ASCE 1193: The Water-Works And Sewerage Of Monterrey, N. L., Mexico Part 1

ASCE 1193: The Water-Works and Sewerage of Monterrey, N. L., Mexico.

by 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, wis.h.i.+ng to render a service to his king, Philip II of Spain, a.s.sembled 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 princ.i.p.al 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 12' west of Mexico City, and in lat.i.tude 26 40' N. It is a distributing railway center on the main line of the National Railroad, 270 km. from the Rio Grande at Laredo, 1,022 km. from Mexico, and 520 km. from Tampico by the Mexican Central Railway. It is the center of many large industries, and is the second largest manufacturing city in the Republic.

THE CONCESSION.

The works described in this paper were carried out under a guaranteed concession granted by His Excellency, General Bernardo Reyes, Governor of the State of Nuevo 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 const.i.tute 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 ma.s.s 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 ma.s.ses of limestone conglomerate and coa.r.s.e 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. x.x.xII (1902), pp.

163-178.

[Ill.u.s.tration: 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 ca.n.a.ls. 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.

[Ill.u.s.tration: 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 munic.i.p.al 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 pa.s.sage 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. a.s.suming 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.

[Ill.u.s.tration: 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.

[Ill.u.s.tration: FIG. 2.--MONTHLY RAINFALL IN MONTERREY COVERING THE PERIOD FROM 1894 TO 1909 INCLUSIVE.]

[Ill.u.s.tration: 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.