Free-surface flows with riparian corridors are known to develop large eddies resulting from the instability associated to the inflectional profile of the longitudinal velocity in the spanwise direction. They periodically generate strong momentum exchanges inside the vegetation corridor, triggering a wave-like motion, detectable as free-surface oscillations and out-of-phase velocity components. We propose a characterization of the flow inside the vegetation corridor, focusing on the wave-like motion and its influence on secondary currents. We conditionally sample the fluid motion to highlight the structure of the phase-averaged coherent structure. Quadrant analysis shows that there is a strong variation of Reynolds stress anisotropy in the spanwise direction, which is one of the key generation mechanisms of secondary currents. Spectrograms of longitudinal and lateral velocity fluctuations reveal that the oscillatory motion is imposed on the whole of the vegetated layer, because of continuity. The analysis of the phase-averaged 2D vertical-longitudinal flow reveals that there is a complex 3D pattern of mass fluxes associated to each large eddy. In particular there is an anti-symmetric net mass imbalance which, by mass conservation, generates a mass flux directed outwards, to the main channel, near the bottom of the channel. The Eulerian expression of this motion is obtained as the spatial average of the flow over the length of the large eddy, resulting in the pattern of the secondary current in the vertical-spanwise plane. It is shown that the secondary motion is a necessary feature of free-surface turbulent flows that develop large-scale inflectional instabilities.

众所周知，具有河岸走廊的自由表面流动会产生大涡流，这是由于与翼展方向纵向速度的拐点剖面相关的不稳定性造成的。它们周期性地在植被走廊内产生强烈的动量交换，触发波状运动，可检测为自由表面振荡和异相速度分量。我们提出了植被走廊内流动的特征，重点关注波浪状运动及其对次级电流的影响。我们有条件地对流体运动进行采样以突出相位平均相干结构的结构。象限分析表明，雷诺应力各向异性在翼展方向存在强烈变化，这是二次电流产生的关键机制之一。纵向和横向速度波动的频谱图表明，由于连续性，振荡运动被施加在整个植被层上。对相位平均的 2D 垂直纵向流的分析表明，每个大涡流都有一个复杂的 3D 质量通量模式。特别是存在反对称的净质量不平衡，其通过质量守恒产生向外指向通道底部附近的主通道的质量通量。该运动的欧拉表达式是作为大涡流长度上流动的空间平均值获得的，从而产生了垂直展向平面中的次级电流模式。结果表明，二次运动是自由表面湍流发展大规模拐点不稳定性的必要特征。