Estimation of spatial and temporal distribution of sediment movement and evacuation in the northern Kyushu heavy rain in July 2017

Takashi KOI, Yoshiki NAGAI, Toshihiro KIKUI, Takuya KOBAYASHI, Hiroyuki OHNO, Masato JYOGASAKI, Tomoyuki NORO, Hideaki MIZUNO and Atsushi TANAKA


The northern Kyushu heavy rain in July 2017 caused many sediment disasters in a wide area and devastating damages. Although various sediment movement phenomena such as collapse and debris flow may have occurred in a basin due to prolonged high‐intensity rainfall, the actual situation has not been grasped. In this study, we assumed the time and spatial distribution of locations of sediment transport phenomena and evacuation based on a questionnaire survey conducted in the Akatani River basin, Asakura City, Fukuoka Prefecture, where severe damage was caused by the heavy rainfall. During this disaster, 57% of the residents, who were near Asakura city on July 5, evacuated, 35% did not evacuate, and 8% could not evacuate. 41% of the evacuees evacuated on their own or rescued after receiving some damage. Evacuation types were classified into three types based on the relationship between the time change of sediment transport and evacuation start time. Because many evacuees started during the period when sediment movement was active, the necessity of evacuation measures on the premise of imminent evacuation was identified as an issue in addition to evacuation before sediment movement occurred.

Key words

sediment transport, evacuation, questionnaire survey, the northern Kyushu heavy rain in July 2017