EVALUATION OF THE IMAPCT OF FLOODED UNDERPASSES ON EVACUATION ROUTES IN OSAKA PREFECTURE

Abstract

 In recent years, Japan has witnessed frequent occurrences of extreme winds and floods, as well as a consequent increase in the number of cases of people in vehicles being stranded in a flood, particularly in underpasses, which are generally found in urban areas. Underpasses are prone to flooding because their elevation is lower than that of the surrounding areas. In this study, we analyzed evacuation routes under normal conditions and flooded underpasses using data from road networks and evacuation centers. We quantitatively evaluated the difference in evacuation distance during flooding and its causes. The results of the analysis on the Osaka Prefecture showed that urban areas were less affected by the flooding because of their high density of evacuation centers; however, in few regions, evacuation routes needed to be detoured more than eight times compared to that of normal conditions. In some areas, the nearest evacuation center differed between normal and flooded areas. In case of flooded underpasses, it is important to consider multiple evacuation routes as a precaution.