2024 Volume 80 Issue 16 Article ID: 23-16060
Gravel riverbeds are disappearing due to the growth of forests in river sections downstream from dams because of the reduction of tractive force by flood control. In this study, the measures to activate riverbed gravel movement by changing the flood control rule was examined for the Yuda Dam upstream of the Waga River, a right tributary of the Kitakami River, where the gravel riverbed is remarkably forested. First, it was confirmed that the Yuda Dam has sufficient flood control capacity from the statistical analysis of the inflow to the Yuda Dam and the flow rate of the Waga River at the time of flood as well as the capacity analysis of the downstream channel. Next, the increase in discharge from the dam during floods was examined within the range of the flood flow capacity of the Waga River channel. The result suggested that the river discharge with a probability of occurrence of 1/5 can be changed from about 1100 m3/s to 1800 m3/s by increasing in the minimum flood discharge. Finally, we calculated changes in bed tractive force using a shallow water flow model and showed that the above changes in the flood control rule can increase the mobility of 10-cm-diameter pebbles which is dominant in the Waga Riverbed.
