Multi time-scale evolution of a wide estuary linear sandbank, the Longe de Boyard, on the French Atlantic coast

Chaumillon, Éric; Bertin, Xavier; Falchetto, Hélène; Allard, Jonathan; Weber, Nicolas; Walker, Patrice; Pouvreau, Nicolas; Wöppelmann, Guy

doi:10.1016/j.margeo.2008.02.014

Cited by 38 publications

(32 citation statements)

References 57 publications

(72 reference statements)

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“…It is about 8 km long and 2 km wide with a tide-dominated morphology (flood lobe), and its bed elevation ranges from about −17 m from mean sea level (MSL) near the flanks up to −3 m MSL at the southern end of the sandbank. The internal architecture of this sandbank was revealed by seismic profiling and three main seismic units were identified : an upper one characterized by fine and medium sand, lying on an old core of coarse sand and gravel, itself lying on a transgressive valley-fill (Chaumillon et al, 2002(Chaumillon et al, , 2008.…”

Section: Geomorphic Settingmentioning

confidence: 99%

“…Seismic reflection exploration of the sediment accretion areas, presented in Chaumillon et al (2002Chaumillon et al ( , 2008, showed inclined reflectors dipping channelward and recording the rhythmic lateral accretion on both sides of the sandbank. explained the observed sediment accretion at the SE part of the sandbank by the crestward convergence of the residual sediment transport.…”

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confidence: 99%

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Wave control on the rhythmic development of a wide estuary mouth sandbank: A process-based modelling study

2016

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Wave control on the rhythmic development of a wide estuary mouth sandbank: A process-based modelling study. Marine Geology, Elsevier, 2016Elsevier, , 380, pp.79 -89. 10.1016Elsevier, /j.margeo.2016 Wave control on the rhythmic development of a wide estuary mouth sandbank : a process-based modelling study AbstractThis study presents the numerical hindcast of the morphological changes and stratigraphy of a wide estuary mouth sandbank located along the French Atlantic coast (Marennes-Oléron Bay), and primarily investigates the respective contribution of tide and waves to its pluri-decadal evolution. Firstly, the morphodynamic hindcast appears strongly improved when tide and waves are considered in the forcing rather than only tide. Secondly, the modelling results suggest that the strong seasonal variation of the wave climate in this area explains the rhythmic lateral accretion of the bank (i.e. normal to the currents main direction) observed in seismic reflection profiles. The grain size variation in the area of sediment accretion is also characterized by a seasonal cycle. Finally, repetitive bathymetric surveys and seismic profiles revealed that the lateral accretion of the bank is associated with about one seismic reflector per year, which is in agreement with our modelling results when suggesting that these seismic reflectors are due to the seasonal variation of the grain size. These new results may be considered for the morphological evolution and the stratigraphy of other tidal sandbanks potentially affected by waves.

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Section: Geomorphic Settingmentioning

confidence: 99%

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confidence: 99%

Wave control on the rhythmic development of a wide estuary mouth sandbank: A process-based modelling study

2016

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“…Cependant, si on compare les simulations avec les observations à plus long terme, on constate que l'on simule un déplacement vers le nord-est des extrémités nord et sud de la Longe, ce qui concorde avec la tendance à long terme observée pour l'extrémité sud du banc mais contredit celle concernant l'extrémité nord (CHAUMILLON et al, 2008 fig. 5), on constate tout d'abord que la présence de vagues diminue fortement l'intensité et le sens de ce transport résiduel.…”

Section: Figure 4 (A) Bathymétrie De La Longe De Boyard De 1824 (B)unclassified

“…La forte fluctuation saisonnière des hauteurs significatives dans l'Atlantique nord-est (DODET et al, 2010) pourrait donc entrainer l'alternance de dépôts de sables fins et grossiers au niveau des flancs de la Longe de Boyard. Les discontinuités (ou réflecteurs) observées sur les profils sismiques présentés par CHAUMILLON et al (2008) pourraient donc correspondre à un enregistrement sédimentaire du cycle saisonnier des hauteurs de vague. En effet ces réflecteurs, obtenus par prospection sismique, sont le plus souvent dus à une variation granulométrique au sein de la colonne sédimentaire (BILLEAUD et al, 2005).…”

Section: Figure 4 (A) Bathymétrie De La Longe De Boyard De 1824 (B)unclassified

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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“…1a) (Bertin et al, 2005) up to the scale of the Pertuis (the part between the islands and the continent) and the islands (Fig. 1a) (Stanisi ere et al, 2006;Chaumillon et al, 2008). Some studies have also focused on the influence of waves on the Saint Trojan beach on the western coast of Olé ron Island (Fig.…”

Section: Existing Knowledge On the Study Areamentioning

confidence: 99%

A simple method to analyse non-cohesive sediment mobility in coastal environment

Idier

Romieu

Pedreros

et al. 2010

Continental Shelf Research

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To cite this version:Déborah Idier, Emmanuel Romieu, Rodrigo Pedreros, Carlos Oliveros. A simple method to analyse non-cohesive sediment mobility in coastal environment. Continental Shelf Research, Elsevier, 2010, 30, pp.365-377. <10.1016/j.csr.2009 .006>. This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. This paper presents a method to investigate the relative influence of waves, wind-induced currents and tidal currents on sediment mobility in coastal environment. It is based on the assumption that, knowing high uncertainties linked to sediment dynamics studies, simple sediment mobility indicators are sufficient tools to provide useful information. This method is based on five main steps: (1) assessing hydrodynamic conditions and related errors spatially and temporally for an area; (2) evaluating the bottom shear stress induced by these hydrodynamic conditions; (3) providing simple sediment mobility indicators; (4) analysing the sensitivity of these indicators to the existing hydrodynamic uncertainties; (5) interpreting indicators knowing their limits (identified in the sensitivity analysis). This methodology is applied to a test site on the inner shelf, seaward of the Pertuis Charentais region in France. Using wave (SWAN) and sea-level and currents (MARS-2DH) modelling, we study the spatial distribution of the relative contribution of waves, tides and wind-induced current in the non-cohesive sediment mobility under storm conditions. The deduced sediment dynamics indicators reveal the dominant action of waves in sediment initiation in the offshore area, in water depths of up to 60 m. The sensitivity study, performed in order to evaluate the validity of results, shows that the sediment mobility indicators still provide relevant information, even for hydrodynamic uncertainties of 7 20% or furthermore when only a qualitative sedimentological knowledge of the area is available.

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Multi time-scale evolution of a wide estuary linear sandbank, the Longe de Boyard, on the French Atlantic coast

Cited by 38 publications

References 57 publications

Wave control on the rhythmic development of a wide estuary mouth sandbank: A process-based modelling study

Wave control on the rhythmic development of a wide estuary mouth sandbank: A process-based modelling study

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

A simple method to analyse non-cohesive sediment mobility in coastal environment

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