Éditeur(s) : HAL CCSD Editions Paralia CFL
Résumé : L'objet de cette communication est la caractérisation hydrodynamique d'un système double de barres festonnées en milieu microtidal. Pour comprendre l'évolution du littoral de Leucate-Plage (Languedoc-Roussillon, France), une campagne de mesures hydrodynamiques in-situ a été réalisée, puis complétée par une étude à l'aide du modèle numérique Quasi-3D SHORECIRC de la houle et des courants dans des conditions plus dynamiques non observées. Les mesures in-situ ont permis de réaliser des cartes de circulation hydrodynamique. Les données modélisées donnent des résultats proches de la réalité en terme d'intensité dans la zone de déferlement, en termes de direction et d'intensité dans la zone deshoaling. This paper deals with the hydrodynamic study of a microtidal double crescentic bars system. To understand the coastal evolution of Leucate-Plage (Languedoc- Roussillon, France), a hydrodynamic survey has been realized, added to numerical studies with Q-3D SHORECIRC model for more dynamic unobserved conditions. Hydrodynamic maps with observed data have been produced. The numeric hydrodynamic maps show good analogies in the shoaling zone but some difference in the surf zone.
ISSN: 1760-8716

hal-00854013
https://hal.archives-ouvertes.fr/hal-00854013
DOI : 10.5150/jngcgc.2008.007-F

Éditeur(s) : HAL CCSD Elsevier
Résumé : SUBSURF
Statistical sequential analysis was performed on a series of sediment cores collected from the Têt prodelta in the Gulf of Lions, northwestern Mediterranean Sea, between October 2003 and October 2004. Seabed changes during that period were correlated to hydrodynamic conditions (waves and currents) and river discharge. Low sediment supply prevents full preservation of new sediment strata on this low-accumulation prodelta located on a microtidal, storm-dominated inner shelf. Severe meteorological events caused a rapid succession of erosion and deposition phases. For example, the December 2003 flood and storm produced a flood layer deposit that persisted for 2 months with only slight transformations due to early diagenesis and/or bioturbation, until a new storm event eroded this layer. A typical sedimentary sequence was observed for the secular deposits composed of a 10-cm-thick sandy layer overlaying siltyclayey layers. These characteristic features were used to analyse the last millennia sedimentary record of the Têt prodelta. The low preservation of freshly deposited sediments and variable sedimentation rates during the last millennia period yield a sedimentary sequence formed by the outcropping of muddy prodeltaic units intersected by heterogeneous siltysandy units similar to those formed under present day hydrodynamic conditions. No flood layer was found related to catastrophic flooding of the last century in the sedimentary record. The Little Ice Age ( 1550–1850 AD) probably favoured the formation of a well-developed muddy prodelta in the mouth of the Têt River. Later on, the decrease of sediment supply by rivers due to climate change and/or human activities (damming, irrigation), and the increase of the number of high-energy storms reaching the coast, induced a coarsening of the top sediment layer on this prodelta. This modern change of the substrate is also observed in the composition of benthic biota found in the substrate
ISSN: 0025-3227

hal-00407662
https://hal.archives-ouvertes.fr/hal-00407662
DOI : 10.1016/j.margeo.2007.04.009

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 Editions Paralia CFL
Résumé : Le lido de Villeneuve-lès-Maguelone (Languedoc-Roussillon) est un archétype de littoral microtidal, dominé par la houle, en érosion, et largement affecté par la submersion marine lors des tempêtes. Les observations réalisées dans le cadre du Système d'Observation Littoral - Trait de Côte (SO LTC) concernent l'hydrodynamique et le transport sédimentaire dans l'avant-côte et la lagune. La tache d'observation MAGOBS (Observatoire Aresquiers-Maguelone-Palavas) de cet observatoire regroupe un dispositif instrumental automatisé composé de 30 points d'acquisition en temps réel entre 6 mètres de profondeur et le haut de plage (à terre) ainsi que dans la lagune. Le dispositif est opérationnel depuis mai 2011. Son déploiement a permis de déverrouiller les difficultés techniques liées à la mesure temps réel en zone littorale : choix du type des appareils de mesure, de la technologie embarquée, des cadences d'acquisition, résolution des questions du transfert de la donnée. Le dispositif produit 2 Tera-octets de données par an. Les données sont stockées sur un ensemble de serveurs dédiés. Les données sont mises en ligne sur le site du SO-LTC (www.soltc.org), immédiatement après premiers traitements et qualification. Elles commencent à être utilisées pour des calculs de niveau d'eau à la côte, et dansdes outils de prédiction des vagues et des niveaux à la côte associant mesure et modélisation.
ISSN: 1760-8716

hal-00854410
https://hal.archives-ouvertes.fr/hal-00854410
DOI : 10.5150/jngcgc.2012.064-G

