Vegetation and ponds
Water in the natural environment interacts with vegetation. This plays a key role in promoting biodiversity, improving water quality and sedimentation. Small amounts of vegetation on the bank of a river or at the bottom of the pond can influence the movement of water around it, affecting mixing.
Vegetation provides resistance against flow, which can increase flow depths in rivers during floods. More importantly however, it introduces fast and slow moving zones of water, and the interface of these zones promotes increased mixing (West et al., 2020).
Managing vegetation and channel maintenance can be used to promote beneficial movement of nutrients or control the movement of pollutants.
Ponds and wetlands have low velocities and often large areas covered by vegetation. In these cases, the water flowing through the vegetation promotes mixing.
Understanding of these effects is useful to evaluate existing, and engineer new, stormwater treatment ponds, such as those used to treat highway run-off (Highways England, 2020).
Real vegetation from an engineering perspective is challenging, it's oddly shaped, points at every imaginable angle and is highly irregular. It's important that we can quantify its effects regardless.
Dr Fred Sonnenwald
91̽»¨
Investigation into how to best characterise vegetation for mixing and how to quantify the dispersion in vegetated flows is currently being carried out at the University of 91̽»¨.
CFD modelling approaches have been developed to allow engineers to investigate vegetation-flow interaction and predict mixing to help ensure that engineered natural systems perform to specification (Sonnenwald et al., 2019).
Relevant articles
- West, P. O., Wallis, S. G., Sonnenwald, F. C., Hart, J. R., Stovin, V. R., and Guymer, I. (2020). . Journal of Hydraulic Research, 1-16.
- Highways England (2020). . (Standards for Highways CD 532).
- Sonnenwald, F., Guymer, I., and Stovin, V. (2019). . Water Resources Research, 55(3), 2322-2347.
- Stovin, V., Guymer, I., Sonnenwald, F. (2019). A validated CFD model for estimating residence times in vegetated stormwater ponds (PDF, 252KB). Novatech 2019, Lyon, France, 1-5 July, 2019.