Forecasting Accidental Marine Pollution Drift: the French Operational Plan P. Daniel & J. Poitevin Meteo-France, 42 Avenue C

Forecasting accidental marine pollution drift: the French operational plan

P. Daniel & J. Poitevin Meteo-France, 42 avenue Coriolis, 31057 Toulouse Cedex,

France

Email: [email protected] [email protected] C. Tiercelin & M. Marchand

Abstract

In case of accidental marine pollution, Cedre and Meteo-France, within the framework of their own public service missions, provide assistance to the French authorities in charge of pollution response. Meteo-France has developed a numerical marine oil pollution transport model, named MOTHY, designed to simulate the transport of oil in three dimensions. A hydrodynamic ocean model is linked to an oil spill model including current shear, vertical movements and fate of the oil. The use of a global atmospheric model for atmospheric forcing enables world-wide application of the model. This oil spill response system has been operational since February 1994. In case of marine pollution, Meteo-

France send meteorological forecasts and oil spill drift forecasts to Cedre. In return, by its experimentations and interventions on actual pollution, Cedre is contributing to the improvement and validation of the model. New developments, exercises and training are conducted jointly. This paper summarizes the key features of MOTHY and presents some examples of model applications.

44 Oil & Hydrocarbon Spills, Modelling, Analysis & Control

1 Background

French response capabilities in case of accidental water pollution are based on Cedre's expertise in mitigation of both oil and chemical spills in marine and inland waters. As a non-profit association under the Ministry of the Environment, Cedre acts for national organisations (such as the

French Navy or Civil Security) or for private companies (oil and chemical industries, and shipping companies). Cedre is also a member of the E.U. Task Force team, to assist European Union and foreign governments in response to accidental pollution. Meteo-France (the French national weather service) has national and international responsibilities to agencies fighting marine oil pollution. Meteo-France can intervene at a national level within the spill response plan POLMAR-MER in case of a threat for the French coastline, and at an international level within the Marine Pollution Emergency Response Support System (MPERSS) for the high seas.

45'W 0* 45'E 90'E 135*E 180' 135'W 90*W

45'N 45'N

45'S

45'W 0" 45'E 90*E 135'E 180" 135~W 90'W

Figure 1 : MPERSS areas

The MPERSS is a World Meteorological Organisation (WMO) system implemented on an experimental basis since 1 January 1994. The

Oil & Hydrocarbon Spills, Modelling, Analysis & Control 45

purpose of this system is to provide meteorological support to marine pollution emergency response operations on the high seas. The oceans and

seas are divided into areas of responsibility where a national meteorological service is designated as area co-ordinator. Meteo-France is the co-ordinator in area II and a supporting service in areas I, III, VII B

and VIII C (figure 1). The support to emergency operations may include a variety of elements such as: basic meteorological forecasts and warning for the area concerned, observation, analysis and forecasting of the values of

specific meteorological and oceanographic variables required as input to marine pollution models, operation of such models and access to national

and international telecommunication facilities.

2 Key features of the model MOTH Y

Only a brief description is given below. More information can be found in

Daniel [3]. The oil slick is modelled as a distribution of independent droplets which move in response to currents, turbulence and buoyancy. Currents are provided by a coupling between a 2D hydrodynamic,

limited area, ocean model and a ID eddy viscosity model. The objective of this approach is to enable a realistic representation of near-surface current

velocity structure. The 2D model is driven by tide components and by winds and sea level pressure forecasts from a global atmospheric model. This atmospheric model can be the IPS model (European Centre for

Medium-Range Weather Forecasts) or the ARPEGE model (Meteo- France) (Courtier et al. [2]). The ID model assumes a bilinear eddy viscosity profile (Poon and Madsen [8]).

Turbulent diffusion is modelled with a three-dimensional random walk technique. The buoyancy force depends on the density and size of the

oil droplets so that larger (more buoyant) droplets tend to remain in the surface layer whereas the smaller droplets are mixed downwards (Elliot [7]). In general, about 65 to 70% of the droplets remain on the sea surface.

If a droplet is moved on to land, then that droplet is considered beached and takes no further part in the simulation.

The model was calibrated on a few well documented pollution incidents such as Torrey Canyon, English Channel, 1967 (Drici [6], Chaussard and Perrin [1]), Amoco Cadiz, English Channel, 1978 (Drici

[6], Chaussard and Perrin [1]), Tanio, English Channel, 1980 (Chaussard and Perrin [1]), Gulf war, Persian Gulf, 1991 (Dervillee and Jouvenot [5]), Aegean Sea, La Coruna, Spain, 1992 (Daniel [4]).

