11 Applications of an Oil Drift and Fate Model for Fairway Design
369
unfavourable pathways of the oil drift (Soomere et al. 2011a; Höglund and Meier
2012). The idea was to design environmentally safe fairways so that semi-persistent
current patterns crossing the fairway would transport the potential oil spill mainly to
offshore areas and in this way effectively increase the oil combating time (Andrejev
et al. 2011). Based on the resulting quantification of the offshore regions, various
methods (such as Monte-Carlo-type optimization, Dijkstra’s algorithm, or simply
following the local maxima or minima of the resulting ‘cost function’) (Soomere
et al. 2011b; Höglund and Meier 2012) can be used to minimize certain estimates
of the cumulated risks along the routes. The typically used measures, with a clear
physical interpretation, are the average residence time of potential adverse impacts
in the offshore (also called particle age, Andrejev et al. 2011; Soomere et al. 2011a)
or the probability of landing (or beaching) of these impacts (called also the probability for coastal hits in Chap. 10). A decent measure of risk should also take into
account the time spent by the vessel at sea (its increase owing to the increase in the
length of the sailing line represents a risk factor in itself) and economical factors as
well.
While the results presented in this book so far are mostly based on theoretical
considerations, the practical use of these emerging fairway designs is only feasible if they are carefully evaluated under economical viewpoints using a classical
ship routing–performance evaluation systems. The final decision about the choice
of the optimum sailing line should therefore account for both the environmental risk
estimates and economical factors. The combined evaluation should thus be based
on a joint measure that incorporates the increased oil residence time at sea (or the
reduced probability of coastal oil landings) along the environmentally optimum fairways, and evaluates this gain against faster sea travel, reduced amount of fuel consumption, and possibly increased other risks (of groundings and collisions).
The analysis presented in the previous chapters provides the user with a manifold of comparable technologies and possibilities to evaluate the data and fairway
designs under different viewpoints. The analysis involved a multitude of pollutant
transport and fate simulations with the goal of statistical evaluation of the characteristic drift patterns. A cluster of fairway design studies (Soomere et al. 2011a,
2011b, 2011c; Lu et al. 2012) were accompanied by high-resolution Lagrangian
surface drifter experiments (Kjelsson and Döös 2012).
A major limitation of the above studies is their focus on the current-driven oil
drift. This viewpoint, although suitable to highlight the key ideas of the technology
of fairway design based on approximately solving the inverse problem of pollution
propagation, has largely ignored other factors affecting the drift and fate of an oil
spill. The pollutant transport has been studied by means of neutrally buoyant (passive) particle drift assessments, where each particle represented a drifting volume
of persistent contaminant and was passively advected. In other words, the pathways
and fate of realistic oil spills were replaced by a cluster of trajectories of small idealized persistent oil drops that were locked in the uppermost layer. Equivalently,
realistic oil spills were substituted by clouds of water parcels (more generally, passive tracers). This means inter alia that all changes to the oil itself as well as wind
and wave effects were completely neglected and exclusively current-driven transport
369
unfavourable pathways of the oil drift (Soomere et al. 2011a; Höglund and Meier
2012). The idea was to design environmentally safe fairways so that semi-persistent
current patterns crossing the fairway would transport the potential oil spill mainly to
offshore areas and in this way effectively increase the oil combating time (Andrejev
et al. 2011). Based on the resulting quantification of the offshore regions, various
methods (such as Monte-Carlo-type optimization, Dijkstra’s algorithm, or simply
following the local maxima or minima of the resulting ‘cost function’) (Soomere
et al. 2011b; Höglund and Meier 2012) can be used to minimize certain estimates
of the cumulated risks along the routes. The typically used measures, with a clear
physical interpretation, are the average residence time of potential adverse impacts
in the offshore (also called particle age, Andrejev et al. 2011; Soomere et al. 2011a)
or the probability of landing (or beaching) of these impacts (called also the probability for coastal hits in Chap. 10). A decent measure of risk should also take into
account the time spent by the vessel at sea (its increase owing to the increase in the
length of the sailing line represents a risk factor in itself) and economical factors as
well.
While the results presented in this book so far are mostly based on theoretical
considerations, the practical use of these emerging fairway designs is only feasible if they are carefully evaluated under economical viewpoints using a classical
ship routing–performance evaluation systems. The final decision about the choice
of the optimum sailing line should therefore account for both the environmental risk
estimates and economical factors. The combined evaluation should thus be based
on a joint measure that incorporates the increased oil residence time at sea (or the
reduced probability of coastal oil landings) along the environmentally optimum fairways, and evaluates this gain against faster sea travel, reduced amount of fuel consumption, and possibly increased other risks (of groundings and collisions).
The analysis presented in the previous chapters provides the user with a manifold of comparable technologies and possibilities to evaluate the data and fairway
designs under different viewpoints. The analysis involved a multitude of pollutant
transport and fate simulations with the goal of statistical evaluation of the characteristic drift patterns. A cluster of fairway design studies (Soomere et al. 2011a,
2011b, 2011c; Lu et al. 2012) were accompanied by high-resolution Lagrangian
surface drifter experiments (Kjelsson and Döös 2012).
A major limitation of the above studies is their focus on the current-driven oil
drift. This viewpoint, although suitable to highlight the key ideas of the technology
of fairway design based on approximately solving the inverse problem of pollution
propagation, has largely ignored other factors affecting the drift and fate of an oil
spill. The pollutant transport has been studied by means of neutrally buoyant (passive) particle drift assessments, where each particle represented a drifting volume
of persistent contaminant and was passively advected. In other words, the pathways
and fate of realistic oil spills were replaced by a cluster of trajectories of small idealized persistent oil drops that were locked in the uppermost layer. Equivalently,
realistic oil spills were substituted by clouds of water parcels (more generally, passive tracers). This means inter alia that all changes to the oil itself as well as wind
and wave effects were completely neglected and exclusively current-driven transport