Effects of vegetation density on flow, mass exchange and sediment transport in lateral cavities

• Published in: Journal of hydrology (Amsterdam) 2024-03, Vol.632, p.130910, Article 130910
• Main Authors: de Oliveira, Luiz E.D., Yamasaki, Taís N., Janzen, Johannes G., Gualtieri, Carlo
• Format: Article
• Language: English
• Subjects: Aquatic vegetation; Computational Fluid Dynamics (CFD); flow resistance; hydrodynamics; kinetic energy; Lateral cavity; Mass exchange; mass transfer; sediment deposition; Sediment transport; turbulent flow; vegetation
• ISSN: 0022-1694; 1879-2707
• DOI: 10.1016/j.jhydrol.2024.130910

•A threshold density for hydrodynamics between sparse and dense vegetation was found.•A secondary gyre that is generally missing in non-vegetated cavities was observed.•The mean retention time cannot be estimated with a single decay fit for all densities.•Vegetation further increases the macro-roughness function of lateral cavities. Large-Eddy Simulations (LES) were used to investigate the hydrodynamics and mass transfer between the flow in the main channel and a vegetated lateral cavity. Fourteen vegetation densities (0 to 10.65 %) were tested, revealing two distinct hydrodynamic patterns. For cavities with low vegetation density (a  3.99 %), two gyres in contact with the interface with low velocity were formed, the thickness of the mixing layer did not grow, and the vorticity and turbulence kinetic energy were low inside the cavity. The mass transport presented the same threshold value as the hydrodynamics (a = 3.99 %). For cavities with low vegetation density, a fast mass transfer occurred through the interface between the main channel and cavity and inside the cavity, while the opposite was observed for cavities with high vegetation density. Finally, the modelled hydrodynamics was used to infer possible sediment deposition patterns and flow resistance.