Prediction of run-out process for a debris flow triggered by a deep rapid landslide

Abstract

Previous studies have shown that numerical simulation models commonly used for debris flows may not be applicable for large-scale debris flows. In this study, we developed a technique for simulation of large-scale stony debris flows. For this purpose, we tested the hypothesis that the motion of fine sediment in these debris flows is similar to that of the interstitial water. We developed key parameters to simulate large-scale debris flows, such as sediment concentration, fluid density, and representative particle diameter based on the hypothesis. We also used a modified version of the continuity equation for sediment in our simulation. We conducted detailed field surveys of a past debris flow in Japan and used topographic data from LiDAR imagery, porosity measurements of soil and weathered bedrock, and the grain size distribution of the debris flow sediments to test our model. We also proposed a new process-based method for determination of hydrographs at the lower end of the landslide scar. Using these new data and methods, we conducted numerical simulations of the past debris flow, which reproduced well the observed erosional and depositional pattern if when the concept of fine sediment behaving like fluids was included in the numerical simulation.