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Dredging Science Node Conference: Results to inform management decisions

31 October 2017

Suction Dredger

The end-of-program 2017 Dredging Science Node Conference brings together the results of one of Australia’s largest and most successful single issue marine research programs in the context of the environmental impact assessment and management process in WA together with an industry perspective.

Dredging is required to develop and maintain ports that are vital to WA’s economy. In 2011-2012 alone, the Environmental Protection Authority assessed four development proposals in the Pilbara with a combined dredged volume of about 130 million cubic metres. The dredging was forecast to take years to complete and in the worst case could cause the permanent loss of about 25km2 of benthic communities. These predictions were based on a range of assumptions and carried significant uncertainty and risk for the environment and for proponents, and little was being done to improve the situation. 

In recognition of the critical importance of this issue in WA and the need for it to be addressed, proponents of new dredging projects were required by government as a condition of approval to contribute funds to research specifically designed to reduce uncertainty. The Dredging Science Node was established by the State Government in collaboration with industry to pool these funds for world-class marine research to:

‘Enhance capacity within Government and the private sector to predict and manage the environmental impacts of dredging in tropical regions of Western Australia.’

The results have been designed to assist regulators and proponents of dredging projects in WA and other tropical regions of Australia and abroad. It’s also hoped the information will be useful for private organisations and individuals with an interest in WA’s marine environment. 

The results are being presented under three key aeas:

  1. physical processes that generate and transport dredged sediment to better quantify the ‘pressure fields;
  2. the responses of key biological assemblages to dredged generated sediments to establish ‘pressure:response’ relationships to inform impact prediction and monitoring/management; and
  3. identifying the timing/locations of key ecological processes, such as reproduction, so that critical environmental windows of sensitivity are known and can be considered in the design and execution of dredging programs.

The outputs directly relevant to predicting and managing dredging in northwest Western Australia (NWWA), involve:

  • benchmarking current knowledge through reviews of relevant scientific literature and reports;
  • analysing available data to characterise actual pressure fields in terms of intensity, duration and frequency, to guide the selection of realistic ranges for pressure parameters for use in experiments;
  • identifying species for use in experiments relevant to NWWA; and
  • using relevant sediments types, including red pindan soils and relevant particle size classes.

The following major outcomes were achieved:

  • Improved understanding of near-field and far-field source terms, their usage in environmental impact assessment, how they can be better estimated and expressed, and recommendations for continual improvement
  • Guidance on contemporary approaches to predicting the pressure fields associated with dredging; including background conditions, deposition and resuspension
  • Quantification of the temporal and spatial patterns in the intensity, duration and frequency of turbidity and suspended sediment pulses associated with actual dredging campaigns in NWWA and flow on effects to light availability and sediment deposition
  • Quantification of changes in light quality and quantity underneath plumes and development of an in situ sediment deposition sensor
  • Guidance on contemporary approaches to sediment transport modelling including; the importance of bathymetry resolution, efficacy of 2D vs 3D models, nearfield modelling and far field modelling; accounting for the effects of benthic communities on sediment deposition and resuspension; remote sensing of turbid plumes for model validation, environmental management and compliance reporting
  • Corals – the relative significance of suspended sediment concentrations, light attenuation and sediment deposition on the health and survival of five coral taxa, with differing morphologies and commonly occurring in NWWA; critical thresholds of sediment deposition and light availability based on laboratory experiments and analyses of industry monitoring data on coral health, survival and recovery potential; bioindicators of dredging-related stress
  • Seagrass – knowledge of the spatial and temporal patterns in seagrass biomass including seasonality, inter-annual variability and recruitment processes for three commonly occurring species in NWWA; the relative significance of sediment deposition and light attenuation associated with dredging plumes on seagrass health; thresholds of sediment deposition and light-related effect and mortality; bioindicators of dredging-related stress
  • Sponges – characterisation of the sponge taxa present in NWWA through analysis of museum records and field collections, development of field guides for sponge identification in NWWA; the relative significance of suspended sediment concentrations, light attenuation and sediment deposition on the health and survival of five sponge taxa, with differing morphologies, nutritional pathways and commonly occurring in NWWA, based on laboratory experiments, field studies and analyses of industry monitoring data on sponge health the prevalence of phototrophic sponges; bioindicators of dredging-related stress
  • Coral spawning – temporal environmental windows of key life cycle processes in NWWA; understanding the pathways by which dredging generated turbidity and sediment deposition affects coral reproduction, fertilisation, larval development and settlement; critical suspended sediment concentration thresholds of effect for impact prediction and dredging management
  • Temporal environmental windows of sensitivity for macroalgae, fish and invertebrates that allow projects to be planned to avoid periods that are critical to their health and survival.

The work of the Node has improved knowledge about how the activity of dredging can affect marine biological communities, focussing on where this information was needed most – the Pilbara region of WA. This allows:

  • proponents to make predictions with greater confidence than before;
  • the community and the EPA to consider and assess the environmental consequences and acceptability of those impacts with greater confidence; and
  • projects to be planned and managed more efficiently and in turn deliver better environmental outcomes.

This is also expected to improve the cost-effectiveness and timeliness of key approvals and regulatory processes.

The next step is to work with key stakeholders to further consolidate research findings with practical experience and prepare a set of clear guidelines and protocols for conducting pre-development surveys, impact prediction and monitoring/management.

It is expected that adoption of more consistent approaches to prediction, monitoring and reporting will generate useful information for proponents and regulators of future proposals and provide a framework for continual improvement over time.

The DSN Conference program and abstracts can be found at www.wamsi.org.au/wamsi-research-conference-2017

 

Dr Ray Masini, Node Leader – Policy

Dr Ross Jones, Node Leader - Science

 

Links:

www.wamsi.org.au/dredging-science-node

www.wamsi.org.au/dredging-science-node/dsn-reports

www.wamsi.org.au/dsn-research-articles

 

The WAMSI Dredging Science Node is made possible through $9.5 million invested by Woodside, Chevron and BHP as environmental offsets. A further $9.5 million has been co-invested by the WAMSI Joint Venture partners, adding significantly more value to this initial industry investment. The node is also supported through critical data provided by Chevron, Woodside and Rio Tinto Iron Ore.

Category: 
Dredging Science