Modeling debris flow propagation and deposition

Abstract

A mathematical model is applied to simulate two debris flows occurred in 1997 and 1998 in Italian Alpine valleys. The flows caused a casualty and significant damages to buildings and roads. The model considers a two-phase mixture of coarse sediments and interstitial fluid. The concentration of the finer 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 interstitial fluid move downstream with the same velocity, the flow of the mixture is described using a two dimensional depth averaged model with a unique 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. Differential equations are integrated with an upwind explicit finite-difference scheme. The total discharge hydrograph at the upstream sections of the alluvial fans was estimated by assuming equilibrium solid concentration values.