LOS ANGELES — As heavy rains pounded a series of atmospheric rivers in California and residents braced for possible flooding, the state on Friday began releasing millions of gallons of water from a major reservoir — despite drought conditions.
The release into Lake Auroville, home to the state’s second-largest reservoir and the nation’s tallest dam, was the first since 2019 and came as a precaution against flooding for communities in case of potential spillover.
The shift from water conservation to flood prevention is the latest in a wave of winter weather hitting California, where 85% of the state was in severe drought three months ago, according to the US Drought Monitor. Now only 19% of the states fall in that category.
“Water management in California is complex, and it becomes even more complex during these challenging climate conditions where we see swings between very, very dry; very, very wet; Back to dry,” Carla Nemeth, director of the Department of Water Resources, said at Friday’s briefing. “Now we’re back to wet.”
An atmospheric river known as the “Pineapple Express” because it carries warm, subtropical moisture from near Hawaii into the Pacific is expected to melt snow at lower altitudes. California’s mountain ranges have produced significant snow this winter under an onslaught of rain from nine atmospheric rivers and storms fueled by Arctic air.
Widespread snow at higher elevations is expected to absorb the rain, but snow at elevations below 4,000 feet prompted the Department of Water Resources to activate its Flood Operations Center.
Water releases for flood control were underway or planned for some reservoirs that were depleted during a three-year drought and were being filled by extraordinary winter rains and snowfalls.
The idea of releasing water that would eventually flow into the Pacific during times of drought may seem counterintuitive, but state officials said they have to be prepared for the possibility of flooding.
“The primary management objective of flood operations is to reduce the risk of downstream flooding rather than to protect against the coming dry season,” said Daniel Swain, a climate scientist at the University of California, Los Angeles and the National Center for Atmospheric Research. ,
“This shows that the flow is large enough and the level of the reservoirs is so high that the authorities do not want to store more water in them for safety reasons,” he said.
California relies on a system of approximately 1,400 man-made surface reservoirs and thousands of miles of dams to manage surface water. About two dozen large reservoirs are responsible for more than half of the total storage.
Reservoirs are designed not only to store water, but also to manage stream flow during periods of heavy rain or snow so that low-lying areas are not flooded.
Seven of the state’s 17 major reservoirs are still below their historical averages this year. Water is also expected to be released at Friant Dam in central California, to free up space in Lake Millerton, according to the US Bureau of Reclamation.
“After three years of drought and low lake heights, it’s really good to see the lake growing from a perspective of providing water to the local community and statewide water users as well,” said Ted Craddock, deputy director of the state water project.
Because most of California’s water reserves come from snowmelt at higher elevations, water officials expect reservoirs to keep filling through the spring.
As of this week, California’s Sierra Nevada snowpack, which provides about one-third of the state’s water supply, is more than 180% above its April 1 average, when it historically peaked.
“We know that drought conditions will return to California, and it’s really moments like these that we have to capture so that we can be resilient in the event of future droughts,” Nemeth said.
auroville lake The supply has increased 180 feet since December 1 and was just 60 feet below capacity before Friday’s storm. Capable of storing more than 3.5 million acre-feet, officials plan to release about 15,000 cubic feet per second. Water officials say that one acre-foot supplies enough water for a year for two typical homes.
The lake is vital to the State Water Project, which provides water to some 27 million residents and flood protection to low-lying communities.
The reservoir was repaired in 2018 after heavy flooding overwhelmed the main spillway and forced the evacuation of more than 180,000 people.
Craddock expressed confidence in the 1960s-era Oroville Dam, saying that the spillway upgrade “has been renovated to modern standards, and we have every confidence that it will be able to pass incoming flow into Lake Oroville.”