Spillway gates on Scott Dam to remain open, curtailing flow into East Branch
PG&E announced this week that the spillway gates on top of Scott Dam will remain open, which will lower the level of Lake Pillsbury by about a quarter, and curtail flow into the East Branch of the Russian River to those of dry years like 2020 and 2021.
PG&E has signaled strongly that it is considering the expedited removal of Scott Dam due to seismic concerns, according to a news item in an industry publication on March 16. In the meantime, the spillway gates at the top of the dam will remain open.
This will cause Lake Pillsbury, the reservoir behind the dam in Lake County, to be ten feet, or 26% lower than it normally is, heading into spring. According to the PG&E article, “With the dam gates remaining open, water availability will be similar to dry year conditions experienced in 2020 and 2021.”
PG&E owns and operates Scott Dam and Lake Pillsbury, along with the rest of the Potter Valley hydropower project, which diverts water from the Eel River into the Russian River. The utility is in the process of developing a plan to surrender the entire project.
Early Friday afternoon, PG&E filed a document with FERC, the Federal Energy Regulatory Commission, explaining that according to the results of a recent analysis, “proactive steps to limit the potential for seismic instability of Scott Dam are necessary at this time;” including maintaining the lower water level in the reservoir. The filing states that, according to a memo prepared by its engineering consultant on March 14, “the proposed restriction will improve the dam’s expected stability and safety performance during a major earthquake.”
The Friends of the Eel River is an environmental group that has questioned the seismic safety of the Potter Valley Project for years. That information is secret due to laws about the confidentiality of infrastructure vulnerabilities. “We’ve been raising concerns about Scott Dam’s location near the Bartlett Springs fault, about the active landslide on the southern abutment, about the knocker, that giant boulder that fits right behind the dam and is the reason that Scott Dam has that really unusual sharp angle in its construction,” said Alicia Hamann, Executive DIrector of Friends of the Eel River. “It’s frankly really kind of validating to see PG&E and FERC starting to take these concerns seriously.”
Elizabeth Salomone is the District Manager for the Russian River Flood Control and Water Conservation Improvement District, a water wholesaler and a leading water manager for the Upper Russian River in Mendocino County. She said the news was “devastating for the Mendocino County Russian River watershed…The upper portion of the Russian River is reliant on Lake Mendocino, which is a reservoir that does not see us through extended drought periods. It needs to refill every winter to meet historical water use levels. And that doesn’t count for carry-over, in case there is a dry winter.”
PG&E has not submitted a plan to remove the dam at this point, but it is already planning to submit a variance request, to manage the flows out of Lake Pillsbury to keep the levels in the Lake Pillsbury reservoir low. The utility is anticipating a minimum flow of 5-25 cubic feet per second to the East Branch of the Russian River, which flows into Lake Mendocino.
The Potter Valley Irrigation District has a separate contract with PG&E for its water. The Irrigation District’s Janet Pauli said a lot of uncertainty remains, but she’s expecting this year’s grapes to make it through the cold. On Friday, she said that, “As far as I know and from what I’ve been told today, we’ll for sure be able to access our frost protection water this spring, which of course is critically important…the way the frost protection works in our contract with PG&E is, we request it. We don’t get just a certain block of water.” Instead, the district has to let PG&E know in advance when frost is in the forecast, and how much they will need to fill ponds for a particular period of frost protection. “What’s going to happen with our summer supply,” she said; “It has yet to be determined.”
Another thing that remains to be determined is exactly how to maintain a cold water pool below Scott Dam. One of the project’s mitigation measures is releasing cold water for salmon from the bottom of the Lake Pillsbury reservoir into the Eel River, though, according to Charlie Schneider, the Lost Coast Project Manager for California Trout, “The habitat below the dam does not make up for the habitat behind the dam,” which is inaccessible to the fish. CalTrout 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 CalTrout’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”
The next-to-the-last sentence of PG&E’s article about keeping the spillway gates open is far from definitive. It reads, “The company plans to continue to develop long-term mitigation measures which could include expedited partial or full removal of Scott Dam.”
Hamann is focusing on the possibility of things moving fast. “I’m a bit of an eternal optimist,” she said on Friday; “so the key word that I hone in on in that sentence is ‘expedited.’”
Salomone is not quite as optimistic about the expedited nature of the much-reduced flow, which is a certainty with the spillway gates staying open as long as the dam is in place. “One proposal that’s been put forward is the removal of Scott Dam, and then continuing with what we call the run of the river, or what would be wintertime transfers from the Eel to the Russian River,” she said. “And with that, there was an understanding that we would need to reduce our reliance on those summertime Eel River diversions, if that was the option that happened in the future. But that was in the future. We thought we had some time to turn the bus around on this. And now we’re finding, dramatically, we do not have time.”