Processi sedimentari, idrodinamica e modellizzazione delle spiagge di Santa Margherita, Solanas, Cala di Trana e La Sciumara (Sardegna – Italia)

Presentation of the results from the study of four representative beaches focusing on sedimentary processes, hydrodynamics and modelling. The sample beaches studied were Santa Margherita (Pula) and Solanas (Sinnai), located respectively in the east and west sections of the Gulf of Cagliari, southern Sardinia. Cala di Trana and La Sciumara were also studied, located in the north of Sardinia (Palau – OT) in the Straits of Boniface area. The study was carried out using methods indicated in the European project Interreg IIIA GERER (AA.VV., 2008), for the first time on Sardinian beaches. A digital system of topographic-bathymetric data acquisition was used and seasonally repeated. The digital data, and sedimentological data, were used to calculate the basis on which the wave motion and hydrodynamic simulations were applied. The results identified the phenomena of coastal refraction, the corresponding hydrodynamic scenarios and the surfzone structures that are generated according to the marine event simulated

Sedimentological map of Bonifacio strait inner shelf

This paper presents the sedimentological map at 1:50,000 scale of the mixed carbonate-silicilastic inner shelf of the Bonifacio straits. The study has been carried out in order to evaluate the relationships between the production and transport of biogenic carbonate and terrigenous sediments and the morphological and hydrodynamical characteristics of the basin

Relationships between carbonate sedimentation and hydrodynamics on the temperate shelf of the Strait of Bonifacio (western Mediterranean)

The sedimentary features of the inner-middle shelf of the strait of Bonifacio (western Mediterranean) were analyzed to evaluate the relationship between the production and transport of biogenic carbonate sediments and the basin morphology and hydrodynamics. A three-dimensional hydrodynamic modeling was performed in order to simulate the influence of waves and currents at the seabed level. Superficial sediments were collected at depths ranging from 5 to 80 m and were analyzed for grain size, mineralogical composition and skeletal carbonate composition. Shallow seismic data (3.5 kHz) were acquired to evaluate the spatial distribution and architecture of sedimentary facies. Posidonia oceanica seagrass meadows border the coasts in a narrow strip at both sides of the strait down to a depth of 40 m. In greater depths, the seabed is characterized by the presence of plateaus and ridges which are controlled by outcropping bedrock morphology. Waves and seabed currents are driven by the prevailing northwest and northeast winds. For both wind directions, higher values for the seabed current velocity, associated with windstorm events, were detected in shallower sectors and along an east–west-oriented belt that connects the western Mediterranean and the Tyrrhenian Seas. The sediments range from sand to gravel and show a mixed biogenic carbonate /siliciclastic composition. This is due to the carbonate production associated with benthic ecosystems and the mixing of modern carbonate with relict sediments. Biogenic gravelly sands were found in association with P. oceanica seagrass meadows and extended down to the circalittoral zone outside the deeper limit of the meadows. This sedimentary facies was derived from the modern carbonate production associated with the P. oceanica ecosystem. Sediments collected outside the deeper limit of the meadows were identified as relict sediments deposited during the stand of the meadows at a deeper level during lower sea-level conditions. Maërl (free-living calcareous red algae) beds are the main carbonate factory and are mainly located at the top of the rocky plateaus (at ~50-55 m) formed by the outcropping of the bedrock. Downward, the increased currents at the seabed level in the east–west-oriented belt, which connects the western Mediterranean and the Tyrrhenian Seas, limit the extension of this carbonate factory. This results in a mixed sedimentary facies composed of biogenic carbonate and relict siliciclastic sandy gravel. Compared to other Mediterranean shelves, the strait of Bonifacio is characterized by a distinct oceanographic setting. This is due to the connection between two basins. The currents at the seabed play a crucial role in controlling the distribution of the carbonate factories

Modern inner-shelf sedimentation: a comparison between Bonifacio Straits and Gulf of Cagliari (Sardinia - IT)

