Numerical analysis of dynamics of debris flow over erodible beds in Wenchuan earthquake-induced area

The basal entrainment of debris flows play a significant role in its amplification and the final volume of deposition could be several to hundred times of its initial volume. In this paper, the shallow water equations coupled with basal material entrainment applied in debris flows have been given to demonstrate the amplification. A new basal entrainment model taking advantage of both Coulomb and Voellmy frictional laws are proposed, providing a unified formula to simulate the stop-and-go process of debris flows. Both time and space second-order MacCormack-TVD finite difference method is suggested to solve the coupled equations. Numerical comparisons with USGS flume experiment and Hongchun gully debris flow in Wenchuan earthquake-induced area are carried out to prove its effectiveness. It is established that the momentum exchange term between the flows and the basal materials has a significant influence on the dynamic characteristics and the entrainment effects are essential to model the dynamic process of debris flows in an earthquake-induced area.