Illawarra Ocean Outfall Trial Studies

Client: Sydney Water Corporation
Year: 2007
Project Reference: 06085
WRL Technical Report: Illawarra Ocean Outfall Field Trials (2007/36)

In 2007, following a series of studies to commission the Illawarra Ocean Outfall, WRL undertook a range of additional near-field dilution trials for Sydney Water Corp. These studies were undertaken over various climatic periods to simulate the range of conditions that would be experienced on site. Three near-field tests were successfully undertaken using Rhodamine WT as a tracer and a detailed technical report was produced. This project compliments the previous near-field and physical modelling investigations undertaken for the site.

The field trials were undertaken by injecting the tracer under controlled conditions at the STP for a period of 4-6 hours. Based on predetermined calculations, the known concentration of Rhodamine WT was then diluted in the near-field. The extent of the dilutions was mapped using a fluorimeter attached to Seabird 19Plus, a differential GPS and a range of sampling equipment such as niskin bottles suspended at various depths. An ADCP and several drogues were used to determine ambient currents, while the Seabird 19Plus was also used to map salinity and temperature profiles. A second fluorimeter was suspended at a prescribed depth to assist in determining plume dilutions. Sampling was undertaken in both anchored positions and by following a series of transects.

The field results provided a wealth of information to map the plume performance and determine the performance of the outfall under a range of conditions. Importantly, the field program required in-depth OH&S and stringent QA protocols that ensured the data quality of many field instruments.