This abstract presents a comparison results on inner shelf sedimentation between Bonifacio Straits (between Sardinia and Corsica) and Cagliari Gulf (South Sardinia). The studies were carried out in the context of the following projects: Interreg IIIA – G.E.R.E.R., “Environmental control system and management of the coastal and marine area of the Gulf of Cagliari - M.I.U.R., CAR.G. Project – “Geological Map of Italy, 1:50,000 scale” and continue thanks to the RIAS project and two fellowship grants funded by the Sardinia Regional government. Seismic and echographic data were recorded and used to identify different acoustic facies (sediment deposits, posidonia meadows and rock outcrops) and bedforms (sandwaves, comet marks, ripples etc.). A total of 230 samples were collected and analyzed. The mineralogical composition of samples was classified by distinguishing bioclasts, lithoclasts, quartz, feldspars, micas and other minerals. The taxonomical classification was performed categorizing sediments in the following groups: Red Algae, Bryozoans, Mollusks, Cnidarians, Arthropods, Echinoderms, Foraminifers, Polychaeta–Serpulida and indeterminate grains. The sedimentological maps were drawn using the classification into sedimentary facies, realized by multivariate statistical techniques, which distinguish sample groups on the basis of different sediment characteristics (texture, mineralogy, taxonomical groups). Different sedimentary facies were recognized: shoreface sediments, coastal detritic sands, reworked detritic sands, mixed gravelly sands, maërl beds, coralligenous and three different types of muddy sandy sediments. Modern inner shelves sedimentation is controlled by eustatic, hydrodynamical and morphological features of the basins and by in situ production of marine ecosystems as Posidonia oceanica (L.) Delile meadows, coralligenous and maërl beds. Both shelves were classified as mixed carbonate-terrigenous shelves

Bars and troughs dynamic and short-term evolution of two beaches on NE Sardina: La Cinta (San Teodoro, OT) and Budoni (OT)

This paper describes the dynamics and evolution trend in two similar beaches located in NE Sardinia. The study began a few days after the flood on the 24th of September 09, which caused a different response on the beaches. La Cinta beach, located in San Teodoro is 5km long and composed of fine quartz rich sand, backed by well-developed dune ridge and San Teodoro’s lagoon. Budoni beach (4 km) is composed of fine to gravelly quarz sand, few seasonal lagoons are developed behind the dunes. Short-term variations have been periodically monitored since October 09. Sedimentary and hydrodynamic characteristics were studied. Short-term evolution of La Cinta beach was tested using topo-bathymetric digital models, derived from data acquired in two different field surveys (2009-10) in order to examine the resilience of the system. From data collected, thematic maps and models were produced. The comparison between them allowed to identify the main controls and distribution mechanisms of the sedimentary paths on the shoreface. Models of wave motion and hydrodynamics were created using Delft3D software. Calibration and application of numerical models for wind-wave propagation were based on marine forecast data recorded in the area and were gauged on in situ observations and measurements (survey 2010). The results obtained from these models (wave ray direction, deep current distribution, structure and surfzone dynamics) allowed to visualize the response of beaches to wind/waves stress, forced from NE, E, SE (wind intensity 18m/s, 10m/s). Our data demonstrate that La Cinta dry-beach extends for about 0.088km2 (width max 51m) in summer to 0.08km2 (width max 45m) in winter, while after the flood it was reduced to 0.054km2. Shoreline prograde seasonally on average between 4-8m; beach slope varied from 1° to 3°. On surf zone, slopes don’t show strong modifications in size of sand bars and troughs, data ranging from 0.75° to 1.14° in 2009 and from 0.68° to 1.21° in 2010. The significant regression recorded in 2009 survey was linked to the recent effects of the lagoon overflowing, which caused the breach of 25 openings on dry-beach and destroyed the fish farming jettys. Data acquired one year later demonstrate the hight resilence of this beach, with tendency to re-establishment of steady state with short relaxation times. On the other hand, in the nortest part of littoral the jettys weren’t rebuilt and beach regression increased. Slight regression was also registered in the south, probably induced by a small harbour built in 2000. Budoni dry-beach surface extents for 0.082 km2 (width max 49 m) in summer and 0.0827 km2 (width max 49 m) in winter. Seasonally average shoreline oscillations ranges from 0.2 to 3.5 m, beach slope ranges from 2° to 9.6° showing strongest variation in the northern area. In conclusion both beaches show mainly a homeostatic behaviour characteristic of an equilibrium system

