Mill Creek Fish Passage - Park to Roosevelt

This project completed fish passage improvements to 2,283 feet of the two-mile-long Mill Creek flood control channel. Modifications of the concrete channel provided depth and velocity conditions favorable to passage of summer steelhead, bull trout, and spring Chinook. Under pre-project conditions, returning adults encountered velocities that were too high for too long of a distance, without any resting opportunities. To improve passage, part of the existing channel was cut and removed. Pre-cast roughness panels replaced the removed concrete. The roughness panels have block-shaped projections which create friction in the water, slowing it to a velocity that the fish can swim for the full distance of the project. Resting pools were also added as an additional measure. During low flow, under pre-project conditions, baffles in the channel created hydraulic conditions that were a barrier to juveniles. The baffles were removed and replaced with new baffles that were sized and spaced to provide volitional passage for juveniles.

This project was originally scoped to improve 5,000 feet of fish passage in the concrete flume portion of Mill Creek that flows through Walla Walla, WA. Due to inflation, the costs of labor and materials for this work increased after the sponsor was awarded funding. The sponsor used all the resources available to stretch funds as far as possible and were only able to correct 4,081 feet of the concrete channel before funding ran out. Due to overlapping project areas the final reported passage in this project is .38 miles (project footprint from Otis to Division streets). The sponsor has leveraged funding across different RCO programs and has reported .39 miles of overlapping project areas in other funded project scopes.

The purpose is to provide adult and juvenile passage for summer steelhead, spring chinook, and bull trout through a segment of the Mill Creek flood control channel. The goals were to reduce high flow velocity, provide resting pools, and provide volitional passage for juveniles.