Port Douglas entrance channel reconfiguration investigation

Port Douglas Boat Harbour is one of eleven state boat harbours strategically positioned along the Queensland coast. The harbour provides sheltered moorings for recreational and commercial boating and supports a range of activities vital to the region's economy. Periodic maintenance dredging of the navigation channels is required to remove accumulated sediment and preserve the overall function of the harbour. The Department of Transport and Main Roads (TMR) sought to investigate options to reduce the frequency of dredging events within the harbour. The current long-term dredge material management strategy includes a land-based disposal facility which is accessed by 5.5 km of temporary pipeline with booster pumps across saltmarsh and wetland areas. On this basis, a reduced dredging frequency would not only reduce potential environmental impacts in the dredge area and along the pipeline route, but also generate significant cost savings to the State. To achieve this, KBR investigated options for amending the entrance channel configuration, width and/or depth, to reduce the overall frequency of maintenance dredging. The investigation covered five primary elements: 1. Detailed review of historical entrance channel siltation trends. 2. Development of wave, hydrodynamic and sediment transport models to evaluate infill rates. 3. Marine sediment sampling to support current and future dredging needs and assessment of sediment characteristics. 4. Ecological mapping of habitats within and surrounding the entrance channel to confirm the potential extent of impacts associated with channel reconfiguration options. 5. Assessment of the costs and benefits of each option to determine if or what options are viable and offer merit to the State if implemented. This paper draws on the outcomes of the coastal modelling assessment and environmental investigations and demonstrates that reconfiguration of the entrance channel results in an overall reduction of maintenance dredging frequency and, in turn, minimises the potential for associated environmental impacts and costs to the State.