ESTIMATING EFFECT OF AGRICALTURAL WATER USE FACILITIES ON RUNOFF AND FLOODING PROCESS IN KUMA RIVER BASIN DURING 2020 KYUSHU FLOOD

We estimated the impact of agricultural water utilization facilities (Hyakutaro-mizo and Kono-mizo) in the basin on flooding process. Both waterways run parallel to the Kuma River on the left bank side, and cross the tributaries in various forms such as level crossing, grade separation, and siphon. We developed a model that can express a series of processes of rainfall, runoff, river flow, and flooding.The analysis was performed assuming the case where both channels exist and the case where they do not exist. As a result, it was confirmed that the presence of both canals raises the water level in the tributary of the drainage destination from an early stage, and the peak water level of the main river also rises slightly. In addition, while the inundation area decreased around both canals, the inundation was concentrated at the confluence of the main tributaries.When conducting the Integrated Flood Management, the impact of agricultural water use facilities cannot be ignored, and it is desirable to consider it explicitly.