A model for grain-size sorting over tidal sand ridges

Walgreen, M.; Swart, H.E. de; Calvete, D.

doi:10.1007/s10236-003-0066-3

Cited by 23 publications

(39 citation statements)

References 24 publications

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“…In reality, the grain size distribution is coupled to the bed forms. Walgreen et al (2004) show that the bed forms cause a sorting of the sediment. In general however, these variations are small.…”

Section: Discussionmentioning

confidence: 99%

Grain size dependency in the occurrence of sand waves

2006

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Sandy shallow seas, like the North Sea, are very dynamic. Several morphological features are present on the bed, from small ripples to sand waves and large tidal sandbanks. The larger patterns induce significant depth variations that have an impact on human activities taking place in this area. Therefore, it is important to know where these largescale features occur, what their natural behaviour is and how they interact with human activities. Here, we extend earlier research that compares the results of an idealized model of large-scale seabed patterns with data of seabed patterns in the North Sea. The idealized model is extended with a grain size dependency. The adaptations lead to more accurate predictions of the occurrence of large-scale bed forms in the North Sea. Therefore, grain size dependency and, in particular, critical shear stress are important to explain the occurrence of sand waves and sandbanks in the North Sea.

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Section: Discussionmentioning

confidence: 99%

Grain size dependency in the occurrence of sand waves

2006

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“…En effet pour un courant relativement fort comme c'est le cas dans cet exemple, le transport du sédiment fin, essentiellement par suspension, prédomine largement celui du sédiment grossier (SOULSBY, 1997). Une répartition de taille de grain caractéristique des dunes sousmarines apparaît alors, avec du sédiment plus grossier au niveau de la zone en érosion (sur la crête et la pente de la dune faisant face au courant), et du sédiment plus fin au niveau de la zone en accrétion (sur le creux et la pente de la dune en aval du courant) (WALGREEN et al, 2003(WALGREEN et al, , 2004HOLLAND & ELMORE, 2008). Grâce au modèle, l'évolution morphologique de la Longe de Boyard est simulée sur une période de 2 ans avec la marée pour seul forçage, définie par ses 19 constituants principaux.…”

Section: Résultatsunclassified

Prise en compte de l'hétérogénéité granulométrique du sédiment en morphodynamique côtière

Guérin¹,

Bertin²,

Chaumillon³

et al. 2014

XIIIèmes JNGCGC Dunkerque

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Résumé :Dans cet article nous montrons l'intérêt de prendre en compte l'hétérogénéité granulométrique naturelle d'un sédiment non-cohésif en modélisation morphodynamique côtière. Pour cela une approche "multi-classe multi-couche" a été utilisée, considérant le fond sédimentaire comme constitué de grains de sable de différentes tailles, ainsi que de plusieurs couches distinctes. Une application au cas 1D de la migration d'une dune hydraulique puis au cas 2DH du banc de sable estuarien de la Longe de Boyard, situé à l'embouchure nord de la Baie de Marennes-Oléron, a mis en évidence la plus-value de cette approche par rapport à celle se limitant à un sédiment complètement homogène. Tout d'abord une modification des vitesses de migration est obtenue, celles-ci étant significativement plus faibles lorsqu'un sédiment hétérogène est pris en compte. Enfin, l'impact de différents forçages sur la distribution granulométrique surfacique et verticale du sédiment a pu être étudié grâce à cette approche.

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“…Furthermore, sediment sorting has a net stabilizing effect on the growth of sfcr, whereas their migration speed becomes larger and their wavelength is only slightly affected. Process-based models have also been developed to investigate grain sorting over other coastal bedforms, such as ripples (Foti and Blondeaux 1995), sorted bedforms on the inner shelf (Murray and Thieler 2004;Coco et al 2007a, b;Huntley et al 2008), tidal sand banks (Walgreen et al 2004;Roos et al 2007), and tidal sand waves (Roos et al 2008;Van Oyen and Blondeaux 2009); see also the review by Holland and Elmore (2008).…”

Section: Introductionmentioning

confidence: 99%

Effect of wave–bedform feedbacks on the formation of, and grain sorting over shoreface-connected sand ridges

2009

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The influence of wave-bedform feedbacks on both the initial formation of shoreface-connected sand ridges (sfcr) and on grain size sorting over these ridges on micro-tidal inner shelves is studied. Also, the effect of sediment sorting on the growth and the migration of sfcr is investigated. This is done by applying a linear stability analysis to an idealized process-based morphodynamic model, which simulates the initial growth of sfcr due to the positive coupling between waves, currents, and an erodible bed. The sediment consists of sand grains with two different sizes. New elements with respect to earlier studies on grain sorting over sfcr are that wave-topography interactions are explicitly accounted for, entrainment of sediment depends on bottom roughness, and transport of suspended sediment involves settling lag effects. The results of the model indicate that sediment sorting causes a reduction of the growth rate and migration speed of sfcr, whereas the wavelength is only slightly affected. In the case where the entrainment of suspended sediment depends on bottom roughness, the coarsest sediment is found in the troughs; otherwise, the finest sediment occurs in the troughs. Compared to previous work, modeled maximum variations in the mean grain size over the topography are in better agreement with field observations. Settling lag effects are important for the damping of high-wavenumber mode instabilities such that a preferred wavelength of the bedforms is obtained.

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A model for grain-size sorting over tidal sand ridges

Cited by 23 publications

References 24 publications

Grain size dependency in the occurrence of sand waves

Grain size dependency in the occurrence of sand waves

Prise en compte de l'hétérogénéité granulométrique du sédiment en morphodynamique côtière

Effect of wave–bedform feedbacks on the formation of, and grain sorting over shoreface-connected sand ridges

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