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Josef Hargrave

Global foresight manager

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Optimisation tool for wastewater outfall locations

Optimisation tool for wastewater outfall locations

Focus Area

Digital, Water


Digital Environments, Public Health Engineering, Resource and Waste Management, Stakeholder Engagement, Water





Wastewater discharges to estuarine and ocean areas have a significant impact on marine ecology and the coastal environment, as well as the potential to endanger human health if an outfall is poorly positioned. The environmental impact of an outfall depends on factors such as the proximity of the discharge location to environmentally sensitive areas and bathing beaches, the level of treatment, the hydrodynamic conditions, and dispersion potential. In assessing the discharge location, it is also important to consider the economic viability of the project. Placing a wastewater discharge location away from sensitive areas reduces the risks, but it could also increase the capital and operating costs.

The traditional approach to evaluating potential discharge locations is based on manual iteration of the discharge location, simulated using numerical hydrodynamic and water quality models. The outputs are analysed based on criteria including acceptable impacts and costs. Setting up and running the simulation model requires the preparation of the model and analysis of the results, and this is a relatively time-consuming process.

This project developed an optimisation tool that would quickly identify potential discharge locations based on a set of outfall performance indicators. It takes into account user-defined criteria such as outfall dispersion, cost of construction, accumulation near sensitive areas, and no-go areas such as shipping lanes. The user sets up a base hydrodynamic model and identifies constraints relevant in decision-making and evaluation. Based these inputs and factors, optimised discharge locations within the area of interest can be determined.

Key Findings

The tool uses a sequential staged approach for analysis and optimisation:
– applying a GIS (geographical information system) to spatially identify any sensitive areas that should be explicitly excluded, for example special habitats, aquatic migratory routes, water intakes, and so forth;
– hydrodynamic analysis addressing bathymetry and ambient currents, to identify shallow zones and potential ‘hot spots’;
– analysis of dispersion processes and the potential for accumulation near sensitive areas;
– for the set of candidate locations identified via the preceding three steps, assess the distance of the outfall from the treatment plant and the capital (CAPEX) and operating (OPEX) costs for each location;
– finally, undertaking a detailed analysis for the location that has been assessed the most economic.

The project team applied the tool in a case study of the Moreton Bay region in Queensland, Australia. Using the staged optimisation approach, the team relatively quickly identified a potential area with advantageous conditions, for which further, in-depth analysis could be directed.

The methodology can also be expanded to assessment of outfalls for desalination plants or other types of water discharge that have similar constraints.



The project developed a methodology that can give stakeholders such as water utilities and industrial firms greater confidence in their outfall solutions.  By implementing automation, the approach lowers the cost of delivery, without diminishing confidence in the solutions obtained.  Until now, no such tool has existed in the water industry.



Protecting waterways has historically been a contentious issue.  Waterways usually become increasingly degraded as populations grow, while those populations are becoming increasingly aware of the importance of protecting ecosystems.

Discharges from municipal wastewater treatment plants and other ‘point sources’ can have a significant impact on marine ecology and the wider environment. The owners of these discharges are under pressure to address this during economic feasibility and environmental approvals of their projects. Unless the optimal location for the outfall is identified, the environment could be unnecessarily damaged.

Through this project, Arup has developed a ground-breaking tool that can quickly help to identify optimal locations for wastewater discharges in marine waterways.   The tool can reduce the risk of unduly damaging the ecology of waterways, reduce potential dangers to human health, and assist water companies in considering the economic impact of their plans.