Western Harbour Tunnel is a NSW Government Initiative by Transport for NSW (formerly Roads and Maritime Services) to provide additional road network capacity across Sydney Harbour.
The preferred design option is an immersed tube tunnel (IMT). The IMT would involve dredging and temporary maritime structures (cofferdams) to allow connection between the IMT units and the land tunnels.
Sydney Harbour is a sensitive waterway within the heart of Sydney having significant ecological and scenic values, and supporting important commercial shipping and recreational boating activities. It was necessary to evaluate whether the IMT design option could be carried out in an environmentally acceptable manner.
This talk would outline the studies undertaken to develop the dredging work methods and assess the potential impacts of the works on the environment. It would include:
- characterisation of the material to be dredged which includes soft silty clays, silty sands, stiff/hard clays and rock;
- selection of dredging work methods including plant and equipment, operating methodology, schedule, and environmental controls. Dredging plant and equipment includes backhoe dredger (BHD), trailing suction hopper dredger (TSHD), cutter suction dredger (CSD), non-propelled (dumb) barges and self-propelled split hopper barges (SHBs);
- selection of methods of disposal of dredged material (unconfined sea disposal off the Sydney coastline and land disposal);
- development of a three dimensional (3D) hydrodynamic and sediment transport model of Sydney Harbour;
- modelling of the hydrodynamic impacts due to temporary maritime structures including changes to ebb tide and flood tide currents, and potential for impact on shorelines and navigation;
- modelling of the dredge plumes associated with the different plant and equipment and material types, including consideration of appropriate source terms to include in modelling as a function of work method and material characteristics.
Greg Britton - Technical Director, Royal HaskoningDHV
Deputy Chair, PIANC Australia & New Zealand
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