Éditeur(s) : HAL CCSD
Résumé : International audience
This communication reports on a field experiment carried out on a microtidal beach in Camargue, France. The analysis is built on the initial work presented by Sous et al. (2016) on swash-groundwater dynamics. The analysis of a cross-shore network of buried pressure sensors allows to monitor the watertable dynamics over the full 2013-2014 winter season. The pressure head gradients are observed to be primarily seaward, forced by a higher level at the landward boundary. The groundwater flux is driven by the relative fluctuations of Still Water Level and inland elevations. Rain and tides have a little effect. A nearly isolated groundwater circulation is driven by wave activity below the swash zone whatever the overall watertable gradient. Estimations of beach groundwater discharge over the Gulf of Beauduc reveal the importance of beach groundwater in the exchanges between coastal aquifer and open sea.
Coastal Dynamics 2017
Helsingor, Denmark

hal-01562908
https://hal.archives-ouvertes.fr/hal-01562908

Éditeur(s) : HAL CCSD
Résumé : International audience
This work aims to better understand the physical processes governing the wave propagation in a vertically shearedcurrent and the resulting nearshore circulation patterns. It is based on a high resolution hydro-morphodynamic fieldcampaign, ROUSTY2014, collecting a comprehensive hydro-morphodynamical dataset during a full winter season.The overall analysis highlights three main circulation patterns, largely controled by the bathymetric features and byco-working or competing wind and waves forcings. Regarding the vertical structuration of the circulation, most of fieldobservations shown seaward directed circulation with onshore component close to the air/sea surface whose intensityvaries according to incoming wave conditions. Forth, vertical shear increase when breaking happen close to sensorlocation and orientation of mean circulation depend on wind direction.
35th International Conference on Coastal Engineering
Antalya, Turkey

hal-01426582
https://hal.archives-ouvertes.fr/hal-01426582

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The Maguelone shore extends along the northern coast of the Gulf of Lions, west of the Rhone Delta and east of high-gradient coastal streams that have provided most of the clastic sediments to the Gulf of Lions margin since the early Miocene. This 10 km-wide area is constituted by a small coastal watershed (15 km long) in low-lying carbonate hills, a kilometre-wide marsh, a sandy beach barrier and a shoreface experiencing local low sedimentation rates. This onshore-offshore transition zone is a key area to understand the relationships between erosion, by-pass, deposition and preservation processes. Unlike the neighbouring Rhone deposits that display numerous thick deltaic sequences related to a continuous sediment flux, the Maguelone shore exhibits peculiar sedimentary bodies. The analysis of about 250 km of new VHR seismic profiles acquired over the study area, 9 short cores and outcrops data allowed us to determine the three-dimensional high-resolution geometry of the coastal system tracts from Quaternary to present-day. This revealed dominant denudation processes in the Upstream catchments associated with the formation of incised valleys during Quaternary lowstands. In addition, this study investigates the erosion and deposition mechanisms controlled by littoral hydrodynamics that have been taken place on this shore since the last transgression. In particular, metre-high and hundreds of metre-long sandy bodies constructed by alongshore hydrodynamics were identified and their effect on the morphodynamics of the whole littoral system is discussed. The Maguelone shore can be used as an experimental study for onshore/offshore dynamics under the influence of microtidal wave/current hydrodynamics and very low river-derived sediment flux during a eustatic cycle. Geometry of system tracts across flood plain to shoreface is usually considered to be controlled by relative sea-level changes, and is successfully analysed with 2D sequence stratigraphy cross-shore models. It is observed that in areas like the Maguelone shore, traditional sequence stratigraphy methods might not be fully relevant and need to integrate alongshore hydrodynamical processes.
ISSN: 0025-3227

hal-00421060
https://hal.archives-ouvertes.fr/hal-00421060
DOI : 10.1016/j.margeo.2009.06.008

