Vegetation greatly affects the flow characteristics and contaminant transport in river confluences. In this study, the flow characteristics and contaminant transport in the non-vegetated/vegetated Y-shaped confluence were explored systematically through a series of experiments. A total of 10 scenarios were designed to answer the three main research questions: what is the difference between the flow characteristics and contaminant transport in (1) asymmetrical and Y-shaped confluences; (2) non-vegetated/vegetated Y-shaped confluences; (3) vegetated Y-shaped confluences with different confluence ratios? The experimental results revealed that vegetation remarkably changes the internal flow structure in Y-shaped confluences. Briefly, the velocity profile can be divided into three vertical layers within the vegetated system, but it remains nearly constant in the non-vegetated channel. Vegetation changes the circulation location and reduces the intensity of the secondary current, weakening the strength of contaminant mixing. However, the turbulent kinetic energy within the vegetated system is larger than that in the non-vegetated case, and it peaks at the top of the vegetation canopy. Under different confluence ratio cases, the overall fluctuation of the longitudinal dispersion coefficients along the cross-sections in the mainstream was similar but increasing the confluence ratio causes the circulation to appear to advance and enhances its intensity. In addition, the vegetation density (200 item/m²) in this study render the manning roughness coefficient at 0.068, which is larger than that under lower vegetation density cases. The outcomes from this study are helpful for both environmental and river management applications.

中文翻译：

---

具有柔性淹没植被的 Y 形汇合处流体动力学和污染物迁移的实验研究

植被对河流汇合处的流动特性和污染物输送有很大影响。在本研究中，通过一系列实验，系统地探索了非植被/植被 Y 形汇合处的流动特性和污染物运移。总共设计了 10 个场景来回答三个主要研究问题：（1）不对称和 Y 形合流中的流动特性和污染物运输之间的区别是什么；(2) 无植被/有植被的 Y 形汇合处；(3) 不同汇合率的植被 Y 形汇合？实验结果表明，植被显着改变了Y形汇流处的内部流动结构。简而言之，速度剖面可以在植被系统内分为三个垂直层，但它在非植被通道中几乎保持不变。植被改变了循环位置，降低了二次流的强度，削弱了污染物混合的强度。然而，植被系统内的湍动能大于非植被情况下的湍动能，并在植被冠层顶部达到峰值。在不同合流比情况下，沿主流断面纵向扩散系数的总体波动相似，但增加合流比会使环流出现提前并增强其强度。此外，植被密度（200 项/m 然而，植被系统内的湍动能大于非植被情况下的湍动能，并在植被冠层顶部达到峰值。在不同合流比情况下，沿主流断面纵向扩散系数的总体波动相似，但增加合流比会使环流出现提前并增强其强度。此外，植被密度（200 项/m 然而，植被系统内的湍动能大于非植被情况下的湍动能，并在植被冠层顶部达到峰值。在不同合流比情况下，沿主流断面纵向扩散系数的总体波动相似，但增加合流比会使环流出现提前并增强其强度。此外，植被密度（200 项/m 沿干流各断面纵向扩散系数的整体波动相似，但合流比的增加会使环流出现提前并增强其强度。此外，植被密度（200 项/m 沿干流各断面纵向扩散系数的整体波动相似，但合流比的增加会使环流出现提前并增强其强度。此外，植被密度（200 项/m² ) 在本研究中，曼宁粗糙度系数为 0.068，大于低植被密度情况下的值。这项研究的结果对环境和河流管理应用都有帮助。