Surface sediment dynamics along with hydrodynamics along the shores of Tunis Gulf (north-eastern Mediterranean)

摘要

The authors report on a study conducted as a part of a project to favour sustainable management of coastal zones, investigating hydrodynamics, sediment dynamics, grain size and mineral composition of surface sediment in Tunis Gulf. Currents, winds and waves affect the erosion, transport and deposition of particles along the coast, leading to an unbalanced sediment budget. Currents recorded in the coastal areas of Port au Prince and Ghar El Melh have an average speed 12 cm s~(-1) during summer but exceeding 20 cm s~(-1) in the case of short strong winds. Numerical simulations of current velocities in the Gulf of Tunis were conducted in both summer and winter. Current velocities reached 20 cm s~(-1) and 10 cm s~(-1) in winter and summer, respectively. The results of grain-size and mineralogical analyses of surface sediments collected at various depths between Sidi El Mekki and Cap Bon (Tunis Gulf) led to identification of their origin, essentially via transport and deposit. Granulometric study showed that detritus materials in the gulf are of continental origin, while mineralogical analyses revealed a clear relationship between recent sedimentary stock from the gulf and the bordering geological formations. As all sediment distribution is controlled by water movement, a high fraction of fine sediments (＞90%) is transported by the major Mediterranean currents and deposited in the gulf's central zone. Coarse sediments, on the other hand, are found at the gulf's entrance in the vicinity of Ghar El Melh Lagoon and, more generally, along the gulf's western shore as a result of littoral transport under wave and swell action.