Influence of topographic condition on numerical simulation of debris flow

Haruka TSUNETAKA, Norifumi HOTTA, Takuro SUZUKI and Satoshi ISHIKAWA

Determination of the effects of topographic condition on the numerical simulation of debris flow is essential for predicting sediment discharge from large]scale landslides. One such effect is sediment deposition and erosion, which is significant at points where the gradient or width of the debris]flow torrent changes, as pointed out by previous studies. In such cases, variation in the numerical simulation is induced mainly by the erosion rate equations employed by researchers. However, the differential effect of various erosion rate equations has not been examined. This study first revealed the difference in the calculated effects of debris flow on channels with altered inclination and undulations of the bed surface using various erosion rate equations. The effect of each erosion rate equation was examined, and results for the final shape of the channel bed profile were obtained from numerical simulations for cases with and without bed surface undulation. Hydrographs of the lower end of the channel showed significant differences depending on the size of the undulations, even with the same erosion rate equation. These results arise from difference in the responses of the erosion rate equations to steep]slope sections and indicate that the complexity of field topographic conditions affects debris]flow hydrographs. These results also suggest that numerical simulations of debris flow can differ depending on the resolution of the simulation domain.