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Bedform migration in a mixed sand and cohesive clay intertidal environment and implications for bed material transport predictions

Lichtman, Ian D.; Baas, Jaco H.; Amoudry, Laurent O.; Thorne, Peter D.; Malarkey, Jonathan; Hope, Julie A.; Peakall, Jeffrey; Paterson, David M.; Bass, Sarah J.; Cooke, Richard D.; Manning, Andrew J.; Davies, Alan G.; Parsons, Daniel R.; Ye, Leiping

Authors

Ian D. Lichtman

Jaco H. Baas

Laurent O. Amoudry

Peter D. Thorne

Jeffrey Peakall

David M. Paterson

Sarah J. Bass

Richard D. Cooke

Andrew J. Manning

Alan G. Davies

Daniel R. Parsons

Leiping Ye



Abstract

Many coastal and estuarine environments are dominated by mixtures of non-cohesive sand and cohesive mud. The migration rate of bedforms, such as ripples and dunes, in these environments is important in determining bed material transport rates to inform and assess numerical models of sediment transport and geomorphology. However, these models tend to ignore parameters describing the physical and biological cohesion (resulting from clay and extracellular polymeric substances, EPS) in natural mixed sediment, largely because of a scarcity of relevant laboratory and field data. To address this gap in knowledge, data were collected on intertidal flats over a spring-neap cycle to determine the bed material transport rates of bedforms in biologically-active mixed sand-mud. Bed cohesive composition changed from below 2 vol% up to 5.4 vol% cohesive clay, as the tide progressed from spring towards neap. The amount of EPS in the bed sediment was found to vary linearly with the clay content. Using multiple linear regression, the transport rate was found to depend on the Shields stress parameter and the bed cohesive clay content. The transport rates decreased with increasing cohesive clay and EPS content, when these contents were below 2.8 vol% and 0.05 wt%, respectively. Above these limits, bedform migration and bed material transport was not detectable by the instruments in the study area. These limits are consistent with recently conducted sand-clay and sand-EPS laboratory experiments on bedform development. This work has important implications for the circumstances under which existing sand-only bedform migration transport formulae may be applied in a mixed sand-clay environment, particularly as 2.8 vol% cohesive clay is well within the commonly adopted definition of “clean sand”.

Citation

Lichtman, I. D., Baas, J. H., Amoudry, L. O., Thorne, P. D., Malarkey, J., Hope, J. A., …Ye, L. (2018). Bedform migration in a mixed sand and cohesive clay intertidal environment and implications for bed material transport predictions. Geomorphology, 315, 17-32. https://doi.org/10.1016/j.geomorph.2018.04.016

Journal Article Type Article
Acceptance Date Apr 29, 2018
Online Publication Date May 1, 2018
Publication Date Aug 15, 2018
Deposit Date Sep 29, 2020
Publicly Available Date Oct 19, 2020
Journal Geomorphology
Print ISSN 0169-555X
Publisher Elsevier
Peer Reviewed Peer Reviewed
Volume 315
Pages 17-32
DOI https://doi.org/10.1016/j.geomorph.2018.04.016
Keywords Bedform migration; Sediment transport; Mixed cohesive clay-sand; Physical and biological cohesion; Current and wave forcing; Tidal flats
Public URL https://hull-repository.worktribe.com/output/843217
Publisher URL https://www.sciencedirect.com/science/article/pii/S0169555X18301776?via%3Dihub

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