Éditeur(s) : Elsevier Science Bv
Résumé : In this study, the Capbreton canyon head, just off the coast, is investigated using high-resolution multibeam bathymetry datasets, sediment samples and numerical modeling. The HR bathymetry analysis reveals a morphological connection between the longshore trough and the head of the canyon. The analysis of recent sediment samples shows a clear correlation between the sediment of the canyon head and that of the nearshore. Hydrodynamic modeling (a coupled wave-flow model) shows that for high-energy waves, the rotational nature of surf-zone circulation reverses and wave-induced currents have the potential to transport large quantities of nearshore sands toward the canyon head. All these arguments support the assumption that the canyon head captures a part of the sand transported by longshore drift. Over the 15 years of observation (1998–2013), time-lapse bathymetry shows that the floor of the canyon head and one lateral gully network experienced significant morphological reworking. In terms of hazards, despite this strong activity, the position of the canyon head and the profile of its longitudinal slope remained stable and appears as a comforting factor. However, the activity of unusual lateral erosions needs to be monitored.
Marine Geology (0025-3227) (Elsevier Science Bv), 2014-05 , Vol. 351 , P. 1-12

Droits : 2014 Elsevier B.V. All rights reserved.
http://archimer.ifremer.fr/doc/00180/29118/27524.pdf
DOI:10.1016/j.margeo2014.03.001
http://archimer.ifremer.fr/doc/00180/29118/

Éditeur(s) : HAL CCSD Coastal Education and Research Foundation
Résumé : The south part nearshore zone of the Gulf of Lions coast (Mediterranean Sea) is characterized by a double crescentic sandbar system. During the winter 2007, a campaign of intensive hydrodynamical measurements (current profiles) was realized. During this campaign, based mainly on ADCPs, the maximal recorded wave height was 1.5 m. Four events were observed; two of those had northern incidence, one with southern incidence and a last one with frontal incidence. This paper proposes 3D hydrodynamical circulation maps over this microtidal bar system. The currents described reveals rip, bed-return and longshore currents strongly influenced by the wind-waves forcing and the bathymetry. At the apex of the oblique incidence events, the longshore component is the most important. The breaker zone is only located over the inner bar. During storm waning conditions, the cross-shore currents appear over the trough of the outer bar. The hydrodynamic circulation is then compared with other observations made in the literature.
ISSN: 0749-0208
Szczecin, Poland

