Abstract
Formation and deformation processes of landslide dams strongly affect on the water and sediment runoff. When a large scale landslide dam collapses, the peak discharge of flood sometimes becomes several times as much as the inflow discharge. Such abrupt increase of flow discharge often causes serious disaster in the downstream area. We proposed a new one-dimensional model for river bed variation and flood runoff which is composed of two-layer model for immature debris flow and bank erosion model. We applied this model to the Mimikawa river basin in Miyazaki prefecture where the “Nonoo landslide dam” was formed by the typhoon 0514 heavy rainfall. This model can reproduce the observed flood runoff process. From this calculation, it is supposed that Mimikawa flood peak discharge is diminished by the limitation of water storage in the landslide dam due to the “Tsukabaru dam”; a concrete dam and exists just upstream of the landslide dam. We also calculate the flood runoff in the assumption that the Tsukabaru dam does not exist. In this case, the peak discharge is three times as much as the actual peak discharge.
