Joëlle Jeltsch: Processus et aléas des laves torrentielles du bassin versant de Chamoson (Valais, Suisse)

The canton of Valais in Switzerland is heavily affected by debris flows. In 2018 and 2019, the village of Chamoson was affected by these destructive phenomena. These debris flows caused a lot of damage and the one in 2019 left 2 victims. As the population grows, the risk becomes significant and mustn’t be neglected. To avoid another disaster, measures must be taken by the commune of Chamoson. In order to make the best possible decisions, the commune must be fully aware of the various processes and hazards of the debris flows in its catchment area as well as the mobilised and mobilisable volumes. Therefore, this work provides the various elements of responses related to debris flows within this Valaisan municipality. A field campaign is being carried out during the summer of 2020 on the catchment area. In 2019, the University of Lausanne conducted a Structure from motion (SFM) campaign. These data as well as various drone flights carried out on the catchment basin in collaboration with the Center for Research on the Alpine Environment (CREALP) in Sion are compared with each other. This comparison can then be used to estimate the different volumes mobilised in debris flow events. In addition, empirical formulas (Kronfellner-Kraus (1984), Agostino (1996), Hampel (1980) and Rickenmann (1997)) are used to adjust this estimation. Finally, a model using the open-source software Flow-R allows the identification of source zones and the monitoring of the propagation phase of these events.