Oil drift modelling

BE-AWARE II Final Conference, 18-19 November, Ronneby, Sweden

Co-financed by the EU – Civil Protection Financial Instrument

• Concept of modelling the development of an oil slick

Oil drift modelling

Objective:How will a given spill will spread, drift, disperse:

1. For oil on surface and oil in the water column2. For all spill location in the BA area3. For all spill sizes4. For all oil types5. For all season6. Include effects of oil spill recovery and chemical

dispersion

=> several "infinities" of model-runs for each scenario

Oil drift modelling

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 modelsDifficulty is to judge:•which processes and scenarios are necessary for the purpose•when is the accuracy sufficient for the purpose

Oil drift modelling

Process regimes:•Oil on the ocean surface•Chemically dispersed oil•A 2x2 km grid •4 seasons, no sea iceParameters:•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

• Oil types included

Drift, spreading and fate

Type Representative substance

19 Crude oil

20 Fuel oil

21 Gasoil, diesel, petroleum, jet fuel and light fuel oil

22 Gasoline

• Spill size classes

Drift, spreading and fate

Spill size class Lower limit [t] Upper limit [t]Representative

size [t]

0 0 0 0.0

1 0 1 0.3

2 1 15 4.0

3 15 300 67.0

4 300 5,000 1,200.0

5 5,000 15,000 8,700.0

6 15,000 50,000 27,000.0

7 50,000 150,000 87,000.0

Spreading, resulting radiusSlick area = Circle with radius RR'= Rgrav + Rtide+windFor the resulting area affected by a slick a radius R' is determined:

1.spreading by gravitation (radial spreading)

2.spreading by tide (ellipsoidal circulation)3.and wind (superposition of wind drift)

Spreading, dispersionChemical 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)

A A

B

C

D E

F

G

• Meteorological areasBased on wind statistics

3 speed classes12 direction classes, 30°

Drift

Location F, Jan - Feb

  Wind speed class 1

Wind speed class 2

Wind speed class 3

Speed interval (m/s) 0.2 - 5 5 - 11 >11

Representative wind speed (m/s)

3.5 7 14

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

Modelling the wind drift:

•Vdrift = 0,023 · W, W: Wind speed (m/s)•Ddrift = D, D: Wind direction (deg)

Drift

A A

B

C

D E

F

G

• Hydrographicalsub-regions

• Drift by wind and• Residual currents

(Mumm model input)

Drift

Meteorological area

Description Residual drift speed (m/s)

Direction of drift (ºN)

A West of Ireland 0,05 45

B NW of Scotland 0,07 45

C West of Norway 0,1 45

D East of UK 0,02 150

E West of Denmark 0,07 45

F Southern North Sea

0,01W, projected 30, 210

G English Channel 0,01W, projected 60, 240

Weathering and natural dispersion

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

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

• Verification on single specific spill

Verification MUMM Oserit single spill

• Effect of several selected spills• SW-wind NW-wind

Verification MUMM Oserit single spill

OSERIT: Specific time seriesBEAWARE: General statistics

Verification MUMM Oserit multiple spill

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

Summarising

Questions?

Thank you

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