
+<p>In Monterrey, where the building lots have a frontage of 41 ft., where
+the houses, as a rule, are only one story high, where the water service
+is metered and paid for, and the sewage flow is also paid for, there
+seems to be no reason to justify the use of 8-in. pipe for the upper
+reaches of the smallest sewers. The sewage flow to be anticipated will
+probably never be sufficient to keep an 8-in. pipe sewer in a good clean
+condition at the upper ends of the lines of sewers without excessive
+flushing; and the sharper or steeper the grade on which it is placed,
+the worse will be the result, because the sharper the
+<!--606.png--><span class="pagenum">572</span>grade, the
+thinner the flowing thread of sewage will be drawn out in the invert; on
+the other hand, if the grades are flat, the slight quantity of sewage
+flow will be spread out in a sluggish stream, without sufficient depth,
+on the bottom of the 8-in. pipe.</p>
+
+<p>Where a wide surface is given to a small quantity of flowing sewage, it
+stagnates slowly along the bottom of the sewer, leaving frequent
+deposits to undergo decomposition and create foul air, if not to choke
+the sewer, a result often produced; and where a circular sewer which is
+too large for the ordinary flow is given a strong velocity by using
+steep grades, the stream, though flowing rapidly, is drawn out to such a
+thin thread that it will not effect the flotation of the solid masses in
+the sewage brought in at house connections, and the shallow and thin
+stream simply flows around such masses until a dam or obstruction forms
+and the sewage is backed up sufficiently to force the obstruction
+farther down, to form another obstruction in a larger pipe below.
+Flushing may possibly keep such a sewer fairly clean; but, as usually
+practiced, it is effective only for a few hundred feet from the
+flush-tank; and the quantity of flush-water required by an 8-in. pipe is
+more than twice as much as that required to keep the 6-in. pipe clean.
+Ventilation is better in the smaller sewer than in the larger, as there
+is less air to move; but the elaborate ventilating stacks provided at
+Monterrey may take care of this; and it is evidently a place where
+ventilation will be needed.</p>
+
+<p>The ideal size and shape of cross-section for a sewer is such as will
+give the best flotation to moving solids which are being carried along
+by the flow; and this means the sewer that, with the expected ordinary
+or average flow, will give the best depth in the invert, when the
+velocity of flow is sufficient to keep suspended solids, grit, etc.,
+moving at a rate of from 2 to 3 ft. per sec. The size, however, is
+limited by practical considerations. The circular pipes cannot well be
+less than 6 in. in diameter, because the house connections cannot well
+be less than 4-in. pipe, and the sewer should be larger than the house
+connections, for various practical reasons; but, in order to secure
+flotation and a scouring flow, the smallest pipe, or the pipe having the
+smallest invert radius, that practical considerations permit, should be
+selected. The grade should be such, and the collecting system so laid
+out, that the flow may be conserved as far as possible, and the sewage
+flow should be kept of as great a depth in the invert, or bottom of the
+sewer, as safety in self-cleansing velocity will permit. This will save
+flush-water and prevent stoppages, and thus reduce the cost of
+maintenance to a minimum. For good sanitary practice, the sewers should
+be designed, first of all, to comply with the requirements of the
+present, or immediately expected, ordinary flow, with some reasonable
+allowance for the future. They should be
+<!--607.png--><span class="pagenum">573</span>neither
+too large nor too
+small, and the grade should neither be too great nor too little, to
+secure the best flotation and scouring effects and the best flush-wave
+action under all circumstances.</p>
+
+<p>The use of cement concrete pipe for sewers seems to be growing in favor;
+nor is this surprising, in view of the many improvements made in their
+design and manufacture. The excellence of the concrete pipe used in
+Monterrey and its success, suggest the query: Why was it not used still
+more extensively?</p>
+
+<p><a href="#TABLE_13">Table 13</a> shows that the cement pipe cost much less than the vitrified
+tile, or "fire-clay" pipe. Thus, the 38.1 cm. (15-in.) fire-clay cost
+6.14 pesos per lin. m., the 45.7 cm. (18-in.) cost 8.80 pesos, and the
+50.8 cm. (20-in.) cost 11.30 pesos. Compared with this, the concrete
+pipe was much the cheaper; the 55.9 cm. (22-in.) cost 5.93 pesos, which
+is less than the cost of the 38.1 cm. (15-in.) fire-clay; and the 61.0
+cm. (25-in.) concrete pipe cost 7.30 pesos, which is less than the 45.7
+cm. (18-in.) fire-clay.</p>
+
+<p>The writer's experience with concrete pipe, derived mainly from a long
+service in sewer design and construction in Brooklyn, N. Y., leads him
+to believe that at Monterrey the whole sewer system might, with
+advantage, have been built of concrete pipe, using an egg-shaped pipe
+with an area slightly larger than an 8-in. circle, designed for a
+discharge equal to an 8-in. pipe for all the smaller sewers. The invert
+of such an egg-shaped pipe would fulfill the present requirements in
+carrying a very small flow with good flotation depth, better than would
+a 6-in. circular pipe, and the reserve capacity of the 8-in. pipe would
+be secured without interfering with good present service. Egg-shaped
+pipes, similar to those used in Brooklyn, the writer believes, would
+have given far better satisfaction throughout the Monterrey sewerage
+system than circular fire-clay pipe, and would have cost no more, but
+probably less. The egg-shaped pipe referred to is made with a flat base
+and a self-centering joint, thus insuring perfect alignment, and a
+smoother interior surface than can be obtained with fire-clay pipes.</p>
+
+<p>Brooklyn has about 450 miles of concrete pipe sewers, of all sizes less
+than 24 in., the greater part of which is egg-shaped. There are also
+about 250 miles of vitrified stoneware circular pipe sewers of similar
+sizes, and the cost of repairs and replacing pipe, over a period of
+years is about the same per mile for each kind. Incidentally, it may be
+stated that the annual cost of repairs per mile on both kinds of pipe is
+very small, and is only about one-fifth of the cost of repairs per mile
+on the brick sewers, of which there are about 200 miles.</p>
+
+<p>The principal advantages and disadvantages of cement concrete pipe
+sewers may be summed up as follows:</p>
+<!--608.png--><p><span class="pagenum">574</span></p>
+
+<div class="center"><span class="smcap">Advantages of Concrete Pipe</span>.</div>
+
+<p class="blockquot" style="text-indent: -1.5em; padding-left: 1.5em;">
+(a) Cement concrete pipe is usually less costly than vitrified pipe.</p>
+
+<p class="blockquot" style="text-indent: -1.5em; padding-left: 1.5em;">
+(b) It can be formed in any shape desired.</p>
+
+<p class="blockquot" style="text-indent: -1.5em; padding-left: 1.5em;">
+(c) It is not cracked by vibration, and resists impact better than
+vitrified pipe, for which reason it is a better material to lay
+near the surface of a street in which there is heavy traffic.</p>
+
+<p class="blockquot" style="text-indent: -1.5em; padding-left: 1.5em;">
+(d) It is not affected by ordinary sewage.</p>
+
+<p class="blockquot" style="text-indent: -1.5em; padding-left: 1.5em;">
+(e) The cost of repairing and maintaining is about the same as for a
+vitrified pipe sewer.</p>
+
+<p class="blockquot" style="text-indent: -1.5em; padding-left: 1.5em;">
+(f) It can be made in the city or town where it is to be installed,
+thus giving the locality the advantage of having some of the money
+paid for labor in its manufacture spent in the place where the
+sewers are being put in, where it is raised as a tax, etc.; also
+saving freight charges, etc.</p>
+
+<p class="blockquot" style="text-indent: -1.5em; padding-left: 1.5em;">
+(g) It can be made under the most careful local supervision and
+inspection, of selected material, by the engineer who is
+responsible for the success of the work. Vitrified pipe can seldom
+be made in this way.</p>
+
+<div class="center"><span class="smcap">Disadvantages of Concrete Pipe</span>.</div>
+
+<p class="blockquot" style="text-indent: -1.5em; padding-left: 1.5em;">
+(a) If not carefully made and of the best of materials, it is subject
+to failure by disintegration, etc.</p>
+
+<p class="blockquot" style="text-indent: -1.5em; padding-left: 1.5em;">
+(b) It will not stand strong chemical action, and therefore the
+smaller sizes should not be used where they are likely to be
+exposed to trade wastes containing strong acids. In the larger
+sizes the quantity of flow mixes so quickly with the trade wastes
+that this danger is minimized, and it is very seldom that even the
+smaller sizes become affected; but vitrified pipe may be used in
+places where chemical action is anticipated.</p>
+
+<p class="blockquot" style="text-indent: -1.5em; padding-left: 1.5em;">
+(c) If not properly made, it will be attacked by steam and hot vapor,
+and by animal fats in the sewage; but, if properly made, it is not
+affected by these.</p>
+
+<p class="blockquot" style="text-indent: -1.5em; padding-left: 1.5em;">
+(d) Unless reinforced or made very thick, it will not stand as great a
+crushing load as the best vitrified stoneware pipe; but, as sewers
+are not intended to be used under very heavy pressure, this is not
+so very important. It is amply strong to withstand any internal
+pressure or any external crushing load to which it probably will
+be submitted.</p>
+
+<p class="blockquot" style="text-indent: -1.5em; padding-left: 1.5em;">
+(e) Under a considerable head of ground-water, it may permit water to
+infiltrate through its walls for a considerable time after it is
+laid, thereby temporarily increasing the flow, which, if the
+sewage is to be pumped, will increase the cost of pumping. This
+difficulty can be met by using a carefully selected mix of
+materials in making the pipe, and by making
+<!--609.png--><span class="pagenum">575</span>the joints carefully.
+Infiltration through concrete diminishes rapidly after the sewer
+is in use; it occurs in vitrified pipe, also, to some extent.</p>
+
+<p>The house connection drain adopted in Monterrey, with the disconnecting
+trap, is very much like one which the writer has seen introduced with
+very bad result. These are being removed as rapidly as possible by one
+of his clients, a sewerage company, in the Southern States. It has been
+a fruitful cause of stoppages and bad smells; the ordinary method now in
+general use is much better. In the design shown, it would seem that
+there may even be some danger that the ventilation of the sewer by the
+stand-pipes in the streets may force the traps.</p>
+
+<p>One is rather surprised to learn that the main outfall sewer is designed
+with a capacity of 90,000,000 liters per day, the present sewage being
+estimated as not more than 18,000,000 liters, and the far future being
+thought to require only 40,000,000 liters. Why this excessive size?
+Possibly the surplus water which it is to carry is to be discharged into
+the sewers from the water supply system direct, and is intended for
+irrigating the land at the disposal area, when the sewage is
+insufficient for this purpose. The author states that all surface water
+is strictly excluded.</p>
+
+<p>The method of sewage disposal gives rise to several questions. It is
+proposed to use an extensive area for growing crops, which are to be
+irrigated with sewage. The paper states that the underlying strata at
+Monterrey contain numerous caverns, and the first question is: What will
+be the effect on the water supply of other towns lower down the valley?
+The writer recollects a serious outbreak of typhoid fever in Bluefield,
+W. Va., caused by the pollution of the water in similar strata finding
+its way through unknown underground caverns and channels to the city's
+water supply.</p>
+
+<p>The next question is: What crops will be grown? It is a well-known fact
+that vegetables grown by the use of sewage as a fertilizer, are unsafe
+in a raw state for human consumption. This is well-known to European
+travelers in China and Japan, where the use of fecal matter as
+fertilizer renders the various water supplies (where not filtered and
+disinfected) and all green vegetables, unsafe, on account of typhoid
+germs. Moreover, crops not intended for human consumption, which are
+grown on lands irrigated by sewage bearing typhoid germs, etc., are
+unsafe for men to handle; even to store them may cause a dissemination
+of disease. It is evident, therefore, that the whole sewage flow should
+be in some manner disinfected at least, if not filtered, before it is
+used.</p>
+
+<p>The method of sewage disposal and the use of merely settled septic
+sewage for irrigation seem to be open to objection. The disposal plant
+is not sufficiently effective to meet the present requirements of
+sanitary
+<!--610.png--><span class="pagenum"><a name="Page_576" id="Page_576">576</a></span>science;
+and the sludge-pit will be certain to breed a pest of
+flies, if it is not also an intolerable nuisance on account of foul
+smells. Monterrey would seem to be a proper place for the introduction
+of the Imhoff tank, with percolating filters, and a final settling tank,
+the effluent being disinfected, before entering the latter tank. The
+flow might then be used safely for irrigation purposes for crops not to
+be eaten uncooked by man. The writer does not see how the method
+provided can possibly fulfill the object stated, to distribute on the
+land an effluent which will be "innocuous and clear," or how any
+consequential degree of purification can be obtained in the tanks
+provided.</p>
+
+<p>While there are described in this paper many things to find fault with,
+there are also many things to commend. The water supply system, with its
+reservoirs, etc., seems to be admirable; and the methods of construction
+by which the expense for forms was reduced is very interesting. The
+parking and ornamentation of the grounds over the reservoir roofs cannot
+fail to benefit the people and popularize the work.</p>
+
+
+<div class="tb"></div>
+
+
+<p><span class="smcap"><a name="Rudolf_Meyer" id="Rudolf_Meyer"></a>Rudolf Meyer, M. AM. Soc</span>. C. E. (by letter).&mdash;The writer, as Engineer
+for the Government (guaranteeing the concessionaires a gross return of
+10% per annum on the capital invested), and as inspector of the various
+works has had exceptional opportunities to become acquainted, not only
+with their construction, but also with events leading up to the granting
+of the final concession under which they were built and will be
+extended. In order to judge of the extent to which the different
+engineers, in their turn contributed toward the design of these works,
+the writer has thought it desirable to submit a complete statement of
+all matters relating to the inception, investigations, surveys, tests,
+etc., previous to the adoption of the present plans.</p>
+
+<p>Data regarding former investigations, plans, and concessions which have
+since lapsed, have been obtained from the Government archives. These
+refer to periods prior to Mr. Conway's engagement, and anterior to the
+retaining of Mr. Schuyler by the concessionaires, and Mr. Binckley's
+connection with the scheme, and they are presented here as complementary
+to the information in the paper.</p>
+
+<p>Samuel M. Gray, M. Am. Soc. C. E., acting in the interest of some
+American capitalists (who had been induced by Col. J. A. Robertson, of
+Monterrey, to look into the merits of a concession acquired by him, for
+building these works), being guided by the Government's proposition to
+supply the city with water by damming the flood-waters of the Santa
+Catarina River in the narrow gorge through which the stream emerges from
+the Sierras, some eight miles from the city, had several soundings made
+and reservoir sites surveyed in the first two box cañons up the river,
+and prepared and presented to the Government several alternative
+projects, besides the one mentioned by Mr. Schuyler. Several different
+dam sites were designated by Mr.
+<!--611.png--><span class="pagenum">577</span>Gray,
+whose investigations extended
+over some two years, and were finally abandoned after he had designed
+the general outlay for a complete network of water mains and sewers for
+the city, on account of the unwillingness of the Government at that
+time, about 1897, to grant any guaranties as to bonds or income to the
+concessionaire or his assigns. Mr. Gray did not favor the general scheme
+of storing flood-waters as a water supply, but strongly recommended to
+the attention of the Government the greater advantages of deriving the
+supply from subterranean flow in the river, by an infiltration gallery
+driven into the water-bearing gravels in the Santa Catarina Cañon (only
+a short distance above the place where Mr. Binckley afterward
+established his bore-holes across the river). He proposed to take
+advantage of the steep slope of the river at a turn in the cañon, and
+from the lower end drive a tunnel through a projecting rock spur, which
+tunnel, though starting well above the ordinary reach of floods, would
+terminate in water-bearing gravel, at a sufficient depth below the
+surface of the river-bed to intercept part of the underflow. Mr. Gray,
+through investigations made under his direction, by Nathaniel Turner, M.
+Am. Soc. C. E., had ascertained that there was an abundant subterranean
+flow, and work had actually been started on the proposed tunnel.</p>
+
+<p>The results of Mr. Gray's investigations were put at the disposal of
+Messrs. Mackenzie, Mann &amp; Co. by Mr. Robertson, at whose offices Mr.
+Binckley prepared the first plans submitted by him for the approval of
+the Government.</p>
+
+<p>After Mr. Gray's investigations, Messrs. Mackin and Dillon (F. H.
+Dillon, Assoc. M. Am. Soc. C. E.), under contract with the Government,
+prepared the following plans: For a dam in the Santa Catarina Cañon; for
+a pipe line, similar to the one proposed by Mr. Gray, to a reservoir and
+settling basin on the left bank of the river (a short distance above
+where the provisional pumping station was established afterward by Mr.
+Binckley), but on the flat above the bluff skirting the river,
+practically at the same elevation as the present high-pressure
+reservoirs; for a complete network of water mains and sewers in the
+city, indicating the approximate direction in which the sewage would be
+disposed of, either by turning it into the river or by spreading it over
+suitable lands, the location of which was to be determined later; and
+also a complete set of specifications.</p>
+
+<p>On these data bids were invited by publication, and inquiries were
+received from several parties. Finally, Messrs. Stocker and Walker, of
+Scranton, Pa., entered into negotiations with the Government, and the
+present concession was agreed upon and granted.</p>
+
+<p>Messrs. Stocker and Walker engaged the late E. Sherman Gould, M. Am.
+Soc. C. E., to prepare a plan for a storage dam in the Santa Catarina
+Cañon, and submitted plans for water distribution and sewers
+<!--612.png--><span class="pagenum">578</span>in the
+city, slightly modifying the original plans of Messrs. Mackin and
+Dillon.</p>
+
+<p>In the fall of 1905, the concession was acquired by Messrs. Mackenzie,
+Mann &amp; Co., of Toronto, Canada, together with all plans, etc., presented
+by the original concessionaires. The new concessionaires stated that
+they would examine the whole situation again, for the purpose of
+presenting modified plans for works.</p>
+
+<p>Mr. Schuyler, in the interest of the new owners, had paid one flying
+visit to Monterrey when Mr. Gray's projects were brought to his notice,
+and the writer had an opportunity to show him the tunnel which had been
+started. Mr. Schuyler left for Brazil and did not return until February,
+1906, when he was accompanied by the Chief Engineer appointed by the
+concessionaires. Messrs. Schuyler and Binckley then prepared plans for
+the water distribution and sewer systems in the city and for a
+provisional water supply to be pumped at San Geronimo, some two miles up
+the river. The new plans for the city work followed closely the general
+disposition by Mr. Gray, the principal difference being that the main
+reservoirs for the permanent water supply were located to the south
+instead of to the west. This change was due to the results of an
+investigation, made during Mr. Schuyler's absence in Brazil, by Mr. F.
+S. Hyde, late Hydraulic Engineer of the Necaxa Water Power plant, who,
+accompanied by the writer, visited the whole water-shed of the Santa
+Catarina River in October, 1905, in search of suitable dam sites and
+prospects of power development. Mr. Hyde extended his studies to the
+Santiago Cañon, southeast of the city, recommending finally that the
+water be brought from that cañon, and that wells be dug in different
+points of the Santa Catarina River between San Geronimo and the entrance
+of the cañon, and tested by pumping, for the purpose of establishing
+levels and ascertaining the available amount of underflow, with a view
+of determining the location for an infiltration gallery high enough up
+the river to permit of a gravity delivery and under good pressure in the
+city.</p>
+
+<p>In view of Mr. Hyde's report, and as the result of a visit to the
+Santiago Cañon, Mr. Schuyler decided to locate the reservoirs south of
+the town, intending to bring in water from the southeast, from springs
+in the Santiago Cañon, and also by infiltration from Santa Catarina, his
+and Mr. Binckley's scheme of water supply being for the same pressure
+throughout the city.</p>
+
+<p>To supply water during construction, and partly meet the demands of the
+city, Mr. Binckley, on his arrival, decided to establish a provisional
+pumping station at the well in the river nearest to town, started by
+direction of Mr. Hyde at San Geronimo. This well was situated within the
+bed of inundation of high floods, on a low bank, at the foot of a
+conglomerate bluff some 20 ft. high, limiting a flat which was above the
+reach of any flood. It was on the same side of the river
+<!--613.png--><span class="pagenum">579</span>as the city,
+and there was plenty of good ground on the flat above for the
+establishment of a reservoir.</p>
+
+<p>A slightly shorter pipe line was secured by crossing the river, building
+the reservoir (a substantial concrete-lined and vaulted-over structure)
+on the opposite bank, laying out the pipe line to follow that bank
+nearly to the city, and finally crossing back again; but the result has
+been that since the flood of August, 1909, in which the river crossings
+were destroyed, the reservoir remains isolated on the other side of the
+river from town, though intended to form part of the permanent works and
+act as a compensating reservoir for equalizing the pressure of the
+high-pressure system. Fortunately, the pumping station, the larger
+pumps, and the boilers, had been moved up the bank (after a rapid rise
+in the river on August 10th, 1909) to the new wells established by Mr.
+Conway on the line of the proposed prolongation of the infiltration
+gallery. The reservoir, however, is left to stand alone on the other
+side of the river, and its usefulness will not be restored until a new
+line is laid across the river, re-establishing its connection with the
+new pump line and the new and permanent pipe line to be laid along the
+north bank from the pumping station to the city. This will free
+Monterrey from the constant menace of a water famine. At present its two
+main water supplies may be cut off by unexpected floods like those of
+1909 and 1910, as both supplies are carried across the river, and though
+only the cast-iron pipe connecting with the water supply from Estanzuela
+was carried away by the flood, the concrete conduit of the San Geronimo
+low-pressure supply was seriously threatened. Such risks are too great
+to be carried for any length of time; besides, a succession of dry years
+would cause such a reduction in the Estanzuela supply as to require an
+additional reserve in the way of pumping stations drawing on the
+under-flow of the river, such as already exists in San Geronimo.</p>
+
+<p>Afterward, Messrs. Schuyler and Binckley submitted preliminary plans and
+profiles for the projected concrete gravity conduit from Estanzuela to
+the reservoir south of the city, and Mr. Binckley submitted excavation
+plans for two reservoirs, only one of which was built, and from designs
+by Mr. Conway.</p>
+
+<p>Stephen E. Kieffer, M. Am. Soc. C. E., was intrusted by Mr. Binckley
+with the revision of the plans of the water distribution and sewers. The
+southern half was approved by the Government and executed according to
+his plans; the northern part was afterward revised by Mr. Conway and has
+been partly built.</p>
+
+<p>The final maturing of the project of an infiltration gallery in San
+Geronimo as a low-pressure gravity supply, the division of the city into
+high- and low-pressure districts corresponding to the two supplies, with
+one reservoir, instead of two to the south of the city, and the other to
+the west at the Obispado, the entire details of both these gravity
+<!--614.png--><span class="pagenum"><a name="Page_580" id="Page_580">580</a></span>schemes,
+and of the whole sewage disposal scheme, as well as the
+modification introduced into the city work for the northern half, are
+unquestionably due to Mr. Conway, independently of the general views
+which may have been held on those points by other engineers.</p>
+
+<p>In March, 1910, Mr. Conway left Monterrey, all the principal works being
+finished. Since that time Vicente Saucedo, Assoc. M. Am. Soc. C. E., has
+put in many additional water mains and sewers in the northern part of
+the city, and is finishing the <i>force majeure</i> work caused by the
+destruction wrought in the districts along the river banks by the
+extraordinary floods.</p>
+
+<p>The writer, having had an opportunity to watch the earnest efforts of
+the several engineers connected with these works, in the course of their
+design and construction, resulting without doubt in being the first of
+their kind built in Mexico, has been induced to contribute this
+discussion in order to bring out clearly the share of each.</p>
+
+<p>Mr. Pitkethly's apprehensions as to the adequacy of the system of
+ventilation adopted have not been realized, in part perhaps because the
+houses, though generally of only one story, have such high ceilings that
+the tops of their vent pipes are generally higher than the ventilating
+columns at the heads of the branch sewers.</p>
+
+<div class="tb"></div>
+
+
+<p><span class="smcap"><a name="George_Robert_Graham_Conway" id="George_Robert_Graham_Conway"></a>George Robert Graham Conway, M. AM. Soc</span>. C. E. (by letter).&mdash;The writer
+regrets that some features of the works described in this paper have
+failed to call forth the many useful criticisms which he expected, and
+his remarks, therefore, are limited to the few points which have been
+raised. He is particularly indebted to Messrs. Schuyler, Meyer, and
+Saucedo for adding supplementary information of value to the paper, but
+regrets that he cannot support Mr. Binckley in his claim that "the
+entire general design of the system, as well as the extensive
+hydrological studies and final selection of the sources of water supply,
+was completed in 1906," etc. On May 1st, 1907, when the writer assumed
+responsibility as Chief Engineer, he was unfortunately confronted with
+the fact that very little data and only a few preliminary and incomplete
+plans were available. His first duty was to report upon the final
+sources of supply, and the recommendations made in his report (dated
+July 12th), received Mr. (now Sir William) Mackenzie's approval during
+the same month. The final plans, upon which the approval of the State
+Government was definitely obtained, were prepared by the writer during
+the summer of 1907, were submitted to the Governor of the State, Gen.
+Bernard Reyes, on October 19th, and received his approval on December
+12th, 1907. No works, with a long preliminary history, such as those at
+Monterrey, can rightly be said to be due to any one individual; many
+engineers contributed to the final result, and the writer willingly
+acknowledges his indebtedness to the able men, who, for ten years prior
+to the construction of the
+<!--615.png--><span class="pagenum">581</span>works,
+investigated the particular problems
+which were met&mdash;problems which were not only of an engineering and
+physical nature, but racial and financial. The responsibility of
+constructing the works in their present form, and leaving them
+practically complete, did, however, fall on the writer's shoulders.</p>
+
+<p>Messrs. Pitkethly and Hammond have criticized the basis of the
+calculations upon which the sewer system was laid down. In considering
+this problem, it is necessary to remember that, in designing this
+system, there was practically no information upon which to base the
+calculations; and the writer believed that the wisest course was to
+anticipate a liberal growth, and provide a large margin of safety. In
+designing a sewer system in older and well-established communities, the
+engineer is generally able to compile considerable information regarding
+the probable sewage flow for which it is necessary to provide. In
+Monterrey this quantity was absolutely unknown. The writer's practice in
+other places has been to assume that about 8% of the total daily
+discharge of sewage will flow off in one hour; and, from many curves
+which he has plotted regarding sewage flow in British towns, this rate
+appears to him to be approximately correct. In Monterrey, however, the
+old Mexican traditions are rapidly changing, and the city is now
+becoming one of the most Americanized in Mexico; the old one-story
+houses will give way in time to buildings of several stories&mdash;a change,
+already noticeable, which has occurred during the past few years,
+particularly in the business portion of the city. Taking these facts
+into consideration, it is believed that it would be, not only bad
+engineering, but bad business, for a company whose concession lasts 99
+years, to provide sewers as small as 6 in., as Mr. Hammond would
+recommend, and then be called upon, under the terms of the concession,
+to relay larger sewers at a future date, thus incurring further capital
+expenditure upon which no Government guaranty would apply, and no
+further revenue be obtained. In matters of this kind, not only the
+engineering, but the commercial, aspect of the question must be kept in
+view, and this point, the writer must frankly admit, he has always
+seriously considered.</p>
+
+<p>The writer's experience with reference to the method of ventilating
+sewers by tall columns extends over many years, and he still maintains
+that no other system gives such satisfactory results. In this view he
+finds considerable support in a recent paper on "Salisbury Drainage," by
+Mr. W. J. E.
+Binnie,<a name="FNanchor_11_11" id="FNanchor_11_11"></a><a href="#Footnote_11_11" class="fnanchor">[11]</a> written
+since the system at Monterrey was
+installed, in which the result of a series of experiments carried on
+during 1906-07 are given. At Salisbury, England, 68 ventilators, 6 in.
+in internal diameter, 30 ft. high, were connected to the main sewer by
+6-in. stoneware pipes. They were placed about 540 ft. apart,
+<!--616.png--><span class="pagenum">582</span>and, from
+careful anemometer readings, the following conclusions were reached:</p>
+
+<div class="footnote"><a name="Footnote_11_11" id="Footnote_11_11"></a><a href="#FNanchor_11_11">
+<span class="label">[11]</span></a> <i>Minutes of Proceedings</i>, Inst. C. E., Vol. CLXXXI, p.
+317.</div>
+
+<p class="blockquot">"(1) That four ventilators all lying in the lower portion of the town
+acted sometimes as air-inlets and sometimes as air-outlets, and that the
+other sixty-four acted as air-outlets.</p>
+
+<p class="blockquot">"(2) That the average velocity of the air escaping up these columns was
+3.2 feet per second, representing the circulation of 3,600,000 cubic
+feet of air per diem, or sufficient to change the air in the sewers
+every 10 minutes.</p>
+
+<p class="blockquot">"(3) That the average velocity of the current of air in the
+ventilating-column increases with the size of the sewer to which it is
+connected, averaging 2.4 feet per second with the 7-inch sewer, 3.6 feet
+per second with the 9-inch sewer, 3.7 feet per second with the 12-inch
+sewer, and 4.1 feet per second with the 15-inch sewer in these
+experiments.</p>
+
+<p class="blockquot">"(4) That the draught in the column is very largely dependent on the
+wind, being at its minimum on a still day, and could therefore be
+readily increased by the use of a suitable cowl.</p>
+
+<p class="blockquot">"(5) That the draught is very little affected by the sewer-gradients. It
+was expected that, in ventilating-columns placed in connection with the
+upper end of a sewer laid at a steep gradient, a strong draught would
+have been obtained. No direct connection, however, was traceable."</p>
+
+<p>As the result of these experiments, Mr. Binnie rightly came to the
+conclusion that this system of ventilation was efficient.</p>
+
+<p>Mr. Hammond anticipates that the house connection trap system at
+Monterrey will lead to bad results, but the writer has seen the system
+at work in many widely different cities with excellent results. He
+believes that it is in accord with the best practice of the most eminent
+sanitarians during the last 20 years, and has no apology to make for
+introducing that system in Monterrey.</p>
+
+<p>Regarding Mr. Hammond's summary of the advantages of concrete pipes for
+sewer construction, the writer is in entire agreement, and would
+willingly have introduced them throughout the whole of the Monterrey
+system, but for the fact that it was an exceedingly difficult matter to
+obtain suitable sand for their manufacture during the early days of
+construction, and considerable delays would have arisen if a complete
+network of such pipes had been used. His later experience at Monterrey,
+when the sand difficulty had been solved, clearly showed that concrete
+pipe could be laid down at much less expense than fire clay.</p>
+
+<p>Both Mr. Pitkethly and Mr. Hammond refer to the system of liquefying
+tanks used at Monterrey preparatory to turning the sewage on the
+irrigation lands, and both express doubts as to their efficiency. The
+writer is now separated from his library and notes by many thousands of
+miles, and cannot quote "chapter and verse" as accurately as he would
+like, in order to support his views that the system adopted
+<!--617.png--><span class="pagenum">583</span>was
+adequate for dealing with a system such as that at Monterrey. It must be
+pointed out that not only was it intended to prevent the sewage from
+becoming a nuisance, but that the sewage flow plus a large quantity of
+surplus water was intended to be used profitably for irrigation
+purposes. With that object, the Company&mdash;or rather its allied Company,
+the Monterrey Railway, Light, and Power Company&mdash;obtained the control of
+2,246 acres of the very finest arable land, with almost perfect natural
+drainage conditions, so that this land could be utilized to create a
+profitable revenue from the use of the sewage. The outfall sewer was
+accordingly designed to carry sufficient water and sewage to irrigate
+about 2,500 acres of land, which area could be considerably extended if
+necessary at any future time.</p>
+
+<p>Most authorities now agree that before turning sewage upon land, a
+preliminary treatment is required to remove as much as possible of the
+suspended matter, and then reduce the latter by subsidence in liquefying
+or septic tanks, so that the quantity remaining in the effluent is so
+small and finely divided that it may be readily decomposed and oxidized
+by bacterial action without risk of clogging the surface or interstices
+of the land upon which it may discharge.<a name="FNanchor_12_12" id="FNanchor_12_12"></a>
+<a href="#Footnote_12_12" class="fnanchor">[12]</a></p>
+
+<div class="footnote"><a name="Footnote_12_12" id="Footnote_12_12"></a><a href="#FNanchor_12_12">
+<span class="label">[12]</span></a> See Raikes, "Sewage Disposal Works," pages 97-98.</div>
+
+<p>Mr. Pitkethly quotes Messrs. Watson and O'Shaughnessy as saying, in
+their evidence before the Royal Commission on Sewage Disposal, that not
+more than 10% of the solids are digested in septic tanks, but it must be
+remembered that in many other places evidence was given before the same
+Commission showing that from 25 to 30% was actually obtained.</p>
+
+<p>Mr. J. D. Watson, in his paper, "Birmingham Sewage-Disposal Works,"
+<a name="FNanchor_13_13" id="FNanchor_13_13"></a>
+<a href="#Footnote_13_13" class="fnanchor">[13]</a>
+read in March, 1910, points out that:</p>
+
+<div class="footnote"><a name="Footnote_13_13" id="Footnote_13_13"></a>
+<a href="#FNanchor_13_13"><span class="label">[13]</span></a> <i>Minutes
+ of Proceedings</i>, Inst. C. E., Vol. CLXXXI, p.
+259.</div>
+
+<p>"The much-maligned sewage-farm still may be allowed (where the
+conditions are favourable) to rank as one of the best methods of
+sewage-disposal. Diverse opinions may be held as to what are favourable
+conditions, particularly as conditions are sure to vary widely with
+locality; but it may be assumed that where there is 1 acre of suitable
+land per 100 persons, as in Berlin and several other important cities,
+the efficiently-worked sewage-farm, when judged solely by the standard
+of the effluent produced, is still in the front rank. Effluents from
+such a farm are remarkable for their paucity of micro-organisms, their
+low albuminoid ammonia, and their unvarying character."</p>
+
+<p>Assuming that not more than 2,000 acres of the irrigated land at
+Monterrey were available for sewage purposes, this area would represent
+the sewage treatment of the present population of not more than 45
+persons per acre, and on the basis of the design, that is, for a
+population of 200,000 persons, this represents not more than 100 persons
+per acre. In many sewage farms on the continent of Europe, the number
+<!--618.png--><span class="pagenum">584</span>treated
+per acre varies between 80 and 200 persons; for example, at
+Breslau it is 187, at Berlin 105, at Brunswick 88, and at Steglitz 185.</p>
+
+<p>Regarding the crops to be grown on the land, very satisfactory results
+were obtained from growing Indian corn, and two excellent crops per
+annum were taken from an area of 500 acres during the period in which
+the writer was responsible for the works. It was also his intention to
+grow alfalfa, and turn a part of the land into a pecan grove, and,
+although he does not share the apprehensions of danger of either Mr.
+Pitkethly or Mr. Hammond as to growing root crops, he believes the
+growth of alfalfa, Indian corn, oats, barley, and pecan and fruit trees
+is eminently suitable for the land, which is a deep rich loam, from 4 to
+8 ft. deep, overlying the "sillar" formation referred to in the paper.
+The writer has seen many sewage farms during the last 18 years, upon
+which root crops of excellent quality have been grown, and not the least
+suspicion has ever been raised regarding their use.</p>
+
+<p>In reference to the adoption of the monolithic form for constructing the
+South Reservoir, the writer is so convinced as to its economy that had
+he to build this reservoir again, he would adopt the same method. Mr.