46 Oil & Hydrocarbon Spills, Modelling, Analysis & Control

3 Operational use

3.1 Operating procedure

A meteorologist on duty at the marine service in Toulouse is able to run the model on request. He provides oil spill position, time and duration of the release and oil type (light crude oil, heavy crude oil, kerosene, gas oil, fuel oil, petrol). The model is then run for the required forecast period

(typically 120 h). The output is oil spill position charts. A 120 hour forecast can be carried out on a main frame in a few minutes. This system enables an investigation of a forecast scenario to be made in real time. Since February 1994, about two interventions each year for accidents were conducted in real time. For some of them, the oil spill didn't reach any coastline, for others slicks were very limited. The biggest spill was for the Sea Empress accident.

3.2 Sea Empress example

The oil tanker Sea Empress ran aground in the entrance to Milford Haven on the rocks at Mill Bay, UK, on the evening of Thursday 15 February

1996. It is estimated that approximately 72,000 tonnes of crude oil and 360 tonnes of heavy fuel oil were released. In terms of quantity of oil spilled, this ranks third for tanker oil spills in United Kingdom waters [9].

After an initial loss of 6000 tonnes of crude oil, the tanker released oil at each low tide until 21 February. On Wednesday 21 in the evening, the tanker was refloated and moved to a jetty in Milford Haven. The greatest release of the heavy fuel oil occurred that evening while the tanker was alongside the jetty.

The actual movement of the surface oil was monitored from aircraft and from helicopters. It has been estimated [9] that a significant fraction of the oil, at least one third, will have evaporated from the sea surface, and a significant amount will have dispersed naturally, especially when sea conditions were rough. Between 5,000 and 15,000 tonnes of oil and emulsion contaminated 200 km of coastline.

Oil & Hydrocarbon Spills, Modelling, Analysis & Control 47

5*30W 5* cow 4" 30'W 4' OO'W St Dmnd'a

51'45'N 51*45'N

St Ann's Ciirmurthevn Buy Caldey l*land

51'30'N 51'30'N

51'15'N 51'15'N

Lundy Island 5'30'W 5'OO'W 4' 30'W 4" OO'W

Figure 2 : Milford Haven study area

In the evening of the initial grounding and the following day, oil came ashore in large quantities in the area close to the entrance to Milford Haven. From 21 February to the 26th small patches of oil landed on

beaches north of the mouth of the Haven from St Ann's Head to Smoker Island, and along the south coast of Pembrokeshire, coming ashore on 24

February with heavy oiling on Castle Beach (south coast of Pembrokeshire - 750 tonnes of emulsion), Pendine Sands on 24, 25 and 26 February (1000 tonnes of emulsion). The most significant day for oil impacting

beaches, accounting for perhaps 70% of the total, was 27 February when large quantities of emulsion came ashore along the western half of Carmarthen Bay from Tenby South Beach to the west of Pendine Sands.

Oil sheens spread over a far wider area, with light oiling reported on Lundy Island [9].

Meteorological conditions explain the main pattern of the oil movement. Until 18 February, the wind was westerly between 15 and 25 knots reaching 35 knots on 18 February, then it changed to approximately

48 Oil & Hydrocarbon Spills, Modelling, Analysis & Control northerly from 19 to 22 February and spreaded the oil offshore. From 23 to 25 February, the wind was southwesterly and the oil came back ashore.

5'30W 5* OO'W 4*30*W 4* OO'W

51'45'N- -5T45'N

51'30'N- -51'30'N

51*15'N 51* 15'N

5* 30'W 5* OO'W 4" 30'W 4" OO'W

Figure 3 : 54 hours simulation during Sea Empress accident. A large dot gives the initial position of the spill. The trajectories of the droplets are in grey and their final position in black.

Ships from France, the Netherlands and the UK, were involved in recovering oil from the water surface between 16 February and 7 March. On 16 February, an expert and an observer from Cedre were on the scene in the framework of the European Union Task Force team. Meteo-France sent oil spill drift forecasts to Cedre. An example of forecast map is presented on figure 3. It is a 54 hours simulation starting on the 22

February 1996 at 12 utc with an observed initial position of a slick (5°05'W, 51°32'N). Wind and atmospheric pressure were provided by IPS model forecasts. The simulation correctly predicted the easterly transport of oil.

Oil & Hydrocarbon Spills, Modelling, Analysis & Control 49

4 Exercises

4.1 Antipol95

The exercise Antipol 95 was conducted by Cedre, the French Navy and

Saudi Petroleum Overseas Ltd..

4*00'W 3* 30'W 3*00'W 2* 30'W 2* OO'W

50* OO'N 50' OO'N

49* 30'N 49* 30'N

49* OO'N 49* OO'N

4* OO'W 3'30'W 3* OO'W 2* 30'W 2* OO'W

Figure 4 : two weeks observed trajectory of buoy (thick line) and modelled trajectories of droplets (thin lines - black disks)

Antipol 95 is a simulation of an accident with a tanker carrying 300,000 tons of light crude oil, including tug operations. The accident is supposed to occur north of Batz island (Brittany, English Channel) at 5hlO utc on 3 October 1995. A drifting buoy simulated the oil slick drift.

