An experimental study of the hydrodynamics and contaminant transport in a Y‐shaped confluence with flexible submerged vegetation

• Published in: Hydrological processes 2022-08, Vol.36 (8), p.n/a
• Main Authors: Tong, Xuneng, Liu, Xiaodong, Yang, Ting, Mohapatra, Sanjeeb, Hua, Zulin, Zhang, Yuan, Chu, Kejian, Xue, Hongqin
• Format: Article
• Language: English
• Subjects: Coefficients; Confluence; contaminant transport; Contaminants; Density; Environmental management; flexible submerged vegetation; Flow characteristics; Flow structures; Hydrodynamics; Internal flow; Kinetic energy; Longitudinal dispersion; Pollution transport; River management; Rivers; Roughness; Roughness coefficient; secondary current; Submerged plants; Transport; Turbulent kinetic energy; Vegetation; Vegetation changes; Velocity distribution; velocity profile; Velocity profiles; Y‐shaped confluence channel
• ISSN: 0885-6087; 1099-1085
• DOI: 10.1002/hyp.14661

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. The interaction of vegetation and channel confluence renders flow characteristics more complex. Vegetation can redistribute the flow velocity zone, change the internal flow structure, and weaken the strength of contaminant mixing. Increasing the confluence ratio causes the circulation to appear to advance and enhances its intensity.