Project Design For Habitat Improvement in Large Streams

In the Coos basin, the Williams River is the largest tributary to the South Fork Coos River, providing important spawning and rearing habitat to fall chinook, coho, steelhead, and other important aquatic species. The Williams subbasin has been heavily impacted by past management practices, degrading instream habitat and water quality in the mainstem Williams River. The lower Williams River is a critical distribution and rearing reach connecting the South Fork Coos River to many high quality spawning habitats located in tributary streams of the Williams River, such as Cedar Creek. Many juvenile fish leave these tributaries to look for high quality rearing habitat such as high velocity refugia and habitat cover which unfortunately is very limited throughout the lower Williams River. To improve this critical rearing habitat, Coos Watershed Association (CoosWA) proposes to produce a design for instream wood structures in the 4 miles of the lower Williams River below the Cedar Creek confluence. Through this Technical Assistance project, CoosWA, BLM, and ODFW propose to conduct a hydraulic analysis and collaborate with other groups throughout the region with large stream experience to develop designs for instream structures for large streams. Through this regional collaboration, CoosWA and its partners are looking to build upon lessons learned and best management practices that have been experienced and utilized throughout the region for wood in large river systems.

Because the projects scheduled start date is before the PCSRF FFY 2020 award opens, no funds allocated for this project are reported as match to PCSRF funds.

The lower Williams River reach has good intrinsic potential for coho salmon (0.6 and greater) and winter steelhead (0.8 and greater) and provides important habitat to other aquatic species such as fall chinook, sea-run and resident cutthroat trout, and Pacific lamprey. Williams River supports multiple life stages of salmonids as it provides spawning habitat as well as winter and summer rearing habitat for juveniles. This project proposes to improve spawning and essential rearing habitat over 4 miles of the lower Williams River.

Habitat surveys and visual assessments have noted this stream reach is a pool-dominated reach with low wood volume and very little high-velocity refugia during the winter flows. This assessment was supported through the further analysis completed in the Upper South Fork Coos River Restoration Action Plan (CoosWA, 2014) where the AQI survey reaches were run through ODFW’s Habitat Limiting Factors Model to estimate the current carrying capacity and overall habitat limitations to coho smolt production in the survey area (Nickelson et al, 1992; Nickelson et al, 1998). In this analysis, wintering rearing was identified as this proposed reach’s limiting factor with low winter habitat quality and moderate summer habitat quality.

Over time, these instream structures will alter and increase the variability in hydraulic conditions resulting in the deposition of coarse sediment, sorting of existing gravels and the development of high velocity refugia and complex pools. Large wood will provide high velocity refugia for juveniles during the winter months through the development of secondary channels, eddies, and alcove and summer time habitat through the development of complex pools and provision of habitat cover. Deposition of coarse sediment will increase hyporheic flow and decrease water surface area and thermal loading, helping to maintain cooler summer-time stream temperatures. Spawning habitat for salmonids will improve through the deposition of coarse bedload material; these gravel deposits and large wood structures also play a role in the nutrient cycling process, such as nutrient retention and habitat diversity for benthic macroinvertebrates, to improve overall rearing conditions. Ultimately, these cumulative benefits are expected to increase the fish production and population vitality within the Williams River subbasin.

In the West Fork Millicoma River, numerous coho and chinook redds have been observed in locations where gravels deposited near the constructed log jams (CLJs), where only bedrock existed pre-project. Additionally, OWEB funded summer and winter snorkel surveys (OWEB #212-2020) on the West Fork Millicoma River confirmed juvenile salmon and steelhead congregate near structures. In this study, juveniles appear to use the structures as cover during the summer, darting under rootwads and boulders when spooked. Observations during winter snorkel surveys suggest that the majority of juvenile coho are found within 5-10 feet of CLJs, presumably to find refuge from higher velocities in the main channel.

Draper, D.R. and Scheidt, N.E. 2014. Upper South Fork Coos River Restoration Action Plan. Coos Watershed Association. Coos Bay, Oregon.

Nickelson, T. E., M. F. Solazzi, S. L. Johnson, and J. D. Rodgers. 1992. Effectiveness of selected stream improvement techniques to create suitable summer and winter rearing habitat for juvenile coho (Oncorhynchus kisutch) in Oregon coastal streams. Canadian Journal of Fisheries and Aquatic Sciences 49:790-794.

Nickelson, T. E. 1998. A Habitat-Based Assessment of coho Salmon Production Potential and Spawner Escapement Needs for Oregon Coastal Streams. Oregon Department. Fish and Wildlife, Information Report, 98-4, Salem. Available at: http://nrimp.dfw.state.or.us/crl/Reports/Info/98-4.pdf