Hydrodynamic and sediment plume modelling in a macro-tidal estuary

A technical study was carried out to develop a methodology to model and analyse the hydrodynamics, wind waves, erosion and accretion patterns in Darwin Harbour for the baseline, present day bathymetry and coastline configuration and after the introduction of the project design modifications associated with dredging operations. A curvilinear, three-dimensional Delft3D hydrodynamic model was developed to properly describe the modelling domain and oceanographic processes within the harbour. The Delft3D modelling system was also used to model sediment transport as a result of the proposed project dredging operations. For each modelling scenario, Delft3D-Flow, coupled with the Delft3D-Wave model, was run for a one year period to realistically reproduce the hydrodynamic, wind and wave conditions representative of the wet, transition and dry seasons. Based on the modelling results, an assessment of potential changes to tidal circulation, wave fields and erosion and accretion patterns ensuing from the proposed development was undertaken. The main advantage of the adopted approach is based on realistic representation of the modelled hydrodynamic fields, which act as driving forces for sediment transport processes in Darwin Harbour. Using the time- and space-varying current fields over a long time allowed seasonal variability in the hydrodynamic regime and wind and wave conditions to be taken into account.