Author(s): Eric M. Valentine; Philip J. Totterdell
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Keywords: Estuaries; Contaminants; Hydrodynamics; Modelling; Tropical; Macro-tidal
Abstract: A study modelling effluent dispersion is underway for Darwin Harbour, a large macrotidal tropical estuary. The behaviour of contaminants released from sewage outfalls needs to be assessed for licensing requirements. The RMA suite of models (in particular RMA-10 and RMA-11) has been applied using a previously developed model mesh. RMA-10 is a three dimensional finite element hydrodynamic model while RMA-11 solves the advection and diffusion equations in three dimensions for defined contaminants given previously determined hydrodynamic results. Initial studies have focussed on a notional conservative contaminant and model calibration has been undertaken using previously performed dye studies from the sewage outfalls of interest. Some mesh refinement has been required. The flow field is produced for 30 day periods from RMA-10 using tidal data. The contaminant is then released into the flow field and dispersion determined over the modelling period using RMA-11. Visualisation of results has been achieved using maximum concentration plume maps, time plots and plume animations. Areas having concentrations greater than half the regulatordefined trigger values have been determined for the notional conservative contaminant. These affected ‘mixing zones ’ are largest in area (3 to 4 km2) for the Ludmilla and Palmerston outfalls. Berrimah and Larrakeyah outfalls have respectively one and two orders of magnitude lower maximum contaminant concentrations. The affected areas are very small for these two outfalls. Current modelling is for two dimensional elements. However the study will be extended to three dimensions in future work.
Year: 2007