This paper considers the hydraulics of a wetland constructed by BP Oil for polishing wastewater from their oil refinery at Bulwer Island, Australia. As this open water surface flow (SF) wetland has a novel design to enhance mixing, a tracer study was performed to analyse the hydraulic flow distribution through the wetland. It is a baseline study, following construction, prior to planting. As introduction to the study, details of the wetland design are provided, together with design justification.

The volume of the wetland active zone is estimated as 70% of the total wetland capacity, which compares very favourably with the active volume expected in flat-bottomed ponds. The large amount of dispersion observed along the length of the wetland bed approaches that of a well-mixed system, supporting the claim that this novel bed structure enhances mixing. We expect to at least retain, and possibly improve the degree of mixing by alternating planted shallow zones with unplanted deep zones.

The first stage of experimental work at this wetland involves creating a baseline of hydraulic data on which to build a mass balance model of the wetlands performance. Tracer studies will be repeated on the planted, mature wetland to determine the changes to flow, which might occur in the operating system. Together with wetland performance results, these studies will underpin investigations into the pollutant removal mechanisms at BP Oil's Bulwer Island wetland.

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