Investigation of erosion characteristics of debris flow based on historical cases

Abstract

Debris flow is one of the most unpredictable geohazards in terms of occurrence and magnitude due to its random nature on flow initiation and changing mass during the flow process. The current approach to calculate erosion and entrainment in debris flow analysis is largely empirical by predetermining and distributing a certain amount of material along its flow path. A rational approach requires detail analysis of flow kinematics in calculating the amount of erosion. However, based on study of several case histories, certain erosional characteristics are found which can be used to calculate changes in the flow mass during the flow process. In this study, a progressive entrainment runout model is used to investigate the erosion characteristics of debris flow and rock avalanche. Four historical cases of debris flow and rock avalanche with long runout distance, steep channel slope, and high travel velocity are being studied. These four cases have some common features but they have different triggering mechanisms, elevation variations and particle size distributions. The results of the analysis show that >50% of erosion occurs in the second half of the flow path. The rate of erosion at the front of the debris is not only dependent on the slope of the flow channel, it also depends on other factors such as the depth of the debris, the velocity of flow and the physical properties of the debris material and the physical characteristics of the flow channel. Most importantly, based on these case studies, it is found that the rate of erosion along the flow channel can be determined based on the velocity, height of the debris and other flow characteristics. The calculated rate of erosion and the amount of entrainment can then be used in debris flow analysis.