+Binckley, in drawing attention to the method of construction, has
+overlooked the fact that the cost of forms for a reservoir 30 ft. deep
+was a very serious item, and warranted the adoption of this new method,
+not only on account of economy but because of rapidity of construction;
+while, in the case of the Obispado Reservoir, which is very much
+shallower, simpler forms could be and were adopted.</p>
+
+<p>Mr. Saucedo's remarks regarding the repetition of the extraordinary
+floods of August, 1909, in September, 1910, are particularly
+interesting, and show how abnormal conditions are in so dry a section of
+Mexico as the State of Nuevo León. These two floods, the writer
+believes, are among the most instructive in North America, particularly
+when one remembers that prior to 1909 the average rainfall during a
+period of 15 years, was less than 22 in. per annum.</p>
+
+<div class="TableHeader">
+TABLE 18.&mdash;<span class="smcap">Comparison of Volume of Floods, Etc.</span>
+</div>
+
+<div class="center">
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<colgroup><col span="1" align="left" /><col span="4" align="center" width="70" /></colgroup>
+<tr><td>River.</td><td>Drainage area, in square miles.</td><td>Maximum recorded flow, in cu. ft. per sec.</td><td>Cu. ft. /sec. per square mile.</td><td>Annual amount of rainfall.</td></tr>
+<tr><td>&nbsp;</td></tr>
+<tr><td>Santa Catarina, Monterrey, August 27th, 1907</td><td> 544</td><td> 235,000</td><td> 432</td><td> 22</td></tr>
+<tr><td>Estanzuela, near Monterrey, August 28th, 1909</td><td> 3.5</td><td> 2,900</td><td> 825</td><td> 25</td></tr>
+<tr><td>Tansa, India</td><td>52.5</td><td>35,000</td><td>666.7</td><td>101</td></tr>
+<tr><td>Krishna, India</td><td>345</td><td>118,000</td><td>342.6</td><td>258</td></tr>
+<tr><td>Coquitlam River, Vancouver</td><td>100</td><td>12,000</td><td>120</td><td>147-189</td></tr>
+<tr><td>Sweetwater, Cal.</td><td>186</td><td>18,150</td><td>99</td><td>...</td></tr>
+<tr><td>Delaware, Lambertville, N. J.</td><td>6,820</td><td>250,000</td><td>36.5</td><td>45</td></tr>
+<tr><td>Colorado, Austin, Tex.</td><td>37,000</td><td>123,000</td><td>3.3</td><td>24.5</td></tr>
+<tr><td>Ohio, Cairo, Ill.</td><td>214,000</td><td>700,000</td><td>3.3</td><td>54.9</td></tr>
+</table></div>
+
+<!--619.png--><p><span class="pagenum">585</span></p>
+
+<p>Table 18, compiled by the writer, shows how very extreme the floods of
+1909 were compared with those on other rivers, while those of 1910,
+referred to by Mr. Saucedo, although not so great, would appear to have
+reached a rate of flow of about 300 cu. ft. per sec. per sq. mile of the
+drainage area.</p>
+
+<p>The writer agrees with Mr. Saucedo that in the semi-arid regions of
+Mexico and the Southern States, and also in India, the possibility of
+these abnormal floods is an important consideration in the design of
+hydraulic works.</p>
+
+<hr style="width: 100%" />
+
+
+<h2><a name="Changes" id="Changes"></a>Changes To This Document</h2>
+
+<pre>
+Transcriber's Note: The table of contents has been added. Blank pages
+have been deleted. Illustrations may have been moved. Discovered
+publisher's punctuation errors have been corrected. Some wide tables
+have been re-formatted to narrower equivalents with some words replaced
+with commonly known abbreviations and possibly a key. Some ditto marks
+have been replaced with the words represented. In addition, the
+following changes or corrections were made:
+
+p. 501: but the tampers had had[del 2nd had] previous experience
+p. 508: shown on Plates VI to IX[VI, VII, VIII, IX[to accomodate links]]
+p. 516: at this place there is a considererable[considerable] area
+p. 538: based on the following rates and and[del 2nd and] percentages
+p. 579: by crossing the river, build-the[building the] reservoir
+p. 550: [For Table 14: added "Total materials cost"]
+p. 566: respectively (Fig. 5)[(Fig. 4)], together with lack of
+p. 584: [Table 17 renamed to Table 18 to avoid duplication.]
+p. 584: Table 17[18], compiled by the writer, shows how very extreme
+</pre>
+
+<div><a href="#Start">Start of text.</a></div>
+
+
+
+
+
+
+
+
+<pre>
+
+
+
+
+
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@@ -0,0 +1,5224 @@
+The Project Gutenberg EBook of ASCE 1193: The Water-Works and Sewerage of
+Monterrey, N. L., Mexico, by George Robert Graham Conway
+
+This eBook is for the use of anyone anywhere at no cost and with
+almost no restrictions whatsoever.  You may copy it, give it away or
+re-use it under the terms of the Project Gutenberg License included
+with this eBook or online at www.gutenberg.org
+
+
+Title: ASCE 1193: The Water-Works and Sewerage of Monterrey, N. L., Mexico
+       The 4th article from the June, 1911, Volume LXXII,
+       Transactions of the American Society of Civil Engineers.
+       Paper No. 1193, Feb. 1, 1911.
+
+Author: George Robert Graham Conway
+
+Release Date: December 31, 2011 [EBook #38455]
+
+Language: English
+
+Character set encoding: ASCII
+
+*** START OF THIS PROJECT GUTENBERG EBOOK ASCE 1193: THE WATER-WORKS ***
+
+
+
+
+Produced by Juliet Sutherland, Henry Gardiner and the
+Online Distributed Proofreading Team at http://www.pgdp.net
+
+
+
+
+
+
+       *       *       *       *       *
+
+Transcriber's Note: Words in italics are indicated like _this_. Subscripts
+are indicated like this: H_{2}O. The original publication has been
+replicated faithfully except as listed at the end of the text.
+
+       *       *       *       *       *
+
+
+
+
+                           TABLE OF CONTENTS
+
+
+          INTRODUCTORY.                                    475
+          THE CONCESSION.                                  476
+          GEOLOGY AND TOPOGRAPHY.                          476
+          POPULATION, AREA, AND MORTALITY.                 479
+          RAINFALL AND TEMPERATURE.                        480
+          AVAILABLE SOURCES OF SUPPLY.                     484
+          MATERIALS FOR CONCRETE.                          491
+          ESTANZUELA SUPPLY.                               494
+          SOUTH DISTRIBUTING RESERVOIR.                    506
+          SAN GERONIMO GRAVITY SUPPLY.                     514
+          DISTRIBUTING RESERVOIR AT OBISPADO.              525
+          COMPARISON OF SOUTH AND OBISPADO RESERVOIRS.     530
+          ANALYSES OF ESTANZUELA AND SAN GERONIMO WATERS.  532
+          CITY WATER DISTRIBUTION SYSTEM.                  532
+          MAIN SEWERAGE SYSTEM.                            539
+          MAIN OUTFALL SEWER.                              542
+          SEWAGE DISPOSAL WORKS AND IRRIGATION LANDS.      545
+          QUALITY OF AND RATES FOR LABOR.                  552
+          COST OF WORKS.                                   552
+          TARIFFS AND SANITARY REGULATIONS.                553
+          ENGINEERS, ETC.                                  556
+          DISCUSSION.                                      557
+          JAMES D. SCHUYLER.                               557
+          DAVID T. PITKETHLY.                              559
+          V. SAUCEDO.                                      563
+          GEORGE T. HAMMOND.                               567
+          RUDOLF MEYER.                                    576
+          GEORGE ROBERT GRAHAM CONWAY.                     580
+
+
+
+
+                   AMERICAN SOCIETY OF CIVIL ENGINEERS
+
+                           INSTITUTED 1852
+
+                             TRANSACTIONS
+
+                            Paper No. 1193
+
+                    THE WATER-WORKS AND SEWERAGE OF
+                       MONTERREY, N. L., MEXICO.[1]
+
+            BY GEORGE ROBERT GRAHAM CONWAY, M. AM. SOC. C. E.
+
+     WITH DISCUSSION BY MESSRS. JAMES D. SCHUYLER, DAVID T. PITKETHLY,
+         GEORGE S. BINCKLEY, VICENTE SAUCEDO, GEORGE T. HAMMOND,
+             RUDOLF MEYER, AND GEORGE ROBERT GRAHAM CONWAY.
+
+
+
+
+                              INTRODUCTORY.
+
+
+[1] Presented at the meeting of February 1st, 1911.
+
+Monterrey, the Capital of the State of Nuevo Leon, Mexico, is built on
+the site of the old village of Santa Lucia de Leon, which was
+established in 1583 by the Governor of the Kingdom of Leon, Don Luis
+Carabajal. Four years later Carabajal was imprisoned by the Inquisition,
+and the village of Santa Lucia was abandoned by its few inhabitants.
+
+In 1596, Captain Diego Montemayor, a resident of Saltillo, in the
+adjoining State, wishing to render a service to his king, Philip II of
+Spain, assembled his friends, and on September 20th of that year,
+proceeded to establish a town on the site of the old village on the
+northern side of the principal spring at the place. The town was named
+"Nuestra Senora de Monterrey" (Our Lady of Monterrey), after the Count
+of Monterrey (Ojos de Santa Lucia y Valle de Extremadura), the ruling
+Governor of New Spain, as Mexico was then called.
+
+Monterrey is approximately in the center of the State of Nuevo Leon, 1 deg.
+12' west of Mexico City, and in latitude 26 deg. 40' N. It is a distributing
+railway center on the main line of the National Railroad, 270 km. from
+the Rio Grande at Laredo, 1,022 km. from Mexico, and 520 km. from
+Tampico by the Mexican Central Railway. It is the center of many large
+industries, and is the second largest manufacturing city in the
+Republic.
+
+
+
+
+                            THE CONCESSION.
+
+
+The works described in this paper were carried out under a guaranteed
+concession granted by His Excellency, General Bernardo Reyes, Governor
+of the State of Nuevo Leon, to Messrs. James D. Stocker and William
+Walker, of Scranton, Pa. The concession is dated October 19th, 1904, and
+is for 99 years from that date; the works for a complete water and
+drainage system were to be finished in 3 years from the time of their
+commencement. Before the works were designed and begun, the concession
+was acquired by Mr. William Mackenzie, of the firm of Mackenzie, Mann
+and Company, Limited, of Toronto, Ont., Canada, who, on May 4th, 1906,
+organized the Monterrey Water-Works and Sewerage Company, Limited
+(Compania de Servicio de Agua y Drenaje de Monterrey, S. A.), under the
+laws of the Dominion of Canada, of which company he is President. Mr.
+Mackenzie is also President of the Monterrey Railway, Light, and Power
+Company, Limited, which was constructing the street railways of
+Monterrey concurrently with the water-works. Under the provisions of the
+concession, the Government appointed a Financial Interventor, who had
+authority to examine and check the company's expenditures, and also a
+Technical Inspector to examine and report on the construction. The
+duties of these officials also apply to the operation of the system when
+the construction is finished. The Government has the right, after the
+system has been operated 40 years, to purchase the entire property,
+subject to 6 months' notice, for a sum equal to 16-2/3 times the average
+annual net proceeds during the 3 preceding years. This right may be
+exercised at the end of 40 years, or at the end of any 10-year period
+thereafter, up to 99 years from the commencement of operations.
+
+
+
+
+                         GEOLOGY AND TOPOGRAPHY.
+
+
+Monterrey lies in a plain at the foot of the Eastern Sierra Madre
+Mountains which constitute the eastern margin of the Mexican Cordilleran
+Plateau, and is surrounded by the magnificent mountains of that group,
+among the most notable of which are the beautiful Mitra and Silla
+Mountains. In the neighborhood of Monterrey these mountains attain
+heights of from 2,000 to 2,400 m., and are noted for their broken and
+jagged sky-lines. The leading geological characteristics of the district
+are the uplifted limestones of the older cretaceous age which form the
+main mass of the mountains.
+
+Primarily, the mountains are compressional folds which, in the Sierra
+Madre, near Monterrey, are close and vertically compressed.[2] The
+drainage areas of the Santa Catarina River, which flows through
+Monterrey, and of the Estanzuela and Silla Rivers, its tributaries, are
+of limestone and shale; originally the shales were above the limestone,
+but the convulsion which formed the Sierra Madre as an anticlinal fold,
+left the originally horizontal strata standing nearly upright, and
+subsequent erosion in the upper part of the anticline has exposed nearly
+vertical strata in many places. The limestone being hard and resisting
+erosion, there is generally, along the line of contact, an abrupt drop
+vertically on the face of the limestone to the shale below. In many
+places this abrupt drop is broken by a limestone talus, but the line of
+contact can generally be traced. Mining operations in these mountains
+have revealed the presence of large caves at a considerable elevation,
+many of which contain large reservoirs of water, delivered to them
+through numerous faults. The river valleys are formed of masses of
+limestone conglomerate and coarse gravels, re-cemented in many cases by
+the lime deposits of the flowing waters. One of the chief
+characteristics of the subsoil of Monterrey itself is a local rock
+called "sillar," which is a superficial deposit of carbonate of lime
+from the evaporated waters. In some places the "sillar" is largely mixed
+with a conglomerate called "tepetate," or "impure sillar."
+
+[2] _Transactions_, Am. Inst. Min. Engrs., Vol. XXXII (1902), pp.
+163-178.
+
+[Illustration: PLATE II.--GENERAL PLAN OF THE WATER SUPPLY AND DRAINAGE
+WORKS FOR MONTERREY, N. L., MEXICO.]
+
+Topographically, the region around Monterrey is distinguished by the
+drainage area of the River Santa Catarina, which rises in the Sierra
+Madre near the Laguna de Sanchez, at an elevation of 1,850 m., as shown
+on Plate II. From this Laguna it follows a tortuous course between
+precipitous mountains through the Boca of Santa Catarina to Monterrey,
+for a distance of 90 km., eventually finding its way to the San Juan
+River, a tributary of the Rio Grande. Throughout its course it
+disappears, flows underground, and again appears; and, except in flood
+time, it has a subsurface flow for a distance of 16 km. above the city.
+In the Canon of Santa Catarina it appears at the surface, having a
+normal flow of about 1,415 liters (50 cu. ft.) per sec., and its waters
+at that point are divided into two parts and carried into irrigation
+canals. The drainage area of the river above Monterrey is 1,410 sq. km.,
+and its bed at Monterrey is between 518 and 545 m. above sea level.
+
+Southward from Monterrey the country rises along the valley of the Silla
+for a distance of 19 km., where the Silla is separated from the San Juan
+by a low divide, the former flowing northward to Monterrey and the
+latter southeastward toward Allende. The Silla Valley is bounded on the
+east and west by the steep ranges of the Silla and Sierra Madre
+Mountains. The floor of this valley is gently rolling, but is cut by
+many arroyos which carry little or no water during the greater part of
+the year. The chief feeder of the Silla River is the Estanzuela, a
+stream which derives its waters from several springs coming to the
+surface near the line of contact between the limestone and the shale, at
+elevations of about 800 and 900 m.[3] above datum. The water-shed of
+this stream is rich with abundant vegetation due to the precipitation
+being greater than on the Santa Catarina water-shed. To the south of the
+divide the country is well wooded, and El Porvenir, 35 km. from
+Monterrey, is the garden spot of the State of Nuevo Leon. Here the
+rainfall is much greater than at any other point near Monterrey, and
+there are many streams which are used for irrigation purposes. Monterrey
+is built on a plain, chiefly on the north side of the Santa Catarina
+River. This plain has a general fall toward the northeast, and beyond
+the city it slopes gently northward for several miles toward the Topo
+Grande River, and then southeastward to join the great coastal plain of
+the Gulf of Mexico. The general elevation of the city lies between the
+519- and 550-m. contours. The Plaza Zaragoza, in the center of the city,
+is 533.90 m. above sea level; the elevation of the highest part of the
+city, at the western boundary, is 550.05 m., and of the lowest part, at
+the northeastern boundary, 518.0 m. above sea level.
+
+[3] Throughout this paper datum refers to the height in meters above the
+mean sea level of the Gulf of Mexico at the Port of Tampico.
+
+[Illustration: PLATE III, FIG. 1.--GENERAL VIEW OF LINE, ESTANZUELA
+AQUEDUCT.]
+
+
+
+
+                    POPULATION, AREA, AND MORTALITY.
+
+
+The population of Monterrey has increased as follows:
+
+                  Census of   1851      14,621
+                    "  "      1861      26,000
+                    "  "      1871      33,811
+                    "  "      1881      39,456
+                    "  "      1891      41,154
+                    "  "      1901      73,508
+                  (Estimated) 1909      86,000 to 90,000
+
+The greatest progress, it will be noted, was between 1891-1901, with an
+increase of more than 22,000 in 10 years. In designing the new works,
+provision has been made for the future requirements of a city of 200,000
+persons.
+
+The actual area within the city limits proper is 960.5 hectares (2,374
+acres), forming the area to be provided with water and drainage, but the
+municipal district extends to many surrounding suburbs, and covers an
+area of 33,758 hectares (83,426 acres).
+
+        TABLE 1.--POPULATION AND DEATH RATE OF MONTERREY, N. L.,
+                  MEXICO, FROM 1901 TO 1909, INCLUSIVE.
+
+  ============+========+=========+========+=========================|
+              |        |         |        |DEATHS FROM TYPHOID FEVER|
+              | Popu-  | Deaths  | Rate   +----+----+----+----+-----+
+     Year.    |lation. |from all |  per   |    |    |    |    |     |
+              |        | causes. | 1,000. |Jan.|Feb.|Mar.|Apr.|May. |
+              |        |         |        |    |    |    |    |     |
+  ------------+--------+---------+--------+----+----+----+----+-----+
+  Census 1901 | 73,508 |   2,965 |  40.3  |  0 |  2 |  1 |  3 |  4  |
+  Estim. 1902 | 74,500 |   3,338 |  44.8  |  1 |  4 |  2 |  3 |  6  |
+     "   1903 | 76,000 |   3,825 |  50.3  |  3 |  2 |  4 |  1 |  0  |
+     "   1904 | 77,500 |   2,905 |  37.4  |  0 |  1 |  1 |  5 |  3  |
+     "   1905 | 79,000 |   2,951 |  37.4  |  2 |  0 |  0 |  3 |  3  |
+     "   1906 | 80,000 |   2,935 |  36.7  |  1 |  2 |  1 |  3 |  3  |
+     "   1907 | 82,500 |   3,269 |  39.6  |  4 |  6 |  3 |  3 |  5  |
+     "   1908 | 84,000 |   3,188 |  37.9  |  5 |  2 |  5 |  3 |  8  |
+     "   1909 | 86,000 |[4]3,477 |  40.4  |  5 |  1 |  4 |  5 | 13  |
+  ============+========+=========+========+====+====+====+====+=====+
+
+  ============+=========================================+==============+
+              |  DEATHS FROM TYPHOID FEVER. (Continued) | Deaths from  |
+              |----+----+----+----+----+----+----+------+ Typhoid fever|
+  Year.       |    |    |    |    |    |    |    |Total | per year per |
+              |Jne.|Jly.|Aug.|Sep.|Oct.|Nov.|Dec.|for   | 100,000      |
+              |    |    |    |    |    |    |    |year. | population.  |
+  ------------+----+----+----+----+----+----+----+------+--------------+
+  Census 1901 |  3 |  6 |  6 |  3 |  6 |  4 |  2 |   40 |     54       |
+  Estim. 1902 |  5 |  3 |  1 |  1 |  2 |  3 |  5 |   36 |     48       |
+     "   1903 |  5 |  3 |  5 |  6 | 16 |  3 |  1 |   49 |     64       |
+     "   1904 |  3 |  3 |  4 |  1 |  5 |  1 |  0 |   27 |     35       |
+     "   1905 |  7 |  6 |  3 |  2 |  7 |  2 |  2 |   37 |     47       |
+     "   1906 |  6 |  5 |  3 |  2 |  1 |  2 |  3 |   32 |     40       |
+     "   1907 |  6 |  4 |  4 |  9 |  3 |  0 |  3 |   50 |     61       |
+     "   1908 |  5 |  9 |  7 |  2 |  7 |  4 |  0 |   57 |     68       |
+     "   1909 | 11 | 15 | 12 |  6 |  8 |  3 |  4 |   87 |    101       |
+  ============+====+====+====+====+====+====+====+======+==============+
+
+[4] Excluding deaths due to drowning in the great flood of August 27th
+and 28th.
+
+Table 1 gives particulars of the death rate for 1901 to 1909, inclusive,
+and data relative to the mortality due to typhoid fever. The high death
+rate is caused by the excessive infantile mortality, which is so
+prevalent throughout the whole of Mexico. The climatic condition of
+Monterrey, with its exceptionally healthy subsoil, ought to make it one
+of the healthiest of cities, if proper care were taken to enforce
+sanitary laws. The data regarding typhoid mortality are probably
+understated, as they were compiled by the writer, in the absence of any
+official publications, from the actual death certificates, but no
+special care is taken by the authorities to insure accuracy in such
+certificates. Attention is called to the typhoid rate in May, June,
+July, and August, 1909; this high rate coincides with a scarcity of
+rainfall and the greatest period of drought experienced in 30 years, and
+immediately precedes the great flood of August 27th. It was probably due
+to the lowering of the ground-water throughout the city and the
+consequent contamination of the private wells, which were largely in use
+during that time. Throughout the city the wells are sunk to a depth of
+about 12 or 15 m., in order to reach the subterranean waters, and the
+cesspools are often in dangerous proximity to them and at a much higher
+level. The nature of the subsoil, which is often much fissured and open
+in the conglomerate and sillar strata, would make the passage of
+contamination an easy matter, and this alone would account for a high
+mortality due to water-borne diseases.
+
+
+
+
+                       RAINFALL AND TEMPERATURE.
+
+
+The precipitation records of Monterrey and its neighborhood are very
+meager, and cannot be relied on for a longer period than from 1894 to
+1909, inclusive. The records are available from 1886, but in the early
+years there are many apparent discrepancies, and they are probably
+inaccurate. The average rainfall for the 15 years (1894-1908) is 21.94
+in.; the driest years for this period are as follows: 1894, 14.14 in.;
+1902, 15.29 in.; 1907, 15.23 in.; 1908, 15.11 in. Assuming the early
+records to be correct, the average rainfall for the period, 1886-1908,
+would be 19.86 in.
+
+At Saltillo, which is 50 miles due southwest, at an elevation of about
+1,520 m. above sea level, the average rainfall for the 23 years,
+1884-1908, inclusive, is given as 21 in. The maximum year was 1889, with
+33-1/2 in., and the minimum 1903, with 7-1/2 in.
+
+At Carmen, in the State of Tamaulipas, 144 km. southwest of Monterrey,
+at an elevation of about 310 m. above sea level, the average fall for 12
+years is 24.70 in., the maximum year being 1897, with a fall of 34.09
+in., and the minimum year, 1905, with 13.41 in.
+
+[Illustration: FIG. 1.--ANNUAL RAINFALL IN MONTERREY COVERING THE PERIOD
+FROM 1894 TO 1909.]
+
+Fig. 1 shows the annual variation of rainfall at Monterrey for
+1894-1909. Fig. 2 shows the monthly variation during the same period,
+and gives the minimum, average, and maximum for each month.
+
+From these diagrams it will be seen that the months of least rainfall
+are December, January, February, and March, with averages of 0.66, 0.59,
+0.79, and 0.93 in., respectively. The months of greatest rainfall are
+August, with an average of 4.39 in., and September with 4.87 in. The
+maximum in any month prior to 1909 was 16.75 in., during September,
+1904.
+
+_Rainfall in 1909._--The rainfall in 1909 was unprecedented, causing the
+disastrous flood in the Santa Catarina River, which will be referred to
+when describing the works. Fig. 3 shows the monthly rainfall for 1906 to
+1909, inclusive, and has been plotted to show the variation of rainfall
+prior to the great precipitation of August, 1909. In that month there
+were two heavy falls, one beginning at midnight on August 9th, and
+during the following 42 hours a fall of 13.28 in. was recorded by the
+gauge at the Water-Works Company's general offices, 10.20 in. of which
+fell, during the first 24 hours. From 6 P. M. to 11 P. M., on August
+10th, 5.019 in. were recorded, or an average of 1 in. per hour.
+
+[Illustration: FIG. 2.--MONTHLY RAINFALL IN MONTERREY COVERING THE
+PERIOD FROM 1894 TO 1909 INCLUSIVE.]
+
+[Illustration: FIG. 3.--MONTHLY VARIATION OF RAINFALL AT MONTERREY
+1906-1907-1908-1909.]
+
+After 13 dry days, another rainstorm began, at 4 P. M., on August 25th,
+and continued more or less intermittently until August 29th. During this
+98-hour period there was an additional fall of 21.61 in., 11.27 in.
+falling in 24 hours.
+
+The total precipitation during the month amounted to 36.00 in. The
+highest previous record for the month of August was in 1895, with a fall
+of 6.61 in. Fig. 4 gives the details of the two heavy precipitations in
+August. As no automatic recording gauge was available, the maximum
+intensity could only be computed approximately, owing to the
+intermittent character of the readings taken from the ordinary rain
+gauge on the roof of the Water-Works Company's office in the city. From
+the readings thus obtained, it was shown that the maximum intensity
+occurred early on the morning of the 28th, and was nearly 2 in. per
+hour. Above Monterrey, in the Santa Catarina water-shed, it is believed
+that the precipitation was considerably greater, but no gauges were
+accessible during the month.
+
+[Illustration: FIG. 4.--CURVE OF RAINFALL AT MONTERREY DURING AUGUST
+10TH & 11TH AND FROM AUGUST 25TH TO 29TH - 1909.]
+
+The total rainfall for 1909 amounted to 47.46 in., of which 75% fell in
+August. This is 50% greater than the previous highest annual record
+(31.65 in. in 1900) for Monterrey.
+
+_Temperature._--Fig. 6 gives a record of the temperature at Monterrey
+from 1901 to 1909, inclusive. These records were taken at an altitude of
+520 m. It will be noted that the lowest recorded temperatures are in
+January and February. The lowest during these years was 24 deg. Fahr., in
+January, 1905. The monthly maxima vary between 80 and 110 deg. Fahr. The
+mean annual temperature is 72.65 deg. Fahr. (The mean annual barometer is
+28.2 in.)
+
+[Illustration: FIG. 6.--DIAGRAM OF TEMPERATURE VARIATION AT MONTERREY,
+1901-09.]
+
+
+
+
+                       AVAILABLE SOURCES OF SUPPLY.
+
+
+The question of the best sources from which Monterrey should be supplied
+with potable water was one that had been long under discussion, and was
+the subject of many investigations prior to the granting of the present
+concession. Several of the original schemes called for an impounding
+reservoir in the Canon of Santa Catarina and it was on the assumption
+that a dam would be built that a clause was inserted in the concession
+for the purpose of making its construction obligatory. The general
+character of the physical and geological conditions surrounding
+Monterrey has already been referred to. A thorough study of these
+conditions proved that no suitable site for impounding the Santa
+Catarina River could be found, apart from the fact that periodically
+this river is subject to enormous floods which tear through the steep
+canon with tremendous velocity.
+
+At the site originally proposed for the dam, a considerable underflow
+was found, and later investigations, carried out under the present
+concession, proved that, although borings were carried to a depth of 54
+m., bed-rock could not be found, the strata being composed of gravels,
+conglomerate and sand. Assuming that such a dam could have been built,
+the quality of the water draining from a comparatively barren
+water-shed, on which many thousands of goats are pastured, would have
+made its filtration an absolute necessity before it could be delivered
+to the consumers.
+
+The various available sources from which water could be delivered to the
+city by gravity were investigated by Mr. F. S. Hyde, in the autumn of
+1905, and also by J. D. Schuyler, M. Am. Soc. C. E., who was afterward
+retained as Consulting Engineer for the Company. The various
+investigations made from time to time showed that the question of a
+satisfactory supply was one of extreme difficulty, requiring prolonged
+observation and study, more particularly into the character of the
+underground sources of supply.
+
+One of the chief characteristics of many of the streams in the State of
+Nuevo Leon, is their disappearance and reappearance at different points
+along their routes, and the Santa Catarina River, under normal
+conditions, as already remarked, is a very notable example of a river
+which is very dry at the surface for many kilometers of its length. In
+the writer's opinion, the waters of this and similar rivers in the State
+pass through many open caverns underground, so that experience gained in
+the investigation of underflow waters in other places would be
+insufficient to determine the quantity passing at any point along the
+river if ascertained by merely computing it from the velocity of the
+underflow and the area of the water-bearing gravels. The rainfall on the
+water-shed of the Santa Catarina River is probably 25% greater than at
+Monterrey, and all ordinary rains sink rapidly into the limestone soils
+and quickly disappear. In another water-shed of a very similar
+character, namely, that of the Rio Blanco, in the southern part of the
+State, the underflow waters appear at the surface at a place called
+Mezquital, where a metamorphosed sandstone barrier prevents them from
+disappearing underground. At this point the normal quantity of water is
+about 5,660 liters (200 cu. ft.) per sec., but it gradually disappears,
+and a few kilometers below it has sunk to an insignificant stream,
+finally disappearing altogether for about 20 km. In the neighborhood of
+Monterrey similar conditions exist with regard to the surface-water
+supplies, and investigations, therefore, were directed toward obtaining
+unpolluted supplies from springs and underground sources.
+
+_Santa Catarina Sources._--The chief points from which it was thought
+desirable to obtain underflow supplies were (1) at the barrier of San
+Geronimo, and (2) at the Canon of Santa Catarina, both shown on Plate
+II.
+
+Conditions at San Geronimo, which is only 6-1/2 km. west of Monterrey,
+were investigated by the State Government in 1892, to determine the
+depth of bed-rock, the rock on either side of the valley being shale,
+with its original bedding planes standing almost vertical. To determine
+this depth, borings were made by driving 2-in. tubes until it was
+assumed that bed-rock had been reached, a method which, in strata
+containing so many boulders, was obviously unreliable. These borings
+indicated that bed-rock was from 12 to 15 m. below the surface. If these
+had proved to be correct, there is no doubt that a development of the
+underground water at this point, by constructing a submerged dam
+combined with an infiltration gallery, would have yielded a large
+supply.
+
+In March, 1906, the Company commenced operations at San Geronimo by
+sinking a well a few meters north of the then dry bed of the river.
+Water was found in considerable quantities a few meters below the
+surface, practically at the level of the river, that is, 570 m. above
+datum. This supply was used for provisional purposes, and will be
+referred to later in describing the San Geronimo gravity supply works.
+
+Between August, 1906, and January, 1907, 4-in. bore-holes were sunk in
+the river bed and on the high ground to the north with a "Keystone"
+driller outfit. These borings showed bed-rock immediately under the
+river bed, at a depth of from 15 to 45 m., but dipping gradually as the
+borings were carried northward.
+
+Boring operations were also carried on at Santa Catarina, during
+November and December, 1906, and in January, 1907, to determine the
+geological conditions, and the results are shown on Fig. 7. From the
+area of water-bearing gravels found, it was proposed to tap the
+underflow water at the 630-m. level by an infiltration gallery. This
+would have necessitated a gravitation tunnel 3,000 m. long, and an
+aqueduct of 14 km., which it was proposed to carry to one of two
+distributing reservoirs at Guadalupe, on the south side of the river,
+opposite Monterrey. In May, 1907, the writer, after making a study of
+all the available data which had been accumulated, had additional
+borings sunk farther across the valley to the north, and these revealed
+a considerable area of water-bearing gravels, and proved that, in former
+geological times, the Santa Catarina flowed about 500 m. north of its
+present position, and to the back of Obispado Mountain, instead of
+through the city. This aspect of the subject was discussed with Mr.
+Schuyler, who agreed with the writer that, in the interest of economy,
+it was better to tap this supply by an infiltration gallery at the
+560-m. level, and bring the water thus obtained to a reservoir to be
+placed at the western limits of the city, dividing the city, for
+distribution purposes, into two interchangeable systems, a high- and a
+low-pressure, the high-pressure system being supplied from Estanzuela,
+18 km. south of the city. One advantage to be gained from this change
+was that the scheme was capable of considerable extension, and any
+future developments at Santa Catarina Canon would form part of the works
+to be constructed for both high- and low-pressure districts.
+
+[Illustration: FIG. 7.--CROSS-SECTION OF SANTA CATARINA RIVER AT SANTA
+CATARINA.]
+
+The future extension of the Santa Catarina sources, the writer believes,
+can be developed best by driving an infiltration gallery 10 m. below the
+surface of the Santa Catarina River, a little west of the village of the
+same name, and then conveying the water through a comparatively short
+gravitation tunnel and pressure conduit to a main reservoir near San
+Geronimo having a top water level at an elevation of about 590 m. above
+datum.
+
+_Southern Sources of Supply._--The available sources of supply southward
+from Monterrey include a number of springs at various points in a
+distance of 40 km. Many of these springs are of uncertain quantity, and
+some are quite dry during periods of drought. The chief perennial
+springs near Monterrey are those which contribute to form the Estanzuela
+and Diente Rivers, both tributaries of the Silla, while farther south,
+at the Potrero Cerna, near El Porvenir, there are excellent springs, at
+a considerable elevation, with a minimum flow of from 170 to 200 liters
+(from 6 to 7 cu. ft.) per sec. The total quantity of water available
+from all these springs during the driest season would probably not be
+less than about 560 or 700 liters (from 20 to 25 cu. ft.) per sec.
+
+The Estanzuela springs issue at the foot of the Sierra Madre Mountains,
+and have a normal flow of from 56 to 85 liters (2 to 3 cu. ft.) per sec.
+in an ordinary dry year; they probably derive their water, through the
+limestone formation, from the neighboring water-shed of Santa Catarina,
+as the catchment area of the stream is only 910 hectares, and the stream
+has never been known to fail, even in the driest periods of prolonged
+drought. The rainfall on the area is about 30 in. per annum, and the
+catchment area is well wooded and covered with abundant vegetation. The
+El Diente springs have an ordinary dry-weather flow of about 28-1/2
+liters (1 cu. ft.) per sec.; but part of the water is carried
+underground, and the real quantity is much greater and could be
+developed by a small submerged dam carried down to bed-rock.
+
+The elevation and the extreme purity of the water of the Estanzuela
+River made its acquisition very desirable, and the Company, therefore,
+purchased the Federal water rights owned by various members of the
+Estanzuela community, amounting to 91 liters per sec., and has since
+acquired a Federal concession to all the flood-waters of that river. It
+was decided, therefore, to adopt the Estanzuela River as the first step
+toward developing the water to the south of Monterrey for a
+high-pressure supply, the advantage of the scheme being that from time
+to time extensions could be made to tap other sources by gravity, as the
+demands of the city required. The Estanzuela scheme, therefore, is a
+preliminary step toward future extensions which will be necessary in
+this direction as the city grows. The springs near El Porvenir, and
+others which contribute to the San Juan River, can be tapped at a
+sufficiently high level to convey them by a gravity pressure line to the
+Estanzuela Aqueduct near Mederos.
+
+The two sources definitely decided on in July, 1907, were those from
+Estanzuela and San Geronimo. The works were designed to supply
+40,000,000 liters daily, which it was assumed would be sufficient for
+all future developments for a population of 200,000 at a per capita
+consumption of 200 liters per day. The present requirements of the
+city's population, assuming that all the water was supplied by the
+Company, would be, at that rate, which is a very liberal one, only
+18,000,000 liters daily. This, it was thought, would be easily met by
+the San Geronimo source alone, as it was estimated that it would provide
+not less than 20,000,000 liters, if the infiltration gallery was driven
+far enough into the water-bearing gravels.
+
+The question of a high-pressure water supply for domestic use in a city
+like Monterrey is not a serious one, as practically nine-tenths of the
+houses are of one story. The increase in the number of large commercial
+buildings, however, will make the demand greater in the future, and this
+point has been kept in mind in arranging the division of the
+distribution systems.
+
+
+
+
+                         MATERIALS FOR CONCRETE.
+
+
+_Cement._--In the early stages of construction the cement for the work
+was obtained from the Associated Portland Cement Manufacturers, Limited,
+of London, which supplied the "Pyramid" brand, from the Knight, Bevan,
+and Sturges Works, but later the supply was obtained from a new factory
+at Hidalgo, near Monterrey. The total quantity of Portland cement used
+was 42,500 bbl. of "Pyramid" and 32,500 bbl. of "Hidalgo." The English
+cement was tested for the Water-Works Company in London before shipment
+and again at Monterrey, to conform to the British Standard
+Specifications; the "Hidalgo" cement was required to pass the Standard
+Specifications advocated by the Special Committee of the American
+Society of Civil Engineers. The quality in each case was of the very
+highest, no difficulties being experienced at any time.
+
+_Sand and Rock._--One of the chief difficulties in connection with the
+construction work in its initial stages was in procuring satisfactory
+sand for the concrete. An investigation of the quality of all the
+available sands in the neighborhood of Monterrey resulted in the
+decision to use a manufactured sand obtained from the calcareous shales
+in the foot-hills opposite the city, on the south side, and near the
+site of one of the proposed reservoirs. A quarry was opened, and the raw
+material was delivered by a gravity plane to a crushing plant, 230 m.
+from the quarry and at a level about 50 m. lower.
+
+The plant consisted of a No. 5 Austin gyratory rock-crusher, fitted with
+elevators and revolving screens of various dimensions, driven by a
+150-h.p. Erie steam engine; two sets of Traylor's heavy-duty crushing
+rolls, one having 30 by 16-in. and the other 18 by 12-in. rolls; and a
+Niagara sand disintegrator. This plant, except during a short period
+when the requirements were beyond its capacity, was able to produce all
+the sand and rock required for construction purposes. More than 40,000
+tons of rock were quarried, the greater part of which was converted into
+crushed stone and sand.
+
+Table 2 gives the chemical analysis of the chief constituents of the
+various sands examined.
