Feds Order South Bay Reservoir Drained Over Safety Risks

Jeffrey Schaub
February 25, 2020 - 6:25 am
Anderson Reservoir Dam in Santa Clara County.

Santa Clara Valley Water District

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The Anderson Reservoir, the largest in Santa Clara County, must be emptied because of federal authorities' fears that its earthen walls might fail during an earthquake. 

The reservoir, between Morgan Hill and San Jose, must be drained beginning in October 1 the Federal Energy Regulatory Commission said Monday. 

The decision could have a significant impact on the water supply in Silicon Valley. The reservoir holds more water than the combined volume of nine other dams operated by Santa Clara Valley Water District, the Mercury News reported

It sits atop potentially unstable soil and has been in need of repairs for years, the federal regulators said. 

If the dam, which was built in 1950, were to fail, Morgan Hill could be flooded beneath 35 feet of water while San Jose could get hit with 8 feet of water. 

Sediments that could liquify have been found at the bottom of the reservoir, said San Jose State University civil engineering professor Patrick Ferraro."

The dam itself was subject to slumping during a large earthquake," he said. 

Due to the order, water district officials warned that South Bay customers might have to significantly cut water use if drought conditions arise.