It started with a warning from state officials more than a decade ago that a major earthquake could cause the crest of Anderson Dam to slump, allowing water to cascade over the top and leave Morgan Hill underwater in mere minutes.
Last week, the Santa Clara Valley Water District finally broke ground on the first phase of what has become a 10-year, $648 million project to retrofit the dam.
The district first started its planning process in 2012. Chris Hakes, who serves as the deputy operating officer of the Valley Water’s dam safety and capital delivery division, told The Beat that at the time it was supposed to be a “relatively straightforward seismic retrofit project.” But over the years, a series of unexpected setbacks increased both the project’s scope and cost.
The original plan –– to add buttressing and materials up and downstream to reinforce the dam –– would take roughly three years and come with a $250 million price tag. But in 2016, that number grew after the district conducted geotechnical borings of the surrounding soil and found evidence of seismic activity in two nearby fault lines previously thought to be inactive.
The discovery led the district to revise its plans from reinforcement to a complete reinstallation of materials at the dam’s embankment.
The following year, 200 miles north of Anderson, a crater began forming in Oroville Dam’s spillway after a particularly wet rainy season. As a result, 188,000 people living downstream were evacuated.
The incident also led the California Department of Water Resources Division of Safety and Dams to revise its spillway design guidelines, prompting Valley Water to, once again, adjust its plans and completely replace Anderson’s existing spillway.
What happened at Oroville Dam served as a warning for crumbling and aging infrastructure across the country. According to a National Inventory of Dams conducted by the U.S. Army Corps of Engineers, there were approximately 15,600 dams classified as “high-hazard structures” in 2019. That means the failure of the dam would result in loss of life and potentially significant economic losses.
And the number of hazardous dams in the United States only has room to grow as infrastructure deteriorates with age. According to a report from the American Society of Civil Engineers, the average age of dams in the United States is 57; by 2030, 7 out of 10 dams in the United States will be over 50 years old.
Despite the delays, Hakes says there wasn’t always a concern that the project to repair the unstable 71-year-old dam wasn’t moving fast enough. After the initial alarm bells from the state in 2009, Valley Water drained the reservoir to 58 percent of capacity.
“From our eyes, even if we had an event, we were going to have the sufficient capacity in the reservoir to hold those holes to make sure they didn’t overflow and create that cascading failure that we talk about these days,” Hakes said. “From that point of view, we thought we were in a good position to move the project forward.”
Last year, Assemblymember Robert Rivas (D-Salinas) made his first attempt to move the Anderson Dam retrofit project forward quicker. AB 3005, which he introduced to the state legislature in February 2020, would have expedited the project’s environmental review and any judicial challenges that may have come with it.
Gov. Gavin Newsom, however, ultimately vetoed the bill, stating that it would set “unrealistic timelines for state entities to expedite deliverables” and would “require staff to be diverted away from other critical projects” also undergoing environmental review.
But on Friday, Newsom signed into law Rivas’ second iteration of the bill –– AB 271 –– which will allow Valley Water to promptly hire the best contractors to keep the project on its 10-year schedule.
“The Anderson Dam Seismic Retrofit Project is the top priority for Valley Water, not only for public safety but for our local water supply as we face another historic drought,” Valley Water Board Chair Tony Estremera said in a statement on the bill’s signing.
With nearly 90,000 acre-feet of capacity, Anderson Reservoir is the district’s largest water reserve. But the Federal Energy Regulatory Commission (FERC) ordered Valley Water to drain Anderson to three percent capacity last year, drastically decreasing the supply ahead of yet another dry California winter.
The timing of the retrofit project puts Valley Water in a precarious position as last month its board voted to mandate a 15 percent water reduction, and CEO Rick Callender proclaimed the district’s “water supplies are in serious jeopardy.”
District 7 Director Gary Kremen told The Beat that “there’s no good time to repair your primary reservoir.”
“We just happen to be in the worst two years of California history from a drought point of view,” he added.
But with some of the “regulatory relief” from the state, Kremen says he believes it won’t take the estimated decade to get Anderson Dam back into commission.
“Hoover Dam didn’t take ten years to build,” Kremen said, referencing the second largest dam in the U.S. after Oroville Dam. “This isn’t Hoover Dam.”
Hakes, for his part, hopes that FERC allows Valley Water to increase its capacity above three percent following the completion of the first phase of the project: a 1,700-foot-long tunnel that will be able to discharge 6,000 cubic square feet of water a second.
He says the dam’s current outlet discharges about 500 cubic square feet a second of water –– or roughly 500 basketballs a second.
“While 500 cubic feet per second sounds like a lot, compared to 90,000-acre-feet, it’s not,” Hakes said. “What you’re basically looking at is a 55-gallon garbage can that’s having a level regulated by a straw punched into the bottom.”
The tunnel project will begin this summer and is expected to take three years. After that, Valley Water will begin work on the retrofitting process by strengthening the dam and the spillway.