Study on Flow in Compound Channels and Effect of River Vegetation

对复式明渠和部分植被明渠的水流泥沙输移进行了室内试验、数值模拟和现场观测。在复式明渠的室内试验中，剪切不稳定在主槽和漫滩交界处产生了较大的水平涡，横向动量交换受旋涡的影响较大，随着主槽深度的增加，次深尺度湍流相对于水平大尺度湍流变得相对强烈，水平涡变得模糊，部分植被明渠的流场比复合明渠的流场更具二维性。采用SDS-2DH湍流模型进行了数值计算，计算结果与试验结果吻合较好。研究了石卡里河河口输沙量。研究了浊度数据与含沙量数据之间的关系，提出了泥沙输移速率的计算公式。利用泥沙和悬移质输运、河床变形和泥沙粒度分布的数值模型，计算了河床年径流量。比较了冲沙径流和推移质径流的计算结果，发现冲沙径流可以解释为推移质径流的一部分。

Laboratory tests, numerical simulations and filed observations of flow and sediment transport in compound open channels and partly vegetated channels were performed in the present study.In the laboratory tests for compound open channels, it was found that the shear instability generates large horizontal vortices at the junctions of main channel and flood plains, and the lateral momentum exchange is much affected by the vortices, As the depth of main channel increases, the subdepth scale turbulence becomes relatively strong compared with the horizontal large scale turbulence, and the horizontal vortices becomes indistinct, In the partly vegetated channels, the flow filed becomes more 2 dimensionally than that in the compound open channels, and which induces the large momentum exchange between main channel and vegetation area.Numerical computations were performed by employing SDS-2DH turbulence model, the results of which agree reasonably well with the experiments.The sediment transport output from river mouth was investigated at Ishikari river. Relationship between turbidity data and suspended sediment concentration data is investigated and a formula to evaluate wash load transport rate is proposed. The annual runoff of the bed material is also calculated by a numerical model for bed load and suspended load transport, bed deformation and grain size distribution of bed material. The results of wash load runoff and bed material load runoff are compared and it is found that wash load runoff can be explained as a part of bed material load.