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DREDGING AND THE GREAT BARRIER REEF
Hall Contracting completes dredging for new harbour adjacent to Australia's Great Barrier Reef

June 1999

Source: World Dredging Mining & Construction

Australian dredging contractor, Hall Contracting Pty Ltd has recently completed dredging at the new Mackay Small Craft Harbour on Queenland's central coast. The new harbour, which will ultimately consist of a 590 berth marina accommodating tourist vessels which service the Great Barrier Reef, has been constructed adjacent to the existing deepwater grain and sugar port at Mackay.

Construction of the new harbour precinct included:Construction of a 1,300 m dynamically stable breakwater, carried out by John Holland Construction.

Dredging of 600,000 m3 of a medium dense sand to depths of RL-4.5 m Lowest Astronomical Tide, 150,000 m3 of this material was used to reclaim a section of the foreshore for future commercial development, 350,000 m3 was pumped through two booster stations a total of 3,500 m to a new industrial estate.

Reclamation of Industrial Estate
Hall Contracting used their Ellicott® B890 14-inch cutter suction (CS) dredge "Kikilu" with a rose cutter for the 3,500 m push to the new Industrial Estate.

Two Caterpillar powered 18/16 in booster pumps were located on the line. Each booster pump station was fitted with residential grade hush kits to ensure minimal effect on the surrounding areas. A telemetry control system, developed by Hall Contracting, was used to control the two booster stations remotely from the wheelhouse of the dredge.

Inlet and outlet pressure, and engine RPM were monitored and controlled from the dredge, greatly improving dredging efficiency, fuel usage and start-up and shut down procedures. This enabled remotely controlled booster stations which also had the obvious savings in labor costs.

Environmental Issues
Being adjacent to the World Heritage Listed Great Barrier Reef Marine Park, one of the world's natural wonders, the project was strictly controlled from and environmental point of view.  Also, directly adjacent to the industrial fill area was a native melaleuca swamp supporting a wide range of protected flora and fauna species.

As such, Hall Contracting prepared a comprehensive Environmental Management Plan for the approval of the Department of Environment. This plan provided for a bunded fill area with a network of weir boxes to control the tailwater quality.

Daily measurement of quality parameters included:
*pH
*Dissolved Oxygen
*Conductivity
*Turbidity
which were carried out and documented in regular reports for the Department of Environment to audit.

Hall Contracting were praised by Mackay Port Authority for the professional finish to the fill in this area, which will form the hub of the harbours commercial and tourism precinct.

GPS Positioning Control
Both dredges were outfitted with Trimble GPS dredge positioning system linked to an automatic tide monitor. The on board computers used this real time tide monitoring in conjunction with the GPS to accurately position the cutterhead in the vertical and horizontal planes. This was absolutely critical at Mackay due to the large tide range at the harbour.

During the planning phase of the project, the area to be dredged was split into distinct zones based upon the swing area of each dredge. These areas were then entered into the onboard computers for the real time monitoring of progress.  Each dredge was then assigned its own working zone for each shift. At the end of each shift, the GPS data was analyzed automatically to determine the volume, extent and accuracy of the dredging.

Mr. Brian Hall, director of Hall Contracting, said, "The dredge mounted GPS software used in conjunction with the real time tide gauges allowed us to confidently and accurately locate the cutter head at any specific time. This was especially critical for this job given the reasonably large tidal range of 6.5 m. It also allowed us to monitor each operators performance for comparison. This saw us reach unprecedented levels of production in terms of cubic meters per hour, and coupled with the accuracy of the dredge which meant no overcut or re-dredge, the job has come in well under time and budget."

Overall, the project has been a complete success for Hall Contracting and the professionalism with which it was carried out has received praise from both John Holland Construction and Mackay Port Authority.

Other Projects
Other projects Hall Contracting are currently involved in include: *Principal contractor for Greg Norman designed Pelican Waters Golf Course at Caloundra in Queensland. *Pelican Waters canal subdivision. *Queensland Alumina tailings dam dredging in Gladstone, Queensland. www.hallcontracting.com.au

Reprinted from World Dredging Mining & Construction

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