INUNDATION RISK EVALUATION BASED ON THE ASSUMPTION OF SIMULTANEOUS FLOODS IN MULTIPLE RIVERS

Abstract

 Under global warming, large-scale linear heavy rainfall systems can cause severe floods over a wide area. In such a case, simultaneous floodings from multiple rivers must be considered. In this study, numerical inundation simulations were implemented considering simultaneous levee breaches in the Kakehashi and Tedori rivers in Ishikawa Prefecture, Japan. Flood disaster risk was evaluated based on the simulation results. The potential window time for evacuation was estimated based on the simulated inundation depth and flood flow velocity at each simulation time. The maximum inundation depth on the right bank of the Kakehashi River was larger in the case of simultaneous levee breaches at the two rivers than that in the case of a levee breach at a single river. The window time for evacuation was shorter in the same area. In an area affected by the two rivers, the arrival times of inundation flow from the two rivers are typically different. Depending on the time lags between the floods in the two rivers, the evacuation window time must be estimated based on the time when the later flood level reaches the evacuation decision water level.