REGIONAL-SCALE DEBRIS-FLOW RISK ASSESSMENT FOR AN ALPINE VALLEY

(**) Institut de geomatique et d'analyse du risque (IGAR), Unil, Lausanne - Switzerland ABSTRACT In this paper, we perform a societal and eco- nomic risk assessment for debris flows at the re - gional scale, for lower Valtellina, Northern Italy. We apply a simple empirical debris-flow model, FLOW-R, which couples a probabilistic flow rout - ing algorithm with an energy line approach, provid- ing the relative probability of transit, and the maxi- mum kinetic energy, for each cell. By assessing a vulnerability to people and to other exposed elements (buildings, public facili- ties, crops, woods, communication lines), and their economic value, we calculated the expected annual losses both in terms of lives (societal risk) and goods (direct economic risk). For societal risk assessment, we distinguish for the day and night scenarios. The distribution of people at different moments of the day was considered, accounting for the occupational and recreational activities, to provide a more real- istic assessment of risk. Market studies were per- formed in order to assess a realistic economic value to goods, structures, and lifelines.