Qualitative assessment of prolonged facility removal for the Klamath River dams

The U.S. Department of the Interior (DOI), as the National Environmental Policy Act (NEPA) lead agency, and the California Department of Fish and Game (DFG), as the California Environmental Quality Act (CEQA) lead agency, are currently developing an Environmental Impact Statement/ Environmental Impact Report (EIS/EIR) for the Klamath Hydroelectric Settlement Agreement (KHSA) and the Klamath Basin Restoration Agreement (KBRA). The EIS/EIR will evaluate the environmental and social effects of a set of alternatives that may include removing all or portions of J.C. Boyle, Copco 1 and 2, and Iron Gate dams on the Klamath River, which would provide volitional fish passage to aid in restoring salmonid fisheries.

The current plan for removing the four dams calls for reservoir drawdown during the winter of 2019 in a controlled manner, releasing the majority of the erodible sediments to the middle and lower Klamath River prior to the summer of 2020. This approach would limit the major fisheries impacts to the winter of 2019 and spring of 2020. Based upon a recent fisheries impacts analysis that considered predicted suspended sediment concentration and duration as well as geographic distribution and life-history traits of focal fish species in the downstream river reaches, suspended sediment impacts would be sub-lethal for most species and life stages, while some species and life stages would experience lethal impacts (Stillwater Sciences 2011).

Some stakeholders involved in the EIS/EIR and Secretarial Determination process have questioned the current dam removal plan and have asked if impacts to aquatic species could be reduced by prolonging the release of erodible sediments over multiple years. A prolonged release period can potentially decrease suspended sediment concentrations at any given point in time but would extend the number of years of relatively high concentrations in the river downstream of the dams.