Study on Flow in Compound Channels and Effect of River Vegetation

通过对复式明渠和部分植被明渠水流泥沙运动的室内试验、数值模拟和现场观测，发现复式明渠的剪切失稳在主槽与漫滩交界处产生较大的水平涡，涡对横向动量交换影响较大，随着主槽水深的增加，次深尺度紊流相对于水平大尺度紊流变得相对较强，水平涡变得不明显。部分植被渠道中的流场比复式明渠中的流场更加二维化，采用SDS-2DH湍流模型进行数值计算，并对石狩川河口输沙量进行了研究。研究了浊度与悬沙浓度的关系，提出了计算冲淤输沙率的公式。通过建立推移质输沙、悬移质输沙、河床变形和床沙粒径分布的数学模型，计算了河床年径流量。将冲沙径流与推移质径流结果进行了比较，发现冲沙径流可以解释为推移质的一部分。

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.