Chemistry Reference
In-Depth Information
the width of the spill continued to increase (Figure 8), the film thickness at
point
A
did not reach the threshold of the detectable level
d
o
(the time
needed to reach this level depends on the oil discharge rate and the degra-
dation half-life of oil (MacDonald et al. 1993)). Typical values for the de-
tectable thickness are
d
o
= 0.1-1 Pm (MacDonald et al. 1993). Assume that
the average thickness of the film
d
= 0.3 Pm when
D
= 2 km. Then the
volume of oil in wastewater will be
V
=
LDd
= 8.0·10
4
·2·10
3
·3·10
-7
=
48.0 m
3
(15100$; 1 barrel = 50$).
2000
1800
1600
1400
1200
1000
800
600
400
200
0
0
2000
4000
6000
8000
10000 12000
Time (seconds)
Fig. 8.
Dependence of the width of the spill in Figure 1a on the residence time.
The location of the dark squares show the measured width of the spreading oil
spill (two sections are shown in Figure 7) as the distance from a ship (point B in
Figure 1b) and thus the residence time of the spill increases. The solid smooth
curve reflects the approximating function
5 Discussion and summary
The geometry of a surface film is formed under the influence of four fac-
tors: spreading/spilling procedure, currents, wind and time. In light winds,
the spatial variability of currents becomes the main cause of a spill advec-
tion. In the two cases in question, the magnitude of the shift was measured
relative to the supposed initial position of a ship's track on a SAR image.
For the first approximation, the magnitude is a linear function of the aver-
age current velocity and the residence time of a given portion of the spill.
