Portions of the San Joaquin Valley floor are sinking at an alarming rate as farmers pump ever more groundwater during California’s extended drought, according to a NASA study released Wednesday.
The report, generated by NASA’s Jet Propulsion Laboratory for the state Department of Water Resources, sheds new light on the phenomenon known as subsidence.
While the land is sinking just a few inches a year, subsidence has been hastened by the drought, and the consequences can mushroom as the dry years pile up. Gravity-fed canal systems don’t function as well. Portions of the Delta-Mendota Canal, which brings water to much of the San Joaquin Valley, have buckled and had to be propped back up. In Firebaugh, west of Fresno, a motor-vehicle bridge has sunk so low it practically sits atop an irrigation canal.
“It is one of those long-term, slow and cumulative impacts,” said Jeanine Jones, interstate resources manager at the Department of Water Resources. “The thing we’re especially concerned about is the damage, long-term damage, to water infrastructure. Over time, that diminishes the ability to move water.”
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Subsidence has been a recurring problem in the San Joaquin Valley, the more arid southern half of California’s heavily farmed Central Valley. In one example that became legendary among groundwater experts, an area near Mendota sank 28 feet between 1925 and 1977. The issue largely abated with the advent of California’s massive man-made plumbing system, which showered the Valley with an abundance of surface water from Northern California. But in recent years, as the Sierra snowpack has dwindled and fresh water supplies have diminished, the woes have returned with a vengeance.
The NASA study, based on satellite imaging, showed significant rates of subsidence in recent times. A spot near Corcoran, in the Tulare basin, sank 13 inches in one recent eight-month period. Researchers found a stretch near the California Aqueduct, the key highway of the State Water Project, that sank 8 inches in four months last year.
The problem isn’t limited to the San Joaquin Valley; a spot near Arbuckle in Colusa County sank 5 inches during the last half of 2014, according to the NASA report.
“Roads can be broken by fissures, pipelines have been exhumed, and the slope of the land can be altered, changing drainage patterns,” the NASA researchers wrote.
California’s vast, natural aquifers were formed by rain and melted snow that percolated into the soil over thousands of years. When water is extracted in huge volumes, and there’s insufficient rain to replace it, the earth gradually sinks.
The rate of subsidence underscores how quickly underground aquifers are being drained. A report earlier this week by UC Davis said farmers are pumping an additional 6 million acre-feet of groundwater this year, compared to 2011, the year before the drought started, to compensate for shortages in deliveries of surface water from the State Water Project and the federal government’s Central Valley Project.
Experts say subsidence will make it harder to replenish the aquifers once the rains come. That’s because subsidence effectively compacts the soil, making it harder to store water underground.
“Groundwater acts as a savings account to provide supplies during drought, but the NASA report shows the consequences of excessive withdrawals as we head into the fifth year of historic drought,” said Mark Cowin, the director of the Department of Water Resources, in a prepared statement. “We will work together with counties, local water districts and affected communities to identify ways to slow the rate of subsidence and protect vital infrastructure such as canals, pumping stations, bridges and wells.”
California had long been the only Western state that didn’t regulate or track groundwater pumping until Gov. Jerry Brown signed a groundwater management bill last fall ordering local jurisdictions to draw up rules. But the deadline for establishing regulations isn’t until 2020 in most areas.
In the meantime, Jones said the state is urging local authorities to begin regulating groundwater pumping right away. But farmers in many parts of the state aren’t eager to see limits placed on their ability to pump.
In the Paso Robles wine country, vineyard owners went to court to challenge a 2013 ordinance giving San Luis Obispo County the authority to limit drilling of new wells and expanding crop acreage. The county won that lawsuit, but hundreds of growers filed a separate suit asserting the water beneath their properties is theirs to use. That suit is still pending.
In nearby Kings County, Supervisor Doug Verboon said he’s gotten fierce pushback from growers when he suggested imposing restrictions on drilling wells on land that hasn’t been farmed before.
“As far as putting a policy in place, all you’re going to do is get yourself sued,” said Verboon, a walnut grower in Hanford. “You have some large farmers that are corporate farmers that can sue you forever.”
Verboon said he’d like to see as much land farmed as possible, but “we’re kind of hurting ourselves, because we only have ‘X’ number of gallons of water that we can farm with, and we’re developing more and more acres that we farm.”
Two of the Sacramento Valley’s main rice-growing counties, Glenn and Colusa, have set temporary moratoriums on issuing permits for new wells. Farm groups say the moratoriums are too broad because they don’t exempt areas of the counties where groundwater supplies are still plentiful.
“Being surgical is the right approach,” said Thad Bettner, general manager of the Glenn-Colusa Irrigation District.
Some farmers say it’s unfair to blame agriculture for the subsidence problems in the Valley. Paul Wenger, a Modesto almond farmer and president of the California Farm Bureau Federation, said the state could fix things by simply letting growers have a bigger share of the available surface water.
Wenger said most of the water that farmers use for irrigation seeps back into the ground anyway, helping to recharge the aquifers.
“Once we put water in the ground, it’s not going to evaporate,” he said. “It’s kind of there.”