Coastal dynamics : shoreline detection in sicilian beach

Abstract EN

In our days Sicilian coast suffer of severe erosion, with a total of 1139.3 km2 of coastal area, 20% of them are in advancement and 33% in recession.

Shoreline position and its celerity of changing in time, can provide important informations for bulwark design (e.g.

breakwater, seawall, ecc.) and to develop coastal management plans.

The shoreline is located between land and sea, it has dynamic nature and for this reason it is subjected to change, both in short and long term.

These changes are caused by geomorphological processes (making of bars, berms, ecc.), hydrodynamic (wave motion, tides and currents) and by unexpected and quick factors as storms and tsunami.

Therefore, the analysis of the shoreline variability, in terms of erosion and expansion, is crucial for an overall understanding of these phenomena.

This research examines the issues related to the uncertainty to identify the shoreline position, that changes in time, as above mentioned.

The study was done considering geological, geomorphological and hydraulic aspects.

The case study investigated is represented by Marsala (Trapani) shoreline.

The beach has sandy sediments from Holocene age.

These sediments are in continuity of sedimentation on whitish debris composed by organic limestone from Pleistocene age.

The diachronic analysis was carried out on both emerged and submerged beach and has also provided a geomorphological characterization performed in situ.

Geomorphological-descriptive data, measured in situ, have been compared to remote sensing data.

It should be noted that the comparison between orthophotos and maps is subjected to several uncertainties, due to graphics and geo-referencing errors.

Moreover, it has to be stressed that the values of tidal and climate waves are related to the particular acquisition time.

As a matter of fact it was necessary to perform a maritime hydraulic study in order to take into account the sea fluctuations during the considered period.

The run-up is related to the height and length (or period) of the waves, as well as to the composition and particle size of the beach sediments, that determine the beach slope (Nielsen and Hanslow, 1991).

The obtained results allowed to assess the uncertainty and the consequent errors in the evaluation of the shoreline position, for fixed slopes.

In particular, it was found that, in many cases, it is not possible to assess the shoreline rise and fall, for values lower than 30 m.