Factors causing the mining of aquifers in arid environments: case of San Luis Potosí valley [Factores que dan origen al minado de acuíferos en ambientes áridos: Caso Valle de San Luis Potosí]

The analysis of historical and recent data on hydrology, geophysics, land use change, climate and water resources management points to a continue decrease of groundwater reserves, which indicates that groundwater mining is taking place in the San Luis Potosi Valley aquifer. The system is formed by a shallow aquifer in a granular medium in alluvial depositions, a middle one of sedimentary material formed by gravels, sands and unconsolidated loams, and a deep aquifer in a volcanic fractured medium, named Latita Portezuelo. The factors negatively affecting the recharge into the valley are: a low permeability of rocky materials surrounding the valley that inhibit the water infiltration into the soil, the scarce precipitation and high evaporation characteristic of arid zones, the soil erosion by deforestation in mountain ranges that prevent water retention, and water dams built on low permeability materials that restrain water runoff to infi ltration zones in the valley. Additionally, the ages of the water in the granular aquifer range from 1300 to 2300 years and from 5300 to 6300 years in the fractured aquifer. Hydrogeological balances from 1995 and 2002 show that the deficit has increased from 36.6×106 to 42.5×106 m3/year. These balances reveal a shortage, with extraction doubling the recharge. According to the climatic and geological conditions in the area, the groundwater in the San Luis Potosi Valley reached a condition of mining.

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