+
+   TABLE 2.--ANALYSIS OF SANDS IN THE NEIGHBORHOOD OF MONTERREY.
+
+              KEY:
+
+              A: Percentage of silica (absolute), SiO_{2}
+              B: Percentage of alumina, Al_{2}O_{3}
+              C: Percentage of sesquioxide, Fe_{2}O_{3}
+              D: Percentage of lime carbonate, CaCO_{3}
+
+  ===+============================+=======+=======+=======+=======+
+  No.| Location.                  |   A   |   B   |   C   |   D   |
+  ---+----------------------------+-------+-------+-------+-------+
+   1.| Arroyo Seco, near          |       |       |       |       |
+     |   brickyard at Monterrey   | 60.10 |17.95  |  2.89 |  8.01 |
+   2.| Arroyo Seco, near          |       |       |       |       |
+     |   brickyard at Monterrey,  |       |       |       |       |
+     |   No. 2                    | 42.92 |14.26  |  4.66 | 34.58 |
+   3.| Near Garcia Station,       |       |       |       |       |
+     |   Mexican National R. R.,  |       |       |       |       |
+     |   Chiquito River, No. 1    | 50.22 | 9.72  |  1.44 | 34.62 |
+   4.| Near Garcia Station.       |       |       |       |       |
+     |   Mexican National R. R.,  |       |       |       |       |
+     |   Chiquito River, No. 2    | 48.7  | 4.92  |  8.28 | 35.43 |
+   5.| San Luis Potosi            | 85.02 | 5.00  |  7.38 |  2.21 |
+   6.| Topo Grande, Pesqueria     |       |       |       |       |
+     |   River                    | 40.20 | 5.15  |  4.25 | 46.50 |
+   7.| Hornos, near Torreon       | 77.9  | 13.1  |  2.4  |  4.9  |
+   8.| Salinas River, at Salinas  | 41.5  |  5.7  |  1.4  | 48.2  |
+   9.| Pits near Caballeros, on   |       |       |       |       |
+     |   Tampico Branch of        |       |       |       |       |
+     |   Mexican Central R. R.    | 73.4  |  5.6  |  4.4  | 10.1  |
+  10.| Santa Catarina River,      |       |       |       |       |
+     |   near San Geronimo        |       |       |       |       |
+     |   (washed sand)            | 12.40 |  2.06 |  1.14 | 81.70 |
+  11.| Santa Catarina River,      |       |       |       |       |
+     |   at Monterrey             | 17.4  |  2.50 |  2.00 | 77.00 |
+  12.| Composition of rock, quarry|       |       |       |       |
+     |   in foot-hills opposite   |       |       |       |       |
+     |   Monterrey, Monterrey     |       |       |       |       |
+     |   Water-Works and Sewer    |       |       |       |       |
+     |   Company's property       | 40.44 | 15.70 |  2.20 | 34.30 |
+  13.| Manufactured sand from     |       |       |       |       |
+     |   above quarry             |       |       |       |       |
+     |   (run of crusher)         | 51.80 | 12.14 |  8.7  | 32.6  |
+     |                            |       |       |       |       |
+  ===+============================+=======+=======+=======+=======+
+
+The chief sands used for ordinary building purposes in Monterrey are
+Nos. 10 and 11, which are procured from the bed of the Santa Catarina
+River. As these sands contain large proportions of lime carbonates,
+which make them very undesirable for important structures, their use was
+limited to relatively unimportant work. The best sands procurable were
+Nos. 5 and 9, but the long distance of the pits from Monterrey, and
+consequently the heavy freight rate, made their use prohibitive on
+economical grounds. The best of the available sands, although it was
+very fine, was No. 7, from Hornos, near Torreon, as it could be depended
+on for uniformity and could be obtained f. o. b. cars at Monterrey for
+3.18[5] pesos per ton.
+
+[5] All costs given in this paper are in Mexican pesos, one peso being
+equivalent to 50 cents in U. S. currency.
+
+The bulk of the sand and crushed rock used was similar to Nos. 12 and
+13, and reference to the cement sand tests in Table 3, will show that
+the manufactured sands gave very satisfactory results.
+
+Table 3 gives the average tests made with the "Hidalgo" cement and
+various sands, alone and in combination, for the purpose of obtaining
+comparative results; the mixtures tested were composed of 3 parts of
+sand to 1 of cement.
+
+        TABLE 3.--TESTS OF "HIDALGO" CEMENT WITH VARIOUS SANDS.
+
+      =====================================+============+============
+                     Sand.                 | At 7 days. | At 28 days.
+      -------------------------------------+------------+------------
+      Ottawa (Standard)                    |  305 lb.   |  414 lb.
+      Monterrey, 1-1/2 parts, }            |            |
+      Hornos, 1-1/2 parts     }            |  188  "    |  313  "
+      Monterrey                            |  253  "    |  365  "
+      Hornos                               |  202  "    |  301  "
+      Manufactured sand, Company's crusher |  372  "    |  566  "
+      Hornos, 2 parts,     }               |            |
+      Crusher sand, 1 part }               |  231  "    |  352  "
+      Hornos, 1-1/2 parts,      }          |            |
+      Crusher sand, 1-1/2 parts }          |  265  "    |  346  "
+      Hornos, 1 part,        }             |            |
+      Crusher sand, 2 parts  }             |  248  "    |  328  "
+      =====================================+============+============
+
+The Hornos sand was used during a few weeks in the latter part of 1908,
+when the crusher was unable to produce all that was required. Its use
+was restricted to thick walls which were required to be water-tight, and
+it was always used in equal proportions with the crusher dust.
+
+
+
+
+                           ESTANZUELA SUPPLY.
+
+
+[Illustration: FIG. 8.--LOCATION PLAN OF ESTANZUELA DAM.]
+
+_Intake Works._--The intake (Fig. 8) is about 1 km. below the lowest
+spring and at a point where the maximum flow of the stream was observed.
+The works consist of a small monolithic concrete dam, placed obliquely
+across the stream at an angle selected for the purpose of obtaining a
+foundation running parallel to the direction of the strata, which at
+this point were lying almost vertically across the bed of the stream.
+Above these strata the stream bed was formed chiefly of large cemented
+limestone blocks and smaller conglomerate. No storage being possible in
+this valley, which has a very precipitous fall, the height of the dam
+was fixed merely to obtain a small settling basin for sand and debris
+brought down in time of flood. The dam foundation was excavated to
+bed-rock, from which the upper disintegrated portions were carefully
+removed; the rock was then stepped, and dovetailed recesses were left
+for properly bonding the concrete.
+
+The dam is carried well into the banks. Its extreme length is 52 m., its
+maximum height 4.50 m., and its greatest thickness 2 m. The up-stream
+face has a batter of 1 in 12, and the down-stream face, 1 in 8. The top
+of the wall is 1 m. thick. For the discharge of flood-water there is a
+weir 10 m. long, and it was calculated that with a depth of 1 m. it
+would discharge about 400 times the ordinary flow, or about 23,000
+liters per sec., but, in addition, the whole length of the dam
+(excluding that occupied by the gate-house) was arranged for the
+discharge of abnormal floods, one of which, on August 27th, reached the
+enormous quantity of 82,070 liters (2,900 cu. ft.) per sec., or 825 cu.
+ft. per sec. per sq. mile of drainage area, a remarkable run-off from so
+small an area as 910 hectares. The concrete forming the dam is a 1:3:5
+mixture. The overflow sill is 692 m. above sea level. When the dam was
+completed it was filled to the overflow level, in order to test the
+water-tightness of the basin, which, when cleared, was found to be
+slightly fissured on the north side. The leakage was sufficient to cause
+a serious loss during periods of drought, and it was then decided to
+line the basin with concrete, so that the stream would enter it without
+being under a head greater than its own depth. The length of the basin,
+measured along the center line of the original stream surface, is 85 m.,
+and its area is 1,100 sq. m. At its upper end it is merely a lined
+channel, 5 m. wide at the entrance. The floor of the basin has a fall of
+4 m. The lining was formed in two thicknesses totaling 30.5 cm. (12
+in.) of 1:2-1/2:3-1/2 concrete, laid in panels approximately 3 m.
+square, the upper panels breaking joint with those immediately below; in
+this way a very satisfactory and water-tight lining was obtained. A
+parapet wall, 45.7 cm. high, surrounds the basin. For scouring out the
+basin a 30.5-cm. (12-in.) cast-iron pipe was taken through the dam at
+the lowest point, this pipe being provided with a gate-valve encased in
+concrete on the down-stream face.
+
+The gate-house was built in connection with the dam at the north end of
+the overflow weir, its inner dimensions being 4.34 by 2.80 m. The
+substructure, to the level of the dam, is of concrete founded on the
+solid rock, and the superstructure is of brick rendered with cement
+plaster. The roof is of framed timber with red French tiles.
+
+The intake pipe is of cast iron. 40.6 cm. (16 in.) in internal diameter,
+fitted outside with a movable copper screen which is further protected
+by a wrought-iron hinged screen to prevent damage from stones, floating
+timber, etc., during times of flood. Inside the gate-house the outlet
+pipe is provided with a 40.6-cm. (16-in.) sluice-valve, operated from
+the floor level by a vertical head-stock with worm-gearing. The
+gate-house has a scour-out pipe (also operated by a head-stock) and
+duplicate copper screens fitted to iron frames. From this house the
+water is conveyed to the upper portion of the conduit, which is a
+45.7-cm. (18-in.) cast-iron pipe.
+
+Of the total area of land, 885 hectares (2,187 acres), owned by the
+company, 392 hectares (970 acres) have been fenced in, to prevent any
+contamination of the springs. This fence is formed of five lines of
+barbed wire protected with stout hog netting at the bottom, in order to
+prevent more particularly the entrance of goats, many thousands of which
+pasture in the adjoining mountains.
+
+On the high ground immediately below the intake, a 3-roomed stone house
+has been constructed for the inspector in charge of the intake works,
+who also keeps in daily touch with the general office and records the
+condition of the stream, particulars of rainfall, etc.
+
+_Aqueduct._--The total length of the aqueduct, from the intake dam to
+the South Reservoir, is 18,700 m., made up as shown in Table 4.
+
+                      TABLE 4.--ESTANZUELA AQUEDUCT.
+
+  +===========================================================+==========+
+  |              Description.                                 |Length,   |
+  |                                                           |in meters |
+  +-----------------------------------------------------------+----------+
+  |                                                           |          |
+  |Cast-iron pipes, 45.7 cm. (18 in.) in diameter, along      |          |
+  |                   the stream bed of the Estanzuela River  |   110    |
+  |                                                           |          |
+  |Concrete tubes, 55.9 cm. (22 in.) in diameter,             |          |
+  |                  to Mederos (including 281 m. of tunnel)  | 4,473.81 |
+  |                                                           |          |
+  |Cast-iron siphons, 45.7 cm. (18 in.)                       |          |
+  |                          in diameter:  Calabozos    239 m |          |
+  |                                        South Virgen 124 " |          |
+  |                                        North Virgen 177 " |          |
+  |                                        Mederos      426 " |          |
+  |                                                     ----- |   966    |
+  |                                                           |          |
+  |Concrete tubes, 63.5 cm. (25 in.) in diameter,             |          |
+  |                               Mederos to South Reservoir. |12,039.19 |
+  |                                                           |          |
+  |Cast-iron siphons, 50.8 cm. (20 in.) in diameter:          |          |
+  |                                        Necaxa       315 m.|          |
+  |                                        San Augustin 796 " |          |
+  |                                                     ----- | 1,111    |
+  |                                                           |          |
+  +-----------------------------------------------------------+----------+
+  |              Total                                        |18,700    |
+  +===========================================================+==========+
+
+The gradient of the concrete pipes is 0.43% from Estanzuela to Mederos,
+and 0.53% from Mederos to the South Reservoir. The calculated
+discharging capacity of the conduit when running full is 364 liters (13
+cu. ft.) per sec. for the upper, and 465 liters (16.4 cu. ft.) per sec.
+for the lower section. For these pipes, the coefficient, _n_, in
+Kutter's formula, was taken at 0.013. At present the line has been
+limited by overflows to discharge three-quarters full.
+
+The increase in the size of the pipes from Mederos is for the purpose of
+receiving the waters of the Mederos River and other springs in the San
+Pablo and Aqua Verde catchment areas, as shown on Plate II.
+
+The invert of the concrete conduit where it leaves the Estanzuela River
+is 684.25 m. above datum, and at the valve-house of the South Reservoir
+it is 589.00 m.
+
+The concrete pipes were manufactured and laid under contract with Mr.
+Arthur S. Bent, of Los Angeles, Cal., the Company providing all
+materials, labor, etc. The contractor was paid 10 cents per lin. ft. of
+pipe manufactured and 10 cents per lin. ft. laid. He was also
+responsible for the satisfactory completion of the work.
+
+[Illustration: FIG. 9.--ESTANZUELA PIPE LINE STEEL FORMS FOR THE
+MANUFACTURE OF CONCRETE PIPE.]
+
+Fig. 9 shows the details of the joint recommended by Mr. Schuyler and
+adopted for these pipes. The 63.5-cm. (25-in.) pipes were 61 cm. long
+and 76 mm. (3 in.) thick. The 55.9-cm. (22-in.) pipes were of the same
+length, but 70 mm. (2-3/4 in.) thick. For the purpose of strengthening
+these pipes while hauling them over very rough roads they were
+reinforced with four rings of No. 6 galvanized-iron wire.
+
+_Manufacture of Pipes._--The pipes were manufactured under the
+Supervision of Mr. H. Stanley Bent, at a pipe yard established below
+the crushing plant, from which the crushed rock and sand were delivered
+by gravity in bogies run on narrow-gauge rails. The area of the pipe
+yard was approximately 1-1/4 hectares, and it was laid out with parallel
+lines of 76-mm. (3-in.) galvanized-iron piping with hose couplings for
+sprinkling purposes. After trials with aggregates of various sizes, the
+concrete for the pipes was proportioned by volume as follows:
+
+  Crushed rock broken to pass through a 19-mm. screen   0.136 cu. m.
+  Manufactured sand (run of rolls)                      0.119  "  "
+  Portland cement                                       0.090  "  "
+                                                        ------------
+  Total                                                 0.345 cu. m.=
+                                                       (12.2 cu. ft.)
+
+
+[Illustration: PLATE III, FIG. 2.--STEEL FORMS FOR MOULDING CONCRETE
+TUBES, ESTANZUELA AQUEDUCT.]
+
+The above quantity manufactured two 63.5-cm. pipes; a 55.9-cm. pipe
+required 0.1415 cu. m. (5 cu. ft.) of the material, in the same
+proportions. Fig. 9 shows the forms for these pipes, and Fig. 2, Plate
+III, illustrates the process of moulding. The forms consist of cast-iron
+bottom rings, to the proper section of the joint, and inner and outer
+steel forms of 3-mm. plate, provided with inner and outer locking
+arrangements. The concrete was poured through a cast-iron hopper which
+fitted to the top of the outer form.
+
+The concrete, which was mixed very dry, in a 1/2-cu. yd. batch, "Smith"
+mixer, was thoroughly tamped with a 22-lb. tamper, and worked until it
+was of a stiff jelly-like consistency, the wire rings being added as the
+concrete was placed. The best results were obtained with the minimum
+quantity of water. The upper joint was moulded with a heavy cast-iron
+ring. The jacket and core forms were loosened immediately, and placed
+over other rings, a sufficient number of bottom rings being used for a
+day's work. For the pipes required for curves, special forms were used
+to give the necessary bevel to the joint. After 24 hours the finished
+pipes were lifted from the bottom ring with a special lifter, and ranged
+in position for coating internally with a Portland cement grout to which
+a little freshly slaked lime was added. The pipes were all numbered, and
+were kept moist for 10 days by constant sprinkling. They were not hauled
+to the work until 28 days after they were moulded, although this rule
+was sometimes broken, to the detriment of the pipes. More than 32,000
+pipes were manufactured, but some were used for purposes other than the
+Estanzuela Aqueduct.
+
+_Cost of Pipes._--The contractor brought with him experienced concrete
+pipe makers from California, and these were afterward assisted by
+Mexican labor. In a day two tampers could manufacture from 45 to 50
+pipes of the larger (63.5-cm,), and from 55 to 60 of the smaller
+(55.9-cm.) size.
+
+The cost varied from 2.75 to 3.25 pesos per pipe for the smaller, and
+from 3.50 to 4.00 pesos for the larger size.
+
+The approximate cost of manufacturing is as follows: Taking, as a fair
+example, one week's work during March, 1908, the wages paid to the 74
+men comprising the total pay-roll (though part of this labor was
+intermittent) amounted to 981 pesos. This includes a general foreman at
+10 pesos per day, four American tampers at 7.50 pesos, and Mexican labor
+varying from 4 to 1 peso, and all labor necessary to handle and finish
+the pipes, including coating the interiors. During this week there were
+made 1,126 of the 63.5-cm. and 1,095 of the 55.9-cm. size. The pay-roll
+includes 520 pesos for the larger pipes (46 cents each) and 461 pesos
+for the smaller pipe (42 cents each). Table 5 shows the quantities and
+cost of the materials used in the manufacture of these pipes.
+
+                    TABLE 5.--COST OF CONCRETE PIPE.
+
+  ========================================+===============================
+                                          | FOR 1,126 PIPES 63.5 CM.
+                                          | IN DIAMETER.
+            Materials.                    +-------------+-----------------
+                                          | Quantities. |  Cost.
+  ----------------------------------------+-------------+-----------------
+  Portland cement, at 8.00 pesos per      |             |
+    bbl., delivered at pipe-making yard.  |   401 bbl.  | 3,208.00 pesos.
+  Sand, at 2.65 pesos per cu. m.          |    85 cu. m.|   225.25  "
+  Crushed rock, 19-mm. (3/4-in.), at 2.65 |             |
+    pesos per cu. m.                      |    62 cu. m.|   164.30  "
+  No. 6 galvanized-wire hoops. 4 rings    |             |
+    to each pipe.                         | 4,504       |   203.00  "
+  ----------------------------------------+-------------+-----------------
+            Totals.                       |   ...       | 3,800.55 pesos.
+  ----------------------------------------+-------------+-----------------
+            Cost per pipe.                |   ...       |     3.37 pesos.
+  ========================================+=============+=================
+
+  ========================================+==============================
+                                          | FOR 1,095 PIPES 55.9 CM.
+                                          | IN DIAMETER.
+            Materials.                    +-------------+----------------
+                                          | Quantities. |  Cost.
+  ----------------------------------------+-------------+----------------
+  Portland cement, at 8.00 pesos per      |             |
+    bbl., delivered at pipe-making yard.  |   303 bbl.  | 2,424.00 pesos.
+  Sand, at 2.65 pesos per cu. m.          |    68 cu. m.|   180.20  "
+  Crushed rock, 19-mm. (3/4-in.), at 2.65 |             |
+    pesos per cu. m.                      |    50 cu. m.|   132.15  "
+  No. 6 galvanized-wire hoops. 4 rings    |             |
+    to each pipe.                         | 4,380       |   183.00  "
+  ----------------------------------------+-------------+----------------
+            Totals.                       |   ...       | 2,919.45 pesos.
+  ----------------------------------------+-------------+----------------
+            Cost per pipe.                |   ...       |     2.66 pesos.
+  ========================================+=============+================
+
+From Table 5 it is seen that the cost of the 63.5-cm. pipes was 3.37
+pesos for material plus 0.46 peso for labor = 3.83 pesos per pipe, or
+6.26 pesos per lin. m. (1.91 pesos per lin. ft.).
+
+The cost of the 55.9-cm. pipes amounted to 2.66 pesos for material plus
+0.42 peso for labor = 3.08 pesos per pipe, or 5.05 pesos per lin. m.
+(1.54 pesos per lin. ft.).
+
+The cost of cement included hauling from the bodega to the yard, a
+distance of about 5 km. At a later date, after the Company had commenced
+using the "Hidalgo" cement, some additional 55.9-cm. pipes were
+manufactured, so as to have them on hand as a reserve in case of
+emergency. In this work only Mexican labor was used, as the previous
+gang had been dispersed, but the tampers had previous experience. Taking
+the cost of 418 pipes made during one period of 9 days, the detailed
+cost was as given in Table 6.
+
+                  TABLE 6.--COST OF 55.9-CM. CONCRETE PIPES.
+
+  ========================================+===============================
+                                          | FOR 1,126 PIPES 63.5 CM.
+                                          | IN DIAMETER.
+            Materials.                    +-------------+-----------------
+                                          | Quantities. |  Cost.
+  ----------------------------------------+-------------+-----------------
+  Portland cement, at 8.00 pesos per      |             |
+    bbl., delivered at pipe-making yard.  |   401 bbl.  | 3,208.00 pesos.
+  Sand, at 2.65 pesos per cu. m.          |    85 cu. m.|   225.25  "
+  Crushed rock, 19-mm. (3/4-in.), at 2.65 |             |
+    pesos per cu. m.                      |    62 cu. m.|   164.30  "
+  No. 6 galvanized-wire hoops. 4 rings    |             |
+    to each pipe.                         | 4,504       |   203.00  "
+  ----------------------------------------+-------------+-----------------
+            Totals.                       |   ...       | 3,800.55 pesos.
+  ----------------------------------------+-------------+-----------------
+            Cost per pipe.                |   ...       |     3.37 pesos.
+  ========================================+=============+=================
+
+  ========================================+==============================
+                                          | FOR 1,095 PIPES 55.9 CM.
+                                          | IN DIAMETER.
+            Materials.                    +-------------+----------------
+                                          | Quantities. |  Cost.
+  ----------------------------------------+-------------+----------------
+  Portland cement, at 8.00 pesos per      |             |
+    bbl., delivered at pipe-making yard.  |   303 bbl.  | 2,424.00 pesos.
+  Sand, at 2.65 pesos per cu. m.          |    68 cu. m.|   180.20  "
+  Crushed rock, 19-mm. (3/4-in.), at 2.65 |             |
+    pesos per cu. m.                      |    50 cu. m.|   132.15  "
+  No. 6 galvanized-wire hoops. 4 rings    |             |
+    to each pipe.                         | 4,380       |   183.00  "
+  ----------------------------------------+-------------+----------------
+            Totals.                       |   ...       | 2,919.45 pesos.
+  ----------------------------------------+-------------+----------------
+            Cost per pipe.                |   ...       |     2.66 pesos.
+  ========================================+=============+================
+
+_Excavation for Pipe Line and Siphons._--The excavation for the pipe
+line and for bridge works, etc., was let by contract to Messrs. Scott
+and Lee, of Monterrey, under three classifications:
+
+      (1) "All material which in the judgment of the Engineer can
+      be economically loosened with picks and handled with
+      shovels."
+
+      (2) "Indurated earth or gravel, shale or rock which can be
+      loosened without blasting, and 'sillar', locally so-called,
+      whether pure or mixed with other substances, and whether it
+      requires blasting or not."
+
+      (3) "All rock not included in the above which requires
+      drilling or blasting."
+
+Locally, this classification is well understood, particularly No. 2, as
+it covers the sillar soils which are common in the neighborhood of
+Monterrey. The contract prices were: No. 1, 50 cents; No. 2, 1.50
+pesos; and No. 3, 2.50 pesos per cu. m. These prices were over and above
+the clearing and grubbing of the line, which was paid for at the rate of
+100 pesos per hectare.
+
+The route of the pipe line being along broken country, at some points
+difficult of access, service roadways, about 3 m. wide, for hauling
+material were constructed, and, for about 7 km., a roadway was made
+along the line of the trench.
+
+The prices for the roadway, under the above classification, were: For
+No. 1, 35 cents; No. 2, 1.50 pesos; and No. 3, 2.50 pesos per cu. m.
+
+The trenches were excavated 5 cm. below the required finishing depth, to
+allow for grading the pipes in selected material, and were taken out to
+an average width of 40 cm. greater than the outside diameter of the
+pipe, to allow for their proper jointing, and also to give sufficient
+room to roll the pipes in the trenches.
+
+The final quantities of excavation were:
+
+          TRENCH:   No. 1             11,115 cu. m.
+                    No. 2             18,096  "  "
+                    No. 3              6,650  "  "
+                                    --------------
+                    Total             35,861 cu. m.
+
+          ROADWAYS: No. 1             4,165 cu. m.
+                    No. 2             1,999  " "
+                    No. 3                30  " "
+                                     -------------
+                    Total             6,194 cu. m.
+
+The route of the pipe line was laid out so as to obtain an average fill
+of not more than 1 m. over the tops of the pipes, but in some cases the
+cuts, for short lengths, were 3 m. deep. The excavation for this work
+began in June, 1907.
+
+_Hauling Pipes._--The pipes were hauled to the site of the work with
+ox-carts and mule teams. The cost of hauling varied from 25 cents per
+pipe at the lower end, to 1 peso per pipe at the upper and,
+comparatively speaking, inaccessible portion of the line. The weight of
+each 55.9-cm. pipe was about 182 kg.; that of each 63.5-cm. pipe was
+about 216 kg.
+
+The breakages in all the pipes cast at the pipe yard amounted to about
+1%, due chiefly to unloading them carelessly near the pipe line.
+
+_Pipe Laying._--The pipe-laying gang was composed of 7 Mexicans under
+the direction of an American foreman, who was in charge of several
+gangs. One gang could lay daily from 60 to 73 m. (from 100 to 120
+pipes). The following was the ordinary pay-roll for one gang:
+
+       1 Foreman at 8 pesos (proportion).         2.00 pesos.
+       1 Pipe layer at 3 pesos.                   3.00  "
+       1 Pipe layer's assistant at 2 pesos.       2.00  "
+       1 Cement mixer at 2 pesos.                 2.00  "
+       2 Outside plasterers at 2.50 pesos.        5.00  "
+       2 Inside plasterers at 2.25 pesos.         4.50  "
+       1 Water boy at 0.50 peso.                  0.50  "
+                                                  -----------
+       Total.                                    20.00 pesos.
+
+This brings the average cost of laying the pipes to 32.8 cents per lin.
+m.
+
+The pipes were jointed with 1:2 cement mortar, the outer joint being
+rounded over both pipes for a width of 12-1/2 cm. (5 in.) and a height
+of about 19 mm. (3/4 in.). In making these joints the pipe layers wore
+rubber gloves. The joints were kept moist, and the trench was
+back-filled with fine, screened material to a depth of 10 cm. above the
+top of the pipe. Inside, the joints were carefully caulked with cement
+and rendered smooth, the plasterers working continuously along with the
+pipe layers, doing from 20 to 35 m. at a time. Water had to be conveyed
+to the trenches by barrels on burros, and during the dry season it was
+sometimes carried 5 or 6 km.
+
+[Illustration: PLATE IV, FIG. 1.--TYPICAL REINFORCED CONCRETE GIRDER
+BRIDGE, ESTANZUELA AQUEDUCT.]
+
+[Illustration: PLATE IV, FIG. 2.--ELLIPTICAL ARCH BRIDGE CARRYING
+ESTANZUELA AQUEDUCT.]
+
+_Bridges._--The line as laid out passed over many gulches and dry
+arroyos, and these were crossed with reinforced concrete bridges of
+varying spans and heights, two being shown on Plate IV.
+
+These bridges were formed of continuous horizontal girders, 1.10 m. deep
+and 1 m. wide, with a cantilever overhang at the abutments, varying in
+length from 1 to 2 m., so as to avoid settlement between the pipes and
+the bridges. The bottom reinforcement consisted of from 2 to 6 twisted
+bars of mild steel, varying in different spans from 12.7 to 19 mm. (1/2
+to 3/4 in.) in diameter. The turned up bars were 28-1/2 mm. (1-1/8 in.)
+in diameter; they were placed on either side, carried over the upper
+part of the beams, and continued along the end for the overhanging part
+of the girder. These bars, when not obtainable of the full length, were
+spliced with a lap of 1.2 m. with No. 6 galvanized-steel wire. The
+vertical stirrups were 4.7 by 25.4 mm. (3/16 by 1 in.), of mild steel;
+they were equally spaced 30.5 cm. (12 in.) apart, and carried all around
+the girders, lapping at the center about 15 cm. (6 in.), all the steel
+being carefully wired together before placing the concrete.
+
+The general type of the piers and abutments is shown by Fig. 1, Plate
+IV, and varies in height with practically every bridge, the foundations
+in every case resting on hard rock. The concrete for the girders was a
+1:2-1/2:3-1/2 mixture, the crushed stone used having all passed a mesh
+of 19 mm. (3/4 in.). The piers were of 1:3-1/2:5-1/2 concrete, and heavy
+"displacers" were embedded within them.
+
+The concrete was placed after the pipes had been laid through the form
+by the pipe contractor, the joints being kept clear of the bottom to the
+required distance by small moulded concrete blocks. The tops of the
+girders were moulded to a slightly segmental form. The bridges were all
+kept watered for about 15 days, and the forms were not struck for 28
+days after placing. At Station 13.4 the pipes were carried over a
+picturesque arroyo on an elliptical arched bridge (Fig. 2, Plate IV) of
+11 m. clear span.
+
+The abutments of all bridges were protected by rubble walls in cement
+mortar carried up 60 cm. above the tops of the girders.
+
+The contract price for the concrete work of these bridges, the Company
+furnishing the steel and cement, was 14 pesos per cu. m., and for
+placing reinforcing steel 35 pesos per metric ton (2,204 lb.).
+
+There are 49 single-span bridges, the larger spans being 9.10 m.; 8
+two-span, and 11 three-span bridges, their total length, including the
+overhang, amounting to 870.50 m., or 4-1/2% of the whole length of
+aqueduct.
+
+_Concrete Aprons._--At 76 points there were small depressions which did
+not necessitate the construction of bridges, and at these places the
+pipes were encased in blocks of concrete carried up the hillside in the
+form of an apron having small abutment walls from 1 to 2 m. apart. This
+also served to protect the pipes from scouring action during rainstorms.
+At the upper end of the line, near the intake, the pipe had to be
+protected by concrete continuously for a distance of about 300 m., in
+order to prevent damage from falling rocks.
+
+[Illustration: PLATE V, FIG. 1.--VENTILATING COLUMN AND ENTRANCE
+MANHOLE, ESTANZUELA AQUEDUCT.]
+
+_Ventilators and Manholes._--Along the route of the concrete pipe there
+are 27 ventilators, one of which, together with an entrance manhole, is
+shown by Fig. 1, Plate V. They consisted of simple concrete columns,
+3.35 m. high, above the ground line, the interior of the shafts being
+formed of fire-clay pipes, 15 cm. (6 in.) in diameter. At each
+ventilator the pipe was cut and a block of concrete, the width of the
+trench, filled in as a foundation. Entrance manholes were also placed at
+49 points, at 27 of which they immediately adjoined the ventilating
+columns.
+
+_Estanzuela Tunnel._--At 1,560 m. from the intake at Estanzuela, the
+conduit is laid through a tunnel 281 m. long. The tunnel was driven
+through hard calcareous strata from the open cuttings at each end. The
+inner dimensions were trimmed to approximately 2 m. high and 1-1/2 m.
+wide. At the ends of the tunnel the rock was moderately easy to take
+out, but the inner section was very hard and difficult to blast.
+Ordinary hand drilling was adopted, and the actual cost of driving
+varied from 28 pesos per lin. m. at the ends to 50 pesos in the center.
+
+The pipes were laid through the tunnel in the ordinary way, and
+back-filled from the center, so as to give a cover of about 45 cm. above
+to protect them from falling pieces of shale.
+
+[Illustration: PLATE V, FIG. 2.--PLACING CONCRETE PIPES IN FORMS FOR
+BRIDGE CROSSING AT NORTH END OF TUNNEL, ESTANZUELA AQUEDUCT.]
+
+_Siphons._--It has already been mentioned that there are 6 cast-iron
+pipe siphons. The head on these varies between 10 and 38 m. All are
+provided with special inlets and outlets, forming combined overflow and
+ventilating chambers, and have wooden hand-sluices to divert the water
+when necessary. The bottoms of all siphons are provided with 20-cm.
+cast-iron scour-out pipes, fitted with valves, and carried down to a
+lower point to obtain a free outlet. The valve-boxes are protected by
+being placed in heavy concrete chambers carried up above the level of
+ordinary floods.
+
+The siphons are formed of cast-iron socket pipes, 3.65 m. (12 ft.) long,
+caulked in the ordinary way with lead joints. The thickness of the
+45.7-cm. (18-in.) pipes is 19 mm.; that of the 50.8-cm. pipes is 21 mm.
+On the steep hillsides the pipes are anchored securely to the rock in
+concrete blocks reinforced with heavy iron chains. In some cases these
+siphons were difficult of access, but ox-teams hauled the pipes in a
+very efficient and satisfactory manner.
+
+_Overflow Chambers._--The ordinary overflows, of which there are 14, are
+similar in design to the siphon inlets.
+
+_Testing, etc._--When the line was completed it was tested for
+water-tightness, and the loss was found to be about 5%, part of which
+was probably due to absorption. At a later date it was found that the
+waters of the Estanzuela River, which contain 150 parts of calcium
+carbonate (CaCO_{3}) per million, deposited a very fine film of lime on the
+interior of the pipes, completely filling any pores there might have
+been. At the present time there is no measurable leakage, thus proving
+that the character of the work is very satisfactory.
+
+The water was turned into the conduit on June 11th, 1908, and delivered
+to the city on the following day through a by-pass, before the reservoir
+was completed.
+
+The pipe line is patrolled daily by an inspector with the authority of a
+gendarme, so as to prevent the unlawful abstraction of water, a very
+necessary precaution in so dry a country.
+
+
+
+
+                       SOUTH DISTRIBUTING RESERVOIR.
+
+
+The distributing reservoir for the Estanzuela supply is at Guadalupe, on
+the foot-hills to the south of the Santa Catarina River, about 2 km.
+from the center of the city. The reservoir is a covered one, of
+reinforced concrete, and its capacity is 38,000,000 liters (10,000,000
+U. S. gal.).
+
+[Illustration: PLATE VIII, FIG. 1.--GENERAL VIEW OF EXCAVATION AND
+EMBANKMENT FOR SOUTH RESERVOIR BEFORE LINING.]
+
+_Excavation and Embankment._--The heavy slope of the ground at the
+selected site made the circular form the most desirable. On the low side
+the ground was excavated about 2 m. below the original ground line,
+while the excavation at the upper part of the slope was about 12 m.
+deep. The excavated material consisted chiefly of sillar and limestone
+conglomerate, which when broken up forms a calcareous clay of an
+excellent character for the formation of embankments, when proper care
+is taken. The dimensions fixed for the internal diameter of the finished
+concrete work of the reservoir were: 81 m. (265.68 ft.) at the top, and
+a depth of water of 9 m., with sides sloping 55 in 100.
+
+[Illustration: FIG. 10.--SOUTH RESERVOIR PLAN OF EXCAVATION.]
+
+Fig. 10 is a plan of the reservoir, with a cross-section of the
+excavation and embankment. On the lower side the original ground line
+was cut down in steps, and all loose earth, roots, etc., were carefully
+removed. The floor of the reservoir was chiefly sillar conglomerate, a
+hard material that required a considerable amount of blasting for its
+removal. The embankments were formed in 10-cm. layers of sillar and
+conglomerate broken into small fragments and then rolled with 3-ton
+sectional rollers drawn by teams of 4 and 6 mules, which assisted in
+disintegrating the mass thoroughly, and produced by constant wetting a
+homogeneous and compact clay. The excavation and embankment were left so
+that 15 cm. of trimming could be done at a later date, immediately prior
+to the lining of the reservoir. The excavated material amounted to about
+34,000 cu. m., and, of this quantity, 31,500 cu. m. were used to form
+the embankment; the remainder was taken to a spoil bank immediately
+adjoining, the black earth stripping being separated and reserved for
+covering the reservoir, etc. The contract prices for the excavated
+material placed in the embankment were:
+
+                                                                     Pesos
+                                                                     per
+                                                                     cubic
+                                                                     meter
+
+  Class 1.--Material which could be removed by plows and scrapers    0.60
+  Class 2.--This consisted chiefly of "sillar"                       1.09
+  Class 3.--Limestone conglomerate (requiring blasting)              1.65
+
+The prices (for the same classification) for material taken to the spoil
+bank, were 0.40, 0.80, and 1.40 pesos, respectively. Of the material
+taken out, 15% came under No. 1 classification, 80% under No. 2, and 5%
+under No. 3.
+
+The excavation was begun at the end of May, 1907, and completed in
+January, 1908, by Scott and Lee, the contractors. The embankments were
+then allowed to stand until the beginning of July, 1908, to permit the
+whole to become thoroughly settled and consolidated prior to beginning
+the lining. In July the work of trimming the embankments and excavating
+for the foundations of the reservoir columns was commenced, under the
+Company's own administration, which completed the entire work.
