Study on Vulnerability of Mega-Underground Space to Extreme Flood

Japanese cities have many underground spaces such as subway and shopping malls. These cities locate in lowland of coastal zone near river mouths and are prone to extreme floods. The vulnerability of underground spaces to extreme floods are treated in this paper by using the results obtained by numerical method in densely urbanized area, Osaka, Japan. Pluvial, fluvial, storm-surge and tsunami flood cases were calculated. It is found that up to 60% of flooded water intrude into underground spaces if no counter measures were taken. Inundation depth and area in the underground shopping mall are different in the four types of extreme floods, and the flooded water enters into connected subway stations. This means that administrators of underground space have to make different counter measures for each type of extreme floods.