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This paper presents the outcomes of a sensitivity study aimed at assessing suspended sediment concentrations from dredge disposal operations. The study was focused at a near-shore area of southern New South Wales. The bathymetry of the area is typical for the region with a relatively steep slope and depths up to 80 m within 5 km offshore. A curvilinear, three-dimensional hydrodynamic model was developed to properly describe the modelling domain and oceanographic processes within it.  The domain incorporated a 5-meter thick surface water layer and for a 10-meter thick near-bottom water layer, both required for further detailed assessments of suspended sediment transport and diffusion and models’ sensitivity. To provide the open-ocean boundary conditions to the three-dimensional hydrodynamic model, two sources of information were used: space varying tidal constituent data and regional-scale, three-dimensional ocean currents. It was assumed that the used open boundary forcing realistically reflected existing oceanographic conditions in the project area for the modelling period. A three-dimensional disposal plume model was then used to evaluate impact zones and exceedances from periodic dumping operations. The modelled sediments consisted of fine fractions of silt and clay. The obtained results demonstrated that using tides only, tides and wind, or currents and tides and wind as the forcing for hydrodynamic and then sediment transport models essentially changes the exceedance map configuration. The outcomes of this study emphasise that any model, independently of how plausible the forcing functions are, needs to be properly calibrated and validated based on the field monitoring data from the area of interest.

Abstract

Dr.Oleg Makarynskyy has over 25 years’ experience and extensive skills in the fields of ocean and coastal program development and project management, numerical modelling, data analysis, as well as quantitative project risk assessments. His professional history embraces climate studies using earth system models; studies of sensitivities of wave and hydrodynamic models; wind, wave and current hindcast, prediction, data assimilation, and model validation studies. In consultation with industry and public stakeholders over the course of the projects, Oleg has been designing and conducting research field campaigns, hydrodynamic and hydrocarbon spill assessments, pollutant discharge and dredging studies.