Heavy rains and full water reservoirs may come as a relief to a state that's been hit hard by drought, but the series of atmospheric rivers drenching the Bay Area this month highlights the risk of a major flooding catastrophe in Santa Clara County.
Of greatest concern is the Anderson Reservoir, the largest body of water managed by the Santa Clara Valley Water District. There's anxiety that the Anderson Dam could fail in a major earthquake. That would spill floodwater along Highway 101 all the way to San Jose, causing floods from the San Francisco Bay to Monterey Bay: a disaster of unprecedented proportions.
Marty Grimes, a spokesman for the water district, said officials on Tuesday were releasing as much water as they safely can from the reservoir, up to 400 cubic feet per second to reduce concerns about the vulnerable structure. Since 2017, the district has kept water levels below 58 percent capacity to reduce the risk of failure.
"We believe that there's ample space right now for the storms that are coming in for Anderson to maintain the level below that seismic restriction that we have, and certainly below the spillway," he said. "But a lot of storms may come in and surprise us. We'll be keeping an eye on that."
The district aims to make a major seismic retrofit of the dam to preclude a failure if a large earthquake were to strike on the Calaveras or Coyote Creek Faults. Planning for the retrofit began in 2011, but construction is not expected to begin until early 2022 due to environmental permitting and is expected to take five years to complete.
While officials are able to manage the risk of catastrophe, for now, they still have to watch levels closely to prevent less severe flooding.
"It's certainly a point in time when you have to look at the creeks downstream," said Grimes. "Because if water's flowing over that spillway, if it's continuing to rise, that's when there could be higher flood risks downstream."
As of Tuesday morning, the Uvas Reservoir was at more than 100 percent capacity—with overflow rushing down the spillway. Three other reservoirs in Santa Clara County—Almaden, Coyote, and Chesbro—are approaching capacity. Meanwhile, the Sierra snowpack is at a very healthy 150 percent of average for this time of year.
The abundance is a far cry from the situation just three years ago, when prolonged, widespread drought exposed the dirt embankments of reservoirs around the state. However, officials hope that water conservation will remain a way of life, and warn that the next drought could be just around the corner.
Written by Jordan Bowen.
