Twentymile Creek Fish Passage

RDG was retained by the Lake County Umbrella Watershed Council and the Lakeview office of the U.S. Bureau of Land Management to assist with evaluation, design, and construction oversight for a concrete fish ladder and horizontal flat plate screen associated with an existing private diversion on Twentymile Creek. The weir-with-orifice fish ladder was designed to meet fish passage criteria for Warner sucker (federally threatened) and Warner Lakes redband trout (species of concern), the two target species in the Twentymile Creek watershed. The innovative ladder design included an orifice and a cobble bed to simulate a natural channel bed hydraulic conditions for passing the benthic-oriented Warner sucker. Removable weir walls were designed to provide flexibility in modifying hydraulic conditions in the event future research suggests a different ladder configuration is more conducive to sucker passage. The ladder design was reviewed by U.S. Fish & Wildlife Service, NOAA-Fisheries, and Oregon Department of Fish and Wildlife. Ladder construction included work area isolation and site dewatering, existing diversion dam modification, and multiple concrete pours.

RDG collaborated with Farmers Conservation Alliance (FCA) on the design and installation of a horizontal, flat-plate Farmers Screen. The screen was designed to accommodate the 6 cfs diversion flow used by the landowner to irrigate pasture down-valley from the diversion.