FLOOD RISK ANALYSIS OF THE ARA RIVER DURING THE TYPHOON NO. 19 IN 2019 BASED ON HINDCAST AND ENSEMBLE FORECAST RAINFALL DATA

Abstract

 The typhoon No. 19 in 2019 caused severe damages in large area of Japan. In the Ara River basin system, a broad inundation was caused due to the collapse of 7 points of levee along tributaries, and a flood risk was also extremely high on the main stream of the Ara river. Here, we estimated that the inundation area is 25.9 km² and the amount of flood water is about 31 million m³ based on the field surveys. In addition, we examined the possibility of flooding in the Ara River where flooding did not occur depending on the difference in rainfall distributions. We conducted runoff analysis by using RRI model and river flow analysis calculating 1-D unsteady flow using hindcast rainfall and ensemble forecast rainfall data. We calculated the river discharge and river water level by these analysis. As a result, we showed that the river flow increased due to the difference in therainfall distribution, and that there were some places where the flood overflow could occur in the Ara River.