DWR received authorization to proceed with its final 2017 construction plan from the California Division of Safety of Dams (DSOD) and the Federal Energy Regulatory Commission (FERC) on July 13 and 15 respectively. The Independent Board of Consultants (BOC) also approved DWR's construction plans in June.
The first phase of construction was completed on November 1, 2017, with the objective of ensuring that the main spillway can safely pass 100,000 cubic feet per second. The first phase of construction included:
- Removal and reconstruction of 2,270 feet of the main spillway with a combination of structural concrete and roller-compacted concrete so the spillway can handle flows of 100,000 cubic feet per second.
- Repairs to the uppermost 730-foot portion of the main spillway that connects to the radial gates. This portion will be demolished and reconstructed in 2018.
In early August 2017, DWR set a target date of December 2017 or January 2018 to complete construction of the secant pile or cut-off wall downhill of the emergency spillway. After gaining information from thorough geologic exploration and test drilling in June, DWR determined the exact location for the underground wall moving it from 300 feet downhill of the emergency spillway to approximately 730 feet downhill of the emergency spillway. This underground wall will prevent the kind of uphill erosion that occurred in February of 2017.
The remaining construction will be completed in 2018, which will also need federal and state approval, includes:
- Addition of structural concrete to the middle portion of the main spillway full reconstruction of the uppermost 730-foot portion of the main spillway so it can handle flows of 270,000 cubic feet per second.
- Resurfacing and hydro-blasting of the energy dissipaters at the base of the main spillway.
- Construction of a roller-compacted concrete buttress (sloped wall) and splashpad on the hillside of the emergency spillway to dissipate the energy of any waterflows.