LOCAL CALIFORNIA

The rain has started to return in Northern California and will continue over the next few days, but officials aren't as concerned about the upcoming weather so much as the damage already done to the Oroville Dam's already compromised main spillway.

The risk of flooding has dropped substantially, but Butte County Sheriff Kory Honea warned residents Wednesday that they remain in "an emergency situation."

150,000 cubic yards of debris stand in the way of Oroville Dam's hydroelectric plant restart

Helicopters ferry sand and rocks from a staging area to the Oroville Dam's emergency spillway repair project. (Brian van der Brug / Los Angeles Times)
Helicopters ferry sand and rocks from a staging area to the Oroville Dam's emergency spillway repair project. (Brian van der Brug / Los Angeles Times)

Officials at Lake Oroville reduced the rate of water release once again Friday as workers continued make repairs to a damaged spillway and clear debris from a hydroelectric plant.

State Department of Water Resources engineers will decrease the flow of water in the Oroville Dam's main spillway from 80,000 cubic feet per second to 60,000 by Saturday morning, giving crews space to dredge debris from a pool at the bottom of the spillway, said DWR acting director Bill Croyle.

Engineers had been pumping water out of the lake at 100,000 cfs for several days to make room for incoming storm runoff and to keep the lake from overflowing like it did over the weekend. That overflow badly eroded an emergency spillway and sent debris flowing into a pool at the bottom, forcing the closure of an underground hydroelectric plant.

“This reduction in flow will allow us to work on the debris pile in the spillway,” Croyle told reporters at a news conference. He estimated that 150,000 cubic yards of sediment and debris were in the pool.

The other focus by workers at the dam is the eroded emergency spillway, Croyle said. Rain began falling again in the area on Thursday and it’s not expected to stop until the middle of next week at the earliest.

The heaviest showers are expected Monday and could drop up to 10 inches of rain onto the mountains and foothills that drain into the reservoir, the National Weather Service said.

The storms aren't likely to produce enough runoff to exceed the lake's capacity, Croyle said.

Hundreds of thousands of tons of rocks and concrete slurry have been dropped into four fissures that threatened a retaining wall of the emergency spillway on Sunday. They were 50%, 75%, 90% and 100% full, respectively, Croyle said.

Rain falling onto the slurry and a small stream that had formed on the hillside Friday did not worry DWR engineers, he said.

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