The floor of the Central Valley is sinking at a record pace as drought-gripped farmers pump out the groundwater beneath them, new satellite data show.
In some places the ground is dropping nearly 2 inches a month, according to measurements taken by the state and NASA. The sinking soil is dragging roads, bridges and other infrastructure with it, raising concern that state pumping restrictions scheduled to take effect in five years won't arrive in time to head off costly damage and environmental ruin.
"I'm a fan of the new groundwater law. It's long overdue," said Peter Gleick, president of the Pacific Institute, a water research organization in Oakland. "But the overdraft of groundwater has to be brought under control faster than the regulation requires or we're going to suffer billions of dollars worth of damages."
Dried-up aquifers in parts of the state have already left some farms and communities without a water supply, Gleick noted. Sinking land is just the latest problem.
Going down
Last year, areas around the Kings County town of Corcoran between Fresno and Bakersfield dropped 13 inches in eight months, according to the data released Wednesday. Arbuckle, in Colusa County north of Sacramento, sank 5 inches in six months, and points along the California Aqueduct, which carries water beside Interstate 5 in the San Joaquin Valley, fell 8 inches in four months.Irrigation canals have begun to buckle, wells have fractured and even streets are cracking. State and federal officials fear that railroad lines and home foundations may be next.
"As extensive groundwater pumping continues, the land is sinking more rapidly, and this puts nearby infrastructure at greater risk of costly damage," said Mark Cowin, director of the state Department of Water Resources, which worked with NASA to collect information from satellites and airplanes about plunging land levels.
Permanent reduction
The sinking land, called subsidence, has been observed for decades. Like a slow leak in an air mattress, underground water is sucked out by wells, causing aquifers to collapse and the land above it to drop.Although aquifers typically recharge during wet times as rainwater percolates into the ground, subsidence can permanently reduce storage capacity, meaning there's less water to pump in the future.
With Central Valley farms receiving less water from rivers and creeks during the four-year drought, increased groundwater pumping has pushed aquifer levels to new lows and subsidence rates to well above what they were during the last dry period between 2007 and 2009, the new data show.
The data were collected primarily in areas where state water officials think the problem is the worst -- a 60-mile-by-25-mile expanse around Corcoran that includes the California Aqueduct, a 25-mile swath near the Madera County city of Chowchilla, and two smaller patches in the Sacramento Valley near Arbuckle and the town of Yolo. State officials say more expansive studies are in the works.
Limits delayed
California officials acknowledged that there's not much they can do to stop the subsidence, at least in the short term. State groundwater regulations approved in September require communities to come up with plans to shore up their aquifer levels and regulate pumping, but not for another five years. In the meantime, farmers and others can pump unlimited amounts of groundwater."There's no doubt that these sort of effects are going to continue to some extent," Cowin said of the subsiding land.
Hard-fought compromise
The extended timeline for implementation of the state's pumping rules followed years of debate over whether groundwater should even be regulated. The Sustainable Groundwater Management Act was a hard-fought compromise for lawmakers who faced opposition from farmers wanting to manage their own aquifers.California remains the only Western state where groundwater pumping is not regulated.
Gov. Jerry Brown's administration pledged Wednesday to work with communities to try to slow pumping and committed $10 million of state aid for counties embarking on such efforts. This year's state budget also called for streamlined environmental reviews for local ordinances restricting pumping.
For Chase Hurley, general manager of the San Luis Canal Co., the recent state moves don't amount to much.
His water agency serves about 90 farmers in Merced County who grow mostly tomatoes, alfalfa and cotton. The agency's dam along the San Joaquin River has sunk about 3 feet in recent years, and Hurley is worried that the dam won't hold up. Without it, the agency will be hard-pressed to find irrigation water.
Raising the dam would cost millions of dollars, which the water agency doesn't have.
"There's been subsidence everywhere," Hurley said, "but I'm in the hot spot."
(c)2015 the San Francisco Chronicle
