Abstract
ABSTRACT Transverse solute mixing across a vegetation generated horizontal shear layer was quantified using laser induced fluorometry techniques for artificial and real vegetation. A two-dimensional finite difference model (FDM) was developed to describe transverse concentration profiles for flows containing transverse variations in velocity and transverse dispersion, from a steady solute input. The FDM was employed inversely, to optimize the parameters describing the transverse distribution of the transverse dispersion coefficient for vegetation generated shear layers. When laboratory data are available, continuous function descriptions produce slightly improved FDM modelled solute concentration profiles compared with simplified step discontinuity velocity and dispersion inputs. When laboratory data are not available, estimates of step or continuous transverse distributions from other work enable concentration profiles to be predicted with a similar goodness of fit. This paper presents a validated, simple, robust finite difference model to describe the mixing of solutes in a channel containing marginal vegetation.
Highlights
Linear wetlands are increasingly used to provide pollution treatment from diffuse sources such as highways, agricultural land and urban environments
The finite difference model (FDM) was employed inversely, to optimize the parameters describing the transverse distribution of the transverse dispersion coefficient for vegetation generated shear layers
This paper presents a validated, simple, robust finite difference model to describe the mixing of solutes in a channel containing marginal vegetation
Summary
Linear wetlands are increasingly used to provide pollution treatment from diffuse sources such as highways, agricultural land and urban environments. The reduction in the mean flow velocity promotes sedimentation, whilst a reduction in contaminant concentration can be achieved through dispersion and bio-chemical degradation. It follows that the detention of contamination, and subsequent bio-chemical degradation, is affected by the reach hydrodynamics (Maji et al, 2020; Persson et al, 1999; Koskiaho, 2003). Vegetation may enhance pollution treatment by increasing the active surface area populated by micro-organisms and, potentially, by promoting dispersion – increasing the likelihood of chemical decay due to sunlight and bio-chemical degradation (Rowinski et al, 2018). Free-surface wetlands, and some rivers, Received 7 August 2019; accepted 19 August 2020/Currently open for discussion
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