+
+[Illustration: PLATE VI.--DETAILS OF BEAMS AND COLUMNS FOR SOUTH
+RESERVOIR.]
+
+[Illustration: PLATE VIII, FIG. 1.--DETAILS OF FORMS FOR SOUTH
+RESERVOIR.]
+
+[Illustration: PLATE VIII, FIG. 2.--VIEW OF WESTERN HALF OF SOUTH
+RESERVOIR, SHOWING FINAL SETTING UP OF DERRICK ON CENTRAL COLUMNS.]
+
+_Concrete Lining and Roof._--The general arrangement and details of the
+side-walls, columns, and roof are shown on Plates VI, VII, VIII and IX.
+The principal feature consists in dividing the reservoir into radial
+sections and supporting the roof on 135 primary and 670 secondary beams,
+from 135 columns, spaced as follows:
+
+           Outer ring, at 34.25 m. from center    40 columns.
+            2d    "    "  27.88 "   "             40  "
+            3d    "    "  21.51 "   "             20  "
+           4th    "    "  15.41 "   "             20  "
+           5th    "    "   8.77 "   "             10  "
+           6th    "    "   2.40 "   "              5  "
+                                                 ---
+               Total                             135 columns.
+
+The inner bottom diameter of the reservoir is 70.32 m. (230.64 ft.); the
+upper inside diameter is 81 m. (265.68 ft.); the water depth at the
+overflow level is 9 m. (29-1/2 ft).
+
+The roof was designed to carry a dead load (the earth cover) of 150 lb.
+per sq. ft., and a live load of 100 lb. The maximum compressive fiber
+stress in the concrete was assumed at 550 lb. per sq. in. for the beams,
+and at 350 lb. for the columns, a low figure, because of their eccentric
+loading. The tensile strength of the steel was taken at 14,500 and
+16,000 lb. per sq. in. The twisted steel used for the column
+reinforcement was made at the local steel plant, but for the beams,
+etc., a twisted lug bar, of higher quality and greater permissible
+tensile stress, was used. The total quantity of steel used was 178 tons.
+It was calculated that the load on the column foundations would not
+exceed 1-1/4 tons per sq. ft. With the exception of the side-wall and
+floor, all the concrete was reinforced with steel, of the sizes and
+spacing shown on Plate VI.
+
+_General Construction and Erection Scheme._--The question of ordinary
+forms, requiring very heavy timber work, was a serious one, as suitable
+lumber is very expensive in Mexico; and the necessity of finishing this
+reservoir before the end of the first term allowed under the concession,
+which expired on December 31st, 1908, led to the adoption of what the
+writer believes is an original scheme for so large a structure. This
+scheme was to cast the columns in short sections, mould the radial and
+secondary beams as separate members, and then place them in position
+with derricks. At the same time, in the case of the beams, it was
+important not to sacrifice either the benefit of that part of the slab
+which is ordinarily assumed to act as a part of the beam, or the
+additional strength due to continuity; and, in case of the columns, the
+strength due to the reinforcement extending from the foundation to the
+beams.
+
+The T-beam section was secured by notching the tops of the moulded
+members, with notches 10 cm. deep, throughout the lengths of the beams,
+as shown on Plate VI. A computation of the maximum flange increment
+shows that these notches are sufficient to transfer the flange stresses
+to the stem, but, for additional security, flat steel bars were bent to
+a Z-shape and embedded in the top of the beam, about 60 cm. apart.
+Continuity in the beams was secured by carrying the steel to the tops of
+the beams over all supports, and, after erection, concreting them into
+the roof slab. The secondary beams, after casting, were dropped into
+recesses left in the radial beams for the purpose.
+
+_Concreting, Mixing, etc._--The radial beams and column sections were
+cast as nearly as possible under their ultimate positions; the secondary
+beams were cast outside and immediately adjoining the reservoir.
+
+The rock and sand was brought from the Company's crushing plant, in
+3-cu. yd., side-dump cars, running on a 30-in. track by gravity a
+distance of 1 km., the last 150 m. requiring hauling with 6 mules. The
+cars returned all the way to the crusher by gravity. These cars dumped
+the material into bins on the high ground above the reservoir; from
+there it was hoppered into cars which carried to the mixer all the
+material for one batch of concrete. Two No. 1 Smith mixers were used,
+and from 25 to 30 batches per hour could be handled in each machine.
+
+The concrete was transported from the mixers to place in 1/2-cu. yd.,
+18-in. gauge, swivel, steel dump-cars pushed by two men. All the
+concrete used in the bottom of the reservoir, for the main beams,
+columns, and floor, amounting to about 2,460 cu. m., was dumped through
+a chute into smaller cars. The chute had so many baffle-plates and bolts
+that it resembled a gravity mixer, but, although it was 12 m. long, it
+effectively prevented the separation of the materials.
+
+_Concrete Placing and Moulding._--The square foundations for the columns
+were deposited _in situ_, a recess being left for the reception of the
+pedestals, which were moulded in place afterward. The capitals and
+pedestals were cast in one piece, and the columns in 1.21-m. (48-in.)
+sections, eight 5-cm. holes being left in them by using wrought-iron
+pipes, held in place by templates and removed when the castings were
+about 3 hours old. The columns were erected by threading them on the
+15.8-mm. (5/8-in.) reinforcing rods, which extended from the pedestals
+up through the capitals. The rods were in two lengths, arranged to lap
+alternately at one-fourth, the center, and three-fourths of the height
+of the columns. In erection, a light timber frame was used in
+conjunction with the derrick, and, as the columns were placed, the
+reinforcing steel was grouted solid with 1:2 cement mortar.
+
+All the erection was done with a combined stiff-leg or guy derrick,
+having an 80-ft. boom and a 50-ft. mast, and fitted with a 30-h.p.
+Lambert hoisting engine. The derrick was erected seven times at the
+circumference, and its final position was on top of the center columns.
+The moving of the derrick a distance of about 45 m. and its subsequent
+erection occupied usually about 48 hours. The erection work was carried
+on continuously, day and night, the placing of the whole of the radial
+and secondary beams and columns occupying 2-1/2 months.
+
+_Forms._--As the erection scheme was designed to reduce the cost of
+forms, economical construction was of considerable importance. The wall
+was formed in 40 panels, about 6 m. wide and 11.27 m. high. The chief
+object in arranging them in this manner was to permit an expansion
+joint, 30 cm. wide, at each panel; this joint was not filled until after
+the completion of the roof, when the temperature inside the reservoir
+was uniform and not subjected to such great fluctuations as if exposed
+alternately to the hot sun and comparatively cool nights. The range of
+temperature during the construction period sometimes amounted to 80 deg.
+Fahr. in 24 hours.
+
+The expansion joints were left to the last, when a uniform temperature
+of about 70 deg. inside permitted the filling of the joints, thus avoiding
+all trouble from expansion cracks.
+
+The forms are shown in detail on Plate VII. They consisted of shutters
+stiffened with four trapezoidal trusses. The bottom posts of the trusses
+were fixed in holes formed in the foundation block; they were propped
+back from the embankment at the top, and secured to anchorages by iron
+rods.
+
+Six sets of these forms were used to construct the whole wall. The
+concrete was placed in position through stove-pipe chutes, 20 cm. in
+diameter, in continuous layers, the workmen treading and spading it well
+as it was deposited. The forms were allowed to remain 4 or 5 days, and
+were then struck and removed to another section. The pedestals and
+capital forms were of lumber, and five of each were used to cast the
+total number required. In the column sections the outer steel forms used
+in the manufacture of the Estanzuela pipes were adapted for this
+purpose. The radial beam forms, shown on Plate VII, were arranged with
+internal wedge-shaped blocks to mould accurately the recess for the
+secondary beams. The bottom forms were left attached to the beams for 28
+days, but the sides and ends were removed after 24 hours. Eight forms
+were sufficient for the whole 135 beams.
+
+For the secondary beams, 29 forms were used for the 670 beams, the
+bottom lumber also being left until they were mature for handling.
+
+By referring to the cross-section of the secondary beam, it will be
+noticed that it is jug-shaped, shelves being left on either side for the
+support of the roof forms, which were placed after the secondary beams
+had been properly grouted to the radial ones. The lagging was laid
+diagonally, so that the short diameter was slightly greater than the
+distance between the beams. This greatly facilitated the removal of the
+lagging, as it was merely necessary to strike the wedge-shaped fillets
+beneath, and turn them clockwise, after tearing out the end lagging.
+
+[Illustration: PLATE IX, FIG. 1.--VIEW OF SEPARATELY MOULDED SECONDARY
+BEAMS IN YARD BELOW SOUTH RESERVOIR.]
+
+[Illustration: PLATE IX, FIG. 2.--SETTING PRIMARY BEAMS, SOUTH
+RESERVOIR.]
+
+The writer believes that the adoption of forms of this type, rather than
+the ordinary kind, led to a saving of lumber of about 400,000 ft. b. m.
+During the erection and placing of the concrete, all the joining
+surfaces were carefully picked and cleaned, particular care being taken
+at the junction of the secondary with the radial beams, and the upper
+surfaces of all beams before laying the roof slab.
+
+After the greater part of the roof was completed, the floor was laid in
+those sections where it was protected from the sun's rays. The concrete
+was placed in two 15-cm. thicknesses, and the work was carried on night
+and day, without any joints. The laying of the floor occupied 8 days, or
+an average of nearly 100 cu. m. daily.
+
+[Illustration: PLATE X, FIG. 1.--VIEW OF COMPLETED SECTION OF SOUTH
+RESERVOIR. EXPANSION JOINTS IN SIDE-WALL NOT YET FILLED.]
+
+_Proportions of Concrete._--All the concrete work was brought to a
+smooth face by careful spading, no plastering being used throughout the
+reservoir, except in the superstructures. The work was kept well watered
+in every case for about 15 days. The whole of the concrete work in
+connection with the reservoir was completed in 5-1/2 months. The
+concrete for the columns and foundations was a 1:3:5 mixture, the
+aggregate consisting of equal parts of 19-mm. (3/4-in.) and 38-mm.
+(1-1/2-in.) crushed stone. The remainder of the concrete, except that
+for the roof, was a 1:2:4 mixture, the aggregate also consisting of
+equal parts of 19-and 38-mm. stone. With the exception of a short length
+of the side-walls, the sand used was that manufactured by the Company.
+When the crushing plant was unable to produce all the sand required, the
+Hornos sand (see Table 3) was used in the side-walls in equal
+proportions with the crusher sand.
+
+_Reservoir Outlet and Entrance Tower._--The outlet, 61 cm. (24 in.) in
+diameter, leads from a well in the center of the reservoir and passes
+under the floor and embankment to an outside valve-pit, 89 m. from the
+center. This pipe was laid in a trench in a solid cutting before the
+construction of the embankment, and was encased in 1:4:8 concrete.
+Where it passes under the embankment a 1:2:4 concrete cut-off wall, 3.6
+m. wide, 2.5 m. high, and 1 m. thick, was placed across it at right
+angles. The cast-iron pipe is curved upward in the central well, and has
+a bellmouth on which rests a movable circular copper screen.
+
+Above the outlet well, and on the roof of the reservoir, there is a
+central tower, giving access to the interior by a steel stairway. This
+tower also serves as a main ventilating shaft, and in it are arranged
+the guide-screens and gearing for raising them for cleaning purposes. In
+addition to the ventilation provided in the tower, 20 circular openings,
+30 cm. in diameter, are carried through the roof of the reservoir at the
+circumference and into the parapet walls.
+
+_Inlet Gate-House, etc._--The inlet gate-house is above the reservoir
+and about 54-1/2 m. from its center. The conduit enters at 589.00 m.
+above datum, and the gate-house contains the valves for controlling the
+inlet pipe to the reservoir, the by-pass, overflow, scour-out pipe, and
+the copper screens. The inlet, which is 45.7 cm. (18 in.) in diameter,
+is of cast-iron flanged pipes, carried on iron hangers on the side-wall
+of the reservoir, and, at a point 90 cm. above the floor level, it is
+turned at right angles to the side-wall and carried on concrete piers to
+the center of the first row of columns. The end of the pipe is closed by
+a blank flange, and the water is deflected at right angles through two
+30-cm. (12-in.) branches, for the purpose of setting up a slight
+circular motion as it enters the reservoir.
+
+The valve-pit is clear of the embankment, and in it are brought together
+the main supply and by-pass pipes on which are placed two 61-cm.
+(24-in.) sluice-valves; and between them there is a 20-cm. (8-in.)
+scour-out pipe, for emptying the reservoir into an adjoining arroyo. The
+arrangement of the valves gives complete control over the contents of
+the reservoir.
+
+_Venturi Meter-House._--Fig. 11 shows the arrangement of the Venturi
+meter and its automatic register in a house over the main supply pipe.
+This house is designed to form a feature of the entrance gateway of the
+reservoir grounds, which cover an area of 12 hectares.
+
+[Illustration: FIG. 11.--VENTURI METER-HOUSE.]
+
+_General._--The roof of the reservoir has been laid out as a garden, and
+the embankments are turfed. The intention is to develop the Company's
+land as a public park, as it commands fine views of the city and the
+surrounding mountains. An inspector's house has been built, and a
+private telephone line provides for communication with the Estanzuela
+intake and also with the general offices in the city.
+
+[Illustration: PLATE XVIII, FIG. 1.--VIEW OF SOUTH RESERVOIR, LOOKING
+TOWARD THE CITY.]
+
+
+
+
+                       SAN GERONIMO GRAVITY SUPPLY.
+
+
+_Provisional Supply._--It has already been stated that the Company began
+operations at San Geronimo in March, 1906, by sinking a well on the
+north bank of the Santa Catarina River at San Geronimo. At this point, a
+little later, a small steam pumping plant, sufficient to handle about
+8,000 liters per min., was installed. The lowest depth to which this
+well was ultimately sunk in water-bearing strata, was 7 m., the normal
+level of the water during 1906 and 1907 never falling lower than 569 m.
+above datum. Tests made from time to time during 1907-08, showed that
+this well was capable of supplying nearly 10,000,000 liters (264,000
+gal.) of water daily.
+
+The excellent supply yielded by this well made it desirable to adopt it
+immediately as a provisional measure, pending the completion of the
+larger works forming the western source of supply. To utilize the well
+to its fullest extent, a reinforced concrete reservoir, of 3,000,000
+liters capacity, was constructed on the south bank of the river, the top
+water level being 585 m. above datum, that is, at the same elevation as
+the proposed reservoir for the Estanzuela supply. The reservoir is 53.80
+m. long, 21 m. wide, and has a water depth of 3.25 m. at the overflow
+level. It is excavated on a steep hill slope, and has an earth
+embankment on the lower side. The lining is of concrete, 20 cm. thick,
+and the roof is of reinforced concrete composed of flat arches springing
+from beams carried on 46 by 35-cm. reinforced columns. There are 68 of
+these columns, and they are 3 m. apart longitudinally and 5 m. apart
+transversely. The roof was not constructed until October and November,
+1907, and prior to that time the necessity of covering the reservoir was
+amply demonstrated by the growth, during hot weather, of considerable
+quantities of green algae, which had to be skimmed from the surface of
+the reservoir every few days.
+
+The delivery pipe from the pumping plant was originally of riveted steel
+and was asphalted. It was 30 cm. in diameter, 2 mm. in thickness, with
+slip joints, and where it crossed the river it was encased in concrete.
+This pipe was afterward replaced by a cast-iron pipe of the same
+diameter. The supply pipe to the city was also of sheet steel, 30 cm. in
+diameter. For a part of its length it was laid in the high ground of the
+south bank of the river, which it crossed near the western limits of the
+city, and was then connected to a 30-cm, cast-iron pipe in the
+distribution system. The total length of the pipe from the reservoir to
+the city distribution system was 2,850 m.
+
+This provisional pipe continued in service from October, 1906, until
+August 27th, 1909, when the river portion was completely swept away,
+together with the provisional pump-house at San Geronimo, during the
+great flood in the Santa Catarina River. Fortunately, the permanent
+supply works were completed at the time, so that the destruction of this
+pipe line, which had already served its original purpose, had no effect
+on the supply of water to the city.
+
+[Illustration: PLATE XI.--SECTION OF INFILTRATION GALLERY, SAN GERONIMO
+GRAVITY SUPPLY.]
+
+_Infiltration Gallery._--The chief feature of the San Geronimo gravity
+supply is the infiltration gallery. By referring to the profile on Plate
+XI it will be seen that at this place there is a considerable area of
+what is undoubtedly water-bearing gravel. The main conditions were
+revealed by the borings previously carried across the valley, but the
+profile has been corrected to show the actual conditions as established
+at a subsequent date by shafts. Practically, the water-bearing strata
+are not limited merely to the sand and coarse gravels, as the clay
+formation lying above and below them is full of small gravel deposits
+containing considerable volumes of water. The main direction of the
+underflow is toward the east, and the hydraulic gradient, which was
+established from wells sunk farther west, was found to be approximately
+1%, or practically the same as the average surface of the bed of the
+river above the line of the infiltration gallery.
+
+The general scheme for tapping this underflow was to drive a main
+gallery at the 560-m. level on a grade of 0.05%, which was sufficiently
+high to take the supply by gravity to the western reservoir, having a
+top water level at 558.75 m. above datum. This elevation is sufficient
+to give an excellent pressure over about 60% of the city, and a fair
+pressure to reach the upper stories of the highest houses, if required,
+over the whole supply district. From this gallery it was proposed to
+sink shafts at frequent intervals, for a total distance of 300 m.,
+carrying them below the gallery level, to tap any water-bearing gravels
+there might be in the clay formation underlying the gravels and sands.
+From the main gallery it was proposed to construct branch galleries up
+stream on a flat gradient, so as to obtain the advantage of an increased
+head due to the steep hydraulic gradient of the underflow water.
+
+[Illustration: FIG. 12.--DIAGRAM SHOWING VARIATION IN WATER PLANE 1905
+TO MARCH 1910 AT SAN GERONIMO.]
+
+In investigations of this kind, it is of first importance to have a
+continuous record of the level of the water plane, and Fig. 12 has been
+plotted to show its variation at San Geronimo from the beginning of
+1905 to March, 1910. From January, 1909, to March 31st, 1910, these
+levels are averages of daily readings taken in 9 shafts sunk along the
+proposed line of the infiltration gallery. In 1902 the water plane was
+standing at 570.18 m. above datum, but from that date until 1905 the
+writer has been unable to find any records. This diagram should be
+examined together with the rainfall diagram, Fig. 3, and it will be
+noticed that the fall in the water plane drops with the general scarcity
+of the rainfall during 1907-08, and until July, 1909. The year previous
+to July, 1909, is regarded, by many competent local observers to have
+been the longest period of extreme drought in 30 years in Nuevo Leon,
+and the evidence which the writer has been able to gather regarding
+stream flow in the neighborhood of Monterrey supports this view. The
+total rainfall at Monterrey for the year prior to July 1st, 1909,
+amounted to 9.98 in., or 4.16 in. less than the lowest record for any
+calender year since 1894, or, in other words, about 45% of the average
+annual rainfall.
+
+The lowest point to which the water plane dropped was during June and
+July, 1909, when the levels stood slightly above 565.00 m., or 5 m.
+above the level of the floor of the infiltration gallery. During this
+period pumping tests were made in the various wells, and from these it
+was quite clear that the infiltration gallery, if carried far enough to
+meet them all, would yield a supply of from 25,000,000 to 40,000,000
+liters daily. During the great rainfall of August, 1909, the water
+levels rose very rapidly; the heavy precipitation between August 9th and
+10th caused the level to rise to 568.00 m. in about 4 days, and 6 days
+after the great flood of August 27th, the water level, which had
+continued rising gradually, reached 571.40 m., and then fell gradually
+until at the end of March, 1910, it was practically the same as it had
+been from 1902 to 1905.
+
+[Illustration: PLATE XII.--SAN GERONIMO GRAVITY SUPPLY.]
+
+It should be noticed that the readings were taken in the shafts on the
+high ground to the west of the present river bed, and were independent
+of any flow there might be in the river. During times of ordinary floods
+in the river, it was very noticeable that, notwithstanding the fact that
+the river water might be turbid to an extreme degree, the well even in
+immediate proximity to the river bed did not show the least sign of
+discoloration.
+
+_Design of Works._--Plate XII shows the general design of the gravity
+scheme, which consists of a main tunnel 550 m. long and a concrete
+aqueduct, 1.06 m. (42 in.) in internal diameter and 2,311 m. in length,
+discharging into a low-service distributing reservoir at the extreme
+western limits of the city. The tunnel and aqueduct were laid on a
+gradient of 0.05%, and the latter was designed to discharge 55,000,000
+liters per day (22.8 cu. ft. per sec.) if flowing to its full capacity.
+
+_Gravitation Tunnel._--This tunnel, shown on Plate XII and Fig. 13, was
+completed prior to driving the infiltration gallery into the
+water-bearing gravel, so that the water encountered in the gallery could
+be easily drained off by gravity, thus avoiding a heavy outlay for
+pumping. The tunnel passes through various strata, the principal ones
+being calcareous shale, conglomerate, and gravels. The tunneling
+operations were carried on from 5 shafts, No. 1 being 23 m. deep, and
+the others varying from 20 to 10 m. The shafts in loose ground were
+timbered in the usual way, having clear inside dimensions of 2 m. Shaft
+No. 1, which was entirely in shale, was taken out approximately to 3.35
+m. in diameter, so as to permit it to be lined with concrete having a
+finished internal diameter of 2.43 m.
+
+[Illustration: FIG. 13.--GENERAL DETAILS SAN GERONIMO GRAVITY PIPE LINE.]
+
+Fig. 13 shows the details of the tunnel, which was lined with concrete,
+the bottom and sides being approximately 23 cm. (9 in.) thick. The
+interior dimension is 0.91 m. at the invert level and 1.016 m. at a
+height of 1.22 m., the corners between the side-walls and the floor
+being slightly curved. The arch is formed of two rings of brickwork in
+cement mortar, this thickness being increased in some lengths to three
+rings. Where the rock was in good condition, and not likely to
+disintegrate easily, the arch, for a distance of 90 m., was left
+unlined. Of the total distance of 550 m., careful timbering was required
+for 300 m. In lining the timbered portion of the tunnel with concrete,
+all the timber was removed, except in loose ground, where the laggings
+were left in position.
+
+While the tunnel was being driven, a start was made to drive the north
+end of the infiltration gallery, which was in rock for a distance of 44
+m. Water appeared at about 35 m., and then the work was temporarily
+suspended until the gravitation tunnel was completed and a length of the
+aqueduct had been constructed far enough down stream on the north bank
+of the river to permit of draining direct to the river. This point was
+reached at 1,170 m. from Shaft No. 1, and there a temporary overflow
+chamber was constructed.
+
+When the tunnel was completed, the two intermediate shafts were filled
+up, the remaining three being retained permanently. Shafts Nos. 2 and 3
+were lined with concrete, 76 cm. (30 in.) in internal diameter, and 23
+cm. thick. They were domed at the top to form circular openings to
+receive cast-iron covers. Progress on this tunnel was slow, taking from
+December, 1907, to November, 1908, to complete, owing chiefly to
+difficulties with an incompetent contractor. The contract was
+subsequently transferred to Mr. John Phillips, of Mexico City (who was
+also the contractor for the aqueduct), who completed it satisfactorily.
+
+_Continuation of the Infiltration Gallery._--When the aqueduct (to be
+referred to again) was completed as far as 1,170 m. from Shaft No. 1,
+the driving of the infiltration gallery, which was 2 m. high and 1-1/2
+m. wide, was continued until gravel was encountered in the roof, at 44
+m. from the shaft. At this point the rock dipped at an angle of 45 deg.,
+and the gravels contained quantities of large boulders mixed with fine
+sand; immediately after encountering the gravel, a flow of about 90
+liters per sec. was met, evidently coming through from a pot-hole in the
+shale. This quantity diminished in about 10 days to about one-fourth,
+but gradually increased again as the driving proceeded. The operations
+of driving the tunnel from 44 m. forward were begun in the dry season,
+in February, 1909, and the gravel was encountered for a distance of 24
+m., or up to 68 m. from the shaft. The center of this gravel bed was
+about 30 m. south of the old river channel, which had been continuously
+dry at the surface for several years. Up to 68 m. the work was very
+difficult, owing to the upper part being of loose gravel and the lower
+in very contorted shale. The timbering of the tunnel in the full gravel
+section consisted of heavy square settings, 1 m. apart. At 68 m. the
+clay and gravel formation was met, and the rate of progress then was
+about 4 or 5 m. a week. A short branch gallery was also driven about 7
+m. up stream near Shaft No. 2. The total distance the infiltration
+gallery was carried from Shaft No. 1, was 100 m., when the floods of
+August, 1909, caused its suspension.
+
+During the progress of the gallery, attempts were made to sink a 3-1/2
+by 2-m. shaft at a point along the line of the infiltration gallery,
+about 130 m. from Shaft No. 1, but water in such abundance was
+encountered that it was practically impossible to sink it in the
+ordinary way more than about 6 m. deep, the quantity of water to be
+dealt with amounting to about 20,000,000 liters daily. Seven shafts were
+then sunk in the high ground to the north of the river, five of these
+being on the line of the gallery and two 30 m. westward. They were sunk
+during the dry season prior to July, 1909. These were ordinary timbered
+shafts, 2 m. square between the walings, and were carried to the depths
+shown on Plate XI. In Shafts Nos. 5, 6, and 7 the water was flowing with
+considerable velocity, while Shaft No. 9 seemed to have penetrated a
+different water plane and one which was probably independent of that
+showing in any of the other shafts, in which the water was practically
+at a uniform level. The evidence obtained showed that if the gallery
+could be carried to Shafts Nos. 6 or 7 a great abundance of water would
+be intercepted. Owing to the difficulties of sinking ordinary shafts in
+the wide river channel, circular shafts were put down. These were 1.37
+m. in internal diameter and 23 cm. thick, and were of concrete
+reinforced with No. 10 vertical rods, 19 mm. in diameter, tied together
+with No. 6 wire. These shafts were provided with steel cutting edges.
+
+Shaft No. 2 was sunk to a depth of 1 m. below the infiltration gallery
+level, No. 3 within 2 m., and No. 4 within 4 m., before August, 1909.
+The shafts were sunk by digging them out and loading them at the top,
+the top of the shafts being kept generally 3 m. out of the ground. Shaft
+No. 3 encountered great volumes of water, and, in order to enable
+sinking operations to proceed, a pumping shaft, 2-1/4 m. square, was
+sunk a little west of it to draw off the water. Notwithstanding the fact
+that the prolonged period of drought had lowered the general water plane
+in all the shafts to 565.00 m. above datum, the difficulties of handling
+the water even at that level were considerable. At the beginning of
+August the work was progressing very satisfactorily, but the
+extraordinary rainfall of that month caused the work to be shut down
+temporarily.
+
+_Effect of the Floods in the Santa Catarina River._--The area of the
+water-shed of the Santa Catarina River above Monterrey is about 1,410
+sq. km. (544 sq. miles), and its area at San Geronimo, owing to its
+configuration, is practically the same. Its general character has
+already been referred to. On the night of August 10th and early on the
+morning of August 11th, a big flood came down the river, flowing at its
+maximum about 1,130 cu. m. (40,000 cu. ft.) per sec., due to the heavy
+rainfall (Fig. 4). This flood carried away all the temporary staging
+around the shafts, seriously wrecking the temporary pumping station, as
+well as destroying the 30-cm. cast-iron pipe, notwithstanding the fact
+that it had been encased in a block of concrete 3 m. wide and 1-1/2 m.
+thick right across the river; but no damage was done to the infiltration
+gallery or to the shafts in the river channel. The effect of the flood
+on this pipe is shown by Fig. 2, Plate XXXI.
+
+[Illustration: PLATE XXXI, FIG. 2.--PROFILE SKETCH, LOOKING UP STREAM ON
+LINE OF 24-INCH MAIN SUPPLY PIPE.]
+
+Following this flood, which had caused the loss of 14 lives in the city,
+3 miles below San Geronimo, there was practically no rain for 13 days.
+Then, on August 25th the second heavy precipitation began and continued
+until August 29th, the details being shown on Fig. 4.
+
+This precipitation, therefore, fell on a water-shed which was completely
+saturated, as it had already absorbed a large proportion of the 13.38
+in. of rain which fell during August 10th and 11th; and at every point
+along the river, prior to August 25th, springs were issuing forth, and
+there had been very little evaporation during the intervening dry spell.
+
+The writer has calculated that at Monterrey this flood reached the
+enormous quantity of 6,650 cu. m. (235,000 cu. ft.) per sec., a rate
+equal to 432 cu. ft. per sec. per sq. mile of water-shed.[6] The effect
+of this flood was to demolish completely about 1,200 "sillar" houses
+(without taking into consideration the numerous wooden houses) at
+Monterrey, and to cause a fearful loss of life, variously estimated
+between 3,000 and 5,000 persons; the lower figure the writer believes is
+approximately correct. At San Geronimo the original pumping station was
+carried away entirely, leaving practically no trace whatever.
+
+[6] The writer, in a brief article contributed to _Engineering News_
+soon after the flood (September 23d, 1909), gave this figure as 271,500,
+or approximately equal to a run-off of 500 cu. ft. per sec. per sq.
+mile; but, from a later and more complete study of the conditions for
+many miles above Monterrey, he believes the above quantity to be
+approximately correct.
+
+Shaft No. 2 was apparently destroyed, while No. 3 was turned at an angle
+of about 50 deg. down stream and filled up completely with sand. The
+infiltration gallery, near Shaft No. 2, was completely blocked with fine
+sand and gravel, and access could only be obtained as far as 54 m. The
+profile, Plate XI, shows the change which had taken place in the river
+bed. The original course of the stream was changed to the north bank, 50
+m. distant, the effect of the scouring action of the flood being to
+lower the general level at this point about 3.65 m., while the southern
+portion of the channel was slightly raised. At present (April, 1910),
+the end of the driven portion of the infiltration gallery is about 35 m.
+from the center of the stream, which is still carrying about 2,270
+liters (80 cu. ft.) per sec.
+
+Immediately after the flood the flow in the gallery was 450 liters (16
+cu. ft.) per sec., and this quantity has remained constant since that
+time. The probable effect of the flood was to disturb the whole
+subsurface above the infiltration gallery and put it in motion,
+completely cleaning the gravels of their surrounding clay, which would
+account for the large infiltration of water in so limited a distance.
+The water has always been limpid and pure, but its hardness remains the
+same as it was prior to the flood.
+
+With the copious supply of water from this source, due of course to
+abnormal conditions and not likely to be permanent, the operations of
+tunneling have been suspended temporarily; but it is proposed to
+continue the driving of the gallery, from a new shaft west of No. 3.
+The water encountered will be drained off by pumping until the main
+water-bearing gravels, in the neighborhood of Shaft No. 5, are reached.
+It is also proposed to reconstruct the 30-cm. high-level pipe line, from
+San Geronimo along the high road on the north bank of the river, so that
+by pumping water can be delivered to the city system from Shafts Nos. 5,
+6, and 7, in the event of a shortness of supply from the Estanzuela
+River.
+
+_Shaft No. 1._--Shaft No. 1 is designed to connect the infiltration
+gallery with the gravitation tunnel. This shaft has an inner diameter of
+2.43 m. (8 ft.) and is fitted with a special gate-valve. In the bottom
+of the door of this valve there is a smaller valve, 30 cm. in diameter,
+so that, when the infiltration gallery is closed for cleaning out the
+sump, the smaller door, which is operated through the same spindle by a
+bevel-geared head-stock at the top of the shaft, can be opened first.
+Space is also left for screens if these should be found necessary.
+Access to this shaft is gained by a reinforced concrete stairway in nine
+stages. The superstructure is to be supported on reinforced concrete
+column foundations carried to the firm rock, owing to the loose
+condition of the strata at the top of the shaft.
+
+_Aqueduct._--The construction of the concrete conduit was begun in
+April, 1908. Fig. 13 shows the general types. Type _A_ was adopted in
+gravel and conglomerate formation, and Type _B_ where the excavation was
+in "sillar," the soft nature of this rock permitting it to be excavated
+exactly to the required external diameter of the concrete lining.
+
+The concrete which was without steel reinforcement was a 1:2-1/2:3-1/2
+mixture, the sand being from the crusher and the aggregate from the
+river bed, screened to pass a 25-mm. mesh. Where the conduit crossed the
+river obliquely, immediately below the gravitation tunnel, it was
+strengthened with mass boulder concrete of Type _C_. During the great
+flood this heavy section withstood its effects without damage of any
+kind, but beyond this point, where the conduit had been laid in compact
+cemented gravels, the scouring action of the flood on the north bank
+lowered the level of the gravels from 2 to 3 m.; the only damage,
+however, was the scouring away of the gravels at the south side of the
+conduit. To prevent such an occurrence in the future, the conduit at
+that point was strengthened with additional concrete for a distance of
+195 m., as shown on Fig. 13. The extra concrete, amounting to 733 cu.
+m., was a 1:3:5 mixture, in which was embedded 20% of heavy boulders.
+The top of this special length now forms a weir for the present river
+flow. Where the conduit enters the bluff on the north side of the river,
+at 1,200 m., there is an overflow chamber which has a sluice-gate 76 cm.
+wide, arranged so that the conduit can overflow at the present time when
+running 76 cm. deep. To deflect the flow in the conduit, a wrought-iron
+plate, provided with a balance weight, is dropped into a groove on the
+lower side. The outlet is a 61 cm. concrete tube, having its invert
+above ordinary flood level, and arranged to be closed by a gate.
+
+At 1,963 m. the conduit is carried over an arroyo on a segmental arch of
+8 m. clear span, as shown on Fig. 13. There are 5 ventilating columns
+and 5 manholes on the aqueduct.
+
+[Illustration: PLATE X, FIG. 2.--SETTING FORMS FOR SAN GERONIMO
+CULVERT.]
+
+The aqueduct terminates in the Obispado distributing reservoir
+valve-house, at a level of 558.50 m. The work in connection with this
+aqueduct was completed by December, 1908.
+
+
+
+
+                   DISTRIBUTING RESERVOIR AT OBISPADO.
+
+
+The main distributing reservoir for the San Geronimo gravity supply is
+immediately below the historic Obispado (Bishop's Palace), at the western
+limits of the city. The general arrangement and lay-out is shown on Plate
+XIII.
+
+[Illustration: PLATE XIII.--GENERAL PLAN AND SECTIONS, OBISPADO
+RESERVOIR.]
+
+_Valve-House._--The invert of the conduit from San Geronimo, where it
+enters the valve-house, is 558.50 m. above datum. The valve-house, which
+is built in the center of the reservoir, is shown on Fig. 2, Plate XVIII.
+One of its special features is the provision of the main overflow at this
+point instead of within the reservoir proper. The inlet, main supply
+tunnel, independent by-pass overflow, scour-out pipes, gate-valves, and
+screens, are all controlled within the valve-house.
+
+[Illustration: PLATE XVIII, FIG. 2.--VIEW OF ROOF OF OBISPADO RESERVOIR,
+LOOKING NORTH.]
+
+_Reservoir._--The reservoir is rectangular, 126 by 81 m. (413.28 by
+265.68 ft.) at the top, and has a water depth of 4 m. (13.1 ft.). In the
+design it was necessary to limit it to the lowest economical depth, so
+as to increase the static pressure over the low-pressure district as
+much as possible.
+
+_Excavation and Embankment._--The excavation, except for a depth of
+about 1 m. which was in black soil, was chiefly in a disintegrated
+"sillar" stratum of a heavy clayey nature, the greater part of which
+could be handled conveniently with plows and scrapers; the actual
+foundation on the eastern half required blasting for the final depths.
+
+The total excavation amounted to 56,479 cu. m., of which 7,255 cu. m.
+were placed in the embankment, the remainder being deposited in the
+immediate neighborhood of the reservoir. The final trimming of the
+banks, which were left 30 cm. full, was not undertaken until the lining
+was begun. The work was done under contract with Mr. J. S. Nickerson, of
+Monterrey. The excavation had only one classification, and the contract
+prices were 0.50 peso per cu. m. for material carried to spoil banks,
+and 1.00 peso for material placed in the embankment. The excavation was
+begun in December, 1907, and completed in April, 1908. The work was then
+left standing until the end of 1908 to allow the banks to consolidate
+thoroughly prior to lining, which was begun on January 4th, 1909.
