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In a context of climate change, we will present the methodology of the modeling approach to analyze the sensitivity of a Mediterranean beach to forcing conditions changes. This paper discusses the abilities of numerical models to predict the nearshore evolution and to set-up vulnerability indicators of sandy beaches against the climate change predictions for 2030. The objectives which we want to reach during this study are multiple. First, we are going to set up a procedure of linking of three codes (the waves, the flow field and the bed evolution models (Telamac)) to be able to simulate realistic climates. This procedure is validated from the point of view of the hydrodynamics and morpho-dynamic evolution (Larroudé, 2008). This technique of simulation will then use to compare and studied the contribution of the various formulae of sedimentary transport (as in Camenen and Larroudé, 2003) on the site of Sète (Languedoc-Roussillon, France). Located in a microtidal, swell-dominated coastal environment, this beach is a linear beach of about 2.5 km length with double straight bar system. The mean significant offshore wave height is about 0.5 m increasing to 3-6 m during storms, (Certain and Barusseau, 2006). We improve this methodology to simulate the Rising-Apex-Waning of a two specific storm event (Robin et al., 2010). We also present a comparison of the velocity at these different periods of the storm. We will present simple indicator methods to analyze the vulnerability of a sandy beach based on the results of simulations for different scenarios. The first method is based on the method described in Idier et al. (2006). In the present study, we calculate the maximum grain size potentially mobilized but with a simpler approach, based on analysis in different point on several cross shore profile

Sabatier et al; International audience; The central part of the Gulf of Lions shoreline is characterized by many coastal wetlands that resulted from the interaction between a process of shoreline regularization by migrations of littoral barriers and a slow filling of the back-barrier areas by the riverine and marine inputs. Analyses of Late-Holocene deposits with a very high-resolution multi-proxy study of two sediment cores, allow us to reconstruct the evolution of this coastal system. Two main Holocene sediment units are identified overlying a Pliocene carbonate continental formation. The lower unit consists of sandy and pebbly marine sediments deposited around 7800 B.P., during the final stand of the last sea level rise. Just above, the upper unit displays lagoonal grey clay silts with shells and some intercalated layers of silty sands related to paleostorm events. The age model was established from radiocarbon dating, for the oldest part of the core. Over the last century, sedimentation rates were calculated using the CFCS 210Pb model, together with 137Cs data. Radiocarbon data show an increase in the accumulation rate from the base to the top of cores. Marine sand units related to the last transgressive deposit allow to refine the curve of Holocene post-glacial sea level rise. Sedimentological and faunal analyses associated with chronological data provide a means for reconstructing the Late-Holocene paleoenvironments along this part of the coast and suggest that the final closure of the coastal lagoon by the sandy barrier occurred at around 730 ± 120 yr cal B.P. The beginning of this closure, together with the progradation of the coastal plain, could be responsible for the decline in economic activity of the Lattara harbour during the Roman period

International audience; A modified 2DH morphodynamical model was employed to simulate the evolution of large-scale features with major implications for beach nourishment. The study was focused on modelling the evolution of material artificially placed in different parts of the profile, extracting or adding material to the natural bars, and quantifying how the profile responds to different wave climates and nourishment placements. The simulated results were compared with field data from a Mediterranean beach.

Improving our knowledge about coastlines worldwide can definitely contribute to understanding how sand coastlines with offshore bar systems operate. The study undertaken on the coastal sedimentary unit on the Bay of Mahdia where moderately active tectonic activity prevails fits into that general approach. This preliminary work presents the morphology and sedimentology of a 15 km long coastline with a sandy beach and an irregular dune ridge bordering the offshore between cape Africa and cape Dimas along the Bay of Mahdia. Morphology displays a sandy sedimentary prism composed of 3 compartments spreading from south to north. At both ends, the prism is poor in sediments along the cape promontory. In the central part, it is more regular for about 7 to 8 km, forming a 1.4 % slope leading, at -10 to -12 m, to a slightly sloping plateau with relief lines highlighting the general contour of the bay. This sedimentary slope is abruptly limited to the north by a relief alignment, located in the extension of the Moknine fault. In the central part, the prism is labeled by the existence of two offshore bars of which the innermost shows instability under the hydrodynamic regime forcing. A bathymetric sounding carried out in August 2006 registered a segmentation of the inner bar, not seen on two sets of previous comparable aerial photos. This segmentation seems to be influenced by the incidence of storms, common during the summer season. A simulated wave refraction diagram of the N to E quadrant swells shows the good relationship of the wave orthogonal deviation with the distribution of the directions of the bar sections observed. The disruption and reorganization of inner bar sections under the influence of average energy storms bear witness to the symptomatic instability of a volume of sand to be displaced that can only be modest in size. Textural analysis and the nature of sediments confirm this diagnosis. The response of sediments to the selection processes shows that grain size assemblage depends on a mixture of sedimentary types in limited numbers, characteristic of the reduction in the number of sedimentary sources. The most important type uses the material from the beach and dune as a reservoir, which is in turn under the influence of reduction processes having required erosion abatement measures. Coarser populations, mainly bioclastic, become incorporated into the fine fraction of the sand whose distribution they modify. The change is however discreet, influencing primarily the asymmetry and leading to bimodality only in rare instances. In the case of Mahdia, the sedimentary sources are therefore exclusively local, rare and in small quantities.