FRESNO, Calif. (AP) — Land in Central California's agricultural region is sinking so quickly because of the state's historic drought that it is forcing farmers to spend millions of dollars upgrading irrigation canals and putting roads, bridges and other infrastructure at risk.
The Central California Irrigation District recently spent $4.5 million to raise the walls of a canal, and the district's manager, Christopher White, says they're about to invest another $2.5 million to replace a bridge that's now below the canal's water line.
"It's a vivid picture of what subsidence can do," said White, who serves 1,900 farmers on the San Joaquin Valley's west side that grow crops such as tomatoes, cotton, fruit and almonds in three counties.
Sinking land has occurred for decades in California because of excessive groundwater pumping during dry years, but NASA data released Wednesday by the state's Department of Water Resources shows the pace has dramatically quickened as the state endures its fourth year of drought.
The study done by NASA's Jet Propulsion Laboratory shows the ground is sinking nearly two inches each month in some places, placing roads, bridges and vital canals that deliver water throughout the state at growing risk of damage.
"We are pumping at historic levels," said Mark Cowin, head of the California Department of Water Resources, adding that groundwater levels are dropping to record levels — up to 100 feet lower than previously recorded.
Gov. Jerry Brown signed historic legislation last year that requires monitoring of groundwater pumping. However, local officials have until 2020 and in some cases until 2022 to write their management plans, so it could take another decade or two before California has a handle on groundwater use, Cowin said.
"I don't think we can end overdraft or subsidence overnight," he said. "We do need to take action."
Meanwhile, the state is launching a $10 million program to help counties with stressed groundwater basins to develop or strengthen local ordinances and conservation plans.
The NASA data showed land near the city of Corcoran sank 13 inches in eight months, and part of the California Aqueduct dropped eight inches in four months last year. The aqueduct provides water to million people and vast farmland in the nation's most productive agricultural state.
NASA's satellite imagery shows a problem that farmers in White's irrigation district have long known. To keep water flowing, they raised the canal walls in order to send higher levels of water, overcoming a drop in elevation. The higher flow also put the bridge below the water line.
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.
Lester Snow, executive director of the California Water Foundation, which promotes water policy, urged more immediate action. He said state and federal officials should offer local agencies financial incentives to reduce pumping.
Investments are also needed in storm water capture during wet winters to offset heavy reliance on groundwater, Snow said.
"As long as this continues, we risk further damage to roads, levees and buildings," he said. "There is no time to waste."