Applications of an Oil Drift and Fate Model for Fairway Design

Pollutants at sea undergo weathering related changes in the composition and are transported by winds, waves and currents. Methods are needed to study the impact of changing weather and ocean conditions on oil chemistry and physics and to estimate all the driving forces of oil transport at sea. The present study highlights the potential of operational oil drift and fate models for the analysis of systematic drift patterns that has been prevented so far by their numerical complexity. A large number of drift simulations are performed to cover a three years period 1992–1994, with 8 releases per month on a grid of 528 release positions in the Gulf of Finland. Although sparse in resolution, the results are still characteristic. Large-scale wind induced drift has been found to dominate the surface transport during windy seasons, and to be of similar magnitude as the current drift during calm seasons. Currents dominate the subsurface transport regime, and become more and more significant at later stages of the spill development, when more and more oil droplets are mixed down by waves. To estimate the combined effects of oil transport and oil weathering, seasonal drift patterns are analysed and alternative fairway designs are derived using a Monte Carlo technique. The quality of the designs is evaluated under environmental and economical viewpoints using professional ship routing software. We demonstrate that it is possible to find balanced solutions that are economically beneficial and that follow green goals like low fuel consumption and reduced risk for coastal oil pollution. Wave-driven advection of oil spills has been studied for the one-year period of 1992, to cover a seasonal cycle. It has been found to impact oil propagation in areas where the wave field exhibits strong gradients, e.g., at locations with depth gradients and in the wind shadow of islands.