Channel‐planform evolution in four rivers of Olympic National Park,Washington, USA: the roles of physical drivers and trophic cascades |
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| Authors: | Amy E East Kurt J Jenkins Patricia J Happe Jennifer A Bountry Timothy J Beechie Mark C Mastin Joel B Sankey Timothy J Randle |
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| Institution: | 1. US Geological Survey, Pacific Coastal and Marine Science Center, Santa Cruz, CA, USA;2. US Geological Survey, Forest and Rangeland Ecosystem Science Center, Olympic Field Station, Port Angeles, WA, USA;3. National Park Service, Olympic National Park, Port Angeles, WA, USA;4. Bureau of Reclamation, Sedimentation and River Hydraulics Group, Denver, CO, USA;5. National Marine Fisheries Service, National Oceanic and Atmospheric Administration, Seattle, WA, USA;6. US Geological Survey, Washington Water Science Center, Tacoma, WA;7. US Geological Survey, Southwest Biological Science Center, Flagstaff, AZ, USA |
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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, USA, to investigate whether physical or trophic‐cascade‐driven ecological factors – excessive elk impacts after wolves were extirpated a century ago – are the dominant drivers of channel planform in these gravel‐bed rivers. We find that channel width and braiding show strong relationships with recent flood history. All four rivers widened significantly after having been relatively narrow in the 1970s, consistent with increased flood activity since then. 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. These rivers demonstrate transmission of climatic signals through relatively short sediment‐routing systems that lack substantial buffering by sediment storage. Legacy effects of anthropogenic modification likely also affect the Quinault River planform. We infer no correspondence between channel 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. Published 2016. This article is a U.S. Government work and is in the public domain in the USA |
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| Keywords: | fluvial geomorphology channel evolution trophic cascades glacier retreat climate signal |
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