The Alluvial Fan Risk Assessment in Piedmont (NW, Italy)

The alluvial fans risk assessment is a very important step for territorial planning of mountainous areas that allows to design preventive protection works and identify actions of civil protection. This work represents an action of the Strategic project Risknat performed by the Piedmont Region to focus on the development of new methods and operational tools to estimate the risk assessment on alluvial fans in Piedmont (NW Italy). Based on geomorphological and geological data, land cover, historical information and climatic factors (all deriving from 1:100,000 to 1:25,000 scale GIS maps and alphanumerical database), the hazard of 893 alluvial fans has been calculated by applying the method proposed by the "Autorita di bacino del fiume Po'', implemented with the catchments basin hazard index (HIcb) calculated with the Alluvial Fan Hazard Evaluation procedure (AFHE). The risk has been evaluated considering the value of human systems and environmental themes, all deriving from 1:10,000 scale GIS maps. AFHE methodology permits the evaluation of the Disequilibrium Index (DI), a useful parameter for the understanding of the debris supply, the rainfall threshold, the channel recharge rate and the catchments mostly influenced by the climate changes. The results are useful to identify the most hazardous situations and to provide additional information for land management. Finally, results need to be verified on a local scale through further study that takes in account in detail the characteristics of each catchment-alluvial fan system.