Meteo-France sent oil slick drift forecasts to Cedre.

50 Oil & Hydrocarbon Spills, Modelling, Analysis & Control

Figure 4 summarizes a two weeks model simulation. It shows the trajectories of the droplets starting from the position of the accident and the trajectory of the buoy. There is one position every six hours. Wind and atmospheric pressure were issued from the ARPEGE model. At the beginning, the winds were Southwest and the droplets moved exactly as the buoy. From the 9 October, the winds were very light and the tide currents dispersed the slick. During this period of light wind, the horizontal dispersion was more important than the drift. The slick was broken into several parts: most of the droplets moved slowly to the north, whereas some of them moved to the south-east, passed south of the island of

Guernsey and then went to the north. The trajectory of the buoy corresponds only to the trajectory of a part of the slick. It appears clearly that the drift of a buoy cannot represent the whole behaviour of the slick.

4.2 Kidour 3

On 17 June 1996, 5000 litres offish oil were poured into the sea, north of Batz island, Brittany. This operation, named Kidour 3, was conducted by Cedre. The aim was to compare the drift of fish oil spill with the drift of several buoys and with the forecasts of numerical models. Two days after the discharge, the buoys were collected and the fish oil spill located. Figure 5 (a) summarizes a two days experimentation and Figure 5 (b) a model simulation with MOTHY for the same period of time. On bothfigures ,th e initial position is represented by a star. Figure 5 (a) shows the trajectories of the buoys and their final positions (black disks). The final position of the fish oil spill is represented by a black square. Figure 5 (b) shows the trajectories of the droplets and their final positions. Wind and atmospheric pressure were issued from the IPS model. During the experiment, the wind was very light and the tide currents dispersed the slick. The trajectory of these droplets is very similar to the trajectory of the buoys and of the fish oil spill.

Oil & Hydrocarbon Spills, Modelling, Analysis & Control 51

4* 12V/ 4' 00 W 3*4flW 3*36W 4'12'W 4'OOVV 3'48'W 3*36"W

48" 48 N 48'48'N He de Batz He deBatz

I* 36'N 4* 12V/ 4*OOW 3'48'W 48* 36 N 48'36'N 4* 12V/ 4* COW 3'48'W 3" 36 W

(a) (b)

Figure 5 : (a) two days observed trajectories of buoys (black disks) and

fish oil spill (black square); (b) two days modelled trajectories of droplets (black disks)

5 Conclusion and future directions

The oil spill model MOTHY is an integrated system that include hydrodynamic coastal ocean modelling and real time atmospheric forcing

with a global atmospheric model. MOTHY demonstrated its capacity to predict accurately the transport of oil in areas with well mixed waters such as English Channel or over the continental shelf in the Bay of Biscay. For stratified seas such as Mediterranean Sea the model is less accurate. The use of a tridimensional hydrodynamic model which takes into account the effects of the deep circulation is under development. Some processes such as evaporation or emulsification, play a significant role during the drift of a slick. The inclusion of a weathering oil model is under study.

52 Oil & Hydrocarbon Spills, Modelling, Analysis & Control

References

[1] Chaussard L. et L. Perrin, 1996: Moderation de la derive des nappes

d'hydrocarbures en mer: application a 1'exercice Antipol95 en Manche et a plusieurs accidents reels de petroliers. Note de travail de I'E.N.M.

n°570. Meteo-France, 111 pp.

[2] Courtier, P., C Freydier, J. F. Geleyn, F. Rabier and M. Rochas,

1991 : The ARPEGE Project at Meteo-France, ECMWF workshop, European center for Medium-Range Weather Forecast, Reading,

England.

[3] Daniel P., 1996: Operational forecasting of oil spill drift at Meteo-

France, Spill Science & Technology Bulletin. Vol. 3, No. 1/2, pp. 53- 64.

[4] Daniel P., 1995: Numerical simulation of the Aegean sea oil spill. Proceedings of the 1995 International Oil Spill Conference, American

Petroleum Institute, Washington, DC , 894-895.

[5] Dervillee L et P. Jouvenot, 1993: Pollution marine. Modelisation de la

derive et de Fetalement d'une nappe d'hydrocarbures. Note de travail del'ENM. Meteo-France, 112 pp.

[6] Drici K, 1994: Modelisation de 1'evolution des nappes d'hydrocarbures a la surface de la mer. Note de travail de I'E.N.M. n°453. Meteo-

France, 64 pp.

[7] Elliott A. J., 1986: Shear diffusion and the spread of oil in the surface

layers of the north sea, Deutsche Hydrographische Zeitschrift 39(3), 113-137.

[8] Poon Y.K. and OS Madsen, 1991: A two layers wind-driven coastal circulation model. J. Geophys. Res.,vol 96, C2, 2535-2548.

[9] Sea Empress Environmental Evaluation Commitee, 1996 : Initial Report, 27 pp.