Study on Flow in Compound Channels and Effect of River Vegetation

本研究对复合明渠和部分植被河道进行了室内试验、数值模拟和现场观测。在复合明渠的室内试验中发现，剪切不稳定性在主河道与洪泛平原交界处产生较大的水平涡旋，横向动量交换受涡旋的影响较大，随着主河道深度的增加，亚深尺度湍流相对于水平大尺度湍流变得较强，水平涡旋变得不明显；与复合明渠相比，水流场变得更加二维化，导致主河道与植被区之间动量交换较大。采用SDS-2DH湍流模型进行了数值计算，计算结果与实验结果吻合较好。对石卡里河河口输沙量进行了研究。研究了浊度数据与悬沙浓度数据之间的关系，提出了一个计算冲洗液输沙率的公式。采用床质输运、悬移输运、床质变形和床质粒度分布的数值模型计算了床质年径流量。比较了冲洗量径流和床质径流的结果，发现冲洗量径流可以解释为床质负荷的一部分。

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.