ABSTRACT Gabarrou, S.; Le Cozannet, G.; Parteli, E.J.R.; Pedreros, R.; Guerber, E.; Millescamps, B.; Mallet, C., and Oliveros, C., 2018. Modelling the Retreat of a Coastal Dune under Changing Winds. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research , Special Issue No. 85, pp. 166–170. Coconut Creek (Florida), ISSN 0749-0208. Coastal dunes can move in response to winds and cause serious hazard to human assets. Changes in wind patterns, potentially occurring as a consequence of climate change or variability, could affect rates of aeolian transport and migration velocity of coastal dunes. However, most of previous modeling studies were conducted assuming that aeolian bedforms are subject to constant wind velocities. This article presents a modeling of the mobility of the Dune du Pilat in Aquitaine, a coastal transverse dune exposed to winds of varying intensity. It applies well-established models and empirical formula for aeolian dune migration, including a model previously validated against measurements of real profiles of desert and coastal dunes. The average migration velocity of Pilat dune predicted by the models is about 3m/year, which is in good agreement with in-situ measurements. To test the response of transverse dune mobility to changing winds, virtual wind time series are generated using a stochastic model. Modelling experiments suggest that more frequent storms have less impacts than more intense winds. Due to the size of the Pilat Dune (altitude of about 100m), these result in moderate changes in the average dune velocity. This study shows that the approach of combining a stochastic model for winds with a morphodynamic dune model can provide valuable insight into how aeolian bedforms respond to changes in flow conditions potentially caused by climate change.

ABSTRACT Le Cozannet, G., Ait-Kaci, H., Colas, S., De Lacaze, X., Lecacheux, S., Mirgon, C., Peinturier, C., Garcin, M., and Oliveros, C., 2013. Recent GIS based national assessments of climate change consequences in France: methods, results and lessons learnt This paper reviews two recent assessments undertaken in France for evaluating national scale consequences of global change for coastal hazards and risks, namely marine submersion and coastal erosion. In a first approach, the potential consequences of climate change were evaluated in a direct quantitative way, however with high uncertainties in the final evaluation. Recognizing that uncertainties could hardly be reduced, a second assessment based on a multi-criteria evaluation was then undertaken. Geomorphological and marine factors that account for physical vulnerability to coastal hazards were evaluated for 21 coastal entities in metropolitan France. The evaluation was structured using the analytical hierarchy process (AHP). The results highlighted the fact that in some specific regions such as Languedoc-Roussillon (Mediterranean coast) and Pertuis (Atlantic coast), the population is expected to increase more than the mean average, while the coastal zone are also likely to be more strongly affected by coastal hazards. While such national scale evaluations in highly diversified coastal environments are still arguable, they may help identifying unsustainability in current trends and help defining priorities for future adaptation strategies.

In French Guiana, the constant migration of large mud banks resulting from the Amazon River's sedimentary discharge has a negative impact on the local economy. Two radar images from the new ASAR / Envisat sensor have been analysed and compared to one ASTER image to assess their potential for mud bank monitoring. Bathymetric data were also recorded at times close to those of the satellite acquisitions, enabling a comparative study of the mud bank morphology and bathymetry and satellite information. The emerged parts of the mud banks, whether consolidated/solid (slikke or mudflats, mud bars, etc. ) or fluid mud are easily detectable on the ASAR images. However, the results show that mud bank covered by a shallow layer of water (a few tens of centimetres) is not detectable on ASAR images. For deeper waters the ASAR signal is independent of water depth. ASAR' s multipolarized images provide little more information than that obtained from older sensors having only a single polarization ( ERS-1/2 and RADARSAT-1 ). The Horizontal transmit and Horizontal receive (HH) and Vertical transmit and Vertical receive (VV) polarizations have equivalent cartographic potentials, markedly superior to that provided by the VH polarization. However, the VH brings out certain information that is hard or impossible to see in HH or VV, for example, some offshore emerged portions of the banks, and provides a better separation between water and coastal mangrove forest. The ASTER image enables effective mapping of the extent of emerged mud banks and identification of three classes of water depth.