An Oil Spill in the Bosporus: The Gotia Accident
Emre N. Otay1 and Orhan Yenigün2
1
Civil Engineering Department, Boğaziçi University, Istanbul, Turkey
2
Institute of Environmental Sciences, Boğaziçi University, Istanbul, Turkey
Abstract
On October 6th, 2002, M/V GOTIA, carrying 163 metric tons of fuel oil in her fuel tanks,
rammed into the Emirgan Pier in the Bosporus. One of the fuel tanks started leaking oil in to
the Bosporus. The ship continued its passage and finally anchored when it reached the
Marmara Sea where the leaking tank was repaired. Following the accident, the strong surface
current, rapidly transported the oil southward all the way to the southern opening to the
Marmara Sea. During the passage, the oil slick contaminated the sea water, the boats, and the
waterfront structures along the western coast of the Bosporus including piers, building,
seawalls, buoys and waste barriers. The amount of spill was estimated as 18 tons of marine
fuel oil with a density of 0.9454 g/cm3 at 15oC. However, most of the damage was caused by
a small fraction of oil which was trapped in small bays along the western coast of the southern
half of the Strait.
1.
Introduction
The Strait of Istanbul (Bosporus) is a narrow waterway with several dangerous curves and a
busy maritime traffic which together increase the risk of accident (Tan & Otay, 1999, and
Özkan 2003). Two major tanker accidents resulting in oil spills had occurred in the past
among hundreds of smaller accidents. In the Independenta accident in 1979, 95,000 tons of
crude oil was spilt at the southern entrance of Bosporus. The Nassia accident in 1994 occurred
at the northern exit of the Bosporus to the Black Sea resulting a spill of 13,500 tons of crude
oil.
2.
Facts About the Accident
Based on ship documents, surveyor reports, and expert witness reports, the following facts are
found about the Gotia accident:
•
Accident Location: Emirgan Pier located on the west coast of the Strait (Fig. 1)
•
Date and Time of the Accident: 6 October 2002, 19:30.
•
Name and Registration of the Ship: M/V GOTIA (formerly CLIPPER TIGER) –
Registered to Malta, Valletta.
•
Construction Place and Year of the Ship: Kurushima Dockyard Co. Ltd, Japan, 1985.
(At the time of accident, 14 years old).
•
Dimensions, Type and Cruising Speed of the Ship: 122 m long (LOA), 20 m wide, 8.3
m draft, 12,349 deadweight tons and 7,159 gross tons, dry good cargo carrier, crusing
speed 13 knots.
Figure 1. Accident Location
3.
Field Monitoring
Three field trips were organized to monitor the damage due to the accident. The first trip was
made on October 17th, 2002 to the accident location. The area from Emirgan to the Bosporus
Bridge was visually monitored from the sea. On October 18th, 2002 a more comprehensive
boat survey was organized. The southern half of the Strait between the initial spill point and
the final anchorage point of the ship was completely surveyed by boat (Fig. 2). At 19 points
along a 45 km long survey route water samples and photographs were taken, position, water
depth and water surface temperatures were measured. The last trip was on November 8th,
2002. The western coast of the Strait between Arnavutköy and Kuruçeşme was revisited to
check the residual contamination in these coves.
Emirgan
Figure 2. Survey Route and Sampling Points during Field Monitoring
According to ship logs and expert witness reports, M/V Gotia was travelling from Conztanza,
Romania to Ravenna, Italy, via the Strait of Istanbul. On October 6th, 2002, while cruising
with a southerly course in the Strait, she reached the curve near Emirgan (Fig. 3).
ACCIDENT
Figure 3. Transit Traffic Lanes and the Accident Location at Emirgan
Due to reasons yet to be determined, the ship failed to complete her turn and around 19:30,
she rammed to the Emirgan Pier on the western coast of the Strait (Fig. 4). Due to the impact,
the upper fuel tank on the starboard side was punctured and started leaking fuel oil into the
sea and on to the passenger platform (Fig. 4).
Figure 4. Oil Pollution at the Emirgan Pier After the Accident (18 Oct 2002)
Twelve days after the spill, patches of oil were still visible on the water. Two samples were
taken from the sea water in front of the pier. In their laboratory analysis, the hydrocarbon oil
concentration was found 10-11 mg/L.
Table 1. Analysis Results of Water Samples Collected at the Emirgan Pier
Water Depth (m)
13
Water Temperature (oC)
17
Oil and Grease
Concentration (mg/l)
10.0 (NE Corner)
11.0 (SE Corner)
Hydrocarbon
Concentration(mg/l)
10.0 (NE Corner)
11.0 (SE Corner)
After the accident, the ship continued her passage and anchored off Zeytinburnu, just outside
of the southern entrance of the Strait (Fig. 2). Photographs taken during the boat survey
showed the damaged tank on the starboard side of the anchored ship which had been repaired
after the accident (Figure 5).
Point of
Ramming
Figure 5. Point of Ramming on the Starboard Side of the Ship (18 Oct 2002)
The boat survey focused on contamination in bays and small coves where oil was more likely
to deposit and the pollution was still visible. Traces of oil pollution on the water surface,
seawalls, anchoring boats, and shore protection structures were recorded. Local residents and
eye witnesses were interviewed. Two laboratory tests were used to analyze the water samples
for the oil, grease and hydrocarbon contents.
