Surface sediment dynamics along the eastern coast of Djerba Island (Gabes Gulf, Tunisia)

International audienceSurface sediment dynamics were studied on the eastern coast of Djerba Island (Gabes Gulf, southern Tunisia) by simultaneously assessing currents, as well as the mineralogy and grain size of bottom sediments. Harmonic analysis of time-series sea data at Ras Taguermess and El Kantara illustrated the dominance of a semi-diurnal tidal component, with a period of 12h 42min. Orthogonal Empirical Functions analysis of tidal currents along the major axis at El Kantara produced a standard deviation of +45 cm s−1 with a main angle of 29°, whereas at Ras Taguermess it was 5 cm s−1 with a north-south direction. Analysis of grain sizes from sediment samples taken between Ras Taguermess and Ras Marmour show that the shallow bottoms (0–10 m) are composed of fine, medium and coarse sands. Mean grain size ranges between 100 and 763 μm, a distribution attributed to a high level of wave activity. Moreover, two mean grain size gradients were evidenced: the first is alongshore from north to south, from Ras Taguermess to Aghir, and the second from south-east to north-west, between Ras Marmour and Bin El Ouediane. Quartz is abundant from Ras Taguermess to Sidi Garous along the many beaches, while it quantitatively decreased in the eroded area between Sidi Garous and Aghir. Thus, transport is from north to south. A high build-up of sediment was observed in Bin El Ouediane, resulting from a barrier island formation