Active seasonal rain fronts and a lot of typhoons in 2004 brought heavy rain and flood in Japan.This paper discusses the background of increasing damage based on those examples.Severe flood damage dueto the dyke break occurred in Niigata Prefecture.Especially many houses were broken and many people failedto evacuate from inundated area in Nakanoshima area along Kariyata River.Numerical analysis for flood flowis useful to manage floodplain risk.General flood simulation is presently being used to predict flooding waterdepth and to make hazard map for evacuation of people in river basin etc.Objects of the general numericalanalysis are not to predict damage due to abrupt flooding flow near dyke break point.We developed a newnumerical analysis model by FDS (Flux Difference Splitting) method for abrupt flooding flow and swept-awayof houses.We made clear the relationship between the flood flow from the Kariyata River and swept-away ofhouses due to dyke break using the numerical model.
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