Abstract
From the end of July to August 2, 2004, the 10th Typhoon (called Namtheun) has damaged to the area around Kisawa Village and Kaminaka Town in Tokushima Prefecture, Japan. There were geologically sediment rocks and a lot of faults in these areas. Especially, on August 1, 2004, it brought extraordinarily heavy rainfall more than 1, 114mm of the daily rainfall-record in Japan onto these areas and a lot of slope failures and debris flows occurred. In the Shiraishi area, in Kaminaka Town, as many residents have paid attention to the occurrence of abnormal phenomena and most of them have opportunely evacuated, no lives were lost by debris flows. In the Azue area, in Kisawa-Village, the tendency of expansion of the landslide area was recognized. The areas, where large-scale debris flows and slope failures occurred, coincided with the areas, where both of a large quantity of cumulative rainfall and large rainfall intensity were brought. However, the critical values of rainfall, which had been related to the occurrence of sedimentrelated disaster, were two to four times greater than those in the cases of granite area in Hiroshima district in Japan.
