Groundwater basins in California are being used as local reservoirs to supplement water supplies. Water managers need more information on the relationship between land subsidence and water extraction. Studies are being conducted in the San Joaquin Valley, the Coachella Valley, and at the Army’s Fort Irwin National Training Center (NTC) in California to provide important information for various Federal, State, and local stakeholders to manage and minimize the impacts of land subsidence upon water-conveyance infrastructures and water deliveries in the two valleys, and upon aircraft runways at the NTC. The studies use conventional and persistent scatter Interferometric Synthetic Aperture Radar (InSAR) remote sensing data derived from several satellites and Global Positioning System (GPS) data to measure land-surface elevation changes, which are then compared to groundwater levels and local geology. In the San Joaquin Valley, subsidence was detected in about half of the valley and includes parts of the California Aqueduct, Delta-Mendota Canal, the San Joaquin River, the Eastside Bypass, the Friant-Kern Canal, and numerous local canals; maximum subsidence rates approached 300 mm per year, and about 12,000 km2 was affected by at least 25 mm during 2008–2010; GPS data indicate those rates have continued through 2015. In the Coachella Valley, as much as 610 mm of subsidence during 1995–2010 was measured using InSAR. By 2015, however, GPS data indicate that subsidence in some parts of the valley has been arrested as groundwater levels rose in response to increased artificial groundwater recharge and decreased demand. In Fort Irwin’s Bicycle Basin, about 425 mm of subsidence during 1992–2015 was measured or estimated using InSAR; the differential subsidence across the basin has caused ground fissuring on and near the runway.
Subsidence contours derived from interferograms generated from the Advanced Land Observing Satellite (ALOS) and the Environmental Satellite (ENVISAT) showing subsidence in the San Joaquin Valley, California, during 2008–2010.