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Soft delta soil could put California water supply at risk in earthquake

Source: Reuters - Sat, 26 Apr 2014 00:11 GMT
Author: Reuters
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By Jennifer Chaussee

April 25 (Reuters) - The soft soil that surrounds a key California water supply could amplify shock waves from a major earthquake and cause flooding that could contaminate the drinking water with seawater, an earthquake researcher said Friday.

Scott Brandenberg, who studies earthquakes at the University of California at Los Angeles, presented his research at a meeting of the Southern California Water Committee, a non-profit water advocacy group whose members include water district administrators, local governments, public utilities and others.

"The seismic hazard is real and it's serious," said Brandenberg, who specializes in geotechnical earthquake engineering.

Water experts in California have long known about the havoc an earthquake could potentially wreak in the farmlands surrounding the Sacramento-San Joaquin River Delta that provides water for more than 25 million people and 3 million acres of farmland in California.

But this is the first time researchers have looked extensively at how seismic activity affects peat soil - a soft, dark soil that intensifies earthquake waves, Brandenberg said in an email. Peat soil sits at the base of the levees surrounding the delta, he said.

"There is this belief that (peat soil) has high damping qualities and won't transmit earthquake waves," Brandenberg said. "It's simply not true. It can amplify waves."

He also noted that the vulnerabilities of the peat soil would likely take days or months to materialize after an earthquake has happened, so although it would not pose an instantaneous threat, it could have a lasting impact on the safety of California's water supply.

The research comes just as California embarks on a controversial multibillion dollar Bay Delta Conservation Plan that would reconstruct the waterway.

Opponents say the project will further endanger the delta and its wildlife while proponents contend it will alleviate the risk of salt water contaminating the supply in the event of an earthquake. (Reporting by Jennifer Chaussee in San Francisco; Editing by Sharon Bernstein and Lisa Shumaker)

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