Knapp-Wham Irrigation Diversion Improvement

Clever diversion design improved fish habitat, saved water and lessened maintenance requirements.

The K-W diversion is an in-stream structure that directs water from the Entiat River into an irrigation system that serves agricultural landowners in the Entiat River valley, Chelan County, WA. The existing K-W diversion failed regularly, requiring annual in-channel maintenance that disturbed fish spawning and rearing habitat and hindered fish passage.

Our client asked GeoEngineers to design a new diversion structure that would:

  • Allow fish passage
  • Provide sufficient irrigation water
  • Enhance habitat
  • Occupy only one side of the river

Approach

GeoEngineers responded to this challenge with an innovative conceptual design that works like a traditional irrigation diversion structure, but looks and functions like an in-channel bar with an associated side channel.

Results

The new diversion structure diverts sufficient water into the combined irrigation system with an overall water savings, but blends into the landscape and provides a refuge for threatened and endangered fish species. The new structure also:

  • Lowers obstacles to fish passage compared to traditional diversions
  • Minimizes the need for costly and disruptive maintenance
  • Integrates seamlessly with the surrounding landscape and disguises the related irrigation structures

Permitting agencies liked the concept so much they were prepared to take the unusual step of authorizing the design in draft stage. GeoEngineers designed, bid, permitted and built the entire project in six months.

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