ANALISI DI RISCHIO DA VALANGHE DI NEVE IN UN COMUNE IN VAL SESIA = RISK ANALYSIS FROM SNOW AVALANCHE IN A MUNICIPALITY IN VAL SESIA

The work carried out in this thesis deals with the case study case reported by Dr. Giovanni Cavagnino, who was assigned the study of snow avalanches on the stretch of provincial road SP82 that connects the municipalities of Piode and Rassa (VC), in Val Sesia, and the design of risk mitigation works. As a part of this study, the numerical modelling of snow avalanches and the drafting of risk maps are two fundamental operations, which will be described in the following chapters. Local evidence shows that almost every time there is a snowfall and a subsequent rise in temperatures, small avalanches involve the road: these are events with an annual recurrence that cause closure for a short period of the road, the only way of communication between the towns. Moreover it is interesting to study events with longer return time Not being in possession of any historical data, it was consulted the C.L.P.V. (Probable Avalanche Localization Card) which substantially highlights three areas involving the street. They are signs derived from photo interpretations of the past, high pressures are likely required to create them. To include these informations in the study the following assumption is done: the most extreme events, associated at return time of 300 eyers, have created these signs. Through runout analysis by means of the RAMMS software, events with different return times were studied: 300, 100, 30 and 10 years. The discriminating parameter to understand when the simulations were acceptable is whether the most extreme events overlap well with the traces of the CLPV, to obtain it has operated varying on the rheological parameters. The analysis are done on digital terrain model with a resolution of 5 m. The runout-output were combined with parameters of hazard in order to draw up a risk map for each return times studied. The IMIRILAND method was chosen to draw the maps: it means that the damage is divided in physical, social, economical and environmental. The method was applied with relative index of value, in this way it is possible to give major weigh at the author's discretion, also because they are not available sufficient data to compute each component in a money cost. Then, some risk mitigation interventions are proposed. In particular the best work could be an avalanche-protection tunnel, but at present local authorities do not have sufficient funds for its realization. However, this intervention would provide total protection, if in the future the necessary funds were found, a design could be carried out including also the rockfall (a minor problem but also present on the SP82). In the final part of this work, the conclusions of the study are provided, together with some considerations about the possible future developments necessary for an in-depth study of the issues addressed.