Calibration and performance assessment of rheological debris-flow models using AvaFrame: The 2010 Rotolon landslide case study

Debris flows represent one of the most complex and hazardous rapid mass movements occurring in mountainous environments due to their high mobility, strong erosive capacity, and significant destructive potential. Accurate numerical simulation of these phenomena is therefore essential for hazard assessment, risk mitigation, and the development of effective protection strategies. The reliability of such simulations strongly depends on the rheological model adopted, as the constitutive formulation directly controls the flow dynamics, propagation behaviour, and deposition patterns. This thesis investigates the behaviour of debris flows through the application and comparison of different rheological models within the open-source numerical framework AvaFrame, originally developed for snow avalanche simulations and currently being extended toward debris-flow applications. The study was conducted at the University of Natural Resources and Life Sciences (BOKU) in Vienna, where ongoing research focuses on improving open-source tools for rapid mass-movement modelling. A theoretical overview of mass movements is first presented, introducing landslides, debris flows, and snow avalanches together with their triggering mechanisms, physical characteristics, and dynamic behaviour. Particular attention is devoted to rheological formulations commonly adopted in depth-averaged numerical models, including the Coulomb, Voellmy, Spatial Voellmy, and Bingham approaches. The practical application of the study focuses on the Rotolon debris-flow event, which occurred in November 2010 in the Vicentine Prealps (north-eastern Italy) and mobilized approximately 300,000 m³ of material. Pre-event and post-event digital terrain models (DTMs) were analyzed in order to reconstruct erosion and deposition patterns and to provide reference data for model calibration and validation. Additional preprocessing operations, including the definition of release areas, secondary release zones, and entrainment sectors, were performed using QGIS. Several numerical simulations were carried out using different rheological models and parameter calibrations. The obtained results were evaluated through a comparative procedure based on the Lee–Salle index and cross-sectional flow-thickness analyses derived from the observed deposits. The comparison highlighted the limitations of the Coulomb model in reproducing the progressive fluidization of the debris flow, while the Spatial Voellmy approach significantly improved the representation of downstream propagation through spatially variable friction parameters. Among all the tested configurations, the Bingham visco-plastic model, and in particular simulation B3, provided the highest overall agreement with the observed event in terms of runout geometry, deposition distribution, and flow-thickness consistency. The results emphasize the importance of selecting rheological formulations capable of representing the fluidization processes that characterize debris flows, especially when interactions with mountain streams and water inflows occur along the propagation path.6 The outcomes of this work demonstrate the strong potential of AvaFrame and future developments such as DebriFrame for debris-flow modelling applications. Furthermore, the study highlights the importance of calibration procedures and comparative evaluation methods for improving the physical reliability of numerical simulations and supporting future hazard assessment activities in similar geomorphological settings.