Yankee Fork WF Confluence

Project Narrative

The Yankee Fork West Fork Confluence project objectives included the following: 1) Re-establish juvenile salmonid rearing habitat and high-flow and thermal refugia. 2) Re-establish connectivity and functions between stream and floodplain. 3) Re-establish adult holding and spawning habitat. 4) Re-establish riparian vegetation, increased channel boundary roughness, improve large wood recruitment potential, increase shading and cover, and increase nutrient inputs and cycling. This project, implemented by Trout Unlimited, restored 1.29 miles of the Yankee Fork Salmon River and West Fork Yankee Fork by relocating the confluence of the two streams back to its historic location from an area altered by dredge-mining. 0.74 miles of stream channel and 0.55 miles of off-channel stream were constructed and/or enhanced using heavy equipment, which included excavating 29 pools and installing 83 LWD structures and 350 individual logs. Additionally, 379 cubic yards of spawning gravel were placed in 0.13 mile of stream. Riparian work included placement of 40 brush-trench structures on the restored floodplain for roughening, removing invasive/noxious weeds annually from 0.52 miles of historic streambed, and revegetating 7.5 acres along both streambanks (1.29 miles of stream).
A 7.4 acre area of floodplain that had been destroyed by placer mining and stockpiling of waste materials for more than 60 years was restored. Dredge tailings were removed and re-graded from 2.8 acres and topsoil added, 4.6 acres of dredge tailings were not removed, but regraded and topsoil added; upland native species were used for re-vegetating these areas to stabilize the effected acres. Four alcove wetlands comprising 0.57 acres were restored during this project; these areas were impacted by the altered hydrology resulting when the historic sinous stream was straightened and stream confined by dredge piles. Some were reconnected through the channel reconfiguration and some had structures installed. Wetland areas were replanted with native species. The majority of project construction was accomplished during the months of July and August in the years 2015 and 2016. A 50-year flood event in the spring 2017 caused un-anticipated changes to the final project. While most of the project remained unaltered or was altered to a naturally functioning condition, a few locations have the potential to trend away from recovery for some time before naturally trending toward recovery. Adaptive management in 2017 included removal of 25 cubic yards of gravel from the inlet to Main Channel 3, replacement of LWD to the Apex Jam at Main Channel 3, a channel-spanning log added to Side Channel 3, and alluvium re-graded on Side Channel 1 floodplain. Additional adaptive management was conducted in 2018 by adding 11 piece of LWD to the bleeder-log-jam at the inlet of Side Channel 1. The outcome of the implemented Yankee Fork West Fork Confluence Project is that the stream and floodplain restoration is addressing the limiting factors for Yankee Fork Chinook and steelhead populations. Habitat metrics in the project area are being monitored and compared to reference sites on a long-term scale using the ChaMPs program. Recruitment and survival of Chinook Salmon and steelhead are being monitored by the Shoshone-Bannock Tribes using PIT tag, weir, and screw trap methods. Increases in abundance and productivity are expected to follow the battery of habitat restoration activities occurring in the Yankee Fork, but long-term trends are not able to be established at the project site level at this early stage. Trout Unlimited implemented this project in coordination with the Bureau of Reclamation, Bonneville Power Administration (BPA), the Shoshone-Bannock Tribes, Idaho Governors Office of Species Conservation, the Salmon-Challis National Forest, National Marine Fisheries Service, the US Fish and Wildlife Service, and Idaho Department of Fish and Game.