Land subsidence in the western states due to groundwater overdraft.

Development of farm lands in most of the western states has required irrigation by surface water or groundwater, supplemental to precipitation. In areas where the supply of surface water has been small, agricultural development has been supported almost wholly by pumping from wells. As a result of the increasing demand for water, pumping draft has exceeded replenishment in many areas. Water levels have been drawn down from 100 to 500 feet, greatly increasing the grain-to-grain stress or effective overburden load on the aquifer systems in which the head depletion has occurred. This increase in stress tends to cause compaction of the deposits and correlative subsidence of the land surface (Poland and Davis, 1969). Examples of major subsidence problems are given and include Houston-Galveston, Texas.