Modelling the marine environmental impacts of dredge operations in Cockburn Sound, WA

Fremantle Ports is proposing to develop infrastructure for a new shipping harbour in Cockburn Sound, Western Australia. The harbour project, known as Kwinana Quay, will include a large reclaimed area that will support expanding container trade. The reclamation will be created by dredging more than 10 Mm3 of sand and rock using a large cutter suction dredge. An integrated modelling study was completed to assess the impact of the expected suspended sediment plumes on the ecology of Cockburn Sound. SSFATE , an advanced sediment fate model was validated against previous dredging works in Cockburn Sound and then used to simulate the Kwinana Quay dredging program. Model inputs included hydrodynamic and wave data from external models, as well as detailed dredging, geotechnical and sediment source parameters to generate a three-dimensional total suspended solids concentration data set. The data set was processed to allow the expected impact on light attenuation to be assessed using parameters derived from site specific laboratory tests. These results were correlated to known habitat areas to translate the effect on light climate to seagrass and benthic habitat health. The effects of suspended sediment plumes on snapper spawn and larvae during the spring and summer periods were also assessed, based on the results of ecotoxicology tests conducted using replicated dredge-generated sediment.