The Debris Flows Inventory of the Aosta Valley Region: An Integrated Natural Hazards Assessment

The Aosta Valley (NW-Italy) is an alpine region where debris flows frequently occur, interacting with human activities and structures. For a best debris flow hazard assessment, research and mapping activities have been organized. First, aerial photo-interpretation and DEMs analyses were performed at a regional scale to inventory alluvial fans. Second, data on debris flow events have been collected from different sources, such as bibliographic and historical data, municipality hazardmaps and drainage basin technical studies. For each event photo-interpretation and geomorphologic analyses have been performed to validate historical data and finally GIS statistical analysis have been carried out. The analysis led to the identification of about 200 single events, thus successfully upgrading a regional database on natural instabilities. Collected data allowed improvements to local knowledge on debris flows, through the recognition of multiple events in the same alluvial fan. Estimation of temporal occurrences led to more precise hazard assessment, useful for proper land planning.