"New NASA radar satellite maps prepared for the California Department of Water Resources (DWR) in the report, Subsidence in California, March 2015-September 2016, show that land continues to sink at in certain areas of the San Joaquin Valley, putting state and federal aqueducts and flood control structures at risk of damage.
A prior August 2015 NASA report prepared for DWR documented record rates of subsidence in the San Joaquin Valley, particularly near Chowchilla and Corcoran, as farmers pumped groundwater in the midst of historic drought. The report released today shows that two main subsidence bowls covering hundreds of square miles grew wider and deeper between spring 2015 and fall 2016. Subsidence also intensified at a third area, near Tranquillity in Fresno County, where the land surface has settled up to 20 inches in an area that extends seven miles.
Additional aircraft-based NASA radar mapping was focused on the California Aqueduct, the main artery of the State Water Project, which supplies 25 million Californians and nearly 1 million acres of farmland. The report shows that subsidence caused by groundwater pumping near Avenal in Kings County has caused the Aqueduct to drop more than two feet. As a result of the sinking, the Aqueduct at this stretch can carry a flow of only 6,650 cubic feet per second (cfs) – 20 percent less than its design capacity of 8,350 cfs. To avoid overtopping the concrete banks of the Aqueduct in those sections that have sunk due to subsidence, water project operators must reduce flows."
Unfortunately, once clay soil groundwater aquifers collapse, they can't be recharged with surface water. Read a summary and the full NASA report on the DWR website: