The hydraulic efficiency of fringing versus banded vegetation in constructed wetlands

This paper describes a numerical model study that has been undertaken to investigate the effects of emergent fringing and banded vegetation on the hydraulic characteristics of constructed wetlands. The model study demonstrates that poorly designed wetlands with inappropriate layout of wetland vegetation can result in a significant reduction in the hydraulic efficiency of the wetland system. An empirical relationship is developed between the vegetation characteristics, the wetland shape and the hydraulic efficiency of the system. The relationship developed allows wetland designers and managers to combine computationally simple continuously stirred tank reactor models of the wetland system with long-term hydrologic analysis to determine the impacts of different design strategies. This relationship also indicates that the hydraulic efficiency will not be significantly influenced by the length-to-width ratio for heavily vegetated wetlands where short-circuiting occurs. The aim of the study has been to aid designers of constructed wetlands by developing a qualitative understanding of the hydraulic effects of wetland vegetation and wetland shape on the hydraulic efficiency of the system.