Comparison of trajectory and concentration methods in oil spill modelling at sea

Oil spills in the marine environment cannot be entirely prevented. In order to diminish their consequences numerous oil spreading and weathering models have been developed. The NAFTA3d model is based on the particle tracking method, its results are usually presented as oil concentrations at specified times. A new module based on the trajectory method showing the probability of oil slick occurrence at a certain location after a spill was added to the model. The article first describes both methods and functioning of the model. In the second part we present the results of performed simulations and analyse the suitability of the trajectory method by comparing concentrations and trajectories in the Gulf of Trieste and in the Northern Adriatic. In the third section we describe the strengths and weaknesses of the trajectory method. The study reveals that the new module is most suitable for oil spill response modelling, its major advantages being high computational speed as well as simple and efficient presentation of the entire area at risk on a single map. Finally, we propose a procedure for practical use of the trajectory method