ASCE 1193: The Water-Works And Sewerage Of Monterrey, N. L., Mexico Part 7

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 relations.h.i.+p 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 quant.i.ties 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._ +--------+-------------+--------+------------ Quant.i.ties, Quant.i.ties, 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-pa.s.ses, and the length of supply pipe where the by-pa.s.s 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.

a.n.a.lYSES OF ESTANZUELA AND SAN GERONIMO WATERS.

Table 8 shows a.n.a.lyses 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.--a.n.a.lYSES 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.

a.n.a.lYSIS 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 Pota.s.sium 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 Alb.u.minoid 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.

[Ill.u.s.tration: 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-pa.s.ses fitted with independent gate-valves.

[Ill.u.s.tration: 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. d.i.c.k, 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 munic.i.p.ality, 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 bra.s.s corporation c.o.c.ks. 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.