he structure diverts water from Auburn Ravine into the Hemphill Canal, located south of the ravine, for delivery to NID raw-water customers. The diversion structure is an approximately eight-foot-high concrete structure, with an approximately 40-foot-long concrete apron extending downstream. It has been operated by NID since its purchase in 1933. Hemphill Diversion has been subject to damage during high flow events, has required ongoing maintenance, and is currently in need of additional repairs. The diversion structure has historically presented a substantial impediment to the passage of migrating anadromous fish species that spawn in Auburn Ravine upstream of the diversion.
NID considered three project alternatives to remove the diversion structure as an impediment to fish passage. The approved project, Alternative 2, will remove the diversion structure, stabilize the diversion site, construct a nature-like roughen rock ramp instream fish passage, install a fish screen, and implement improvements to a portion of the Hemphill Canal. The project is designed to allow anadromous fish to migrate past the Hemphill Diversion Structure site unimpeded.