Channel-planform evolution in four rivers of Olympic National Park, Washington, U.S.A.: The roles of physical drivers and trophic cascades

Earth Surface Processes and Landforms
By: , and 

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Abstract

Identifying the relative contributions of physical and ecological processes to channel evolution remains a substantial challenge in fluvial geomorphology. We use a 74-year aerial photographic record of the Hoh, Queets, Quinault, and Elwha Rivers, Olympic National Park, Washington, U.S.A., to investigate whether physical or trophic-cascade-driven ecological factors—excessive elk impacts after wolves were extirpated a century ago—are the dominant controls on channel planform of these gravel-bed rivers. We find that channel width and braiding show strong relationships with recent flood history. All four rivers have widened significantly in recent decades, consistent with increased flood activity since the 1970s. Channel planform also reflects sediment-supply changes, evident from landslide response on the Elwha River. We surmise that the Hoh River, which shows a multi-decadal trend toward greater braiding, is adjusting to increased sediment supply associated with rapid glacial retreat. In this sediment-routing system with high connectivity, such climate-driven signals appear to propagate downstream without being buffered substantially by sediment storage. Legacy effects of anthropogenic modification likely also affect the Quinault River planform. We infer no correspondence between channel geomorphic evolution and elk abundance, suggesting that trophic-cascade effects in this setting are subsidiary to physical controls on channel morphology. Our findings differ from previous interpretations of Olympic National Park fluvial dynamics and contrast with the classic example of Yellowstone National Park, where legacy effects of elk overuse are apparent in channel morphology; we attribute these differences to hydrologic regime and large-wood availability.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Channel-planform evolution in four rivers of Olympic National Park, Washington, U.S.A.: The roles of physical drivers and trophic cascades
Series title Earth Surface Processes and Landforms
DOI 10.1002/esp.4048
Volume 42
Issue 7
Year Published 2017
Language English
Publisher Wiley
Contributing office(s) Pacific Coastal and Marine Science Center, Forest and Rangeland Ecosystem Science Center
Description 22 p.
First page 1011
Last page 1032
Country United States
State Washington
Other Geospatial Olympic National Park