Oil drift modelling

1. BE-AWARE II Final Conference, 18-19 November, Ronneby, Sweden Oil drift modelling Co-financed by the EU – Civil Protection Financial Instrument

2. Concept of modelling the development of an oil slick • Oil drift modelling

3. Objective: How will a given spill will spread, drift, disperse: • For oil on surface and oil in the water column • For all spill location in the BA area • For all spill sizes • For all oil types • For all season • Include effects of oil spill recovery and chemical dispersion => several "infinities" of model-runs for each scenario • Oil drift modelling

4. Method: Limit the calculations to a reasonable amount and still obtain a satisfying answer by conducting "Strategic oil spill modelling": • including only necessary processes • modelling with a sufficient accuracy • sensitivity analyses, comparing with other models Difficulty is to judge: • which processes and scenarios are necessary for the purpose • when is the accuracy sufficient for the purpose • Oil drift modelling

5. Process regimes: • Oil on the ocean surface • Chemically dispersed oil • A 2x2 km grid • 4 seasons, no sea ice Parameters: • Sea temperature • Frequency of wind velocity and direction • Wave height (wind waves) • Frequency of fog and mist • The daily hours with sunlight • Drift, spreading and fate

6. Oil types included • Drift, spreading and fate

7. Spill size classes • Drift, spreading and fate

8. Spreading, resulting radius Slick area = Circle with radius RR'= Rgrav + Rtide+wind For the resulting area affected by a slick a radius R' is determined: • spreading by gravitation (radial spreading) • spreading by tide (ellipsoidal circulation) • and wind (superposition of wind drift)

9. Spreading, dispersion Chemical dispersion occurs after approx. 18 hrs (alarm, mobilisation, flight time , effect time): • Phase1: Before application of dispersants (t < 18 hrs)Surface oil: R: Oil slick radius develops due to gravity Drift: as surface drift (Wind+current) • Phase 2: After application of dispersants (t > 18 hrs) Dispersed oil: R:= R0+0.01x (based on observation of oceanic plumes)Radius increases 1/100 with downstream distance (tide effect included, not wind)Oil concentration based on plume depth := 30mDrift as for residual current (no wind effect)

10. Meteorological areas Based on wind statistics3 speed classes 12 direction classes, 30° • Drift Location F, Jan - Feb

11. DRIFTSchematic illustration of resulting drift velocity (yellow) as a superposition of • wind drift (light blue) and • residual current drift (dark blue). • Wind and current drift

12. Modelling the wind drift: • Vdrift = 0,023 · W, W: Wind speed (m/s) • Ddrift = D, D: Wind direction (deg) • Drift

13. Hydrographicalsub-regions • Drift by wind and • Residual currents (Mumm model input) • Drift

14. Weathering and natural dispersion Volume of oil and water in oil emulsion on the sea surface (ITOPF, 2006). Group 1: diesel Group 2 & 3: light and heave crude oil Group 4: bunker oil

15. Simulation stop when 5% of the oil is left on the sea surface. The rest of the oil is either • Weathered • Floated on shore • Drifted out of the model area over boundaries to the Atlantic • Removed by response action • Moddeling stop criteria

16. Verification on single specific spill • Verification MUMM Oserit single spill

17. Effect of several selected spills • SW-wind NW-wind • Verification MUMM Oserit single spill

18. OSERIT: Specific time series BEAWARE: General statistics • Verification MUMM Oserit multiple spill

19. Objective:Distribution of spilt oil after spreading, drift and weathering • All places (several hundreds) • spill sizes (7) • all oil types (4) • all winds (3 speeds and 12 directions) • all seasons (4) • Summarising

20. Thank youbeaware.bonnagreement.org Questions?