Simulating debris flow mobility with erosion in r.avaflow using a mechanical model

Erosion and entrainment are dominant mechanical processes in debris flows that can amplify the flow volume by several orders of magnitude, enhance mobility, significantly increase impact forces and expand the inundation area. Reliable simulations that include erosion processes are thus critical for hazard assessment. However, existing computational debris flow models do not correctly account for the erosion-induced net momentum production. Instead, they utilize empirical approaches to erosion that rely on data from past events for calibration, often resulting in parameters that vary widely and sometimes assume unrealistic values. We have implemented the mechanical model presented in Pudasaini and Krautblatter (2021), which explains erosion-induced mass flow mobility based on erosion velocity, mechanically described erosion rate, and flow inertia, into the open source, multi-phase computational tool r.avaflow, that we extended for use in both field and laboratory conditions. To verify the correct implementation of the mechanical erosion model into r.avaflow, we are using data from large-scale laboratory flume experiments with an erodible bed and varying material composition, bed morphology and flow conditions. Here, we present simulation results from an erosive laboratory setting and the highly erosive field event “Bauhof-torrent”, Königssee (Bavaria, Germany), using the newly expanded r.avaflow, which now includes erosion-induced net momentum production. The results show that the model correctly captures the characteristic effects of erosive mass transport, such as enhanced flow mobility and energetically nonlinear volume bulking, leading to amplified surges, increased flow height, longer flow durations, and much wider inundation areas. Additionally, important phenomena such as phase separation with a solid-rich front and fluid-dominated tail, as well as different deposition speeds of the frictional solid phase and the viscous fluid phase, are observed.