Vegetation occurring along river margins deeply alters the hydrodynamic flow structure, inducing a characteristic shear layer profile and triggering the onset of large scale vortices, which, in turn, govern the lateral exchanges across the vegetated interface. In such systems, vegetative drag plays a key role, regulating the velocity difference between the vegetated area and the adjacent main channel. In this study, the link between vegetation density, differential velocity ratio, and presence of large scale coherent structures is experimentally explored. Tests were performed considering different vegetation density and focusing on the lateral distributions of velocity statistics and presence of coherent turbulent structures. Results showed that, with decreasing vegetation density, the favorable conditions for the onset of large scale structures can disappear with direct effects on velocity distributions and efficiency of lateral momentum transport. Based on the test results, a critical value of differential velocity ratio is suggested.

沿河边缘发生的植被极大地改变了水动力流结构，诱发了特征性的剪切层剖面并触发了大尺度涡旋的发生，进而控制了整个植被界面的横向交换。在这样的系统中，植物阻力起着关键作用，调节着植物区和相邻主河道之间的速度差。在这项研究中，通过实验探索了植被密度，速度比与大型相干结构之间的联系。在考虑不同植被密度的情况下进行了测试，并侧重于速度统计的横向分布和相干湍流结构的存在。结果表明，随着植被密度的降低，直接影响速度分布和横向动量传输效率的大型结构开始出现的有利条件会消失。根据测试结果，提出了差速比的临界值。