Influence of plume advection and particle settling on wastewater dispersion and distribution

Oceanographic processes are examined and used to assess their effect on the movement and dilution of wastewater discharged from Sydney's three deepwater ocean outfalls. Such processes link wastewater discharges with observed changes in biological communities and the accumulation of contaminants in the sediments. The East Australian Current, coastal trapped waves and local winds contribute 40%, 20% and 10% respectively to the total spectral energy in the along-shore currents off Sydney. Median dilutions at the edge of the initial dilution zone range between 185:1 and 347:1. Plumes remain submerged 95% of the time, surfacing only in the middle of winter and during large storms. Negatively buoyant particles sink from the plumes and first reach the ocean floor within 10 km of the discharge location. Resuspension of the sediments due to currents occurs 2.5% of the time and due to waves 1%-4% of the time.