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 floodprone width of approximately 300 feet. The Nursery Bridge Reach is a highly altered portion of the Walla Walla River that includes several road and railroad crossings. Currently, the energetic, leveed reach above the grade control structure (GCS) transports sediment through the Nursery Bridge reach where it locally deposits sediment in the vicinity of the GCS, largely due to the geometry of the river at this location and hydraulic shading from bridge piers in the channel.





This project is intended to address the factors identified above that impact ESA-listed salmonids. The objective of this project is 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.





Fish passage stability will be achieved through a combination of designed features. An armored bar immediately upstream of the GCS is intended to realign the channel with the Eastside Fishway entrance and the WWRID diversion. A shallow notch in the GCS and an approximately 350-foot roughened riffle low flow channel will be constructed to maintain mobility of bedload through the reach and a stable low-flow channel directly upstream of the GCS across the Eastside Fishway and WWRID diversion entrances. The proposed channel alignment and designed structures will reduce the need for annual dredging and provide access to critical sections of the channel that would allow for maintenance without mobilizing equipment into the stream. Instream restoration actions upstream of the GCS and roughened riffle include excavating approximately 2,645 linear feet of side channel to reinitiate perennial flow and installing 25 engineered log jams in the main channel and in side channels.





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.





PCSRF funds for this project would specifically be spent on subcontract fees for constructing the roughened riffle structure to enhance fish passage.





Worksite #1 Proposed Work:



This project is intended to enhance fish passage and increase instream habitat in an approximately 3,075-foot reach in the vicinity of Nursery Bridge by creating an 18-inch deep by 20-foot wide notch in the crest of the GCS near the entrance of the Eastside Fishway, and constructing an approximately 350-foot long roughened riffle with low flow channel and armored bar to maintain channel alignment with the GCS notch. The grade-controlled low flow channel is designed to maintain water surface elevations to reliably deliver water to the entrance to the Eastside Fishway and the WWRID point of diversion with minimal annual maintenance and disturbance to the channel.





Upstream of the GCS, the CTUIR is proposing to excavate 2,645 feet of side channel to reinitiate perennial flow to provide off-channel rearing habitat for ESA-listed salmonids at a variety of flows. 25 engineered log structures, including bar apex jams, bank habitat jams, and log revetments, will be placed in the approximately ½ mile above the GCS. The CTUIR is proposing installing 334 pieces of large wood

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.