THREE-DIMENSIONAL FLOOD SIMULATION AROUND THE LOWER ASAHI RIVER FIXED DIVERSION WEIR CONSIDERING DISTRIBUTED VEGETATION CONDITIONS DURING THE HEAVY RAIN EVENT OF JULY 2018

Abstract

 Flooding with a discharge of approximately 4200 m³/s occurred in the lower Asahi River during the Heavy Rain Event of July 2018. The flood flow over the historic diversion weir was the first time ever observed after its renewal work. For flood control tasks, hydraulic engineers have examined the diversion discharge by laboratorial experiments and two-dimensional (2-D) numerical simulations. However, the flood impacts on the subsequent changes of both vegetation and riverbed conditions have not been fully investigated yet in the earlier works. Furthermore, the 2-D flow model commonly cannot allow for reproducibility of flows around the actual river section with a complicated bed geometry and heavily vegetated conditions. Therefore, a new 3-D numerical model has been proposed herein for flood flow simulation based on a porous model considering distributed vegetation establishment using airborne laser bathymetry (ALB) data before and after the rainfall event. Simulated results demonstrated that the proposed model performed well, compared with the existing 2-D model and field observations.