Silicon Valley’s Key Reservoir May Collapse

A pricey retrofitting project at one of Santa Clara County’s largest dams has been delayed by a full year after engineers discovered nearby “trace faults” that could elevate the risk of the dam’s collapse in the event of a strong earthquake.

Santa Clara Valley Water District officials had hoped to begin the $193 million project to strengthen Anderson Reservoir in early 2017, but will now begin in early 2018, according to the San Jose Mercury News. The project will not completed until 2021 or 2022.

“We have to get it right,” water district operating officer Katherine Oven told the paper. “We want that dam to stay intact, operate and provide water supply for the next 50 years. We want to be well-informed of the potential seismic dangers.”

An earlier article in the Mercury News pointed out the dilemma over draining the dam, which is Silicon Valley’s main water provider, during the worst drought in California’s recent history.

The reservoir has been closed to recreational vessels since August due to low water levels.

Even with more water, however, Anderson Reservoir cannot currently be filled to more than 68 percent capacity; a 2009 engineering study revealed that if the reservoir were filled to full capacity, a strong earthquake on the nearby Calaveras Fault could cause the dam to fail. The dam’s failure would reportedly send a 35-foot-high wall of water into downtown Morgan Hill and ultimately, into San Jose, where thousands could potentially die in the flooding.

The reservoir must be fully drained in order to complete the construction, another headache for water officials during California’s record four-year-long drought. The reservoir is currently only 34 percent full.

“Draining it during a drought is problematic,” water district board chairman Gary Kremen told the Mercury News. “You’re damned if you do, damned if you don’t. But it’s got to be fixed.”

Kremen added that if the drought persists for the next few years, the water district could decide to suspend the project, as it will need the water.

Compounding problems at the construction site was the discovery of a type of rare shrub called coyote ceanothus. Department of Fish and Wildlife biologists have since mandated the water district conduct studies and take preventative measures to avoid harming the plant.