Hydrology BC ENV 3025

Mexico City/Ogallala case studies

Mexico City

when the pressure in confined aquifer aquifers is reduced, the aquifer gets compacted
in instances where overlying units (or interlayers within the aquifer system) are clays, pumping the confined aquifer has two effects. The first is to increase the effective stress on the aquifer and the second is to de-water the clay units (analogue to mud cracks) => land subsidence
in Mexico City the lowering of the potentiometric surface in the Mexico City Aquifer has resulted in the removal of water from the overlying clays. The land surface has subsided by some 7.5 m in the central part of Mexico City (Fig. 7.15)
in the photo below, taken in central Mexico City, the young boy is not leaning against a utility pole, but a well casing, once completely below the land surface. Land Subsidence in Mexico City
consequences are extensive damage to the city's infrastructure, building foundations and the sewer system
the city is bordered by Texcoco Lake-the natural low point of the southern portion of the Basin of Mexico. In 1900, the lake bottom was 3 meters below the median level of the city center, in 1970 it was 2 meters above the city! => floods

extend of the Ogallala aquifer The High Plains Aquifer Revisited
aquifer provides irrigation for 15% of the country's corn and wheat, 25% of its cotton, and 40% of its feedlot beef
the current rate of pumping is ~8 times the estimated recharge rate
by 2020, 1/4 of the water will be pumped out of the ground
total irrogated land is already decling in 5 states using the aquifer
Texas is second only to California in its use of ground water, in 1960 Texas withdrew about a fifth of all the ground water used in the United States
the Ogallala aquifer in the Texas Plains stored 250 million acre-feet initially, at the end of 1961, 50 million acre-feet already had been pumped out
low recharge rate, dry region, flat topography
the average annual rate of decline in Texas decreased from 0.84 foot, from predevelopment to 1980, to 0.22 foot, from 1980 to 1994
rises of water table related to wetter than average years >1980
artificial recharge of rain water is being tried
the economy of the High Plains area is firmly based on ground-water mining

National Research Council (NRC). 1995b. Mexico City's Water Supply: Improving the Outlook for Sustainability. Washington: National Academy Press.
Dugan, J. T., and D. E. Cox. 1994. Water-level changes in the High Plains aquifer-predevelopment to 1993. U.S. Geological Survey Water-Resources Investigations Report 94-4157.
Recharge and Groundwater Management in the High Plains: A Historical Perspective