2001 Volume 53 Issue 5 Pages 17-25
Heavy rain attacked Fukushima Prefecture during August 26-31, 1998. Consequently, very severe disasters generated.
Then, the investigation was made to get the site status and by inquiring of the inhabitants about generation time of the disaster, their behavior, and investigating geologically.
The following finding and the lesson were obtained by these investigations.
1) To get the proper standard rainfall for warning and evacuation, we have to set rainfall gauge more densely toward east-west direction.
2) It has been understood to be effective to use a single rainfall index of accumulated rainfall or working rainfall, decrease to half in 24 hours over.
And many collapses occurred when working rainfall (decrease to half in 72 hours) is over 370mm.
3) There was differences of about two hours in the generation time of disasters between the collapse sites which are located only 200m distance. It was presumed that this would be caused by the difference of the catchment area, and depth of permeable layer.