Sedimentary and morphodynamic processes of microtidal wave dominated mediterranean beaches (Villasimius - SE Sardinia)

This paper shows the results of the morpho-sedimentogical study of Porto Giunco-Simius-Is Traias beach system; the beaches are 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) 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”. The aim was to understand the sedimentological and hydrodynamic processes of the studied area and to map the granulometric distribution of the emerged and submerged beach (drybeach and shoreface). 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 ship belonging to the Osservatorio Coste E Ambiente Naturale Sottomarino (OCEANS) of Cagliari University. 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. Through the data elaborated (DTM and sedimentology) wave 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. Mz values on dune zone show sediments that consist of fine sands, compared to those of the backshore that consist of medium sands. The sediments of the shoreline is characterized by medium and fine sands while the submerged beach is characterized by fine and very fine sands. This distribution is typical of coastal systems dominated by the waves, characterized by a decrease in energy towards the sea. From a compositional point of view the results show sediments prevalently formed by siliciclastic materials (quartz, feldspars, biotites, heavy minerals and lithoclasts). The poor bioclastic component is formed by the foramol association related to the presence of Posidonia oceanica meadow. The hydrodynamic models allowed the identification of the main events that control the sedimentary exchange processes and structure the bars and troughs zone (surfzone). The hydrodynamic models demonstrate that Sirocco wind (135°) mainly controls the exchange processes and sets the surfzone. These events produce longshore and rip-currents and several circulation cells which shape a system of bars and troughs, with a surfzone extension over 100 metres. The several thematic maps produced (bathimetry, refraction, bottom current distribution, texture, facies distribution, surfzone dynamic etc.) and the reults obteined show the main mechanisms of sediment flows. The general results underline clearly the main mechanisms of control and behavior of sedimentary fluxes between dune-drybeach-shoreface

Short-term evolution of the Budoni beach on NE Sardinia (Italy)

Dynamics and evolution trend in Budoni beach are described. The beach (long about 4km) is composed of fine to gravelly quarz sand, few seasonal lagoons are developed behind the dunes. Short- term variations have been periodically monitored since October 09. Sedimentary and hydrodynamic characteristics were studied. Short- term evolution was tested using topo-bathymetric digital models, derived from data acquired in 3 different field; models of wave motion and hydrodynamics were created using Delft3D software. The results obtained from these models (wave ray direction, deep current distribution, structure and surfzone dynamics) allowed to visualize the response of beach to wind/waves stress, forced from NE, E, SE (wind intensity 18m/s, 10m/s). Gregale and Sirocco are the winds that generate the widest surfzone, the currents created by the these win- ds cause mainly longshore transportation in the early hours of the meteo-marine event. The beach shows an homeostatic behavior characteristics typical of balanced systems

Morpho-sedimentological map of Chia beaches - SCI ITB042230 “Porto Campana” (SW Sardinia, Mediterranean Sea - Italy)

