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Feds order huge South Bay reservoir drained

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Washington DC agency demands Anderson Reservoir dried up for fear of dam failure in a major earthquake that could effectively destroy the South Bay

A view of the dam at Anderson Reservoir, an earthen dam with a placid looking lake behind it and a tree-lined hillside in front.
Anderson Dam.
Photo by Justin Sullivan/Getty Images

A critical Bay Area dam is in danger of failing during a major earthquake and destroying huge swaths of the South Bay, including most of San Jose, so the federal government wants it drained until seismic upgrades are finished.

But nearby cities and the local water district, who rely on that reservoir, say that following the federal orders could swap one disaster for another by inviting water shortages and possibly provoking immediate flooding right now, leading to a standoff over what to do with the billions of gallons of water pooled behind this crucial yet dicey piece of Bay Area infrastructure.

The 240-foot Anderson Dam was built in 1950 and creates the Anderson Reservoir that, according to the Santa Clara Valley Water District, ensures “a reliable supply of water to Santa Clara County.” At capacity, it stores over 89,000 acre-feet of water—roughly 29 billion gallons, more than all the other South Bay reservoirs combined.

But for over a decade, the reservoir size has been limited—right now it’s held at 58 percent capacity, down from a 68 percent cap in 2009—due to seismic instability. A 2011 study found that a large earthquake could cause the dam to fail and unleash disaster untold on the South Bay.

While such a scenario might sound like an exaggeration, in 2019, the district produced a sobering 79-second video showing the likely effects of dam failure after a major earthquake.

If the dam “slumps” (i.e., slides downhill), within minutes a wall of water could swamp Morgan Hill. Within six hours, flooding would reach the outskirts of San Jose. And within about 12 hours, water could cut clear through San Jose and into the San Francisco Bay.

Extensive flooding to the south of the dam could even spread all the way to Monterey Bay The death and destruction in this wake would be almost impossible to fathom—even as the rest of the region deals with the fallout of the biggest earthquake in generations.

At the current levels of capacity, the district projects that even a “slumped” and cracked dam could hold back the reservoir—but of course, that means keeping water levels capped.

The district plans to start construction on $550 million in earthquake proofing in 2022 and estimates that the project will take about five years, after which dam risks will be critically reduced and the reservoir can fill up again.

But the Federal Energy Regulatory Commission (FERC) says that’s not good enough. Last week, FERC Director David Capka sent a letter to the district alleging that the current water levels aren’t safe and the dam retrofit hasn’t worked fast enough.

FERC wants the reservoir drained completely—and they want it done by October 1 to avoid winter storms ahead.

“Your actions to date do not demonstrate an appropriate sense of urgency regarding the interim conditions at the project,” Capka scolded the water agency, characterizing current conditions at the dam as essentially a disaster in waiting.

Responding to the order this week, Valley Water CEO Norma Camacho called the dam retrofit “vital” and repeated warnings that a sufficiently large quake could cause “uncontrolled release of water that could inundate cities and rural areas, [...] including much of Silicon Valley.”

However, Camacho also alleges that responding to the federal order by draining the reservoir could itself be dangerous. In fact, as Camacho claims, a false move during a draining operation could damage equipment used to control outflow and “give us no way to control water flows out of the reservoir,” which could lead to flooding.

And of course, there are practical matters to consider: The reason the dam exists is to provide water for the South Bay, and it’s particularly crucial for replenishing the groundwater supply.

The region does have other water resources, but a long dry period (the U.S. Drought Monitor calculates that the Bay Area is not currently in drought conditions but like the rest of the state is “abnormally dry” right now) could leave South Bay cities pressed for every gallon it can get in the near future.

Oddly enough, for people living in the Bay Area, this may all sound like business as usual. After all, when aren’t we worried about earthquakes, potential water shortages, and local and federal agencies butting heads?

But the current conflict is a reminder that the Bay Area relies on a huge number of institutions that we usually take for granted—even just leaning on one of those pillars can leave the entire region shaken.

For the record, the reservoir is presently less than 30 percent full, due to the paucity of rain in the forecast. But that hasn’t stopped the feds from fretting.