Landslide hazard assessment of the Cilento rocky coasts (Southern Italy)

This paper deals with natural and human causes giving rise to the erosion of the Cilento rocky coasts. It is predictable that, in 2100, along the coasts of the Mediterranean Sea a sea level rise varying between 9 and 30 cm will be attained. This increase will also cause a marked rise in the erosion of rocky coasts because a wide extension of highly erodible rock masses characterizes the studied area. Data regarding failure mechanisms, landslide mobility as well as run out distances of about 228 landslides directly or indirectly triggered by the wave motion were collected. Using these data and the IFFI Catalogue (“Inventario Fenomeni Franosi Italiani”), a Coastal Landslide Density Map was drawn that displays landslide density areas varying between 2 and 10 landslides per km2. In addition to climatic, geomorphological and geological causes, coastal erosion is worsened by a poor supply of sediments providing beaches, coming from the nine main rivers of the area. Furthermore, these sediments show a granulometric sorting mainly towards fine sands and silts which are not suitable for the beach-nourishment. In order to obtain a relative estimate of net erosion and deposition along the bed rivers, the USPED (Unit Stream Power - based Erosion Deposition) model was applied that allowed to calculate a value of solid discharge, from the rivers of the area, of about 11 millions of T/year. An assessment of the potential degree of landslide hazard and rockfall mobility was performed by means of heuristic approaches based on the “Rock Engineering System” and “Reach Probability” methods. In spite of inevitable approximations, employed methods revealed that almost 56% of the coastal area displays high landslide hazard, 27% is characterized by medium landslide hazard, whereas only 17% is characterized by low landslide hazard.