FLOOD ANALYSIS IN THE NUTA RIVER BASIN DURING THE HEAVY RAIN IN JULY 2018

Abstract

 The heavy rainfall from 5 to 7 July 2018 in the western Japan have caused severe flood damage. The Nuta River basin is one of the most suffered areas from the flood inundation, which was induced by overflows, bank erosion, and several levee breaches in tributaries. This study aims to reveal the runoff characteristics of the Nuta River basin and to discuss the causes of the flooding by numerical simulation results. We applied the Rainfall-Runoff-Inundation model to the river basin to discuss the rainfall runoff characteristics, taking the operations of Fukutomi and Mukunashi Dams into account. Two-dimensional flood flow simulation was carried out in the Funaki district of the river to clarify the flow resistance of tree growth in the reach. Numerical results show that the increase in flow resistance by tree growth is attributed to increasing in water level in the Funaki district in addition to the extremely heavy rain.