Better predictions for dredge plumes

Key experts from the public and private sectors have come together to discuss the development of the first science-based guidelines on modelling to predict and manage the environmental impacts caused by dredging in Western Australia, based on the work undertaken by the Western Australian Marine Science Institution (WAMSI) Dredging Science Node researchers.

The workshop, led by CSIRO scientists who are working on the numerical modelling project and the Dredging Science Node leaders, with leading practitioners from a number of environmental consulting companies representing the private sector, focused on the challenges and priorities of the guidelines to ensure they can be readily applied for Environmental Impact Assessment (EIA) in Western Australia.

The accuracy of dredge plume modelling results rely on the quality of input data, correct formulations of internal physics, and appropriate parameterizations of processes that are not fully simulated by the model. Currently there is large uncertainty in model input and parameterizations. Given these challenges, there is a critical need to develop detailed protocols for measurement and modelling of sediments resuspended from dredging operations to improve the impact predictions of proposed future dredging operations.

The project is focused on the transport and fate of sediments released by the dredging process and improving the predictive capacity of dredge plume models. CSIRO researcher Dr Chaojiao Sun and her team are undertaking a detailed investigation on the primary sources of uncertainty in the impact prediction modelling process. The outcomes will provide improved protocols and methods for modelling of suspended sediments and focus effort on critical aspects of the modelling process. The purpose of the workshop was to brainstorm with the EIA modelling practitioners to identify EIA modelling challenges and pathways forward.

A CTD rosette was lowered into the turbid water near Onslow where dredging was taking place at the Chevron Wheatstone site. The instruments on the rosette included CTD, Niskin Bottles, LISST-100x, SBE 19plus, Hydroscat-6, and Hydrorad2. They measured seawater properties, optical backscatter, sediment particle size distribution and volume concentration, downwelling solar signal and upwelling light signal at depths, backscatter and florescence (Image: CSIRO).

A number of challenges have been identified at the workshop such as; uncertainties around dredging program at the EIA stage, lack of information on source terms and spill rates, lack of knowledge in some critical model parameters, feasible ways in defining zones of impact, robust metrics for estimating uncertainty in model prediction, designing monitoring campaign that are useful for model validation, and making model output interpretable for ecologists at temporal and spatial scales of interest for assessing ecological impact. The experts agree that a comprehensive “parameter library” including source terms and model parameter ranges that are typical for the tropical Australian environment would be valuable for future dredge plume modelling.

When the WAMSI Dredging Science Node releases its final report for the projects in 2017, one of the outcomes will be the first set of guidelines on dredge plume modelling that can be applied not only to EIA requirements in Western Australia, but also to other tropical environments in Australia. These guidelines will include recommendations on data collection procedures for model calibration and validation, best-practice process algorithms and parameterizations, metrics for assessing robustness of the model, and linkages to ecological modelling. They will provide greater consistency in the modelling practice and communication of model uncertainty and help improve impact predictions from proposed dredging operations.

A clearly visible dredge plume around the dredges near Onslow (Image: CSIRO).

To stay informed of new publications follow the Dredging Science Node on the WAMSI website or WAMSI Dredging Science Node on Linkedin

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.



Dredging Science