The influence of hydraulic characteristics to flow and bed form in compound meandering channels

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Most of the Japanese rivers are compound meandering rivers. Resistance and river topography in a compound meandering channel change due to the hydraulic condition such as the relative depth and sinuosity of meandering. We have developed the numerical model which can evaluate the flow and bed topography affected by the ratio of width and the ration of roughness between flood plain and main channel in a compound meandering river. In this study, the change in the flow field and bed form in compound meandering channels due to the width, depth, roughness, sinuosity is examined and the characteristics of flow fields and mechanism of bed formation is cleared. The following conclusions were obtained.When the longitudinal change of bed loads is more effective due to the change in velocity, the bed from have becomes one of the single meandering flow. To the contrary, when the transverse change of bed loads is more effective due to secondary flow, the bed from have becomes one of the compound mea … More ndering flow. The maximum velocity line of main flow appears around the Apex and river bed is continuously scoured, because going straight of the flow increase in the small sinuosity. As the results, the classification figure of the flow characteristics is proposed. The possibility that about 15% errors in discharge observation arise due to the selection of the observation section in a compound meandering rover was shown. At the rising stage in unsteady discharge with the small relative depth, the momentum of main channel is transported to the flood plain. As the flow from the flood plain to the main channel hardly occur, the flow of main channel is not influenced by the roughness of flood plain and velocity in a main channel increases with the increasing of depth. When the momentum exchange between the water in the main channel and over flood plain becomes large, the velocity in the main channel decreases. When the depth on the flood plain becomes large, the velocity in the main channel increases again because of high velocity on the flood plain. Less