Operational high resolution oceanographic circulation models for Australian waters – Application to the Great Barrier Reef

Dr Jason Antenucci1, Ms Caroline Lai1, Mr Sam Dickson1, Mr Simon Mortensen2, Mr Paul Irving3, Dr Sabine Knapp4

1DHI Water And Environment, Perth, Australia,

2DHI Water And Environment, Gold Coast, Australia,

3Australian Maritime Safety Authority, Canberra, Australia,

4Seven Ocean Research, Melbourne, Australia

INTRODUCTION

Increasing computer power and data availability, combined with advanced numerical techniques, is opening up significant new opportunities in the development of oceanographic circulation models for operational use.

The development of forecasting and risk management systems in the ocean is heavily reliant on a solid modelling foundation, as errors accumulate rapidly. This is particularly the case when forecasting the path of stricken vessels and oil spills.

In this presentation we outline a new generation of coupled hydrodynamic and wave models being used in operational settings in Australian waters. The models provide simulations under a flexible mesh approach to avoid nesting and allow resolution down to 500 metres in all ports. We will highlight the role of IMOS in the calibration and validation of the models, along with other publically available data.

The models have been integrated with stricken drifting vessel models, oil spill models and mooring analysis models to provide the operational systems for government and industry outcomes. Probabilistic approaches are also incorporated where relevant to allow for uncertainty in forcing predictions and response. Applications of these models will be presented, including the forecasting of stricken vessels for the Australian Maritime Safety Authority, along with mooring system responses in harbours to improve operability and minimise risk.

METHODOLOGY

Standard techniques to build numerical models for oceanographic circulation generally involve the use of regular Cartesian grids. This limits the models to a uniform resolution across the model domain, requiring nesting of models if regions of higher resolution are required. We apply a flexible mesh approach using triangular elements that allows for regions of varying resolution depending on the local topographic features and model requirements. This means only a single model domain is required, allowing for significant efficiencies in computational and processing requirements.

The objective of the model constructed for the Great Barrier Reef was to resolve currents impacting stricken vessels. This requires particular focus on shipping lanes, and must include the effects of both large scale oceanographic currents and tidally driven currents. The bathymetric representation of the reef itself is paramount, as it heavily dictates the behavior of nearshore tidal currents and a number of shipping lanes pass directly through the reef.

The model was constructed with a spatial resolution varying from 500 metres to 9000 metres. The flexible mesh allowed for excellent definition of key bathymetric features such as shipping channels that are not included in other models available for the region. The domain extends from Fraser Island in the south through to Papua New Guinea in the north, and from Cape York in the west to 500 km offshore of Bundaberg in the east, covering an area of 1.8 million square kilometres using approximately 300,000 elements (Figure 1). The model is constructed using the MIKE 3 FM software, and contains 36 vertical layers down to a depth of approximately 4800 metres. The size of the model requires High Performance Computing infrastructure, with the model highly parallelized across 480 cores and typically running 90 times real-time on Magnus at the Pawsey SuperComputing Centre.

The model is calibrated against water levels and current measurements collected at ports along the coast as well as data from the Integrated Marine Observation System (IMOS – www.imos.org.au).

OUTCOMES

The project has delivered a high resolution, highly accurate hydrodynamic model to predict current velocities, primarily for use in assisting the Australian Maritime Safety Authority in managing shipping incidents in the vicinity of the reef. The model has been run to produce 6 years of hindcasts of currents at hourly resolution to be used in risk assessments associated with shipping. The model is also being operationalised, where 2 days forecasts (available after less than an hour of simulation) will be developed and fed into AMSA’s operational response system.

The high resolution model is available for use by other agencies, and can be coupled with water quality and agent-based models to develop risk assessments based on water quality and ecological factors. The availability of the 6 year hindcast opens up numerous opportunities for such studies, and is an important resource in ongoing management of the reef.

Figure 1: Great Barrier Reef model domain, showing sample current vectors and temperature contours.


Biography

Jason has a PhD in Environmental Fluid Mechanics and a BE(Hons) in Environmental Engineering, with 17 years of experience in surface water environments, including lakes, reservoirs, estuaries, and the coastal ocean. His modelling expertise extends to hydrodynamics, water quality, eutrophication, and aquatic ecology from zero to three dimensions. He has extensive experience in outfall design and assessment, including hydraulics and environmental mixing, and developed new business and technologies in water and environmental management. Technology development includes software, numerical models, and real-time decision support systems.

He has published 45 peer-reviewed papers in international journals (attracting over 2000 citations), more than 40 conference papers and one book chapter on various topics associated with water management and water quality from catchment to the coastal ocean.

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