Ralston Afterbay Maintenance and Enhancement/Restoration Activities Project

Ralston Afterbay Maintenance and Enhancement/Restoration Activities Project

The Project is located on the Middle Fork American River (MFAR), approximately five miles east of Foresthill in El Dorado and Placer Counties. Project activities include: excavation and dredging of sediment from Ralston Afterbay; relocation of suitable excavated material to downstream MFAR sediment augmentation sites and spawning gravel habitat sites; and sediment pass-through. The Project is required under the Sediment Management Plan and Spawning Habitat Improvement Plan (plans), which are included in PCWA’s 2020 Federal Energy Regulatory Commission (FERC) license for the Middle Fork American River Hydroelectric Project (Hydroelectric Project), also referred to as FERC Project No. 2079. In part, the plans aim to ensure the downstream movement of sediments and gravels that are otherwise retained in Ralston Afterbay, as well as enhance spawning habitat and overall aquatic and riparian habitats along the MFAR downstream of Ralston Afterbay. PCWA anticipates beginning Project sediment removal activities (i.e., excavation and dredging) during the Hydroelectric Project 2025 Fall Outage Period (i.e., late September or early October 2025) and continue Project implementation periodically over the effective period of the USACE permit. Lands in the vicinity of Ralston Afterbay are owned primarily by the United States Forest Service. Sediment removal activities help maintain the Hydroelectric Project system reliability by restoring Ralston Afterbay’s storage capacity and removing accumulated sediments adjacent to Ralston Powerhouse’s outlet works. Approximately once every five years, between 1969 and 2023, approximately 45,000 cubic yards of sediment was removed from Ralston Afterbay. The Project objectives are to: (1) periodically remove sediment from Ralston Afterbay via excavation or dredging on an as-needed basis to allow for safe and reliable operation of the Hydroelectric Project and provide sediment for downstream aquatic habitat enhancement/restoration; (2) relocate sediment captured in Ralston Afterbay to the Indian Bar and Junction Bar sediment augmentation areas immediately downstream of Ralston Afterbay; (3) selectively relocate Ralston Afterbay gravels to help re-establish four rainbow trout spawning gravel sites immediately below Ralston Afterbay Dam; and (4) periodically open Ralston Afterbay Dam’s low-level outlet during flows of more than 3,500 cubic feet per second to facilitate sediment transport and enhance downstream aquatic and riparian habitat. PCWA plans to commence dewatering of Ralston Afterbay at the start of the Hydroelectric Project maintenance outage period (typically October). Ralston Afterbay will be partially dewatered by shutting down generation at the Ralston Powerhouse and continuing generation at Oxbow Powerhouse. After Ralston Afterbay’s reservoir elevation level is near the bottom of the Oxbow Powerhouse intake, generation at Oxbow Powerhouse will cease. The stream maintenance release valve and/or radial gates on the Ralston Afterbay Dam will then be slowly opened to allow Ralston Afterbay to decline to the spillway crest. Dewatering is necessary to expose areas with accumulated sediment in the upper portion of Ralston Afterbay. When dewatered, the natural MFAR and Rubicon River low-flow channels converge and continue through Ralston Afterbay. The low flow channels in the dewatered Ralston Afterbay will convey inflows to the afterbay past the sediment removal area and downstream to Ralston Afterbay Dam. Equipment (e.g., excavators, loaders, bulldozers, and haul trucks) will primarily access Ralston Afterbay via the existing Ralston Afterbay Sediment Removal Access Point Boat Launch. On June 27, 2019, PG&E filed an application with the Federal Energy Regulatory Commission for a subsequent license to continue operation and maintenance of the Camp Far West Transmission Line Project (Project). The Project transmits power approximately 10.9 miles from the Camp Far West Hydroelectric Project’s switchyard to a switch on the Smartville-Nicholas No. 1 60 kV line at Beale Air Force Base. On July 13, 2023, PG&E applied for a water quality certification from the State Water Resource Control Board. Proposed operation and maintenance of the Project involves: (1) routine inspections, (2) minor repairs, (3) tree trimming and hazard tree reduction, (4) wood pole testing and treatment, (5) maintenance of tubular steel poles, (6) pole repair and replacement, and (7) conductor repair and replacement. Project operation and maintenance will not result in a change to the design or function of the transmission line. By maintaining the functionality of the transmission line, the Project will continue transmitting power to the California wholesale electric market.

El Dorado, Placer

Citywide, Countywide, Northern California, Unincorporated

El Dorado, Placer