Laboratory study of the effects of flexible vegetation on solute diffusion in unidirectional flow
Open Access
- 5 July 2021
- journal article
- research article
- Published by Springer Science and Business Media LLC in Environmental Sciences Europe
- Vol. 33 (1), 1-12
- https://doi.org/10.1186/s12302-021-00521-y
Abstract
Background: Flexible vegetation is an important part of the riverine ecosystem, which can reduce flow velocity, change turbulence structure, and affect the processes of solute transport. Compared with the flow with rigid vegetation, which has been reported in many previous studies, bending of flexible vegetation increases the complexity of the flow–vegetation–solute interactions. In this study, laboratory experiments are carried out to investigate the influence of flexible vegetation on solute transport, and methods for estimating the lateral and longitudinal diffusion coefficients in the rigid vegetated flow are examined for their applications to the flow with flexible vegetation. Results: The experimental observations find that vegetation can significantly reduce flow velocity, and the Manning coefficient increases with increasing vegetation density and decreases with inflow discharge. Under all the cases, the vertical peak of the solute concentration moves towards the bottom bed along the flow, and the values of vertical peak concentration longitudinally decreases from the injection point. The lateral diffusion coefficients Dy increase with vegetation density, while the longitudinal diffusion coefficients DL are opposite. Both Dy and DL increase with the inflow discharge. To estimate the Dy and DL in the flow with flexible vegetation, an effective submerged vegetation height considering vegetation bending is incorporated in the methods proposed for flow with rigid vegetation (Lou et al. Environ Sci Eur 32:15, 2020). The modified approach can well predict the diffusion coefficients in the experiments with the relative errors in the range of 5%–12%. Conclusions: The methods proposed in this study can be used to estimate the lateral and longitudinal diffusion coefficients in flows through both rigid and flexible vegetations using the effective submerged vegetation height.Funding Information
- Natural Science Foundation of China (42072281)
- International Cooperation Program of Shanghai Innovation Action Plan (20230742500)
- Shanghai Peak Discipline Program for Civil Engineering School Tongji University (2019010207)
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