緩勾配斜面における表層崩壊・土石流発生に及ぼす地表流の影響

In recent years, terrible sediment disasters due to unprecedented heavy rainfalls occur frequently in Japan. One of the characteristics of these disasters is that many shallow failures occur in gentle slopes near mountain ridges where few shallow failures occurred previously. Our field survey showed a possibility that overland flow due to these unprecedented heavy rainfalls caused these slope failures. However, previous numerical models can be applied to a situation where only subsurface flow is generated, but they cannot analyze shallow failures in gentle slope areas. Therefore, we propose a method to evaluate the destabilization of the surface layer (e.g., slope failures and debris flows) caused by overland flow, assuming that the length of the slope is infinite. This method enables us to evaluate the destabilization of the surface layer in gentle slopes where the gradient is less than 20°.