Clarification and application of inundation processes in basins with insufficient observation devices installed

Torrential rain possibly due to climate change has begun causing disasters annually, with water and sediment resulting from heavy rainfall in relatively narrow upper basins often arising in short periods. Because most of these basins are traversed by class B rivers administered by local governments, data on disasters are not accumulated comprehensively. Targeting the Sumiyo River basin on Amami Oshima Island, this study involved field surveys and numerical simulations to clarify inundation features in areas short on data based on hearings from investigation results. Calculation results have reproduced water levels, together with hearing results, including the initial inundation process in which rain water flowed directly from mountain slopes and later inundation processes mainly caused by overtopping and dike breach on the Sumiyo River. (Note that river bed fluctuations and dike breach progress are to be addressed in the future.).