The two largest reservoirs in California, Shasta Lake and Lake Oroville, have been nearing capacity in recent weeks, and so their giant spillways are back in use, releasing millions of gallons of water.
It's that time of year in a rainy winter when the dams at Oroville and Shasta may need to open their spigots. And that has been happening at both reservoirs after the heavy rains of last week and this week. (Last week we also saw the even more rarely used "morning glory"-style spillway in action at Lake Berryessa.)
As Bay Area News Group reports, Shasta Lake (or, if you prefer, Lake Shasta), rose 22 feet in the first week of February, and Lake Oroville rose 23 feet. Both reservoirs are enormous — Shasta has a surface area of 30,000 acres — and water in reservoirs is measured in acre-feet, so yes, that a ton of water.
Shasta Lake was at 90% capacity as of February 1, and that was brought down to 84% as of February 12.
Since Saturday, Shasta Dam had been letting out 60,000 cubic feet, or 450,000 gallons, per second — or, as Bay Area News Group explains, the equivalent of 40 Olympic swimming pools every minute. As the Redding Record Searchlight reports, that was dialed back today to 40,000 cubic feet per second, due to flooding that the water release is causing along the Sacramento River between Redding and Cottonwood — flooding parks, streets, and backyards.
The California Department of Water resources says that reservoirs across the state are in good shape already this winter, most well over their historic average water levels. And while some may say we need all the water and none of it should be released, things can get dicey if the reservoirs get too full too fast — as we saw at Lake Oroville in 2017.
"It’s always troubling for people to see water let out," says Jeff Mount, a professor emeritus at UC Davis and senior fellow at the Public Policy Institute of California’s Water Policy Center, speaking to Bay Area News Group. "But you have to keep some space to catch floods, and then hope the melting snow in the spring fills the reservoir back to the top."
Mount also noted that this is our third wet winter in a row, which is fairly unusual. And the drought years are still fresh in everyone's memory.
In February 2017, there was a crisis at Oroville Dam as its main spillway cracked open and began to show signs of potential failure, just as the lake filled to capacity. An emergency spillway, which was essentially just a dirt berm next to the main spillway, was put into use for the first time in the dam's 50-year history, leading to further erosion and fears of a catastrophic dam failure.
That led to an evacuation order impacting 188,000 people downstream along the Feather River. But the dam survived, and a two-year repair job on the spillway began immediately that spring.
Related: Lake Berryessa's 'Glory Hole' Spillway Activated For the First Time In Six Years
Top image: Photo by George Rose/Getty Images
