Damages to the hydraulic system

Mexico City has at present the largest and most complex hydraulic system in the world. To provide drinking water to more than 10,000,000 persons the supply system has the following sources: water from the western zone, provided by the Lerma and Cutazmala rivers; underground waters via wells located mainly in the south, north, and center of the city and some important springs located in the southeast. The eastern region is supplied from sources out of the Federal District which makes this area extremely vulnerable.

The city has a hydraulic infrastructure (Table 14) which permits it to have an average of 35.4 cubic meters per second of drinking water. That is enough to satisfy about 97% of the needs of the population with home connections. The remaining 3% is supplied by water tank trucks. (Figure 9) The combined drainage system for the removal of sewage and rain waters is made up of 12,300 kilometers of secondary networks with diameters of less than 0.60 meters; 1,200 kilometers of collectors with diameters ranging from 0.60 to 4.00 meters, and 64 pumping plants with a total installed capacity of 500 cubic meters per second as well as 400 kilometers of main drains for the waterworks of the City. (32) A deep drainage system formed by interceptors that converge on a single system for the removal of sewage and rain waters also exists.

Table 14. Hydraulic Infrastructure of Mexico, D.F., 1985

Source: Reference (32).

Figure 9. Network of Treated Water

Figure 10. Zones with Water Problems in the Federal District from September 19, 1985 (Date of Earthquake) Through September 23.

At present, the drainage system serves about 74% of the population. Irregular housing, located on the outskirts of the city, does not have this service. The supply system of water was the most affected by the earthquake. Thirty-eight cracks occurred in the southeastern aqueducts, secondary drains of San Luis, Tulyehualco, La Noria, Chalco and Tecomitl thereby interrupting the delivery of 7,600 liters per second, which represented about 22% of the total city supply. As a result of these damages approximately 2,000,000 inhabitants of the eastern and central parts of the city were left without water (Figure 10).

The most common failure in the aqueducts occurred at the joints of the pipes which did not permit longitudinal displacements. One hundred and sixty-eight (168) leaks occurred in pipes made of asbestos, cement and reinforced concrete of the primary network, and mainly in the Cuauhtemoc, Venustiano Carranza, Ixtacalco, Ixtapalapa and Gustavo Madero delegations. Leaks occurred in many ways such as incrustation between two pipes, uncoupling, etc.

In the secondary networks, a total of 7,220 leaks were repaired. These were caused mainly by the rupture of special pieces made of cast iron in the valve boxes; by the changes in direction near the joints or by incrustation of two or more tubes. The reestablishment of normal services was achieved after 40 days of around-the-clock work.

Drainage System

Irregularities were identified in important structures of La Piedad and Churubusco rivers, Central Supply and the Central-Western Interceptor.

The collector of the southern towns, a pressurized conduct of the primary network located in the Xochimilco delegation, suffered cracks all along its extension. The same situation was to be found in various collectors that discharge by pump to the main drainage canal. This canal was deformed near the pumping plants due to the differential sinking produced by the earthquakes.

The oxidation lagoon of San Luis Tlaxialtemalco, located in the south of the city, was practically unable to function.

Fissures occurred at some of the sewage pumping plants as well as in other installations such as storm drains, subcollectors, etc. In general, the damages to the drainage system were less than those to the conduction and distribution systems of potable water. This was probably due to the fact that the conducts are less flexible in their joints, have more freedom to twist and move and are buried deeper.

Repairs to the aqueducts were started immediately thanks to the availability of a large selection of special materials and spare parts. In spite of this, it was necessary to begin intensive production of additional spare parts for the reestablishment of the primary networks and aqueducts.

Water Quality

During the emergency period, the General Division of Hydraulic Operation and Construction (DGCOH) analyzed a total of 59,400 samples to control water quality of the city (for comparison, a total of 40,000 samples are taken throughout the whole year).

In order to compensate the lack of water service to shelters, hospitals, nurseries, etc. a total of 15,000 plastic water bags, provided by a plant in the Benito Juárez delegation, were distributed daily.

Water distribution was carried out by 480 water tank trucks from nearby states, the army, other institutions and the Federal District. In some affected zones, 90 portable water tanks were installed, each with an 11,000 liter capacity and with multiple faucets for public use. All these measures permitted the strict control of water quality. Nevertheless, bacterial contamination was detected and treated by hyperchlorinization until residual chlorine registered 2 parts per million in network tanks and water tank trucks.

In spite of apparent water contamination, no diarrhea! outbreaks were detected. The increase in the frequency of diarrheal episodes in some shelters was probably due to alimentary contamination (33).

Environmental health services, as well as water storage, delivery and sewage systems, are vulnerable to disasters. The installations may be damaged, the channels broken or the operations disrupted for lack of electricity. Disaster preparedness plans should include provisions to store enough water for the affected population.