INVESTIGATION ON THE CHARACTERISTICS OF FLOOD FLOWS IN THE CHIKUGO-GAWA RIVER SYSTEM BASED ON WATER LEVEL INFORMATION DURING THE HEAVY RAINFALL IN JULY 2020

This study summarizes the rainfall and damage in the Chikugo River system, which was severely damaged by the torrential rains in July 2020. One-dimensional flood flow analysis based on water level information was conducted in the Chikugo-gawa River system of the upper basin, where inundation by river water occurred, to understand the behavior of flood flows in the Chikugo, Kusu, Kuma, Shode, and Kagetsu Rivers. As a result, it was found that (1) the amount of the heavy rainfall was the planned magnitude, (2) in the Chikugo River basin, inundation by river water and inside levee occurred and road and railroad bridges were washed away, and (3) based on the flow hydrographs estimated in this study at Senjo, Ogase, Obuchi, Kuma, Kagetsu and Arase stations, the flow discharge in the Chikugo, Shode, and Kusu Rivers where the water level rose near or exceeded the design high water level was near or above the flow discharge which is maintenance target.