Dredging and dredge material disposal

Dredging takes place to establish and maintain safe access channels for ships and other vessels at ports or marinas.

Types of dredging

Capital dredging is undertaken to create new channels or enlarge existing ones, as well as berth areas, swing basins, marinas and boat harbour areas.

Maintenance dredging is undertaken to maintain existing port and marina facilities.

Depending on the location along the Great Barrier Reef, dredging and the disposal of dredge material at sea can occur inside or outside the Marine Park boundary.

The Great Barrier Reef Marine Park Authority’s (GBRMPA) preference is for land-based disposal of dredge material.

Potential impacts

Dredging and disposal of dredge material can potentially reduce water quality, change hydrodynamics (the movement of water), smother plants and animals that live on the seabed, and displace marine life.

Disposed material may also move from its original disposal location, transported by wind, waves and tides, and oceanic currents.

Dredging and disposal activities need to be appropriately managed to prevent environmental harm.

Legislation

Applications for dredging and disposal of dredge material within the Great Barrier Reef Marine Park or World Heritage Area must undergo a comprehensive environmental assessment.

There are also international, Commonwealth and state laws that cover dredging and disposal at sea. These include requirements for evaluating disposal alternatives such as land-based options, as well as waste minimisation, site and impact assessments, and management and monitoring programs.

A permit under the Environment Protection (Sea Dumping) Act 1981 is required for the loading and disposal of dredge material. Approvals for dredging and dredge disposal may also be required under the Environment Protection and Biodiversity Conservation Act 1999 and/or the Great Barrier Reef Marine Park Act 1975.

A permit application must comply with the National Assessment Guidelines for Dredging 2009, which describe the procedures for sampling, testing and assessing whether material is suitable to be disposed of at sea and the procedures for evaluating and monitoring disposal sites.

Proposed disposal activities must also comply with the 1996 Protocol to the Convention on the Prevention of Marine Pollution by Dumping of Wastes and Other Matter 1972 (the London Protocol) which sets out guidelines for assessing these proposals.

The London Protocol requires that other alternatives be considered including land-based disposal, recycling, or treatment of the material in a way that doesn’t pose a risk to human health or the environment or involves disproportionate costs. The National Assessment Guidelines for Dredging state if viable alternatives to sea disposal exist, a permit is unlikely to be granted.

Applicants are also required to undertake modelling in accordance with GBRMPA's hydrodynamic guidelines to predict the extent of dredge or disposal-generated sediment plumes.

If a permit is granted, the permission will specify certain conditions, which may include an approved environmental management plan, environmental site supervision and monitoring of water quality and other factors.

Research

The agency has worked with the Australian Institute of Marine Science to compile existing scientific knowledge of how dredging and disposal impacts on the Great Barrier Reef and identify what further research is needed.

The Dredge Synthesis Report, published in March 2015, focuses on physical, chemical and ecological aspects such as how sediment moves, settles and disperses, and looks at the ecological impacts on reefs, seagrass and other key species and habitats.

The Improved dredge material management in the Great Barrier Region project, completed in July 2013, reviewed options for the beneficial reuse and land disposal of dredge material.

It also developed a framework for water quality monitoring and management programs, and assessed potential alternative dredge material placement sites in six study areas along the Great Barrier Reef coast.

The research, funded by the Australian Government and carried out by Sinclair Knight Merz and Asia-Pacific Applied Science Associates, was the first to incorporate the combined influence of waves, tides, local winds and large-scale currents when modelling the movement of dredge material over 12 months at multiple locations.

We also developed an interpretive statement of the findings.

Other policies and guidelines