A 2012 independent engineering study identified Calero Dam as a seismic risk due to the presence of alluvium – gravel and sand from the underlying creek bed – under the downstream dam embankment. That material could liquefy during a major earthquake on a nearby fault and cause the dam to deform significantly, risking an uncontrolled release of reservoir water. In response, the state Division of Safety and Dams (DSOD) imposed storage restrictions for the reservoir of 19-feet below the spillway crest, keeping water levels lower than normal to prevent topping in the event of a major earthquake until the water district assesses and conducts corrective action to restore the dam’s full integrity.
Project update
The Calero Dam Seismic Retrofit Project is on hold due to changes in the scope and schedule of the Anderson Dam Seismic Retrofit Project.
Water supply operations require that Anderson and Calero dams not be out of service at the same time as they are the only two terminal reservoirs, which are reservoirs connected by pipes that are used to move water around Santa Clara County. To preserve water supply reliability, Calero Dam can only be repaired once work on Anderson Dam is completed in 2031.
The consultant for the Calero Project submitted 60 percent design documentation to Valley Water in late 2018. Design work is expected to restart in 2024, followed by the preparation of environmental documentation and procurement of permits.
The Calero Dam Seismic Retrofit Project will:
- Stabilize dam embankments
- Replace and modernize the outlet works
- Replace and modernize the spillway to increase freeboard
- Breach Fellow’s Dike, an older and smaller dam located on the southern-most section of the reservoir that is severely deteriorated.
The Santa Clara Valley Water District built the Calero Dam during the Great Depression, completing it in 1935 after acquiring land as the Santa Clara Valley Water Conservation District. The dam and reservoir is one of the six original reservoirs approved for construction by voters in May 1934.
The reservoir has a surface area of 349 acres and is a popular venue for boating, water skiing and jet skiing. The dam is critical to the district's water storage and management, capturing runoff from the nearby foothills and transfers Almaden Reservoir.