Influence of flow resistance stresses on debris flow runout

Abstract

The hydrodynamic modeling of debris flows is challenged by the complicated mechanism of debris flow and the large variability of material composition. Therefore, in the dynamic continuum modeling of debris flows it is essential to select suitable rheological and associated friction parameters. The quadratic rheological model is the most comprehensive approach because it considers the effects of viscous behavior, solid-particle resistance, turbulent properties, and friction characteristics of debris flow. Therefore, this study adopted the quadratic model as the governing flow resistance stress and analyzed the influence of various flow resistance stresses to evaluate the runout performance. The shallow-water equations with modified bottom friction were discretized and the developed model was validated against a dam break flow and a ‘spreading of circular cone’ problem. Then, to investigate the relationship between the flow resistance relations and the bottom shear stresses exerted by the cones and dry bed, the model was applied to runout in a rectangular domain with three cone-shaped obstacles. An actual field runout event that occurred in Korea in 2011 was replicated and the runout paths and flow patterns were analyzed according to the various resistance stresses. By considering both the extremely rapid runout velocity and the striking run-up height, the results obtained by the quadratic stress relation achieved the best performance. However, for the successful application of the quadratic approach, three parameters had to be adjusted with consideration to locality.