The ship surveyor who investigated the tank damage and the remaining oil after the accident
had estimated the total amount of oil spilled from the ship as 18 metric tons (Bağ, 2002). The
type and density of the oil was reported as marine fuel oil with 0.9454 g/cm3 density at 15o C
in the fuel survey worksheet (Kalinowski, 2002).
During the field monitoring, oil pollution was recorded mainly on the western coast of the
Strait. Oil contamination were concentrated in Arnavutkoy, Kuruçeşme and Ortaköy which
are the three coves on the west coast of the Strait where the main surface current is known to
change course and does not control the local circulation in these coves. It was evident that part
of the oil escaped the main current of the Strait and was trapped in these coves causing oil
pollution by the seawalls and waterfront buildings (Fig. 6 and 7)
Figure 6. Oily Waste Trapped in Ortaköy (18 Oct 2002)
Figure 7. Oily Waste Trapped in Kuruçeşme (18 Oct 2002)
Surface booms are used to capture the oil slick which was carried southward by the main
current in the Strait (Fig. 8 & 9). However, due to strong density currents in the Strait, oil
slick escaped the barriers and reached the Marmara Sea where it was mixed into the water
column. Therefore, the rescue operations focused to capture the oil which was trapped in calm
waters along the Strait where the local circulation was branching out from the main stream.
Figure 8. Booms Used to Capture Oil on the Water Surface near Kuruçeşme (17 Oct 2002)
Figure 9. Oily Waste Collected by Booms at Kuruçeşme. (18 Oct 2002)
During the cleaning operations, one of the most effective equipment used to protect the coast
was the oil sponge (Fig. 10). These were large cylindrical pillows with approximately 30 cm
diameter made of a soft sponge-like material. The disadvantage was that they could be used
only once.
Besides the protective booms and sponges installed after the accident, the existing waste
barriers between Arnavutköy and Kuruçeşme helped to keep the oil slick away from the coast
and the waterfront buildings. After the accident, these barriers were cleaned to prevent further
contamination (Figure 11).
Figure 10. Oil Sponges and Waste Barriers at Arnavutköy (18 Oct 2002)
Figure 11. Cleaning of the Waste Barriers at Arnavutköy (8 Nov 2002)
4.
Laboratory Analysis
Analysis of Oil and Grease
To analyze the oil and grease contents in water samples, the gravimetric method is used. This
method is based on seperation of oil and grease from water with the help of n-hexane. The
method is useful to measure pollutants in surface water, sea water, industrial and domestic
waste waters which can be extracted with n-hexane. In the oil and grease analysis, the
absolute quantity of a specific constituent cannot be measured. Instead, a combined group of
similar physical characteristics can be quantitatively estimated based on its solvubility in nhexane. Therefore, the term oil and grease includes hydrocarbons, oil acids, soaps, oils, vaxes,
and all other oily materials. During the gravimetric processes, at the stage of removal of
solvents, some of the fractions with low boiling point dissappear. Therefore, certain fractions
including heating oil and gasoline cannot be well analysed with this method.
Analysis of Hydrocarbons
Silica jel has the ability to absorb polar material. When a solution of hydrocarbons and oil is
mixed with silica jel in a nonpolar solvent the oily material is selectively removed from the
solution. The material which cannot be eliminated with the silica jel absorbance is the
hydrocarbon. The method is useful to measure the hydrocarbon content in surface water, sea
water, industrial and domestic waste waters which can be extracted with n-hexane.
The concentrations of oil, grease and hydrocarbons at 18 measurement points along the Strait
are given in Table 2. All samples, except one (No.14 Ortaköy) have been randomly collected
from the water surface. The sample in Ortaköy was taken for reference purposes from the
middle of a floating oily waste accumulated in a calm corner of the cove.
Table 2. Oil, Grease and Hydrocarbon Concentrations Measured in Sea Water
Station
Oil and Grease (mg/L)
Hydrocarbon (mg/L)
1 Emirgan Pier (North)
10.0
10.0
1 Emirgan İskelesi (South)
11.0
11.0
2 Kanlıca
1.8
1.8
3 Göksu
1.8
1.2
4 Küçüksu Koyu
9.2
8.8
5 Kandilli
2.2
1.3
6 Çengelköy
2.3
2.3
7 Beşiktaş
0.0
0.0
8 Üsküdar
12.6
12.6
9 Doğancılar
6.1
6.1
10 Kadıköy
8.0
8.0
11 Marmara Çıkışı
6.1
6.1
12 Eminönü
4.8
4.8
13 Kabataş
3.2
3.2
14 Ortaköy*
300.0
55.3
15 A Kuruçeşme
4.0
0.0
16 Arnavutköy
7.8
4.0
17 Bebek
4.8
4.8
18 Boğaziçi Univ.
6.0
0.0
*This sample is directly taken from an oily waste accumulation to establish a reference value.
