Thompson Falls Hydroelectric Project – Biological Assessment

Thompson Falls Dam is a 93 MW hydropower facility, built in 1917, on the Clark Fork River near Thompson Falls, Montana. GEI prepared a Biological Assessment (BA) on the federally-listed threatened and endangered species in the project area. Our assessment covered two species of fish (bull and westslope cutthroat trout), three species of mammals (wolves, lynx, and grizzly bears), and one species of bird (bald eagle).

GEI researched the current condition of the listed species, their life histories, and distribution in the project area. We also reviewed project operations, facility design, reservoir configuration, plant operations, hydrologic and hydraulic data, reservoir and tailwater elevations, water quality, spillway hydraulics, design of intakes, turbines and other hydraulic passage routes, transmission lines and substation design, and other technical literature.

GEI’s report conformed to the format used by the USFWS to determine if further actions would be needed on the project. The evaluation of the project’s impacts on bull trout was completed using the guidance contained in the U.S. Fish & Wildlife Service’s publication, A Framework to Assist in Making Endangered Species Act Determinations of Effect for Individual or Grouped Actions at the Bull Trout Subpopulation Watershed Scale.

Most attention was paid to the bull and westslope cutthroat trout. These species are migratory, but the dam does not have facilities to allow for upstream fish passage. Downstream passage was evaluated to be good due to the modern design of the new powerhouse. Conservation measures were recommended to reduce project effects. The project was not determined to effect wolves, lynx, or grizzly bears.