Observation and modeling of tide- and wind-induced surface currents in Galway Bay

A high-frequency radar system has been deployed in Galway Bay, a semi-enclosed bay on the west coast of Ireland. The system provides surface currents with fine spatial resolution every hour. Prior to its use for model validation, the accuracy of the radar data was verified through comparison with measurements from acoustic Doppler current profilers （ADCPs） and a good correlation between time series of surface current speeds and directions obtained from radar data and ADCP data. Since Galway Bay is located on the coast of the Atlantic Ocean, it is subject to relatively windy conditions, and surface currents are therefore strongly wind-driven. With a view to assimilating the radar data for forecasting purposes, a three-dimensional numerical model of Galway Bay, the Environmental Fluid Dynamics Code （EFDC）, was developed based on a terrain-following vertical （sigma） coordinate system. This study shows that the performance and accuracy of the numerical model, particularly with regard to tide- and wind-induced surface currents, are sensitive to the vertical layer structure. Results of five models with different layer structures are presented and compared with radar measurements. A variable vertical structure with thin layers at the bottom and the surface and thicker layers in the middle of the water column was found to be the optimal layer structure for reproduction of tideand wind-induced surface currents. This structure ensures that wind shear can properly propagate from the surface layer to the sub-surface layers, thereby ensuring that wind forcing is not overdamped by tidal forcing. The vertical layer structure affects not only the velocities at the surface layer but also the velocities further down in the water column.

Sediment provenance of a carbonate bioclastic pocket beach—Le Dune(Ionian Sea,South Italy)

This study focuses on the analysis of a carbonate bioclastic pocket beach located along a coastal sector of the Apulia Ionian Sea,Le Dune beach,South Italy.The beach develops for about 800 m and it is exposed to the south-westerly and southerly seas.Coastal sediments range from very coarse to medium-fine sands and they are mainly composed of bioclasts(more than 90%)which include molluscs,foraminifers,echinoderms,algae branched,bryozoans,spicules of sponges and arthropods.The study area is one part of a marine protected reserve characterised by 15 different habitats of the typical Mediterranean submerged populations and the presence of Posidonia oceanica meadows.The aim of our research is to highlight the correlation between physical and biological processes influencing Le Dune beach dynamics and its sediment provenance by analysing the textural and compositional characteristics of beach sands,which is fundamental for pocket beach conservation.The beach sand analysis,deriving from textural,compositional and bioclast investigations,underlines that one of the main indicators of the beach dynamics is the bioclast component,which provides relevant information about sand provenance and sediment transport.The beach constitutes a semi-close system only nourished by the shells of organisms and by the erosion of headlands and dunes without important sediment interchange with adjacent littoral sectors.