DESCRIPTION
Mill Creek is a priority for Mid-Columbia summer steelhead recovery in the Walla Walla basin and the Tri-State Steelheaders have been partnering with the SRSRB, WDFW and CTUIR to fund and implement fish passage through the USACOE regulated flood control structure through the City of Walla Walla. The Reach Type 7 passage barrier is located in four areas of the concrete channel; the first is just upstream from 3rd St, the second is under 2nd St the 3rd is in the underground tunnel downstream from Colville St and the last is between Spokane St and Palouse St.. In total the reach type is ~1,200 ft long. A design will need to be completed for the 1,200 ft prior to initiating permitting for construction.
A flood control project on Mill Creek at Walla Walla includes a diversion dam, storage reservoir, and a 6.7 mile long flood control channel, which includes 263 channel spanning weirs (sills) and and a concrete flume.
The flood control channel creates water quality problems and presents a series of complex fish passage barriers. ESA listed steelhead, and bull trout, and reintroduced spring Chinook utilize the flood control channel during migrations. Returning adults encounter flow-dependent passage problems associated with channel spanning weirs, light attraction barriers (in the underground sections), and a lack of resting water in the concrete channel section, among other problems. Juvenile fish encounter low spring flows, and high water temperatures in late spring. Often by mid-May adults and juveniles become trapped in the flood control channel where they experience lethal temperatures. Many of these passage issues are considered as imminent threats in the Snake River Salmon Recovery Plan. Mill Creek, upstream of the flood control project, is a critical and under-utilized area for spawning and rearing of ESA listed species, and provides for an important recovery opportunity for those listed fish, as well as good habitat for other native fish and reintroduction efforts for spring Chinook.
This project will build on the design and flow model tests produced in the Mill Creek Barrier Assessment completed in 2009 and scale model tests to provide fish passage through the concrete flume section of the flood channel. Fish passage alternative have been identified in the assessment and include the development of resting pools and increased roughness through much of the existing channel. Reach Type 7 is short in length totaling 600 feet in length. The channel is rectangular with a center divider with a trench and on each side. The restoration alternatives for this reach have not yet been modled.
Walla Walla River Population
