The cost to bring Anderson Dam, which holds back the largest reservoir in California’s Santa Clara County, up to modern earthquake standards has increased to $2.3 billion, water officials said Monday. That’s double what was estimated a year ago, triple the price tag from two years ago, and nearly certain to drive water rates higher next year across Silicon Valley.
Major renovations will begin Wednesday on the Anderson Dam tunnel project in Santa Clara County. The project will require the reservoir to be drained – and it will be unable to be used for 10 years.
The Santa Clara Valley Water District has been lowering the water level on the Anderson Dam since Oct. 1 to keep the region safe from potentially catastrophic flooding in the event of a major earthquake.
The Anderson Reservoir can hold up to 90,000 acre-feet of water and is now at three percent capacity, which is the lowest feasible level given the position of the existing outlet tunnel. At its current level, even a heavy rainy season would not pose dam failure and flooding risk; keeping some water in the reservoir helps preserve some wildlife habitat. Beyond immediate safety, one of the main reasons for lowering the water level is to allow for construction to begin on a major seismic retrofit project for the dam. The reservoir has been closed for recreational use since October and is expected to remain shuttered for the duration of the project.
In an effort to move forward a $576 million Anderson Dam Seismic Retrofit Project, the California State Assembly passed AB 3005 on June 8, the Expedited Dam Safety for Silicon Valley Act, facilitating the construction of the project.
Assemblyman Robert Rivas (D-Hollister, Calif.), who wrote the bill, says the overwhelming vote of bipartisan support shows the importance in fixing the dam. “The clock is ticking on a catastrophic dam failure in case of a large earthquake,” he says, “and we can’t allow bureaucratic delay to increase risks to public safety, water security and environmental protections.”
Three months after federal dam safety regulators ordered Anderson Reservoir, the largest reservoir in Santa Clara County, to be drained due to earthquake concerns, new details are emerging on what will happen to all that water, the fish that depend on it, and the water supply for Silicon Valley.
The Santa Clara Valley Water District, which owns the 7-mile-long reservoir located east of Highway 101 between Morgan Hill and San Jose, has drawn up plans to begin emptying it starting Oct. 1.
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