The Geomorphology and Hydrogeology of Pre-Restoration West Fork Teanaway River, WA, USA S. Magdeline Egan*; Lisa Ely, PhD; Carey Gazis, PhD; Jennifer Lipton, PhD Project Mentor(s): Lisa Ely, PhD; Carey Gazis, PhD; Jennifer Lipton, PhD The West Fork Teanaway (WFT) River, Kittitas County, WA is a bedrock river channel with shallow stream depth, low alluvium sediment, and high surface-water temperatures that are inhospitable for spawning and rearing of native anadromous fish. Stream restoration of the WFT with the intent to halt bedrock incision, retain channel sediment, raise river water depth, and raise floodplain groundwater levels will begin in 2026. This research characterized the pre-restoration hydrogeology and geomorphology of the WFT to later quantify changes in these factors after restoration completion. WFT floodplain stratigraphy, floodplain sediment grain sizes, floodplain groundwater levels, and river stage were analyzed over the 2024–2025 water year. Stable isotope geochemistry ( δ 2 Hydrogen and δ 18 Oxygen) of river surface water and floodplain groundwater, as well as hydrographs of groundwater and river stage in the 2024–2025 water year, indicate a rapid connection between river surface water and floodplain groundwater. The WFT floodplain stratigraphy, predominately coarse-grained sand-, gravel-, and pebble-sized sediment, probably facilitates this rapid response between floodplain groundwater and river surface water. Additionally, the WFT floodplain stratigraphy and floodplain groundwater levels were compared with those of the North Fork and mainstem Teanaway River to determine differences in shallow floodplain aquifer characteristics across the Teanaway River Basin. The results provide a baseline to assess the efficacy of river restoration methods with achieving their design objectives at the WFT and quantify the effects of two different stream restoration techniques on a shallow floodplain aquifer in a mountainous headwater system. Presentation Type: Poster Presentation (May 21, 9:30am–3:00pm) Keywords: stream restoration, West Fork Teanaway River, geomorphology, hydrogeology SOURCE Form ID: 107
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