Modelling the space–time evolution of bed entrainment for flow-like landslides

The paper discusses the space–time evolution of bed entrainment for some typical flow-like landslides in three different test areas. First, the attention is focused on debris avalanches (DA), whose lateral spreading is highly affected by bed entrainment. Two cases of debris avalanches turning into debris flows (DF)—i.e., channelized flows—are then investigated to discuss the potential occurrence of complex bed entrainment scenarios. A quasi-3D (depth-integrated) coupled SPH (Smooth Particle Hydrodynamic) model is used. The numerical results show that i) the eroded thicknesses have maximum values in the intermediate portion of the debris avalanche path and ii) the computed time variations of eroded thicknesses and the entrainment rates are consistent with those indicated in recent literature for DAs at the studied areas. In addition, the computed scenarios are differentiated in terms of unitary flow discharge, identifying the typical behaviour of small volume DA, landslides propagating inside gullies as DFs, and combined DFs and DAs.