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diff --git a/38455.txt b/38455.txt new file mode 100644 index 0000000..83174a6 --- /dev/null +++ b/38455.txt @@ -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 + +*** END OF THIS PROJECT GUTENBERG EBOOK ASCE 1193: THE WATER-WORKS *** + +***** This file should be named 38455.txt or 38455.zip ***** +This and all associated files of various formats will be found in: + http://www.gutenberg.org/3/8/4/5/38455/ + +Produced by Juliet Sutherland, Henry Gardiner and the +Online Distributed Proofreading Team at http://www.pgdp.net + + +Updated editions will replace the previous one--the old editions +will be renamed. + +Creating the works from public domain print editions means that no +one owns a United States copyright in these works, so the Foundation +(and you!) can copy and distribute it in the United States without +permission and without paying copyright royalties. Special rules, +set forth in the General Terms of Use part of this license, apply to +copying and distributing Project Gutenberg-tm electronic works to +protect the PROJECT GUTENBERG-tm concept and trademark. 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