Anthropogenic influence on coastal evolution: A case history from the Catania Gulf shoreline (eastern Sicily, Italy)

摘要

We present the results of a study carried out on the littoral extending south of the Catania town (eastern Sicily) with the aim of identifying the causes responsible for the strong erosional processes, started after the 1950s and accentuated in the last decade. This shoreline, known as "La Plaja" beach, represents one of the unique areas of eastern Sicily, from geological, ecological and socio-economic point of views, and its progressive thinning has a strong impact especially for environmental as well as touristic aspects. The variations of shoreline evolution through time, as they are connected to the Simeto River mouth evolution, have been evaluated through the comparison of the available cartographic sources, which comprehend topographic maps, aerial photos and satellite images. Moreover, the retreating process occurring in the last four decades has been quantitatively estimated along fourteen transects perpendicular to the shoreline direction. Our data point to more severe erosion close to the Simeto River mouth and in the southern tract of the shoreline (maximum retreat of about 204 m, with average rates of 2.75 m/yr), and slower retreat in the northern one (maximum retreat of about 55 m, with average rates of 0.74 m/yr). The analysis of the variations in the hydrological parameters occurring upstream within the Simeto River drainage basin, highlights a drastic reduction of the solid and liquid discharge, coinciding with the entry into operation of several hydraulic works, including dams, fluvial barrages and artificial embankments, after the 1950s. Such a reduction cannot be blamed on a variation in the plu-viometric regime of the area, as the statistical analysis of the rainfall data indicates an almost steady trend during the last century which could not have produced any relevant effect Neither could a variation in the wave regime have triggered more intense erosional processes along the shoreline, as no significant change is observable in the wave parameters either. Thus, the sediment supply reduction and the consequent coastline retreating, is mainly attributable to the installation of hydraulic works, coupled with the progressive destruction of the coastal dune belt due to human building activities. In the absence of suitable interventions, which should also consider the possibility of removing some of the existing hydraulic works, a further reduction, ranging from 20 to 100 m, of the coastline stretch is expected in the next ten years.