Nursery Bridge Reach Phase II Fish Passage and In-stream Habitat Enhancement

The Nursery Bridge Reach of the Walla Walla River is one of two major fish passage bottlenecks in the Walla Walla subbasin that currently impact recovery of Middle Columbia River summer steelhead, Columbia River bull trout, and spring Chinook salmon. Over a century of impacts from urbanization, channelization, and agriculture has resulted in extreme constriction of the Walla Walla River, reducing its nearly 5-mile-wide active alluvial fan to the current flood prone width of approximately 300 feet. The Nursery Bridge Reach is a highly altered portion of the Walla Walla River near Milton-Freewater, Oregon, that includes several road and railroad crossings, a significant point of diversion for senior water users of the Walla Walla River Irrigation District (WWRID), and an extensive US Army Corps of Engineers-authorized flood risk management project consisting of a levee system and a large grade control structure with two associated fishways.



The Nursery Bridge Phase II Fish Passage and In-stream Enhancement Project (hereafter “the Project”) was intended to address the factors identified above that impact ESA-listed salmonids. The objective of this project was to provide stable fish passage connectivity to the Eastside Fishway at the GCS, reliable inflows to the WWRID diversion, and habitat for salmonids over a range of flows.



Since this project was initiated in FY2019, CTUIR has worked with project partners and stakeholders to implement a phased project to address fish passage in the Nursery Bridge vicinity of the Walla Walla River. In that time, CTUIR produced 60% designs in spring 2020, shortly before the February 2020 high flow event materially changed the infrastructure in the reach. CTUIR continued to develop new concepts and preliminary designs to respond to the changed site conditions and stakeholder needs and settled on a focused set of actions to address fish passage, including a notch in the grade control structure and relocating the Eastside irrigation point of diversion. Stakeholders have broadly agreed on evaluating the proposed actions, but consensus among critical project partners on the required memorandum of understanding for permitting has been difficult to obtain.



While CTUIR and critical project partners continue to negotiate the memorandum of understanding, CTUIR used a portion of the FY2019 PCSRF award to advance the project design, producing draft permit ready designs, as well as advancing hydraulic modelling of the proposed consolidated Eastside irrigation point of diversion and water delivery system.



Ultimately, the changed conditions from the 2020 high flow event and difficulties with negotiating with critical project stakeholders have delayed progress on project implementation beyond the timeline of this grant award. As a result, the projected goals and objectives of the original project were not met and this project was terminated. However, providing reliable, volitional fish passage to the critical spawning and rearing habitat in the upper Walla Walla River remains a priority for the CTUIR and work will continue to address passage at this location.

Limiting factors for Middle Columbia River summer steelhead in the Nursery Bridge Reach include: blocked and impaired passage, degraded floodplain connectivity and function, degraded water temperature, altered sediment routing, and hydrologic alterations (NMFS 2009). Due to the infrastructure constraints in the reach, it may not be feasible to address all of the identified limiting factors; however, this project intends to address fish passage and floodplain connectivity and function in the reach.



The proposed GCS notch and low flow channel in the immediate vicinity of the GCS will create a more stable channel adjacent to the entrance to the Eastside Fishway. Providing reliable fish passage at the Nursery Bridge GCS allows access to over 70 miles of some of the highest quality spawning and rearing habitat in the Walla Walla Subbasin, located within the North and South Forks of the Walla Walla River and Couse Creek. This project would increase the efficacy of the Eastside Fishway at the GCS and allow volitional passage for all life stages of ESA-listed salmonids to meet ODFW and NMFS fish passage requirements. Additionally, the roughened riffle and low flow channel proposed in this project will remediate fish passage deficiencies at the rock weir constructed to maintain gravity flow to the WWRID point of diversion upstream of the GCS. The current rock weir has degraded such that it presents a partial fish passage barrier to some life stages of salmonids at some flows.





Degraded floodplain connectivity and function will also be addressed as a result of this project. Floodplain connectivity will be enhanced by reinitiating 2,645 feet of side channel which will increase floodplain activation at lower flows to provide off channel summer rearing habitat and low velocity refugia for winter rearing salmonids on the floodplain. Large wood additions will also increase complexity and functionality of the floodplain for juvenile salmonid rearing.



Due to the constrained nature of the flood control project in the Nursery Bridge reach, this project will likely not address the remaining limiting factors of degraded water temperature, altered sediment routing, and hydrologic alteration. These factors will be addressed in future phases of the Nursery Bridge reach project.