Conceptual designs have been developed for correcting fish passage in Mill Creek, Walla Walla, Wa.  The existing Mill Creek channel is a 50 ft wide concrete-lined channel that has 10 ft high vertical side walls, 1V:5H sloping overbank areas and a 9 ft wide by 1.7 ft deep central trench fitted with 6.0 ft wide by 1 ft high baffles spaced a 60 ft along the length of the channel.  For the concrete flume portion, the designs depend on artificial roughness and fish resting pools for passage.  Reach Type 3 (more than 60% of the flume length) has lengths in excess of 5000 feet which will require a more detailed understanding of the proposed hydraulics to ensure fish passage.  Costs for correction of the Reach Type 3 are estimated at 7 million dollars.  

Given the costs and risks associated with passage through such a long reach, a hydraulic model study is proposed.  A 400 foot long section of the Reach Type 3 flume will be modeled and tested at the design flows.  The model scale will be 1:8.  Design testing will consist of modeling the existing flume to verify depths and velocities from field measurements already made, and then modeling of the selected roughened channel design concept with resting pools.

The model study is being funded by $98,000 from the SRFB and $102,000 CTUIR funds (=$200,000).  Work on the Mill Creek project is being directed by the Mill Creek Working Group.