The geographical distribution of concentrations in Table 2 for oil and grease (Fig. 12) and
hydrocarbons (Fig. 13) are shown along the Strait. The locations are recorded using a
handheld GPS receiver with an accuracy of approximetely 10 meters.
Figure 12. Distribution of oil and grease concentrations along the Strait
The colors on the map changing from yellow to red indicate an increase in concentration. No
correlation has been found between the measured concentrations and the travel distance from
the initial spill point.
Figure 13. Distribution of hydrocarbon concentration along the Strait
During the boat survey, surface water temperature was recorded at every sampling point.
Figure 14 shows approximately uniform temperatures throughout the Strait at around 17o C.
T [oC]
Distance from the Accident Point [m]
Figure 14. Water Surface Temperatures South of the Accident Point
5.
Weather and Sea Conditions during and after the Accident
In addition to the field survey, meteorological conditions during and after the oil spill were
obtained from the Kireçburnu Weather Station located 5 km north of the accident. Weather
and sea parameters are analyzed for the evening of October 6th and the following day to
examine the environmental conditions which might have affected the fate of oil in water
(Table 3).
Table 3. Meteorological Parameters Measured at the Kireçburnu Weather Station
6 Oct 2002
7 Oct 2002
pm
Am
Noon
pm
Wind Direction
NE
S
SW
W
Wind Speed (knots)
0-1
1-2
2-3
1-2
Wave Height (m)
0-0.1
0-0.1
0-0.1
0-0.1
Visibility (km)
20
20
20
20
Daily Min-Max Air Temp (C)
Total Daily Rain (mm)
12.1-19.6
14.6-21.6
0
1.5
The weather conditions during the accident and in the following few hours were favorable for
minimizing the impact of the oil spill. During the motion of the oil slick in the Strait, the wind
was mostly calm. A mild breeze from the northeast pushed the oil towards the western coast.
It is known that the surface current in the Strait is controlled by strong salinity currents
flowing towards the South under calm and mild wind conditions. Therefore, it can be
concluded that the majority of the oil was transported with the ambient surface current into
the Marmara Sea.
Analysis of the wind record for the last three weeks of October 2002 indicated no storms in
the area which might have affected the fate of the trapped oil in calm sections of the Strait.
Wind Direction [ o N]
N
hourly average wind
daily maximum wind
W
S
E
N
6
10
15
20
25
hourly average wind
daily maximum wind
10
Wind Speed [m/s]
30
5
0
6
10
15
20
25
30
Day in October 2002
Figure 15. Wind Data Measured at the Kireçburnu Weather Station (6-31 Oct 2002)
The histograms of wind speed and wind directions showed that in the last three weeks of the
month October, winds were mainly from NE or SW with speeds upto 4.5 m/s with mean
velocity of 1.5 m/s. These results again indicate that no extreme event has occurred that might
have caused unexpected changes in the trapped oil concentrations.
No. of Occurrences
Histogram of Wind Directions
No. of Occurrences
Histogram of Wind Speed
wind speed [m/s]
Figure 16. Histogram of Wind Speed and Directions in the Strait (6-31 October 2002).
6.
Conclusions
On October 6th, 2002, a 122 m long and 12349 dwt cargo ship rammed to the Emirgan Pier
while transiting the Bosporus. Due to the impact, oil has leaked to the sea from a fuel oil tank.
The spill was estimated as 18 tons of marine fuel oil with a density of 0.9454 g/cm3 at 15o C.
Within the following few hours, the oil slick was rapidly carried by the ambient surface
current in the Strait to the southern exit where it was discharged to the Marmara Sea. Efforts
to stop the slick with booms failed due to strong currents. Therefore most of the oil could not
be recovered. Due to mild northeasterly winds, it was concluded that the surface current was
to the South which the ambient current direction in the Bosporus. Very seldom, the direction
of the surface current changes to the North when there is extremely strong southerly wind.
However, this was not the case in the Gotia accident. Under these conditions, the travel time
for the oil slick to reach the southern entrance of the Strait was estimated as 6 hours. By the
time when recovery operations started, the oil slick has already left the Strait.
The original spill point was located at the western coast of the Strait. With the wind drag, the
oil slick was pushed to small coves along the western coast where some of the oil was trapped
in these calm waters close to the seawall. During the boat surveys, oil contamination was
mainly observed in coves between Arnavutköy and Ortaköy. Although the exact amount of
the trapped oil could not be measured, it was estimated to be at most half of the original spill.
Random grab samples taken from the surface water were analyzed in the laboratory. The
resulting concentrations of oil, grease and hydrocarbon were extremely high. Also, there was
no correlation between the measured concentratrions and the distance of samples from the
spill point. On the other hand, the largest concentrations were found on the other side of the
Strait where oil did not reach at all. Therefore it was concluded that the measurement results,
except the reference samples taken between Arnavutköy and Ortakoy, indicate a high ambient
contamination in the Strait.
Both visually and by laboratory tests, evidence was found that some of the oil was trapped in
calm areas along the western coast of the Strait. It was concluded that the observed
contamination was due to branching out of smaller portions of the main oil slick from the
main stream carried by the strong ambient salinity current in the strait and trapped in calm
waters along the coast.
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