Whychus Creek –Fish Passage and Screening in the Upper Deschutes Basin

River Design Group, Inc. collaborated with the Upper Deschutes Watershed Council, Three Sisters Irrigation District (TSID), and the U.S. Forest Service to prepare fish passage and screening solutions for Whychus Creek, a tributary to the Deschutes River near Sisters, Oregon. Whychus Creek drains the eastern flank of the Three Sisters within the Cascade Mountain range of central Oregon. Stream geomorphology is influenced by alluvial fan processes including abundant bedload and dynamic channel conditions, and historical channel manipulations undertaken for flood water management. Periodic rain-on-snow events result in flashy, high magnitude runoff that affect channel stability.

Constructed in the early 1970s, the TSID dam is the third diversion dam built in the Whychus Creek project reach. The previous two structures were undermined by historical flood events and abandoned by TSID. The operational dam diverts water into the irrigation network and is believed to be a complete upstream fish migration barrier due to excessive jump height during low flows and elevated velocities during high flows. With recent actions to reintroduce mid-Columbia steelhead and spring Chinook salmon, addressing fish passage barriers in the Deschutes River basin is necessary to return reintroduced steelhead and salmon to natal streams.

RDG implemented a roughened channel design in October 2010. A 10-year rain-on-snow event in January 2011 affected vertical channel stability, compromising the project’s goal of fish passage. A post-runoff survey was completed to build surface and hydraulic models to investigate storm hydraulics and the channel degradation process. Investigation results will be used to prepare a maintenance design for the TSID site, and a preliminary design for a similar downstream fish passage barrier. A complementary project component included designing and implementing a vertical panel fish screen for a 2.3 cfs diversion that was relocated as part of the roughened channel implementation.