Anderson aerial view

Water level in Anderson Reservoir reaches 3% capacity

Since Oct. 1, Valley Water has gradually released water from Anderson Reservoir through the existing outlet. Water levels in Anderson Reservoir recently dropped to 3% of capacity, the lowest level that can be reached through the existing outlet tunnel.

Valley Water will maintain this 3% level moving forward as we work on projects designed to strengthen Anderson Dam and provide greater control of water levels in the reservoir.

Valley Water lowered the water levels in Anderson Reservoir in response to an order by the Federal Energy Regulatory Committee to reduce the risk to the public should Anderson Dam fail during a major earthquake. Valley Water released water at a rate of about 200-acre feet, or 65 million gallons a day.

Because of the lack of early-season rain, Anderson reached the 3% level in less than three months. Valley Water may continue to release water from Anderson Reservoir once it begins capturing storm runoff from winter rains.

The next step in our work at Anderson Dam is to build a 1,700-foot-long tunnel, up to 24-feet in diameter, on the left side of the dam looking towards the reservoir. The new tunnel will increase the amount of water that can be released from Anderson by five times, allowing Valley Water greater control over water levels in the reservoir. Work on the outlet tunnel is expected to begin in early 2021, and we estimate it will take two to three years to complete.

Valley Water will begin work on retrofitting the dam embankment and spillway once the tunnel is complete.  That effort, known as the Anderson Dam Seismic Retrofit Project, is estimated to start in 2024 and will last about seven years.

For more project information, including meeting materials, frequently asked questions, reports and other project-related documents, please visit the project web page at


  1. Once the Seismic Retrofit Project is underway – will the old dam be removed completely ? what’s the plan for controlling high cfm runoff from large storms to prevent local flooding ?


    1. We will remove all liquefiable material and reconstruct the dam embankment. We will keep the dam’s clay core. Valley Water is building a high-capacity channel that will accommodate the water flow from a bigger outlet valve. Those larger flows will be about 2,500 cfs, up from about 500 cfs. This allows Valley Water to leave Coyote Creek intact as it is now. Coyote Creek will continue to flow for the entire 10-years of construction using the pump station pipe outlet near the base of the dam. For more information, including recordings of recent public meetings and presentation, please visit


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