Deterministic analysis of the debris flow propagation phase for hazard zoning

Debris flows are generally characterized by an almost total absence of warning signals, high propagation velocities and long travelled distances. For these characteristics, debris flows are considered extremely dangerous. Their destructive power can be reduced by a sound design of risk mitigation measures based on an accurate forecasting of propagation and depositional phases aimed at identifying the velocities and depths of the moving mass as well as the depositional area. Indeed, kinematic characteristics of the moving mass and the geometry of propagation and depositional areas are key factors for both the debris flow susceptibility assessment and the estimation of the impact force on exposed elements. For this purpose, the present paper is aimed at underlying the role of the propagation path and debris fan simulated by the numerical code “smoothed particle hydrodynamics” (SPH) in landslide hazard zoning. In the SPH it is necessary to choose the rheological model of the soil-water mixture, to this regard laboratory tests have been carried out for different solid concentration by volume. The soils involved by propagation phase derive by weathering of crystalline rocks and are characterised by a high variability of weathering grade. The last aspect represents the main predisposing factor of debris flow inception that periodically occur in the study area located in the Municipality of Scilla (Calabria, Italy). The obtained results by the simulation of a significant debris flow occurred in the area show a good agreement with real run-out and debris fan and represent the starting point for the quantitative assessment of debris flow hazard.