FLOOD RISK RANK EVALUATION AND POSSIBLE EVACUATION TIME ESTIMATION BASED ON FLOOD SIMULATION

Abstract

 For flood risk assessments, a risk rank was proposed. Risk rank is defined by using inundation depth and inundation flow velocity. In this study, we evaluated the risk rank using the results of flood simulation for the Kakehashi River basin. Through the calculation process of risk rank, it is possible to estimate the time limit of evacuation, or the time when people cannot evacuate on foot. Then, we calculated the possible evacuation time as the difference between the time of evacuation limit and of the announcement of evacuation recommendation. The risk rank is defined by its maximum value. On the other hand, the possible evacuation time, or the degree of evacuation difficulty, is affected by difference in temporal pattern of flood. In this study, evacuation was more difficult in the case of lower risk rank. These results indicate that the larger flood event does not always cause the difficult condition for evacuation, but the smaller flood could make evacuation more difficult. Evacuation activity is quite important to reduce human loss in the case of large-scale flood which brings inundation by breaked levees. Therefore, it is equally important to estimate both the risk rank based on the maximum inundation depth and the possible evacuation time by considering various patterns of flood. Possible evacuation time can be estimated for individual area in the target region. Thus, it is clear and useful information to decide when each person should start evacuation activity to escape safely.