Chewuch Diversion Renovation
Project Location: Chewuch River
Landowner: WA Department of Fish and Wildlife
Species Benefitted: Spring Chinook Salmon, Steelhead Trout, Bull Trout
Funding: Bureau of Reclamation (Phase 3)
Partners:Chewuch Basin Council, Bureau of Reclamation, Chewuch Canal Company
For nearly 100 years, the Chewuch Diversion dam has provided irrigation to local farmers and ranchers in this fertile region just north of Winthrop, Washington. The dam has seen many modifications since its original construction. The most recent, designed by U.S. Bureau of Reclamation in 2005, was built to improve fish passage and irrigation reliability. A feature of the 2005 structure was a natural cobble bed fish bypass channel. Unfortunately, high sedimentation at the site compromised fish passage, forcing the local irrigation canal company to enter the river annually to clear sediment from the channel.
The main reason for the high sedimentation at this site was the existence of a large, re-circulating, standing wave just downstream from the dam, resulting from the hydrology of the dam structure itself. In addition to depositing large amounts of sediment in the fish passage, this permanent wave also posed a significant hazard to the recreating public.
As irrigation diversion renovations over the last four years have removed fish passage barriers on the Chewuch River, boater activity has increased. Increased recreational activity called for sensible dam renovations that would improve human safety and protect the three threatened and endangered fish species that pass through this system.
In the spring of 2008, MSRF partnered with the Bureau of Reclamation to assist with permitting and constructing the needed modifications to address fish passage and boater concerns at the structure. Unique to this effort, the Bureau developed a scale model at their hydraulic laboratory in Denver, Colorado to physically assess the effects of potential improvements to the Chewuch Diversion dam. This modeling effort led to the design and construction of a grouted rock ramp below the crest of the dam, which reduced the wave energy and so lessened sediment deposition in the fish channel, while improving boater safety by eliminating the standing wave.
MSRF will oversee reseeding and site restoration in the spring of 2009 and continue to monitor the Chewuch Dam diversion through 2012, ensuring that lasting benefits are maintained.