Too much rain, snow could have flooding consequences

State officials are considering releasing water from some reservoirs that are already full to make sure there's enough space to handle the rest of the rainy and snowmelt seasons.

That was the situation at Lake Mendocino almost three weeks ago.

Most reservoirs leave space for snowmelt, but significant rainfall complicates that.

The Sierra snowpack provides some 30% of the state's water, as well as replenishing reservoirs and underground aquifers. Currently, the snowpack across the Sierra Range is twice the historical normal for this week — the best in 40 years.

That snowpack already contains about 3 feet of water that will flow down rivers, streams, and into reservoirs.

"We are readying ourselves to make sure that we can take advantage of that snowmelt, which, given the snowpack, is likely to be excessive," said California Water Resources Director Karla Nemeth.

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There's an opportunity to fill the reservoirs as much as possible while maintaining enough space to catch potential coming water.

"So, we really don't know, here on Feb. 1, whether this is the peak of our snowpack. And those are really important data points that help us manage water in California," said Nemeth.

But there's a danger, as seen six years ago when water overtopped the Oroville Dam.

"Depending on how fast that melt kicks off sometime in April or May, it has the potential to overwhelm how much inflow those reservoirs down there can handle," said DWR Hydrologist David Rizzardo.

The California Nevada River Forecast Center said the water content im the snowpack is already extreme, more than 150% of normal. That means high flows with the runoff going down the wide and high volume Sacramento River to the San Francisco Bay, which can handle flows ten times bigger than flows going down the San Joaquin River.

The San Joaquin River has the potential of serious flooding if more atmospheric rivers line up and mountain temperatures warm up too soon.

"It's a balancing act. It's a tricky balancing act for them to try to manage flood flows while maintaining as much storage as they can," said Hydrologist Rizzardo.