To make matters worse, flood patterns seem to be changing these days. Heavy
rains >100 mm per hour are more frequent since the beginning of the Heisei era in
1989. Flooding of underground area is recently becoming a serious problem. For example,
flooding of the underground shopping area in Fukuoka city in 1999 killed one
person and caused enormous economic damage (Takeuchi, 2002). Confronted with these
problems, the MLIT has shifted its main emphasis to urban inundation and extreme
flows. Nowadays, even in very flood prone areas, river mangers must consider environmental
and flood control aspects simultaneously, which demands a high level solution
for not only managers but also researchers.