In the early hours of the morning on the 11th of March 2009 the Pacific Adventurer encountered severe weather conditions (as a result of nearby Tropical Cyclone Hamish) whilst on route from Newcastle to Indonesia. As a result of the severe weather conditions, 31 shipping containers (containing a total of approximately 600 tonnes of ammonium nitrate) were lost overboard. Several of the containers ruptured the ship's fuel tanks, which resulted in the loss of 270 tonnes of heavy fuel oil to the marine environment (Asia-Pacific ASA 2009). At the request of the Australian Maritime Safety Authority (AMSA), Asia-Pacific ASA provided modelling support to the response teams to determine the likely fates and possible shoreline strikes of the heavy fuel oil (HFO) and the dissolved concentrations of the ammonium nitrate in the water column.
Panels in Fig. 25.2 show the various model runs completed using OILMAP to determine the likely trajectory of the HFO. Environmental forecast data was sourced from the COASTMAP EDS. Specifically NCOM and BLUElink forecast ocean currents aggregated with tidal currents provided the current forcing, whilst GFS and NOGAPS wind forecast models provided wind forcing. To account for variability in the inputs (such as wind gusts) uncertainty particles are included in the model runs. These uncertainty particles are subjected to winds and water currents that have been varied by up to ±30% of their strength and ±30° in direction.
The black dots represent the likely surface oil locations, the white dots represent the water surface swept by the oil, the light grey represents the uncertainty particles used by the model, and the red indicates the full extents of the shoreline oil stranding, as reported by Maritime Safety Queensland.
As shown, there is a general consensus between the model forecasts. All four model forecasts show that the shorelines on the northern end of Moreton Island and the beaches near Kawana will be impacted, with the possibility of shoreline impacts to the beaches both north and south of the Kawana Beach region. The best correlation between the model predicted shoreline impacts and observed shoreline impacts was attained by using NCOM predicted currents aggregated with tidal currents, and the GFS forecast winds (bottom left panel of Fig. 25.2).
The simulation of a mass release of the entire contents of all overboard containers was completed using the CHEMMAP software. This was indicative of a worst case scenario where all 31 of the lost containers would rupture expelling ammonium nitrate over a period of 4 hours after hitting the seabed. NCOM plus tides and GFS winds were used as the forcing data for the CHEMMAP model run. The CHEM-MAP system predicted that a release of 600 tonnes of ammonium nitrate would quickly dissolve in the water column.
The results are shown below in Fig. 25.3, which describes the re-projected location of the reported incident and the projected path of the simulated ammonium nitrate spill over 96 hours. The key indicates the dissolved concentration of the chemical in the water column in milligrams per cubic meter, from the surface to depths divided into five layers. The concentrations of ammonium nitrate within the water column fell to 1 mg/L (1,000 mg/m3) within 4 days following the event. Due to the near seabed release, dissolved concentrations remain near the bottom well away from the surface where they might enter Moreton Bay.
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