Diffusion-Drift Model of Spilt Oil
Yoshiharu Nishikawa
Environment & Safety Control Dept.
TONEN CORPORATIONINTRODUCTION
The Petroleum Association of Japan (PAJ) has been conducting a project, using subsidies
from the government, to reinforce large oil spill response capability since 1991. The projectis consisted of two elements ; one is stockpiling of oil spill cleanup equipment and materials,
and another is studies and development work concerning topics such as oil spill trajectorymodel, experiments on fate and behavior of spilt oils.
At an oil spill incident, it is essential to prepare and implement quickly contingency plan
for rapid arrangement of cleanup equipment, based on prediction for extent of the spilt oil,properties of oil slick, and coastal or other areas at risk.
As the background of these, PAJ has been promoted investigation to develop an oil spillmodel, which forecasts the oil behavior expected to take place within 48 hours in the coastal
waters of Japan or nearby sea areas, where oil refiners are located, and recently developed β-version and released it to the concerned. This paper outlines this forecast system. Inaddition, the development work is entrusted to FUJI RESEARCH INSTITUTECORPORATION, and the author is participating in the project as research associates.

DETAILS OF INVESTIGATION
Extensively reviewing about 37 model systems (their application areas, structure,characteristics, practical use, utility, verification, etc.), we confirmed that algorithms for theprocesses (advection, spreading, evaporation, emulsification, etc.) have been developed forprediction of oil behavior on the surface up to 2~3 days after the spill, and that some of thespill models are already practically used.
An application of these models to Japanese waters, however, is concluded to beinappropriate due to unknown details of model structure (know-how, proprietary rights,remodeling, etc.), wide variety of Japanese waters, and possible necessity to revise
environmental base data in the future.
Based on these results, PAJ decided to prepare newly an original model suitable toJapanese waters, and, in 1992, developed a prototype model and tested its function on the work
station for model development, in prallel with preparation of data base relative to weather andcurrent in Tokyo bay, as well as oils data.
In 1993, trial preparation of the model system applicable in Tokyo bay was completed
and released to the concerned, after test run following a conversion to the PCs in domestic
refineries, as well as improvement of manipulation and user interface. In 1994, the model
system for other enclosed sea areas (Ise and Osaka bays, and Seto Inland Sea) have beenreleased.

STRUCTURE OF THE MODEL1) Characteristics
The major characteristics of the forecast model is as follows.
‑It forecasts the behavior of marine oil spills within 48 hours after spill, with aprecision effective for oil spill response.
‑
The target forecast sea areas include the coastal waters of Japan where oil
refiners are located.
‑
Oil behavior can be easily and swiftly forecasted at a practical speed (about 20minutes) using personal computer.
2) Structure
The major components of this model are as follows.
① Input : - Oil data : volume and kind of spilt oil, physical and chemical properties, oil spill
scenario, etc.
- Environmental data : wind, currents, temperature, river inflow, etc.
② Fates algorithms : advection, spreading, evaporation, emulsification, etc.
③ Output : extent of the spilt oil on surface, oil mass balance (e.g. surface, atmosphere, etc.),
components as a function of time, etc.
Embeded within the system are high resolution data for coastlines and currents,
statistical winds, and a library of oil types. The model system relies on an easy-to-use
graphical interface, which enables the user simply to execute computation by defining
minimal input data (e.g. wind, spill location and start/end times, etc.).
This system is run with personal computer under MS-Windows 3.1 environment.
3) Fates algorithmsThis system (β-version) currently includes following representative algorithms as thecandidates for fate processes, and allows the users to select which algorithms are to be
used for the prediction.
‑
Advection : Empirical approach with wind factor method, etc.
‑
Spreading : Mackay’ model (1980) etc.
‑
Evaporation : Payne etal. (1980), etc.
‑
Emulsification : Mackay etal (1980), etc.
‑
Vertical dispersion : Spaulding etal. (1982), etc…

FUTURE TOPICS
Current status of the model system is a kind ofβ-version, and it is necessary to be
improved and verified. Therefore, its version-up will be carried out based on the demand
derived from the trial use by the concerned. The major topics to be improved are as follows.
1) Introduction of wind mesh data
Wind data at the spill location is currently used as the representative value for whole seaarea. Wind direction and velocity are different, however, by location of sea also in theclosed sea areas. Therefore, PAJ is planning to introduce into the system wind mesh data
(maximum horizontal resolution=2km).
2) Improvement of algorithms for spreading process
From a comparison between the results of oil release experiment (North sea) and modelprediction, it is found that oil slick presents long elliptical shape toward wind direction.
3) Tuning of process model parameter.
This system uses parameters introduced in the documents for each of process model.
Regarding these parameters, we are investigating pertinent value based on comparison
between example of oil spill incident and model prediction, or experiment on a drift in
actual sea areas.

FUTURE PLAN
Together with version-up of this model system, PAJ is planning to develop other models
applicable to the coastal open ocean areas of Japan in the near future.

PAJ Diffusion-Drift Model of Spilt Oil

Modeling of Oil SpillEnclosed Sea Areas of Oil Spill Model

Coastal Areas of Oil Spill Model

Window of Diffusion-Drift Model of Spilt Oil (Tokyo Bay)

Set Calculation Conditions

Trajectory of Oil Slick (Tokyo Bay)

Predicted Distribution of Oil Slick (Tokyo Bay)

Vectoral Sum of Wind, Tidal Current, etc. (Tokyo Bay)

Comparison of the Trajectories
between the Model Result and the Experiment