Mega reservoir Oroville needs to make room for more water

OROVILLE, Calif. - The nation's tallest dam which forced nearly 200,000 people to evacuate their homes and properties six years ago, is now doing something few thought might ever happen again: getting rid of water in a still rainy season to make room for more.

This was necessary at noon on Friday because Lake Oroville has too much water in it to maintain a proper safety margin for massive expected additional inflows. 

"We began increasing releases out of Lake Oroville to preserve storage in the lake for flood protection and risk reduction for the downstream communities," said California Department of Resources State Water Project executive Ted Craddock.

Only the second time after it was rebuilt, the spillway at the dam used a minimal flood gate for opening and releasing the overabundance of water down the 3000-foot-long, 180-foot-wide spillway.  

Six years ago, the old spillway had to be rebuilt after the overtopping of the entire dam which also led to severe damage.

In the coming weeks, much more rain runoff and snowpack melt are expected.

If too much comes into the lake too fast, the gate would be opened and flow vastly increased, while still protecting those downstream. 

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"These adjustments will be done in close coordination with the United States Army Corps of Engineers and our downstream flood control partners," said Craddock.

This requires a complex and difficult balance of managing the new climate reality to keep supplies adequate over multi-year periods. 

"Given the new reality that we're dealing with of more extreme swings between both drought and wet conditions," said Craddock.

"We're expecting the lake to reach full capacity later this spring and summer which will provide opportunities for using the lake while it's full," he said.

Beyond recreation, Lake Oroville will be able to service cities, farms and 27 million residents. Oroville is the second-largest of the state's mega reservoirs.

Combined, the big six reservoirs now average 88% of their historical average water holdings to this date. With more precipitation coming, they may be 100% of normal or better when the rainy season ends in June.