Environmental consciousness in dredging is a very important matter for the industry. The case of Gladstone port in Australia is a success story showing how to get the job done minimizing the impact to the environment.
Between 2011 and 2017, important investments have been made to develop the port of Gladstone in Queensland, Australia. As part of these developments, which include the construction of liquified natural gas (LNG) plants and a new coal terminal, intensive dredging operations were required.
The port of Gladstone is located near the Great Barrier Reef Marine Park, which protects a large area of the world-famous reef from damage. One of the measures in place is for commercial shipping traffic to use defined routes that avoid the most sensitive areas of the park.
For that reason, but also in view of the ecological value of animals and plants, the dredging operations had to be carried out with great care for the environment within the harbour.
The LNG plants have been established on Curtis Island in the Western Basin of Gladstone, whereas the coal terminal is at Golden Point on Wiggins Island, which lies opposite Curtis Island. The investor in the terminal is Wiggins Island Coal Export Terminal Pty Ltd (WICET), a consortium of several companies from the bulk commodity industry.
The terminal is being operated on behalf of WICET by Gladstone Ports Corporation (GPC), which already runs the two existing coal terminals in the port – RG Tanna and Barney Point.
Three dredging contracts
A number of large-scale dredging operations had to be carried out in Gladstone’s Western Basin to make the new terminals accessible for LNG tankers and coal carriers. In 2011, GPC awarded three contracts as part of the Western Basin Dredging and Disposal Project (WBDDP) to a joint venture of Van Oord Australia Pty Ltd and Dredging International (Australia) Pty Ltd (a member of the DEME group). This collaboration was given the name VODI JV.
Dredging contract one
The first contract involved Parcel 5 of the WBDDP, and included the creation of a three km long construction access channel and the berth pockets near the LNG plants on Curtis Island. In order to create the required depth of -7.5m LAT, a total of six million cubic metres of material had to be dredged.Two thirds of this has been moved to an offshore disposal site, known as the East Bank Spoil Ground, approximately 45 kilometres offshore. The remaining two million cubic metres were pumped ashore within the port area.One of the main criteria for choosing the relocation area was whether it contained potential acid sulphate soil (PASS). This has the potential to release acid sulphates by oxidation when exposed to air for more than 24 hours and needs to be stored underwater.
On Parcel 5, VODI JV deployed the cutter suction dredger (CSD) AL MAHAAR, with a total installed power of 11,224kW. It utilised the backhoe dredgers, BIG BOSS, RAZENDE BOL, HIPPOPOTES and backacter SIMSON. The grab dredger TARVOS was also chartered.
Dredging contract two
The second contract involved Parcels 1, 3 and 4 of the WBDDP, and required various channels, swing basins and bypass channels to be dredged to a depth of -13m LAT to serve the new LNG plants.
Of the 16.5 million cubic metres of material that had to be dredged, 14.5 million has been pumped ashore to a new reclamation area measuring 274 hectares. The remaining two million cubic metres have been placed in the offshore disposal site.
Dredging contract three
While the dredging works for the first two contracts were needed to make the LNG plants accessible, the third contract –Parcel 7– serves the new coal terminal. This required 2.9 million cubic metres of material to be dredged in order to create two berth pockets, an access channel and a swing basin. This was pumped into a reclamation site on Wiggins Island. The target depth for Parcel 7 was -16m LAT, which will allow the handling of vessels of up to 220,000dwt.
Workhorse TSHD ROTTERDAM
Van Oord’s 21,665m3 trailing suction hopper dredger (TSHD) ROTTERDAM has played a major role in the dredging works for these two contracts. The vessel is one of the world’s first jumbo hopper dredgers, and was built at the shipyard of Royal IHC and Van der Giessen de Noord in Krimpen aan den Ijssel (The Netherlands) in 2001.
In view of the environmentally sensitive area, overflow restrictions were applied during the dredging operations. Thanks to its large hopper volume, the ROTTERDAM was able to carry out the necessary work efficiently, despite the restriction. Other dredging equipment included the CSDs AL MAHAAR and CASTOR (total installed power 14,261kW), as well as five floating booster stations.
Protecting the environment
To minimise the environmental impact, GPC has established an extensive water quality, sea grass and environmental monitoring programme. With respect to the water quality, a wide range of parameters have been monitored, including turbidity, dissolved oxygen, pH and nutrient levels, salinity and conductivity, temperature, light (photosynthetically active radiation), chlorophyll, and metal content.
GPC and VODI JV have demonstrated that, with cutting-edge dredging equipment and the right working methods, a large dredging project such as WBDDP can be executed efficiently, even in a highly sensitive environment.