Author(s): Mitsuhiro Terada, Taisuke Ishigaki, Taira Ozaki, Yasuyuki Baba, Keiich Toda
Linked Author(s): Taisuke Ishigaki
Keywords: Urban flood, subway inundation, fluvial flood, numerical model, evacuation
Abstract: Mega cities in Japan, for instance Tokyo, Nagoya or Osaka, are susceptible to floods, because they are located in lowlands which are below flood water level of rivers. These areas are prone to floods caused by rainwater, river-water and sea-water. More than 640 subway stations and 78 underground malls are located in Japan. And so many underground parking, underpasses and basements are also in these cities. Underground inundation has been investigated in the case of pluvial, fluvial, tsunami and storm surge flooding in Osaka, Japan by authors. In a fluvial flooding case, the flood water covers almost all area and 42 percent of total amount of overtopping flood water intrudes into underground spaces such as underground shopping mall, subway stations and underground parking areas. This intruded flood water flows through subway tunnels, however, spreading process has been investigated only in the pluvial flooding case before by authors. In this paper, subway inundation in this study area is investigated by using a numerical model including underground mall, subway stations and ten subway lines. From calculation results of inundation by fluvial flooding, it is found that subway inundation quickly spreads through subway tunnels. Subway inundation spreads through subway lines and stations located in the area, where ground level inundation has not occurred, are also inundated or filled up. At some stations, the flood water spills out to the ground. In this case, people on platform should evacuate until flood water recedes. The critical condition of safe evacuation from inundated underground spaces has been investigated by the authors and the criteria of safe evacuation has been pointed out by authors. By using the criteria and calculation results, the lead time for safe evacuation is also investigated here and the result shows that people on the platform should evacuate as soon as possible
Year: 2017