Water & Drought

Oroville Dam update: Power plant back in operation, easing pressure on damaged spillway

Crews have restarted the critical hydroelectric plant at Oroville Dam, a move that could mean operators don’t have to activate the dam’s badly damaged main spillway even as a winter storm bears down this weekend.

“This is a big day,” Bill Croyle, acting director of the California Department of Water Resources, said at a Friday news conference.

One of six turbines at the Hyatt Power Plant was operational as of 10 a.m. Friday. The turbine’s outlet allows for 1,750 cubic feet of water per second to exit Lake Oroville, California’s second-largest reservoir.

The hope, Croyle said, was that by day’s end, 3,000 cfs could be released. That won’t be enough to match the amount of runoff washing into the reservoir from the Sierra Nevada watershed, but Croyle said the state will work to restart four more turbines in the next few days. That would allow the plant to ramp up to its release capacity of 14,500 cfs, enough to largely counter anticipated inflows from the weekend storm.

The water level in Lake Oroville may rise a few feet from the storm runoff, Croyle said, but it is not expected to climb high enough to be of concern, especially with a period of dry weather likely to follow. The extended dry spell forecast should allow sufficient time to draw lake levels down again using just the hydroelectric plant, Croyle said.

The power plant stopped functioning in recent weeks as massive erosion from the dam’s fractured main spillway formed a mound of concrete, earth and rocky debris in the channel below the 3,000-foot span. The mound, estimated to contain more than 1 million cubic yards of material, raised channel levels below the dam to the point that the power plant couldn’t operate. While the main spillway serves as a critical flood-control valve during California’s rainy season, the plant is the dam’s primary outlet the rest of the year.

On Monday, officials completely shut down releases from the broken main spillway to give crews time to assess damage, clear out the debris pile and lower water levels in the channel. Croyle said crews have worked day and night to clear approximately 168,000 cubic yards of debris from the channel, using excavators and dredging machinery. On Friday, a gush of muddy, brown water flowed out of the power plant at the base of Oroville’s earthen dam for the first time in weeks.

Meanwhile, reservoir levels remain more than 50 feet below the lip of Oroville Dam’s emergency spillway. Last month, water overtopped the emergency structure for the first time in the dam’s 48-year history. The hillside below quickly and dangerously eroded, prompting the temporary evacuation of 188,000 residents in Butte, Yuba and Sutter counties.

Croyle said Friday that crews continue to shore up both spillways in case they have to be used again. That includes bolstering the top two-thirds of the main concrete spillway above the fissure.

“We have a contractor in grouting and sealing any of the little holes or cracks – anything they can find,” he said.

Dale Kasler: 916-321-1066, @dakasler

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