Éditeur(s) : HAL CCSD Société géologique de France
Résumé : A study combining very high resolution seismic and sediment core data has been carried out on the Thau lagoon (Mediterranean coast, microtidal setting, SE France) in order to understand more clearly the dynamics and Holocene chronology of its closure through the different stages of its filling. One main seismic unit (U2) has been defined into the infill, above the rocky basement (U0) and a composite unit U1, which is interpreted as remnants of Pleistocene fluvial terraces or/and to early marine Holocene deposits. Unit U2, that reaches locally 9 m in thickness, rests conformably on U1 in the central part of the lagoon and onlaps U0 or U1 close to the edge of the lagoon. It is divided in two sub-units, U2-1 and U2-2. U2-2 rests paraconformably on U2-1 in the central part of the lagoon where the infill is the thickest, while a marked erosional unconformity is observed between U2-1 and U2-2 on topographic highs of the basement and on the seaward edge of the lagoon. A total of seven elementary sequences have been observed in U2-1 and U2-2.;According to core data, U2 consists in a series of mud-dominated sequences, with shell fragments dispersed at the base. The vertical distribution of the fauna into U2-1 and U2-2 reveals a lagoonal environment. However in U2-1, marine species are more abundant in the south of the lagoon. C-14 AMS dating provides three ages: similar to 6000 cal yr B.P. in the lower part of U2-1 on CAL1, 5400 cal yr B.P. just above the boundary between U2-1 and U2-2 on CAL4, similar to 3000 cal yr B.P. in the middle of U2-2 on CAL4.;A scenario to explain the lagoon infill stratigraphy and geometry is proposed. The beginning of the lagoon infill occurred with the initiation of the barrier construction, as soon as the sea-level rise slowed down significantly, i.e. between 7000-6000 yr B.P. The sediment-fill began into the back-barrier system, with a high rate of sedimentation for U2-1, according to the radiocarbon data. At 5400 yr B.P., the barrier is assumed to be totally closed leading to the deposition of the fully lagoonal U2-2 succession. The unconformity between U2-1 and U2-2 is interpreted as the result of a rapid landward retreat of the barrier. This severe retreat could be related to climate forcing and/or brutal change in sediment discharge driven by the Rhone River, which is the main sediment source of the longshore drift. In this scenario, the last sub-unit, U2-2, represents most of the late Holocene infill. In this framework, the elementary sequences observed in U2-2 could be related to high frequency climate changes of about 1000-1500 years periodicity according to C-14 dates.
EISSN: 1777-5817

hal-00486386
https://hal.archives-ouvertes.fr/hal-00486386
DOI : 10.2113/gssgfbull.181.2.197

Éditeur(s) : HAL CCSD Société géologique de France
Résumé : The Maguelone shore extends along the northern coast of the Gulf of Lions margin, West of the Rhone delta and East of some high gradient coastal streams that have been providing most of the elastic sediments to the Gulf of Lions margin since the early Miocene. This 10 km wide area comprises an onshore small coastal watershed (15 km long) in low-lying carbonate hills, kilometer wide marshes, sandy beach and shoreface featuring local low sedimentation. Deposit architecture in such a coastal zone records dynamics of incised valley fill under the influence of rivers and wave/current hydrodynamics in a microtidal environment during an eustatic cycle.;A detailed analysis of about 250 km of very high resolution seismic profiles, tens of cores and outcrops data revealed the evolution of the Maguelone coastal system from Late-Quaternary to present-day. It highlighted also dominant denudation processes in the upstream catchments associated to the formation of incised valley seaward during Quaternary. Combination of this inherited morphology together with hydrodynamics controlled the lagoonal environment evolution since the last transgression. In particular, the Maguelone shore is characterized by the formation of built-over-rias lagoonal systems and records an evolution from partially protected lagoon to isolated lagoon environment. These two stages of lagoon evolution correspond to distinct deposit environments. Correlation of fauna contents with deposit geometry improves lagoonal environment models.
EISSN: 1777-5817

hal-00486370
https://hal.archives-ouvertes.fr/hal-00486370
DOI : 10.2113/gssgfbull.181.2.211

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
This manuscript reports on a novel field experiment carried out on a microtidal beach in Camargue, France. For the first time in the field, a comprehensive description of the groundwater dynamics under sandy beach swash zone is presented. A cross-shore network of 15 buried pressure sensors is combined with terrestrial LiDAR measurements to study the swash-groundwater dynamics. The presented data focus on the decay of a moderate storm which allows to monitor the evolution of the groundwater pressure field in response to the retreat of the swash zone. Both horizontal and vertical head gradients are measured within the porous sand soil to estimate the groundwater flow field using Darcy’s law. Time-averaged analysis demonstrates the presence of a rather consistent groundwater circulation pattern under the swash zone, shifting offshore with the swash zone. The main tendency is an offshore directed flow, with infiltration/exfiltration in the upper/lower parts of the swash zone. Time-resolved analysis highlights the typical groundwater response to swash events which consists mainly of an overall infiltration flow during the bed inundation by the swash tongue, a seaward flow during the swash retreat and, for long backwash events, a localized exfiltration flow under the next incoming uprush.
ISSN: 0309-1708

hal-01412450
https://hal.archives-ouvertes.fr/hal-01412450
DOI : 10.1016/j.advwatres.2016.09.009

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