SEDIMENTARY PROCESSES, MORPHODYNAMICS AND SEDIMENTOLOGICAL MAP OF PORTO GIUNCO-SIMIUS-IS TRAIAS BEACHES (VILLASIMIUS - SE SARDINIA)

The morpho-sedimentogical study of Porto Giunco-Simius-Is Traias beach system is presented; the beach is situated in the Site of Community Importance (SCI) area ITB 040020 “Isola dei Cavoli, Serpentara, Punta Molentis”, in the municipality of Villasimius (Sardinia SE). The research was carried out as part of the European project Life+ Nature & Biodiversity Providune (LIFE07NAT/IT/000519) (DE MURO et alii, 2010) using the standards and the survey methodology identified by the European project Interreg IIIA GERER “Gestion intègrèe de l’environnement à haute risque d’èrosion” (DE MURO AND PUSCEDDU, 2009). The aim was to understand the sedimentological and hydrodynamic processes of the studied area and to produce a 1:5,000 scale map of the beach (drybeach and shoreface). The geology of the area is characterized by outcrops of granite rocks belonging to the intrusive plutonic complex of the Upper Permian Carboniferous (Hercynian basement). The outcrops are tonalitic granodiorites, inequigranular monzogranitic granodiorites and sodic syenites. There are both acid and basic dykes through the granitic complex running mainly NW-SE. No Paloezoic, Mesozoic and Tertiary covers are present in the area. Quaternary deposits are however present, mainly alluvial sediments and deposits from the Upper Pleistocene made up of conglomerates, beach sandstones and biocalcarenites. The Holocene deposits are represented by alluvial gravels, aeolian sands, sands of emerged and submerged beach and by pelitic sediments from the lagoon. The formation of Notteri lagoon, which is the only important humid zone in the area, is associated to the high stand of the Versilian Transgression. The survey was carried out by taking topographic measurements referring to a geodetic network purposefully created, based on the point IGM95 ETRF2000 n.235902, near the port of Villasimius. The dry beach was examined using the DGPS system on 1Hz frequency; the submerged beach, using Reson Navisound 215/DGPS Omnistar 8300HP with Reson PDS2000 navigation software, installed on the Marino660 belonging to the Osservatorio Coste E Ambiente Naturale Sottomarino (OCEANS) Department of Land Science University of Cagliari. The survey was carried out on the emerged and submerged beach at the same time, on an acquisition grid with 50m per side. The DTM created was the basis of the land-sea sedimentology study. 117 samples were collected and studied from the submerged beach (using Van Veen 5 lt grab), the drybeach, the shore-line and the dune area. The samples were first studied according to the Folk and Ward (1957) method, and then a compositional analysis was carried out through the semi-quantitative identification of quartz, feldspars, micas, accessory minerals, lithoclasts and bioclasts. The data showed a general trend of the distribution of the present superficial sediment. Through the data elaborated (DTM and sedimentology) wave swell and hydrodynamic models were constructed using Delft3D software, WAVE and FLOW modules. The models were based on the meteo-marine data recorded in the area and calibrated with observations and measurements in situ. The hydrodynamic models allowed the identification of the main events that control the exchange processes and structure the bars and troughs zone (surfzone). The thematic maps produced (bathymetric, wave ray direction, deep current distribution, structure and surfzone dynamics) and the results obtained, allowed the visualization of the main control and distribution mechanisms of the sedimentary flows dune-dry beach-shoreface.