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

日本的河流大多是曲曲折折的复合河。复合曲流河道的阻力和河道地形受曲流相对深度和曲度等水力条件的影响而发生变化。建立了复合曲流河河漫滩与主河道宽度比和粗糙度比对河底水流和河床地形影响的数值模型。研究了复合曲流河道中流场和河床形态随宽度、深度、粗糙度和曲度的变化规律，明确了流场特征和河床形成机理。得到以下结论：当流速的变化使河床荷载的纵向变化更加有效时，河床就变成了单一的曲流。相反，当二次流作用使床层荷载横向变化更有效时，床层已成为复合流场之一。由于水流的直行在小弯度处增加，水流的最大速度线出现在顶点附近，河床被不断冲刷。据此，提出了流动特性的分类图。分析了复合曲径漫游者在放电观测中由于观测段的选择而产生约15%误差的可能性。在相对深度较小的非定常流量上升阶段，主河道动量被输送到冲积平原。由于河漫滩向主河道的水流很少，因此主河道的水流不受河漫滩粗糙度的影响，主河道的流速随深度的增加而增加。当主河道与漫滩水动量交换变大时，主河道流速减小。当河漫滩深度变大时，由于河漫滩上的流速较高，主河道流速再次增大。少

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