Four dams on the Klamath River owned by PacifiCorp (Iron Gate, Copco 1 and 2, and J.C. Boyle) are being considered for removal to improve fish passage and water quality. Numerical modeling under various scenarios predicted that dam removal could release up to 3.2 million tons of reservoir sediment to downstream reaches, the majority of which would be released in the first year following removal (GEC 2006, Stillwater Sciences 2008). Little sedimentation or increase in flood stage heights are expected to occur downstream of Iron Gate Dam (Stillwater Sciences 2008). Additional studies assessed the potential effects of dam removal on fish and water quality in the lower Klamath River (Stillwater Sciences 2009a, Stillwater Sciences 2009b). This study was commissioned by the California State Coastal Conservancy to place them anticipated sediment release from dam removal into the context of background sediment delivery from watershed sources. Specific objectives of the study included (1) summarizing existing information about the quantity and size distribution of background sediment delivery from the watershed to the Klamath River, (2) comparing estimates of the cumulative background sediment delivery with independent estimates of total sediment flux, and (3) comparing modeled estimates of sediment release from dam removal with estimates of background sediment delivery.
The Klamath River traverses 254 mi and drains a 15,722 mi2 area that includes the Modoc Plateau, Cascade Range, Klamath Mountains, and Northern Coast Range. The Klamath River watershed can be divided into upper and lower basins with distinctly different climatic, geologic, geomorphic, and hydrologic characteristics. The geologic boundary between the upper and lower basins occurs a short distance downstream of Iron Gate Dam near Cottonwood Creek.Keyword Tags: