Trimarchi and Keane, 2007:

"Ports Corporation of Queensland (PCQ) completed major capital dredging works at the Port of Hay Point, Queensland in October 2006. Initial capital dredging totalled almost 9,000,000 million cubic metres of seabed material. Implementation of the project followed the completion of a detailed Environment Impact Statement (EIS) and Environmental Management Plan (EMP).

The project is located within the Great Barrier Reef World Heritage Areas and partially within the Great Barrier Reef Marine Park. A number of sensitive environmental habitats, including fringing coral reefs are located in close proximity to the Port at Round Top Island and Victor Islet.

The development of the EIS and EMP was undertaken in close partnership with approval agencies to ensure all environmental issues were addressed within the context of the project and sensitive environment in which it was to be undertaken, but also having due regard to the practicalities of undertaking the works. An important outcome of the approvals process was that the project EMP (GHD 2006a) identified engineering, technical and economic constraints which had been identified at the commencement of the EIS process and considered throughout the assessment.

The EMP outlined mitigation strategies to protect flora, fauna, water quality, cultural heritage and the social environment, and detailed integrated and innovative monitoring programs to be undertaken to assess potential environmental impacts and investigate long-term effects (GHD 2006a). The EMP formed the basis for approvals and management of the project.

The monitoring program was designed to enable gradual reduction in monitoring intensity, if environmental impacts were demonstrated to be below predicted levels. This maintained the focus on environmental outcomes rather than proceeding with excessive monitoring.

The EMP included detailed water quality and coral condition monitoring programs as well as a validation program for hydrodynamic modelling. Water quality monitoring was primarily undertaken through the use of remotely accessed telemetry based water quality loggers. The TSS trigger value for the project was 100 mg/L for a period of at least six continuous hours. An assessment of all TSS data recorded pre-dredging, during dredging and post-dredging identified a total of 31 water quality trigger exceedences at Victor Islet and none at Round Top Island.

All exceedences at Victor Islet were recorded during dredging and post-dredging. Six exceedence events were recorded during the dredging period, with a maximum duration of 20.6 hours and a total of 21 exceedences were recorded during the post-dredging period (38.2 hour maximum duration).

Coral condition monitoring undertaken showed evidence that sediment deposition associated with the migration of the dredge plume occurred at both Round Top Island and Victor Islet. This deposition resulted in damage to some corals between three and six months after the start of dredging, with a maximum of about 4 per cent (Round Top Island) and 6.5 per cent (Victor Islet) of corals showing some patches of mortality.

Whilst it was considered that the measurement of coral bleaching does not provide a significant indicator for dredge impact, it assists with the ‘big picture’ consideration of coral health and demonstrates what is occurring regionally. Therefore bleaching should be investigated pre and post-dredging. However it is uncertain what mucous production information (from Porites) indicates about coral health, so it may be worth reviewing whether this parameter should be measured in the future.

The post dredge survey conducted six months following completion of dredging repeated the April 2006 baseline survey. The nominal but not significant reduction in hard coral cover at Round Top Island and Victor Islet since the 2006 baseline survey was 1 peer cent and 3 per cent respectively similar to the reduction recorded at the Slade Islet reference location (1 per cent) and much less than the significant 20 per cent reduction at the Keswick Island reference location. The EIS indicated that a reasonable conservative expectation for coral mortality due to the impacts of the dredge plume might be 16 per cent live coral cover at Round Top Island, with mortality at Victor Islet being unspecified. Dredging activities do not appear to have influenced overall percentage coral cover at the impact locations during the dredging program
by more than a fraction of 1 per cent.

The validation of the hydrodynamic indicated that the model generally performed well when comparing the predicted TSS (above background)
concentrations against measured TSS concentrations. For Round Top Island, there was good agreement between predicted and measured TSS over the whole simulation period. For Victor Islet, the predicted TSS concentrations compare well against the measured values for low
TSS concentrations but less well against the higher TSS concentrations. Shallow depth, wind driven re-suspension and poor representation of actual background concentrations at Victor Islet are factors as to why the model does not ‘capture’ the high TSS concentrations.

Management of the dredging program was overseen by a Management Reference Group (MRG) comprising representatives of each of the approval agencies for the project. Community representatives who had been involved in the development of the EIS and EMP were also kept informed through the Technical Advisory and Consultative Committee.

A lessons learned workshop was undertaken after the completion of dredging to review project outcomes. The workshop was attended by MRG
members as well as coral, seagrass, hydrodynamic modelling and water quality specialists involved throughout the project.

The workshop reviewed all aspects of the project from approval processes through to implementation and environmental outcomes. From the three key regulators providing conditions of approval for the project, the implementation of the EMP was generally seen as a positive
outcome of the integrated approval. It was noted that this project was a one-off and did not result in any significant environmental impact.

Overall, the project was able to be successfully undertaken and achieved the environmental goals set in the EIS and EMP with no significant environmental impact occurring. The outcomes of the monitoring program reinforcing the link between the investigations and findings of the EIS and the effectiveness of the monitoring programs set by the EMP and implemented during works."

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Citation and/or URL

Trimarchi, S. & Keane, J. Port of Hay Point apron areas and departure path capital dredging project: environmental review, Ports Corporation of Queensland Limited, EcoPorts Monograph Series: 24, Brisbane

Spatial Coverage

Hay Point

Temporal Coverage

2006-2007

Update Frequency

Not applicable 

Other Information

None