+
+_Concrete Lining and Roof._--Plate XIII shows the general plan and
+sections, the main feature being the simple division of the reservoir
+into 24 rows of columns longitudinally and 15 rows transversely, making
+a total of 360 columns, less the four left out at the central tower. All
+the columns are 5 m. apart both ways. The roof was designed for a live
+load of 100 lb. and a dead load of 150 lb., the same as at the South
+Reservoir. With the exception of the floor, all the concrete work was
+reinforced with twisted steel lug bars. The foundation load on the
+columns for the eastern half of the reservoir is 0.9 ton per sq. ft.;
+that on the columns for the western half, where the foundation is of
+very hard sillar and conglomerate, is 1.95 tons per sq. ft.
+
+_Under-drainage of the Floor._--To provide for proper drainage in case
+of seepage, the floor was underdrained with rubble drains, 30 cm. wide
+and 23 cm. deep, filled with large round gravel carted from the bed of
+the Santa Catarina River. The total length of these underdrains is 1,160
+m. In order to facilitate the detection of any seepage, they were
+conducted to a permanent inspection pit outside of the reservoir.
+
+_Main Distributing Conduit._--The main distributing conduit is laid
+along the inside of the reservoir, at the inlet end, and carried on
+elliptical arches of 2 m. span to a height of 71 cm. above the finished
+floor level. This conduit is 76 cm. high and 45.7 cm. wide, and it
+branches in two directions from the inlet tunnel to each side of the
+reservoir, its total length being 69 m. In order to prevent any
+stagnation and to give a continuous circulation, the water is delivered
+at eight points, in the length of the distributing pipe, through square
+openings with semicircular tops, the areas of the openings increasing
+toward the ends. These inlets are placed so that the current will not
+strike the roof columns.
+
+_Outlet Tunnel and Valve-House._--The outlet tunnel is at the north end
+of the reservoir, and was excavated in hard sillar rock. The tunnel is
+lined with concrete 30 cm. thick, the finished internal dimensions being
+1.52 by 0.91 m. The length of the tunnel is 22.5 m. to the point where
+it enters the outlet-house. This house is divided by a wall 45 cm.
+thick, which supports a 76-cm. (30-in.) penstock-valve. The supply pipe
+to the city leaves this chamber in the west wall, and is also fitted
+with a 76-cm. penstock-valve. The supply pipe has a copper screen of the
+same design and dimensions as those in the inlet-house. A 30-cm.
+(12-in.) scour-out pipe in this chamber provides for draining the
+contents of the reservoir to a neighboring irrigation ditch, when
+necessary.
+
+The superstructure of the valve-house is of concrete, and at the floor
+level there are bevel-geared head-stocks to raise the valves, etc.
+
+_By-Pass and Supply Pipes._--The by-pass and supply pipes are carried
+below the reservoir embankment to join the main 76-cm. (30-in.)
+cast-iron distributing pipe to the city. For this short distance they
+were constructed of concrete, 76 cm. in internal diameter, 10 cm. (4
+in.) thick, reinforced with 6-1/2-mm. square steel longitudinal rods, 30
+cm. from center to center in the circumference, and hooped with
+6-1/2-mm. square steel rods spaced 30 cm. apart. The concrete forming
+these pipes was a 1:1-1/2:2-1/2 mixture.
+
+_Parapet Walls._--The parapet walls have 12 piers at each side and 8 at
+each end. In these piers there are ventilating openings branching at the
+top to each side of the parapet, with outlets provided with cast-iron
+screens. This arrangement gives 4 sq. m. of ventilating space (exclusive
+of that provided in the central tower), equally distributed at 40 points
+around the walls of the reservoir.
+
+_General Construction Scheme._--The concrete mixing plant, which
+consisted of two No. 1 Smith mixers, was arranged in connection with the
+bins and hoppers for the rock and sand on the high ground to the west,
+and from there the material was conveyed on a framed timber gangway
+carried right across the center of the reservoir, as shown by Fig. 1,
+Plate XVII. From this central platform the concrete for the columns was
+filled from stages placed on the top of traveling towers, 5 m. high,
+which were run between two rows of columns on standard-gauge rails laid
+on the floor of the reservoir. By this arrangement 24 columns could be
+filled from each length of track. A main narrow track was also laid
+right around the reservoir, with the necessary turn-outs.
+
+[Illustration: PLATE XVII, FIG. 1.--FILLING PRIMARY BEAMS FROM TRAVELING
+TOWER, OBISPADO RESERVOIR.]
+
+[Illustration: PLATE XV, FIG. 1.--CONSTRUCTION OF WEST SIDE-WALL OF
+OBISPADO RESERVOIR.]
+
+[Illustration: PLATE XV, FIG. 2.--PRIMARY BEAMS AND COLUMNS, OBISPADO
+RESERVOIR.]
+
+[Illustration: PLATE XIV.--DETAILS OF FORMS FOR CONCRETE WORK, OBISPADO
+RESERVOIR.]
+
+The forms for the columns, primary and secondary beams, are shown on
+Plate XIV. The side forms for the primary beams were struck in 24 hours,
+so as to economize lumber; but the bottom lumber was left in position
+for 28 days. To avoid much unnecessary timber, the secondary beam forms
+were supported at the ends on reinforced concrete corbels cast on the
+primary beams.
+
+For placing the side-walls, a special traveling form was used, the
+details of which are shown clearly on Plate XIV. At the end of each form
+an expansion joint of 25 cm. was left to be filled after the roof was
+placed in position. The concrete was delivered to the wall through
+stove-pipe chutes, and carefully spaded by workmen in the limited space
+between the forms and the embankment. The wall form was removed after 36
+hours, by loosening the jacks and pulling forward the hooked tie-rods.
+This form is also shown on Fig. 2, Plate XVI.
+
+[Illustration: PLATE XVI, FIG. 2.--TRAVELING SIDE-WALL FORM, OBISPADO
+RESERVOIR.]
+
+[Illustration: PLATE XVI, FIG. 1.--PREPARING FLOOR FOR CONCRETING,
+OBISPADO RESERVOIR.]
+
+The concreting of the roof slab was carried on continuously, and, when
+partly completed, the floor was laid in the shade. The bottom layer of
+the floor, 13 cm. thick, was laid in continuous panels between the
+columns, and brought to a fairly smooth surface. On this surface, after
+keeping it wet for 10 days and then allowing it to dry thoroughly, a
+layer of asphaltum, supplied by the American Asphaltum and Rubber
+Company, of Chicago, was placed. The work was done by ordinary Mexican
+laborers after they had received a few days' instruction from one of the
+Asphaltum Company's superintendents. The surface of the lower layer was
+kept perfectly clean, and then received one coat of "Pioneer" paint. The
+asphaltum, heated in a boiler inside the reservoir to a temperature of
+approximately 425 deg. Fahr., was then poured over the floor from buckets,
+in a layer approximately 4 mm. thick. Where the floor joined the column
+pedestals, and at each new panel section, a double thickness was used.
+The labor cost of water-proofing, including superintendence, etc.,
+amounted to 3.3 cents (Mexican) per sq. m. for painting with "Pioneer"
+paint, and 5.4 cents for the asphaltum coating, or a total labor cost of
+8.7 cents per sq. m. for the complete water-proofing. This cost is based
+on a rate of 8.00 pesos per day for a foreman, and 1.00 peso for each
+laborer. It required 50 U. S. gal. of the paint to cover 265.2 sq. m.,
+and an average of about 6 lb. of asphaltum for 1 sq. m.
+
+The upper concrete layer of the floor, 10 cm. thick, was placed so as to
+break joint with the lower, and was brought to a smooth surface with
+wooden floats sheathed with steel and reaching across the panels. In
+this way a perfectly smooth surface was obtained without any plastering.
+
+[Illustration: PLATE XVII, FIG. 2.--CENTRAL TOWER AND STAIRWAY, OBISPADO
+RESERVOIR.]
+
+The concrete for the beams, columns, side-walls, and floor, was a
+1:2-1/2:4 mixture, crushed sand and stone being used throughout. In the
+roof slab the mixture was 1:2:3.
+
+The whole of the concrete work of the reservoir was completed in 6
+months, by the Company's own administration, and the reservoir was first
+put into service a few days after the great flood of August 27th, when
+the Estanzuela supply main, crossing the Santa Catarina River, was
+partly destroyed. Since that time frequent examinations of the
+inspection pit, which is connected by a pipe to the rubble drains under
+the floor, have never revealed the slightest leakage.
+
+_Lay-Out of the Reservoir Roof and Grounds._--The Company owns about
+11-1/2 hectares of land, which includes that occupied by the reservoir
+and its surroundings, and as this property is in an attractive
+situation, commanding fine views of the Sierra Madre Mountains, the
+whole of the works have been given a pleasing architectural character,
+and the grounds laid out to form a public park for the citizens of
+Monterrey.
+
+[Illustration: FIG. 14.--SKETCH PLAN OF LAY OUT AT OBISPADO RESERVOIR.]
+
+The general plan of the scheme is shown by Fig. 14 and Fig. 2, Plate
+XVIII. The roof, which has an area of 1 hectare, has been laid out with
+walks and grass plots, and the surrounding embankments have been
+converted into driveways. Above the reservoir a small plazuela of 1/2
+hectare has been laid out with a space above it for a band-stand. The
+whole of the ground has been encircled with carriage drives, on which it
+is the intention to plant shade trees. The lay-out of this land also
+embraced the scheme for protecting the reservoir by draining the
+surface-water away to the irrigation ditches.
+
+
+
+
+               COMPARISON OF SOUTH AND OBISPADO RESERVOIRS.
+
+
+The two reservoirs are practically of the same capacity, the only
+difference being the level of the overflows in their relationship to the
+roof, which gives the Obispado Reservoir a slightly greater capacity.
+Some comparative figures may be of interest, owing to the differences in
+type and construction. Table 7 gives the comparative quantities of
+material in each reservoir proper, that is to say, exclusive of the
+valve-houses, lay-out of grounds, etc.
+
+  TABLE 7.--COMPARISON OF MATERIALS IN SOUTH AND OBISPADO RESERVOIRS.
+
+  ==========================+===============================+============
+                            |    SOUTH RESERVOIR.  | _OBISPADO RESERVOIR._
+                            +--------+-------------+--------+------------
+                            |        | Quantities, |        | Quantities,
+                            |   No.  | in cubic    |   No.  | in cubic
+                            |        | meters.     |        | meters.
+  --------------------------+--------+-------------+--------+------------
+  _Earthwork:_              |        |             |        |
+      Total excavation      |  ...   |   34,000    |   ...  |   56,479
+      Placed in embankment  |  ...   |   31,500    |   ...  |    7,255
+      Placed in spoil banks |  ...   |    2,500    |   ...  |   49,224
+                            +--------+-------------+--------+------------
+  _Concrete:_               |        |             |        |
+      Columns (including    |        |             |        |
+               foundations) |  135   |    1,240    |   356  |      543
+      Primary beams         |  135   |      440    |   374  |      462
+      Secondary beams       |  670   |      515    | 1,252  |      576
+      Side-walls            |  ...   |    1,255    |   ...  |      710
+                            |        |             |        |
+                            | Square |             | Square |
+                            | meters.|             | meters.|
+      Roof slab             | 5,140  |      520    | 10,206 |    1,020
+      Floor                 | 4,070  |      780    |  9,200 |    2,120
+      Parapet walls         |  ...   |       90    |   ...  |      165
+                            +--------+-------------+--------+------------
+           Total concrete   |  ...   |    4,840    |   ...  |    5,596
+                            +--------+-------------+--------+------------
+                            |        |  Pounds.    |        |  Pounds.
+  Reinforcing steel bars    |  ...   |  387,000    |   ...  |  380,000
+                            |        |             |        |
+                            |        |  Square     |        |  Square
+                            |        |  meters.    |        |  meters.
+  Expanded metal in roofs,  |        |             |        |
+                slabs, etc. |  ...   |    5,691    |   ...  |   10,490
+  ==========================+========+=============+========+============
+
+The total cost of these reservoirs, including valve-houses, by-passes,
+and the length of supply pipe where the by-pass joins, and including all
+engineering expenses, etc., but exclusive of the cost of lands,
+planting, fencing, and special work in connection with the formation of
+parks, was as follows:
+
+South Reservoir: 394,000 pesos, or 10,368 pesos per million liters.
+
+Obispado Reservoir: 375,000 pesos, or 9,375 pesos[7] per million liters.
+
+[7] Mexican currency.
+
+These rates may be regarded as reasonable when taking into consideration
+the special difficulties of construction in Mexico, and the high cost of
+all imported material, on which heavy duties are levied.
+
+The value of the materials alone in these reservoirs amounted to more
+than 70% of their total cost.
+
+
+
+
+              ANALYSES OF ESTANZUELA AND SAN GERONIMO WATERS.
+
+
+Table 8 shows analyses of the Estanzuela and San Geronimo waters, made
+in February, 1910, by Messrs. Ledoux, of New York City. The Estanzuela
+sample was taken at the valve-house of the South Reservoir, while that
+of San Geronimo was taken in Shaft No. 1 of the infiltration gallery
+when flowing at the rate of about 450 liters per sec. Both waters are
+absolutely free from turbidity.
+
+         TABLE 8.--ANALYSES OF ESTANZUELA AND SAN GERONIMO WATERS.
+                          In Parts per Million.
+
+  ==================================+================+===============
+                                    |                | San Geronimo
+                                    | Estanzuela.    | Infiltration
+                                    |                | Gallery.
+  ----------------------------------+----------------+---------------
+  Total solid matter in solution    |     209.00     |    305.00
+  Organic and volatile matter       | Not weighable. | Not weighable.
+                                    |                |
+  ANALYSIS OF SOLIDS:               |                |
+      Silica                        |      10.5      |     12.0
+      Iron and Alumina              |    Traces.     |   Traces.
+      Lime                          |      85.4      |    112.6
+      Magnesia                      |       3.8      |     22.6
+      Soda (Na_{2}O)                |      13.3      |     20.2
+      Potash (K_{2}O)               |       2.0      |      1.9
+      Sulphuric Acid                |      24.4      |     11.5
+      Chlorine                      |       2.0      |      2.8
+                                    +----------------+---------------
+  PROBABLE COMBINATION OF BASES &   |                |
+    ACID RADICALS IN THE SOLIDS:    |                |
+      Silica                        |      10.5      |     12.0
+      Iron and Alumina              |    Traces.     |   Traces.
+      Sodium Chloride               |       3.3      |      4.6
+      Potassium Sulphate            |       3.7      |      3.5
+      Sodium Sulphate               |      26.3      |     40.8
+      Calcium Sulphate              |      13.3      |     22.1
+      Calcium Carbonate             |     142.7      |    184.8
+      Magnesium Carbonate           |       8.4      |     49.8
+                                    +----------------+---------------
+                                    |     208.2      |    317.6
+                                    |                |
+  Nitrogen as Free Ammonia          |       0.004    |      0.032
+  Nitrogen as Albuminoid Ammonia    |       0.006    |      0.022
+  Nitrogen as Nitrites (N_{2}O_{3}) |       0.002    |      0.002
+  Nitrogen as Nitrates (N_{2}O_{3}) |       0.100    |      1.85
+  Total Hardness (as CaCO_{3})      |     155.0      |    220.0
+  Alkalinity (as CaCO_{3})          |     121.0      |    180.0
+  ==================================+================+===============
+
+
+
+
+                     CITY WATER DISTRIBUTION SYSTEM.
+
+
+[Illustration: PLATE XIX.--DIAGRAM OF THE MAIN WATER PIPES OF MONTERREY.]
+
+The distribution system was begun in September, 1906, but the general
+lay-out of the mains was modified in July, 1907, in view of the division
+of the system into two services, for high and low pressure. Plate XIX
+shows in skeleton form the lines of the cast-iron mains. These are laid
+at the present time along routes containing houses (excluding wooden
+shacks) which can be served immediately. The distribution system is
+arranged to serve as follows:
+
+               Estanzuela supply              4,150 houses.
+               San Geronimo supply            8,600   "
+                                             --------------
+                   Total                     12,750 houses.
+
+This represents, at the present time, a division of the city of 32-1/2%
+for the Estanzuela, and 67-1/2% for the San Geronimo supply. Of the area
+of the supply district north of Santa Catarina River, 57% will be
+supplied from San Geronimo and 43% from Estanzuela. The real development
+of the city, however, is northward in the area of the low-pressure
+supply.
+
+The static pressure over the city in the two sections varies as follows:
+
+                Estanzuela supply             85 to 50 lb.
+                San Geronimo supply           55 to 29 lb.
+
+The main supply pipe from the South Reservoir is 61 cm. (24 in.) in
+internal diameter, and this size allows ample provision for future
+extensions. The supply pipe from the Obispado Reservoir is 76 cm. (30
+in.) in internal diameter. On this main, in Calle de Cinco de Mayo, at a
+distance of 320 m. from the reservoir, has been placed a 76-cm. (30-in.)
+Venturi meter, the recording apparatus being in the house on the side of
+the road. Both these supply pipes are carried well into the city, and
+from them the distribution mains are laid; these are 45.7 and 30 cm. (18
+and 12 in.) in internal diameter, with intermediate sections of 15 and
+10 cm. (6 in. and 4 in.). Along Calle de Cinco de Mayo, where the
+division between the two services takes place, two lines are laid, a
+30-cm. for high pressure and a 38-cm. (15-in.) for the low pressure. A
+duplicate pipe, 30 cm. (12 in.) in diameter, is also laid in Calle de
+Dr. Coss. On Calle de Alvarez the low-pressure pipe is 61 cm. (24 in.),
+and the high-pressure, 45.7 cm. (18 in.) in diameter. Provision is also
+made for extending the range of the two services to other districts.
+Practically every block is provided with gate-valves to cut off the
+supply in any direction. On the 76-cm. main, 61-cm. (24-in.) valves are
+used, and are connected by tapers to the pipe. On the 61-cm. mains,
+45.7-cm. (18-in.) valves are used. The actual frictional loss by
+reducing the valve being small, this method permitted the use of valves
+of a more convenient size. On all the larger valves there are 15-cm.
+by-passes fitted with independent gate-valves.
+
+[Illustration: FIG. 15.--CONNECTION BETWEEN HIGH-AND LOW-PRESSURE AREAS
+AND THE INTERSECTION OF CINCO DE MAYO AND ALVAREZ STREETS.]
+
+Scour-out pipes, 10 cm. (4 in.) and 15 cm. (6 in.) in diameter, are
+placed in various parts of the system, draining to the sewers.
+Air-valves, both double and single, are also placed at high points in
+different parts of the system.
+
+_Reducing Valves._--At four points in the system the mains are arranged
+so that the supply can be interchangeable. Fig. 15 shows the arrangement
+of the mains at the junction of Cinco de Mayo and Alvarez Streets, and
+is typical of the arrangement at the other points.
+
+Each reducing valve is placed on a 30-cm. (12-in.) branch main between
+the two services. These valves adjust themselves automatically to the
+pressure required, after they have been properly regulated to the
+different pressures on either side. To allow repairs to be easily made,
+there are ordinary gate-valves at each end enclosed in the same pit. If
+necessary, as in case of fire, any part of the system can be changed
+into high pressure temporarily by closing the valves against the San
+Geronimo supply.
+
+Table 9 gives the length of the mains as laid, and the number of valves.
+
+                    TABLE 9.--LENGTH OF WATER MAINS.
+
+      =========================+=====================+=============
+            DIAMETER:          |                     |
+      --------------+----------+ Length, in meters.  | Number of
+       Centimeters. |  Inches. |                     | gate-valves.
+      --------------+----------+---------------------+-------------
+           10.2     |     4    |     49,831.68       |    677
+           15.2     |     6    |     31,918.31       |    306
+           30.5     |    12    |     14,461.31       |    117
+           38.1     |    15    |      1,661.98       |     11
+           45.7     |    18    |      4,522.61       |      5
+           61.0     |    24    |      2,826.54       |     10
+           76.2     |    30    |      1,454.40       |
+      --------------+----------+---------------------+-------------
+                 Totals        |    106,676.83       |  1,126
+      =========================+=====================+=============
+
+The pipes were all cast according to the British Standard Specification,
+in 3.65-m. (12-ft.) lengths, and were supplied by Messrs. D. Y. Stewart
+and Company, and Messrs. Dick, Kerr and Company, of Kilmarnock and
+London. The valves were all of standard design, faced with gun-metal,
+and were supplied by Messrs. Glenfield and Kennedy, Limited, of
+Kilmarnock, Scotland.
+
+In the distribution system it is proposed to provide 200 fire-hydrants,
+by arrangement with the municipality, but only a few of these have been
+placed. The general type is a double hydrant for two 63.5-mm.
+(2-1/2-in.) streams. These are to be placed at the corner of every block
+in the business portion of the city; single-way hydrants will be used in
+the residential districts.
+
+_Laying Cast-iron Pipes._--Table 10 has been prepared to show what can
+be accomplished with Mexican labor in laying pipes. In this kind of work
+the labor was particularly efficient; after the gangs were once drilled
+into shape, the work proceeded systematically, and at very good speed.
+All the pipes, after being laid, were tested to 150 lb. per sq. in. in
+the presence of the Technical Inspector.
+
+Table 11 gives the details of the excavation, the material, and the
+average cost, of laying about 106.6 km. of pipes.
+
+_House Connections._--The ordinary house connections, which are of
+19-mm. (3/4-in.) galvanized-steel pipe, are connected to the mains by
+lead goosenecks and brass corporation cocks. The Company's obligation
+under the concession extended to the edge of the sidewalk, and at this
+point curb-boxes, chiefly of the Hays pattern, were placed; but,
+subsequently, owing to the metering of every house service in the city,
+the control of the Company extended to the meter, which, as a rule, is
+placed immediately inside of the house. Owing to the rapid deterioration
+of the house service pipes in some districts of the northern part of the
+city, where the soil is formed of decaying organic matter, it has been
+decided to use lead pipe entirely from the main to the meter.
+
+_Damage Due to Floods._--During the night of August 27th, the main
+61-cm. pipe, under the river bed of Santa Catarina, at the point where
+the main entered the city, was destroyed for a distance of 130 m., due
+to the scouring away of a whole block of city property. The Venturi
+meter register chart at the South Reservoir showed that the break
+occurred a few minutes before midnight. The location of this pipe is
+shown by Fig. 5; its broken end was in proximity to an old bridge pier.
+Fortunately, at the time of the flood, the Obispado Reservoir works were
+completed, and the whole city was supplied with water from San Geronimo
+within 48 hours. As only about 1,500 services had then been connected,
+this delay was not serious; in fact, in the lower part of the city, the
+water in the mains was sufficient until the San Geronimo supply could be
+connected. To make a temporary connection to conduct the high-pressure
+water to the city, a 15-cm. steel pipe was placed above ground, on the
+line of the main, for a distance of 100 m. This pipe was supported by a
+cable, 30 mm. in diameter, and by timber trestles. By limiting the
+supply district, this pipe was of sufficient capacity to serve until the
+large main could be safely restored.
+
+   TABLE 10.--COST OF LAYING AND JOINTING CAST-IRON PIPES, EXCLUDING
+   LOWERING AND TESTING.
+
+  +--------------+----------+----------------------------------------+
+  |              |          | 76 CM. (30 IN.)                        |
+  |              |          +-------+------------+--------+----------+
+  | Employees.   | Rate for | Total | Total cost | No. of | Cost per |
+  |              | 10-hour  | No.   | of labor.  | pipes  | linear   |
+  |              | day.     | men.  | Pesos.     | laid.  | meter.   |
+  |              | Pesos.   |       |            |        | Pesos.   |
+  +--------------+----------+-------+------------+--------+----------+
+  | Foreman      | 4.50     |  1    |  4.50      | ...    |   ...    |
+  | Caulkers     | 3.00     |  4    | 12.00      | ...    |   ...    |
+  | Lead pourers | 2.00     |  2    |  4.00      | ...    |   ...    |
+  | Lead melter  | 1.50     |  1    |  1.50      |  20    | 0.498    |
+  | Pipe cutter  | 2.00     |  1    |  2.00      | ...    |   ...    |
+  | Peons        | 1.00     | 12    | 12.00      | ...    |   ...    |
+  | Water boy    | 0.50     |  1    |  0.50      | ...    |   ...    |
+  |              |          |       |            |        |          |
+  |              | ...      | 22    | 36.50      | ...    |   ...    |
+  +--------------+----------+-------+------------+--------+----------+
+  |              |          | 61 CM. (24 IN.)                        |
+  |              |          +-------+------------+--------+----------+
+  | Employees.   | Rate for | Total | Total cost | No. of | Cost per |
+  |              | 10-hour  | No.   | of labor.  | pipes  | linear   |
+  |              | day.     | men.  | Pesos.     | laid.  | meter.   |
+  |              | Pesos.   |       |            |        | Pesos.   |
+  +--------------+----------+-------+------------+--------+----------+
+  | Foreman      | 4.50     |  1    |   4.50     | ...    |   ...    |
+  | Caulkers     | 3.00     |  5    |  15.00     | ...    |   ...    |
+  | Lead pourers | 2.00     |  2    |   4.00     | ...    |   ...    |
+  | Lead melter  | 1.50     |  1    |   1.50     |  25    | 0.410    |
+  | Pipe cutter  | 2.00     |  1    |   2.00     | ...    |   ...    |
+  | Peons        | 1.00     | 10    |  10.00     | ...    |   ...    |
+  | Water boy    | 0.50     |  1    |   0.50     | ...    |   ...    |
+  |              |          |       |            |        |          |
+  |              | ...      | 21    |  37.50     | ...    |   ...    |
+  +--------------+----------+-------+------------+--------+----------+
+  |              |          | 50 CM. (20 IN.)                        |
+  |              |          +-------+------------+--------+----------+
+  |              | Rate for | Total | Total cost | No. of | Cost per |
+  | Employees.   | 10-hour  | No.   | of labor.  | pipes  | linear   |
+  |              | day.     | men.  | Pesos.     | laid.  | meter.   |
+  |              | Pesos.   |       |            |        | Pesos.   |
+  +--------------+----------+-------+------------+--------+----------+
+  | Foreman      | 4.50     |  1    |  4.50      | ...    |   ...    |
+  | Caulkers     | 3.00     |  4    | 12.00      | ...    |   ...    |
+  | Lead pourers | 2.00     |  2    |  4.00      | ...    |   ...    |
+  | Lead melter  | 1.50     |  1    |  1.50      |  35    | 0.287    |
+  | Pipe cutter  | 2.00     |  1    |  2.00      | ...    |   ...    |
+  | Peons        | 1.00     | 12    | 12.00      | ...    |   ...    |
+  | Water boy    | 0.50     |  1    |  0.50      | ...    |   ...    |
+  |              |          |       |            |        |          |
+  |              |          | 22    | 36.50      | ...    |   ...    |
+  +--------------+----------+-------+------------+--------+----------+
+  |              |          | 45.7 CM. (18 IN.)                      |
+  |              |          +-------+------------+--------+----------+
+  |              | Rate for | Total | Total cost | No. of | Cost per |
+  | Employees.   | 10-hour  | No.   | of labor.  | pipes  | linear   |
+  |              | day.     | men.  | Pesos.     | laid.  | meter.   |
+  |              | Pesos.   |       |            |        | Pesos.   |
+  +--------------+----------+-------+------------+--------+----------+
+  | Foreman      | 4.50     |  1    |   4.50     | ...    |   ...    |
+  | Caulkers     | 3.00     |  4    |  12.00     | ...    |   ...    |
+  | Lead pourers | 2.00     |  2    |   4.00     | ...    |   ...    |
+  | Lead melter  | 1.50     |  1    |   1.50     |  40    | 0.221    |
+  | Pipe cutter  | 2.00     |  1    |   2.00     | ...    |   ...    |
+  | Peons        | 1.00     |  8    |   8.00     | ...    |   ...    |
+  | Water boy    | 0.50     |  1    |   0.50     | ...    |   ...    |
+  |              |          |       |            |        |          |
+  |              |          | 18    |  32.50     | ...    |   ...    |
+  +--------------+----------+-------+------------+--------+----------+
+  |              |          | 38 CM. (15 IN.)                        |
+  |              |          +-------+------------+--------+----------+
+  |              | Rate for | Total | Total cost | No. of | Cost per |
+  | Employees.   | 10-hour  | No.   | of labor.  | pipes  | linear   |
+  |              | day.     | men.  | Pesos.     | laid.  | meter.   |
+  |              | Pesos.   |       |            |        | Pesos.   |
+  +--------------+----------+-------+------------+--------+----------+
+  | Foreman      | 4.50     |  1    |  4.50      | ...    |   ...    |
+  | Caulkers     | 3.00     |  4    | 12.00      | ...    |   ...    |
+  | Lead pourers | 2.00     |  2    |  4.00      | ...    |   ...    |
+  | Lead melter  | 1.50     |  1    |  1.50      |  45    | 0.196    |
+  | Pipe cutter  | 2.00     |  1    |  2.00      | ...    |   ...    |
+  | Peons        | 1.00     |  8    |  8.00      | ...    |   ...    |
+  | Water boy    | 0.50     |  1    |  0.50      | ...    |   ...    |
+  |              |          |       |            |        |          |
+  |              |          | 18    | 32.50      | ...    |   ...    |
+  +--------------+----------+-------+------------+-------------------+
+  |              |          | 30.5 CM. (12 IN.)                      |
+  |              |          +-------+------------+--------+----------+
+  |              | Rate for | Total | Total cost | No. of | Cost per |
+  | Employees.   | 10-hour  | No.   | of labor.  | pipes  | linear   |
+  |              | day.     | men.  | Pesos.     | laid.  | meter.   |
+  |              | Pesos.   |       |            |        | Pesos.   |
+  +--------------+----------+-------+------------+--------+----------+
+  | Foreman      | 4.50     |  1    |   4.50     | ...    |   ...    |
+  | Caulkers     | 3.00     |  4    |  12.00     | ...    |   ...    |
+  | Lead pourers | 2.00     |  2    |   4.00     | ...    |   ...    |
+  | Lead melter  | 1.50     |  1    |   1.50     |  60    | 0.147    |
+  | Pipe cutter  | 2.00     |  1    |   2.00     | ...    |   ...    |
+  | Peons        | 1.00     |  8    |   8.00     | ...    |   ...    |
+  | Water boy    | 0.50     |  1    |   0.50     | ...    |   ...    |
+  |              |          |       |            |        |          |
+  |              |          | 18    |  32.50     | ...    |   ...    |
+  +--------------+----------+-------+------------+--------+----------+
+  |              |          | 15 CM. (6 IN.)                         |
+  |              |          +-------+------------+--------+----------+
+  | Employees.   | Rate for | Total | Total cost | No. of | Cost per |
+  |              | 10-hour  | No.   | of labor.  | pipes  | linear   |
+  |              | day.     | men.  | Pesos.     | laid.  | meter.   |
+  |              | Pesos.   |       |            |        | Pesos.   |
+  +--------------+----------+-------+------------+--------+----------+
+  | Foreman      | 4.50     |  1    |  4.50      | ...    |   ...    |
+  | Caulkers     | 3.00     |  4    | 12.00      | ...    |   ...    |
+  | Lead pourers | 2.00     |  2    |  4.00      | ...    |   ...    |
+  | Lead melter  | 1.50     |  1    |  1.50      | 100    | 0.082    |
+  | Pipe cutter  | 2.00     |  1    |  2.00      | ...    |   ...    |
+  | Peons        | 1.00     |  6    |  6.00      | ...    |   ...    |
+  | Water boy    | 0.50     |  1    |  0.50      | ...    |   ...    |
+  |              |          |       |            |        |          |
+  |              |          | 16    | 30.50      | ...    |   ...    |
+  +--------------+----------+-------+------------+--------+----------+
+  |              |          | 10 CM.  (4 IN.)                        |
+  |              |          +-------+------------+--------+----------+
+  | Employees.   | Rate for | Total | Total cost | No. of | Cost per |
+  |              | 10-hour  | No.   | of labor.  | pipes  | linear   |
+  |              | day.     | men.  | Pesos.     | laid.  | meter.   |
+  |              | Pesos.   |       |            |        | Pesos.   |
+  +--------------+----------+-------+------------+--------+----------+
+  | Foreman      | 4.50     |  1    |   4.50     | ...    |   ...    |
+  | Caulkers     | 3.00     |  4    |  12.00     | ...    |   ...    |
+  | Lead pourers | 2.00     |  2    |   4.00     | ...    |   ...    |
+  | Lead melter  | 1.50     |  1    |   1.50     | 150    | 0.0574   |
+  | Pipe cutter  | 2.00     |  1    |   2.00     | ...    |   ...    |
+  | Peons        | 1.00     |  6    |   6.00     | ...    |   ...    |
+  | Water boy    | 0.50     |  1    |   0.50     | ...    |   ...    |
+  |              |          |       |            |        |          |
+  |              |          | 16    |  30.50     | ...    |   ...    |
+  +--------------+----------+-------+------------+--------+----------+
+
+                TABLE 11.--CAST-IRON WATER PIPES.--COST
+                 OF MATERIALS AND LAYING AT MONTERREY.
+
+                 MATERIALS PER STANDARD LENGTH OF PIPE .
+
+ Key: cm = centimeter in = inch mm = millimeter kg = kilogram m = linear meter
+ +-----------+------+-------+--------+-------------+--------+--------+-------+
+ |   PIPE    |      |Weight |Cost/   |    LEAD     |  OAKUM |CHARCOAL| Total |
+ | DIAMETER  |Thick-|  of   |piece   +------+------+--------+--------+ Ma-   |
+ +------+----+ ness | Pipe  |fob Mon-|Weight| Cost |  Cost  | Cost   |terial |
+ |      |    |      |       |terrey  |      |      |        |        | Cost  |
+ |  cm  | in |  mm  |  kg   | pesos  |  kg  |pesos | pesos  | pesos  | per m |
+ +------+----+------+-------+--------+------+------+--------+--------+-------+
+ | 10   |  4 | 10.3 |   109 |  11.65 |  2.0 | 0.37 | 0.025  | 0.0525 |  3.30 |
+ | 15   |  6 | 11.1 |   163 |  15.74 |  3.7 | 0.67 | 0.0675 | 0.065  |  4.51 |
+ | 30.5 | 12 | 15.8 |   463 |  76.50 |  7.9 | 1.44 | 0.1225 | 0.1    | 21.35 |
+ | 38   | 15 | 17.4 |   680 |  79.36 | 10.6 | 1.94 | 0.175  | 0.12   | 22.30 |
+ | 45.7 | 18 | 19.0 |   871 |  90.28 | 13.4 | 2.42 | 0.2375 | 0.1375 | 25.42 |
+ | 61   | 24 | 22.2 | 1,261 | 117.60 | 18.8 | 3.42 | 0.335  | 0.175  | 33.20 |
+ | 76   | 30 | 25.4 | 1,946 | 199.05 | 24.5 | 4.42 | 0.44   | 0.2125 | 55.77 |
+ +------+----+------+-------+--------+------+------+--------+--------+-------+
+
+                           LABOR.
+
+  Key: cm = centimeter, in = inch, m = meter
+  +-----------+------+------+------+------+-------+-------+----
+  |           |      |      |      |      |       |Total  |
+  | DIAMETER  |      |      | Cubic| Cost |Back-  |cost,  |
+  | OF PIPE:  | Width|Depth |meters| of   |filling|exca-  |
+  |           |  of  |      | per  |exca- |and re-|vation |
+  +------+----+trench|      |linear|vation|moving |back-  | Continues
+  |      |    |      |      | meter| per  |surplus|filling|
+  |  cm  | in |  m   |  m   |      |lin. m|Pesos  |etc.   |
+  |      |    |      |      |      |      |       |Pesos  |
+  +------+----+------+------+------+------+-------+-------+----
+  | 10   |  4 | 0.55 | 0.90 | 0.50 | 0.60 | 0.18  | 0.78  |
+  | 15   |  6 | 0.60 | 1.00 | 0.60 | 0.72 | 0.22  | 0.94  |
+  | 30.5 | 12 | 0.65 | 1.20 | 0.78 | 0.94 | 0.29  | 1.23  |
+  | 38   | 15 | 0.70 | 1.30 | 0.91 | 1.10 | 0.34  | 1.44  | Below
+  | 45.7 | 18 | 0.80 | 1.40 | 1.12 | 1.34 | 0.41  | 1.75  |
+  | 61   | 24 | 1.00 | 1.50 | 1.50 | 1.80 | 0.55  | 2.35  |
+  | 76   | 30 | 1.10 | 1.60 | 1.76 | 2.11 | 0.65  | 2.76  |
+  +------+----+------+------+------+------+-------+-------+----
+
+  --+----------------+--------+--------+--------+
+    |  HAULING PER   |  Cost  | Total  | Total  |
+    |                |  of    |hauling |excava- |
+    |  LINEAR METER  | laying | and    |tion and|
+    |                |  per   |laying  |laying, |
+    +--------+-------+ linear | per    |labor,  |
+    | Haul-  | Misc. | meter  |linear  |complete|
+    |  ing   | Pesos |        | meter  |        |
+    | Pesos  |       | Pesos  | Pesos  | Pesos  |
+  --+--------+-------+--------+--------+--------+
+    | 0.0275 | 0.005 | 0.06   | 0.0925 | 0.8725 |
+    | 0.45   | 0.005 | 0.825  | 0.1325 | 1.0725 |
+    | 0.18   | 0.0075| 0.1475 | 0.335  | 1.565  |
+    | 0.2725 | 0.01  | 0.19   | 0.4775 | 1.9125 |
+    | 0.2725 | 0.01  | 0.245  | 0.5275 | 2.2775 |
+    | 0.825  | 0.08  | 0.41   | 1.315  | 3.665  |
+    | 0.83   | 0.10  | 0.53   | 1.46   | 4.22   |
+  --+--------+-------+--------+--------+--------+
+
+NOTE.--The above costs of earthwork are based on the following rates and
+percentages over the whole city:
+
+              Earth, per cubic meter      | 0.35 pesos | 50%
+              Soft sillar                 | 0.75   "   | 20%
+              Hard sillar                 | 1.50   "   | 20%
+              Rock (chiefly conglomerate) | 4.00   "   | 10%
+
+                          SUMMARY OF TABLE 11.
