BfR-Wissenschaft 
11 
In a first step the Sea Track Web drift model from the Federal Agency for Hydrology was ex 
tended. It is now possible to calculate the oil/dispersant drift in the water column and com 
pare it with the oil drift on the water surface. With the results of this comparison it is possible 
to evaluate the effectivity of the use of dispersants in regard to the impact on different parts 
of the marine ecosystem (e.g. oil ashore or in the water column). 
With assistance of the Federal Institute for Hydrology we executed several drift calculations. 
Our test calculations are still under evaluation but some findings can already be summarized. 
As this model calculates with an effectiveness of 100% dispersed oil the findings do not 
show the reality. Even when using a dispersant there will be some oil left on the water sur 
face but hopefully the main part dispersed in the water column. 
Offshore wind 
In case of offshore wind the use of dispersants is not necessary because the oil will not 
reach the shoreline. Having enough time mechanical recovery should be performed. With the 
drift model the development of the situation can be monitored and in case of a change of the 
wind direction the situation can be re-evaluated. 
Onshore wind 
Depending on the distance to the shoreline of the Wadden Sea and the time available to ap 
ply the dispersant it may be possible to prevent the oil to reach the shoreline. This could also 
be an option for the estuaries of the big rivers Elbe and Weser. 
In those cases the first thing to do is to compare the results of the drift modelling of oil with 
and without dispersant. Given enough time to mobilize and apply the dispersant it is possible 
to prevent a significant amount of the oil coming ashore. To support that decision a NEBA is 
needed which supports the decision to disperse the oil at sea. 
In a second step the CCME is going to tender a net environmental benefit analysis in the 
beginning of 2016 to find areas and situations which would benefit from the use of disper 
sants. As the use of dispersants is a time critical process, it is important to define the frame 
of action prior to the spill. The operational decision makers need solid information to weigh 
the pros and cons of the use of dispersants. This information should be available already 
before the spill happens. In general, there is no time for a profound NEBA during a spill. 
To support the decision making process all the data collected in advance should be integrat 
ed in a decision tree. The spill managers can work through this tree to get to the right deci 
sion very quick while having a proper documentation. This is one of the most demanding 
projects for the next year. The process to decide whether the use of dispersants is or is not 
beneficial for the ecosystem is a difficult task. The spill managers will be under constant 
pressure during a spill and have to justify the actions they are taking. Even among biologists 
there are often different opinions whether it is better to use dispersants to save the birds or to 
protect the benthic and pelagic organisms. 
The decision making tree should enable the spill manager to take right decision very quick 
and well supported. Part of this tree are the following questions: 
• Mechanical recovery not possible or sufficient? 
• Use of dispersants is predicted to be effective? 
• Weather conditions are in favour for dispersant use?