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Water 2017, 9(8), 564; https://doi.org/10.3390/w9080564

Modelling Fine Sediment Dynamics: Towards a Common Erosion Law for Fine Sand, Mud and Mixtures

1
IFREMER/DYNECO/DHYSED, centre de Bretagne, ZI de la pointe du Diable CS 10070, 29280 Plouzané, France
2
AAMP (Agence des Aires Marines Protégées), 16 quai de la Douane, 29200 Brest, France
3
SHOM/DOPS/HOM/Sédimentologie, 13 rue du Châtellier CS 92803, 29228 Brest, France
*
Author to whom correspondence should be addressed.
Received: 7 June 2017 / Revised: 17 July 2017 / Accepted: 18 July 2017 / Published: 27 July 2017
(This article belongs to the Special Issue Sediment Transport in Coastal Waters)
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Abstract

This study describes the building of a common erosion law for fine sand and mud, mixed or not, in the case of a typical continental shelf environment, the Bay of Biscay shelf, characterized by slightly energetic conditions and a seabed mainly composed of fine sand and muddy sediments. A 3D realistic hydro-sedimentary model was used to assess the influence of the erosion law setting on sediment dynamics (turbidity, seabed evolution). A pure sand erosion law was applied when the mud fraction in the surficial sediment was lower than a first critical value, and a pure mud erosion law above a second critical value. Both sand and mud erosion laws are formulated similarly, with different parameters (erodibility parameter, critical shear stress and power of the excess shear stress). Several transition trends (linear or exponential) describing variations in these erosion-related parameters between the two critical mud fractions were tested. Suspended sediment concentrations obtained from simulations were compared to measurements taken on the Bay of Biscay shelf with an acoustic profiler over the entire water column. On the one hand, results show that defining an abrupt exponential transition improves model results regarding measurements. On the other hand, they underline the need to define a first critical mud fraction of 10 to 20%, corresponding to a critical clay content of 3–6%, below which pure sand erosion should be prescribed. Both conclusions agree with results of experimental studies reported in the literature mentioning a drastic change in erosion mode above a critical clay content of 2–10% in the mixture. Results also provide evidence for the importance of considering advection in this kind of validation with in situ observations, which is likely to considerably influence both water column and seabed sediment dynamics. View Full-Text
Keywords: sand-mud mixture erosion; numerical modelling; non-cohesive to cohesive transition sand-mud mixture erosion; numerical modelling; non-cohesive to cohesive transition
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).
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Mengual, B.; Hir, P.L.; Cayocca, F.; Garlan, T. Modelling Fine Sediment Dynamics: Towards a Common Erosion Law for Fine Sand, Mud and Mixtures. Water 2017, 9, 564.

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