BE-AWARE II Final Conference, 18-19 November, Ronneby, Sweden
Oil drift modelling
Co-financed by the EU – Civil
Protection Financial Instrument
Oil drift modelling
• Concept of modelling the development of an oil
slick
Oil drift modelling
Objective:
How will a given spill will spread, drift, disperse:
1.
2.
3.
4.
5.
6.
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
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
Drift, spreading and fate
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
• Oil types included
Type
Representative substance
19
Crude oil
20
Fuel oil
21
Gasoil, diesel, petroleum, jet fuel and light fuel oil
22
Gasoline
Drift, spreading and fate
• Spill size classes
Representative
Spill size class
Lower limit [t]
Upper limit [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
size [t]
Spreading, resulting radius
Slick area = Circle with radius R
R'= Rgrav + Rtide+wind
For 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, 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 := 30m
Drift as for residual current (no wind effect)
Drift
• Meteorological areas
Based on wind statistics
3 speed classes
12 direction classes, 30°
C
Speed interval
(m/s)
Representative
wind speed (m/s)
Wind speed
class 1
Wind speed
class 2
Wind speed
class 3
0.2 - 5
5 - 11
>11
3.5
7
14
B
E
D
Location F, Jan - Feb
A
F
G
Wind and current drift
DRIFT
Schematic illustration of resulting drift velocity (yellow)
as a superposition of
•
wind drift (light blue) and
•
residual current drift (dark blue).
Drift
Modelling the wind drift:
•Vdrift = 0,023 · W,
•Ddrift = D,
W: Wind speed (m/s)
D: Wind direction (deg)
Drift
• Hydrographical
sub-regions
•
•
Meteorologi
cal area
Drift by wind and
Residual currents
(Mumm model input)
Description
C
B
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
E
D
A
F
G
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
Moddeling stop criteria
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
Verification MUMM Oserit single spill
• Verification on single specific spill
Verification MUMM Oserit single spill
• Effect of several selected spills
• SW-wind
NW-wind
Verification MUMM Oserit multiple spill
OSERIT: Specific time series
BEAWARE: General statistics
Summarising
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)
Questions?
Thank you
beaware.bonnagreement.org