Beach Shoreline Trends along the Western Coast of Sardinia Island (Western Mediterranean Sea)

The changes in shoreline position in sandy beaches and their rates are often interpreted as indicator of coastal erosion or accretion. The retreat/accretion of the shorelines can be influenced by several factors that can influence the shoreline behaviour at different time scales. Here we present a study on shoreline trends carried out on several beaches located along the Sardinia Island, western Mediterranean Sea. The studied area includes different beach types: from large open beaches up to geologically controlled and embayed beaches. Aerial images covering a time interval of about 60 years (from 1954 to 2019) were used to investigate the trends of the shorelines. Shoreline positions were digitized from each image and trends in shoreline position were obtained by using the DSAS tools. Effect on shoreline migration caused by sea level rise has been taken into account estimating the values of migration based on the application of the Bruun formula. Migration values obtained by this application were then compared with the landward space beyond beaches. Considering the averaged values of the net shoreline movement calculated for each beach the majority of beaches experienced a little retreat, with maximum values accounted for retreat for more than 100 m in correspondence to a river mouth. Hot spot of erosion has been also found in proximity of area in which human activities are present and have modified the shoreline setting and along areas where beaches are mainly composed by reworked relict sediment and no sediment sources are active at present days. The landward migration of the shoreline was compared with the features of the back beach and the great landward migration did not interfere with physical boundaries. In some cases, also with moderate shoreline retreat the presence of human infrastructure on the back beach can influence the shoreline final position and consequently can have a role in the adaptation capacity of the beach.