Modeling floodplain and watershed restoration for salmon recovery in the Tolt River Watershed – A Snoqualmie Tribe and U.S. EPA collaborative effort.

This Snoqualmie Tribe–EPA collaborative modeling project revolved around salmon habitat restoration activities in the Tolt River Floodplain at its confluence with the Snoqualmie River about twenty miles east of Seattle, Washington. We used EPA's VELMA ecohydrological model and Penumbra landscape shading and stream temperature model to help identify floodplain and upper watershed best management practices for improving floodplain salmon habitat quality, especially cooler water, increased summer low flows, and decreased peak flows during periods of salmon spawning and rearing. Our methods focused on addressing a set of management questions toward these objectives, and builds upon the Lower Tolt River Floodplain Restoration Project initiated by King County and their partners in 2009. The range of temporal and spatial scales modeled encompassed days to decades and individual stream reaches to whole watershed. No restoration management scenarios were introduced that would not be feasible to implement to benefit floodplain salmon habitat quality across these scales. Our joint model applications have illuminated underlying causal relationships, demonstrated tradeoffs, provided a scientific basis for informing management and policy decisions, and to discover new questions to further advance salmon habitat restoration efforts within the Tribe’s ancestral lands.

Impact/Purpose

This collaborative effort brought together EPA-ORD, EPA Region 10, and Puget Sound’s Snoqualmie Tribe to use state of the art EPA modeling tools – the VELMA ecohydrology model and Penumbra stream temperature model – to illuminate underlying causal relationships, demonstrate tradeoffs, and provide a scientific basis for informing management and policy decisions to advance salmon habitat restoration efforts in the Tolt River watershed and its floodplain. VELMA-Penumbra results summarized herein set forth a practical set of salmon habitat management solutions aimed at reversing historically recent declines in salmon populations. The waters, fauna, and flora of these ancestral lands have been central to the Tribe’s cultural identity and well-being since time immemorial.

Citation

McKane, Bob, J. Halama, P. Pettus, B. Barnhart, A. Brookes, K. Djang, V. Phan, S. Chokshi, L. Chang, M. Rylko, M. Baerwalde, C. Spiry, D. Steiner, AND B. Cluer. Modeling floodplain and watershed restoration for salmon recovery in the Tolt River Watershed – A Snoqualmie Tribe and U.S. EPA collaborative effort. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-24/130, 2025.

• MCKANEETAL-TOLT-REPORT _508 COMPLIANT.PDF (PDF)  (NA  pp, 16.5 MB, about PDF)