Effects of sediment release following dam removal on the aquatic biota of the Klamath River. Final Technical Report

Four dams on the Klamath River are under consideration for removal: Iron Gate, Copco 1 and 2, and J.C. Boyle. These dams are located between river miles 196 and 225 in Oregon (J.C. Boyle) and California (Iron Gate, Copco 1 and 2), downstream of the Upper Klamath Lake. Dam removal options currently under consideration would result in 1.3–2.9 million metric tons of fine sediment (sand, silt, and finer) being transported into downstream reaches of the Klamath River (Stillwater Sciences 2008), resulting in high suspended sediment loads, which can result in deleterious effects on aquatic habitats and species. This report first summarizes Stillwater Sciences’s analyses of the physical properties and concentrations of suspended sediment likely to result from sediment releases. It then focuses on the potential biological effects of sediment release on aquatic habitats and species if the dams were to be removed. In addition, opportunities to reduce the impacts of dam removal were explored, and recommendations are presented based on our analysis. The long-term benefits of dam removal (although assumed crucial to recovery of the aquatic biota) were not analyzed as a part of this study.