Modeling Debris Flows in Anomalous Basin-Fan Systems

The paper proposes a modeling analysis of debris flows in anomalous basin-fan systems. Previous studies pointed out that the main geo-hydrological hazard in anomalous basin-fan systems is really related to the occurrence of debris flows, favored by the presence of large amount of loose debris on high slopes, which also favor the predominance of the entrainment process in determining the magnitude of the events. Consequently, the pseudo-3D model RAMMS DEBRIS FLOW was used in order to simulate the debris flow dynamic in anomalous systems. At this aim, a back analysis was carried out on the debris flow that occurred in July 2013 in the Gadria catchment (Val Venosta, northern Italy). This event was characterized by a quite small source area located in the head zone of the basin, whereas the volume that reached the basin outlet was quite large, because of entrainment process. The frictional parameters were calibrated using the entrainment simulation, obtaining values more similar to the ones typical of rock avalanches than the values generally used for the simulation of debris flows.