+
+   +------------------------+-------------+------------+------------+
+   | DIAMETER               | Total labor | Materials. | Total cost |
+   | OF PIPE :              | cost.       | Pesos.     | per linear |
+   +--------------+---------+ In pesos.   |            | meter, in  |
+   | Centimeters. | Inches. |             |            | pesos.     |
+   +--------------+---------+-------------+------------+------------+
+   | 10           |  4      | 0.8725      |  3.30      |  4.1725    |
+   | 15           |  6      | 1.0725      |  4.51      |  5.5825    |
+   | 30.5         | 12      | 1.565       | 21.35      | 22.915     |
+   | 38           | 15      | 1.9125      | 22.30      | 24.2125    |
+   | 45.7         | 18      | 2.2775      | 25.42      | 27.6975    |
+   | 61           | 24      | 3.665       | 33.20      | 36.865     |
+   | 76           | 30      | 4.22        | 55.77      | 59.99      |
+   +--------------+---------+-------------+------------+------------+
+
+The flood destroyed about 1,200 houses in the neighborhood of the river.
+In a number of blocks the smaller mains were scoured away, but
+considerable salvage was done afterward, and, as it is the intention of
+the authorities not to permit rebuilding along the flood-path of the
+river, these mains do not require reconstruction.
+
+
+
+
+                          MAIN SEWERAGE SYSTEM.
+
+
+The Company's obligations, as far as drainage is concerned, were limited
+to the removal and disposal of sewage, no provision being required for
+storm-water, which is allowed to find its way to the natural
+watercourses. Apart from that fact, however, the best system for a city
+like Monterrey, where rainfall for many months at a time is very scarce,
+is the strictly "separate system." In the design advantage was taken of
+the natural topography of the drainage district, which is almost an
+ideal one for a gravitation system of sewers, the general fall in all
+directions being northeast; it was also in this direction that the best
+available land could be obtained for disposal purposes.
+
+[Illustration: PLATE XX.--DIAGRAM OF THE MAIN SEWERS OF MONTERREY.]
+
+Plate XX shows in skeleton form the general lay-out of the sewers. Two
+drainage districts are arranged, divided by Calle de Washington, which may
+be regarded as practically the center of the city, and each of these
+districts has an independent main collector connecting to the outfall
+sewer at the northeast extremity of the city.
+
+The system has been designed so that extensions may be made and may cover
+any part within the city limits; the main collectors are large enough for
+the whole area when fully built up.
+
+The sewers are designed on a very liberal basis, namely, on the assumption
+that when flowing half full the quantity to be dealt with will be 380
+liters per capita per day, with a maximum rate of flow of 200 per cent. It
+was assumed that each house would be occupied by 7 persons and have a
+frontage of 12-1/2 m. The minimum velocities in the sewers, when running
+full, vary between 0.91 and 1.5 m. per sec., with the exception of a few
+blocks.
+
+The minimum size adopted was 24.3 cm. (8 in.) in internal diameter. The
+sewers of diameters between 24.3 and 50 cm., are 0.91 m. (36 in.) long,
+and are of salt-glazed vitrified clay, imported from San Antonio, Tex.
+
+Table 12 gives the details of the length of the various sewers laid.
+
+                      TABLE 12.--LENGTH OF SEWERS.
+
+   +----------+------------------------------------------+-----------+
+   |DIAMETER: |                                          |           |
+   +-----+----+        Kind.                             | Length,   |
+   |  cm | in.|                                          | in meters.|
+   +-----+----+------------------------------------------+-----------+
+   |24.3 |  8 |    Fire-clay                             | 38,332.85 |
+   |25.4 | 10 |       "                                  | 16,400.69 |
+   |30.5 | 12 |       "                                  |  7,953.15 |
+   |38.1 | 15 |       "                                  |  4,850.56 |
+   |45.7 | 18 |       "                                  |  2,023.40 |
+   |50.8 | 20 |       "                                  |  1,450.53 |
+   |55.9 | 22 | Reinforced concrete tubes, 6.9 cm. thick |  3,134.20 |
+   |61.0 | 25 |     "         "       "    7.6 "     "   |    357.40 |
+   |68.6 | 27 |       Brick and concrete                 |    484.05 |
+   |76.2 | 30 |         "    "     "                     |    662.69 |
+   |     |    |                                          |           |
+   |     |    |                                 Total    | 75,649.15 |
+   +-----+----+------------------------------------------+-----------+
+
+The greater number of the manholes are of brickwork, 23 cm. thick, and
+have concrete inverts. They have a diameter of 1.2 m., which is reduced to
+0.61 m. at the top, and each is provided with a heavy cast-iron frame and
+closed cover weighing about 190 kg. There are 521 manholes, and they are
+placed at every block and on long lines about 80 m. apart.
+
+[Illustration: FIG. 16.--STANDARD 300-GAL. FLUSH TANKS.]
+
+The sewers are flushed with 15-cm. (6-in.) automatic flushing siphons of
+the Miller pattern with 20-cm. (8-in.) discharge pipes. There are 278 of
+these siphons, and they are placed in flush-tanks (Fig. 16) built of
+brickwork and plastered with 1:1 cement mortar. Their capacity varies from
+800 to 1,200 liters, and they discharge from 22-1/2 to 28-1/2 liters per
+sec. They are timed to flush once in 24 hours.
+
+The system is at present ventilated by 23-cm. (9-in.) steel ventilating
+columns (Fig. 16), with ornamental cast-iron bases. There are 220 of these
+columns. Most of them are 7.85 m. above the level of the edge of the
+sidewalk, and are connected to special 15-cm. branch pipes leading from
+the sewer on the outside of the flush-tanks. In the center of the city
+they are provided with extension lengths, giving a total height of 12 m.
+
+Table 13 gives the particulars of the average distributed cost of laying
+the 75.6 km. of sewers.
+
+        TABLE 13.--AVERAGE COST, PER LINEAR METER, FOR 75.6 KM.
+            OF SEWERS, FOR MATERIALS AND LABOR COMPLETE.
+
+  +----------+-----------+--------+-----------------------------+--------+
+  |          | INTERNAL  |Cost of |    EARTHWORK AND LABOR:     | Total  |
+  |          | DIAMETER  | mater- |-------+------------+--------| cost of|
+  |          |   OF      | ials   |       | Cost of    |Cost of | sewer  |
+  |          |  SEWERS.  |includ- |Average| excavation,|labor   |complete|
+  |Kind of   +------+----+ ing    | depth | including  |  in    |  per   |
+  |  Sewer.  |      |    |10-cm.  |  of   | back-      |laying  | linear |
+  |          |      |    |(4-in.) | sewer | filling,   |(includ-| meter. |
+  |          |  cm. | in.|branches|       | removing   | ing    |        |
+  |          |      |    |every   |   m.  | surplus,   |hauling,|        |
+  |          |      |    |4-1/2 m.|       | etc.       | etc.). |        |
+  |          |      |    |Pesos.  |       | Pesos.     | Pesos. |        |
+  +----------+------+----+--------+-------+------------+--------+--------+
+  |Fire-clay | 24.3 |  8 |  2.00  |  2.10 |    3.46    | 0.21   | 5.67   |
+  |    "     | 25.4 | 10 |  2.78  |  2.25 |    3.97    | 0.2625 | 7.0125 |
+  |    "     | 30.5 | 12 |  3.64  |  2.50 |    4.705   | 0.305  | 8.65   |
+  |    "     | 38.1 | 15 |  6.14  |  2.75 |    5.50    | 0.4375 |12.0775 |
+  |    "     | 45.7 | 18 |  8.80  |  3.00 |    6.745   | 0.645  |16.19   |
+  |    "     | 50.8 | 20 | 11.30  |  3.50 |    8.275   | 0.815  |20.39   |
+  |Concrete  | 55.9 | 22 |  5.93  |  3.50 |    9.19    | 1.325  |16.445  |
+  |    "     | 61.0 | 25 |  7.30  |  3.75 |   11.245   | 1.685  |20.23   |
+  |One brick}|      |    |        |       |            |        |        |
+  |thick on }| 68.6 | 27 |  7.17  |  3.75 |   11.735   | 3.93   |22.835  |
+  |concrete }| 76.2 | 30 |  7.925 |  4.00 |    14.53   | 4.515  |26.97   |
+  |founda-  }|      |    |        |       |            |        |        |
+  |tions    }|      |    |        |       |            |        |        |
+  +----------+------+----+--------+-------+------------+--------+--------+
+
+[Illustration: FIG. 17.--SKETCH SHOWING DISCONNECTING TRAP ON HOUSE
+DRAIN.]
+
+The house connections are chiefly of 10-cm. (4-in.) pipes, laid on a
+minimum gradient of 2-1/2%, from oblique branches on the sewer to siphon
+intercepting traps near the house, as shown by Fig. 17. From this trap a
+10-cm. fire-clay inspection pipe is carried up and capped at the sidewalk
+level with a cast-iron box having a locked cover. From this inspection
+pipe a branch is connected to a cast-iron fresh-air inlet, in most cases
+set in the wall of the house, the inlet being 30 cm. above the level of
+the pavement.
+
+_Effect of the Flood on Sewers._--The flood of August 27th and 28th, 1909,
+partly destroyed one of the main collectors, which was laid along the
+banks of the river and encased in concrete. This has now been relaid
+farther north, and out of the way of any future floods. The total length
+of the new sewers replacing those damaged amounts to 1200 m., and they
+vary in internal diameter from 20 to 55.9 cm. (8 to 22 in.).
+
+
+
+
+                          MAIN OUTFALL SEWER.
+
+
+The direction of the main outfall sewer was determined after a thorough
+study of all the available land lying to the north and northeast of the
+city, as it was the intention of the Company to utilize for irrigation
+purposes the sewage and any surplus waters that might be developed. The
+best available site was found to be about 12 km. north of the city, a
+little northwest of the village of San Nicolas de los Garzas, as shown on
+Plate II. The long length of outfall required was justified by the cheap
+cost of the land and its excellent character for sewage irrigation. The
+sewer was designed for a capacity of 90,000,000 liters a day (36.76 cu.
+ft. per sec.) in order to allow for conveying surplus waters as well as
+sewage.
+
+[Illustration: PLATE XXII.--OUTFALL SEWER: PLAN OF GROUND SHOWING SEWER;
+ALSO DETAILS OF VARIOUS SECTIONS.]
+
+The outfall intercepts the two main branches of the city sewers at Calle
+de Allende and Calle de Tapia, and its total length is approximately
+11,900 m. The chief type adopted is shown on Plate XXII. It is formed
+with an invert of radial bricks laid in 1:2 cement mortar, on a foundation
+of 1:3:5 concrete approximately 7 cm. thick. As the ground was chiefly in
+hard sillar, only a little concrete was required to mould the bottom to
+the correct shape. The arch was formed of special radial bricks, 15 cm. (6
+in.) deep, laid in cement mortar. These bricks were adopted in preference
+to concrete, owing to the heavy cost of sand and rock, due to the long
+haul, and for the purpose of obtaining rapid work. Plate XXI shows the
+sewer arch, and one of the ventilating columns and manholes. The bricks
+were obtained from the local brick plant, and form a very satisfactory
+material for sewers, being well burnt, thoroughly hard, and absorbing not
+more than 7-1/2% of their weight of water. The contract prices for the
+labor on the brickwork were 1.25 pesos per sq. m., and 1.38 pesos for the
+arch.
+
+[Illustration: PLATE XXI, FIG. 1.--VIEW OF ARCH, OUTFALL SEWER.]
+
+[Illustration: PLATE XXI, FIG. 2.--VENTILATING COLUMN AND MANHOLE, OUTFALL
+SEWER.]
+
+The general route of the sewer is very direct, long straight lines of
+several kilometers being possible, and these were joined by curves of
+approximately 30 m. radius. The gradient of the sewer invert is 0.2% (1 in
+500) which is approximately the general fall of the ground northward from
+Monterrey.
+
+The total quantity of excavation was as follows:
+
+                 No. 1, soft earth          8,960 cu. m.
+                 No. 2, sillar             18,492  "  "
+                 No. 3, conglomerate rock   9,822  "  "
+                                           ------
+                 Total                     37,274 cu. m.
+
+The contract prices for this excavation were: for No. 1, 32 cents; No. 2,
+85 cents; and No. 3, 2.17 pesos per cu. m.
+
+All the excavation was in perfectly dry ground. Where the sewer was partly
+out of the ground it had a foundation of concrete, 1.75 m. wide, from 15
+to 23 cm. thick, below the bottom of the brickwork, and carried up to the
+springing of the arch, and a well-tamped embankment, with slopes of 1-1/2
+to 1, to protect the sewer to a height of 30 cm. (12 in.) above the arch.
+For 342 m. at the Monterrey end of the line, the sewer was constructed in
+tunnel, from, the open end and from two intermediate shafts. The tunnel
+throughout was in sillar, and the contract price for excavation was 24.50
+pesos per lin. m. This work was done without timbering of any kind, except
+at the shaft lengths. Plate XXII shows the lining of the tunnel, which
+was of concrete with a brick invert. At four places the sewer passes under
+main railway tracks, which at these points were carried on steel girders
+supported on concrete abutments, the sewer being carried under the tracks
+in the ordinary way.
+
+_Bridges._--At three points the sewer was carried over arroyos on
+reinforced concrete girders. No. 1, at Station 5,600, consisted of four
+10-m. spans; No. 2, at Station 8,365, over the Estanscia Arroyo, consisted
+of nine 10-m. spans; and No. 3, at Station 8,960, over the Topo Chico
+Arroyo, consisted of three 10-m. spans. One of these bridges is shown on
+Plate XXIII. They were designed as two parallel continuous girders with
+connecting top and bottom slabs. The concrete for the girders was a
+1:2-1/2:3-1/2 mixture, the sand being from the crusher and the rock gauged
+to pass a 19-mm. (3/4-in.) screen. The inside was rendered with a coat of
+1:1 cement mortar, 7 mm. thick, for water-tightness.
+
+[Illustration: PLATE XXIII, FIG. 1.--FORMS FOR MAIN GIRDERS, ESTANSCIA
+BRIDGE, OUTFALL SEWER.]
+
+[Illustration: PLATE XXIII, FIG. 2.--VIEW OF ESTANSCIA BRIDGE, COMPLETED.]
+
+The piers of the Estanscia Bridge (Plate XXIII) were carried down through
+soft earth to a stiff clay from 4-1/2 to 6 m. below the surface, and the
+foundations were spread so that the pressure would not exceed 1 ton per
+sq. ft. The ends of the bridges were protected by rubble wing-walls
+supporting the embankment over the sewer. A 1:3:5 concrete was used for
+the upper part of the piers, and the lower part was of the same mixture
+with 30% of large boulders. There are 70 manholes (Fig. 19) along the line
+of the sewer, and they vary from 150 to 230 m. apart. The sewer is
+ventilated with 30 concrete towers (Fig. 18, and Fig. 2, Plate XXI), 2.9
+m. high, having 20-cm. (8-in.) shafts.
+
+[Illustration: FIG. 18.--DETAILS OF VENTILATORS ON OUTFALL SEWER.]
+
+[Illustration: FIG. 19.--DETAILS OF MANHOLES ON OUTFALL SEWER.]
+
+The works for the outfall sewer were carried out satisfactorily under a
+contract with Mr. John Phillips, of Mexico City, the Company supplying the
+greater part of the materials. The work was begun on March 16th, and
+finished on November 12th, 1908.
+
+
+
+
+                SEWAGE DISPOSAL WORKS AND IRRIGATION LANDS.
+
+
+For the purpose of disposing of the sewage and using it profitably, the
+Company purchased 909 hectares (2,246 acres) of land from the Community of
+San Nicolas de los Garzas, the outfall sewer being carried to the
+southwestern boundary of the land acquired. This area has a general fall
+in all directions to the northeastern boundary, with a gradual fall of
+about 25 m. across the diagonal of the land. The area purchased was
+practically virgin land, only small portions having been cultivated. The
+greater part was covered with a growth of mezquite trees and small shrubs.
+The quality of the land is excellent, if properly irrigated, and capable
+of yielding abundant crops of every description. The limits of this land
+are shown on Plate II.
+
+_Sewage Purification Tanks._--For the purpose of obtaining a satisfactory
+effluent to discharge on the land without causing nuisance, the Company
+built a system of detritus chambers and liquefying tanks at the end of the
+outfall sewer. One difficulty to be faced, in designing these works, was
+the fact that there were no data regarding the probable quantity of
+dry-weather sewage, nor any particulars as to its general character;
+there was also the probability that the outfall sewer would have to carry
+large quantities of surplus water. Therefore, the system was designed so
+as to be capable of extension if necessary, and the sizes of the various
+tanks were limited at present, because of the septic processes which would
+be set up in the long length of outfall sewer. The tanks were designed to
+deal with 10,000,000 liters of sewage proper per day, and the channels,
+etc., were proportioned to take the full flow of the sewer if necessary.
+Provision was also made for discharging large volumes of surplus water
+directly on the land, independent of the tanks. To do this a by-pass was
+taken from the sewer a short distance before reaching the site of the
+tanks. By properly timing the flow, arrangements could be made to
+discharge these waters in the early hours of the morning, by allowing the
+scour-pipes in the distribution system to be opened at night when the
+domestic sewage flow was at its minimum. As the area of land available is
+very great, the degree of purification in the tanks was relatively
+unimportant; the object to be obtained consisted chiefly in distributing
+on the land an effluent which would be innocuous and clear.
+
+The general design of the works is shown on Plate XXIV, and they consist
+essentially of a screen chamber, duplicate detritus tanks, and three
+liquefying tanks. There is also a sludge-pit 629 m. from the tanks.
+
+[Illustration: PLATE XXIV.--SEWAGE DISPOSAL WORKS AT SAN NICOLAS DE LOS
+GARZAS; GENERAL PLAN OF DETRITUS AND LIQUEFYING TANKS, WITH DETAILS OF THE
+LATTER.]
+
+_Screen Chamber and Detritus Tanks._--Enlarged details of the screen
+chamber are shown on Plate XXV. The invert, where the sewer enters the
+screen chamber, is 489.45 m. above datum. This chamber has duplicate
+screens which are fully detailed on Plate XXX. For cleaning purposes the
+screens are raised by a steel-framed head-gear, which is arranged so that
+they may be lowered to a small traveling bogie, out of the way of the
+screen chamber.
+
+[Illustration: PLATE XXV.--SEWAGE DISPOSAL WORKS AT SAN NICOLAS DE LOS
+GARZAS. DETAILS OF DETRITUS CHAMBERS AND INLET CHANNELS.]
+
+[Illustration: PLATE XXVI.--SEWAGE DISPOSAL WORKS AT SAN NICOLAS DE LOS
+GARZAS DETRITUS AND LIQUEFYING TANKS; DETAILS OF DISTRIBUTING CHANNELS.]
+
+[Illustration: PLATE XXX.--SEWAGE DISPOSAL WORKS AT SAN NICOLAS DE LOS
+GARZAS. DETAILS OF SCREENING APPARATUS.]
+
+From the screen chamber there are two main channels, 1.22 m. wide,
+branching to the two concrete detritus chambers. Each channel has a square
+penstock, so that the sewage can be diverted into either chamber when
+necessary.
+
+The detritus chambers are octagonal in plan, 4 m. in diameter, and each is
+provided with an outlet weir 1.50 m. wide. At the weir level the chambers
+have a depth of 1.75 m., with drainage channels below that level. The
+coping is 1 m. above the outlet weir of the detritus tanks. To drain off
+these chambers, each has a scour-out pipe, 30 cm. in diameter, controlled
+from valves with spindles carried above the coping level. Each of these
+pipes is connected to a central chamber, and leads to a 56-cm. (22-in.)
+sludge-pipe. The chambers as designed are of smaller capacity than those
+usually provided, but, as all surface water is strictly excluded from the
+sewerage system, the quantity of detritus reaching the chambers may be
+small. The velocity through them when both are in use will be
+approximately 0.082 m. (0.27 ft.) per sec.
+
+From these chambers the sewage is carried to the three liquefying tanks by
+a main channel, 11.5 m. long and 1.50 m. wide.
+
+[Illustration: PLATE XXVII, FIG. 1.--CAST CONCRETE BEAMS BEING PLACED IN
+POSITION, LIQUEFYING TANKS.]
+
+[Illustration: PLATE XXVII, FIG. 2.--INLET WEIRS TO LIQUEFYING TANKS,
+DURING CONSTRUCTION.]
+
+[Illustration: PLATE XXVIII, FIG. 1.--VIEW OF LIQUEFYING TANKS, FROM INLET
+END.]
+
+The tanks are of concrete and have reinforced concrete roofs. Each is 66
+m. long and 6 m. wide; the minimum depth for the sewage is 1.50 m. at the
+outlet end, and 2.25 m. at the inlet, increasing to a maximum depth of
+2.75 m. at the lowest depth at the scour-out channel. Their combined
+capacity is 2,500,000 liters, which is equivalent to 6 hours' flow of the
+quantity of sewage for which they were designed. The sewage passes from
+the main channel, through penstock-valves which control the flow, into one
+or the other of the tanks. From these valve openings it flows over
+concrete weirs, 5 m. long, and is deflected to the bottom of the tank by a
+reinforced concrete scum-plate, extending across each tank, with a
+clearance of 15 cm. at each end. This scum-plate is 1.5 m. deep and 10 cm.
+thick, and is placed 40 cm. from the end walls.
+
+[Illustration: PLATE XXIX.--SEWAGE DISPOSAL WORKS AT SAN NICOLAS DE LOS
+GARZAS; DETAILS OF OUTLET CHANNELS AND WEIR BOX.]
+
+The details of the concrete division and outside walls are shown on Plate
+XXIX. The floor was constructed in two layers, and its surface is divided
+into 6 channels formed by small walls, 20 cm. wide and 15 cm. deep, the
+object of these channels being to facilitate the cleaning of the floor by
+scouring it out to a specially arranged channel at the deepest point of
+the tank, near the inlet end. Each scour-out channel has a 30-cm. (12-in.)
+gate-valve, controlled from the roof of the tank, the three scour-pipes
+meeting in a concrete chamber outside of the tanks, from which a 56-cm.
+(22-in.) concrete pipe discharges the contents of the tanks to the
+sludge-pit during cleaning operations. The velocity through the tanks,
+when they are used in combination, is 0.0253 m. (0.083 ft.) per sec., the
+tanks being made as long as economically possible, in order to obtain this
+low velocity and thus permit the proper sedimentation of the suspended
+matters. The roof of each tank is 1 m. above the weir level. Each tank has
+four ventilating columns, 3.7 m. high and 30 cm. in diameter, vitrified
+clay pipes, with an exterior casing of contrete, being used for the
+shafts. The roof is enclosed within parapet walls, and is covered with a
+layer of earth 25 cm. thick.
+
+The outlet channel from the tanks leads to a measuring chamber, 3 m.
+square, as shown on Plate XXIX. This chamber is fitted with penstocks,
+1.83 m. wide, and measuring weirs. From this chamber the sewage is
+delivered to two main irrigation ditches, which distribute the sewage in
+two directions, one northward and the other to the western extremity of
+the lands.
+
+_Construction of Tanks._--The excavation for the tanks was in soft earth
+for a depth of 1-1/2 m.; the lower depths were in a firm foundation of
+sillar and calcareous clay. The total excavation in the tanks, channels,
+etc., was 8,335 cu. m., and the actual cost was 45-3/4 cents per cu. m. To
+facilitate the construction, about six-tenths of the concrete beams were
+cast as single monoliths and placed in position by sliding them across the
+tanks on temporary timbers. The remainder of the beams, the roof, and the
+slab were placed in position in the ordinary way with timber forms. The
+total quantity of concrete placed was 1,360 cu. m. A 1:2-1/2:4-1/2
+concrete was used for the walls, channels, etc., and a 1:2:3 mixture for
+the roof slab and beams.
+
+Table 14 gives the average cost per cubic meter for all the concrete work.
+
+    TABLE 14.--AVERAGE COST PER CUBIC METER FOR CONCRETE IN TANKS.
+
+   +-----------------------------------------+-----------+-----------+
+   |                                         | Pesos per | Pesos per |
+   |                                         | cubic     | cubic     |
+   |                                         | meter.    | meter.    |
+   +-----------------------------------------+-----------+-----------+
+   | LABOR :                                 |           |           |
+   |  Mixing and placing                     |  5.20     |           |
+   |  Carpenter work in forms, framing, etc. |  4.20     |           |
+   |                                         |  _____    |           |
+   | Total labor cost                        |           |  9.40     |
+   |                                         |           |           |
+   | MATERIALS :                             |           |           |
+   | Screened gravel                         |  4.04     |           |
+   | Sand (from neighboring arroyo)          |  4.98     |           |
+   | Cement (including hauling)              | 15.19     |           |
+   | Lumber, nails, and other supplies       |  1.90     | 26.11     |
+   +-----------------------------------------+-----------+-----------+
+   | Total cost of concrete per cubic meter                35.51     |
+   +-----------------------------------------------------------------+
+
+_Sludge-pit._--The sludge-pit, used when cleaning out the tanks, is
+carried 639 m. northward, far enough to get the available fall to drain
+the bottom of the detritus chambers and liquefying tanks. The drainage
+pipe was formed of 56-cm. (22-in.) concrete tubes. The sludge-pit is
+merely an excavation in the earth 20 m. square and 2 m. deep, the sides
+having a slope of 1-1/2 to 1. An overflow drains the pit to an irrigation
+ditch, the solid matter being allowed to settle and the liquid to drain
+off. From time to time it is proposed to dig out the solids and plow them
+into the land.
+
+_General._--To the east of the tanks a 3-roomed house has been built for
+the inspector.
+
+In order to provide a good supply of water for cleaning operations, a well
+22 m. deep has been sunk and is fitted with pumps operated by an Eclipse
+windmill, 4 m. in diameter, on a tower 22 m. high, which delivers the pump
+water to a circular wooden tank of 20,000 liters capacity.
+
+The work in connection with the purification tanks was carried out by the
+Company's own staff; it was begun on September 10th, 1908, and practically
+completed by the first week in January, 1909.
+
+At the time of writing, the tanks have to deal with the sewage from a
+population of only 10,000 persons, as only from 15 to 20% of the
+connections have been made. The sewage, therefore, has been diluted with
+several times its volume of surplus water, and the necessary scum on the
+top of the sewage in the tanks has not yet assumed the usual thick matty
+condition observed in most systems. As there are no available means in
+Monterrey of having proper determinations made of the degree of
+purification which takes place in the passage of the sewage through the
+liquefying tanks, a few simple tests have been made. These tests were
+limited to the determination of the amount of oxygen absorbed in 4 hours,
+and show a purification of 50% in passing from the detritus chambers to
+the outlet. The sewage, although very black and full of suspended matter
+as it enters the tanks, leaves them in a very clarified condition.
+
+Of the total area of land acquired by the Company, 904 hectares (2,234
+acres) have been leased to the Monterrey Railway, Light, and Power
+Company, for 99 years, the Water-Works Company reserving 5 hectares (12
+acres) absolutely for future extensions of the sewage works. By giving 12
+months' notice, the Company also reserves the right to utilize any part of
+145 hectares (358 acres) near the tanks, should it be required at any time
+in the future for sewage purification purposes.
+
+
+
+
+                    QUALITY OF AND RATES FOR LABOR.
+
+
+All the work was practically under the direction of English-speaking
+superintendents and general foremen. For the ordinary skilled and
+low-skilled labor, Mexicans were employed exclusively, and, on the work,
+which was quite new to them, they proved entirely efficient and
+satisfactory; throughout the work, on which at some periods between 2,000
+and 3,000 men were employed, chiefly under the Company's direct
+administration, they were very tractable and willing to do their best, and
+no trouble was experienced at any time. The Mexican "peon," and also the
+ordinary skilled workman in the north of Mexico, is intelligent, and is
+excellent for purely routine work, but he is not adaptable or resourceful
+in cases of emergency. Under intelligent and careful supervision, however,
+it is quite possible to get as good results as could be obtained anywhere.
+
+The daily rates of wages for a 10-hour day were approximately as given in
+Table 15, these rates being varied in special cases.
+
+                       TABLE 15.--RATES OF WAGES
+
+      +-----------------------------------+-------------------+
+      |                                   | Pesos per day.    |
+      +-----------------------------------+-------------------+
+      | General foreman                   |  8.00  to 10.00   |
+      | Foreman                           |  6.00  "   8.00   |
+      | Cabos                             |  2.00  "   4.00   |
+      | Masons                            |  3.00  "   4.00   |
+      | Bricklayers                       |  3.00  "   4.00   |
+      | Masons and bricklayers helpers    |       1.50        |
+      | Cast-iron pipe jointers (foreman) |       4.50        |
+      |  "   " caulkers                   |       3.00        |
+      |  "   " helpers                    |  1.50  to  2.00   |
+      | Fire-clay pipe layers             |       1.75        |
+      |  "   " helpers                    |  1.25  to  1.50   |
+      | Drillers                          |  1.25  "   1.50   |
+      | Carpenters                        |  2.00  "   2.50   |
+      | Blacksmiths                       |       2.50        |
+      | Crane men                         |       6.00        |
+      | Peons (laborers)                  |  1.00  to  1.25   |
+      | Boys (watering concrete)          |  0.37-1/2 to 0.50 |
+      | Watchman                          |       1.00        |
+      | Timekeepers                       |  22.00 per week.  |
+      +-----------------------------------+-------------------+
+
+
+
+
+                             COST OF WORKS.
+
+
+Table 16 gives the main items of the approximate expenditure. These
+include all expenses for preliminary location, engineering,
+superintendence, purchase of lands, water rights, etc., but do not include
+other heavy expenditures chargeable to the concession, such, for example,
+as general expenses, interest at the rate of 6% during the construction
+period, preliminary expenses for investigations, etc., items which would
+increase the total by nearly 25 per cent.
+
+              TABLE 16.--PRINCIPAL ITEMS OF EXPENDITURE.
+
+  +---------------------------------------------+--------------------+
+  |                                             | Pesos,             |
+  |                                             | Mexican currency.  |
+  +---------------------------------------------+--------------------+
+  | ESTANZUELA SUPPLY :                         |                    |
+  |  Aqueduct and dam                           | 502,000            |
+  |  South Reservoir                            | 429,000            |
+  |                                             | -------    931,000 |
+  |                                             |                    |
+  | SAN GERONIMO GRAVITY SUPPLY :               |                    |
+  |  Aqueduct, tunnel, and infiltration gallery | 223,000            |
+  |  Obispado Reservoir                         | 436,000            |
+  |                                             | -------    659,000 |
+  |                                             |                    |
+  | SAN GERONIMO PROVISIONAL SUPPLY ,           |                    |
+  |  including boring operations, etc.          |            130,000 |
+  |                                             |                    |
+  | CITY WATER DISTRIBUTION SYSTEM              |          1,195,700 |
+  |                                             |                    |
+  | CITY SEWER SYSTEM                           |          1,036,000 |
+  |                                             |                    |
+  | OUTFALL :                                   |                    |
+  |  Main outfall sewer                         | 425,000            |
+  |  Sewage purification works                  |  75,000            |
+  |                                             | -------    500,000 |
+  +---------------------------------------------+--------------------+
+  | Total                                                  4,451,700 |
+  +---------------------------------------------+--------------------+
+
+As a general statement, the actual cost of labor is about 33-1/3% of the
+total cost of the construction work, including materials. Fig. 20 shows in
+graphic form the amount of the labor pay-rolls and the progress of the
+work during the whole construction period from 1906 to 1909, inclusive,
+comprising also that done under contract.
+
+[Illustration: FIG. 20.--PROGRESS DIAGRAM SHOWING MONTHLY LABOR PAY-ROLLS
+DURING THE CONSTRUCTION PERIOD.]
+
+
+
+
+                    TARIFFS AND SANITARY REGULATIONS.
+
+
+_Tariffs._--The tariffs charged for the water and drainage service (Table
+17) were approved by the State Government (which accepts the
+responsibility for their collection), under a compulsory State law which
+came into force on March 1st, 1910, for the southern portion of the city,
+and on July 1st, for the northern half, the penalty for non-compliance
+being a tax of 10% on the monthly rental value of the property, as
+assessed by the State officials.
+
+The basis of the tariffs (which were published on February 22d, 1909) is a
+charge for water varying between 12 and 16 cents (Mexican) per 1,000
+liters, with a minimum monthly rate for each different class of property
+connected to the system. The rate for house drainage is fixed at 80% of
+the minimum water rate levied on the consumer. The minimum rates have been
+fixed so that the poorer classes of the community will not be overtaxed,
+while at the same time the rate is actually levied on the quantity of
+water used, as indicated by the meter. All the services at the present
+time are metered, and the meter system will be used throughout.
+
+                        TABLE 17.--THE TARIFFS.
+
+  +-----+------------+---------+-----------+---------+----------+--------+
+  |     | Monthly    | Liters  | Price for | Minimum | Rate for | Total  |
+  |Class| property   |   of    | 1,000     | monthly | drainage | rate   |
+  |     | rental.    |  water  | liters.   | rate.   | service. |payable.|
+  |     | Pesos.     | allowed.| Cents.    | Pesos.  | Pesos.   | Pesos. |
+  +-----+------------+---------+-----------+---------+----------+--------+
+  |   I | Up to 20   |  7,800  |   16      | 1.25    |   1.09   |  2.25  |
+  |  II | 21 to 40   | 12,500  |   16      | 2.00    |   1.60   |  3.60  |
+  | III | 41 to 60   | 18,750  |   16      | 3.00    |   2.40   |  5.40  |
+  |  IV | 61 to 120  | 23,350  |   15      | 3.50    |   2.80   |  6.30  |
+  |   V | 121 to 300 | 30,000  |   15      | 4.50    |   3.60   |  8.10  |
+  |  VI | 301 upward | 33,350  |   15      | 5.00    |   4.00   |  9.00  |
+  +-----+------------+---------+-----------+---------+----------+--------+
+
+    "Notes: (1st) The rental for the water meters 5/8-in. size
+    (15-1/2 mm.), which shall always be considered the property
+    of the Company, will be 20 cents per month. Houses of the
+    first and second classes shall be exempt from paying such
+    rental for one year's time, counting from this date.
+
+    "(2d) All excess consumption of water over that allowed by the
+    tariff will be charged for at 2 cents less than the price
+    shown in the tariff per thousand liters.
+
+    "(3d) Extra large houses, large establishments, such as
+    colleges, hotels, etc., etc., having a consumption of 50,000
+    to 60,000 liters of water per month, will pay at the rate of
+    14 cents per thousand liters. The drainage rate for such
+    buildings will be arranged in proportion to the water tariff,
+    or 80% of the value of the water.
+
+    "(4th) The laundry establishments, bath-houses, etc., when
+    using 50,000 liters or upward, can arrive at some agreement so
+    as to pay 12 cents per 1,000 liters.
+
+    "(5th) Groups can be formed of two or more small houses so as
+    to obtain a joint service under the proportion shown in the
+    tariff.
+
+    "(6th) Any other combination that cannot be entered into under
+    the basis of this tariff, will be arranged by specially agreed
+    upon prices, such agreement being as much as possible subject
+    to the basis mentioned."
+
+_Sanitary Regulations._--The State Government, on March 1st, 1909,
+published regulations for the proper installation of the water and
+drainage services within the houses.
+
+At the Government's request, a draft of the proposed regulations was
+submitted by the writer, who prepared it, after a study of American and
+British sanitary by-laws, to suit the special conditions of Monterrey.
