Emergency spillway work

Workers from Kiewit Infrastructure use wood to construct forms for the construction of a concrete beam to be anchored to the top of the underground secant pile, or cut-off wall, at the Lake Oroville flood control spillway site on Feb. 15, 2018.

Though the final phase of repair work on the main spillway at Lake Oroville is now on the back burner until spring, Department of Water Resources officials said crews are making significant progress on repairing the emergency spillway.

Kiewit Infrastructure West Co., the company in charge of repairing the reservoir’s damaged spillways by January 2019, stopped heavy construction on the main chute over the winter months.

“Our crews will be ready to go May 1, weather permitting,” said Jeff Petersen, project director for Kiewit.

An update by DWR and Kiewit was provided to the media Wednesday morning, via a phone conference.

The final phase of reconstruction of the main spillway will include replacing the upper portion of the chute, going over the middle chute that only received roller-compacted concrete last year with structural concrete, replacing some walls with structural concrete and resurfacing of the energy dissipaters at the bottom of the spillway.

When all is said and done, the main spillway will have the ability to release and handle up to 270,000 cubic feet of water per second. It is unlikely that much water would be released at any one time, considering releases have never exceeded 160,000 cfs and downstream levees would be unable to handle the larger release.

Ted Craddock, DWR’s assistant deputy director of the State Water Project, said most of the major work over the past two months has been focused on the emergency spillway.

The goal is to build a secant pile wall below the crest of the emergency spillway to prevent or mitigate the hillside from eroding when water flows over the structure – which is what led the Butte County sheriff to initiate the mandatory evacuation last year.

In addition to the wall, crews are planning on constructing a roller-compacted concrete (RCC) splashpad that will help armor against uphill erosion.

Petersen said the secant pile wall is 95 percent complete and is expected to be finished by March. Then, as early as next week, crews will begin placing some of the initial RCC for the splash pad.

Craddock said the final touches will include constructing an RCC buttress at the base of the emergency spillway later this year to reinforce the structure further.

Dry winter conditions 

With little rain and a meager snowpack, concerns of drought conditions returning to the state have been a talking point around the water world as of late. 

To mitigate the chance of having to use the spillway this year while construction was ongoing, DWR chose to keep the lake’s elevation below normal levels. 

Erin Mellon, assistant director of Public Affairs for DWR, said the lake’s elevation was at about 725 feet as of Wednesday, or 41 percent of its capacity. However, the low level isn’t really a concern for DWR as of yet, she said.

“In terms of the dry conditions we’ve seen, obviously we are still in the middle of the rainy season, so we don’t know what the weather has in store for us,” Mellon said. “As far as the state as a whole, while Oroville is lower than average, the rest of the state’s large reservoirs are well above average, so we are in a pretty good place at this point to be able to manage for the next year, based on last year being so wet.”

Cost of project

The current estimate for repair and recovery costs is approximately $870 million. That cost, Mellon said, includes Kiewit’s $500 million contract, $210 million in other related recovery costs, as well as the $160 million for emergency response immediately after the initial spillway incident last year.

“That $870 million is still a good estimate, although that’s based on some completed work and a lot of projected work, so it might shift,” Mellon said.

There have also been some concerns raised about whether or not the Federal Emergency Management Agency will reimburse the state for up to 75 percent of those costs. Mellon said there has been no indication that the federal agency will not reimburse DWR.

“We are still operating under the assumption that we will receive FEMA reimbursement until they tell us otherwise,” Mellon said.

If that plan was to fall through, she said, contractors who are a part of the State Water Project would likely cover the costs, considering Lake Oroville is a State Water Project facility. 

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