Recently, though the drainage maintenance is roughly completed in the metropolitan area in Japan, the flood damage by the heavy rain happens frequently. It is because localized torrential rain that 1 hour rainfall greatly locally exceeds the plan scale of drainage has been generated.
In the present study, recent characteristics of rainfall were analyzed, and the investigation of damage was done with the inundation simulation. In particular, we search 10-minute rainfall, rainfall duration, flood damage and status of the city sewage targeted at the heavy rains were observed in government-designated major cities. In addition, modeling the ground level and sewer pipe at areas in Tokyo etc., we simulated flooding using runoff analysis model (MOUSE).
Then we examined necessary measures in the sewers, and three conclusions obtained:
• The sewer department needs to take measures to the rain: 10-minute rainfall is over planned, and 1 hour rainfall is less planned.
• The simulation results show that flood damage occurs locally in the upper portion of the branch line in a short time, but no damage in the downstream portion of the trunk line for room of tube drainage capacity.
• Complementary measures that make effective use of existing facilities is valid rather than building a large arterial bypass pipe has been previously built as technique measures for sewer.