Oroville Dam spillway reconstruction

A drone overview of the Lake Oroville emergency spillway construction site, shows progress of the splashpad that will armor the hillside between the emergency spillway and the secant pile wall at the Butte County, California site. Photo taken April 13, 2018.

Reconstruction efforts to the main spillway at Lake Oroville could start to ramp up as early as this week if federal officials sign off on the Department of Water Resources’ operational plans for 2018. 

DWR officials submitted the updated plans to the Federal Energy Regulatory Commission and the California Division of Safety of Dams for approval on Tuesday, requesting that crews be allowed to start the final phase of reconstruction as soon as possible.

Kiewit Infrastructure West Co. has a contract to finish the repairs by January 2019. Erin Mellon, a DWR spokeswoman, said it’s a tight window, but achievable. 

“This year we actually have more concrete to place than we did last year so there’s a lot of work to do,” Mellon said. “We’re obviously very confident in Kiewit’s ability to do the job and they’ve met all expectations so far. Of course, there may be some unknowns (weather, etc.) that could impact our timelines but if that happens we’ll be sure to communicate it to the media and the surrounding community.”

DWR also requested that it be allowed to close the main spillway gates for the remainder of the construction season starting

May 8 to allow for heavy construction.

Below-average snowpack in the region means inflows into the lake will be low this summer, officials believe. The lake’s level as of Thursday was just over 800 feet. The main spillway cannot be used until the lake’s elevation is up to 813 feet. 

In its submitted plans for 2018, DWR requested that the lake level target approximately 830 feet before triggering more aggressive outflows to provide more flexibility in managing dynamic weather in real time, according to a press release.

Mellon said the reservoir and its facilities have held up well throughout the winter. 

“There are no current concerns with the Oroville complex and crews are ready to get back on the main spillway to finish the reconstruction efforts,” she said.

Plans moving forward

DWR is targeting April 25 to start on prep work for the resurfacing of the middle part of the main chute that only received roller-compacted concrete last year. The work will consist of resurfacing the top layer to create a flush surface to prepare for the placement of steel-reinforced structural concrete slabs. 

Once given the go ahead to start the final phase of reconstruction, crews will demolish the upper chute of the main spillway and replace it with steel-reinforced structural concrete slabs and walls. 

They will also remove the RCC walls in the middle portion and replace them with structural concrete walls with a permanent drainage system. 

The bottom of the chute – namely the energy dissipaters at the base – will be hydro-blasted and resurfaced. 

As for the emergency spillway, the secant pile cutoff wall has been completed. Crews are currently placing a concrete cap on top of the cutoff wall to further reinforce the wall. 

Crews are also currently constructing an RCC splashpad that will cover the area between the emergency spillway and the cutoff wall to further armor the hillside. There are plans for later this year to construct an RCC buttress at the base of the emergency spillway structure to further reinforce the area.

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