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Water Table Draw Down or Groundwater "Mining"


Circular Irrigation Plots in the Plains States

Most aquifers are replenished naturally by infiltration of water from precipitation of rain and snow in the recharge area which may be many miles from the point of withdrawal from wells. If water is pumped from many wells at a withdrawal rate in an aquifer that exceeds the natural recharge rate, the water table drops. As shown in the diagram, a cone of depression may form around a well. Depending upon the depth, other wells in the area may go dry. If this situation prevails for any significant amount of time, this is called water "mining". This may happen from rapid withdrawals for irrigation purposes from so called "fossil aquifers" which get very little if any recharge.
Such "fossil aquifers" underlie the Sahara and Kalahari deserts in Africa, the Great Artesian Basin in Australia, the central Asia basins, and the Ogallala Aquifer in the western Mid-West of the United States.