Sydney Deepwater Outfalls: In Situ Observations of Plume Characteristics

The NSW Environment Protection Authority has conducted a series of five experiments, in-conjunction with the Australian Nuclear Science and Technology Organisation, Australian Water and Coastal Studies Pty Ltd and University of New South Wales, to investigate the dispersion of effluent discharged from Sydney's new deep water sewage outfalls. A combination of Conductivity/Temperature/Depth (CTD) and radioisotope techniques was successfully used to define near and far field plume characteristics. Ambient ocean conditions were monitored during each experiment. Experimental conditions included both surfacing and submerged effluent fields, with one labelled submerged field detected 35 km downstream from the outfall. Initial effluent dilutions were typically between 1:200 and 1:1300 with good agreement between dilution estimates based on CTD and radioisotope techniques.