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ABSTRACT Garlan, T.; Mathias, X.; Brenon E.; Favretto-Cristini, N.; Deschamps, A.; Beucler, E., Guyomard P., and Morio, O., 2018. Circular sedimentary figures of anthropic origin in a sediment stability context. 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. 411–415. Coconut Creek (Florida), ISSN 0749-0208. The French POSA project studies the seismic energy released by bomb and mine blasting. This project is based on seismological and acoustical measurements recording during blasting actions in order to study seismic wave propagation nucleated by controlled sources (location and explosive energy). These measurements are compared to numerical modeling of the acoustic and seismic wave propagation based on the most faithful 3D representation of the seabed sediments and underlying rocks. This project first focused on the 3D environment representation based on specific surveys and on two blasting experiments which consist in exploding bombs of different loads at two distinct environmental places. The in-situ measurements reveal several hundred circular figures with very specific characteristics which clearly differentiate them from other sedimentary, biological and geological figures encountered on the seabed. They are found within the whole studied area and their diameter is from 10 to 130 m. About 30 circles by kilometer square are observed without correlation with the depth which varies from 10 to 150m. These sedimentary structures indicate that they have been generated by the explosion of bombs, but at different periods. The oldest ones most probably result from bombs dropped in 1940 and 1944 during the landing of the Allied forces in the region of Toulon. These original anthropic sedimentary figures and their differences compared with other circular structures observed on the seabed are described. [ABSTRACT FROM AUTHOR]

Sénéchal, N., Sottolichio A., Bertrand, F., Goeldner-Giannella, L., Garlan, T., 2013. Analysis of currents and storm surge in a mixed-energy tidal inlet during storm conditions. Coastal morphodynamic processes around tidal inlets in mixed-energy environments are particularly complex due to severe tide and wave conditions. Collecting data in this area is generally very challenging. Here we present the first hydrodynamic data collected in the outer inlet of the Arcachon lagoon, a mixed-energy inlet situated on the southern part of the French Atlantic coast. Data consist in vertical current profiles and sea surface elevations collected on the offshore edge of the ebb delta under various tidal and wave conditions. In particular data were collected during the severe Joachim storm associated to wave heights up to 8 m. Preliminary results indicate that current profiles, intensities and direction are very sensitive to wave conditions. Under energetic conditions, the vertical profile of currents become uniform and the longshore drift is enhanced (up to 1.5 m/s). Nevertheless data show that under severe wave conditions (Hm0 > 6.0m) and despite high incidence of waves, the longshore drift is weaker (l< 1 m/s) than under 'usual' storm conditions associated to Hm0 = 4 - 5m. More surprisingly, directions of the longshore drift are not always consistent with wave incidence under those severe storm conditions and the cross-shore components are very weak while under less energetic conditions we observe intense offshore currents (up to 0.8 m/s). [ABSTRACT FROM AUTHOR]

Garlan, T.; Almar, R.; Gauduin, H.; Gosselin, M.; Morio, O., and Labarthe, C., 2020. 3D variability of sediment granulometry in two tropical environments: Nha Trang (Vietnam) and Saint-Louis (Sénégal). In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 495–499. Coconut Creek (Florida), ISSN 0749-0208. The sediment variability of two tropical beaches was studied in order to provide the input data of the COASTVAR project's morphodynamic models. The longshore, cross-shore and vertical sediment organization of the first decimeters seems important to take into account in modeling. In particular, the presence of coarser underlying sediments, very frequently observed at all latitudes, may be at the origin of the slope of the beach. And these coarser sediments can also cause significant changes in sedimentary dynamics, when the most energetic events come to set them in motion. But the 3D characterization of beach sediments is not easy and the methods to achieve it are presented here. [ABSTRACT FROM AUTHOR]

Bergsma, E.W.J.; Sadio, M.; Sakho, I.; Almar, R.; Garlan, T.; Gosselin, M., and Gauduin, H., 2020. Sand-spit evolution and inlet dynamics derived from space-borne optical imagery: Is the Senegal-river inlet closing? In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 372-376. Coconut Creek (Florida), ISSN 0749-0208. With the majority of the world' population living in urbanised coastal zones, regional-scale coastal monitoring is a paramount tool to assess the risk exposure of local areas. At St. Louis, Senegal the coast experienced a recent acceleration in coastal erosion. Additionally, the sand-spit South of St. Louis is highly dynamic with one of the largest migration rates worldwide. In this study we showcase the use of satellite imagery to assess the morphological change of the St. Louis inlet position over more than 3 decades. The Senegal river inlet was artificially opened in 2003 Northward of its natural position. The effect of this opening is measured through local shoreline erosion and use of satellite data to predict the next closure of the Senegal-river inlet. Since the artificial breach coastal erosion at the fishmarket of St. Louis was measured, while the sand-spit initially accreted. Southerly sand-spit migration rates that varied from 475 m per year (before an artificial breach in 2003) to 590 m per year after the breach. With these migration rates and assuming limited changes in, for example, river run-off and wave environment, the inlet will close again around 2050 and 2055. [ABSTRACT FROM AUTHOR]