抄録
The deluge on July 21 2009 in Hofu-Yamaguchi triggered tremendous damage and resulted in many causalities in the area. Geologically, the area consists of granite and has had many sediment-related disasters such as the one in August 1993. According to an interview with local residents, such a serious disaster had not occurred for more than 200 years. Therefore, it will be very effective for planning disaster-prevention measures counting the regularity of sediment deposition, if we can obtain it accurately.
In this report, we considered the regularity of sediment deposition in Hofu-Yamaguchi, by using the result of carbon dating of carbonized wood gathered at Upper region of Gyokusen Pond and Ishihara region, as well as considering the situation of black soil layers including carbonized wood. Consequently, the sediment disaster as intense as the one on July 21 2009 is estimated to occur once in every 185-370 years in Upper region of Gyokusen Pond and once in every 145-220 years in Ishihara region.