hal-00767593
https://hal.archives-ouvertes.fr/hal-00767593

Éditeur(s) : HAL CCSD
Résumé : The sandy coasts of Languedoc-Roussillon are a zone vulnerable to erosion and flooding. These hazards are generally associated with a combination of natural factors such as waves, wind, rising sea levels and the importance of sediment supply, and are therefore worsened during storms. For the management of such risks, a better knowledge of the hydrodynamic phenomena occuring from the surf zone through to the coastal scale is essential. This need led to the development of a numerical modelling platform consisting of the 3D ocean circulation model Symphonie, usually dedicated to regional and coastal scales, which was modified to include the wave forcing, modeled by the WaveWatch III or Swan models. Using this platform the entire littoral and coastal regions can be accurately represented. The model was tested in several academic cases. Measurements on the barred beach of Sète during the winter of 2008-2009 served to refine the model, which is able to successfully reproduce the characteristics of the currents in coastal areas, drifts or rip currents over more complex bathymetries and also the vertical profiles of currents. To validate the model on the inner-shelf, we compared the simulations with measurements taken during a winter storm in 2004 around the mouth of the Têt river, as well as during storms in 2007 and 2008 in the Gulf of Aigues-Mortes. Currents are generally well reproduced. However, the scope of wave action seems limited to a depth of 30m. The characteristics of our model allow a good reproduction of the currents at all scales and the 3D nature of the model permits a more precise calculation of the shear stress and bottom current responsible, respectively, for the suspension and advection of sediments.
Le littoral sableux du Languedoc-Roussillon est un système vulnérable aux risques d'érosion et de submersion. Ces aléas sont liés à la conjonction des facteurs naturels que sont les vagues, vent, élévation du niveau de la mer et apports sédimentaires et sont donc aggravés en période de tempête. En vue d'une gestion des risques, une meilleure connaissance des phénomènes hydrodynamiques de l'échelle littorale à l'échelle côtière est essentielle. Ce travail a conduit à la réalisation d'une plateforme de modélisation numérique composée du modèle de circulation océanique 3D Symphonie, traditionnellement dédié aux échelles régionales et côtières, qui a été modifié pour inclure le forçage par les vagues, modélisées par les modèles Wavewatch III ou Swan, et ainsi étendre sa validité au littoral. Le modèle a été testé sur des cas académiques littoraux. Des mesures sur la plage à double barres de Sète pendant l'hiver 2008-2009, ont également servi à parfaire le modèle qui reproduit ainsi avec succès les caractéristiques des courants en zone littorale : la dérive, les courants sagittaux sur des bathymétries plus complexes et les profils verticaux des courants. Pour valider le modèle à des échelles plus côtières, nous avons confronté ses résultats à des mesures réalisées pendant une tempête hivernale en 2004 aux alentours de l'embouchure de la Têt, mais également sur des tempêtes de 2007 et 2008 dans le Golfe d'Aigues-Mortes. Les courants sont globalement bien reproduits. Les zones d'action des vagues semblent limitées aux zones de profondeur inférieure à 30 m. Notre modèle autorise une reproduction correcte des courants à toutes les échelles et sa nature 3D permet un calcul plus précis de la tension de cisaillement de fond et du courant près du fond, responsables respectivement de la mise en suspension et de l'advection des sédiments.
https://tel.archives-ouvertes.fr/tel-00680405

tel-00680405
https://tel.archives-ouvertes.fr/tel-00680405
https://tel.archives-ouvertes.fr/tel-00680405v2/document
https://tel.archives-ouvertes.fr/tel-00680405/file/2011_MICHAUD.pdf

Éditeur(s) : HAL CCSD Elsevier
Résumé : The Gulf of Aigues-Mortes (NW Mediterranean Sea) is a midshelf zone whose scale is an intermediate between the nearshore scale (0–10 m depth) and the coastal scale (including the whole continental shelf). Its hydrodynamics is investigated for the first time. ADCP, CTD and thermosalinograph data were collected during three short cruises (HYGAM; March 6–7, 20–21, April 5–6, 2005). They were scheduled approximately every 15 days to sample the gulf circulation under different weather conditions. Moreover, the cruise data were used to validate the Symphonie model, a 3D primitive equations circulation model. The circulation features displayed by in situ data were well reproduced by Symphonie. A downscaling modelling approach was implemented, the largest scale being obtained by the replay of the MFSTEP regional model of the North-Western Mediterranean Sea. The analysis, closely coupling in situ measurements and model results, provides information that would not have been obtained using data separately. The great variability of the oceanic circulation at this scale is well evidenced. Winds are the main forces, not only locally but also at a larger scale. North winds generate coherent structures interacting with the general Mediterranean circulation. The explanation of the induced currents is then not straightforward, some of them being, for example, northward. South and southeast winds reinforce the sloping surface, the latter allowing the geostrophic equilibrium with longshore currents. This study, focused on the end of winter 2004–2005, also enhances the heat fluxes from offshore to nearshore, as well as the initiation of shelf dense waters. The knowledge of the midshelf oceanic circulation is then applied to run a numerical experiment which describes both the dispersion of a fictive contaminant from a point S (at the centre of the GAM), and evaluates the risk of contamination of the beaches along the GAM shores.
ISSN: 0278-4343

hal-00196620
https://hal.archives-ouvertes.fr/hal-00196620
DOI : 10.1016/j.csr.2007.06.006

