Routine Sydney Deepwater Outfall Modelling

Client: Sydney Water Corporation
Year: 1992-Ongoing
Project Reference: 07035
WRL Technical Reports: Sydney Deepwater Outfalls Plume Modelling (AWACS 1996/19); Analysis of Data Provision Services during 2002 for Routine Modelling of the Sydney Deep Water Outfalls (2003/04)

Sydney Water currently employs three major sewage treatment plants to treat a large portion of Sydney’s sewage waste. The North Head, Bondi and Malabar deepwater outfalls are located approximately 3 to 5 km’s off the coast in between 40 and 60 m of water.

A data collection ocean reference station provides current, temperature, salinity and pressure data. Previously, this data was collected using termister strings, pressure transducers, salinity probes and current metres suspended beneath a bouy. This system was updated in 2005 to consist of a bed mounted ADCP (Acoustic Doppler Current Profiler) with termisters, pressure transducers and salinity probes extending through the water column from the bed to 7 m below MSL (mean sea level AHD).

This data is input into numerous models to predict plume behaviour. WRL provides numerical modelling of the outfall plumes in 3D and supplies the results to Sydney Water via the internet. This includes near-field and far-field modelling, pollutant source identification, stratified hydrodynamics, harbour and estuarine impacts and beach water quality assessment. Dilution rates are calculated in conjunction with floatable and settleable particle tracking.