Figure 1: Location of the development

Nelly Bay on North Queensland’s Magnetic Island (Figure 1) has been the focus of much controversy in relation the development of a State government funded ferry terminal to replace the aging Picnic Bay Jetty and a commercial residential precinct for more than 15 years.

The Nelly Bay Harbour development at is now complete and was officially opened by the Premier of Queensland, the Honourable Peter Beattie on 12 September 2003.

The initial construction at the Nelly Bay site commenced in 1988, that project was to construct and operate a marina. However, the collapse of the financial institution which was funding the development meant that the project was abandoned after being only partially constructed (see Figure 2).

The proposal was subsequently taken over by the Queensland Government and was substantially modified from the original proposal. Amendments included (with the development now reflecting these); a harbour, ferry landing pontoon, boat ramp, barge ramp and residential and commercial properties adjacent to the Great Barrier Reef Marine Park.

Figure 2: The abandoned development site as it appeared in January 2000	Figure 3: The Harbour site as it appeared at 4 June 2003.

There was intense scrutiny of the decisions associated with allowing the developments at Nelly Bay to proceed. The project underwent:

• a Public Environment Report and an Environmental Impact Statement,
• a Commonwealth appointed independent review (the Whitehouse Review), and
• two Administrative Appeal Tribunal decision reviews.
  

The major works associated with the development within the Marine Park were completed in December 2002. Works to satisfy permit requirements including the re-establishment of water flow under the breakwater bridge were completed by June 2003. The last requirement for the approval of the Harbour Operational Plan (Environmental Management Plan) was provided on 28 August 2003.

Environmental Impact Management

Figure 4: Flow chart of management regime

The project’s effect on the environment is managed using a team approach involving a number of government departments, the developer and independently contracted companies. Some of the environmental impact management strategies that have been implemented include:

• an Environmental Impact Management Plan
• full-time Environmental Site Supervision
• an innovative, risk responsive reactive monitoring program and
• an environmental bond.

The main elements of the Environmental Impact Management Plan for the Nelly Bay project were:

• a defined reporting structure
• details of construction methodologies
• performance indicators for construction and environmental parameters
• identified management actions for incidents should they occur
• contingency plans.
  

Figure 5: The structure of the monitoring program

The Environmental Site Supervisor (ESS) was independently contracted after a competitive tender process was conducted. The holder of this position had the power to cease works that cause, or have the potential to cause, harm to the environment.

The monitoring program was designed to detect environmental impacts as they occur. The program has a cascading design. This is primarily to ensure that the risks of unacceptable environmental impacts are minimised while avoiding unnecessary monitoring requirements. Essentially each parameter has two trigger levels which lead to identified management responses including increased vigilance in monitoring and/or ceasing of works that cause impacts. 

The core component of the program over the last year has been Discharge Monitoring. This monitoring continually provided data on the quality of the waters being discharged from the construction site whilst the dry excavation works were being conducted. Water quality remained the key monitoring parameter for works whilst dredging of the access channel to the harbour occurred.

The structure of the reactive monitoring program ensured that the size, intensity and cost of the monitoring program reflects the environmental risks associated with construction management.

Impacts as a result of construction works were controlled using this reactive monitoring structure, to ensure the protection of the ecosystem of the Great Barrier Reef Marine Park and World Heritage Area.

Figure 7: Fibre-web slings carefully placed under the Porites bommie for lifting.

The relocation of corals

One of the exciting elements to the project was the relocation of a number of Porites coral bommies.

Porites is a genus of coral that exhibits a number of different forms, one of which is that of large massive colonies. A number of these colonies were situated in the path of the proposed access channel to the harbour. Rather than destroy these corals the decision was made to attempt their relocation.

The relocation exercise was hugely successful. It was conducted by commercial divers with the use of a barge-mounted crane with slings around the protruding edges of the bommies. The bommies were lifted and transported through the water and placed carefully in nearby locations of similar substrate, depth and conditions as were experienced by the corals in their original locations.

Checks on the health of these relocated corals following the completion of marine works indicates that all relocated colonies remain in good health.

Silt curtaining experiences

One of the construction elements of the project was the dredging of the access channel to the harbour. Sediments produced by dredging may pose a risk to adjacent coral reefs through deposition of sediment and light reduction. Silt curtains were installed as a safety measure and physical barrier to protect the reefs from sediment prior to the commencement of dredging. The curtain proved very effective in containing the sediment disturbed from dredging.

Although a series of temporary piles were driven to secure the curtain, during installation the silt curtain billowed out and caught on adjacent corals. Some material from the curtain became detached and entangled on corals causing some damage adjacent to the access channel.

Two types of damage occurred. Firstly, shredded fibrous material from the silt curtain enmeshed the corals; and secondly, some corals suffered structural damage including abrasion from loose curtain rubbing on surfaces of the coral, and physical impacts of broken tips and branches on staghorn and plate colonies.

Figure 8: The silt curtain is deployed below the yellow float-line. You can see the clear outer water distinctly separated from the turbid, sediment-filled water on the inner side of the curtain where the barge-mounted excavator is working.	Figure 9: Acropora colony entangled in silt curtain lining. Situated roughly 6 m from curtain. 3.5 m depth.

