Feds say largest reservoir in Silicon Valley must be drained, citing earthquake risk

Federal authorities announced Monday the largest reservoir in Silicon Valley must be drained, saying an earthquake could rupture its earthen dam and send water into nearby communities, inundating an area stretching from the San Francisco Bay to Monterey, including much of Silicon Valley. less Federal authorities announced Monday the largest reservoir in Silicon Valley must be drained, saying an earthquake could rupture its earthen dam and send water into nearby communities, inundating an area ... more Photo: Yelp / Rob. M Photo: Yelp / Rob. M Image 1 of / 15 Caption Close Feds say largest reservoir in Silicon Valley must be drained, citing earthquake risk 1 / 15 Back to Gallery

Federal authorities announced Monday the largest reservoir in Silicon Valley must be drained.

According to authorities, an earthquake could rupture its earthen dam and send water into nearby communities, inundating an area stretching from the San Francisco Bay to Monterey, including much of Silicon Valley.

Located between Morgan Hill and San Jose off Highway 101, Anderson Reservoir is currently operating below its threshold level as a safety precaution; the Federal Energy Regulatory Commission and the state Division Safety of Dams have ordered a complete drawdown by Oct. 1, 2020.

Operated by Santa Clara Valley Water, Anderson Reservoir is held back by Anderson Dam, which was built in 1950. The lake is the largest in Valley Water's nine reservoir system. It's near the Calaveras fault and studies show the dam could fail in a 7.2 earthquake.

Valley Water CEO Norma Camacho said in a statement the retrofit project is "complicated" and "time consuming."

"A priority will be to design and build a large outlet pipe, which will provide greater control over the water levels and increase public safety," Camacho said.

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Camacho said the project could impact water supplies and wildlife in the ecosystem of the reservoir and Coyote Creek, including “sensitive native fish, amphibians, reptiles, wetlands, and riparian habitats.”

Amy Graff is a digital editor with SFGATE. Email her: agraff@sfgate.com.