Geomorphic calibration of friction and entrainment parameters for a snowmelt-induced muddy debris flow in the Longiarù Valley, Dolomites

Abstract Snowmelt- and rainfall-triggered debris flows are important geomorphic hazards in alpine environments, yet frictional and entrainment parameters are rarely available for individual events. This study constrains these parameters for a snowmelt-induced muddy debris flow that occurred in the Seres Creek catchment, Longiarù Valley, Dolomites, on 17–18 June 2024. A pre-event DEM from 2010 and a post-event LiDAR-derived DEM from 2024 were used to derive a DEM of Difference (DoD) and characterize the spatial distribution of erosion and deposition associated with the event. The observed geomorphic response was then used to constrain the internal friction, basal friction, turbulent friction, and entrainment parameters through iterative r.avaflow simulations. The calibrated parameter combination comprised an internal friction angle of 17°, a basal friction angle of 9°, a turbulent friction parameter of 10 m/s², and an entrainment coefficient of kg⁻¹. The resulting simulation reproduced the major spatial characteristics of the observed event, including the transition from erosion and channel incision in the upper and intermediate reaches to deposition downstream. Comparisons of selected turbulent friction and entrainment values showed that turbulent friction strongly affected flow mobility, erosion, and runout, whereas entrainment substantially influenced flow momentum, erosion, and the downstream position of deposition. Comparison of simulated and DoD-derived geomorphic changes along the main flow path and at three representative cross-sections showed good spatial agreement in the major erosion–deposition patterns, with relatively minor localized differences in erosion and deposition magnitude. The results show that spatially distributed geomorphic change can provide constraints on frictional and entrainment parameters beyond runout extent alone, providing a spatially informed basis for event-scale debris-flow modelling.