10/23/2026
In 2020, as a result of significant geotechnical investigations, engineering review, and predictive modeling, FERC and CA DSOD issued a safety directive to Valley Water to restrict the water elevation such that the reservoir could only contain 3% of its total 89,000 acre-feet storage capacity until the dam and facilities could be rebuilt to current design & safety standards. With the current reservoir outlet capacity at only 48”, this existing infrastructure cannot keep the reservoir from rising rapidly during periods of heavy precipitation such as occurred in 2017. If an earthquake occurs with a high reservoir level, the dam & existing infrastructure could sustain serious damage and potentially fail.
The Anderson Dam Tunnel Project (ADTP) is the precursor to the much larger scale project that will follow it, the Anderson Dam Seismic Retrofit Project (ADSRP) where the physical earthen dam will be deconstructed and re-built with modern methods and facilities. The steel piping installed for ADTP serves purposes both during the construction phase of ADSRP and after ADSRP is completed. In its current configuration, the steel piping and valves serve as a controlled drain (Low-Level Outlet) for the reservoir in the event of a large inflow of water AND a compromising of the existing 48” outlet piping. Once the ADSRP project progresses to the point of completion, the piping installed during ADTP will no longer serve as the Low-Level Outlet, but as the High-Level Outlet that will be the primary means of controlling reservoir elevation before water rises to the point of cresting the spillway. The 13’ steel pipe will be blocked off at the current tunnel elevation upstream of the shaft bottom lateral, and new piping will be installed from the reservoir connecting to the 13’ horizontal pipe that protrudes from the concrete structure at the top of the shaft.
