Thursday, November 4, 2010

[californiadisasters] Santa Clara Co's Anderson Dam at Risk of Collapse in Major EQ



Study: Santa Clara County's Anderson Dam at risk of collapse in major earthquake


Santa Clara County's largest dam -- Anderson Reservoir -- is at risk of collapsing in a major earthquake, potentially releasing billions of gallons of water that could flood Morgan Hill and San Jose within just minutes in a worst-case scenario, new tests show.

"We're not crying wolf. We're saying it's here and we have to deal with it," said Richard Santos, chairman of the Santa Clara Valley Water District's board of directors. "We're not going to run from it."

Confirming a problem highlighted in studies a year ago, preliminary findings released Wednesday indicate that Anderson Dam could experience significant slumping -- but only if a magnitude 7.25 earthquake were to occur on the Calaveras Fault within two kilometers of the dam.

As a result, the district's dam operators plan to keep the reservoir no more than 56 percent full until further analysis is completed and until it can be retrofitted to survive such an earthquake. Currently, Anderson Reservoir is 54 percent full.

"The first order of business is protecting public safety, and we plan on doing that by maintaining water at a low enough elevation so if there was an earthquake that the water is contained behind the dam," said Frank Maitski, deputy operating officer at the Santa Clara Valley Water District. "We're committed to doing a remediation as quickly as we can."

Since January 2009, Anderson Reservoir has been no more than 74 percent full -- a restriction set by the


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California Division of Safety of Dams based on information then that indicated the dam's foundation contains sand and gravel that could liquefy in a big quake.


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View entire article here: http://www.mercurynews.com/science/ci_16333054

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