Flume Experiments for Optimizing the Hydraulic Performance of a Deep-Water Wetland Utilizing Emergent Vegetation and Obstructions

Abstract

Constructed ponds and wetlands are widely used in urban areas for stormwater management, ecological conservation, and pollution treatment. The treatment efficiency of these systems is strongly related to the hydrodynamics and hydraulic residence time. In this study, we developed a physical model and used rhodamine-WT as a tracer to conduct flume experiments. An equivalent Reynolds number was assumed, and the flume was a 1/25-scale model. Emergent obstructions (EOs), submerged obstructions (SOs), and high-and low-density emergent vegetation were placed along the sides of the flume, and 49 tracer tests were performed. We altered the density, spatial extent, aspect ratio, and configurations of the obstructions and emergent vegetation to observe changes in the hydraulic efficiency of a deep-water wetland. In the cases of low-aspect-ratio obstructions, the effects of the EOs on the hydraulic efficiency were significantly stronger than those of the SOs. In contrast, in the cases of high-aspect-ratio obstructions, the improvement effects of the EOs were weaker than those of the SOs. The high-aspect-ratio EOs altered the flow direction and constrained the water conveyance area, which apparently caused a short-circuited flow phenomenon, resulting in a decrease in hydraulic efficiency. Most cases revealed that the emergent vegetation improved the hydraulic efficiency more than the EOs. The high-density emergent vegetation (HEV) improved the hydraulic efficiency more than the low-density emergent vegetation (LEV). Three cases involving HEV, two cases involving LEV, and one case involving EOs attained a good hydraulic efficiency (λ > 0.75). To achieve greater water purification, aquatic planting in constructed wetlands should not be overly dense. The HEV configuration in case 3-1 achieved optimum hydraulic performance for compliance with applicable water treatment standards.

National Large-Scale Wetland Creation in Agricultural Areas—Potential versus Realized Effects on Nutrient Transports

“…This emphasizes that there are also other factors that are important to consider for obtaining high nutrient removal in created wetlands in agricultural catchments. These can be factors related to wetland design and biological composition [33][34][35][36][37][38], as well as concentrations and form of the nutrients in inflowing water or other factors related to catchment characteristics [6,23,27,32]. Further studies are needed to identify and evaluate the important factors affecting the nutrient removal efficiency of created wetlands in agricultural catchments.…”

To Investigate the Flow Structure of Discontinuous Vegetation Patches of Two Vertically Different Layers in an Open Channel

“…In his research work, turbulence properties were investigated by applying a k-ε turbulence model. Xia and Nehal [17] and Shih et al [18] experimentally investigated the features of flow in an open channel with vegetation. They used various arrangements of vegetation and investigated hydraulic characteristics in open channel flows.…”

Tracer Experiments and Hydraulic Performance Improvements in a Treatment Pond

“…where t n is the mean residence time in [h], as shown in Equation (3), and t m is the nominal retention time in [h] calculated from the first moment of the tracer response curve [6]:…”

“…In addition, Shih et al [6] and Chang et al [14] suggested that the addition of emergent baffles could considerably alter the hydraulic efficiency in a deep-water wetland. Therefore, several baffles with different lengths, widths, and aspect ratios were modeled.…”

“…Treatment ponds are one type of artificial wetlands designed to provide multiple functions [1][2][3][4][5]. Such ponds are widely used in urban areas for storm water management, ecological conservation, and pollution treatment [6]. Degradation by microorganisms and adsorption by plants are two of the primary mechanisms for pollutant removal and degradation [7].…”