| On September 10, 2015, unprecedented flood was occurred in Kinugawa Riverbasin located on eastern Japan. It inundated 40 km2 of flood plain in Joso city,Ibaraki Prefecture, and more than 4000 people there called for help despitesupposedly having sufficient time to evacuate. Some said that small initialflood before main severe flood arrived made them make a mistake in decidingwhether to evacuate or stay there, despite having to actually evacuate in reality.This study focused on flood behaviour in this area, in particular, the effectof a small drainage channel lying on the flood plain which caused fast flooddiffusion in case of occurring huge overflowing. Field investigations startingon time of the disaster with high-resolution positioning system were conductedto obtain spatial maps of flood depth and height. For appropriatemodelling of the effect of small channel, we applied simulation model coupling1-dimensional (1D) and 2-dimensional (2D) hydraulic scheme on thefield and compared results from the 1D/2D coupled model and model without1D scheme. The models provided information that the flood could reach 4hours earlier to the city central of Joso city comparing in case of model without1D scheme. The water depth rose irregularly and it was more confusingand difficult for the victims to make appropriate evacuation act. |
