Date of Award

1995

Document Type

Thesis

Publisher

Edith Cowan University

Degree Name

Bachelor of Science Honours

Faculty

Faculty of Science, Technology and Engineering

First Supervisor

Dr Paul Lavery

Abstract

This study was conducted to review effective design criteria for constructed wetlaads treating urban stormwater and to assess the design features of local constructed wetlands in relation to the theoretically ideal design features. The study was generated out of Water Authority of Western Australia (WAWA) concern that existing inconsistent design criteria may result in constructed wetlands not meeting contaminant removal objectives. Three components to the study involved: design criteria compiled from a critical review of relevant literature, field assessment of selected sites with significant differences in design, and a design critique of those sites based on the compiled design criteria. The sites selected were Bartram Road and Hird Road wetlands on the South Jandakot Drainage Scheme and Russell Street wetland on the Bayswater Main Drain, all in the Perth Metropolitan area. Reporting of current constructed wetlands in journal literature was limited and the projects that were published reported widely ranging designs and performances. There was not a single constructed wetland project reviewed that satisfied all of the design criteria and this was concluded to be the major contributing factor to the reported inconsistent performances of constructed wetland systems. Assessment of flow regimes at the wetland sites using fluorometer analysis of Rhodamine WT tracer dye showed that the flow path in each of the wetlands was short-circuited, significantly reducing theoretical residence times. Performance evaluation at each wetland analysing the difference between import nutrient loads and export loads over a three day period showed that none of the wetlands met their design phosphorus removal objectives for the study period. All sites exported net Total Phosphorus (TP) and Bartram Road was the only site to retain net Total Nitrogen. There was a dramatic variation in daily contaminant removal efficiency at all sites over the three days. Given that the design critique revealed significant flaws in the individual design criteria the poor performance of the study site wetlands was not surprising. The study concludes that there is effective design criteria for contaminant removal from stormwater. However, it is not being implemented as accepted practice. For this reason it is recommended that the stormwater management agencies formalise the design criteria researched in this study and persist with constructed wetlands as a stormwater treatment strategy.

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