San Joaquin Land Settling Is Finished, Geologists Say

The problem of sinking land in the San Joaquin Valley, which gave the region some cockeyed buildings and cracked canals, is coming to a halt, a U.S. Geological Survey report says.

Sags in the valley floor were first noticed in the mid-1920s, after farmers began drawing irrigation water from the ground much faster than nature could replace it.

As the levels of aquifers fell, the crust of the land sank like the surface of a falling cake.

Today, imported water from federal and state water projects and a series of wet winters in the 1980s have eased the overdraft and rebuilt supplies in the aquifers, said R. L. Ireland, a retired hydrology technician who wrote the report.

Returned to Older Levels

“Ground water levels in the most actively subsiding areas of the San Joaquin Valley have returned to or recovered above their 1940-50 levels and subsidence has slowed considerably or stopped,” Ireland wrote.

Ireland worked for many years as an aide to Joseph F. Poland, a Geological Survey scientist and international authority on land subsidence. Both now live in retirement in Sacramento.

Findings of their research are still being published by the federal agency. Among them is a study of land subsidence in the San Jose area that will be released next year.

Time also is easing a second major cause of land sinkage in the San Joaquin region, Ireland said. It is a phenomenon geologists call hydrocompaction--the shrinkage of historically dry soil that is subjected to irrigation. It was a factor in sagging in parts of the valley’s arid West Side after large-scale irrigation began in the 1960s.

Dropped Foot or More

Altogether, more than 5,200 square miles of the valley floor have lost at least a foot in elevation since subsidence was first noted in the mid-1920s, Ireland wrote.

In some places the effects are startling.

In western Fresno County near Interstate 5, the level of the land in one spot is almost 30 feet lower than in 1926, when government agencies began measuring subsidence.

At the hamlet of Three Rocks on California 33 west of Fresno, customers in old business buildings get the feeling of walking slightly uphill or downhill on the floors, because subsidence has left the structures out of plumb.

Up to 20 Feet

Land sinkage of as much as 20 feet has been measured in a rural area 25 miles west of Hanford. A 12-foot sinkage has been noted in the region north of Delano, along with an eight-foot subsidence in the Maricopa region southwest of Bakersfield.

Most residents of the valley weren’t affected, but over the years subsidence quietly cost farmers and water users a lot of money, especially on the San Joaquin’s west side.

“Growers would find their fields, expensively leveled for irrigation, were turning into rolling country,” recalled George Ferry, retired director of the University of California Extension Service in Kings County. “The water wouldn’t flow. They’d have to level the land again. You’d get breaking of well casings, and they’d have to drill new wells every few years.”

Ferry says subsidence helped hasten the use of sprinkler irrigation in the region, because sprinklers don’t require level land.

Breaks in Aqueduct

The 450-mile-long California Aqueduct, built in the 1960s to carry Northern California water south, was designed to allow for sinkage of up to 18 inches in the lower San Joaquin Valley, said Cliff Lucas, chief of civil maintenance for the State Water Project.

Near Taft, the concrete lining of the canal is broken in many places because of subsidence and is under constant repair, Lucas adds.

“We’ve had several bridges over the aqueduct damaged because of collapsing soil,” he said. “The bridges have to be raised and their abutments repaired.”

However, Lucas said that subsidence never threatened to put the aqueduct out of business.

In the early 1900s, underground water was so plentiful in the valley that growers merely had to pierce the clay strata just below the surface to reach it. By the 1950s they were drilling wells hundreds of feet deep to stay in business.

Some small sags were recorded during the 1976-78 drought, when the overdraft of underground water temporarily reached a level of about 3 million acre-feet a year. But when water became plentiful after the drought, the land surface regained most of the lost elevation.

The Geological Survey in 1983 ended a 30-year study of the problem.