Towards an integrated approach for characterization of sinkhole hazards in urban environments: the unstable coastal site of Casalabate, Lecce, Italy

Sinkholes occur in many areas of the world, especially where carbonate rocks crop out. They are formed due to natural processes or caused by man's activities. In both cases, severe consequences have to be registered on the anthropogenic environment and related infrastructures. Knowledge of both the mechanism of the sinkhole formation and the localization of this subtle geohazard is therefore necessary for planners and decision makers to perform the most appropriate and suitable programs of land use and development. The Apulia region of southern Italy is characterized for most of its extension by carbonate rocks, which makes it one of the most remarkable examples of karst in the Mediterranean basin. The sinkhole formation in Apulia urban areas has recently produced severe damages, especially along its coastal planes, where different types of sinkholes occur. The detection of cavities, that could collapse and create a sinkhole, in an urban environment presents numerous difficulties (buried networks, reworked soils, etc). A methodology has been developed to respond to this need based on the integration of four complementary methods: geological analysis of outcrops and existing borehole descriptions, aerophotogrammetric interpretation of aerial photos, electrical resistivity tomography (ERT) and ground penetrating radar (GPR). The combination of these methods, applied to a test sector in the city of Casalabate, made it possible to locate the principal karstic conduits beneath the study area and identify a zone of high sinkhole geohazard associated with one such feature.