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Sediment dynamics across gravel-sand transitions; implications for river stability and floodplain recycling

Elizabeth H. Dingle, Hugh D. Sinclair, Jeremy G. Venditti, Mikael Attal, Tim C. Kinnaird, Maggie Creed, Laura Quick, Jeffrey A. Nittrouer and Dilip Gautam
Sediment dynamics across gravel-sand transitions; implications for river stability and floodplain recycling
Geology (Boulder) (February 2020) 48 (5): 468-472

Abstract

The gravel-sand transition (GST) is commonly observed along rivers. It is characterized by an abrupt reduction in median grain size, from gravel- to sand-size sediment, and by a shift in sand transport mode from wash load-dominated to suspended bed material load. We documented changes in channel stability, suspended sediment concentration, flux, and grain size across the GST of the Karnali River, Nepal. Upstream of the GST, gravel-bed channels are stable over hundred- to thousand-year time scales. Downstream, floodplain sediment is reworked by lateral bank erosion, particularly during monsoon discharges. Suspended sediment concentration, grain size, and flux reveal counterintuitive increases downstream of the GST. The results demonstrate a dramatic change in channel dynamics across the GST, from relatively fixed, steep gravel-bed rivers with infrequent avulsion to lower-gradient, relatively mobile sand-bed channels. The increase in sediment concentration and near-bed suspended grain size may be caused by enhanced channel mobility, which facilitates exchange between bed and bank material. These results bring new constraints on channel stability at mountain fronts and indicate that temporally and spatially limited sediment flux measurements downstream of GSTs are more indicative of flow stage and floodplain recycling than of continental-scale sediment flux and denudation rate estimates.


ISSN: 0091-7613
EISSN: 1943-2682
Coden: GLGYBA
Serial Title: Geology (Boulder)
Serial Volume: 48
Serial Issue: 5
Title: Sediment dynamics across gravel-sand transitions; implications for river stability and floodplain recycling
Affiliation: Simon Fraser University, Department of Geography, Burnaby, BC, Canada
Pages: 468-472
Published: 20200214
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 31
Accession Number: 2020-028690
Categories: Quaternary geologyGeochronology
Document Type: Serial
Bibliographic Level: Analytic
Annotation: GSA Data Repository item 2020126
Illustration Description: illus. incl. geol. sketch map
N27°00'00" - N30°15'00", E80°00'00" - E88°00'00"
Secondary Affiliation: University of Edinburgh, GBR, United KingdomUniversity of Saint Andrews, GBR, United KingdomRice University, USA, United StatesPractical Action Consulting, NPL, Nepal
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2020, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 202019
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