Coastal Oceanographic Processes and Numerical Modelling for the Kurnell Desalination Plant

Client: Sydney Water Corporation
Year: 2006-2007
Project Reference: 06076
WRL Technical Report: Coastal Oceanographic Processes and Numerical Modelling for the Proposed Kurnell Desalination Plant (2007/02)

As part of the NSW Government’s Metropolitan Water Strategy, desalination was proposed as an option to significantly augment Sydney Water’s drinking water supply in times of drought. A planning study identified Kurnell as the proposed location for a desalination plant.

Discharge of undiluted seawater concentrate from a desalination plant would be expected to cause environmental impacts, so it has been important to consider the design of a suitable outfall diffuser to dilute the seawater concentrate with the surrounding seawater.

Typical ocean currents offshore of Sydney

RMA-10 finite element mesh used in the investigation

The zone around the diffuser is referred to as the near-field zone. After the near-field zone, the diluted seawater concentrate is conveyed by currents in the far-field. Within a near-field zone, the buoyancy differences and turbulent momentum of the discharging jet cause the discharged seawater concentrate to rapidly mix with surrounding seawater. In a separate study, the Water Research Laboratory undertook substantial physical modelling of a seawater concentrate diffuser to achieve adequate dilutions very close to the diffuser. The results from the physical modelling of the near-field have been used in this study as input data to the numerical models that simulate the far-field dispersion of the seawater concentrate.

During the Environmental Monitoring Program (EMP) for the Sydney Deepwater Outfalls at North Head, Bondi and Malabar, complex numerical models were established to predict the fate and dilution of these deepwater outfall plumes. To improve the knowledge of the coastal processes in Kurnell, these models were refined and re-calibrated against additional oceanographic field data in the vicinity of Kurnell. The RMA-10, three dimensional, hydrodynamic and water quality models extended over the whole Sydney region including Botany Bay.

The calibrated and refined numerical models were able to address two main oceanographic issues relating to a desalination plant at Kurnell; these being intake quality and the fate of seawater concentrate discharge. These models helped confirm the locations and the designs of the intakes and outlets.