| Present study proposes a method for predicting sediment runoff volume at each stream channel in mountainous drainage basins during heavy rainfalls, combining an occurrence model of landslides and a runoff process model of soil blocks. The proposed method is applied to the Akatani drainage basin which was severely damaged owing to landslides and debris flows in the northern Kyushu rainfall event in July 2017. The simulated sediment runoff volume ranges from 0.5 to 2 times to the sediment runoff estimated by the differences in elevation before and after the disaster. The result shows the sediment runoff is determined not only by the spatial distribution of landslide and the gradient of the river channel but also by the content ratio of the fine sediment that specifies the equilibrium gradient of debris flows. |
