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Oroville spillway crews remain confident as deadline approaches

OROVILLE, Calif. - Time is ticking to have the entire 3,000 foot spillway ready to take on 100,000 cubic feet per second by the next rainy season. 

"On a scale of 1-10, I have a confidence level of 11 that we are going to get this work done before November 1st," said the Department of Water Resources Assistant Director of Public Affairs, Erin Mellon.

DWR said the top 730 feet of the spillway closest to the gates will remain as is this year, with the exception of a few patches and improvements. Mellon said that concrete is in really good shape with very good contact with the rock beneath it and it's much thicker than the part of the spillway that eroded in February. 

The next portion is considered the upper chute, which is 870 feet. This has already been demolished and is currently being filled with structural concrete. The middle portion of the spillway is 1,050 feet. That will be filled with roller compacted concrete for now, for the sake of time. Next year, it will be filled with the more durable structural concrete as well. 

"There are many dams and spillways across the country that are built entirely of roller compacted concrete," Mellon explained. "But, structural concrete has some added benefit, which is why that's what our final plan includes."

Kiewet Corporation said it is working around the clock and does expect to meet the deadline, but even the project director, Jeff Petersen, called this a 'pretty intense workload.' Petersen said his first reaction was "Holy cow. I'd never seen anything like it, since I'd been on the Mt. St. Helens highway reconstruction when I went up and saw that, and to see what mother nature did to this canyon was pretty crazy."

It's a first for many, including DWR officials who insist that they're doing everything they can so locals won't be seeing another repeat of the mass evacuation deemed necessary earlier this year. 

"Everything that we're doing right now is to ensure that doesn't happen again," Mellon explained. "That includes our construction deadlines, prioritizing the main spillway and reconstructing it by November 1, we're also dropping the lake level to about 700 feet elevation by November 1st."

She reiterated that the safety of the people living in Oroville and south is their first priority and there was no way to see this near catastrophe coming.

The goal to lower the lake to 700 feet is about 200 feet below maximum capacity, before water starts going down the emergency spillway. A cutoff wall is also being constructed on that emergency spillway, which should stop any erosion to the hillside, should it need to be used again.

DWR also stressed that construction will continue well into 2018, so this November 1 deadline is more of a milestone. Come November 1, the plan is to have the spillway fully functional with a capacity to withstand 100,000 cfs if need be. But another layer of structural concrete will replace the roller compacted concrete in the middle portion next year, making the spillway even stronger.


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