Modeling the debris flow expansion on alluvial fan areas - A comparison of different modeling approaches

Sosio, Rosanna and Pozzoni, Maurizio and Ambrosi, Christian and Crosta, Giovanni Battista (2006) Modeling the debris flow expansion on alluvial fan areas - A comparison of different modeling approaches. In: Geophysical Research Abstracts European Geosciences Meeting, 02.04.2006 - 07.04.2006, Wien, Austria.

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Numerical models represent a tool commonly used to delineate hazard areas affected by debris flows activity. There are several modelling approaches documented in the literature, their applicability depends largely on a series of factors, such as e.g. the mixture rheology and alluvial fan or transport and deposition area topography. We applied two different numerical models to simulate the well documented debris flow event of the Rossiga Valley (Italian Southern Alps) of November 2002. The event mobilized about 90’000 m3 of material and spread it over the alluvial fan, damaging 3 buildings and killing some livestock. The models are both two-dimensional, but differ greatly in their approaches, how the debris flow expansion is modelled. The first model is a rather simple, empirical model (DFWalk), based on a multiple flow direction algorithm for the flow routing and a two-parameters approach for the debris flow velocity (Gamma, 2000). The second one, (Flo 2D) is physically based, and models the expansion of a non-Newtonian single phase flow based on a given inflow hydrograph (O’Brien et al., 1993). The two models were applied to the Rossiga Valley debris flow event, and their outputs were compared. The Flo 2D model is able to replicate the inundation extent and flow velocity, but it requires more input data and computational time. The model results are very sensitive to the imposed input data. The DFWalk model needs less input data, but it seems not useful at replicating huge events such as the Rossiga debris flow. The model results are sensitive to the topography and the grid cell size.

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