Coastal protections in Tyrrhenian Calabria (Italy): morphological and sedimentological feedback on the vulnerable area of Belvedere Marittimo

Abstract

This study provides with the results of a morphological and sedimentological study carried out along the coast of Belvedere Marittimo (Tyrrhenian Calabria, Southern Italy). From 1873 to 1955 the coast has been overall stable, even if local erosion occurred. As from the end of the ‘50s this area underwent erosion processes, which greatly have increased during the following years. In order to check the severe erosion of the shoreline, and to minimize the risks coming from it, several kinds of coastal engineering structures, like breakwaters, seawalls and groins, have been constructed during the time all along the considered coast. The specific aim of the present study has been to single out the evolutionary trend of the shore, and to define the sedimentological characteristics of the bottom and the morphology of the seafloor up to –15 meters. Moreover, underwater observations of the structures allowed an evaluation of the present conditions. The analysis of the shoreline changes occurred between 1873 and 1955, showed an overall beach stability. Later on the erosion processes, already active at the end of the ’50s, enlarged becoming particularly strong for some areas during the period between 1955-2002. Depth surveys by echosounder and local direct observations allowed an investigation of the morphological features of the submarine coastal area. The seafloor up to –15 meters shows a regular pattern, except for local articulations near Capo Tirone. Moreover, for a sector of the northern part of the studied area, where a larger number of groins, seawalls and breakwaters were present, the comparison between depth data prior to the engineering structures and data following it, has been carried out. The result allowed a singling out of accumulations and erosion areas, as well as the marked influence that the structures have on the local sedimentary dynamics. The sedimentological analysis of 108 bottom samples taken at –15, –10, –5, –2 and 0 meters, and the cluster analysis of phi percentage, showed two main clusters: the first includes samples of fine and mediumfine sand, medium sorted with symmetric grain size distribution; conversely, the second includes coarse sand, usually pebbly, few or poorly sorted, with negative skewness. Morphological changes that occurred on the seafloor and spatial sediment distribution in the area defended by engineering structures show that sediments lying behind these structures tend to flow away from the seashore, mainly because of frequent western waves.