Modelling the probability of occurence of shallow landslides and channelized debris flow using GEOtop-FS

This paper describes a coupled, distributed, hydrological-geotechnical model, GEOtop-FS, which simulates the probability of occurrence of shallow landslides and debris flows. We use a hydrological distributed model, GEOtop, which, models latent and sensible heat fluxes and surface runoff, and computes soil moisture in 3-D by solving Richards’equation numerically, together with an infinite-slope geotechnical model, GEOtop-FS. The combined model allows both the hydraulic and geotechnical properties of soil to be considered and realistically modelled. In particular, the model has been conceived to make direct use of field surveys, geotechnical characteristics and soil moisture measurements. In the model the depth of available sediments is also used to characterize the hydraulic properties of the area examined. To account for the uncertainty related to the natural variability in the factors influencing the stability of natural slopes, the safety factor is computed with a probabilistic approach. In order to determine the likelihood of slope failures, soil parameters are assigned distributions instead of single deterministic values. The analysis presented was carried out for an alpine watershed, located in the Friuli region, Italy, for which some geological and geotechnical data were available. In the past, this watershed experienced landslides and debris flows during intense storms following long and moderate intensity rainfall events. The distributed coupled GEOtop-FS model was calibrated by reproducing some of these events and validated in order to map future failure probabilities