CALIFORNIA, FEBRUARY 10, 2017 -- The California Department of Water Resources has released a new report from NASA showing that areas of the San Joaquin Valley continue to experience significant subsidence, resulting in damage to state and federal water infrastructure.
According to DWR, sinking land, known as subsidence, is caused by excessive groundwater pumping and is a well-known and long-term issue for California that often accelerates during times of drought. Over time, subsidence can permanently reduce an underground aquifer's water storage capacity.
The new NASA data show that areas of subsidence in Corcoran and near Chowchilla, which were previously identified by NASA in August 2015, have grown wider and deeper, while a third area of significant subsidence in Fresno County has been identified. In a seven-mile area near Tranquility in Fresno County, land has settled up to 20 inches, according to the report.
"The rates of San Joaquin Valley subsidence documented since 2014 by NASA are troubling and unsustainable," said DWR Director William Croyle in a statement. "Subsidence has long plagued certain regions of California. But the current rates jeopardize infrastructure serving millions of people. Groundwater pumping now puts at risk the very system that brings water to the San Joaquin Valley. The situation is untenable."
Subsidence already has caused sections of the California Aqueduct to sink by more than two feet near Avenal in Kings County. As a result, water project operators have been forced to reduce flows in those sections by 20% to avoid overtopping the concrete banks of the aqueduct, according to DWR. DWR warns that if the State Water Project allocation reaches 85% or greater this year, water deliveries may be impaired.
The NASA analysis also found subsidence of up to 22 inches along the Delta-Mendota Canal, a key part of the federal Central Valley Project. While the Eastside Bypass, which carries flood flow off the San Joaquin River, runs through an area of land that has sunk 16-20 inches since May 2015.
In response to the report's findings, DWR is investigating measuring for reducing subsidence risk to infrastructure, including groundwater pumping curtailment, creation of groundwater management zones near critical infrastructure and county ordinance requirements. Additionally, DWR is working with local water managers to identify specific actions to reduce long-term subsidence risk, and is considering whether reduction of subsidence risk should be emphasized as part of the ongoing implementation of the Sustainable Groundwater Management Act.
The full NASA report is available here.