Dredging and Australian Ports: Subtropical and Tropical Ports

Posted on
May 21, 2019

The objective of this report is to provide a basis for improved discussion on port related dredging in subtropical and tropical areas of Australia and associated environmental impacts. It also highlights the importance of ports and shipping channels to the Australian economy and the critical role of dredging in port operations and growth.

The report provides an overview of the approval processes associated with dredging and at-sea placement of dredged material, the nature of environmental monitoring programs associated with recent port related dredging projects and, through a comparison of monitored environmental impacts with those approved by government, determines that recent port related dredging projects in northern Australia have performed well.

The report relates specially to dredging and at-sea placement of dredged material in subtropical and tropical Australian ports (northern Australia) as;

  • large capital dredging projects are frequently occurring and proposed in these regions (eg for mineral resource development in the Pilbara and Queensland);
  • public interest is focused on dredging in these areas (eg the Great Barrier Reef Region); and,
  • because dredging environmental risks and associated management needs differ to southern temperate regions of Australia. Legacy contamination issues are much less frequently involved in dredging projects in northern parts of Australia than the historically more developed parts of southern Australia where dredging in old established ports with a long industrial history can involve large volumes of contaminated sediments that require specific management approaches.

Key Report Findings

Section 11 of this report provides a comprehensive list of  findings:

  • Dredging and dredged material placement are subject to detailed and complex approval processes under international, commonwealth and state legislation.
  • Australia’s National Assessment Guidelines for Dredging (NAGD), which form the basis of impact assessment for all dredging projects, are recognised internationally as industry-leading guidelines.
  • Any application to place material at sea must comprehensively evaluate alternatives such as beneficial re-use or land based placement.
  • Any dredged material approved for at-sea placement must use
  • A designated Dredged Material Placement Area (DMPA), many of which have been successfully used for decades. These are typically located in un-vegetated areas distant from coral reefs or similar.• Toxic material cannot be placed at sea.
  • Rigorous site selection and master planning endeavours to ensure relevant environmental values and potentially impacting processes are properly understood as part of port infrastructure planning may assist in avoiding or minimising the need for capital or maintenance dredging.
  • Dredging and at-sea placement of dredge material in northern Australian ports over recent years has been subject to environmental monitoring designed to ensure a designated level of environmental protection, especially to any nearby areas of high conservation value (all major capital works are monitored although some maintenance works may not be as impacts, or lack of, are well understood).
  • Most monitoring programs involved reactive monitoring during dredging so that, where necessary, management actions (eg modify or cease dredging) could be taken in time to prevent or minimise ecological impacts.
  • Monitoring programs associated with recent dredging and dredged material placement projects in northern Australia examined in
  • this review almost all showed reported impacts consistent with (generally no impact to a sensitive receptor), or less than, those approved or predicted.
  • Two exceptions were noted where project water turbidity impacts were greater. Monitoring indicated one of these resulted in lesser impacts to corals than approved but is likely to have prevented the normal seasonal recruitment of a deep water seagrass species for one year (with higher than pre-dredging seagrass cover recorded the following year). Monitoring of the other project did not indicate impacts to sensitive receptors (seagrass).
  • A risk based approach based on scientific assessment is essential to the approvals process for future dredging and dredged material placement projects and defining potential environmental monitoring requirements. This needs to take into account the results of previous monitoring programs undertaken in similar environmental settings.
  • Monitoring during many dredging projects has shown that regular natural events such as cyclones or goods may result in much greater and more prolonged environmental changes to coral and seagrass communities than those related to dredging.

Dredging is an essential part of port operation. It will always be required to ensure shipping channels are developed and maintained to enable international trade and the economic growth of Australia.

Many ports operating and developing in northern Australia have implemented monitoring programs in association with dredging that demonstrate leading practice. These reduce the level of uncertainty associated with predicting dredging related impacts and enable continual improvement in managing the environmental impacts of dredging and at-sea placement.

Assumptions by some stakeholders of widespread and unintended impacts to areas of high conservation value, such as the Great Barrier Reef, are not supported by the results from extensive monitoring of many recent dredging projects in northern Australia undertaken in similar environmental settings.

It is important that ports and regulators inform stakeholders of the effectiveness of existing management measures for dredging, that recent dredging and dredged material placement projects in northern Australia have not resulted in unapproved impacts to environmental resources of high conservation value and that impacts have been consistent with those approved by regulatory agencies.

Improved stakeholder awareness of both the impact assessment process and the actual extent of impacts from recent dredging/ at-sea placement projects would improve public confidence in the environmental management of port related dredging enabling a more informed and factually based discussion on future projects.

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