Subsidence in United States Due to Ground-Water Withdrawal

Land subsidence due to ground-water withdrawal in the United States is summarized. The characteristic geologic environment for subsidence due to ground-water withdrawal is that of young unconsolidated sediments of high porosity laid down in alluvial, lacustrine, or shallow marine environments. All areas are underlain by semiconfined or confined aquifer systems containing aquifers of sand or gravel, or both, of low compressibility interbedded with clayey aquitards of low vertical permeability and high compressibility under virgin stresses. Subsidence ranges from 0.3 m at Savannah, Georgia, to 9.0 m in the San Joaquin Valley, California. The volume of subsidence in the San Joaquin Valley is very large—about 19,250 hm³. The usable storage capacity of the aquifer system, defined as the volume that can be taken from or recharged to the system, is not changed appreciably by the compaction of the aquitards but the specific storage is greatly reduced for later cycles of water-level decline through the same pore pressure range.