Full Paper 11 th ISE 2016, Melbourne, Australia QUANTIFYING SOLUTE MIXING AND FLOW FIELDS IN LOW VELOCITY, REAL EMERGENT VEGETATION PATRICK WEST School of Engineering, University of Warwick, Coventry, CV4 7AL, UK JAMES HART School of Engineering, University of Warwick, Coventry, CV4 7AL, UK IAN GUYMER School of Engineering, University of Warwick, Coventry, CV4 7AL, UK VIRGINIA STOVIN Department of Civil and Structural Engineering, University of Sheffield, Sheffield, S1 3JD, UK The heterogeneous distribution and morphology of real vegetation in shear layer environments leads to significantly different flow fields and mixing properties when compared to artificial cases. Velocity profiles and tracer concentrations were recorded in emergent, artificial vegetation and winter growth Typha between the free flow and the vegetation. While the velocity shear and concentration distribution skew were less apparent in the Typha than the artificial vegetation, the overall mixing, in terms of increase in variance, was greater. The increased mixing and deviation from the classical shear layer flow field is attributed to the spatial heterogeneity in vegetation distribution and a less-well defined shear layer interface due to the prevalence of sparsely vegetated zones. 1 INTRODUCTION Diffuse, or non-point source, contamination is the most significant contributor to surface water pollution in the UK and Europe [1]. Pond environments are becoming popular methods of providing appropriate pre-treatment before the contaminated water enters sensitive watercourses [2,3]. As well as offering amenity to local residents and ecological habitat, ponds provide an integrated approach to sustainable water resource management. Prevalent vegetation in ponds is a habitat for organisms [4] and encourages bio-chemical degradation of contaminants [5,6,7,8]. Moreover, vegetation affects the local hydrodynamics and thus the installation’s detention characteristics [9,10]. Pond systems generally comprise of border and patches of vegetation (Fig. 1). This paper considers the effects of emergent vegetation; although analogies between emergent and submerged are applicable and are discussed where appropriate. These patches lead to a lateral heterogeneity in drag, influencing the velocity field and creating complex, three-dimensional systems [10,11,12,13,14,15,16]. Figure 1 shows the early stage of a field trace study in a large treatment pond [17]. A fluorescent trace is used to highlight the spatially variable nature of the flow field associated with patches and borders of vegetation. The trace indicates the preferential flow routes around the more dense vegetation elements. The majority of the flow is deviated around the vegetation and can lead to the generation of vortices along the shear layer interface.