Presenter/s: Tracy Drury
Symposium Session: 2020 - 10 Prioritizing restoration
Topics covered: beavers, fish passage, fish-salmon, floodplain, hydraulics, lessons learned, modeling, and sediment transport
The Tucannon River was identified as a priority watershed in the 2008 BiOp and determined to be critical to recovery of Snake River Spring Chinook. Geomorphic analysis and restoration prioritization was conducted in 2010 and more than 12 million dollars has been spent implementing restoration projects based on that prioritization effort. Given the large investment over the past decade, extensive additional data available, and continued restoration effort, a more in-depth, data driven, analysis and prioritization was desired by project proponents. A part of the newly available data was fish presence and use within the watershed that was previously mostly unknown. In addition, we developed a 2-D model for 50 miles of the watershed and conducted various hydraulic and physical process analyses using green LiDAR collected in 2017. We also conducted a physical change analysis comparing the 2017 green LiDAR to red LiDAR collected in 2010.
Key components of the geomorphic analysis and restoration prioritization were floodplain connectivity analysis, channel complexity analysis, and excess transport capacity analysis. Connectivity analysis looked at the potential floodplain available for connection to floodwaters during a 5-year recurrence flow or lower. These potential floodplain areas were compared to current 2-year recurrence floodplain areas and the ability to extend them to the 5-year extent by removing blocking features such as levees, or placing log structures to retain mobile sediments and raise the river bed elevation. Complexity analysis utilized a complexity index based initially on the River Complexity Index (RCI) that added in a parameter to better capture the size, or perimeter of an island feature to better value channel margins critical for juvenile salmonids. Excess transport capacity was evaluated to help identify high energy areas to treat in order to help promote temporary storage of sediment and identify potential locations for gravel augmentation.
The prioritization is a data driven analysis that is largely comprised of the connectivity and complexity analyses with the excess transport capacity being more of an indicator and differentiator among closely rated river segments. Excess transport capacity was also used to help develop the basin scale gravel augmentation plan and identify key locations for gravel reintroduction to help “jump start” natural processes and minimize the timeline to reaching restoration potential within a given project site. Project sites are easily compared and key elements necessary of realizing restoration potential are documented and easily retrievable for all sites. The end product from this effort in not a list, but a tool that can be constantly updated as projects are completed and more information becomes available. This method presents a new look at how to use widely available information to help maximize the use of our limited restoration dollars as salmonid stocks continue to dwindle and competition for funding continues to increase.