Assessment of coastal vulnerability to erosion: the case of Tiber River Delta (Tyrrhenian Sea, Central Italy)

Coasts are highly sensitive to dynamic geomorphic processes that determine rapid environmental changes and landscape modifications and are potentially vulnerable to accelerated erosion hazard. Coasts densely inhabited and settled by human infrastructures are threatened by severe erosional processes; therefore the coastal vulnerability analysis may represent an essential tool for hazard mitigation and management purposes. Tiber River delta has been selected as study area because it has a particularly high vulnerability to sea erosion that has made necessary several protection interventions in recent decades. The Local Vulnerability Assessment (LVA) methodology proposed differs from the previous ones for two aspects: the working scale (with its morphological and climatic implications), and the distinction between potential (due to natural conditions alone) and effective vulnerability (where the anthropogenic action is present and may contribute to vulnerability mitigation or less). The LVA takes into account quantitative and qualitative spatial variables that express morphometric and morphodynamic natural factors of vulnerability, as well as selected anthropogenic factors. Based on a system of numerical weights and scores, the LVA allows the construction of a local vulnerability map in which the Coastal Vulnerability Index (CVI) is represented for different sectors of the study area. The aim of LVA is to single out he main vulnerable zones that should have priority in the mitigation strategy performed within the study area. This is the first study finalized to calculate CVI at local scale and its results show that the whole coast strip of the study area has high and very high values of potential vulnerability, while the values of effective vulnerability decrease where suitable defences are present.