HYDRAULIC TRACER STUDIES IN A PILOT-SCALE SUBSURFACE FLOW CONSTRUCTEDWETLAND

Current design procedures for Subsurface Flow (SSF) Wetlands are based on the simplifying assumptions of plug flow and first order decay of pollutants. These design procedures do yield functional wetlands but r esult in over-design and inadequate descriptions of the pollutant remo val mechanisms which occur within them. Even though these deficiencies are often noted, few authors have attempted to improve modelling of e ither flow or pollutant removal in such systems.Consequently the Oxley Creek Wetland, a pilot scale SSF wetland designed to enable rigorous monitoring, has recently been constructed in Brisbane, Australia. Trac er studies have been carried out in order to determine the hydraulics of this wetland prior to commissioning it with sealed sewage. The trac er studies will continue during the wetland's commissioning and operat ional phases. These studies will improve our understanding of the hydr aulics of newly built SSF wetlands and the changes brought on by opera tional factors such as biological films and wetland plant root structu res. Results to date indicate that the flow through the gravel beds is not uniform and cannot be adequately modelled by a single parameter, plug flow with dispersion, model. We have developed a multiparameter m odel, incorporating four plug flow reactors, which provides a better a pproximation of our experimental data. With further development this m odel will allow improvements to current SSF wetland design procedures and operational strategies, and will underpin investigations into the pollutant removal mechanisms at the Oxley Creek Wetland. (C) 1997 IAWQ . Published by Elsevier Science Ltd.