INVESTIGATION ON RAINFALL-RUNOFF AND FLOOD INUNDATION PROCESS IN THE KUMA RIVER BASIN DURING THE HEAVY RAINFALL IN JULY 2020

Abstract

 This study examines a rainfall-runoff and flood-inundation process in the Kuma River basin during the heavy rainfall event in July 2020. A field survey and a numerical simulation of the rainfall-runoff and flood inundation were conducted. The results show the followings. (1) The heavy rainfall exceeded the planned rainfall. (2) Two levees were breached, and 11 bridges were overflowed or flooded. (3) The heavy rainfall area moved from the upper to the middle of the Kuma River basin. And then from the northwest of the middle to the southeast of the upper basin. (4) In the area upstream from Watari to the confluence of the Maegawa River, the main river overflows. And the flooded area expanded from the narrowed area to the upstream side. In the Hitoyoshi urban area, backwater caused flooding in the branch rivers. And then the main river overflowed, expanding the inundation area. The model can now capture the behavior of rainwater at the watershed level.