Maintenance dredging in the Great Barrier Reef World Heritage Area

Ports are critical to Australia's economy, creating jobs and prosperity, and providing opportunities for businesses to expand. With 90% of global trade moving via the oceans on ships, ports are the key gateway for essential goods and supplies. All the world's vital raw materials like energy, metals and minerals travel through ports as well as everyday consumer goods, including electronics, furniture, food, and medicine.

Ports play a critical role connecting remote communities and are vital for major exporting industries such as the resources and agricultural sectors. Ports provide facilities for national defence operations and encourage tourism by providing facilities for cruise shipping, reef passenger ferries, the fishing fleet, and recreational marine facilities.

As an island nation, Australia conducts 98% of its trade through ports. In 2022–23, Queensland ports had a total trade throughput of 337.8 million tonnes and 9,194 vessels trading vessel visits, handling imports and exports worth $189.64 billion.

Queensland’s 21 ports, along the 7,000km coastline, are highly critical infrastructure in Queensland’s supply chain and economy, forming a trade gateway connecting Queensland and Australia to the rest of the world. Of Queensland’s ports, 12 of them are within or adjoin the Great Barrier Reef World Heritage Area. The 12 Great Barrier Reef World Heritage Area ports are managed and operated by 4 government owned port authorities.

Like land transport infrastructure, port infrastructure, needs to be established and maintained. Capital dredging is undertaken to establish new, or improve existing channels, berths and swing basins to accommodate changes in vessel sizes and shipping requirements. Maintenance dredging is an essential operational requirement at Queensland ports that is undertaken to ensure safe and efficient ship navigation. Maintenance dredging involves removing the build-up of mainly fine sediments that accumulate over time due to siltation and natural sediment transport processes. Once sediments are dredged, the material is either beneficially reused (for example, in reclamation, beach nourishment or restoration purposes), placed on land or at sea. All dredged material management options require detailed assessment, and material placement must only occur in approved areas.

The need to undertake maintenance dredging depends on local port characteristics however most ports cannot sustainably function without maintenance dredging. Queensland ports located within the Great Barrier Reef World Heritage Area reside in a variety of coastal environments and are subject to different local ocean conditions, resulting in varying rates of sedimentation. Maintenance dredging is generally undertaken annually at the ports of Cairns, Gladstone and Townsville. The ports of Mackay and Hay Point typically require maintenance dredging every 3 to 5 years, and the Port of Rockhampton every 5 years, or potentially longer depending on local conditions. Limited maintenance dredging has been required at the ports of Abbot Point and Cooktown.

Sedimentation at different ports is typically driven by several key coastal processes. For most of the ports within the Great Barrier Reef World Heritage Area, sedimentation during typical conditions is primarily a result of wave and current induced resuspension. Severe weather conditions such as cyclones and flooding also play an important role in the amount of sediment deposited within port areas. For example, the ports of Cairns and Townsville are both shallow harbours with shipping channels that require routine dredging due to higher levels of natural sediment transportation and coastal storm events. Consequently, they require annual maintenance dredging. Other Great Barrier Reef World Heritage Area ports like Cape Flattery or Lucinda which have trestle wharves do not require maintenance dredging due to berths being in deep water.