The California Dept. of Water Resources (DWR) on April 17 awarded a contract to Kiewit Infrastructure West Co. for repair work on Oroville Dam’s spillways. DWR says work is scheduled to begin immediately to have the system operational by November 1, the traditional start of the winter rainy season.

DWR is implementing its recovery plan to ensure the system can safely accommodate potentially heavy inflows from the Feather River watershed to Lake Oroville and subsequent releases from the lake. The complete recovery or replacement of the spillways will be done in multiple phases due to the enormity of the project and the time limitations of the construction season.

Kiewit's work will include a complete rebuild of the main spillway as well additional work to the emergency spillway, says DWR Information Officer Doug Carlson. He says Kiewit has already begun some preparation work on the project, including road construction and stabilizing and hardening the ground around the emergency spillway that was just bare ground that flood water began to spill over and onto. Kiewit will create a channel for this water to reach a diversion pool at the base of the dam spillways.

Carlson says major infrastructure work should began next week. "The issue holding up major construction work is that we are still in the wet season and we still have to have the damaged spillway act as a release channel for water that continues to flow into the dam, and that will probably continue to the last of the spring storms have passed and we are able to lower the dam reservoir level to a level considered to be within the parameters of safety to avoid future flooding," he says.

Kiewit’s bid of $275,443,850 was the lowest responsive bid out of three contractors on the shortlist. Kiewit beat-out Barnard Ames JV (MT), which had a bid of $276,965,690; and Oroville Dam Constructors (CA), with a bid of $344,129,100.

DWR this week also provided a corrected Engineer’s Estimate of $231,715,373 for the work, after finding an error in the original estimate of $220,100,000. The agency says that details of the three bids will not be made public, as they contain design information that is considered Critical Energy/Electric Infrastructure Information by federal regulators and could cause a security risk if released.

Severe erosion of the Lake Oroville flood control spillway was observed on February 7, amid a series of atmospheric river storms that rapidly filled the reservoir. On February 11, the emergency spillway at Lake Oroville was used for the first time in its 49-year history. Erosion at the base of the spillway triggered the evacuation of nearly 200,000 people downstream on February 12.

Oroville Dam and Lake Oroville lie in the foothills on the western slope of the Sierra Nevada, one mile downstream of the junction of the Feather River's major tributaries. The lake stores winter and spring runoff which is released into the Feather River to meet the Project's needs. It also provides pumped-storage capacity, 750,000 acre-feet of flood control storage, recreation, and freshwater releases to control salinity intrusion in the Sacramento-San Joaquin Delta and for fish and wildlife protection.