FACTORS AFFECTING LAND SUBSIDENCE CAUSED BY GROUNDWATER EXTRACTION IN THE BASIN OF MEXICO

The Basin of Mexico has a large aquifer system, where the main hydrogeological unit is the Quaternary alluvial unit (Qal) on which the extraction wells are located. This main unit is partially covered by Quaternary lacustrine deposits (Qla) which in pre-pumping times confined part of the aquifer system. The Basin’s aquifer system provides nearly 70% of the Basin’s total water supply. The large groundwater extraction from the aquifer system has caused a regional drawdown of the groundwater potentiometric level. In general, the drawdown rate is around 1 m/year, but in some areas this rate reaches 2.5 m/year. The lowering of the potentiometric level has caused land subsidence due to the compressible nature of the lacustrine sediments that overlie most of the regional aquifer system. To analyze the factors that affect land subsidence in the Mexico City Metropolitan Zone, the spatial distribution of the subsidence rates determined from late 2002 to early 2007 through radar interferometry are studied along the spatial distribution of drawdown rates and an estimate of the Basin's aquifer geometry.