ESTIMATION OF THE EFFECT OF KAWABEGAWA DAM IN KUMAGAWA RIVER CATCHMENT ON FLOOD MITIGATION DOWNSTREAM CONSIDERING POSSIBLE WORST CASE SCENARIO

Abstract

 This paper presents an attempt to establish a methodology for visualizing the effect of dam on flood mitigation in an easy to understand way for public. The target river basin is Kumagawa River catchment. Specifically, the Kawabegawa dam which is supposed to be constructed in near future in the catchment was dealt with. The discharges into Ichifusa dam and planned Kawabegawa dam for the rainfall event of July 2020 were first reproduced using a storage function model and radar-raingauge analyzed data. Then, the inflow to Kawabegawa dam was converted to outflow considering its dam operations. Using the inflow/outflow, the effect of Kawabegawa dam on flood mitigation in downstream area was estimated. Herein a shallow water equation model tailored for supercomputer Fugaku was used to carry out large scale computation at downstream to estimate the flood depths. Finally, two worst case scenarios out of 1000 ensemble flood simulations were considered to investigate the effect of Kawabegawa dam at a worst situation. As a result, it was shown that Kawabegawa dam has certain effect on flood mitigation.