Geomembrane Installation at Salt Springs CFRD Dam

Salt Springs Dam, owned by Pacific Gas & Electric Co. (PG&E) is the fifth oldest Concrete Faced Rockfill Dam (CFRD) in the world and the first CFRD to reach 328 ft. (100 m) in height. It is located in California, south and east of Sacramento, high in the Sierra Nevada Mountain Range. In the 1930s, construction of the dam was halted at about mid-height due to winter weather. When rock placement resumed in the spring, the lift height was reduced and sluicing techniques were improved to gain better consolidation. These changes created a zone of differential settlement in the dam where the concrete face has required continual repairs over its 70+ year history. In 2001, seepage in this zone increased significantly, exceeding the limit set by the California Department of Water Resources, Division of Safety of Dams. Immediately, and at considerable expense, PG&E hired divers to make temporary repairs as it began to investigate how to permanently fix the upstream face at Salt Springs Dam. The conclusion was to install a PVC geomembrane system over the upstream face with the goal of reducing seepage to 12 cfs (340 l/s). The work was done in two phases. In the spring of 2004, Phase I repairs began with the installation of the CARPI geomembrane system over the center of the face in the so called “transition zone” to mitigate the risk of significant seepage increases, as occurred in 2001. 10 pp., 6 references. [Also presented at Dam Safety 2005]