Pacific Gas and Electric Company (PG&E) has raised concerns about the seismic stability of Scott Dam, and plans to restrict water flow to lower the water level in the reservoir. This will be an expedited measure to limit potential seismic instability of the dam. The decision has been influenced by a recent analysis by the utility’s engineering consultant, which shows that the proposed restriction will improve the dam’s expected stability and safety performance during a major earthquake.
PG&E owns and operates Scott Dam and Lake Pillsbury, including the rest of the Potter Valley hydropower project. In the meantime, the spillway gates at the top of the dam will remain open, causing Lake Pillsbury to be 26% lower than it normally is, leading into spring. According to PG&E, with the dam gates remaining open, water availability will be similar to dry year conditions experienced in 2020 and 2021.
Environmental group Friends of the Eel River has long questioned the seismic safety of the Potter Valley Project due to its location near the Bartlett Springs fault, an active landslide on the southern abutment, and a giant boulder that fits right behind the dam. However, due to laws about the confidentiality of infrastructure vulnerabilities, that information is secret. The district manager for the Russian River Flood Control and Water Conservation Improvement District, Elizabeth Salomone, stated that the news was “devastating for the Mendocino County Russian River watershed,” as the upper portion of the Russian River is reliant on Lake Mendocino, which is a reservoir that does not see them through extended drought periods.
PG&E is yet to submit a plan to remove the dam, but it is already planning to submit a variance request to manage the flows out of Lake Pillsbury to keep the levels in the reservoir low. The Potter Valley Irrigation District has a separate contract with PG&E for its water. Janet Pauli, a representative of the Irrigation District, said that a lot of uncertainty remains, but she is expecting this year’s grapes to make it through the cold.
One of the Potter Valley Project’s mitigation measures is releasing cold water for salmon from the bottom of the Lake Pillsbury reservoir into the Eel River. Charlie Schneider, the Lost Coast Project Manager for California Trout, has stated that the habitat below the dam does not make up for the habitat behind the dam, which is inaccessible to the fish. California Trout has long advocated for the full removal of the Potter Valley Project, including Cape Horn Dam and the Van Arsdale reservoir in Potter Valley. Schneider said that California Trout’s main concern is “to make sure that this obsolete project that’s kind of falling apart now is still able to take care of the fishery and manage its impact on the Eel River in that interim period before the project is decommissioned…so we want to make sure that the ultimate outcome here is dam removal, which is going to benefit the river and the fishery, but in that interim period, we want to make sure we’re not killing off all the fish.”
PG&E has not submitted a plan to remove the dam, but it is considering the expedited partial or full removal of Scott Dam as a long-term mitigation measure. The utility company is in the process of developing a plan to surrender the entire Potter Valley hydropower project.