Author(s): Ryuichi Hirakawa; Terunori Ohmoto

Linked Author(s): Terunori Ohmoto, Ryuichi Hirakawa

Keywords: Meandering channel; Compound open-channel flow; River bank; Stereo-PIV

Abstract: The heavy rainfall in July of 2020 caused significant damage in the vicinity of the Chaya hamlet in Watari village, Kumamoto prefecture, Japan. The floodwaters exceeded the levees and rapidly flowed along the railway line, resulting in house collapses in the levee area. In Japan, rivers often have dual-section configurations with low channels and high floodplains to accommodate different flow rates during normal and flood conditions, and the Kuma River is no exception. This study aimed to investigate the flow structure and turbulence characteristics in unsteady flow by installing levees in a dual-section meandering channel. Laboratory experiments using stereo PIV measured water depth and flow velocity in steady and unsteady conditions with and without levees. The results showed that without levees, there was little difference in water level, but with levees, water levels dropped before and after surpassing the levees, and the water level increased in the inner part of the levee. Observations of the main flow velocity distribution revealed faster flow in both the low channel and the high floodplain, correlating with the distribution of house collapses in the Chaya hamlet caused by the heavy rainfall in July of 2020. Additionally, turbulence characteristics showed larger values during the reduced water flow period.

DOI:

Year: 2024