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Modeling Long Term Effects of Riparian Restoration for Salmon Recovery in the Lower Tolt River
Citation:
Halama, J. AND R. McKane. Modeling Long Term Effects of Riparian Restoration for Salmon Recovery in the Lower Tolt River. 2019 Northwest Indian Fisheries Commission (NWIFC) Habitat Conference, Skokomish, WA, October 23 - 24, 2019.
Impact/Purpose:
The Northwest Indian Fisheries Commission (NWIFC) – a natural resources management support service organization for 20 treaty Indian tribes in western Washington – holds an annual Habitat Conference each year to discuss and coordinate tribal fisheries habitat restoration projects throughout the region. The Snoqualmie Tribe and EPA’s Pacific Ecological Systems Division (PESD) are collaborating to utilize two PESD models – a watershed simulator (VELMA), and a riparian shade and stream temperature model (Penumbra) – to help inform salmon habitat protection and restoration planning efforts for the Tribe’s traditional lands in the Snoqualmie River Basin. The Snoqualmie Tribe invited PESD staff to codevelop a NWIFC Conference poster describing how these models are being used to inform the Tribe’s riparian restoration efforts in the Tolt River floodplain. Impacts of logging, agriculture, urbanization and flood control in the flooplain have severely diminished freshwater habitat quality. Reduced summer stream flows coupled with increased temperatures in the floodplain have especially limited spawning and rearing success of culturally-prized and endangered populations Puget Sound Chinook, Coho and Steelhead. Our collaborative modeling and Lower Tolt River restoration efforts aim to improve in-stream thermal refuges (cool spots) that potentially can be accentuated through well-targeted riparian tree plantings. The Tribe has been leading the community-based Lower Tolt tree-planting program since 2013.
Description:
Under a pilot study, the Snoqualmie Tribe and US EPA collaborated to utilize a previously developed watershed-scale model combined with related tools to help inform habitat protection and restoration planning efforts for the Tribe’s traditional lands in the Snoqualmie River Basin. Since 2013 the Tribe has been leading a community based effort to restore degraded riparian habitat along both sides of the lower Tolt River in Carnation, WA. Habitat quality and quantity along the lower Tolt has been diminished due to impacts from logging, agriculture, infrastructure, urbanization and flood control resulting in increased temperature and sedimentation, decreased large woody debris and biodiversity, and altered flow regimes. Collectively, these changes have contributed to declines in fresh water productivity for multiple species of salmonids including key populations of ESA listed Puget Sound Chinook, Coho and Steelhead. EPA’s VELMA (Visualizing Ecosystem Land Management Assessments) model has been used to quantify the effects of forest management on streamflow, water quality and quantity, large woody debris and forest productivity in the Pacific Northwest (1). EPA’s Penumbra model has been used to estimate effects of topography and vegetation on ground-level shade and irradiance at high spatial resolutions across landscapes (2). VELMA and Penumbra working in conjunction allows for dynamic simulations of forest and riparian restoration actions including: change in stream flow, the impact of solar energy due to increased shading, and resulting net impacts on habitat (large woody debris, stream temperature, forest structure). To assess effects of the Tribe’s 20-acre riparian restoration site on the south side of the lower Tolt river, we used Penumbra to model projected (present – 2100) increases in riparian shading as a result of increases in tree cover and height due to the Tribe’s lower Tolt river tree planting program. Using 2009 LiDAR tree cover and height data, Penumbra simulated ground-level shading at that time. To estimate future gains in riparian shading resulting from growth of plantings over the next 80 years, we substituted projected future heights of riparian plantings established since 2013. We then subtracted Penumbra’s simulated future shading from present-day shading. This approach allowed us to estimate the future increase in shading due to the Tribe’s riparian forest restoration efforts. Next steps include using Penumbra and VELMA in combination to dynamically estimate how long-term changes in shading and streamflow impact stream temperature and floodplain habitat suitability for salmonids. This modeling approach has drawn interest from various local stakeholders from the Snohomish River Basin and it is hoped that further modeling work will help provide a basis for future applications in the broader context of Puget Sound salmon recovery.