Mexico city aquifer case study.

Some notes on the Mexico city aquifer and the effects of over abstraction. 

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Mexico City
Mexico City is the capital city of Mexico. The 2009 estimated
population for the city was around 8.84 million people,
making it Mexico's largest city. 70% of Mexico City's water
supply comes from the aquifer below the city. As the city is
using so much water from the aquifer it is making the city
sink as the aquifer doesn't fill up at the same rate as the
water is being removed. The city rests on the
heavily-saturated clay of the former Lake Texoco. This soft
base is collapsing due to the over-extraction of groundwater.
Land subsidence in Mexico City caused by groundwater overexploitation during the last
hundred years has been up to 9
meters, resulting in damages to
buildings, streets, sidewalks, sewers,
storm water drains and other
infrastructure. The collapse in the
central region of the city reached 10m
at the end of the 20th century, while in
the sub-basin Chalco-Xochimilco, it
reached 7m. Current subsidence rates
lie between five and 40 cm/year.
Mexico City's exponential population growth has depleted its groundwater resources.
Currently, 4 of the 14 aquifers in the Valley of Mexico Basin are overexploited. The per capita
rechargeable water available for the Valley of México in 2010 is calculated at 163m3, whereas
in 2030, it is predicted that rechargeable water per capita will be 148m3. Recharge of the
aquifer is about 31.6 m3/s compared to abstraction of 59.5 m3/s, resulting in an overdraft of
about 28 m3/s. In 1983, systematic monitoring of the water levels in the aquifer began.
Since that time, the average annual declines in ground water levels range from 0.1 to 1.5
meters per year in different zones. At the current rate of depletion, it has been calculated
that the estimated volume of storage corresponds to between 200 and 350 times the
annual abstraction.
Flooding is common in Mexico City, swamping highways and sidewalks. In low-lying
neighborhoods such as Iztapalapa, residents are so accustomed to seeing a fetid sea of
sewage rise in the streets that they have built miniature dikes in front of their
homes. Flooding is caused both by the sinking together and increased soil impermeability
due to urbanization. If the Emisor Central should fail during the rainy season, modelling
shows that a major flood would occur that would inundate the historic center, the Mexico

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City International Airport and the eastern boroughs of Mexico City. Urban growth reduces
the permeability of the soil in groundwater recharge areas and increases the risk of flooding.
Poor water quality is a concern both at the source and at the point of use. Groundwater
below Mexico City was initially believed to be protected from contamination by a thick
impervious layer. However, this layer has fractured due to land subsidence.…read more


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