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Morphodynamic evolution following sediment release from the world’s largest dam removal

January 1, 2018

Sediment pulses can cause widespread, complex changes to rivers and coastal regions. Quantifying landscape response to sediment-supply changes is a long-standing problem in geomorphology, but the unanticipated nature of most sediment pulses rarely allows for detailed measurement of associated landscape processes and evolution. The intentional removal of two large dams on the Elwha River (Washington, USA) exposed ~30 Mt of impounded sediment to fluvial erosion, presenting a unique opportunity to quantify source-to-sink river and coastal responses to a massive sediment-source perturbation. Here we evaluate geomorphic evolution during and after the sediment pulse, presenting a 5-year sediment budget and morphodynamic analysis of the Elwha River and its delta. Approximately 65% of the sediment was eroded, of which only ~10% was deposited in the fluvial system. This restored fluvial supply of sand, gravel, and wood substantially changed the channel morphology. The remaining ~90% of the released sediment was transported to the coast, causing ~60 ha of delta growth. Although metrics of geomorphic change did not follow simple time-coherent paths, many signals peaked 1–2 years after the start of dam removal, indicating combined impulse and step-change disturbance responses.

Publication Year 2018
Title Morphodynamic evolution following sediment release from the world’s largest dam removal
DOI 10.1038/s41598-018-30817-8
Authors Andrew C. Ritchie, Jonathan Warrick, Amy E. East, Christopher S. Magirl, Andrew W. Stevens, Jennifer A. Bountry, Timothy J. Randle, Christopher A. Curran, Robert C. Hilldale, Jeffrey J. Duda, Ian M. Miller, George R. Pess, Emily Eidam, Melissa M. Foley, Randall McCoy, Andrea S. Ogston
Publication Type Article
Publication Subtype Journal Article
Series Title Scientific Reports
Index ID 70204982
Record Source USGS Publications Warehouse
USGS Organization Arizona Water Science Center; Pacific Coastal and Marine Science Center; Washington Water Science Center; Western Fisheries Research Center