The beach erosion on the left side of the Sele river mouth (Gulf of Salerno, Southern Italy): Nearshore dynamics and proposals for the coastal protection

Abstract

The examined area is part of the widest phisiographic unit of the littoral plain of the Sele River, which represents the coastal edge of a vast tectonic depression (pery-Tyrrhenian Graben of the Gulf of Salerno). From a geomorphological point of view, we can distinguish two sectors: The first, between the Sele River mouth (Foce Sele) and Pontile, extends about 3 km. Within this area the environment appears still "natural". The second sector further south, between the Pontile and Lido Nettuno near Paestum, extended about 2 km, is completely urbanized (bathing structures are evident all along the coast). The sandy or sandy-pebble backshore is limited towards the hinterland by a narrow mobile dune and then from a series of reforested dune ridges which are deeply degraded because of the marine action. Two zones can be observed in the submarine beach: The first one, within a -5 m depth, shows a very articulated morphology due to the presence of an alternating series of bar-trough systems and shoals; the second one, between a -5 and -10 m depth, shows a gently sloped seabottom. The study of the littoral regime has shown that the greater energetic potential concerns the sector 230° - 280° N which is subject to 72% of the total energy of the area; the maximum wave height, with a 30 year return period, ranges between 2.93 m (170° N azimuth) and 8.78 m (280° N azimuth), while the average direction of wave approach is from 230° N azimuth, orthogonally to the coast. The research confirms a clear erosional tendency concerning above all the area between the Sele River mouth (Foce Sele) and Pontile, where the shoreline underwent a retreat of 1-2 m/year from 1978 to 1997 and a loss of sediment in the emerged beach consisting of more than 70,000 m3 (2 m3 per linear meter of coast per year) from 1982 to 1997. During the period in which the backshore has been monitored (November 1996 - November 1997), violent storms coming from 240° N azimuth struck the area causing a strong erosion of the beach and of the dune systems. As a result of the reduction of detrital supply due to human activities (Cocco et aL, 1992) the coastal processes along the studied area can be attributed to the energetic factors in the nearshore zone. Thus we propose a coastal defence project which consists in the following parts: 1) reduction of the energy of the incident wave on the coast by the construction of submerged breakwaters; 2) artificial beach nourishment; 3) restoration of the foredune system by remodelling artificially the profile and by planting native species.