California Storm Paradox: Too Much Water in Reservoirs, Too Soon

Excess heads to the ocean, which is good for fish but bad for water supplies

PUBLISHED MAR 11, 2023 8:54 P.M.
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The snow-lined South Fork of the American River on March 3, 2023.

The snow-lined South Fork of the American River on March 3, 2023.   Fred Greaves, California Department of Water Resources

BY ALASTAIR BLAND , CalMatters

Two winters’ worth of snow has already fallen in the Sierra Nevada since Christmas, pulling California from the depths of extreme drought into one of its wettest winters in memory.

But as a series of tropical storms slams the state, that bounty has become a flood risk as warm rains fall on the state’s record snowpack, causing rapid melting and jeopardizing Central Valley towns still soggy from January’s deluges.

The expected surge of mountain runoff forced state officials on March 8 to open the “floodgates” of Lake Oroville and other large reservoirs that store water for millions of Southern Californians and Central Valley farms. Releasing the water will make room for the storm’s water and melted snow, prevent the reservoirs from flooding local communities—and send more water downstream, into San Francisco Bay. The increased flows in the Sacramento-San Joaquin Delta could help endangered salmon migrate to the ocean.

So what’s the downside? These same storms are prematurely melting a deep and valuable snowpack that ideally would last later into the spring and summer, when farmers and cities need water the most.

The storms have created a tricky situation for officials who manage state and federal reservoirs in California, since they have to juggle the risk of flooding Central Valley communities with the risk of letting too much water go from reservoirs. They must strike a balance between holding as much water in storage, as long as they can, while maintaining room in reservoirs for more water later in the season.

To make room for more water, state and federal officials who manage California’s major dams and reservoirs are releasing water. Some will flow into the ocean—which aggravates many water managers, Central Valley legislators and growers, who often say freshwater that reaches the bay or ocean is wasted. However, efforts are underway to divert much of the released water into depleted groundwater storage basins.

The article titled “California storms create paradox: Too much water in reservoirs, too soon” was first published by CalMatters. See the full version, plus a graph of water levels in California’s major reservoirs, on CalMatters.org.

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