Éditeur(s) : HAL CCSD Editions Paralia CFL
Résumé : The wave-dominated beach barrier of Villeneuve-Lès-Maguelone extends between Palavas and Frontignan (Gul f of Lions, northernmost Me diterranean Sea), along a slightly natural sandy protected area char acterized by typical and well-expressed morphologies. In the nearshore, the sea bottom shows one or two approximately rectilinear sand bars. In 2010-2011, we pe rformed a 6 month-long monitoring (autumn 2010/late spring 2011) of a 500 meter-long se gment along this sand barrier. We used RTK D-GPS offering centimeter resolution to acquire sets of elevation data on the beach and the upper shoreface. The study is innovative because a full morphologic monitoring was performed each time the wave/ wind conditions changed significantly. These changes were tracked in real-time thanks to a set of hydrodynamic equipments deployed at sea, including well-known DREAL buoys. We identify from well- documented data: (1) a beach reconstruction cycle at the shorelin e after a moderate storm event (wave height at 3-4 m) and (2) how a sand bar in the nearshore migrates to the shoreline and drives the shoreline shift.
ISSN: 1760-8716

hal-00854402
https://hal.archives-ouvertes.fr/hal-00854402
DOI : 10.5150/jngcgc.2012.023-C

Éditeur(s) : HAL CCSD
Résumé : Quasi-3D model SHORECIRC simulates circulation on simple nearshore domains. It is modified in order to handle realistic bathymetries : beaches with complex shoreline and/or emerged structures. Added improvements are validated against other models and measurements on various configurations. New SHORECIRC version is then applied to the study of the circulation dynamics of Leucate, a sandy beach of Languedoc- Roussillon (France) with crescentic bars.
Le modèle numérique de circulation quasi-tridimensionnel SHORECIRC, initialement prévu pour fonctionner sur des bathymétries simples, a été modifié afin de pouvoir prendre en compte les caractéristiques complexes des bathymétries réalistes de la zone littorale : trait de côte irrégulier et présence d'objets émergés. Les modifications apportées ont ´été validées par comparaison avec des résultats d'autres modèles numériques et avec des données mesurées sur plusieurs configurations. Enfin, le modèle modifié a été appliqué à l'étude de la dynamique de la circulation sur une plage sableuse à barres en festons (Plage de Leucate, Languedoc-Roussillon, FR).
https://tel.archives-ouvertes.fr/tel-00438713

tel-00438713
https://tel.archives-ouvertes.fr/tel-00438713
https://tel.archives-ouvertes.fr/tel-00438713/document
https://tel.archives-ouvertes.fr/tel-00438713/file/thesebujan.pdf

Éditeur(s) : HAL CCSD Coastal Education and Research Foundation
Résumé : Nearshore bars are generally present on sandy coasts and play a significant role in wave breaking and sediment exchange between beach and shoreface. The study area is located on the Languedoc-Roussillon coast in the Gulf of Lions (southern part of the French Mediterranean coast). This microtidal environment is classified as a wave-dominated coast. The sand coast displays different bar systems (single or multiple; straight or crescentic). The alongshore variability of bar morphology in the nearshore zone was investigated in August 2009 during one week, using a topo-bathymetric LIDAR data set (300 km(2)). LIDAR makes it possible to cover a large area in a very short time with a high resolution. The topo-bathymetric LIDAR offers the added benefit of morphological information about the beach-sea transition in very shallow water (below I in), data often difficult if not impossible to obtain with traditional techniques. The purpose of this paper is 1) to depict the distribution of bars and their characteristics along the 180 km coast of the Gulf of Lions; 2) to update the classifications of sand bars typologies in Languedoc-Roussillon; 3) to pay particular attention to the description of the intricate inner system. Globally, cross-shore distribution of subtidal morphologies is characterized by both an outer and an inner system. The outer system is crescent-shaped in the south and straight in the northern part with a distinctive regional delimitation. The inner system comprises an inner bar and, near the coast, a complex fluctuating bar called Low Bar Beach (LBB). Several intermediate states were identified and added to the new classification proposed in this paper. These results clearly emphasize the importance of LIDAR technology for a better understanding of bar behaviour and single and/or multi-bar beach organisation.
ISSN: 0749-0208

hal-00783187
https://hal.archives-ouvertes.fr/hal-00783187