DEVELOPMENT OF A TWO-DIMENSIONAL FLOOD FLOW SIMULATION METHOD CONSIDERING OF INFILTRATION INTO FLOOD PLAINS AND SAND LAYERS DURING FLOOD EVENT

Abstract

 The middle Arakawa River has large flood plains and many cross-levees, which can delay the timing of a peak flow rate during a flood event. However, the delay of the peak flow rate obtained from the actual data of flow rate in the 2019 Typhoon Hagibis was large, and the phenomenon could not be explained only by the effect of the cross-levees. In this study, a simulation method that combined two-dimensional flood flow and one-dimensional or quasi-two-dimensional infiltration analysis was developed to investigate the effect of infiltration into flood plains during floods on the flow rate and water level in the Arakawa River. It was shown that the accuracy of the shape of the water level hydrograph (water level rise rate) is improved in this simulation method considering the horizontal infiltration not only from the upper surface of the flood plain but also from the low-water channel to the flood plains. The accuracy of the maximum water level around the First Arakawa Regulating Pond was not high. However, this study demonstrated that the infiltration into flood plains is important to be considered for accurately calculating the time to begin the overflow to the regulating reservoir.