Gladstone Western Basin dredging project

Challenge

Faced with the global commodity boom since 2005 and inadequate investment in its ports and harbours the last decade, Australia felt the need to catch up. Both on the east- and west coast of the continent, this had led to some of the biggest marine infrastructure projects that are being executed in the southern hemisphere. The development of the Western Basin area in the multi-commodity- and industrial port of Gladstone is just one of these mega-projects.

The scope of the Gladstone Western Basin contract is both enormous and challenging.
In 2011, Dredging International was assigned the Western Basin Development  to facilitate the use of the Gladstone port by three Liquefied Natural Gas Proponents (QCLNG, APLNG, GLNG) with each its own LNG plant on Curtis Island and its own LNG export terminal.  This is part of the largest LNG-developments in Australia, whereby Coal Seam Gas (methane between coal layers) that is produced in the Surat and Bowen basins in eastern Queensland is transported by pipeline over a distance of 450 km to the gas liquefaction facilities in Gladstone. In 2012, an additional scope of works was included for the expansion of the Wiggins Island Coal Export Port to take advantage of the presence of large dredging plant mobilised from overseas.

The total dredging volume for this development amounts to 25 million m3 for all channels (-13m), swing basins, berth pockets (-14m) and early handover of the Material Offloading Facilities (MOF to -7m).

Challenges included:

  • Mobilisation of a wide variety of dredging plant on very short notice and very narrow execution window.
     
  • Interface management with the existing port operations and other marine contractors involved in the construction of LNG wharves and loading platforms.
     
  • The ever present issue of high wear-and-tear gravels/clays and other heterogeneuos soils.
     
  • Finally, full compliance with stringent environmental permit conditions.
     
  • the very strict  obligations under the Dredging Environmental Management Plan, the Water Quality Monitoring Frameworkrequirements are imposed, including water quality monitoring, management of the possible acid sulphate soil, and special care for dugongs, birds, turtles, mangrove, and all other pristine habitat.
 
 

Our solution

 
 

The successful completion of two preliminary contracts in Gladstone, was instrumental for awarding the Main Western Basin Dredging project to Dredging International. In 2008, a contract was awarded for the capital dredging project to facilitate Rio Tinto’s Alumina Refinery Expansion. In 2010, a second contract was awarded for the Early Works Dredging Package to facilitate initial access to a proposad LNG site on Curtis Island.

The Main Gladstone Western Basin dredging project is of another size altogether. At one time more than 35 marine units and vessels were deployed simultaneously, and employment on site was boosted to a peak of 900.

Due to the massive scale of the works, the requirement to mobilise large number of plant and the expectations to complete the works within a short execution period, the project was carried out in joint-venture to be able to make use of all available resources from within both companies.

A network of over 20km of submerged steel pipeline was installed on the seabed to accommodate the ongoing shipping movements within the port. The suitable dredging materials were pumped through this network of pipes to the bunded reclamation area creating new areas for the development of future wharfs.

The gravels and stiff clays resulted in very high wear & tear of the soil touching parts and pipes.  This requires a thorough logistical organisation with timely order and supply of spare parts. Regular turning and/or replacement of long stretches of submerged pipelines had to be scheduled in close cooperations with the port authorties.

Selective dredging had to be carried out due to the heterogeneous nature of the soils and the limited storage capacity within the reclamation areas. Potential acid sulphate soils (PASS) were removed selectively by backhoe dredge equipment and partly disposed offshore and remaining quantities at lower levels within the reclamation area.  Suitable materials were dredged and pumped alongside the inner side of the embankments to seal the reclamation bunds and soft silty/clayey materials were pumped into silt ponds.

Prior to the start of the works, a detailed Dredge Environmental Management Plan (DEMP) was established for submission and approval by the Department of Environment and Resource Management.
The operations had to be managed in such a way to be in full compliance with all obligations under the DEMP and under the Water Quality Monitoring Frameworks. In addition, all fauna & flora monitoring and reporting requirements to be in accordance to the Flora and Fauna Management Plan.

The whole of the works was handed over well within the Client’s expectations/schedule, early access to Curtis Island was provided through the dredged material offloading facilities allowing timely commencement of the constructing of the LNG plant and the dredging operations were completed without any environmental breach of the permit conditions.

 

 

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