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

Abstract

 Under the global warming condition, it is a great concern that a large scale linear heavy rainfall system causes severe flood disaster in a wide area. In such a case, it would be important to consider simultaneous floodings from multiple rivers. In this study, numerical inundation simulations were implemented under the consideration of simultaneous levee breaches in Kakehashi River and Tedori River in Ishikawa Prefecture, Japan. Based on the simulation results, water-related disaster risk was evaluated. At the same time, based on simulated inundation depth and flood water velocity at each simulation time, potential window time for evacuation was estimated. In the case of simultaneous levee breaches at the two rivers, in the right bank of the Kakehashi River, the maximum inundation depth became larger than in the case of levee breach at a single river. The window time for evacuation became shorter in the same area. In an area affected by the two rivers, arrival times of inundation flow from the two rivers are usually different. Depending on time lags between floods in two rivers, evacuation window time has to be estimated based on the time when the later flood level reaches the evacuation warning water level.