Mexico City's Water Supply Improving the Outlook for Sustainability (1995) / Chapter Skim
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3 Description of the Mexico City Aquifer and its Exploitation
3 Description of the Mexico City Aquifer and its Exploitation
Pages 8-18
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From page 8... ...
The history of exploitation of the Mexico City Aquifer and the associated problems of subsidence are briefly examined' and the quantity of water available in ground water storage is reviewed. PHYSICAL CHARACTERISTICS AND HYDROGEOLOGY The Basin of Mexico is located in the central part of the Trans-Mexican Volcanic Belt and has an approximate area of 9,000 square kilometers.
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From page 9... ...
This material is inters/ratified with Pleistocene and recent basalt deposits that together comprise the upper portion of the principal water supply aquifer (Units 2, 3, and 4 of Figure 3-21. A lower unit of the principal aquifer is composed of stratified volcanic deposits, 100 to 600 meters thick, and reaches to a depth of 500 to approximately 1000 meters (Unit 6 of Figure 3-21.
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From page 10... ...
The Sierra Chichinautzin is the most natural important recharge zone for the Mexico City Aquifer due to the high permeability of its basalt roclc The large Xochimilco springs on the basin floor are a discharge point for the underground flow, and some of the most productive wells are located there. The conceptual model for the Mexico City Aquifer identifies two deeper permeable units an intermediate and a deep aquifer.
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From page 11... ...
Source: Adapted from Mooser, 1990. WATER LEVEL DECLINES IN THE AQUIFER AND LAND SUBSIDENCE Beginning in the fourteenth century, the Aztec city of Tenochtitlan made use of an elaborate system of aqueducts to carry spring water from higher elevations of the southern portion of the Basin of Mexico down to the city situated on land reclaimed from the saline Lake Texcoco.
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From page 12... ...
Over the next century, a combination of increasing ground water extraction and artificial diversions to drain the valley resulted in the drying of many natural springs, shrinking of lakes, and a loss of pressure and subsequent consolidation of the lacustrian clay formation on which the city is built. Consequent land subsidence has been a serious problem in the MCMA since the early 1900s.
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From page 13... ...
In 1983, systematic monitoring of the water levels in the aquifer began (Lesser-Illades et al., 19901. Since that time, the average annual declines in ground water levels range from 0.1 to 1.5 meters per year in the different zones of the MCMA.
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From page 14... ...
According to the Mexico Valley Water Authonty (Gerencia de Aguas del Valle de Mexico) , the net subsidence over the last 100 years has lowered the central, urbanized area of the MCMA by an average of 7.5 meters.
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From page 15... ...
. The original gravity-fed system was disrupted by subsidence and, by 1950, pumping was necessary (sistem de Borneo)
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From page 16... ...
a) ~ 2235 cn 2234 _ 2233 1930 1940 Mexico City Center 1950 1960 1970 1980 1990 2000 Year FIGURE 3-5 Subsidence ',~easure'~,e',ts in the center city area of Mexico City and the Chalco Plain, an area Alters 'pore recent Fouled water exlractio', has occurred.
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From page 17... ...
is not acting as a confining layer for approximately 30 percent of its extent where water levels have sunk below this limiting layer. On the basis of both field measurements and modeling in this region, the total saturated volume of the aquifer in the southern portion of the basin has been estimated to be 1,189.3 billion cubic meters.
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From page 18... ...
in the late 1980's have indicated a likelihood of geologically-induced water quality problems with increasing aquifer depth. More precise information on the sustainability of continued extraction from the aquifer would require specific studies including field observations and the use of computational models (see AIC-ANIAC, 1995, for additional details on water balance, hydrogeology, and exploitation of the aquifer)
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