In the 19th century, the Calaveras Valley, which the reservoir now fills, was primarily an agricultural region. Because of San Francisco’s increasing demand for drinking water at the turn of the 20th century, the farmers in the region were forced to sell their land to the Spring Valley Water Company, which in turn sold it to the San Francisco Water Company. The first dam on the site, built in 1913 by the Spring Valley Water Company, rapidly changed the sensitive hydrology and natural environment of the Calaveras Valley. It suffered a partial collapse of the upstream slope in 1918 due to engineering flaws. Its replacement, the current Calaveras Dam, at its completion in 1925 was the largest earthfill dam in the world. It is 245 feet high, with a length of 1,200 feet at its crest. The City and County of San Francisco owns and operates the dam and reservoir for municipal water supply.
Since 2001, in response to seismic stability concerns from the California DSOD about this 90-year-old hydraulic fill dam that was subject to liquefaction failure, the San Francisco Public Utilities Commission (SFPUC) has lowered water levels in the Calaveras Reservoir to about 39% of its 96,850-acre-foot capacity. To restore reservoir capacity, a replacement dam and new appurtenant works were designed to remain functional after the design earthquake, which is a magnitude 7.25 MCE on the Calaveras Fault, located 0.3 miles from the dam. The MCE peak ground acceleration would be 1.1g.
AECOM was retained to provide consulting services, including formulating project objectives, conceptual design of dam and spillway replacement alternatives, project delivery alternatives evaluation, permitting strategy, and project cost and schedule estimates. Our team evaluated repair and replacement alternatives for the dam with respect to environmental constraints, cost, construction duration, constructability, construction material availability, and seismic performance. Subsequently, AECOM prepared a conceptual engineering report.
AECOM’s contract was amended to include the conceptual and final engineering design of the replacement dam, geotechnical investigations, fault investigations, earthquake engineering analyses, and coordination of environmental permitting efforts for the Calaveras Dam Replacement Project.
AECOM completed the final design and assisted with the California DSOD dam safety and stringent environmental regulatory compliance requirements to gain project approval. AECOM also assisted with review of the draft EIR and permit applications for the USACE, Regional Water Quality Control Board, Cal/OSHA, and Bay Area Air Quality Management District.
AECOM is currently providing construction phase support services, including engineering and compliance assistance with environmental permits and permit amendments associated with minor project modifications.