This contract provides matching funds to the construction portion of our Mill Creek Passage - Gose St project.   This project is expected to be majoritively funded through the Brian Abbott Fish Barrier Removal Board.

In February of 2020, a flood of record in the Walla Walla watershed had the Mill Creek flood control channel operating at capacity for hours. The flood flow scoured the channel bed downstream of an existing fishway, and the downcutting resulted in a five-foot high jump for fish to enter the fishway. A short term, emergency passage fix was completed in October 2020, but it is not expected to be a permanent fix.

In our geomorphic analysis conducted for the conceptual design, we've identified significant scour further downstream of the fish ladder that, if not addressed, will create new passage barriers as the creek continues to incise. Since the installation of the flood control channel upstream, which cut off this reach from sediment movement, there has been up to 20 ft of incision over the last 75+ years. Without intervention, this incision will continue unabated. An ecological concern is the poor instream conditions downstream of the flood channel. The channel is deeply incised and disconnected from the flood plain. High energy and sediment-starved flow contributes to the down cutting downstream of fishway.

The project addresses the barrier at the downstream end of the Mill Creek flood control channel. Mill Creek is a tributary of the Walla Walla River. The Gose Street bridge is at approximately river mile four of Mill Creek, at the transition between the flood control channel and the natural channel. The Snake River Salmon Recovery Plan for SE Washington identifies Mill Creek as a major spawning area for ESA-listed Mid-Columbia summer steelhead (Chapter 5 of the Recovery Plan [Section 5.5.2.3 pp 155-156]). Additionally, this section of Mill Creek serves as a migratory corridor for reintroduced Mid-Columbia Spring Chinook, and Bull Trout. Fishway improvements at Gose Street will improve access to at least 2 miles upstream; the next fish passage barrier upstream is the Mill Creek concrete flood control channel, which is the subject of passage improvements through state and federal agencies external to BPA. Passage improvements throughout these heavily modified reaches of Mill Creek will facilitate migrating fish accessing high quality spawning and rearing habitat in the headwaters of the Mill Creek watershed.

The Mill Creek reach at Gose St. and downstream is configured so that fish passage, flood protection, and secure infrastructure are provided in a long-term, low-maintenance manner. Our goal is to provide volitional fish passage for target species mid-Columbia Steelhead, Bull Trout, and reintroduced Chinook adults and juveniles. Out of stream construction is scheduled to begin as early as fall of 2025, pending landowner approval. The remainder of in-stream work is expected to begin during WDFW's approved in-stream work window for 2026 (July 15 to September 15).

Engineering designs were reviewed and approved through HIP in Contract 94694. Final designs and supporting documents are on file with the BPA EC Lead. The bulk of the BPA funding for implementation will be allocated for staff time for construction oversight and some on-the-ground work. The majority of implementation funding will be provided through cost-share sources external to BPA.