Simulating short‐circuiting flow in a constructed wetland: the implications of bathymetry and vegetation effects

Abstract

Abstract:Short-circuiting flow, commonly experienced in many constructed wetlands, reduces hydraulic retention times in unit wetland cells and decreases the treatment efficiency. A two-dimensional (2-D), physically based, distributed modelling approach was used to systematically address the effects of bathymetry and vegetation on short-circuiting flow, which previously have been neglected or lumped in one-dimensional wetland flow models. In this study, a 2-D transient hydrodynamics with advectiondispersion model was developed using MIKE 21 and calibrated with bromide tracer data collected at the Orlando Easterly Wetland Cell 7. The estimated topographic difference between short-circuiting flow zone and adjacent area ranged from 0Ð3 to 0Ð8 m. A range of the Manning roughness coefficient at the short-circuiting flow zone was estimated (0Ð022-0Ð045 s m 1/3 ). Sensitivity analysis of topographical and vegetative heterogeneity deduced during model calibration shows that relic ditches or other ditch-shaped landforms and the associated sparse vegetation along the main flow direction intensify the short-circuiting pattern, considerably affecting 2-D solute transport simulation. In terms of hydraulic efficiency, this study indicates that the bathymetry effect on short-circuiting flow is more important than the vegetation effect.

Tracer behaviour and analysis of hydraulics in experimental free water surface wetlands

“…However, published literature reveals many studies where the latter comparisons are not considered (Wörman and Kronnäs, 2005;Wang and Jawitz, 2006;Min & Wise, 2009;Keefe et al, 2010). For the present study, the consequence of such comparisons showed that Gauss-based parameter values, especially from EVWs, were generally not reliable (Table A in Consequently, these N-values were considered as unreliable compared to the ones based on measured data and also compared to the other modelled N-values.…”

“…Instead, the focus of most published wetland hydraulic studies has been comparing effects on wetland hydraulics caused by different vegetation layouts (Persson et al, 1999;Dal Cin and Persson 2000;Jenkins and Greenway, 2005) or vegetation heterogeneity levels within the same vegetation type (Wörman and Kronnäs, 2005;Kjellin et al, 2007;Min and Wise, 2009). …”

Tracer Experiments and Hydraulic Performance Improvements in a Treatment Pond

“…A number of additional studies have confirmed this finding [16][17][18]. The hydraulics of ponds and wetlands can generally be evaluated through mathematical modeling [19,20] and tracer experiments [21,22]. This study investigated the flow hydrodynamics, residence time distribution, and hydraulic performance of a treatment pond using tracer experiments and mathematical modeling.…”

Capturing Spatial Variability of Biogeochemical Mass Exchanges and Reaction Rates in Wetland Water and Soil through Model Compartmentalization

“…A common phenomenon that is observed in natural and constructed wetlands is short-circuiting of flow and formation of stagnant zones that are only indirectly available to the inflow waters (Min and Wise 2009). Such stagnant zones can offset treatment effectiveness of wetlands by reducing active volume and consequently shortening the hydraulic retention time (Kadlec and Wallace 2008).…”