67 / 2023-12-28 16:31:05

Difficulty of Evacuation Considering Evacuation Distance in case of Flood inundation Hazard

flood inundation hazard,hazard map,walking in a stream,evacuation distance,difficulty of evacuation

In recent years, record-breaking rainfalls and urbanization have caused flood inundation hazard in many parts of Japan. Hazard maps are sometimes used for evacuation in the event of flooding, but conventional hazard map generally only show the depth of flooding. However, in the case of evacuation involving walking in the water, it is considered that the flow velocity and evacuation distance may also be affected.



The purpose of this study is to define difficulty of evacuation in the event of internal flood inundation hazard as an index that includes more than just the depth of flood inundation. The target area is A District in Maebashi City, Gunma Prefecture, Japan. Flood inundation analysis was conducted to calculate depths and velocities of inundation in the event of internal inundation hazard. Flood inundation analysis was established using historical data for 5-, 10-, and 100-year probability rainfall for short-term rainfall in the target area. The definition of difficulty of evacuation was calculated using three parameters: α, the rate of safe action, which is an index for walking in a stream; β, the rate of shortage of designated emergency evacuation sites, which is an index for evacuation distance; and γ, the rate of shortage of effective walking space, which is the effect of openings on the road.



The evaluation of difficulty of evacuation indicated that evacuation was smaller near the evacuation site and larger away from the evacuation site. It was found that its evacuation depended on the depth of flood inundation, the velocity of the flow and evacuation distance. And γ, the rate of shortage of effective walking space affected locally.



In the previous studies, the locations and routes were limited, however, this study showed visualize and evaluated the entire target area. The combined effect of evacuation distance and road area is an advanced one. The results also suggest the possibility of visualizing new evacuation difficulty points.