Rush Creek restoration continues to be delayed as construction of the long-awaited modification to Grant Lake Reservoir is complicated by the replacement of the 88-year-old broken rotovalve buried 80 feet below the edge of the reservoir within the aqueduct intake tunnel. Replacing the broken valve is a major undertaking and is now, along with the outlet modification of the reservoir, wrapped up in a much larger project that requires safety improvements. The Los Angeles Department of Water & Power (DWP) is proposing a complex project that will allow for the eventual replacement of the rotovalve infrastructure after the construction of buried siphons along the spillway.
The project schedule proposes multiple design and construction phases that must be carefully synchronized to allow for water to pass out of the reservoir to Rush Creek during the work. The project includes an upgrade of the existing spillway, temporary bypass pumps and flows to the return ditch over the nearby moraine, sealing of the intake tunnel to isolate the rotovalve, construction of siphons along the spillway, and, potentially, the complete excavation of the 80-foot-deep intake tunnel and replacement of the rotovalve and valve housing. The approval of the California Department of Water Resources Division of Safety of Dams is integral throughout the project design and phasing.
The former proposed modification using Langemann gates may now be replaced with siphons, which could deliver required high flows to Rush Creek while also functioning as a mid-level outlet for the reservoir during the replacement of the rotovalve and during work on the spillway. The Committee will be engaged to ensure that any new design will reliably deliver the required Stream Ecosystem Flows consistent with the 2013 Stream Restoration Agreement with DWP. The entire project could span up to seven years with multiple, complicated phases of planning, inspections, geotechnical investigations, review, and construction.
In September, DWP briefed the California Department of Fish & Wildlife, CalTrout, and the Mono Lake Committee on the project status—an important and helpful step in relation to the 2021 State Water Board Stream Restoration Order that expected the outlet modification to be completed and operational by October 2025.
This post was also published as an article in the Fall 2024 Mono Lake Newsletter. Top photo by Elin Ljung.