|PG&E Admits Scott Dam Faces Serious Seismic Risks
As mentioned above, PG&E announced last week that they will never again close the gates on top of Scott Dam. This will permanently reduce the Lake Pillsbury reservoir capacity by about 20,000 acre feet. The company says they made this decision “out of an abundance of caution in the interest of community safety”.
In a filing to the Federal Energy Regulatory Commission a few days later, PG&E explained that a March 14 memo from their engineering consultants Gannett Fleming, Inc is what prompted this sudden action to reduce the volume of water in the reservoir. The referenced memo is, of course, classified as Critical Energy Infrastructure Information (CEII) and not available to the public, but it’s clear that the contents of that memo startled the company enough to prompt immediate action.
Friends of the Eel River has been focused on the questionable dam safety analysis at the Potter Valley Project for years. We’ve even gone so far as to publicly question whether PG&E is concealing dam safety liabilities.
Analysis of the San Andreas Fault system by the USGS reveals that the Bartlett Springs Fault, one of three major structures in the system, is capable of producing up to a magnitude 7 earthquake. We also know, from a study we commissioned by Miller Pacific Engineering in 2018, that the active landslide adjacent to the south abutment of Scott Dam presents significant geologic hazard to the dam.
And of course, we can’t forget about the unusual construction of Scott Dam. As we outlined in one of our dam safety blogs two years ago, Scott Dam had to be redesigned mid-construction to accommodate a large unstable boulder that was originally thought to be bedrock. This boulder, named “the knocker”, now sits just behind the dam near the sharp angle that resulted from the seat-of-the-pants redesign back in 1920. Without more transparency from PG&E, we are left wondering whether that design change resulted in a weaker structure.
This reduction in reservoir capacity may make it more challenging for PG&E to maintain temperatures appropriate for salmon and steelhead. However, thanks to our pending Endangered Species Act litigation against PG&E and FERC, both entities are on notice that continued harms to Eel River fish will not be tolerated. We have reason to believe that the National Marine Fisheries Service will once again be firm that PG&E must maintain at least a 30,000 acre foot pool of cold water in the reservoir to ensure that downstream releases are cold enough for native fish to survive.
Further reading here.