22nd IAHR-APD CONGRESS 2020 IN SAPPORO

Session6: Water-related Disaster Risk Reduction

6-3

Title: UNDERGROUND INUNDATION BY PLUVIAL FLOOD IN FULLY URBANIZED AREA OF OSAKA

Kaito Kusano, Taisuke Ishigaki, Taira Ozaki


In recent years, the frequency of local short-time heavy rain in urban areas is increasing. On August 27, 2013, an extreme heavy rain of 77.5mm per hour was observed in Osaka city. At this time, inundation caused damage such as flooding above floor level. In addition, flood water flowed into the mega-underground space in Osaka city, but there was no casualty. When local heavy rain would fall in a short time, not only pluvial flooding but also the risk of underground inundation was increasing. In this study, a simulation model considering sewerage drainage system in Tsumori treatment area in Osaka city is built. Underground inundation is investigated in the case of extreme rainfall condition of which maximum rainfall intensity was 146.5mm/hr in 2008 Okazaki flood. The results show that about 80% of the roads are flooded, and there were places where the flood depth is 1m or more. The inflow into the underground space goes through the subway station entrance. In particular, Osaka Metro Awaza Station has a high risk of inflow. Beside, in the underground malls, the inflow of flood water is smaller than the subway and underground parking lot. At underpasses, the inflow start time is fastest in underground spaces. In addition, the water depth exceeds the escape limit water depth of 0.56m in about 50 minutes from the beginning of rainfall. The inflow characteristics through the underground entrances in the Tsumori treatment area are clarified.





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