+These regulations were afterward modified by him in collaboration with the
+Government Technical Inspector and Financial Interventor, and, in their
+final form, though not as stringent as those adopted in many northern
+cities, are probably more complete than those in any other Mexican city.
+Under these regulations only registered plumbers can undertake plumbing
+installations, and they have to execute a bond to the satisfaction of the
+_Alcalde Primero_ (City Mayor) for the sum of 2,000 pesos as a guaranty of
+responsibility. For defective workmanship or any infraction of the
+plumbing regulations, they are liable to heavy fines, and can be called on
+to make good all defects in workmanship, without extra charge to the owner
+of the property. The provisions of the regulations are carried out under
+the supervision of the Government Technical Inspector, the Company's
+obligations extending only to the sidewalk and to the meters placed within
+the houses.
+
+
+
+
+                             ENGINEERS, ETC.
+
+
+G. S. Binckley, M. Am. Soc. C. E., was Chief Engineer of the Company from
+February to December, 1906. The writer was Chief Engineer from May
+1st, 1907, until April, 1910, and is responsible for the design and
+construction of the works carried out during that period. Mr. J. D.
+Schuyler advised the Company throughout all preliminary studies and
+investigations, and acted as Consulting Engineer until February, 1908. The
+Technical Inspector, on behalf of the Government, throughout the whole
+progress of the works, has been Rudolf Meyer, M. Am. Soc. C. E., and the
+writer wishes to record the valuable assistance the Company has received
+from him.
+
+In conclusion the writer may be permitted to pay a tribute to the devoted
+public spirit shown by his Excellency, General Bernardo Reyes, the
+Governor of the State of Nuevo Leon from 1885 to February, 1910, and who,
+untiring in his devotion to the interests of the city, was primarily
+responsible for the inception of the works and their successful
+completion.
+
+
+
+
+                               DISCUSSION.
+
+
+JAMES D. SCHUYLER, M. AM. SOC. C. E. (by letter).--For completeness of
+detail and wide range of subjects of general interest to engineers, this
+paper is certainly one of the notable contributions to recent engineering
+literature. It is a minute and painstaking record of the successful
+accomplishment of construction work under unusual climatic conditions and
+difficult circumstances, and reflects credit on the author, not only in
+his capacity as an engineer, but as a faithful recorder of facts. It was
+particularly fortunate that he was an eyewitness of the disastrous and
+extraordinary flood which swept through Monterrey, destroying many lives
+and much property, and has thus been able to give an intelligent estimate
+of the maximum discharge of the river during the height of the flood wave
+of August 27th-28th, 1909, when the rate of run-off per unit of area of
+water-shed drained reached an amount which has seldom been equalled or
+exceeded, as far as reliable records extend. It is worthy of note that
+works deriving their water supply from the source of such torrential
+floods should have survived with so little actual damage, and with
+scarcely any interruption of service. The repair of all damages to the
+system was estimated to have cost not more than $20,000.
+
+As Mr. Conway did not assume charge of construction until May, 1907, he
+was spared the responsibility of deciding on the general plan of securing
+an abundant supply of pure water from sources permitting of delivery by
+gravity under adequate pressure for fire protection--a responsibility
+which devolved on the writer, assisted by G. S. Binckley, M. Am. Soc. C.
+E., Mr. Conway's predecessor, as Chief Engineer. Not only the water-works,
+but the system of sewerage and sewage disposal by broad irrigation were
+subsequently carried out on the plans submitted to the State Government by
+the writer in 1906, and given provisional acquiescence at that time.
+
+There was no lack of water at hand for the supply of a city of that size,
+as there are large perennial springs which flow out of the travertine of
+the plain, and are used for irrigation in the valley below the city. One
+of the largest of these, near the civic center, has a normal flow of
+nearly 30 cu. ft. per sec.; another nearby, also within the city limits,
+flows some 10 or 12 sec-ft., while both the Estanscia and Robalar springs,
+but a few miles below (shown on Plate II), discharge more than 20 sec-ft.,
+as nearly as memory serves. Besides this supply, the water to be developed
+by sinking shafts in certain parts of the plain, as demonstrated at the
+brewery and elsewhere, was apparently a reliable source of large volume.
+
+To utilize these sources, however, would have involved condemnation of the
+water-rights in the case of the springs, depriving present owners of the
+use of the water, and this Governor Reyes wished to avoid. Besides, it
+would have necessitated pumping the water for the city in perpetuity, an
+expense which the Governor was equally anxious to save; hence a gravity
+supply was made the prime requisite of the plans.
+
+Until the concession was granted, and for a year or more afterward, it was
+assumed that an adequate supply could only be obtained by the storage of
+the flood-water of the Santa Catarina River in a large reservoir; and the
+earlier plans of the concessionaires were based on the construction of a
+high masonry storage dam at the upper end of the "narrows," where the
+river turns from a western direction to a course almost due east, between
+high vertical cliffs of limestone. The concession distinctly provided for
+such a dam, and among the plans on file in the State Capitol is one
+prepared by the late E. Sherman Gould, M. Am. Soc. C. E., for a masonry
+weir across the gorge. Samuel M. Gray, M. Am. Soc. C. E., also filed a
+plan and report proposing a capacious, shallow, storage reservoir near the
+city, to be filled by a large flood-water canal from the Santa Catarina
+Canon.
+
+Although the writer could not have anticipated the occurrence of floods of
+the magnitude of the one of August, 1909, which would surely have
+destroyed any reservoir built in the Canon, he was unable to endorse the
+storage plan of water development, chiefly because of the uncertainty of
+the water-tightness of the reservoir in a cavernous limestone formation,
+and also because of the probable impurity of water draining from such
+extensive goat pastures. He, therefore, urged the development of the
+underflow of the river, which was manifesting itself in the springs
+referred to. Mr. Binckley secured two Keystone drilling machines and
+proceeded to profile the bed-rock at Santa Catarina Canon and at San
+Geronimo, the two places on the stream where the river flows between walls
+of rock _in situ_. At both sites the strata were standing nearly vertical
+across the channel, and, by careful sampling and testing, it was found
+that in both locations there were thick strata of limestone so highly
+silicious as to be insoluble, and hence free from caverns. From this
+determination it was concluded that all the water which appeared in the
+valley below must pass through the sections where the borings were made.
+The results of this drilling, however, proved conclusively that the depth
+to bed-rock at either place was too great to permit of a masonry dam being
+considered as practical, and demonstrated the inadequacy of methods which
+had been used in the earlier investigations when dams were regarded as
+feasible.
+
+The results have also shown that the subterranean supply at the lower
+cross-section of the river, at San Geronimo, is abundant, and can probably
+be increased to an indefinite degree by continuing the filtration gallery;
+while at Santa Catarina the same type of development can be made for a
+high-source supply, although requiring a long and expensive tunnel and
+conduit.
+
+
+DAVID T. PITKETHLY, ASSOC. M. AM. SOC. C. E. (by letter).--Having been
+engaged on the design of sewerage systems for some years, the writer finds
+this paper of peculiar interest, particularly the sewerage portion. There
+are some points in the design, however, which do not appear to be clear.
+
+The system is described as "strictly separate," and yet the sewers are
+designed to run half-full, providing a capacity of 200%, the 100% basis,
+or 380 liters per capita, being 90%, or 180 liters, in excess of the
+calculated water supply of 200 liters per capita.
+
+It has been the writer's practice to design sanitary sewer systems on the
+basis of the water consumption, and to assume the whole daily amount to
+reach the sewer in 16 hours, thus providing capacity sufficient to care
+for the maximum or wash-day flow without causing the sewers to run above
+the calculated hydraulic gradient, which should be placed within the pipe
+so as to provide air space for ventilation under all circumstances.
+
+The practice of calculating sanitary sewers to run half-full is a good one
+when ground-water is expected in sufficient amount to fill the remaining
+portion of the sewer, but when no ground-water, or roof-, or surface-water
+is allowed to enter the system, or all precautions are taken to exclude
+such, then the system may be designed so that the expected maximum, or
+wash-day flow, will fill the sewer to the desired hydraulic gradient.
+
+The method of ventilating the sewers does not seem practicable. The houses
+are principally of one story, and yet the stand-pipes on the sewers have
+openings 25 ft. 9 in. above the sidewalk. Are the ventilating or vent
+pipes of the house plumbing carried to a height to balance this, or will
+these chimneys draw the air from the house drains and fresh-air pipes,
+breaking the seal in the so-called disconnecting traps, thus causing the
+circulation of air in the house piping to be downward through the sewers
+instead of upward through the fresh-air inlets and vents, as designed?
+
+It is interesting to note that crude sewage, as well as the liquefying
+(septic) tank effluent, is to be applied to land for irrigation purposes,
+but the application of crude sewage without any attempt at removing the
+suspended matter, or the effluent from the septic tanks where only a
+partial removal occurs, seems to be bad practice.
+
+The author states that:
+
+"The degree of purification in the tanks was relatively unimportant; the
+object to be obtained consisted chiefly in distributing on the land an
+effluent which would be innocuous and clear."
+
+How he expects to obtain such an effluent by passage through screens,
+detritus tanks, and septic tanks only, is more than the writer can
+understand.
+
+The removal of suspended matter in a septic tank depends on the strength
+of the sewage, the time of retention, the time elapsing between cleaning,
+the presence of trade wastes, etc., and seldom exceeds 38 per cent.
+
+The subject of septic tanks and their effect on sewage is discussed in the
+"Fifth Report of the Royal Commission on Sewage Disposal" (England, 1908),
+and the following extracts, relative to the application of crude sewage to
+land and the effect of septic tanks on sewage, seem apropos:
+
+    "23. * * * There are also many cases in which crude sewage has
+    been passed over land, but the evidence shows that land treatment
+    of crude sewage is liable to give rise to nuisance by the
+    accumulation of solids on the surface of the land. Moreover, in
+    some cases these solids are apt to form an impervious layer,
+    which interferes with the aeration of the soil, and so impairs
+    the efficiency of the treatment."
+
+    "31. * * * At that time it was claimed that the septic tank
+    possessed the following, among other, advantages:
+
+    "That it solved the sludge difficulty, inasmuch as practically all
+    the organic solid matter was digested in the tank.
+
+    "That it destroyed any pathogenic organisms which there might be
+    in the sewage."
+
+    "32. As regards the first of these claims, it is now clearly
+    established that, in practice, all the organic solids are not
+    digested by septic tanks, and that the actual amount of digestion
+    varies to some extent with the character of the sewage, the size
+    of the tanks relative to the volume treated, and the frequency of
+    cleansing."
+
+    "At Huddersfield, Mr. Campbell estimated that about 38 per cent.
+    of the solids were converted into gas or digested; * * * while at
+    Birmingham, Messrs. Watson and O'Shaughnessy say that the figures
+    available indicated a digestion of not more than 10 per cent. of
+    the suspended matter entering the tanks."
+
+    "33. As regards the second claim, we find as a result of a very
+    large number of observations that the sewage issuing from the
+    septic tanks is, bacteriologically, almost as impure as the sewage
+    entering the tanks."
+
+Messrs. Winslow and Phelps, in their interesting paper, "Investigations on
+the Purification of Boston Sewage,"[8] quote a suggestion made by
+Stoddart (1905):
+
+[8] Water Supply and Irrigation Paper No. 185, p. 125.
+
+    "He finds, in a septic tank of several compartments, a
+    considerable deposit of sludge in the first compartment, giving
+    a fairly clear supernatant liquid, which in the last chamber of
+    all undergoes a secondary decomposition, leading to the
+    throwing down of an additional precipitate of offensive
+    sludge."
+
+What took place in the case referred to by Stoddart corresponds to the
+author's observations of the liquid leaving the tanks in a clarified
+condition, but the secondary decomposition must take place in some manner,
+and, when it does, a nuisance seems to be unavoidable where no provision
+is made to care for it.
+
+In view of the experience of others, some further treatment seems to be
+necessary. Such treatment should include disinfection, as no method of
+disposal yet devised has succeeded in reducing materially the pathogenic
+germs usually to be found in sewage and tank effluents.
+
+If the crops to be irrigated are to be eaten, uncooked, by mankind, then
+disinfection at least is imperative.
+
+
+GEORGE S. BINCKLEY, M. AM. SOC. C. E. (by letter).--Mr. Conway's admirable
+paper is of special interest to the writer, as the entire general design
+of the system, as well as the extensive hydrological studies and final
+selection of the sources of water supply, was completed during 1906
+through the joint labors of the writer, as Chief Engineer, and James D.
+Schuyler, M. Am. Soc. C. E., as Consulting Engineer.
+
+In this work, Mr. Schuyler and the writer had the rare privilege of
+dealing from its inception with the problem of designing a complete and
+somewhat extensive system of municipal water supply and drainage,
+unhampered by any existing works to which the new systems would have to be
+adapted. It would probably be difficult to find in the United States a
+city of 85,000 inhabitants, previously totally lacking either a water
+supply or sewerage system, which, under a consistent and harmonious
+design, has been provided with both in the degree of completeness and
+structural excellence exemplified in the works at Monterrey.
+
+The few important changes or amplifications made in the original design,
+and the manner in which its detail has been executed is naturally most
+interesting to the writer, and this excellent paper should be of very
+substantial value, particularly to engineers engaged on similar work in
+Mexico or Spanish America.
+
+The very novel construction method adopted by Mr. Conway in the roofing of
+the South or Guadalupe Reservoir, seems to the writer rather to invite
+criticism, and the fact that in the subsequent construction of the roof
+over the rectangular Obispado Reservoir the customary monolithic concrete
+construction was apparently reverted to after experience with the
+separate-unit plan previously used, would indicate that Mr. Conway reached
+the same conclusion.
+
+The original design of the circular Guadalupe Reservoir contemplated just
+about the same arrangement of columns and roof support as that actually
+used, but the writer had expected that the columns would be cast in place,
+and that the system of primary and secondary beams would be filled at the
+same time as, and integral with, the roof slab, the reinforcement being
+placed in accordance with what may be described as conventional practice.
+The writer believes that the efficiency of the concrete and steel placed
+in this manner would be notably higher than under the system actually
+adopted, which, in effect, is pretty much the same as constructing the
+supporting system of units of cut stone. If, with all the elements of
+structural weakness involved in the multiplicity of mortised joints,
+discontinuous reinforcement, etc., this construction is strong enough, it
+would seem that an important reduction in the dimensions of the members
+could have been effected by monolithic construction and continuous
+reinforcement, without sacrifice of strength.
+
+The comparison, in Table 7, of the costs of these two reservoirs, is
+interesting, but very moderately illuminating, as the comparative unit
+cost of the most important element in their construction--the concrete--is
+not given. The total excavation cost for each reservoir is practically the
+same, and the general expense, engineering, and cost of fittings and
+accessories presumably so, but the total cost of the Guadalupe Reservoir
+as given is $19,000 (pesos) in excess of that of the Obispado Reservoir,
+while, in the latter, there were 756 cu. m. more concrete. This certainly
+indicates a much higher cost of concrete per unit as laid in the South
+(Guadalupe) Reservoir. An actual comparison of the cost per unit of
+concrete laid under the two systems would be instructive.
+
+The writer is interested to observe that the same system of sub-drainage
+used by him in the construction of the reservoir for the provisional
+supply of water from San Geronimo, has been used by the author in the
+Obispado Reservoir. This arrangement of drains under the floor of the
+reservoir at San Geronimo was devised as a safeguard against damage to the
+lining through the accumulation of water inside the impervious bank
+against its back.
+
+It was realized that, in such a climate as that of Monterrey, perfect
+water-tightness of the lining might be difficult to secure or maintain,
+and, if leaks existed, a sudden draft on the contents of the reservoir
+might result in serious damage through the static pressure exerted against
+the lining of the sides or upward thrust against the floor. In the
+writer's opinion, such a system of drains is an important element, as not
+alone the fact but the quantity of leakage may be determined, and danger
+of saturation of the supporting bank avoided--a matter of importance
+where, as is sometimes the case, the material of such a bank is unfit to
+resist the effects of saturation. The author does not state whether or not
+this safeguard was omitted in the Guadalupe Reservoir. Incidentally,
+however, the matter of saturation of the bank is not important in either
+reservoir, as the material of which these banks are constructed is such
+that settlement or failure through saturation is out of the question. It
+may be remarked, however, that in fixing the angle of the sides of the
+Guadalupe Reservoir at 60 deg. the writer contemplated the same system of
+constructing the bank as he used in that of the San Geronimo Reservoir. In
+this case, the bank was built up by spreading the material in thin layers,
+wetting down, and rolling and puddling by the passage of the ox-carts used
+for the transportation of the material, the wheels of the carts, and
+especially the cloven hoofs of the animals, producing a most excellent
+effect. The inside slope was built up in this fashion to a much lower
+angle, and with a top width considerably in excess of the finished
+dimensions. The excess material was then picked off to the line, and
+exactly to the slope. Thus the finished slope presented a surface which
+was compacted to a degree impossible to attain at or near the surface of
+the bank as built, and presenting a support of the best possible character
+for the concrete lining and coping.
+
+
+V. SAUCEDO, ASSOC. M. AM. SOC. C. E. (by letter).--The author's
+description of the water-works and sewerage of Monterrey, one of the most
+extensive schemes in Mexico, will be of general interest to engineers,
+especially those engaged in hydraulic and sanitary problems. The writer,
+having been connected with the works for four years, knows the local
+conditions well, and presents herewith some complementary data on what he
+considers an important feature, the subject of floods, mentioned by the
+author on different occasions, especially as certain developments in the
+works show the importance of such occurrences as a factor in designing.
+
+Abnormal rainfalls of long duration and high intensity are common in the
+semi-arid region of Mexico. They come at irregular intervals, though
+tending to coincide with the early fall. The floods of August, 1909, were
+a repetition of similar occurrences in the past; and, though there are no
+numerical records of previous cases, local traditions and historical state
+documents describe them as having occurred since the foundation of the
+city, at intervals of from 15 to 40 years. The graphic descriptions of the
+places flooded are in accord with the character of the floods of August,
+1909, and September, 1910.
+
+The diagram, Fig. 21, is a record of the rainfall during the latter flood,
+and was plotted from intermittent readings of standard gauges. It
+demonstrates that the intensity increased toward the mountains on the
+south, which form the tributary water-shed of the Santa Catarina River,
+showing a difference of 10.54 in. between the city and the Estanzuela Dam,
+which is not quite 12 miles to the southeast.
+
+[Illustration: FIG. 21.--RAINFALL DURING FLOODS OF SEPTEMBER 14TH-16TH,
+1910, IN MONTERREY.]
+
+An estimate of the volume of discharge of the river at the time of maximum
+flood is only a reasonable conjecture which (without special reference to
+accuracy) aims to impress those who have not witnessed such occurrences
+with the tremendous volume coming from barren steep surfaces previously
+saturated.
+
+The original computation, referred to by the author, was obtained from the
+average of two different methods which gave results close to each other.
+In one method the extent and nature of the water-shed were considered,
+together with the maximum period of precipitation that occurred,
+sufficient to gather a maximum volume of water in the river. In the other
+method the volume was derived from a cross-section of the wetted perimeter
+of the river at the time of maximum flow, in combination with velocity
+approximations obtained by using rough floats. This gave 271,500 cu. ft.
+per sec. The figure submitted by the author, 235,000 cu, ft. per sec., is
+in accord with the proposed formula[9] for impervious surfaces by C. E.
+Gregory, M. Am. Soc. C. E. In the first and last methods, the intensity, a
+governing factor, is more or less of an assumption, and the
+cross-sectional method is also unreliable, as the river-bed was greatly
+disturbed, due to the high velocity of the water, which deepens the
+channel to a considerable extent at times of maximum flood, the gravels
+being redeposited during the period of subsidence. Such was the case
+during the flood of September, 1910, when the depth of gravel above the
+roof of the San Geronimo Infiltration Gallery was diminished to such an
+extent that it was so inefficient as a filter for the flood as to permit
+the percolation of turbid water into the underground supply.
+
+[9] _Transactions_. Am. Soc. C. E., Vol. LVIII. p. 458.
+
+During the floods of August, 1909, Shafts Nos. 2 and 3 were damaged beyond
+repair, and sand and gravel, entering through them, blocked up the
+gallery to within about 150 ft. of Shaft No. 1. The interior timbering
+probably collapsed, due to cavings and disturbance in the river-bed during
+the period of maximum flood, but no explorations have been possible on
+account of the great quantity of water still coming through (at present
+more than 650 liters per sec.). For this reason the work of driving the
+gallery, as well as lining Shaft No. 1, has been suspended.
+
+[Illustration: PLATE XXVIII, FIG. 2.--VIEW OF SANTA CATARINA RIVER IN
+FLOOD, ON AUGUST 28TH, 1909.]
+
+[Illustration: PLATE XXXI, FIG. 1.--FLUSH-TANK CARRIED DOWN BY FLOOD OF
+AUGUST 27TH-28TH, 1909.]
+
+[Illustration: PLATE XXXI, FIG. 2.--VIEW SHOWING SCOURING EFFECT OF FLOOD
+ON SAN GERONIMO AQUEDUCT.]
+
+[Illustration: PLATE XXXII, FIG. 1.--VIEW OF SANTA CATARINA RIVER AFTER
+THE FLOOD.]
+
+[Illustration: PLATE XXXII, FIG. 2.--VIEW OF SANTA CATARINA RIVER FLOWING
+THROUGH LOW-LYING STREETS, 8 DAYS AFTER THE FLOOD.]
+
+On reaching the city, the flood of August, 1909, swept away two streets
+adjoining the river. These streets had been built on made ground, in what
+was originally the river-bed. The sewers and water mains laid in them were
+destroyed entirely, and some 460 ft. of the 24-in. cast-iron pipe, buried
+under the river-bed at a depth of 8 ft., were carried away. In relaying
+this portion of the main, and for protecting the remainder of it across
+the river, it is now proposed to encase it in a solid rubble concrete
+block, 8 ft. square, which will impart weight and stability against the
+scouring effect of floods.
+
+The South Reservoir is circular in shape, with an interior diameter of
+165.68 ft. at the top, and is partly excavated in the ground and partly
+completed by an embankment of vast proportions (Fig. 10). Right after the
+flood of August, 1909, a wet spot appeared on the northeastern toe of the
+embankment, and it was supposed for some time that it was the effect of
+the saturation produced by the preceding rains, but, as it persisted for
+several months, it was obvious that its origin was in the interior of the
+reservoir, which was emptied when the writer took charge of the work. The
+first inspection revealed a horizontal crack in the concrete lining, about
+310 ft. long and extending about 153 deg. around the circumference on the
+north side. Throughout its length it coincided with the line of cut and
+fill. Vertical cracks, coinciding with the panel points in the lining, had
+also developed, and extended from the main horizontal crack to the roof.
+The circumstances originating this development can be conjectured by
+considering the position of the main crack, its characteristic features,
+and the conditions that preceded its formation. The coincidence of the
+crack with the joint of cut and fill, points to this line as a source of
+danger. An examination showed, besides, that the fracture was clean and
+sharp, ranging in thickness from a hair line at the ends to 3/16 in. at
+the center, and that its upper border projected over the lower one
+perceptibly, a proof that horizontal motion had taken place. The vertical
+cracks were a secondary effect, the consequence of the displacement
+immediately after it was scoured. A fracture was discovered in the floor
+of the reservoir. It started at the center and branched out into two
+diverging lines in a radial direction.
+
+The circumstance of two abnormal rainfalls, giving 35 in. in 9 days, the
+precipitation being concentrated in two periods, not far apart, of 42
+hours and 98 hours, respectively (Fig. 4), together with lack of provision
+for shedding the water from the roof of the reservoir and from the
+surrounding embankment, lead to the inference that the latter became
+saturated, increasing thereby in weight and decreasing in stability,
+especially in its steep inner face. A settlement and the consequent
+horizontal displacement, under these conditions, was natural. The concrete
+lining, only 16 in. thick at that height, was not sufficient to sustain
+the resulting strain, and the main fracture developed, permitting the
+stored-up water to leak into the bank. In time this seepage found its way
+under the bottom of the reservoir, softening the ground and producing a
+slight settlement which caused the crack in the floor. Had under-drainage
+been provided, as at the Obispado Reservoir, the actual conditions would
+have been noticed earlier. However, as the embankment is of vast
+proportions, stable in itself to sustain with a large margin of safety the
+weight of the stored-up water, there was no actual danger of failure,
+except for the fact that the material forming the structure, on account of
+its calcareous nature, is dissolved by water. Long exposure to this
+condition would, in time, open passages in the embankment, and it is
+certain that there would be cavings in its interior.
+
+The necessary grouting has been done, and provision is being made for
+water-proofing the interior of the reservoir and shedding the water from
+the roof and from the embankment, thus relieving the structure of the
+consequent strain.
+
+Another place in the works where floods have had a damaging effect is the
+Estanzuela intake basin, which, when the dam was completed, was filled to
+the overflow level in order to test its water-tightness. As this basin,
+when cleaned, was found to be slightly fissured on the north side, it was
+decided to line it with concrete. As shown in Fig. 8, the lining does not
+cover its entire area, but only the central portion, leaving a strip on
+either side without protection. The flood of September, 1910, coming in
+greater volume than the previous ones of August, 1909, in passing through
+the narrow gorge at the entrance, undermined the lining in those places
+where it was not founded on solid rock. Figs. 1, 2, and 3, Plate XXXIII,
+show some of the damage caused by this flood. The buoyant effect of the
+water and the impact of large rolling boulders caused fractures all over
+the surface, and lifted the concrete lining bodily; but the dam proper,
+being founded on rock bottom, did not suffer any injury. In the future, in
+order to avoid the seepage of the ordinary supply, alluded to by the
+author, the water will be carried to the valve-house in an open rubble
+concrete channel, lined with cement mortar and built high up against the
+western hillside. The remainder of the basin will be paved with large
+boulders.
+
+[Illustration: PLATE XXXIII, FIG. 1.--ESTANZUELA DAM: BROKEN CONCRETE
+BASIN LINING.]
+
+[Illustration: PLATE XXXIII, FIG. 2.--ESTANZUELA DAM: BROKEN CONCRETE
+BASIN LINING, EAST SIDE.]
+
+[Illustration: PLATE XXXIII, FIG. 3.--ESTANZUELA DAM SEPT. 26, 1910: VIEW
+OF SHEARING FRACTURES OF WALL AND LINING AFTER FLOOD SEPT. 14-17, 1910.]
+
+In conclusion, the writer wishes to emphasize the point that,
+notwithstanding the severity of the test, relatively small damage was
+inflicted on the extensive works carried out under the author's design and
+direction. A test so severe that it caused serious damage and immense
+losses in the entire region, washing away kilometers of railroad track and
+destroying practically all the bridges within reach of the flood, is an
+occurrence of paramount importance, and should be remembered as a leading
+factor in the design of engineering works.
+
+
+GEORGE T. HAMMOND, M. AM. SOC. C. E. (by letter).--In a country, such as
+that described in this paper, where water is valuable, and a shortage is
+at times possible, where the majority of the population is very poor, and
+water and sewage discharge are both to be paid for on a basis of volume,
+the question of the expected quantity of daily water supply and sewage
+flow per capita is of primary importance. This question, notwithstanding
+its difficulty, should be given a first place in the studies for
+water-works and sewerage projects, and should never be lost sight of in
+the design, which should be such that, while proper for the expected
+future flow for a reasonable time, should also be proper and economical
+for conditions which at present obtain and may change but slowly.
+
+It is desirable, of course, to get as much capacity in works as one can
+for the outlay, but there are instances where one can get too much for the
+money, as where a larger pipe than is necessary is used for a sewer,
+merely because it costs about the same as a smaller one, and as a result
+the cost of maintenance is permanently increased.
+
+The water-works were designed to supply 40,000,000 liters (10,582,000
+gal.) daily, which it was assumed would be sufficient for all future
+developments in Monterrey for a population of 200,000 at a per capita
+consumption of 200 liters (about 53 gal.) per day. The present population
+of the city is given as less than 90,000, there having been an increase of
+22,000 in ten years (1891-1901), but it is evident that in the last ten
+years (1901-1911) this rate of increase has not continued. Taking into
+account all the data known to the writer, it does not seem that the city
+will attain a population of 200,000 in a great many years, if it ever
+does; but this is a matter of personal opinion, and is only stated as
+such.
+
+The present requirements of the city's population, assuming that each
+person uses 200 liters (53 gal.) per day, would be, at that rate, which is
+a very liberal one, only 18,000,000 liters (4,762,000 gal.) per day, or
+less than half the amount which may be provided.
+
+If the water were not to be metered and the sewage discharge paid for by
+measure, it is possible that the free use of water might lead to the usual
+waste with which all are fairly familiar; but the use of meters, and the
+rates charged, will reduce the water consumption to a minimum. This end
+will especially result from Section 5 of the Tariffs which provides that:
+
+"Groups can be formed of two or more small houses so as to obtain a joint
+service under the proportion shown in the tariff."
+
+This provision will keep down the per capita supply, among the majority of
+the people, to about 37-1/2 liters (10 gal.) per day. A similar provision
+led to abuse in Santiago de Cuba, as well as in other Cuban cities, where
+one householder, taking water, frequently delivers it to adjoining houses
+and tenements through rubber hose. As many as ten or twelve families are
+sometimes found to be supplied from one tap in this manner. Indeed, it may
+be stated as a rule, having but few exceptions, that where water is paid
+for by meter its use is always restricted.
+
+The water mains and distribution system, however, are so well laid out,
+and the whole design is so good, that the writer would not anticipate much
+difficulty because it is on rather too liberal lines for the present or
+probable future. It may, perhaps, be argued that it may cost more to keep
+the mains in such a system clean; but this extra cost will scarcely be of
+much moment, and will be offset by the greater lasting quality of the
+larger pipes. There is another feature of the problem, however, which is
+not affected favorably by a too liberal forecast of the per capita water
+supply, namely, the sewerage system.
+
+If it is assumed that, using 200 liters per capita per day, the total
+water supply of the city for the present population will be 18,000,000
+liters, and that this may double in fifty years, or even amount to
+40,000,000 liters in that time, it would seem that a rather liberal
+provision has been made for the water supply, and that this will scarcely
+be exceeded by the sewage, for the latter must come from the water supply,
+there being little or no ground-water and no storm-water taken into the
+sewers. Designing the sewers to flow half full for all diameters less than
+18 in., and seven-tenths full for all larger sizes, it would seem that
+this would give ample capacity for all time to come in such a city, and
+that good practice would not exceed these figures, it being more desirable
+that the sewers should not be too large to work well, than that they
+should be large enough in all places to meet every possible contingency.
+If all the sewers of a system are too large, the condition is incurably
+bad; while, if a few miles prove to be too small, on account of growth and
+prosperity not anticipated by the designer, it will be easy enough to
+relay such parts when this becomes necessary.
+
+Mr. Conway states that:
+
+"The sewers are designed on a very liberal basis, namely, on the
+assumption that when flowing half full the quantity to be dealt with will
+be 380 liters [100 gal.] per capita per day, with a maximum rate of flow
+of 200 per cent."
+
+If the writer understands this statement correctly, it means that the
+sewers, flowing half full, will carry 380 liters per capita in 12 hours,
+or are designed with 200% of the capacity required to take the assumed
+flow in 24 hours.
+
+It was assumed that each house would be occupied by 7 persons and have a
+frontage of 12-1/2 m. (about 41 ft.), that is, about 700 gal. per day per
+house, the maximum flow rate being 200%, or at the rate of 700 gal. per
+house in 12 hours.
+
+It is to be remembered that nearly all the houses are of one story, and
+that, as a rule in tropical and sub-tropical countries, the per capita use
+of water diminishes with some function of the increasing number of
+inhabitants in one house. Most of the water is used in the kitchen, and
+where there are 7 persons instead of 5, the quantity used by the smaller
+number will generally serve the larger.
+
+The writer is unable to understand how this quantity of sewage will be
+produced, especially as the author states that, as far as the company is
+concerned, it is limited to the removal and disposal of the sewage, and is
+not required to provide for storm-water. He also states that:
+
+"Apart from that fact, however, the best system for a city like Monterrey,
+where rainfall for many months at a time is very scarce, is the strictly
+'separate system'."
+
+The minimum velocities in the sewers, when running full, vary between 0.91
+and 1.5 m. (from 3 to 5 ft.) per sec., and will be the same flowing half
+full.
+
+From the foregoing data it will be observed that:
+
+    (1) The water supply is the only source from which sewage flow
+    is anticipated;
+
+    (2) The water supply is very liberally estimated at 200 liters
+    (53 gal.) per capita daily;
+
+    (3) For purposes of sewer design, the daily flow of sewage
+    expected (all of which is derived from the water supply of 200
+    liters per capita) is estimated at 380 liters per capita, with a
+    maximum rate of flow of 200% (or at the rate of 760 liters per
+    capita), and with this quantity the sewers are designed to flow
+    only half full;
+
+    (4) The gradients are such that a velocity of from 3 to 5 ft.
+    (0.91 to 1.5 m.) per sec. will be secured in the sewers flowing
+    half full with the above quantity of flow per capita.
+
+The writer does not agree with this method of computation, as he feels
+sure that it will give sewers which are too large, with grades too steep
+for the best obtainable results. His experience, extending over more than
+twenty years in sewer design and hydraulic work, convinces him that the
+method pursued is wrong in principle.
+
+The principles involved in sewer design are first of all hydraulic. The
+quantity of flow, in the nature of things, cannot be forecasted
+accurately; success depends on getting the nearest possible approximation
+to average conditions. If 200 liters per capita per day is a liberal
+allowance, and 40,000,000 liters per day is a liberal expectation at this
+rate for double the present population, and the sewers are designed to
+flow half full only, why should this again be doubled?
+
+The design of a sewer system for a city such as Monterrey is, in fact, a
+very difficult problem, especially as the quantity of sewage will be very
+limited, flush-water will have to be used in considerable quantities, and
+water in that part of the world is precious at all times and often scarce.
+Under these circumstances, the size or shape of the pipes selected for the
+lateral sewers, should have been such as would more nearly agree with the
+requirements than does the 8-in. circular.
+
+A. P. Folwell, M. Am. Soc. C. E., writing of the 8-in. circular size,
+states:[10]
+
+[10] "Sewerage," by A. P. Folwell, M. Am, Soc. C. E.
+
+    "To secure a flow in this pipe having an average depth of 4
+    inches would require the sewage from a population of 6,500. In
+    general it may be said that the ordinary depth of flow in any
+    sewer should not be less than 2 inches, nor should it be less
+    than 1/2 the radius of the invert, since if it is so there is
+    much more danger of deposits forming along the edges and even in
+    the center of the stream. It will sometimes be impossible to
+    meet this requirement fully, but it should be kept in mind as
+    extremely desirable."
+
+Sewers of small size should be proportioned throughout the system so that
+the depth of the minimum daily flow in the invert, and the velocity of
+flow, will be the best possible to prevent deposits. The transporting
+power of water is dependent mainly on the depth of flow, a minimum
+velocity being selected rather than a minimum depth of flow. To those who
+have had charge of the maintenance of sewers, as well as of their design
+and construction, this principle seems so obvious that it is always a
+surprise to see it disregarded by designers, who in these days seem
+inclined to consider sewerage as a system of grades and sizes of pipes
+installed for ideal, rather than for actual, conditions. Messrs. Staley
+and Pierson have well stated the principle involved as follows:
+
+"A stream having a depth of flow sufficient to immerse solid matter held
+in suspension, to a certain extent lifts it and carries it forward. The
+entire surface is also exposed to the action of the current. A stream
+having an equal velocity but a less depth in proportion to the diameter of
+the solid matters to be transported, evidently has less transporting
+power. * * * An amount of sewage which can be properly transported by a
+circular sewer of a given size, cannot be as efficiently transported by
+one of larger diameter."
+
+From some strange idea, which is apparently without foundation in logic or
+based on any actual justification from experience, it has of late years
+become the practice of designing engineers to make the 8-in. circular
+pipe the smallest size for sewers; and it is not improbable that the
+designer of the Monterrey system has merely followed this example. It has
+also become the frequent practice of designers to give every length of
+sewer all the grade possible, regardless of the fact, taught both by
+hydraulics and experience, that the best grade is that which will give as
+much depth of flow as is consistent with a scouring velocity.
+
+Some years ago it was the standard practice, in the "strictly separate
+system" of sewers, to use the 6-in. pipe as the minimum size, and, as far
+as the writer has been able to discover, after giving the matter a rather
+extensive investigation, the 6-in. size has given excellent results
+wherever its use was proper. In places where it has not succeeded there
+were excellent reasons why it should not have been selected, and these
+could easily have been observed at the time the designs were made. The
+best sizes for the sewers in a given system is always a matter to be
+determined by local conditions; but there seems to be no reason why the
+6-in. size should not be used where the flow is so slight that the 8-in.
