120 / 2024-02-12 15:53:29

Hydraulic characteristics of Meandering Compound Channel Flows with Embankment

meandering channel,compound open-channel flow,river bank,stereo-PIV

In the Kuma River in Kumamoto Prefecture, Kyushu, Japan, which was severely damaged by the torrential rainfall in July 2020, the floodwaters overflowed the levees upstream of the bend in the Kuma River, causing downstream flooding in Imamura and Chaya villages in the Watari district of Kuma Village, located on the inner bank of the meandering section of the river. The houses on the levee side were spared from being swept away.

In this study, we installed a levee at the boundary between the inner bank and the low channel of a compound meandering channel, and clarified the flow structure and turbulence characteristics of the inner bank in steady and unsteady flow. The width of the low channel was 14 cm, and the width of the high water bed was 46 cm. The meander section was 2.5 wavelengths with one wavelength of 90 cm, and the last wavelength was used as the measurement section. The height of the high water bed was 5 cm and the height of the embankment was 1 cm. Ultrasonic displacement sensors were used to measure water depth. The measurement interval was 1 cm in both the x- and y-directions. The Stereo-PIV method was used to measure the flow velocity. A laser light sheet was irradiated from the side of the channel, and horizontal cross sections were photographed. The images were taken at 125 fps for approximately 35 seconds.

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 settlement caused by the heavy rainfall in July of Reiwa 2.