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

Author(s)

Alyssa DeMott

Faculty Mentor(s)

Lisa Ely (Geological Sciences)

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.

Keywords: Rivers, Restoration, Dams

Presentation

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

  1. Great presentation, Alyssa. Your results will be of interest in other rivers where dam removals are being considered.

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