This paper presents a 1:5,000 scale morpho-sedimentological map of the emerged and submerged area of Chia beaches, located in the ITB042230 “Porto Campana” SCI of Natura2000 network (SW Sardinia, Mediterranean Sea - Italy). The Chia beaches continuity is interrupted by two low rocky headlands which divide it into three areas from NE to SW called Sa Colonia, Campana and Su Giudeu. The map is compiled using sonograms and sedimentological data and it shows the granulometric distribution of the emerged and submerged beach (up to -50m depth). The geological setting is characterized by a Precambrian and Palaeozoic basement formed by metamorphic rocks (ortogneiss and micaceous shales) and granitoid lithotypes. Moreover crops of “Bithia Formation” (Precambian?-Lower Cambrian), formed by phyllites, metasandstones, marbles and basic metavolcanic rocks are observed. On the Palaeozoic basement, Quaternary deposits lie, which are formed from Holocenic and recent beach sands, ancient and recent alluvial deposits related to the main rivers and colluvial deposits on the slope floors. The surface beyond the backshore is characterized by colluvial-alluvial deposits made up of sandy matrix clastic sediments, while the alluvial plains present are composed of sandy-gravelly deposits. The data were collected during four different surveys conducted in 2009. The surveys were conducted by field measurements referred to a geodetic net based on the IGM95 ETRF2000 n.239901 point, located in Monte Filau. The topography of the emerged beach was surveyed with a DGPS system, obtaining the points with xyz coordinates on 1Hz frequency. For the submerged beach, a system of interfaced Reson Navisound 215 echosounder/Omnistar 8300HP DGPS through Reson PDS2000 navigation software, was used, installed on the Novamarine RH580 ship of the “Osservatorio Coste E Ambiente Naturale Sottomarino” (OCEANS) of Chemical and Geological Sciences Department (Cagliari University). The surveys were obtained together on submerged and dry beach on a 50m side grid. In “post-processing mode” all data were processed and filtered to realize a studied area DTM, it permits to realize a detailed topography and bathymetry of the study area, reported on the map. Then a sedimentological survey, along prefixed land-sea transects was carried out. During this survey the following sample were collected: 67 samples from the submerged beach (using 5 liter van veen grab), 42 samples from emerged beach and shoreline and 74 samples from the dune area. Granulometric analysis was made following the ASTM International standard metodology, with sieves spaced on ¼Φ between 2000μm and 63μm (Udden-Wentworth scale, 1922). The grainsize parameters of Folk and Ward (1957): Meansize (Mz), sorting (σI), skewness (SkI) e kurtosis (KG) were obtained for every sample. Moreover an ortophotos analysis was carried out to evaluate the historical and the anthropical evolution of the area that were reported on the map. The sediments were described and mapped and they consist in 5 legend terms: Coarse Sand, Medium-Coarse Sand, Medium Sand, Medium-Fine Sand and Fine Sand. The map also shows rocky outcrops and Posidonia oceanica (L.) Delile meadow coverage. The meadow plays a decisive role in the production, selection and transport of bioclastic sediments and it contains the terrigenous sedimentation between the coastline and its upper boundary

Coastal dunes vulnerability. GAVAM checklist method used at three Mediterranean microtidal wave dominated beaches (Gulf of Cagliari)

The study shows the results achieved by using Geomorphology, Aeolian, Vegetation, Anthropogenic, Marine influences, (GAVAM) checklist, in three coastal dune zones of beaches located in southern Sardinia. The aim is the experimentation of reproducibility of GAVAM checklist in three Mediterranean microtidal wave dominated beaches. The studied dune zones are located at three Site of Community Importance (SCI) sites: ITB 042230 “Porto Campana”, ITB 042218 “Stagno di Piscinnì” e ITB 040020 “Isola dei Cavoli, Serpentara, Punta Molentis” (southern Sardinia). By the application of GAVAM checklist the Partial Index Vulnerability (IVp) and the Dune Vulnerability Index (DVI) or total (IV) values are sequentially derived. IV index either partial or total ranges between 0 and 1, and as the index increases, the ability of the dune system to withstand further interventions decreases. The methodology has allowed an objective deduction to both potential vulnerability and the main source of imposed changes, as well major threats/stress factors have been assessed. DVI values range between 0.47 e 0.59 and indicate medium to high vulnerability. Moreover, the use of aerial photographs also highlighted the need for the implementation of the checklist using additional parameters related to fluvial-lacustrine processes and of particular anthropogenic activities