A mathematical model is applied to simulate two debris flows occurred in 19
97 and 1998 in Italian Alpine valleys. The flows caused a casualty and sign
ificant damages to buildings and roads. The model considers a two-phase mix
ture of coarse sediments and interstitial fluid. The concentration of the f
iner solid fraction in the interstitial fluid is assumed to be negligible,
so that this fluid acts as clean water. Assuming that the solids and the in
terstitial fluid move downstream with the same velocity, the flow of the mi
xture is described using a two dimensional depth averaged model with a uniq
ue 2D momentum equation and two mass balance equations for the mixture and
the sediments, respectively. Erosion and deposition rates are computed with
a modified version of the relationship developed by Egashira-Ashida. Diffe
rential equations are integrated with art upwind explicit finite-difference
scheme. The total discharge hydrograph at the upstream sections of the all
uvial fans was estimated by assuming equilibrium solid concentration values
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