Garrison Creek is a distributary of Mill Creek that flows through the cities of Walla Walla and College Place. Water is diverted from Mill Creek at the Yellowhawk Diversion Dam near the Mill Creek Flood Control Office. After passing through the culverts under Reservoir Road, the diverted waters enter a division box that splits the Yellowhawk water and the Garrison Creek water. In general, about 19 cfs is sent down Yellowhawk Creek and 4-6 cfs is diverted into Garrison Creek. Although the primary function of these distributaries is to handle a portion of flood waters during high water events, anadromous fish use Yellowhawk as a passage alternative to coming up the Mill Creek Flood Control Channel.
Numerous passage barriers prevent upstream migration of salmonids on Garrision Creek but the unscreened diversion allowed juvenile out-migrants to pass into Garrison and become stranded, resulting in high levels of mortality. In 2008, the WWCCD and its partners embarked on a design-construct project to install a site specific state-of-the-art self cleaning fish screen using the newest technology to meet NOAA Fisheries screen requirements and eliminate the “take” that historically occurred through irrigation withdrawal. A number of challenges had to be overcome due to the project being sited on land controlled by the U.S. Army Corps of Engineers, the unique nature of the diversion, and a short time frame. But all partners worked to make the project happen. The project had excellent support from the Corps, WDFW, and the Confederated Tribes of the Umatilla Indian Reservation. The Washington State Salmon Recovery Office agreed to a time extension on the grant providing most of the funding. The design team from HDR-Fish Pro, in consultation with the WDFW Yakima screen shop, completed the design in record time. The Conservation District brought these groups together, hired the best available contractors, and result is a new screen that protects endangered fish species while allowing continued irrigation from Garrison Creek. Click here to read the final report: Final Report For Garrison Creek Screening