Calero Dam Seismic Retrofit Project
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.
Calero Dam Background
Calero Dam was built in 1935. It measures 98 feet tall and 840 feet long and can store 10,000 acre-feet of drinking water. A 2012 Study determined that the dam embankment would fail during an earthquake of 7.9 or higher magnitude. Valley Water is completing its design phase with improvements to address this finding effectively.
Calero Dam Objectives
Alluvium, a material that consists of gravel and sand, exists at Calero Dam under the downstream embankment and could liquify during a major earthquake. In addition to potentially causing the dam to deform, there's a risk of uncontrolled release of reservoir water. Planned dam improvements include:
- Earthquake Safety: reconstructing and thickening the dam’s embankment;
- System Upgrades: constructing a new outlet system (releases water from the reservoir);
- Flood Protection: constructing a new spillway to current design standards and,
- Historic Structures Relocation: Relocating a historic house from Bailey Ranch and breaching Fellows Dike; and
- Safety Enhancements: incorporate other measures to address seismic and safety issues.
Project Update and Timeline
Initially, Calero Dam repairs would have required fully draining the reservoir to maintain water supply reliability. However, Valley Water developed a strategy to perform significant portions of the retrofit without reservoir drawdown, allowing for faster project completion. A new design consultant is evaluating construction phasing, prioritizing embankment and spillway upgrades before outlet work improvements. The 50% design for the first phase is done and is being reviewed by DSOD. The Draft Environmental Impact Report is expected to be available for public review in summer 2026. The remaining improvements will be designed under a Phase Two timeline. Current project costs are estimated at $142 million.
January 2025 Public Meeting
The presentation from the January 23 public meeting is available to download, and a recording of the meeting is also available to view.