NASA report shows San Joaquin Valley rapidly sinking due to drought

As Californians continue pumping groundwater in response to the ongoing drought, the Department of Water Resources has released a new report from NASA that shows land in the San Joaquin Valley is sinking faster than ever before, nearly two inches per month in some locations.

SACRAMENTO, CA, Aug. 20, 2015 -- As Californians continue pumping groundwater in response to the ongoing drought, the Department of Water Resources recently released a new report from NASA that shows land in the San Joaquin Valley is sinking faster than ever before, nearly two inches per month in some locations.

Sinking land, known as subsidence, has occurred for decades in California because of excessive groundwater pumping during drought conditions, but the new data shows the sinking is happening faster, putting infrastructure on the surface at growing risk of damage. NASA obtained the information by comparing satellite images of the Earth's surface over time.

"Because of increased pumping, groundwater levels are reaching record lows -- up to 100 feet lower than previous records," said Department of Water Resources Director Mark Cowin. "As extensive groundwater pumping continues, the land is sinking more rapidly, and this puts nearby infrastructure at greater risk of costly damage."

Land near Corcoran in the Tulare basin, for example, sank 13 inches in just eight months -- about 1.6 inches per month. Another area, in the Sacramento Valley, was sinking approximately half-an-inch per month, faster than previous measurements. NASA also found areas near the California Aqueduct that sank up to 12.5 inches, with eight inches of that occurring in just four months of 2014.

The increased subsidence rates have the potential to damage local, state and federal infrastructure, including aqueducts, bridges, roads, and flood-control structures. Long-term subsidence has already destroyed thousands of public and private groundwater well casings in the San Joaquin Valley. Over time, subsidence can permanently reduce the underground aquifer's water storage capacity.

In response to the new findings, and as part of an ongoing effort to respond to the effects of the drought, the Governor's Drought Task Force has committed to working with affected communities to develop near- and long-term recommendations to reduce the rate of sinking and address risks to infrastructure.

This action builds on the Sustainable Groundwater Management Act, enacted by Governor Edmund G. Brown Jr. in September 2014, which requires local governments to form sustainable groundwater agencies that will regulate pumping and recharge to better manage groundwater supplies (see: "California's Water Woes - A Deeper Look at the Sustainable Groundwater Management Act").

The Department of Water Resources is also launching a $10-million program to help counties with stressed groundwater basins to develop or strengthen local ordinances and conservation plans. This funding comes from the statewide Water Bond passed last year, and applications for funding will be posted in the coming days. This year's budget, passed in July, also enables streamlined environmental review for any county ordinance that reduces groundwater pumping.

NASA will also continue its subsidence monitoring, using data from the European Space Agency's recently launched Sentinel-1 mission to cover a broader area and identify more vulnerable locations.

See also:

NASA study shows CA’s 'rain debt' equal to average full year of precipitation"

"NASA to launch first-of-its-kind satellite to measure Earth's soil moisture"

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