Page 7 - Assessment

D. Melaku Canu et al. / Marine Pollution Bulletin xxx (2015) xxx–xxx 7

Fig. 5. HI 1,1,I index and HI 10,1,I for autumn, 1-day and 10-day spill events, from a spill occurring at R1.
variability of the wind forcing and heat fluxes led to a strong vari- indication of the maximum density of stranded particles at the
ability of the main surface circulation patterns. In particular, along coast, expressed as the ratio between the maximum number of
the northern Sicilian coasts, the west to east intense residual sur- particles stranded in the same area and the total number of
face flow, which characterizes the winter and autumn seasons, is stranded particles.
not present during the summer and spring period. This is in line As an example, in spring, 18% of the particles released at source
with the wind field analysis, which evidences the presence during R5 reach the coast within 10 days, and 10% of those that reach the
the cold months of more frequent and intense Mistral wind events coast (1.8% of total released) are stranded at the same coastal site.
able to stimulate the west to east surface currents. Within the The results show that coastal impacts are greatest for oil spills
Sicilian Channel, the residual flow is generally characterized by a occurring during the winter and autumn at any of the 6 sources,
south-eastern flow field, with southern velocity components tend- with more than 25% of the released particles reaching the coast
ing to oscillate at seasonal frequency. In this case, the variability of within 10 days. During spring and summer, only approximately
the surface flows is less correlated with the wind variability and 15% of the particles become stranded at the shore.
more correlated with the seasonal oscillation of the The 6 sources and related groups of particles can be divided into
Mediterranean thermohaline circulation. The residual surface 3 groups in relation to the results:
circulation patterns result from statistical analysis of the hourly
surface current fields computed by the model and they provide A first group comprises the particles released from areas R1 and
early indications of particle trajectories. R2, which presented the highest % of stranding (between 24%
and 29%). The % of onshore particles is highest in winter (up
ST to 47–50%), but with a relatively lower maximum for R1. This
3.2. Hazard indexes H RI ,HI R,i HI R,T,I
indicates that for R1, the winter currents tend to increase the
The stranding time hazards for each spill source and for each sea- slick at the coast but spread it over a wider area. By contrast,
son have been produced and are represented in Fig. 4 for the autumn the winter maximum for R2 is 19%, occurring at the island of
conditions as an example. Colour shades indicate how long it takes Pantelleria.
the particles released from each of the 6 sources (R1–R6) to reach A second group, comprising the particles released from sources
the coast and where they strand. Alternatively, the map can be seen R4, R5 and R6, presented the lowest % of average stranding
as the period of time that lapses before oil spilled from each of the (between 13% and 17%), with a spring maximum of 23% for
releasing sources R reaches a coastal area. This representation R3 and an autumn maximum of approximately 33% for R6.
enables one to associate, for the autumn season, each spill source A third group comprising the particles released from R3 had an
with its corresponding impacted coastal area. It also highlights the intermediate % of stranded particles (20%) and a summer maxi-
coastal sites that are impacted first following a spill and therefore mum of 39% stranding.
where the time-dependent hazard is high. This result can thereby
contribute to risk management and risk preparedness procedures. Considering the particles released from R2, the lower % strand-
Table 1 illustrates the results of the statistical analysis of oil ing events could be related to the presence of the west to east cur-
drift, which gives – in total, for each release area, for each season rent along the southern Sicilian coastline, which has the potential
– the % of stranded particles with respect to the release and an to drive most of the particles eastward away from the coastal area.

Please cite this article in press as: Melaku Canu, D., et al. Assessment of oil slick hazard and risk at vulnerable coastal sites. Mar. Pollut. Bull. (2015), http://
dx.doi.org/10.1016/j.marpolbul.2015.03.006