Twentymile Creek Fish Passage Improvement
Fish Passage and Screening
Client / Agency
Lake County Umbrella Watershed Councils
Ruby Pipeline Mitigation Fund, U.S. Bureau of Land Management, U.S. Fish Wildlife Service, and Oregon Department of Fish and Wildlife
The Lake County Umbrella Watershed Councils (LCUWC) with funding provided by the Ruby Pipeline Mitigation Fund, retained River Design Group, Inc. (RDG) to evaluate an existing diversion dam on Twentymile Creek near Adel, Oregon. Twentymile Creek through the Dyke Diversion reach is bedrock-dominated with the local geology serving as a lateral and vertical channel control. Sediment deposition upstream of the dam and highly turbid water clarity during annual high flows suggest sediment and debris are readily mobilized through the reach.
The existing concrete diversion dam is believed to have been originally constructed in the 1950s and rebuilt in 1991. The dam creates sufficient hydraulic head to divert streamflow into a diversion ditch that then delivers water for flood irrigation. A steep-pass fish ladder was constructed on the river-right side of the dam when the structure was rebuilt in 1991. The fish ladder does not meet current Oregon Department of Fish and Wildlife fish passage criteria for endemic Warner sucker or Warner Lakes redband trout, and is believed to possibly be a complete upstream passage barrier.
RDG is currently evaluating three fish passage alternatives that will provide passage while maintaining a surface water diversion for the irrigator.