July 13, 2009

Pumping depletes San Joaquin aquifers

Groundwater pumping in California's San Joaquin Valley has reduced aquifers to historic lows, a government report indicates.

A massive study of the region's groundwater supplies by the U.S. Geological Survey shows the agriculture-intensive valley has lost 60 million acre-feet of groundwater since 1961, and is approaching new lows as farmers pump more from aquifers to make up for surface water lost to drought, The Sacramento (Calif.) Bee reported.

That situation also is exacerbating the problem of subsidence, in which lower groundwater levels cause the valley floor to sink. That, in turn, threatens the stability of the state's vital, 444-mile California Aqueduct, which delivers drinking water to more than 20 million people, the newspaper said.

Al Steele, an engineering geologist at the state Department of Water Resources in Fresno, told the Bee state land survey data shows two highways near the city have subsided a number of feet in the past 40 years, but how much the aqueduct has subsided is unclear.

The newspaper said a new satellite mapping technology may be able to pinpoint where groundwater pumping most threatens the canal and farming in those areas and could be stopped.