Vulnerability to Mega Underground Inundation and Evacuation Assuming Devastating Urban Flood

Abstract

In urban areas of Japan, there are numerous underground spaces, such as subways and shopping malls. These areas hold the possibility of being inundated not only above the ground but also underground when intense rainfall causes pluvial flooding. For this reason, it is necessary to take measures to anticipate urban floods. In this study, an analysis of inundation on the ground surface and underground spaces was performed, and the risk of underground inundation was evaluated using the index of safe evacuation. In addition, as one of the countermeasures against underground inundation, the effect of flood boards on inundation prevention was examined. Furthermore, the factors for improving the success rate of evacuation are discussed by simulating the evacuation of users from an underground mall during inundation. From the results, the water inflow to underground spaces was larger as rainfall was greater, and the reduction effect of flood boards on underground inundation was only temporary if the inflow to the underground mall was large. In addition, the success rate of evacuation depended on the timing of evacuation because the flooded water spread broadly and rapidly across the underground mall. These results show that users in an underground mall should move with a quick response to flash flood from high intensity rainfall and would be useful in creating a safe and prompt evacuation plan.