Drought conditions have resulted in more groundwater pumping

By WES SANDER

Capital Press

The federal government will conduct a study to measure the extent of ground subsidence beneath the California Aqueduct, addressing a major concern of Central Valley water managers.

The aqueduct, the main artery of the State Water Project, carries water from the Sacramento-San Joaquin Delta to the San Joaquin Valley and Southern California.

The U.S. Geological Survey says it will conduct the study on behalf of the state Department of Water Resources.

Researchers will use a satellite-imaging system to pinpoint changes in surface elevations from 2003 to 2010.

With drought conditions having resulted in increased groundwater pumping throughout the Central Valley, land subsidence has been a critical concern for state water planners.

The federal government says it will contribute $53,000 of the effort's $255,000 cost, with the state taking up the rest. The study will help the state minimize the impacts of subsidence on the aqueduct, USGS says. The agency expects to publish its results within three years.

The study will take place in the area of the Westlands Water District, on the San Joaquin Valley's west side.

The district has been hit hard by drought conditions exacerbated by federal restrictions on pumping from the Sacramento-San Joaquin Delta to protected imperiled fish.

The federal Central Valley Project, which delivers Westlands' water, cut its deliveries to 10 percent of contracted allocations this year, causing many farmers to rely heavily on groundwater.

Dating to the 1920s, land subsidence in the Central Valley has reached as much as 28 feet in some locations, according to USGS.

Subsidence halted as the state and federal water projects delivered surface water around the state, but droughts in the 1970s and late-1980s caused the land to subside again.

Aquifer levels are now approaching historic lows, again causing subsidence and potentially costing the state millions for upkeep of water-delivery infrastructure.

Staff writer Wes Sander is based in Sacramento. E-mail: wsander@capitalpress.com.

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