Lake Oroville Spillways Construction Team completes Underground Secant Pile Cutoff Wall

Intense work continues at the Lake Oroville Spillways and the Department of Water Resources (DWR) recently announced in its most recent update that the emergency spillway’s underground secant pile cutoff wall was completed on March 7 and marks a major milestone for 2018 construction. The secant pile wall is 1,450- feet long and located 730-feet downhill of the emergency spillway at depths of 35 to 65 feet.

Construction of a roller-compacted concrete (RCC) splashpad began in late February and will cover the hillside between the emergency spillway and secant pile wall. The splashpad, in conjunction with the secant pile wall, will help to armor the existing terrain to significantly reduce the type of uphill erosion that occurred during the February 2017 incident at Lake Oroville. The splashpad will armor the hillside between the emergency spillway and the secant pile wall to prevent erosion if the emergency spillway is ever used again. Later this year, an RCC buttress will be constructed adjacent to the emergency spillway to provide further reinforcement.

Construction of Phase II on the main spillway is expected to begin in May though the project is dependent on weather conditions. DWR has already begun conducting early preparation work on the RCC middle chute by temporarily sealing its surface. Later this spring, crews will begin resurfacing the top layer of RCC to create a uniform surface before placement of steel-reinforced structural concrete slabs.

Phase II work for this year will include:

• Demolition of the original 730 feet of the upper chute leading to the radial gates and reconstruction with steel-reinforced structural concrete slabs and walls.
• Placement of 2.5-foot, steel-reinforced structural concrete slabs over the RCC middle chute.
• Removal of the RCC walls in the middle chute and replacement with structural concrete walls.
• Hydro-blasting and resurfacing of the energy dissipaters at the base of the main spillway.

In addition to the construction updates, DWR has also shared ongoing logistical information in its quest for improved communications and outreach. The department has submitted its outline to address recommendations and findings in the Independent Forensic Team’s final report at the request of the Federal Energy Regulatory Commission.

Future updates will include 2017/18 Lake Oroville Winter Operations Plan which will be updated after DWR’s April 1 snowpack survey. The updated plan will account for snowpack runoff forecasts and reservoir conditions for the remainder of the rainy season. Additionally, will meet with the Independent Board of Consultants (BOC) for the 16th time on Wednesday-Thursday, March 28 and 29. DWR will post the BOC’s memo recapping the meeting on the Lake Oroville spillways’ webpage after it is received.

For information on the Lake Oroville Spillways February 2017 incident, including live video streams, go to: https://www.water.ca.gov/What-We-Do/Emergency-Response/Oroville-Spillways.