11 Applications of an Oil Drift and Fate Model for Fairway Design
409
wave heights in 1992 at the lee-side of Gogland (it is exposed to waves with rather
long fetch, some even generated in the Baltic Proper) indicate that the shadow extends to about 21 km. For waves coming from the west, the strongest wave energy
gradients occur at the northern and the southern cape of the island and generate
northerly and southerly currents at the southern and the northern end of the island,
respectively. Depending on the local topography, wave interaction creates systems
of eddies in up- and downwave direction, clearly seen in panels A2, B2 of Fig. 11.11.
The eddies carry away pollutants approaching from several coastal stretches where
the wave-induced currents point offshore. There is also a high chance for the enhanced onshore transport at some locations. Their impact amounts to significant
differences in the residence time of up to 1.3 days and in the probability of landing
of about 10 %.
This example study of oil propagation and weathering shows that the impact of
wind waves on oil at sea may be very strong at selected locations. It still remains
open how this affects the fairway design. Although the developed fairways ignore
wave-induced transport, they naturally avoid the vicinity of islands and normally
do not enter the nearshore regions where these effects are the strongest, and thus
avoid the most critical zones in this respect. It would be highly interesting (although
computationally expensive) to perform a closer evaluation of the properties of waveinduced drift along the presented fairways and an assessment of the impact of waves
on the fairway performance.
11.7 Summary and Conclusions
The presented results expand the outcome of the previous chapters of this book towards a systematic inclusion of the realistic properties of oil drift into the preventive
technology for environmental management of semi-enclosed seas. Additionally to
the above-described effects of currents on the transport of ‘ideal’ pollutants, we have
estimated, to a first approximation, the joint influence of realistic systems of winds,
waves and currents on the optimum fairway design and have also examined seasonal
variations of the characteristic drift patterns for the Gulf of Finland.
Consistently with the estimates made for the ideal pollution solely driven by surface currents, it has been found that a relocation of release positions to regions with
favourable drift properties leads to an increase in the average residence time of oil
at sea by at least 3 days and to a decrease of the probability of landing by more than
30 %. As a key new development, we established the presence of substantial and to a
certain extent counter-intuitive patterns of seasonal variability in the location of the
favourable fairways. Its major source is the seasonal variation of the wind properties, first of all wind speed and direction. Its presence demonstrates the importance
of wind-driven dynamics of oil drift and associated drift patterns in the study area
and apparently in other similar regions.
Surface currents play a dominant role in oil propagation during relatively calm
periods. The reason for the strong influence of wind is the de facto limitation of
409
wave heights in 1992 at the lee-side of Gogland (it is exposed to waves with rather
long fetch, some even generated in the Baltic Proper) indicate that the shadow extends to about 21 km. For waves coming from the west, the strongest wave energy
gradients occur at the northern and the southern cape of the island and generate
northerly and southerly currents at the southern and the northern end of the island,
respectively. Depending on the local topography, wave interaction creates systems
of eddies in up- and downwave direction, clearly seen in panels A2, B2 of Fig. 11.11.
The eddies carry away pollutants approaching from several coastal stretches where
the wave-induced currents point offshore. There is also a high chance for the enhanced onshore transport at some locations. Their impact amounts to significant
differences in the residence time of up to 1.3 days and in the probability of landing
of about 10 %.
This example study of oil propagation and weathering shows that the impact of
wind waves on oil at sea may be very strong at selected locations. It still remains
open how this affects the fairway design. Although the developed fairways ignore
wave-induced transport, they naturally avoid the vicinity of islands and normally
do not enter the nearshore regions where these effects are the strongest, and thus
avoid the most critical zones in this respect. It would be highly interesting (although
computationally expensive) to perform a closer evaluation of the properties of waveinduced drift along the presented fairways and an assessment of the impact of waves
on the fairway performance.
11.7 Summary and Conclusions
The presented results expand the outcome of the previous chapters of this book towards a systematic inclusion of the realistic properties of oil drift into the preventive
technology for environmental management of semi-enclosed seas. Additionally to
the above-described effects of currents on the transport of ‘ideal’ pollutants, we have
estimated, to a first approximation, the joint influence of realistic systems of winds,
waves and currents on the optimum fairway design and have also examined seasonal
variations of the characteristic drift patterns for the Gulf of Finland.
Consistently with the estimates made for the ideal pollution solely driven by surface currents, it has been found that a relocation of release positions to regions with
favourable drift properties leads to an increase in the average residence time of oil
at sea by at least 3 days and to a decrease of the probability of landing by more than
30 %. As a key new development, we established the presence of substantial and to a
certain extent counter-intuitive patterns of seasonal variability in the location of the
favourable fairways. Its major source is the seasonal variation of the wind properties, first of all wind speed and direction. Its presence demonstrates the importance
of wind-driven dynamics of oil drift and associated drift patterns in the study area
and apparently in other similar regions.
Surface currents play a dominant role in oil propagation during relatively calm
periods. The reason for the strong influence of wind is the de facto limitation of