2024 Volume 80 Issue 16 Article ID: 23-16020
Fluvial bar movements are an important subject for sediment hydraulics and river managements. In this study, fluvial bar movements at a river confluence of Tone River and Karasu River, which caused the burring of water level gauge of Yatta-jima WLGS in 2011 due to the elongation of leftbank bar at the confluence, were investigated by using long-term analyses of aerophotos and hydrological data, and by conducting movable bed experiments. In conclusions, the elongation of leftbank bar started almost from about 2001. It was suggested that this elongation was caused by the change of river discharge ratio due to precipitation changes at upstream river basins. On the basis of this suggestion, movable bed experiments and visualization by using fluorescent sands by using a simple open-channel flume of Y-shaped confluence were conducted by varying the river discharge ratio. From experimental results, it was revealed that floods due to the Tone impact, which indicated river discharges of Tone River were larger than those of Karasu River, caused the expand and elongation of leftbank bar at river confluence and those due to the Karasu impact after the Tone impact flood caused the straight-shaped elongation of leftbank bar, which was almost the same shape with field bar as shown in final aerophoto in 2011.
