Evacuation planning tools for river flooding: a case study of Matsukawa River

Flood damage is becoming increasingly frequent and diverse because of the effects of climate change and other factors. In Japan, recent flood prevention measures include providing information to residents through risk information maps called ‘hazard maps’ as ‘non-structural measures’, thereby ensuring suitable evacuation behaviour and raising awareness. This study developed tools for local government officials to provide residents detailed inundation information for small- and medium-sized rivers. Typhoon Hagibis flooded the Shinano River, causing severe damage to Obuse Town in northern Nagano Prefecture. Focusing on this event, a video was created to link the information on the map to actual evacuation behaviour. Flood inundation simulations were performed using the International River Interface Cooperative (iRIC) software and the Nays2DFlood solver. The terrain model for the simulation was created using a digital elevation model (DEM). In the iRIC simulation, sufficient reproducibility was obtained using a 10 m × 10 m mesh, a simple modification of the levee portion of the DEM, and the installation of a drainage pump station. The simulation allowed the adjustment of rainfall intensity and river flow, enabling the prediction of rainfall and flood damage. The new inundation information, including spatiotemporal flood patterns, can be used for evacuation planning.