Australia: Fremantle Harbour Deepening Enters Phase 2

Fremantle Harbour and its approach channels are being deepened so that bigger ships now servicing Australian trade can call fully loaded.

In the first phase of dredging earlier this year, the softer material from the harbour and its approach channels was successfully removed. Phase 2 of the Inner Harbour deepening project is to remove harder limestone material from the seabed.

The deepening will take the container berths at North Quay to a depth of 14.7 metres. This depth is essential to ensure that Western Australia’s importers and exporters retain access to direct services by the major shipping lines. The $250-million deepening project, Fremantle Ports’ biggest infrastructure project for decades, is being conducted under stringent environmental conditions.

Environmental monitoring

The first phase of the deepening created some temporary cloudiness in nearby waters, which is unavoidable with dredging. However, the independent environmental monitoring of water, sediments and mussels demonstrated that the work posed no risk to public health and no unacceptable impacts on the marine environment.

The results of the extensive monitoring program confirmed the pre-dredging testing, which was the basis of the project’s environmental approval.

This monitoring program will continue during Phase 2 of the dredging. As with the first phase, the monitoring results will be posted on Fremantle Ports’ website and reported to the Environmental Protection Authority. Fremantle Ports’ Dredging Reference Group will also continue to be kept well informed.

The average size of container ships calling at Fremantle has increased by more than 85 per cent in the past 15 years. Deepening will avoid the port being bypassed and ensure that services by the more efficient larger ships are retained. This is important to keep Western Australia’s imports and exports competitive, with benefits passed on to consumers.

Services by the larger, more modern container ships also offer environmental savings in terms of increased fuel efficiency with increased cargo-carrying capacity. Fewer ship visits are required.

Dredging process

Two types of dredge vessels are needed during Phase 2 for the removal of limestone material. The cutter suction dredge uses a rotating cutter head, fitted with pick points or teeth, which is lowered to the seabed to break up the material. A hopper dredge, similar to that used for Phase 1 of the deepening, will transport the material to an approved disposal area.

The disposal site is located about seven kilometres offshore in a natural seabed depression at the western end of Gage Roads. It is an area largely devoid of vegetation except for a few small patches of Halophila ovalis seagrass. Modelling undertaken as part of the environmental approvals process has demonstrated that it is a stable site for the material even under severe storm conditions. Phase 2 of dredging will create some temporary cloudiness in the water due to the limestone removal.

The dredge vessels will be operating almost continuously, primarily in the Inner Harbour and Entrance Channel, and the extent of the impact on water clarity will vary with the tide and currents. It is important to note that the limestone to be dredged is uncontaminated and this has been demonstrated through comprehensive sampling and testing that was required to obtain environmental approval to place the material offshore. The cutting and removal of the limestone material is scheduled to be completed in November 2010.

The last of the deepening work involves removing a narrow strip of limestone from immediately in front of the berths. The timing of this work depends on completion of the sheet piling now underway to hold back the slopes beneath the container berths.

Deepening around the world

With the trend towards bigger ships, many ports around the world have either deepened or are planning to deepen. Like Fremantle Ports, these port authorities consider deepening essential to remaining competitive and ensuring the main shipping lines continue to call. In Australia, the ports of Adelaide and Melbourne have recently completed their deepening projects. In New Zealand, the ports of Tauranga, Lyttleton and Otago are all currently seeking planning and environmental approval for their own large-scale deepening projects. The bigger ships coming into service are called post-Panamax because they are too big to fit through the Panama Canal. Right now, one of the largest construction projects in the world is the Panama Canal Authority’s $6 billion expansion project to cater for these ships. It involves creating a third set of locks alongside the existing canal system, excavating new access channels, widening and deepening existing navigation channels and raising the level of Gatun Lake. By the time the Panama project is completed in 2014, the more efficient post-Panamax ships will have become commonplace on the main global shipping routes and will certainly be regular visitors to Fremantle.


Source: fremantle ports, July 27, 2010