Abstract
Abstract. In the present paper some of the problems related to the application of the continuum mechanics modelling to debris flow runout simulation are discussed. Particularly, a procedure is proposed to face the uncertainties in the choice of a numerical code and in the setting of rheological parameter values that arise when the prediction of a debris flow propagation is required. In this frame, the two codes RASH3D and FLO2D are used to numerically analyse the propagation of potential debris flows affecting two study sites in Southern Italy. For these two study sites, a lack in information prevents that the rheological parameters can be obtained from the back analysis of similar well documented debris flow events in the area. As a prediction of the possible runout area is however required by decision makers, an alternative approach based on the analysis of the alluvial fans existing at the toe of the two studied basins is proposed to calibrate rheological parameters on the safe side. From the comparison of the results obtained with RASH3D (where a Voellmy and a Quadratic rheologies are implemented) and FLO2D (where a Quadratic rheology is implemented) it emerges that, for the two examined cases, numerical analyses carried out with RASH3D assuming a Voellmy rheology can be considered on the safe side respect to those carried out with a Quadratic rheology.
Highlights
Many of the world’s most devastating landslide disasters, as measured by loss of life and/or economic value, can be attributed to debris flows and their volcanic counterparts called lahars (Jakob and Hungr, 2005)
As a prediction of the possible runout area is, required by decision makers, an alternative approach based on the analysis (a) of the geological and geomorphological settings that characterize the two study basins, (b) of the alluvial fans existing at their respective toe and (c) of the rheological parameter values obtained from the literature, when the backanalysis of similar historical events are carried out, have been proposed to calibrate rheological parameters for the two study sites
From the results obtained with RASH3D and FLO2D assuming a Voellmy or a Quadratic rheology it emerges that: 1. Even if FLO2D and RASH3D have a different initiation mechanism, it can be observed that, by adopting the same calibrated Quadratic rheological parameters and by relating the peak discharge (FLO2D) and the triggering volume (RASH3D) with the Rickenmann’s formula, the two codes give a similar runout for both the study sites
Summary
Many of the world’s most devastating landslide disasters, as measured by loss of life and/or economic value, can be attributed to debris flows and their volcanic counterparts called lahars (Jakob and Hungr, 2005). An approach based on the analysis of the geological and geomorphological settings that characterize a study basin and of the alluvial fans that may exist at the its toe is proposed to calibrate rheological parameters To support this approach and to compare different rheologies, numerical analyses have been carried out for two study sites in Southern Italy affected by debris flows. For both the study sites, a lack in information prevents the calibration of rheological parameters through the back analysis of well documented events in the area but quantitative information to be used for susceptibility and hazard analyses are required by decision makers.
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