DATA UNCERTAINTY AND VARIABILITY IN MODELING DEBRIS FLOW PROPAGATION

Abstract

We replicate the propagation of the Val Rossiga debris flow (November 2002, Central Italian Alps), a 90,000 m 3 event triggered by a rapid retrogressive landslide with high water content. The rheologi- cal model combines in a linear sum the viscoplastic terms of the Bingham model and a quadratic inertial term. The model requires as input data the bulked hydrograph and the empirical coefficients which de- scribe the exponential dependence of the rheological parameters (i.e. Bingham viscosity and yield stress) on sediment concentration. We provided these data through different methods. Alternative hydrographs were produced by simulating the propagation of the triggering landslide according to different rheologies (i.e. rigid block model, frictional material, and Voe- llmy material). The rheological parameters are either determined by back analyses and directly through laboratory measurements and field investigation. Lab- oratory measurements were performed using a Ball Measuring System and a vane apparatus connected to a rotational rheometer on three samples from different sectors of flow path (i.e. source, channel and fan de- posit). The samples were analyzed at varying the solid concentration and the grain size included in the tested suspensions (maximum grain size of 0.425 mm). The alterative conditions assumed for the input data were modeled on topographies of 5 m and 10 m cell-size. The seven scenarios we obtained were optimized by back analyses of the rheological parameters.