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Formation and erosion of sediment cover in an experimental bedrock-alluvial channel

Hodge, R.A.; Hoey, T.; Maniatis, G.; Leprêtre, E.

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Authors

T. Hoey

G. Maniatis

E. Leprêtre



Abstract

Sediment grains in a bedrock-alluvial river will be deposited within or adjacent to a sediment patch, or as isolated grains on the bedrock surface. Previous analysis of grain geometry has demonstrated that these arrangements produce significant differences in grain entrainment shear stress. However, this analysis neglected potential interactions between the sediment patches, local hydraulics and grain entrainment. We present a series of flume experiments that measure the influence of sediment patches on grain entrainment. The flume had a planar bed with roughness that was much smaller than the diameters of the mobile grains. In each experiment sediment was added either as individual grains or as a single sediment pulse. Flow was then increased until the sediment was entrained. Analysis of the experiments demonstrates that: 1) for individual grains, coarse grains are entrained at a higher discharge than fine grains; 2) once sediment patches are present, the different in entrainment discharge between coarse and fine grains is greatly reduced; 3) the sheltering effect of patches also increases the entrainment discharge of isolated grains; 4) entire sediment patches break-up and are eroded quickly, rather than through progressive grain-by-grain erosion, and 5) as discharge increases there is some tendency for patches to become more elongate and flow-aligned, and more randomly distributed across the bed. One implication of this research is that the critical shear stress in bedrock-alluvial channels will be a function of the extent of the sediment cover. Another is that the influence of sediment patches equalises critical shear stresses between different grain sizes and grain locations, meaning that these factors may not need to be accounted for. Further research is needed to quantify interactions between sediment patches, grain entrainment and local hydraulics on rougher bedrock surfaces, and under different types of sediment supply.

Citation

Hodge, R., Hoey, T., Maniatis, G., & Leprêtre, E. (2016). Formation and erosion of sediment cover in an experimental bedrock-alluvial channel. Earth Surface Processes and Landforms, 41(10), 1409-1420. https://doi.org/10.1002/esp.3924

Journal Article Type Article
Acceptance Date Feb 15, 2016
Online Publication Date Feb 24, 2016
Publication Date Aug 1, 2016
Deposit Date Mar 11, 2016
Publicly Available Date Feb 24, 2017
Journal Earth Surface Processes and Landforms
Print ISSN 0197-9337
Electronic ISSN 1096-9837
Publisher British Society for Geomorphology
Peer Reviewed Peer Reviewed
Volume 41
Issue 10
Pages 1409-1420
DOI https://doi.org/10.1002/esp.3924
Public URL https://durham-repository.worktribe.com/output/1417366

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Copyright Statement
This is the accepted version of the following article: Hodge, R.A., Hoey, T., Maniatis, G. and Leprêtre, E. (2016) 'Formation and erosion of sediment cover in an experimental bedrock-alluvial channel.', Earth surface processes and landforms, 41(10): 1409-1420, which has been published in final form at http://dx.doi.org/10.1002/esp.3924. This article may be used for non-commercial purposes in accordance With Wiley Terms and Conditions for self-archiving.






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