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Reservoir releases underway as California braces for atmospheric rivers

California has begun using its reservoirs as flood control devices, even though in many cases it means releasing the state's most precious resource into the ocean.

SACRAMENTO, Calif. (CN) — Once mired in drought, California now has too much of a good thing and has opened spillways on key reservoirs as the first of two atmospheric rivers made landfall Thursday afternoon.

The Golden State activated the Flood Operation Center ahead of the incoming storms, to notify officials of high water levels and support local flood relief efforts.

At a state Department of Water Resources briefing, climatologist Michael Anderson predicted two storms in the next six days, with at least an inch of rain expected in the Central and Sacramento valleys. The first storm brings warmer air so two to four inches of rain could fall on top of near record-breaking snow at higher elevations.

Anderson said scientists are researching the effects of the January storms on California’s drought.

A comparison of California water conditions between fall 2022 up to March 2023. (Department of Water Resources via Courthouse News)

“Back at Christmas, we were well on our way to a fourth year of drought. We’re in a very different condition now,” Anderson said.

The department’s director Karla Nemeth said the state is working to move stormwater into underwater ground supply, which has been highly depleted. 

“Water management in California is complicated and it’s made even more complex during these challenging climate conditions where we see swings between very, very dry back to wet,” Nemeth said. “Those groundwater basins will take longer to recover.”

Of the coming storms she said, “It does have the potential to be a dangerous situation, especially in areas that experienced flooding before.”

Jeremy Arrich, the department’s manager of flood management, said 23 river locations are being monitored, with 11 projected at flood risk and none in the “danger” or disaster category. 

A map of California water reservoir levels updated midnight March 8, 2023. (California Data Exchange Center)

The U.S. Bureau of Reclamation’s director Ernest Conant said the Central Valley Water Project is seeing varying conditions at different reservoirs. Shasta Lake has gone up 1.4 million acre-feet since December and is 61% full, while the nearby Trinity Lake is only 33% full.

California officials are concerned about managing inflows as storms bring heavy rain and melt snowpack.

“Operators in the central and southern Sierra will have significant challenges this year with managing inflows that can be expected from this snowpack," Levi Johnson, deputy operations manager at federal Central Valley Water Project, said.

That means while reservoirs capture valuable rainfall, they also must begin releasing to maintain space for flood protection. Johnson said Folsom Lake began releasing water Thursday despite being at 64% capacity, based on federal rules for maximum reservoir levels at this time of year. 

Ted Craddock, deputy director at the State Water Project, said Lake Oroville also started releasing water Wednesday. Officials will begin using the lake’s new gated spillway Friday, which has been routinely inspected and tested for consistency with the state’s flood control plan. 

With up to 20 inches of rain possible in parts of the Sierra, Craddock said Lake Oroville will increase the amount of water released and adjust as the storms progress.

Willie Whittlesey, general manager at the Yuba Water Agency north of Sacramento, said his agency has also begun releasing flows. 

“We don’t expect our flows to get into an extreme situation, but we will monitor them and make sure the forecast doesn't increase to a situation that’s concerning,” he said. He said in 2017 flows on Yuba River got “dangerously high,” but there was no significant flood damage thanks to levee system improvements. 

Arrich said the Sacramento Valley reservoirs further north have the capacity to absorb projected flows, but some counties may have weaker levees and must be monitored. 

The department’s Paul Gosselin said reservoir releases are done with local agencies to maximize groundwater recharge, and said “Compared to January, this is going to be a lot more of a coordinated effort," he said.

Evacuation warnings have gone up in parts of the state, including Santa Cruz County. On Thursday, Governor Gavin Newsom proclaimed an expanded state of emergency to widen storm relief efforts to 21 additional counties, most in Northern California. So much snow has fallen in the Sierra and other mountain ranges that residents are still struggling to dig out days after earlier storms.

Newsom last week proclaimed a state of emergency in 13 counties and activated the California Guard and State Operations Center to support local emergency response efforts and coordinate mutual aid. That includes more than 4,000 crew members deploying to hundreds of incidents, with six shelters and food donations in counties like San Bernardino. 

“The state is working around the clock with local partners to deploy life-saving equipment and first responders to communities across California,” said Newsom. 

Categories: Environment Regional

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