San Clemente Dam: An Example of Funding Barriers in Dam Removal

The Coastal Division of California-American Water (Cal Am) owns and operates San Clemente Dam, providing public water service in Monterey County, CA. This thin arch concrete dam is located 18.5 miles upstream from the mouth of the Carmel River, below its confluence with San Clemente Creek. The dam was constructed as a water supply project and provides a physical diversion point on the Carmel River. Engineering studies conducted in the early 1990's concluded that the dam could suffer severe structural damage leading to the potential loss of the reservoir during a Maximum Credible Earthquake (MCE) or under the Probable Maximum Flood (PMF). Based on these findings, the California Division of Safety of Dams (DSOD) has required that San Clemente Dam be brought into compliance with current safety standards. The California Department of Water Resources (DWR) and the U.S. Army Corps of Engineers (USACE) are completing a joint Environmental Impact Report (EIR) and Environmental Impact Statement (EIS) on the San Clemente Dam Seismic Safety Project. The proposed project alternatives evaluated in the EIR/EIS include thickening or notching the dam, and removing it. Among the removal alternatives considered is one (Carmel River Reroute and Dam Removal) that would reroute the Carmel River to allow sediment accumulated behind San Clemente Dam to be stabilized and permanently stored in place (Figures 1 and 2). Carmel River flows would be routed into San Clemente Creek, a tributary that joins the Carmel River immediately above the dam. San Clemente Creek would be restored to handle the combined flow of the Carmel River, and the Carmel River would flow freely past the stored sediment and the old dam site. Key issues associated with the project are threatened species and sediment management. The existing San Clemente dam includes a fish ladder that allows steelhead, a federally listed threatened species, to ascend 68 feet over the dam to use the upper watershed. The California red-legged frog, another federally listed threatened species, also uses habitat at the reservoir and along the river and creek, The dam initially impounded a reservoir of about 1,425 acre-feet. More than 2.5 million cubic yards of sediment have accumulated behind the dam since it was constructed in 1921.