Abstract
On October 20, 2010, a heavy rainfall event occurred in Amami region. A record-breaking heavy rainfall amount was observed and it caused overflow in the Sumiyo River. In this study, in order to clarify the characteristics of flood flows in the Sumiyo River Basin where observation data are insufficient, a field survey and numerical analysis were conducted. According to numerical analysis, the direction of inundation flow obtained from hearing investigations and flood level mark recorded in the Nishi-nakama district were reproduced by numerical results. These results suggest that numerical analysis using only rainfall dataset can reproduce inundation processes in the Sumiyo River basin in Amami Osima Island on October 20, 2010. Furthermore, levee failure on the left hand side of the Hiya River accelerated the starting time of the water level rise in the Nishi-Nakama area. In addition, mangrove forests at the river mouth did not affect water level rise in the upper reach of the Sumiyo River.
