Monday, April 10, 2017

Engineers: The next California earthquake could “liquefy” 235-foot-high dam and unleash 29 billion gallons of water onto Silicon Valley

The Golden State just can’t seem to catch a break. Officials say that the Leroy Anderson Dam, near Morgan Hill, could “liquefy” in the event of an earthquake. The dam’s embankments have been deemed “seismically unstable.” Safety concerns about the dam continue to rise, especially after the Coyote Creek flooding that devastated thousands in San Jose, CA in February 2017.

Since 2009, the state’s Division of the Safety of Dams has had a restriction in place that limits the Anderson Dam to keeping a water level at or below 68 percent of its full capacity. CBS reported in February that the dam was at 90 percent  —  clearly, the concern about the safety of the dam is more than justified, especially after the Oroville Dam incident.

The rising water level and subsequent flooding have prompted Santa Clara Valley Water District Board of Directors Chair John Varela to send out a public letter informing area residents of the concerns surrounding the Anderson reservoir. “What would happen if a massive quake did occur? There’s a chance that the dam could be damaged, but the chance of immediate dam failure is exceedingly remote,” Varela said in the letter.

State officials from the Water District have cautioned that a 7.25 magnitude earthquake is all it would take to at least partially damage the dam. Depending on the level of collapse, a wall of water up to 35 feet high could be released and potentially flood Morgan Hill, Gilroy and San Martin. The district plans on beginning a seismic retrofitting project to secure the dam, but the project will not begin until 2020. It is expected to take four years to complete — leaving a very large window of time for that earthquake in question to shake the dam and flood the area.

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