Evolutionary trends in the beaches of the Tagliamento river delta

The morphodynamic analysis of the beaches of the Tagliamento river delta (from Punta Baseleghe to the Lignano inlet) showed that some littoral zones are undergoing endemic erosion while others seem to be advancing or stable. These results, based on 132 topographic and bathymetric profiles collected perpendicular to the coast, were obtained in the study area in 2002 and 2003 and compared to the 1987 bathymetric profiles. From the analysis of the bathy-morphological data, the areas prone to great changes are located near the river mouth where a series of detached breakwaters have been placed for stabilization. These defences have partly stopped or generally slowed the erosive processes but have given rise to conditions of instability in the adjacent areas. Important erosive processes are evident, more westwards, in the area denominated Lame di Revelino - Pineta Punta Faro, where a progressive withdrawal of the beach, the disappearance of the low-tide terrace and the thinning of the upper shoreface zones is currently occurring. The central and western part of the Bibione shore display different characteristics. Here, the beaches are essentially characterized by a stable or advancing regime. The beach, in correspondence to the Baseleghe inlet, initially thins in width which has nothing to do with erosion, and shows an important development seawards and further expansion westwards. This kind of behaviour of the beach further highlights a trend towards an occlusion of the Baseleghe inlet. The eastern lobe of the delta is represented by a beach with a concave geometry, marked by the presence of groins. These structures have captured and stabilized the sand within the cells between pairs of adjoining groins. At the same time, however they also prevent the drift of sediments towards the east, determining a substantial decrease of the sedimentary flow toward the beaches in that direction. The central portion of the Lignano shore shows a typically stable character with natural progradation phases which were also confirmed by a long time-series of observations. Instead, the coastal belt close to the Lignano harbour fairway is slightly unstable; a series of groins and seawall revetments are located in this area.