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Published on: November 18, 2015
Morphodynamic evolution following sediment release from the world's largest dam removal.
Andrew C Ritchie1, Jonathan A Warrick2, Amy E East2
1Pacific Coastal and Marine Science Center, United States Geological Survey, Santa Cruz, CA, USA. aritchie@usgs.gov.
Scientific Reports
|September 7, 2018
Summary
Dam removal released massive sediment, altering the Elwha River and delta. Most sediment went to the coast, causing significant delta growth and changing river morphology.
Area of Science:
- Geomorphology
- River Science
- Coastal Processes
Background:
- Sediment pulses cause complex river and coastal changes.
- Quantifying landscape response to sediment supply is challenging due to unpredictable events.
- Elwha River dam removal provided a rare opportunity to study a massive sediment pulse.
Purpose of the Study:
- To quantify the geomorphic evolution of the Elwha River and its delta following dam removal.
- To analyze the source-to-sink response to a large-scale sediment perturbation.
- To establish a 5-year sediment budget and morphodynamic analysis.
Main Methods:
- Sediment budget analysis over five years.
- Morphodynamic analysis of river and delta evolution.
- Measurement of landscape processes and evolution post-dam removal.
Main Results:
- Approximately 65% of impounded sediment was eroded.
- ~10% of eroded sediment deposited in the fluvial system, altering channel morphology.
- ~90% of sediment transported to the coast, resulting in ~60 ha of delta growth.
- Geomorphic change signals peaked 1-2 years after dam removal.
Conclusions:
- The Elwha River dam removal served as a unique natural experiment for studying sediment pulse impacts.
- Riverine and coastal systems exhibited significant, albeit complex, responses to the massive sediment release.
- The findings highlight the importance of sediment supply in shaping river and delta dynamics.
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