摘要：

In the past five years six major seawater reverse osmosis desalination plants have been built to serve Australias largest coastal cities, with smaller desalination facilities proposed for mine sites and remote towns. With strict brine dispersion criteria imposed by Australian Environmental Protection Agencies, a range of modelling tools have been used to develop engineering solutions. This paper presents the use of three dispersion prediction tools, with reference to ease of use and accuracy. The Roberts empirical mixing model was used by Sinclair Knight Merz to predict near-field mixing for the concept and detailed design of the Gold Coast and Sydney desalination plants, and for tender designs for Melbourne and Adelaide desalination plants. While flexible and rapid in application, drawbacks related to model simplicity include the inability to analyse complex interactions between plumes from multiport structures. However, a yearlong monitoring program recently completed at the Gold Coast desalination plant has shown that the predicted mixing ratios have been met and exceeded for a range of actual ocean conditions and plant flows. In addition, brine plume dynamics for the Adelaide and Melbourne desalination plant tender designs were modelled by computational fluid dynamics (CFD) using ANSYS FLUENT software. When calibrated to empirical data the model provided an acceptable model result, though somewhat under-predicting mixing in the near field. In the mid- to far-field, the CFD model did not replicate the expected decay of turbulent mixing recorded. With these limitations, FLUENT can be used to give an indication of multi-plume dynamics and interactions in both calm waters and under the influence of currents. For far field plume dispersion modelling, Sinclair Knight Merz has engaged the specialist oceanographic modelling services of GEMS. Given brine plume data, and historic current and meteorological data, GEMS GCOM3D software can be used to produce a continuous animation of brine plume fate, including imagery indicating the percentage time where plume dispersion may not meet regulatory conditions. These three modelling techniques have allowed desalination plant marine outfalls to be designed with confidence that the required dispersion criteria can be met.

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