+will not work well; or where the velocity must of necessity be so great
+that a flotation depth of flow cannot be maintained in the larger size. As
+to likelihood of clogging and stoppage, the writer's opinion, based on the
+maintenance of three rather extensive systems in different parts of the
+United States, in each of which the 6-in. size comprises more than 75% of
+the whole length of pipe, and of three other systems, one having 12-in.
+and two having 8-in. as the minimum sizes, is that the 6-in. size, where
+properly used, is less likely to become clogged than either of the others
+used improperly. The cost of maintaining the 6-in. pipe lateral, under
+these circumstances, is much less than that of maintaining the 8-in.
+lateral.
+
+The 6-in. pipe is not being used now as much as the 8-in., and in most
+cases this is probably because the capacity of the latter is nearly double
+that of the 6-in., and costs only a few cents more per foot. If there is a
+sufficient population per acre, or if, within 30 or 40 years, such a
+population is anticipated as will fill the 8-in. pipe half full, its use,
+of course, is justified and necessary; but where it is quite evident that
+this will never occur, its use is counter-indicated.
+
+In Monterrey, where the building lots have a frontage of 41 ft., where the
+houses, as a rule, are only one story high, where the water service is
+metered and paid for, and the sewage flow is also paid for, there seems to
+be no reason to justify the use of 8-in. pipe for the upper reaches of the
+smallest sewers. The sewage flow to be anticipated will probably never be
+sufficient to keep an 8-in. pipe sewer in a good clean condition at the
+upper ends of the lines of sewers without excessive flushing; and the
+sharper or steeper the grade on which it is placed, the worse will be the
+result, because the sharper the grade, the thinner the flowing thread of
+sewage will be drawn out in the invert; on the other hand, if the grades
+are flat, the slight quantity of sewage flow will be spread out in a
+sluggish stream, without sufficient depth, on the bottom of the 8-in.
+pipe.
+
+Where a wide surface is given to a small quantity of flowing sewage, it
+stagnates slowly along the bottom of the sewer, leaving frequent deposits
+to undergo decomposition and create foul air, if not to choke the sewer, a
+result often produced; and where a circular sewer which is too large for
+the ordinary flow is given a strong velocity by using steep grades, the
+stream, though flowing rapidly, is drawn out to such a thin thread that it
+will not effect the flotation of the solid masses in the sewage brought in
+at house connections, and the shallow and thin stream simply flows around
+such masses until a dam or obstruction forms and the sewage is backed up
+sufficiently to force the obstruction farther down, to form another
+obstruction in a larger pipe below. Flushing may possibly keep such a
+sewer fairly clean; but, as usually practiced, it is effective only for a
+few hundred feet from the flush-tank; and the quantity of flush-water
+required by an 8-in. pipe is more than twice as much as that required to
+keep the 6-in. pipe clean. Ventilation is better in the smaller sewer than
+in the larger, as there is less air to move; but the elaborate ventilating
+stacks provided at Monterrey may take care of this; and it is evidently a
+place where ventilation will be needed.
+
+The ideal size and shape of cross-section for a sewer is such as will give
+the best flotation to moving solids which are being carried along by the
+flow; and this means the sewer that, with the expected ordinary or average
+flow, will give the best depth in the invert, when the velocity of flow is
+sufficient to keep suspended solids, grit, etc., moving at a rate of from
+2 to 3 ft. per sec. The size, however, is limited by practical
+considerations. The circular pipes cannot well be less than 6 in. in
+diameter, because the house connections cannot well be less than 4-in.
+pipe, and the sewer should be larger than the house connections, for
+various practical reasons; but, in order to secure flotation and a
+scouring flow, the smallest pipe, or the pipe having the smallest invert
+radius, that practical considerations permit, should be selected. The
+grade should be such, and the collecting system so laid out, that the flow
+may be conserved as far as possible, and the sewage flow should be kept of
+as great a depth in the invert, or bottom of the sewer, as safety in
+self-cleansing velocity will permit. This will save flush-water and
+prevent stoppages, and thus reduce the cost of maintenance to a minimum.
+For good sanitary practice, the sewers should be designed, first of all,
+to comply with the requirements of the present, or immediately expected,
+ordinary flow, with some reasonable allowance for the future. They should
+be neither too large nor too small, and the grade should neither be too
+great nor too little, to secure the best flotation and scouring effects
+and the best flush-wave action under all circumstances.
+
+The use of cement concrete pipe for sewers seems to be growing in favor;
+nor is this surprising, in view of the many improvements made in their
+design and manufacture. The excellence of the concrete pipe used in
+Monterrey and its success, suggest the query: Why was it not used still
+more extensively?
+
+Table 13 shows that the cement pipe cost much less than the vitrified
+tile, or "fire-clay" pipe. Thus, the 38.1 cm. (15-in.) fire-clay cost 6.14
+pesos per lin. m., the 45.7 cm. (18-in.) cost 8.80 pesos, and the 50.8 cm.
+(20-in.) cost 11.30 pesos. Compared with this, the concrete pipe was much
+the cheaper; the 55.9 cm. (22-in.) cost 5.93 pesos, which is less than the
+cost of the 38.1 cm. (15-in.) fire-clay; and the 61.0 cm. (25-in.)
+concrete pipe cost 7.30 pesos, which is less than the 45.7 cm. (18-in.)
+fire-clay.
+
+The writer's experience with concrete pipe, derived mainly from a long
+service in sewer design and construction in Brooklyn, N. Y., leads him to
+believe that at Monterrey the whole sewer system might, with advantage,
+have been built of concrete pipe, using an egg-shaped pipe with an area
+slightly larger than an 8-in. circle, designed for a discharge equal to an
+8-in. pipe for all the smaller sewers. The invert of such an egg-shaped
+pipe would fulfill the present requirements in carrying a very small flow
+with good flotation depth, better than would a 6-in. circular pipe, and
+the reserve capacity of the 8-in. pipe would be secured without
+interfering with good present service. Egg-shaped pipes, similar to those
+used in Brooklyn, the writer believes, would have given far better
+satisfaction throughout the Monterrey sewerage system than circular
+fire-clay pipe, and would have cost no more, but probably less. The
+egg-shaped pipe referred to is made with a flat base and a self-centering
+joint, thus insuring perfect alignment, and a smoother interior surface
+than can be obtained with fire-clay pipes.
+
+Brooklyn has about 450 miles of concrete pipe sewers, of all sizes less
+than 24 in., the greater part of which is egg-shaped. There are also about
+250 miles of vitrified stoneware circular pipe sewers of similar sizes,
+and the cost of repairs and replacing pipe, over a period of years is
+about the same per mile for each kind. Incidentally, it may be stated that
+the annual cost of repairs per mile on both kinds of pipe is very small,
+and is only about one-fifth of the cost of repairs per mile on the brick
+sewers, of which there are about 200 miles.
+
+The principal advantages and disadvantages of cement concrete pipe sewers
+may be summed up as follows:
+
+                      ADVANTAGES OF CONCRETE PIPE.
+
+  (a) Cement concrete pipe is usually less costly than vitrified
+      pipe.
+
+  (b) It can be formed in any shape desired.
+
+  (c) It is not cracked by vibration, and resists impact better than
+      vitrified pipe, for which reason it is a better material to
+      lay near the surface of a street in which there is heavy
+      traffic.
+
+  (d) It is not affected by ordinary sewage.
+
+  (e) The cost of repairing and maintaining is about the same as for
+      a vitrified pipe sewer.
+
+  (f) It can be made in the city or town where it is to be
+      installed, thus giving the locality the advantage of having
+      some of the money paid for labor in its manufacture spent in
+      the place where the sewers are being put in, where it is
+      raised as a tax, etc.; also saving freight charges, etc.
+
+  (g) It can be made under the most careful local supervision and
+      inspection, of selected material, by the engineer who is
+      responsible for the success of the work. Vitrified pipe can
+      seldom be made in this way.
+
+                      DISADVANTAGES OF CONCRETE PIPE.
+
+  (a) If not carefully made and of the best of materials, it is
+      subject to failure by disintegration, etc.
+
+  (b) It will not stand strong chemical action, and therefore the
+      smaller sizes should not be used where they are likely to be
+      exposed to trade wastes containing strong acids. In the larger
+      sizes the quantity of flow mixes so quickly with the trade
+      wastes that this danger is minimized, and it is very seldom
+      that even the smaller sizes become affected; but vitrified
+      pipe may be used in places where chemical action is
+      anticipated.
+
+  (c) If not properly made, it will be attacked by steam and hot
+      vapor, and by animal fats in the sewage; but, if properly
+      made, it is not affected by these.
+
+  (d) Unless reinforced or made very thick, it will not stand as
+      great a crushing load as the best vitrified stoneware pipe;
+      but, as sewers are not intended to be used under very heavy
+      pressure, this is not so very important. It is amply strong to
+      withstand any internal pressure or any external crushing load
+      to which it probably will be submitted.
+
+  (e) Under a considerable head of ground-water, it may permit water
+      to infiltrate through its walls for a considerable time after
+      it is laid, thereby temporarily increasing the flow, which, if
+      the sewage is to be pumped, will increase the cost of pumping.
+      This difficulty can be met by using a carefully selected mix
+      of materials in making the pipe, and by making the joints
+      carefully. Infiltration through concrete diminishes rapidly
+      after the sewer is in use; it occurs in vitrified pipe, also,
+      to some extent.
+
+The house connection drain adopted in Monterrey, with the disconnecting
+trap, is very much like one which the writer has seen introduced with very
+bad result. These are being removed as rapidly as possible by one of his
+clients, a sewerage company, in the Southern States. It has been a
+fruitful cause of stoppages and bad smells; the ordinary method now in
+general use is much better. In the design shown, it would seem that there
+may even be some danger that the ventilation of the sewer by the
+stand-pipes in the streets may force the traps.
+
+One is rather surprised to learn that the main outfall sewer is designed
+with a capacity of 90,000,000 liters per day, the present sewage being
+estimated as not more than 18,000,000 liters, and the far future being
+thought to require only 40,000,000 liters. Why this excessive size?
+Possibly the surplus water which it is to carry is to be discharged into
+the sewers from the water supply system direct, and is intended for
+irrigating the land at the disposal area, when the sewage is insufficient
+for this purpose. The author states that all surface water is strictly
+excluded.
+
+The method of sewage disposal gives rise to several questions. It is
+proposed to use an extensive area for growing crops, which are to be
+irrigated with sewage. The paper states that the underlying strata at
+Monterrey contain numerous caverns, and the first question is: What will
+be the effect on the water supply of other towns lower down the valley?
+The writer recollects a serious outbreak of typhoid fever in Bluefield, W.
+Va., caused by the pollution of the water in similar strata finding its
+way through unknown underground caverns and channels to the city's water
+supply.
+
+The next question is: What crops will be grown? It is a well-known fact
+that vegetables grown by the use of sewage as a fertilizer, are unsafe in
+a raw state for human consumption. This is well-known to European
+travelers in China and Japan, where the use of fecal matter as fertilizer
+renders the various water supplies (where not filtered and disinfected)
+and all green vegetables, unsafe, on account of typhoid germs. Moreover,
+crops not intended for human consumption, which are grown on lands
+irrigated by sewage bearing typhoid germs, etc., are unsafe for men to
+handle; even to store them may cause a dissemination of disease. It is
+evident, therefore, that the whole sewage flow should be in some manner
+disinfected at least, if not filtered, before it is used.
+
+The method of sewage disposal and the use of merely settled septic sewage
+for irrigation seem to be open to objection. The disposal plant is not
+sufficiently effective to meet the present requirements of sanitary
+science; and the sludge-pit will be certain to breed a pest of flies, if
+it is not also an intolerable nuisance on account of foul smells.
+Monterrey would seem to be a proper place for the introduction of the
+Imhoff tank, with percolating filters, and a final settling tank, the
+effluent being disinfected, before entering the latter tank. The flow
+might then be used safely for irrigation purposes for crops not to be
+eaten uncooked by man. The writer does not see how the method provided can
+possibly fulfill the object stated, to distribute on the land an effluent
+which will be "innocuous and clear," or how any consequential degree of
+purification can be obtained in the tanks provided.
+
+While there are described in this paper many things to find fault with,
+there are also many things to commend. The water supply system, with its
+reservoirs, etc., seems to be admirable; and the methods of construction
+by which the expense for forms was reduced is very interesting. The
+parking and ornamentation of the grounds over the reservoir roofs cannot
+fail to benefit the people and popularize the work.
+
+
+RUDOLF MEYER, M. AM. SOC. C. E. (by letter).--The writer, as Engineer for
+the Government (guaranteeing the concessionaires a gross return of 10% per
+annum on the capital invested), and as inspector of the various works has
+had exceptional opportunities to become acquainted, not only with their
+construction, but also with events leading up to the granting of the final
+concession under which they were built and will be extended. In order to
+judge of the extent to which the different engineers, in their turn
+contributed toward the design of these works, the writer has thought it
+desirable to submit a complete statement of all matters relating to the
+inception, investigations, surveys, tests, etc., previous to the adoption
+of the present plans.
+
+Data regarding former investigations, plans, and concessions which have
+since lapsed, have been obtained from the Government archives. These refer
+to periods prior to Mr. Conway's engagement, and anterior to the retaining
+of Mr. Schuyler by the concessionaires, and Mr. Binckley's connection with
+the scheme, and they are presented here as complementary to the
+information in the paper.
+
+Samuel M. Gray, M. Am. Soc. C. E., acting in the interest of some American
+capitalists (who had been induced by Col. J. A. Robertson, of Monterrey,
+to look into the merits of a concession acquired by him, for building
+these works), being guided by the Government's proposition to supply the
+city with water by damming the flood-waters of the Santa Catarina River in
+the narrow gorge through which the stream emerges from the Sierras, some
+eight miles from the city, had several soundings made and reservoir sites
+surveyed in the first two box canons up the river, and prepared and
+presented to the Government several alternative projects, besides the one
+mentioned by Mr. Schuyler. Several different dam sites were designated by
+Mr. Gray, whose investigations extended over some two years, and were
+finally abandoned after he had designed the general outlay for a complete
+network of water mains and sewers for the city, on account of the
+unwillingness of the Government at that time, about 1897, to grant any
+guaranties as to bonds or income to the concessionaire or his assigns. Mr.
+Gray did not favor the general scheme of storing flood-waters as a water
+supply, but strongly recommended to the attention of the Government the
+greater advantages of deriving the supply from subterranean flow in the
+river, by an infiltration gallery driven into the water-bearing gravels in
+the Santa Catarina Canon (only a short distance above the place where Mr.
+Binckley afterward established his bore-holes across the river). He
+proposed to take advantage of the steep slope of the river at a turn in
+the canon, and from the lower end drive a tunnel through a projecting rock
+spur, which tunnel, though starting well above the ordinary reach of
+floods, would terminate in water-bearing gravel, at a sufficient depth
+below the surface of the river-bed to intercept part of the underflow. Mr.
+Gray, through investigations made under his direction, by Nathaniel
+Turner, M. Am. Soc. C. E., had ascertained that there was an abundant
+subterranean flow, and work had actually been started on the proposed
+tunnel.
+
+The results of Mr. Gray's investigations were put at the disposal of
+Messrs. Mackenzie, Mann & Co. by Mr. Robertson, at whose offices Mr.
+Binckley prepared the first plans submitted by him for the approval of the
+Government.
+
+After Mr. Gray's investigations, Messrs. Mackin and Dillon (F. H. Dillon,
+Assoc. M. Am. Soc. C. E.), under contract with the Government, prepared
+the following plans: For a dam in the Santa Catarina Canon; for a pipe
+line, similar to the one proposed by Mr. Gray, to a reservoir and settling
+basin on the left bank of the river (a short distance above where the
+provisional pumping station was established afterward by Mr. Binckley),
+but on the flat above the bluff skirting the river, practically at the
+same elevation as the present high-pressure reservoirs; for a complete
+network of water mains and sewers in the city, indicating the approximate
+direction in which the sewage would be disposed of, either by turning it
+into the river or by spreading it over suitable lands, the location of
+which was to be determined later; and also a complete set of
+specifications.
+
+On these data bids were invited by publication, and inquiries were
+received from several parties. Finally, Messrs. Stocker and Walker, of
+Scranton, Pa., entered into negotiations with the Government, and the
+present concession was agreed upon and granted.
+
+Messrs. Stocker and Walker engaged the late E. Sherman Gould, M. Am. Soc.
+C. E., to prepare a plan for a storage dam in the Santa Catarina Canon,
+and submitted plans for water distribution and sewers in the city,
+slightly modifying the original plans of Messrs. Mackin and Dillon.
+
+In the fall of 1905, the concession was acquired by Messrs. Mackenzie,
+Mann & Co., of Toronto, Canada, together with all plans, etc.,
+presented by the original concessionaires. The new concessionaires stated
+that they would examine the whole situation again, for the purpose of
+presenting modified plans for works.
+
+Mr. Schuyler, in the interest of the new owners, had paid one flying visit
+to Monterrey when Mr. Gray's projects were brought to his notice, and the
+writer had an opportunity to show him the tunnel which had been started.
+Mr. Schuyler left for Brazil and did not return until February, 1906, when
+he was accompanied by the Chief Engineer appointed by the concessionaires.
+Messrs. Schuyler and Binckley then prepared plans for the water
+distribution and sewer systems in the city and for a provisional water
+supply to be pumped at San Geronimo, some two miles up the river. The new
+plans for the city work followed closely the general disposition by Mr.
+Gray, the principal difference being that the main reservoirs for the
+permanent water supply were located to the south instead of to the west.
+This change was due to the results of an investigation, made during Mr.
+Schuyler's absence in Brazil, by Mr. F. S. Hyde, late Hydraulic Engineer
+of the Necaxa Water Power plant, who, accompanied by the writer, visited
+the whole water-shed of the Santa Catarina River in October, 1905, in
+search of suitable dam sites and prospects of power development. Mr. Hyde
+extended his studies to the Santiago Canon, southeast of the city,
+recommending finally that the water be brought from that canon, and that
+wells be dug in different points of the Santa Catarina River between San
+Geronimo and the entrance of the canon, and tested by pumping, for the
+purpose of establishing levels and ascertaining the available amount of
+underflow, with a view of determining the location for an infiltration
+gallery high enough up the river to permit of a gravity delivery and under
+good pressure in the city.
+
+In view of Mr. Hyde's report, and as the result of a visit to the Santiago
+Canon, Mr. Schuyler decided to locate the reservoirs south of the town,
+intending to bring in water from the southeast, from springs in the
+Santiago Canon, and also by infiltration from Santa Catarina, his and Mr.
+Binckley's scheme of water supply being for the same pressure throughout
+the city.
+
+To supply water during construction, and partly meet the demands of the
+city, Mr. Binckley, on his arrival, decided to establish a provisional
+pumping station at the well in the river nearest to town, started by
+direction of Mr. Hyde at San Geronimo. This well was situated within the
+bed of inundation of high floods, on a low bank, at the foot of a
+conglomerate bluff some 20 ft. high, limiting a flat which was above the
+reach of any flood. It was on the same side of the river as the city, and
+there was plenty of good ground on the flat above for the establishment of
+a reservoir.
+
+A slightly shorter pipe line was secured by crossing the river, building
+the reservoir (a substantial concrete-lined and vaulted-over structure) on
+the opposite bank, laying out the pipe line to follow that bank nearly to
+the city, and finally crossing back again; but the result has been that
+since the flood of August, 1909, in which the river crossings were
+destroyed, the reservoir remains isolated on the other side of the river
+from town, though intended to form part of the permanent works and act as
+a compensating reservoir for equalizing the pressure of the high-pressure
+system. Fortunately, the pumping station, the larger pumps, and the
+boilers, had been moved up the bank (after a rapid rise in the river on
+August 10th, 1909) to the new wells established by Mr. Conway on the line
+of the proposed prolongation of the infiltration gallery. The reservoir,
+however, is left to stand alone on the other side of the river, and its
+usefulness will not be restored until a new line is laid across the river,
+re-establishing its connection with the new pump line and the new and
+permanent pipe line to be laid along the north bank from the pumping
+station to the city. This will free Monterrey from the constant menace of
+a water famine. At present its two main water supplies may be cut off by
+unexpected floods like those of 1909 and 1910, as both supplies are
+carried across the river, and though only the cast-iron pipe connecting
+with the water supply from Estanzuela was carried away by the flood, the
+concrete conduit of the San Geronimo low-pressure supply was seriously
+threatened. Such risks are too great to be carried for any length of time;
+besides, a succession of dry years would cause such a reduction in the
+Estanzuela supply as to require an additional reserve in the way of
+pumping stations drawing on the under-flow of the river, such as already
+exists in San Geronimo.
+
+Afterward, Messrs. Schuyler and Binckley submitted preliminary plans and
+profiles for the projected concrete gravity conduit from Estanzuela to the
+reservoir south of the city, and Mr. Binckley submitted excavation plans
+for two reservoirs, only one of which was built, and from designs by Mr.
+Conway.
+
+Stephen E. Kieffer, M. Am. Soc. C. E., was intrusted by Mr. Binckley with
+the revision of the plans of the water distribution and sewers. The
+southern half was approved by the Government and executed according to his
+plans; the northern part was afterward revised by Mr. Conway and has been
+partly built.
+
+The final maturing of the project of an infiltration gallery in San
+Geronimo as a low-pressure gravity supply, the division of the city into
+high- and low-pressure districts corresponding to the two supplies, with
+one reservoir, instead of two to the south of the city, and the other to
+the west at the Obispado, the entire details of both these gravity
+schemes, and of the whole sewage disposal scheme, as well as the
+modification introduced into the city work for the northern half, are
+unquestionably due to Mr. Conway, independently of the general views which
+may have been held on those points by other engineers.
+
+In March, 1910, Mr. Conway left Monterrey, all the principal works being
+finished. Since that time Vicente Saucedo, Assoc. M. Am. Soc. C. E., has
+put in many additional water mains and sewers in the northern part of the
+city, and is finishing the _force majeure_ work caused by the destruction
+wrought in the districts along the river banks by the extraordinary
+floods.
+
+The writer, having had an opportunity to watch the earnest efforts of the
+several engineers connected with these works, in the course of their
+design and construction, resulting without doubt in being the first of
+their kind built in Mexico, has been induced to contribute this discussion
+in order to bring out clearly the share of each.
+
+Mr. Pitkethly's apprehensions as to the adequacy of the system of
+ventilation adopted have not been realized, in part perhaps because the
+houses, though generally of only one story, have such high ceilings that
+the tops of their vent pipes are generally higher than the ventilating
+columns at the heads of the branch sewers.
+
+
+GEORGE ROBERT GRAHAM CONWAY, M. AM. SOC. C. E. (by letter).--The writer
+regrets that some features of the works described in this paper have
+failed to call forth the many useful criticisms which he expected, and his
+remarks, therefore, are limited to the few points which have been raised.
+He is particularly indebted to Messrs. Schuyler, Meyer, and Saucedo for
+adding supplementary information of value to the paper, but regrets that
+he cannot support Mr. Binckley in his claim that "the entire general
+design of the system, as well as the extensive hydrological studies and
+final selection of the sources of water supply, was completed in 1906,"
+etc. On May 1st, 1907, when the writer assumed responsibility as Chief
+Engineer, he was unfortunately confronted with the fact that very little
+data and only a few preliminary and incomplete plans were available. His
+first duty was to report upon the final sources of supply, and the
+recommendations made in his report (dated July 12th), received Mr. (now
+Sir William) Mackenzie's approval during the same month. The final plans,
+upon which the approval of the State Government was definitely obtained,
+were prepared by the writer during the summer of 1907, were submitted to
+the Governor of the State, Gen. Bernard Reyes, on October 19th, and
+received his approval on December 12th, 1907. No works, with a long
+preliminary history, such as those at Monterrey, can rightly be said to be
+due to any one individual; many engineers contributed to the final result,
+and the writer willingly acknowledges his indebtedness to the able men,
+who, for ten years prior to the construction of the works, investigated
+the particular problems which were met--problems which were not only of an
+engineering and physical nature, but racial and financial. The
+responsibility of constructing the works in their present form, and
+leaving them practically complete, did, however, fall on the writer's
+shoulders.
+
+Messrs. Pitkethly and Hammond have criticized the basis of the
+calculations upon which the sewer system was laid down. In considering
+this problem, it is necessary to remember that, in designing this system,
+there was practically no information upon which to base the calculations;
+and the writer believed that the wisest course was to anticipate a liberal
+growth, and provide a large margin of safety. In designing a sewer system
+in older and well-established communities, the engineer is generally able
+to compile considerable information regarding the probable sewage flow for
+which it is necessary to provide. In Monterrey this quantity was
+absolutely unknown. The writer's practice in other places has been to
+assume that about 8% of the total daily discharge of sewage will flow off
+in one hour; and, from many curves which he has plotted regarding sewage
+flow in British towns, this rate appears to him to be approximately
+correct. In Monterrey, however, the old Mexican traditions are rapidly
+changing, and the city is now becoming one of the most Americanized in
+Mexico; the old one-story houses will give way in time to buildings of
+several stories--a change, already noticeable, which has occurred during
+the past few years, particularly in the business portion of the city.
+Taking these facts into consideration, it is believed that it would be,
+not only bad engineering, but bad business, for a company whose concession
+lasts 99 years, to provide sewers as small as 6 in., as Mr. Hammond would
+recommend, and then be called upon, under the terms of the concession, to
+relay larger sewers at a future date, thus incurring further capital
+expenditure upon which no Government guaranty would apply, and no further
+revenue be obtained. In matters of this kind, not only the engineering,
+but the commercial, aspect of the question must be kept in view, and this
+point, the writer must frankly admit, he has always seriously considered.
+
+The writer's experience with reference to the method of ventilating sewers
+by tall columns extends over many years, and he still maintains that no
+other system gives such satisfactory results. In this view he finds
+considerable support in a recent paper on "Salisbury Drainage," by Mr. W.
+J. E. Binnie,[11] written since the system at Monterrey was installed, in
+which the result of a series of experiments carried on during 1906-07 are
+given. At Salisbury, England, 68 ventilators, 6 in. in internal diameter,
+30 ft. high, were connected to the main sewer by 6-in. stoneware pipes.
+They were placed about 540 ft. apart, and, from careful anemometer
+readings, the following conclusions were reached:
+
+[11] _Minutes of Proceedings_, Inst. C. E., Vol. CLXXXI, p. 317.
+
+  "(1) That four ventilators all lying in the lower portion of the
+       town acted sometimes as air-inlets and sometimes as
+       air-outlets, and that the other sixty-four acted as
+       air-outlets.
+
+  "(2) That the average velocity of the air escaping up these
+       columns was 3.2 feet per second, representing the circulation
+       of 3,600,000 cubic feet of air per diem, or sufficient to
+       change the air in the sewers every 10 minutes.
+
+  "(3) That the average velocity of the current of air in the
+       ventilating-column increases with the size of the sewer to
+       which it is connected, averaging 2.4 feet per second with the
+       7-inch sewer, 3.6 feet per second with the 9-inch sewer, 3.7
+       feet per second with the 12-inch sewer, and 4.1 feet per
+       second with the 15-inch sewer in these experiments.
+
+  "(4) That the draught in the column is very largely dependent on
+       the wind, being at its minimum on a still day, and could
+       therefore be readily increased by the use of a suitable cowl.
+
+  "(5) That the draught is very little affected by the
+       sewer-gradients. It was expected that, in ventilating-columns
+       placed in connection with the upper end of a sewer laid at a
+       steep gradient, a strong draught would have been obtained. No
+       direct connection, however, was traceable."
+
+As the result of these experiments, Mr. Binnie rightly came to the
+conclusion that this system of ventilation was efficient.
+
+Mr. Hammond anticipates that the house connection trap system at Monterrey
+will lead to bad results, but the writer has seen the system at work in
+many widely different cities with excellent results. He believes that it
+is in accord with the best practice of the most eminent sanitarians during
+the last 20 years, and has no apology to make for introducing that system
+in Monterrey.
+
+Regarding Mr. Hammond's summary of the advantages of concrete pipes for
+sewer construction, the writer is in entire agreement, and would willingly
+have introduced them throughout the whole of the Monterrey system, but for
+the fact that it was an exceedingly difficult matter to obtain suitable
+sand for their manufacture during the early days of construction, and
+considerable delays would have arisen if a complete network of such pipes
+had been used. His later experience at Monterrey, when the sand difficulty
+had been solved, clearly showed that concrete pipe could be laid down at
+much less expense than fire clay.
+
+Both Mr. Pitkethly and Mr. Hammond refer to the system of liquefying tanks
+used at Monterrey preparatory to turning the sewage on the irrigation
+lands, and both express doubts as to their efficiency. The writer is now
+separated from his library and notes by many thousands of miles, and
+cannot quote "chapter and verse" as accurately as he would like, in order
+to support his views that the system adopted was adequate for dealing
+with a system such as that at Monterrey. It must be pointed out that not
+only was it intended to prevent the sewage from becoming a nuisance, but
+that the sewage flow plus a large quantity of surplus water was intended
+to be used profitably for irrigation purposes. With that object, the
+Company--or rather its allied Company, the Monterrey Railway, Light, and
+Power Company--obtained the control of 2,246 acres of the very finest
+arable land, with almost perfect natural drainage conditions, so that this
+land could be utilized to create a profitable revenue from the use of the
+sewage. The outfall sewer was accordingly designed to carry sufficient
+water and sewage to irrigate about 2,500 acres of land, which area could
+be considerably extended if necessary at any future time.
+
+Most authorities now agree that before turning sewage upon land, a
+preliminary treatment is required to remove as much as possible of the
+suspended matter, and then reduce the latter by subsidence in liquefying
+or septic tanks, so that the quantity remaining in the effluent is so
+small and finely divided that it may be readily decomposed and oxidized by
+bacterial action without risk of clogging the surface or interstices of
+the land upon which it may discharge.[12]
+
+[12] See Raikes, "Sewage Disposal Works," pages 97-98.
+
+Mr. Pitkethly quotes Messrs. Watson and O'Shaughnessy as saying, in their
+evidence before the Royal Commission on Sewage Disposal, that not more
+than 10% of the solids are digested in septic tanks, but it must be
+remembered that in many other places evidence was given before the same
+Commission showing that from 25 to 30% was actually obtained.
+
+Mr. J. D. Watson, in his paper, "Birmingham Sewage-Disposal Works,"[13]
+read in March, 1910, points out that:
+
+[13] _Minutes of Proceedings_, Inst. C. E., Vol. CLXXXI, p. 259.
+
+    "The much-maligned sewage-farm still may be allowed (where the
+    conditions are favourable) to rank as one of the best methods
+    of sewage-disposal. Diverse opinions may be held as to what are
+    favourable conditions, particularly as conditions are sure to
+    vary widely with locality; but it may be assumed that where
+    there is 1 acre of suitable land per 100 persons, as in Berlin
+    and several other important cities, the efficiently-worked
+    sewage-farm, when judged solely by the standard of the effluent
+    produced, is still in the front rank. Effluents from such a
+    farm are remarkable for their paucity of micro-organisms, their
+    low albuminoid ammonia, and their unvarying character."
+
+Assuming that not more than 2,000 acres of the irrigated land at Monterrey
+were available for sewage purposes, this area would represent the sewage
+treatment of the present population of not more than 45 persons per acre,
+and on the basis of the design, that is, for a population of 200,000
+persons, this represents not more than 100 persons per acre. In many
+sewage farms on the continent of Europe, the number treated per acre
+varies between 80 and 200 persons; for example, at Breslau it is 187, at
+Berlin 105, at Brunswick 88, and at Steglitz 185.
+
+Regarding the crops to be grown on the land, very satisfactory results
+were obtained from growing Indian corn, and two excellent crops per annum
+were taken from an area of 500 acres during the period in which the writer
+was responsible for the works. It was also his intention to grow alfalfa,
+and turn a part of the land into a pecan grove, and, although he does not
+share the apprehensions of danger of either Mr. Pitkethly or Mr. Hammond
+as to growing root crops, he believes the growth of alfalfa, Indian corn,
+oats, barley, and pecan and fruit trees is eminently suitable for the
+land, which is a deep rich loam, from 4 to 8 ft. deep, overlying the
+"sillar" formation referred to in the paper. The writer has seen many
+sewage farms during the last 18 years, upon which root crops of excellent
+quality have been grown, and not the least suspicion has ever been raised
+regarding their use.
+
+In reference to the adoption of the monolithic form for constructing the
+South Reservoir, the writer is so convinced as to its economy that had he
+to build this reservoir again, he would adopt the same method. Mr.
+Binckley, in drawing attention to the method of construction, has
+overlooked the fact that the cost of forms for a reservoir 30 ft. deep was
+a very serious item, and warranted the adoption of this new method, not
+only on account of economy but because of rapidity of construction; while,
+in the case of the Obispado Reservoir, which is very much shallower,
+simpler forms could be and were adopted.
+
+Mr. Saucedo's remarks regarding the repetition of the extraordinary floods
+of August, 1909, in September, 1910, are particularly interesting, and
+show how abnormal conditions are in so dry a section of Mexico as the
+State of Nuevo Leon. These two floods, the writer believes, are among the
+most instructive in North America, particularly when one remembers that
+prior to 1909 the average rainfall during a period of 15 years, was less
+than 22 in. per annum.
+
+             TABLE 18.--COMPARISON OF VOLUME OF FLOODS, ETC.
+
+  +------------------------------+-----------+----------+-------+--------+
+  |                              |           | Maximum  |Cu. ft.| Annual |
+  |                              | Drainage  | recorded | /sec. | amount |
+  | River.                       | area, in  | flow, in | per   |   of   |
+  |                              | square    |  cu. ft. |square |  rain- |
+  |                              | miles.    | per sec. | mile. |  fall. |
+  +------------------------------+-----------+----------+-------+--------+
+  | Santa Catarina, Monterrey,   |           |          |       |        |
+  |   August 27th, 1907          |      544  | 235,000  | 432   |  22    |
+  | Estanzuela, near Monterrey,  |           |          |       |        |
+  |   August 28th, 1909          |       3.5 |   2,900  | 825   |  25    |
+  | Tansa, India                 |      52.5 |  35,000  | 666.7 | 101    |
+  | Krishna, India               |     345   | 118,000  | 342.6 | 258    |
+  | Coquitlam River, Vancouver   |     100   |  12,000  | 120   |147-189 |
+  | Sweetwater, Cal.             |     186   |  18,150  |  99   |  ...   |
+  | Delaware, Lambertville, N. J.|   6,820   | 250,000  |  36.5 |  45    |
+  | Colorado, Austin, Tex.       |  37,000   | 123,000  |   3.3 |  24.5  |
+  | Ohio, Cairo, Ill.            | 214,000   | 700,000  |   3.3 |  54.9  |
+  +------------------------------+-----------+----------+-------+--------+
+
+Table 18, compiled by the writer, shows how very extreme the floods of
+1909 were compared with those on other rivers, while those of 1910,
+referred to by Mr. Saucedo, although not so great, would appear to have
+reached a rate of flow of about 300 cu. ft. per sec. per sq. mile of the
+drainage area.
+
+The writer agrees with Mr. Saucedo that in the semi-arid regions of Mexico
+and the Southern States, and also in India, the possibility of these
+abnormal floods is an important consideration in the design of hydraulic
+works.
+
+       *       *       *       *       *
+
+                       Changes To This Document
+
+Transcriber's Note: The table of contents has been added. Blank pages
+have been deleted. Illustrations may have been moved. Discovered
+publisher's punctuation errors have been corrected. Some wide tables
+have been re-formatted to narrower equivalents with some words replaced
+with commonly known abbreviations and possibly a key. Some ditto marks
+have been replaced with the words represented. In addition, the
+following changes or corrections were made:
+
+ p. 501: but the tampers had had[del 2nd had] previous experience
+ p. 508: shown on Plates VI to IX[VI, VII, VIII, IX[to accomodate links]]
+ p. 516: at this place there is a considererable[considerable] area
+ p. 538: based on the following rates and and[del 2nd and] percentages
+ p. 579: by crossing the river, build-the[building the] reservoir
+ p. 550: [For Table 14: added "Total materials cost"]
+ p. 566: respectively (Fig. 5)[(Fig. 4)], together with lack of
+ p. 584: [Table 17 renamed to Table 18 to avoid duplication.]
+ p. 584: Table 17[18], compiled by the writer, shows how very extreme
+
+       *       *       *       *       *
+
+
+
+
+
+End of the Project Gutenberg EBook of ASCE 1193: The Water-Works and
+Sewerage of Monterrey, N. L., Mexico, by George Robert Graham Conway
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