Water & Drought

Oroville Dam spillway shutting down for summer repairs

Oroville Dam’s heavily damaged main spillway will stop being used Friday, May 19, so that crews can work full-time repairing it.
Oroville Dam’s heavily damaged main spillway will stop being used Friday, May 19, so that crews can work full-time repairing it. Special to the Bee

Water will stop flowing from Oroville Dam’s badly damaged spillway on Friday, in the hopes it’s the last time it will be used before the next rainy season.

Even with a heavy snowpack waiting to melt in the mountains above Lake Oroville, state officials say they’ve drained the reservoir down to the point where they can manage its level through the dam’s primary powerplant outlet. The lake was at 74 percent of its total capacity Wednesday.

Department of Water Resources officials say they have a contingency plan in place to use the spillway one more time in case their snowmelt runoff calculations are incorrect.

With no more water gushing down the spillway, contractors working for DWR will start working full-time to shore up the spillway before next winter.

The plan is to fill the giant crater that formed in the spillway with concrete and render it functional to handle storms by Nov. 1, the start of the traditional rainy season. DWR officials say work will continue after Nov. 1, but it will depend on winter rains and the need to use the spillway.

Work is expected to continue well into 2018.

A massive sinkhole formed in Oroville’s main spillway on Feb. 7 during heavy storms. A huge rainstorm filled Lake Oroville so high that water started flowing over the adjacent emergency spillway – a concrete lip above an unlined hillside – for the first time in the dam’s history.

The hillside eroded badly, prompting fears that the emergency spillway would crumble and release a “wall of water.” That triggered the emergency evacuation of 188,000 residents downstream on Feb. 12.

Since the crisis, the main spillway and has been used a handful of times to release water from the lake. In between, crews have temporarily shored up what’s left of the structure. Crews also have been beefing up the hillside below the emergency spillway with concrete.

The state has borrowed up to $500 million in the hopes that most of the funds will be reimbursed by the federal government. Kiewit Corp., of Omaha, has won a $275.4 million contract for the repairs.

State officials say the Southern California and Bay Area water agencies that store water in Lake Oroville will have to cover the costs that the federal government doesn’t pay.

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