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Titolo: Bars and troughs dynamic and short-term evolution of two beaches on NE Sardina: La Cinta (San Teodoro, OT) and Budoni (OT)
Data di pubblicazione: 2011
Abstract: 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.
ISBN: 978-84-615-1755-8
Tipologia:4.1 Contributo in Atti di convegno

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