Environmental Monitoring and Assessment

, Volume 186, Issue 10, pp 6107–6125 | Cite as

Modelling the dispersion of treated wastewater in a shallow coastal wind-driven environment, Geographe Bay, Western Australia: implications for environmental management

  • Ryan J. K. Dunn
  • Sasha Zigic
  • Glenn R. Shiell


Numerical models are useful for predicting the transport and fate of contaminants in dynamic marine environments, and are increasingly a practical solution to environmental impact assessments. In this study, a three-dimensional hydrodynamic model and field data were used to validate a far-field dispersion model that, in turn, was used to determine the fate of treated wastewater (TWW) discharged to the ocean via a submarine ocean outfall under hypothetical TWW flows. The models were validated with respect to bottom and surface water current speed and direction, and in situ measurements of total nitrogen and faecal coliforms. Variations in surface and bottom currents were accurately predicted by the model as were nutrient and coliform concentrations. Results indicated that the ocean circulation was predominately wind driven, evidenced by relatively small oscillations in the current speeds along the time-scale of the tide, and that dilution mixing zones were orientated in a predominantly north-eastern direction from the outfall and parallel to the coastline. Outputs of the model were used to determine the ‘footprint’ of the TWW plume under a differing discharge scenario and, particularly, whether the resultant changes in TWW contaminants, total nitrogen and faecal coliforms would meet local environmental quality objectives (EQO) for ecosystem integrity, shellfish harvesting and primary recreation. Modelling provided a practical solution for predicting the dilution of contaminants under a hypothetical discharge scenario and a means for determining the aerial extent of exclusion zones, where the EQOs for shellfish harvesting and primary recreation may not always be met. Results of this study add to the understanding of regional discharge conditions and provide a practical case study for managing impacts to marine environments under a differing TWW discharge scenario, in comparison to an existing scenario.


Outfall Water quality modelling Hydrodynamic BFHYDRO WQMAP Bunbury 



The authors would like to thank RPS ASA for access to the modelling software and program code. Philip Kindleysides (PK) kindly dedicated his own time to prepare the map, which is much improved over the original. The authors are also thankful to the Water Corporation of Western Australia for providing current profiler and water quality data in addition to kindly allowing the publication of this article. This study benefited greatly from data collected as part of the Bunbury Ocean Outlet Monitoring (BOOM) and the Perth Long-term Ocean Outlet Monitoring (PLOOM) programs undertaken since 2002 and the mid-1990s, respectively.


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Copyright information

© Springer International Publishing Switzerland 2014

Authors and Affiliations

  • Ryan J. K. Dunn
    • 1
  • Sasha Zigic
    • 1
  • Glenn R. Shiell
    • 2
    • 3
  1. 1.RPS APASA Pty. Ltd.Gold Coast CityAustralia
  2. 2.BMT Oceanica Pty. Ltd.PerthAustralia
  3. 3.School of Plant Biology (Botany M090)University of Western AustraliaPerthAustralia

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