The Australian port of Cairns in Queensland will undergo capital dredging under the Cairns Shipping Development Project that aims to attract larger cruise ships.
A representative for Far North Queensland Ports Corporation – better known as Ports North – told DPC that Danish dredging contractor Rohde Nielsen’s Australian subsidiary RN Dredging has been awarded the contract to dredge the waters, working together with Hall Contracting, the largest dredging company in Queensland.
The USD120 million project involves dredging to widen and deepen the existing outer shipping channel, the Trinity Inlet; upgrading the existing cruise shipping Trinity wharves 1 to 5; partial demolition of wharf 6 to allow for extension of wharf 5; and relocation and installation of new navigational aids.
From the time the Cairns Shipping Development Project was proposed in 2012, the paperwork for the environmental impact assessments and public consultations was prepared. However, a five-year hiatus ensued as the scope of the environmental impact assessment was continually revised.
The aim of widening and deepening the existing navigation channel is to allow larger cruise ships of up to 300 m length to berth at the Cairns Cruise Liner Terminal to accommodate the forecasted demand of 150 cruise ship calls through the port of Cairns per year by 2031.
Cruise travel is growing in Asia, especially with growing affluence in China. Ports such as Busan and Incheon in South Korea, besides Lyttelton and Marlborough in New Zealand, are all embarking on expansion to take in larger cruise ships.
Scope of work
Up to 1 million m3 of sediment from Cairns port’s existing navigation channel will be dredged.
Approximately 4 km of the 10 km outer channel is proposed to be widened and the inner channel widened to maintain safe navigation of ships. The channel’s declared depth will be increased by 0.5 m from 8.3 to 8.8 m. Dredging operations involve the removal of uncontaminated sediment from within and adjacent to the existing channel and placing that material on land. No dredged material will be disposed at sea.
Dredging is due to be undertaken from May to September 2019, involving the separate removal of soft and stiff clays. The soft clays, which comprise most of the material to be dredged, have poor engineering qualities with hardly any possibility of being reused. On the other hand, the hard clays have better qualities and could be reused for land development.
Two sites were identified as providing the best environmental outcomes: port land at Tingira Street, Portsmith, for the stiff clay material and the Northern Sands site for the placement of soft clay material. The Northern Sands site is a sand extraction mine, which has low environmental value and is in an area dominated by sugarcane plantations. The site has been approved for the disposal of construction material and potential acid sulphate soils. The dredged material will be delivered by barges.
The use of port land at Tingira Street for the stiff clays will allow this material to be beneficially reused as surcharge material on the land and ultimately incorporated into future land development. The stiff clay will be dredged using a backhoe dredge.
The soft clays will be dredged by a trailing suction hopper dredger and then pumped to the Barron Delta site by the dredger when moored at a temporary site, approximately 3 km offshore from the mouth of Richters Creek. A temporary delivery pipeline will transport the material from the dredge pump-out facility to the placement site, mostly through cane lands, with excess water being returned to the Barron River at the Captain Cook Highway bridge via a temporary clean tailwater discharge pipeline.
To prepare this site for the deposit of the dredged material, the existing sand mine will be expanded and a temporary flood protection bund wall put up around the placement area while the dredging takes place. This temporary flood protection bund wall will be removed at the end of the project and the remaining void in the dredge material placement area will continue to receive waste and be ultimately filled to ground level in accordance with the site rehabilitation requirements.
Ports North said that the project was planned with a firm commitment to understand the existing environment within Trinity Bay and to minimise any potential adverse environmental, social and economic impacts of the project, while maximising potential economic benefits. The port operator aimed to deliver a viable solution for Cairns, while protecting the Great Barrier Reef.
Ports North said: “The project has been designed to be consistent with the Queensland government’s key plans and strategies adopted to protect the Great Barrier Reef such as the Reef 2050 Long-Term Sustainability Plan and the Queensland Ports Strategy.”
“Considerable emphasis was placed on examining all options to minimise the amount of dredging required. After completing extensive marine studies of currents and winds in Trinity Inlet, Ports North used cruise simulation technology in collaboration with cruise ship companies and the Cairns Regional harbour master to make the most effective use of the channel design while providing additional access for cruise ships up to 300 m.”
Advanced water quality and sediment transport computer modelling has also been undertaken to consider a range of potential impact scenarios from best to worst case. A conservative approach has been adopted to ensure that risks are comprehensively identified and appropriate strategies developed so that potential impacts can be effectively managed and eased.
Transport and Main Roads Minister Mark Bailey said, “The upgraded channel would also enable future expansion of the HMAS Cairns Navy base, improve access and efficiency for bulk cargo and larger visiting Navy vessels, and provide increased resilience for the port against extreme weather events.”
Ports North’s project team is now working through the detailed planning, design, and downstream approvals phase as well as securing specialist consultants and contractors to deliver the works, with a final delivery date in 2020.