A Field Study for Calibration of a Water Quality Model for Darwin Harbour

Hydrodynamic and water quality models provide a tool for environmental management and infrastructure planning in Darwin Harbour, a tropical estuary located in northern Australia. These models are relied upon by both private industry and government for planning and environmental problem solving. A validation study using a fluorescent tracer and a number of drogues was carried out in order to verify and calibrate the models. An Acoustic Doppler Current Profiler was also deployed close to the outfall locations for the period of the study. The tracer and drogues were released on two consecutive days and at two locations corresponding to a proposed waste water outfall extension route. The tracer was released at different depths on each day and the drogues tracked the subsurface current at 1.5m depth. The movement of the tracer plume body differed somewhat to the drogues' paths, revealing a time lag in near field vertical mixing close to the surface. Darwin's large tidal range was thought to generate rapid vertical mixing, however field studies in this area have not been carried out previously. This study confirms that 2-D modelling is appropriate to characterise the vertical mixing in the study area for the proposed waste water outfall.