Numerical Simulation of Post-Entrainment Debris Flow at Alluvial Fan Using FLO-2D Model
The FLO-2D model has long been validated as an efficient tool to simulate the motion behavior of debris flow, but could not consider bed-sediment entrainment in the simulation. Bed sediment entrainment is an important feature of debris flow and sometimes amplifies the debris flow magnitude manifold. In this paper, we present a simple preliminary approach to evaluate the potential entrainment and incorporate it into the FLO-2D model. In the presented approach, the bed sediment entrainment is simplified as the process that bed shear stress of the flow is sufficiently high to overcome the basal resistance of the bed and incorporate this part of the bed into the flow. In this way, we obtain a solution to calculate the potential entrainment depth of bed sediment by debris flow. To estimate the total entrainment volume along the path, as well as the variation of hydraulic condition of post-entrainment debris flow, we divide the path into finite segments, calculate the entrainment volume of each segment, and obtain the variation of hydraulic condition by a discrete algorithm. In order to demonstrate this approach, a debris flow event occurred at Yohutagawa region, Japan, 2010, is selected as a case study. We calculate the post-entrainment volume and hydraulic condition of debris flow of this case. Furthermore, we also reproduce this event by the FLO-2D model. Results show that both the calculated total erosion volume and simulated deposition results are in good agreement with the field investigation.
KeywordsDebris flow Bed sediment entrainment Numerical simulation FLO-2D model Yohutagawa
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