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Wave ripple development on mixed clay-sand substrates: Effects of clay winnowing and armoring

Wu, Xuxu; Baas, Jaco H.; Parsons, Daniel R.; Eggenhuisen, Joris; Amoudry, Laurent; Cartigny, Matthieu; McLelland, Stuart; Mouazé, Dominique; Ruessink, Gerben

Authors

Jaco H. Baas

Joris Eggenhuisen

Laurent Amoudry

Matthieu Cartigny

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Dr Stuart McLelland S.J.McLelland@hull.ac.uk
Deputy Director of the Energy and Environment Institute

Dominique Mouazé

Gerben Ruessink



Abstract

Based on bed form experiments in a large‐scale flume, we demonstrate that the rate of development of wave ripples on a mixed sand‐clay bed under regular waves is significantly lower than on a pure‐sand bed, even at clay fractions as low as 4.2%, and that this rate of development decreases exponentially from 4.2% to 7.4% clay. These experiments also showed that, despite the slow growth of the bed forms in the mixed sand‐clay, the equilibrium length and height of the wave ripples were independent of the initial bed clay fraction. Given that the ripple crests were composed of pure sand at the end of all the experiments that started with well‐mixed sand‐clay, it is inferred that the clay was removed from the bed during the development of the wave ripples through winnowing into the water column, and possibly also by sieving into the subsurface, where the final clay fractions were found to be higher than the initial clay fractions. These clay removal processes are interpreted to have facilitated the wave ripples to reach equilibrium lengths and heights that are similar to those in pure sand. Clay‐carrying pore flow initiated by pressure gradients between the wave ripple troughs and crests might also have contributed to the accumulation of clay in the sediment below the wave ripples. The formation of the clay‐enriched “armoring” layer in the substrate is likely to further reduce erosion rates and could influence the dispersion of nutrients and pollutants in coastal seas.

Citation

Wu, X., Baas, J. H., Parsons, D. R., Eggenhuisen, J., Amoudry, L., Cartigny, M., …Ruessink, G. (2018). Wave ripple development on mixed clay-sand substrates: Effects of clay winnowing and armoring. Journal of Geophysical Research: Earth Surface, 123(11), 2784-2801. https://doi.org/10.1029/2018JF004681

Journal Article Type Article
Acceptance Date Oct 4, 2018
Online Publication Date Oct 10, 2018
Publication Date 2018-11
Deposit Date Nov 9, 2018
Publicly Available Date Apr 11, 2019
Journal Journal of Geophysical Research: Earth Surface
Print ISSN 2169-9011
Electronic ISSN 2169-9011
Publisher American Geophysical Union
Peer Reviewed Peer Reviewed
Volume 123
Issue 11
Pages 2784-2801
DOI https://doi.org/10.1029/2018JF004681
Keywords Wave-induced ripple; Cohesive sediments; Ripple development
Public URL https://hull-repository.worktribe.com/output/1146925
Publisher URL https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018JF004681

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Copyright Statement
©2018. American Geophysical Union.All Rights Reserved.





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