The developer was required by the GBRMPA to implement a clean-up program for the corals. The process was a delicate and time-consuming one, since it was important to remove the fabric without breaking the coral. The fibrous material was cleaned-up by hand, by a team of SCUBA divers over a period of more than 500 hours at a cost to the developer in the order of $AU30, 000.

Since November 2001 several silt curtain configurations have been deployed, their deployment was generally confined to the more sheltered area closer to the entrance of the harbour.

The silt curtain configurations included:

1. Open ended - silt curtains along side of channel only
2. Enclosed - silt curtain enclosing all dredging works
3. Staged - smaller area of the enclosed slit curtain were maintained to minimise likelihood of failure
4. Box silt curtain - deployed (8m by 6m) with chains at approximately 2.5m depth and on the channel floor to ensure the curtain hung vertically.

What we have learned from this development

There are many things have been learnt from this project. As with building a house, major construction projects may “blow out” in terms of the time and cost associated with construction. It has been important to maintain sufficient flexibility in the environmental management regime to contemplate amendments throughout the development.

Silt Curtains

Silt curtains proved a very effective means of preventing silt mobilisation. It is vital that they are adequately secured to the substrate and are made of material appropriate to the prevailing weather and construction environment.

During the later stages of dredging, the contractor requested to undertake dredging in the vicinity of the fringing coral reef without a silt curtain. It was proposed that the silt curtain slowed down dredging operations, particularly in rough weather conditions. A “box” silt curtain arrangement was decided upon for use in this instance, however because of the small size of the structure and the inability for the excavator operator to “feel” the sides of the box silt curtain, the material was torn on a number of occasion requiring work to cease whilst repairs were undertaken.

Dredging methodologies

The dredging methodologies used at the Nelly Bay Harbour site to attain design specification were proposed by the principal contractor and not the Management Agencies. The variety of methodologies trailed appears to indicate that an overall dredging plan was effectively put into place prior to the commencement of dredging, with the original dredging plan indicated that dredging would be undertaken in three (3) bouts of three (3) days. However, in fact, the dredging of the Harbour Channel was completed after more than 382 days of dredging, over more than 19 months. This was not contemplated in the original overall dredging plan.

Bucket Excavator

Initial access channel dredging was undertaken using a barge mounted bucket excavator. This methodology proved too slow and inaccurate in the conditions prevailing at Nelly Bay. That method also was shown to produce significant amounts of turbidity that required further management.

Cutter Suction Dredges

A cutter suction dredge was utilised to attempt to level out some of the remaining height points in the channel and to remove some of the sediment that had built up within the silt curtain enclosures. However, the machinery that was brought onto site proved to be not powerful enough to adequately remove the substrate and also was found to be unstable in high wind conditions at Nelly Bay.

In the final stages of dredging a more powerful cutter suction dredge was brought to site to remove all accumulated sediment from the harbour channel. This method of “clean up” proved to be successful.

Bed Levelling

A bed leveller was used in an attempt to “remove” high points from within the harbour channel. This proved to be ineffectual on the first attempt and required further work with the bucket excavator to ‘soften’ up the substrate so that it could be moved with the blade. The bed leveller was used for periods of less than three hours at any one time. Monitoring of turbidity though this activity indicated that plumes were intense, however they were found to dissipate rapidly. If bed levelling was to be considered as a dredging methodology that was to be used more frequently, greater restrictions on turbidity management would be required.

Summary

The Environmental Management Regime at Nelly Bay, including the Impact Monitoring Program, has effectively protected the environment. Corrective actions were initiated on over 70 separate occasions to prevent damage to the adjacent reef. There is no evidence to suggest that the reef outside the construction buffer zones in Nelly Bay and Geoffrey Bay have suffered any damage from construction works over the 28 months of construction. Given the proximity of the reef habitat to the construction site this is a very significant achievement.

More information

Following is a list of publications available on the Nelly Bay Harbour Development. The GBRMPA Library Services can assist you in locating a copy of these works

• Environment Australia and Queensland Environment Protection Agency (1999) Environment Assessment Report Nelly Bay Harbour Development, Magnetic Island, NQ
• Honchin, C (2001) IN Proceedings: Coasts and Ports 2001. The 15th Australasian Coastal and Engineering Conference. The 8th Australasian Port and Harbour Conference. 25-28 September 2001. Marriott Resort. Gold Coast, Queensland, Australia.
• Stafford-Smith MG, Kaly UL, Choat JH (1994) Reactive monitoring (short-term responses) of coral species. In: Benson LJ, Goldsworthy PM, Butler IR, Oliver JK (eds) Townsville Port Authority capital dredging works. 1993: Environmental monitoring programme. Townsville Port Authority
• Voisey, C and Apelt, C. (2001). Recent Dredging Projects in Sensitive Areas in Queensland. CRC for Sustainable Tourism. 213 pp.
• Whitehouse, JF (1992) Review of the Magnetic Island Marina Development