A Methodology For Debris Flow Risk Analysis

Landslide susceptibility and hazard analysis is the first step for assessing landslide risk and suggesting the areas where risk mitigation measures should be implemented. Debris flow susceptibility and hazard analysis can be pursued by different methods classified by Soeters and van Westen (1996) in heuristic, statistical, and deterministic methods. Especially if deterministic methods are used at the centre of the susceptibility and hazard assessment as well as the protection measure design there is the analysed landslide and then the involved soils. In weathered gneiss, debris flows present a failure surface generally located at the contact between residual soils and less weathered soil layers. Due to the heterogeneity of these soils and the difficulty of undisturbed sample taking, the geotechnical characterization is very complex, and as consequence experimental studies on naturally weathered rocks are limited (Gullà et al., 2006). In this context, debris flow susceptibility and hazard assessment is also extremely complex. To this regard, the paper proposes a methodology for debris flow susceptibility and hazard analysis based on the combined use of two physically based models “Transient Rainfall Infiltration and Grid-Based Regional Slope-Stability model” (TRIGRS) and “Smoothed Particle Hydrodynamics” (SPH). TRIGRS was used for the analysis of the triggering phase and allowed estimating the mobilized triggering volumes; SPH, using TRIGRS results, allowed the analysis of the propagation phase. The proposed methodology was calibrated on two debris flows occurred in Calabria (southern Italy).