Calaveras Dam Spillway Replacement Project

CLIENT: San Francisco Public Utilities Commission

The San Francisco Public Utilities Commission (SFPUC) supplies water to 2.4 million residents of the San Francisco Bay Area. Calaveras Reservoir is its largest local supply reservoir. Analysis showed that the existing dam does not meet modern seismic requirements and for this reason, storage has been restricted to 30% of its design capacity in recent years. To restore this important source of San Francisco's water supply, URS Corporation (URS) designed a new dam and spillway to be constructed just downstream of the existing dam. The Probable Maximum Flood (PMF) for this project was calculated at 40,000 cfs. In order to reduce costs, the chosen spillway design was unique, and for that reason, verification of the design was necessary to ensure that it will work as intended.

URS engaged NHC to design and construct a 1:36 scale physical model of the spillway. Ultimately, the intention of testing was to find the balance between excavation costs and hydraulic efficiency. The particular concerns at the entrance to the spillway were the approach channel topography, the geometry of the spillway approach walls, and the depth of the spillway trough. The model was also used to determine the magnitude of the flow super-elevation along the outside of the chute bend, the magnitude of cross waves, and the energy dissipation capabilities of the stilling basin.