Compiling and expanding knowledge of dredging

An independent panel of experts has compiled existing scientific knowledge of how dredging and disposal impacts on the Great Barrier Reef.

Brought together under a joint initiative of the Great Barrier Reef Marine Park Authority and the Australian Institute of Marine Science, the panel reviewed information on the physical and biological effects of dredging and disposal.

The panel's report titled Synthesis of current knowledge of the biophysical impacts of dredging and disposal on the Great Barrier Reef summarises what is known about the effects of dredging, what is scientifically contentious, and the key gaps in our knowledge.

Consisting of 19 technical and scientific experts, the panel represented a broad range of skills, experience and perspectives — from oceanographic modelling to coral ecology.

Among its key findings, the report concluded:

  • In terms of direct effects, dredging and burial of seafloor habitats during disposal can have substantial impacts at a local level, but have only a small impact on the broader Great Barrier Reef and its biodiversity as a whole.

  • In terms of indirect effects, sediments released by dredging and disposal have the potential to stay suspended in the water and move. This may be contributing significantly to the long-term chronic increase in fine suspended sediments in inshore areas, however there wasn’t consensus among the panelists on the extent to which this happens and its impact on biodiversity.

  • Dredging and disposal may be a significant source of fine sediments in the World Heritage Area, in addition to other sources, such as land run-off. A general comparison shows that past large dredging projects produced amounts of fine sediment similar in magnitude to natural loads coming from land run-off in the same region.

  • The recent policy commitments to ban disposal of capital dredge material in marine environments will mean future disposal, which will be limited to maintenance dredging, will contribute much less fine sediment. This reduced amount will still need to be considered in the context of other cumulative impacts on the Great Barrier Reef.

The knowledge gaps identified by the panel are likely to guide further research into the effects of dredging and disposal.

Improving our understanding of the effects of dredging will also help us further develop policy and best practice guidelines.

All management actions are based on best available knowledge — it is part of our adaptive management approach to ensure this knowledge is updated.

Project scope

This work focuses on physical, chemical and ecological aspects such as how sediment moves, settles and disperses and looks at ecological impacts on reefs, seagrass and other key species and habitats.

Although the social, economic, cultural and heritage aspects of dredging are important, these are beyond the scope of this phase of the project.