Elementary analysis on the bed-sediment entrainment by debris flow and its application using the TopFlowDF model

The Geographic Information System (GIS)-based TopFlowDF model is an effective simulation tool to analyse the debris-flow propagation on the fan. It has been validated in the previous research works and shows a satisfactory accuracy. We review the framework of the model in this paper and discuss that the simulation results are rather sensitive to the input conditions (e.g. the user-defined start point and debris-flow volume). In fact, previous studies have elucidated that sediment entrainment by debris flow conspicuously influences these input conditions. In this paper, we develop an elementary static approach with a three-layer model to estimate the entrainment and determine the amplification of total mass volume and peak discharge. Subsequently a new concept of critical line is proposed to detect the erodible reaches in the channel. Two cases in Japan and Norway are selected to illustrate the approach; analytical results show a good agreement with the in situ survey. The presented approach can provide a better solution to the input conditions as required by TopFlowDF model.