Qualitative Assessment of the Cliff Instability Susceptibility at a Given Scale with a New Multidirectional Method

This paper aims to present a new predictive method for the assessment of rocky cliff instability susceptibility at a given scale in carbonate environment. The method (CISA, Cliff Instability Susceptibility Assessment) entails in situ specific geomechanical and morphological surveys, laboratory geotechnical tests, analysis of meteo-marine data together with human-related variables controlling cliff recession potential. The first step of the method consists of the subdivision of the coastal stretch in sectors based above all on morphological and geological criteria. Then, according to an heuristic approach, 28 conditioning parameters were divided in four categories (geomechanical, morphological, meteo-marine and anthropogenic) and weighted on the basis of a multifactor spatial GIS analysis using physical geographically-based measures. For each parameter 5 classes of rating were proposed; the cliff classification, in terms of cliff instability susceptibility, was obtain from the total rating which represents the summation of the single rating of the individual parameter. An application of the CISA method was here presented through a case study along the Murgia coastline South of Bari (Apulia, SE Italy). The stretch of coastline considered in this study is entirely in the territory of the municipality of Polignano a Mare, between the localities of San Vito and Largo Ardito; it is made up of cliffs, up to 20 m high, and shore platforms interrupted by small pocket beaches. The coastal outcrops consist of Mesozoic carbonate rocks, mainly white-greyish calcilutites well stratified and, moderately to highly fractured and karstified, which are overlain by massive PlioPleistocene calcarenites.