Title

Long-term geomorphic effects of the Glines Canyon Dam removal on the Elwha River, WA, USA

Document Type

Oral Presentation

Campus where you would like to present

Ellensburg

Event Website

https://digitalcommons.cwu.edu/source

Start Date

16-5-2021

End Date

22-5-2021

Keywords

Rivers, Restoration, Dams

Abstract

Over the last few decades, it has become well-understood that dams inflict serious damage to riverine ecosystems. Because of this, dam removals are becoming more common. The Elwha River in western Washington once provided vital habitat for a variety of salmonid species, but after two dams were emplaced on the river in the early 1900s, habitat diminished and salmon populations declined. In 2014, after decades of effort, the dams were finally removed to restore the Elwha ecosystem. Because dam removals are a relatively new phenomenon, the changes that occur on river channels after large dam removals are not well understood. With this project, I analyzed how the morphology of the Elwha River changed after the Glines Canyon Dam removal. This project focused on four parameters: large wood in the channel, channel sinuosity, channel braiding, and sedimentation. High-resolution imagery from 2012-2020 was used to map large wood and digitize main and secondary river channels, and field surveys were completed to assess sediment-size distribution. My analysis revealed that the most drastic changes in the river occurred during the dam removal process, specifically individual log content and channel braiding, which increased during the removal process and then stabilized after the completion. However, some parameters like logjam area, sinuosity, and sediment-size changed throughout the 8-year study period. While some of my results suggest the Elwha River has reached a new equilibrium state, others suggest that the river is still evolving 6 years after the completion of the dam removal.

Faculty Mentor(s)

Lisa Ely

Department/Program

Geological Sciences

Additional Mentoring Department

https://cwu.studentopportunitycenter.com/long-term-geomorphic-effects-of-the-glines-canyon-dam-removal-on-the-elwha-river-wa-usa/

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May 16th, 12:00 PM May 22nd, 12:00 PM

Long-term geomorphic effects of the Glines Canyon Dam removal on the Elwha River, WA, USA

Ellensburg

Over the last few decades, it has become well-understood that dams inflict serious damage to riverine ecosystems. Because of this, dam removals are becoming more common. The Elwha River in western Washington once provided vital habitat for a variety of salmonid species, but after two dams were emplaced on the river in the early 1900s, habitat diminished and salmon populations declined. In 2014, after decades of effort, the dams were finally removed to restore the Elwha ecosystem. Because dam removals are a relatively new phenomenon, the changes that occur on river channels after large dam removals are not well understood. With this project, I analyzed how the morphology of the Elwha River changed after the Glines Canyon Dam removal. This project focused on four parameters: large wood in the channel, channel sinuosity, channel braiding, and sedimentation. High-resolution imagery from 2012-2020 was used to map large wood and digitize main and secondary river channels, and field surveys were completed to assess sediment-size distribution. My analysis revealed that the most drastic changes in the river occurred during the dam removal process, specifically individual log content and channel braiding, which increased during the removal process and then stabilized after the completion. However, some parameters like logjam area, sinuosity, and sediment-size changed throughout the 8-year study period. While some of my results suggest the Elwha River has reached a new equilibrium state, others suggest that the river is still evolving 6 years after the completion of the dam removal.

https://digitalcommons.cwu.edu/source/2021/COTS/53