The Santa Clara Valley Water District has been undertaking seismic stability analyses of its 10 reservoirs to evaluate the integrity of the dams based on current engineering standards and to ensure a reliable water supply. The preliminary data of the 75-year-old Calero Dam indicate the presence of alluvium—gravel and sand from underlying creek bed—under the downstream dam embankment, which could make the dam vulnerable to damage during a major earthquake.
Safety is the district’s highest priority. As such, the district will keep the water at no higher than 20 feet below the dam crest until the full integrity of the dam can be assessed or corrective action can be completed.
In August 2009, the district hired a highly qualified geotechnical consulting firm to conduct the evaluation of Calero Dam. Since then, the consultant has drilled borings at various locations on the downstream and upstream faces of the dam, conducted laboratory testing, and begun engineering analyses to determine if the materials used to construct the dam are sufficient to withstand a major quake.
Construction in progress on Calero Dam, Sept. 12, 1935.
"Calera" is the Spanish word for limekiln or limestone quarry. In 1935, the Santa Clara Valley Water Conservation District obtained land for the proposed Calero Reservoir from the Newman brothers. They had operated a ranch since they purchased the land in 1905 from the Bailey family, who owned 873 acres in what was then known as Calero Valley. Calero dam and reservoir is one of the six original reservoirs approved for construction by voters in May 1934. The dam and reservoir are located on Calero Creek. The 2.2-miles-long reservoir can store 9,934 acre-feet of water. Its surface area is 349 acres.*
Water from Calero Reservoir is provided directly to drinking water treatment plants where it is treated and tested for safety. The water is then distributed to water retailers to be sold to the county’s 1.8 million residents. Calero also captures and stores winter runoff to recharge groundwater basins, helps store water from the nearby Almaden Reservoir watershed and accepts imported water.
*Reservoir storage values have been updated to reflect recent survey results.