From the Department of Water Resources:
Today the Department of Water Resources (DWR) provided an update on construction-related activities for the Lake Oroville Spillways Emergency Recovery Project.
Update to the 2018 Operations Plan
DWR has updated the 2018 Lake Oroville Operations Plan to begin construction as soon as possible this spring and maximize the 2018 construction window to ensure the main spillway is fully reconstructed before next winter. The plan was submitted yesterday to the Federal Energy Regulatory Commission (FERC) and the California Division of Safety of Dams (DSOD) for approval.
With inflows into Lake Oroville expected to be low this summer due to below-average snowpack and snow water content in the Northern Sierra, the updated plan targets a lake level of approximately 830 feet before triggering more aggressive outflows. The plan provides flexibility to manage dynamic weather in real time.
The current lake level is 808 feet, and the main spillways are at elevation 813 feet. Once the lake level surpasses 813 feet, DWR anticipates some water will pass through the gates onto the main spillway. Minimal amounts of water have passed through the main spillway gates since original construction, and the gate seals were replaced in 2014 and 2015.
Lake levels will fluctuate through the year as DWR manages the lake to meet multiple uses and benefits, including flood protection, environmental releases, recreation, salinity control and flow requirements in the Delta, and contractual water deliveries to senior water users locally and to State Water Project water users.
Construction on the Main Spillway
- DWR has requested approval from FERC and DSOD to close the main spillway gates on May 8 to allow construction to resume for the remainder of the construction season.
- Prep work to resurface, or mill, the top layer of the roller-compacted concrete (RCC) middle chute is targeted to begin on April 25, which will create a uniform surface to prepare for placement of steel-reinforced structural concrete slabs. Crews will remove up to five inches of the surface of the RCC section of the chute.
- Overall plans for Phase Two construction on the main spillway 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 three-foot, steel-reinforced structural concrete slabs over the RCC middle chute, and placement of a drainage system.
- Removal of the RCC walls in the middle chute and replacement with structural concrete walls, with a permanent drainage system.
- Hydro-blasting and resurfacing of the energy dissipaters at the base of the main spillway.
Construction at the Emergency Spillway
- DWR has requested approval from FERC and DSOD to begin removal of the remaining surface layer of the grouted rip rap on the emergency spillway hillside on April 25. This is the rip rap that was placed as part of the February 2017 emergency response.
- Crews are currently placing a concrete cap, or grade beam, on the recently completed underground secant pile cutoff wall. The cap will reinforce the structural concrete piles and secure the wall to the RCC splashpad. The secant pile wall is 1,450 feet long and located 750 feet downhill of the emergency spillway with concrete piles at depths of 35 to 65 feet.
- Crews continue to construct the RCC splashpad, which will cover the hillside between the emergency spillway and secant pile wall. The splashpad, in conjunction with the secant pile wall, will armor the existing hillside to significantly reduce the type of uphill erosion that occurred during the February 2017 incident.
- Later this year, an RCC buttress will be constructed at the base of the emergency spillway structure to provide further reinforcement.
Additional Updates
- Over the next four to six weeks, DWR will be conducting routine maintenance on three of the six turbines (turbines four, five, and six) at Hyatt Powerplant.
- This maintenance will ensure the performance of Hyatt Powerplant throughout the construction season when the main spillway will be unavailable.
- DWR had planned to begin this maintenance at the beginning of April but delayed the work to provide full outflow capacity from Hyatt Powerplant to safely manage lake levels during recent storms.
- Turbine one is undergoing an extensive upgrade and has been offline since 2015. Work on turbine one is targeted for completion by the end of this year.
- With two turbines active, Hyatt Powerplant has an outflow capacity of 5,000 cubic-feet per second.
- As reported in January, DWR’s Design Team has been in consultation with the Independent Board of Consultants (BOC) regarding a section of structural concrete wall placed last year that is 1 percent out of alignment. Memo #16 from the BOC, which was posted this week, concurs with the Design Team’s recommendation to leave the wall in place, saying it is “in the best interest of the project not to demolish and reconstruct the walls.”
- DWR will meet with the BOC for the 17th time on April 23 and 24.
To view photos and video of the Lake Oroville Spillways construction, visit DWR’s Oroville Spillway photo gallery and YouTube channel.
The latest video from the Department of Water Resources …
Crews remove material from the hillside near the upper chute of the main spillway. Excavators dig out the new section of cut-off wall while roller-compacted concrete (RCC) continues to be laid for the splashpad.
Photos from Oroville …
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