Valley Water reaches milestone in tunnel project at Anderson Dam; planning continues for seismic retrofit project

Valley Water reached a milestone in the summer of 2024 when construction crews completed the final stretch of a 1,736-foot-long tunnel next to Anderson Dam.

Construction crews used a specialized Micro-tunnel Boring Machine to tunnel the final 347 feet, driving 30 feet below the water's surface. Once the machine drove through the last piece of hillside, crews needed to remove it. In September, a team of divers and other construction workers attached a large crane to the machine sections and lifted them from the reservoir.

While the tunneling is complete, work still needs to be done before construction on the dam begins. Valley Water is preparing the downstream creek channel to safely convey the higher flows of water from the new outlet tunnel. We are also doing more work inside the tunnel, including installing a lining to provide additional structural support.

Once completed, the new, larger tunnel will increase Valley Water's ability to release water from the reservoir during an emergency.

Valley Water is also making significant progress on a massive structure between the tunnel entrance and Coyote Creek. This diversion outlet structure, which has walls 30 feet tall, will be connected to the tunnel with large-diameter steel pipes. It is designed to reduce the speed of water leaving the reservoir before it enters Coyote Creek.

We anticipate completing the tunnel project by mid-2025. Once we finish building the tunnel, we can start on the project's next phase, which involves strengthening the dam to withstand a large earthquake. We're aiming to begin construction on the dam retrofit in 2026. Our agency is now finalizing the project's design, permitting process, and environmental review.

Our work to retrofit Anderson Dam is a significant undertaking. We must work closely with state and federal regulators, the community, and our contractors to successfully deliver these projects.

Valley Water's top priority is rebuilding Anderson Dam. Once completed, Anderson Reservoir will be able to store nearly 90,000 acre-feet of water, enough to supply almost 1 million people for a year. This project will help ensure public safety, protect our regional water supply and provide environmental benefits for future generations.