Land Subsidence Along the California Aqueduct

Science Center Objects

Subsidence is a global problem and, in the United States, more than 17,000 square miles in 45 States, an area roughly the size of New Hampshire and Vermont combined, have been directly affected by subsidence. More than 80 percent of the identified subsidence in the United States is a consequence of human impact on subsurface water.

map of San Joaquin Valley shaded by 2008-2010 subsidence in millimeters

Map showing estimated regions of subsidence derived from interferograms for 2008–2010 and selected surface-water conveyance infrastructure in the San Joaquin Valley area of the Central Valley, California. (Public domain.)

There are concerns that fluctuating land-surface elevations due to subsidence and uplift in the valley could cause serious operational-maintenance and design construction problems for the California Aqueduct surface-water delivery system.

Surface-water imports via the California Aqueduct in the late 1960's and early 1970's, and the associated decrease in groundwater pumping, resulted in a steady recovery of water levels and a reduced rate of compaction. During the droughts of 1976-77, 1987-92, and 2007-09, diminished deliveries of imported water prompted increased groundwater pumping to meet irrigation demands. This increased pumping resulted in water-level declines reaching near historic lows and periods of renewed compaction. Following each of these droughts, recovery to pre-drought water levels was rapid and compaction virtually ceased.