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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B7. Istanbul 2004 
The harmful effects of oil spill on the environment are many. Oil 
kills plants and animals in the estuarine zone. Oil settles on beaches 
and kills organisms that live there, It also settles on ocean floor and 
kills benthic (bottom-dwelling) organisms such as crabs. Oil poisons 
algae, disrupts major food chains and decreases the yield of edible 
crustaceans. It also coats birds, impairing their flight or reducing the 
insulative property of their feathers, thus making the birds more 
vulnerable to cold. Oil endangers fish hatcheries in coastal waters 
and as well contaminates the flesh of commercially valuable fish. 
In a bid to clean oil spills by the use of oil dispersants, serious toxic 
effects will be exerted on plankton thereby poisoning marine 
animals. This can further lead to food poisoning and loss of lives. 
Another effect of oil slicks is loss of economic resources to the 
government when spilled oil is not quickly recovered, it will be 
dispersed abroad by the combine action of tide, wind and current. 
The oil will therefore spread into thin films, dissolve in water and 
undergo photochemical oxidation, which will lead to its 
decomposition. The impacts of some major oil spill incidents are 
given below. 
The movement for the survival of Ogoni People (MOSOP) and 
other Ogoni activists have on several occasions called on the 
Nigerian Federal Government to regulate the oil exploration, 
drilling, and processing activities of Shell Oil and other oil 
companies in the oil producing regions of Nigeria. The Ogoni 
have received virtually none of the $30 billion from oil pumped 
out of their lands, and they have been actively demonstrating 
against such injustices. Mr. Ken Saro-Wiwa, along with eight 
other MOSOP members, were arrested and charged with the 
murder of four traditional chiefs belonging to a pro-government 
group in the Ogoni region. The murders occurred during a bloody 
clash in May 1994 between Ogoni activists and Federal 
Government soldiers. On October 31, 1995, a Federal military 
tribunal sentenced them to death. On November 10, 1995 the 
Nigerian Federal Government hanged Ken Saro-Wiwa and eight 
others, in Port Harcourt. 
The death of the Ogoni activists led to the suspension of Nigeria 
from the Commonwealth of Britain (a group comprising of 
Britain and its former colonies); Under extreme pressure, the 
International Finance Corporation cancelled a proposed 
$100million loan and $80 million equity deal to Nigeria LNG, a 
company owned by the Nigerian Government and the top oil 
producers in Nigeria (Shell, EIf and Agip), to produce a gas plant 
and pipeline in the Niger Delta (TED Case Studies, 1997). 
4.0 AGENTS OF OIL SPILL DISPERSAL ALONG 
THE NIGERIAN COAST 
Factors such as wind drift current, wind waves, average surface 
current, tides, sea bottom topography and density of the spilled oil 
influence oil spill dispersal. Oil on spillage also goes through the 
process of evaporation, emulsification, dissolution, photochemical 
oxidation and biodegradation. The factors influencing oil spill 
dispersal on our coastal waters are described below. 
4.1 Advection 
Advection is the main mechanism that governs the drifting of 
suspended oil and surface oil slick. The combined effects of 
surface currents and wind drag cause the advection of the surface 
oil. The advection of suspended oil is the movement of oil 
droplets entrained in the water column due to the water current. In 
most of the oil spill models, drift factor approach has been used, 
which is considered to be a most practical method for predicting 
the advection of oil slicks. 
4.2 Tidal Current 
The astronomical forces of the moon and sun cause tides in the 
ocean which have both vertical and horizontal motions. The tidal 
current successively completes approximately a 360 degree rotation 
in one cycle, from one high tide to the next high. The tidal current 
decreases gradually with increasing depth through the surface and 
intermediate layers and decreases rapidly with increasing depth near 
the bottom. Tidal motions combine with topographical feature give 
rise to three types of tidal currents. These tidal currents are: 
a. The rotary type, illustrated by currents in the open ocean and 
along sea coast. 
D. The rectilinear or reversing type, illustrated by currents in most 
inland bodies of water. 
C. The hydraulic type, illustrated by the currents in straights 
connecting two independent tidal bodies of water. 
A hydrodynamic model could be used for estimating tidal amplitude 
and phase. 
4.3 Waves 
Wind blowing over the water surface generates surface waves (or 
wind waves). Although waves look as if they move horizontally 
through water, they are actually the vertical movement of water 
(USGS et al, 1998). The size of a wave depends upon the force of 
the wind (magnitude), the length of time the wind blows 
(duration), and the amount of open water over which the wind can 
blow (fetch). 
4.4 Longshore Currents 
Although waves tend to become parallel with the coast as a result of 
refraction, they usually break at a slight angle to the shore, with the 
result that a littoral or longshore current is induced and is effective in 
moving a mass of water slowly along the coast. 
Longshore drift is the prevalent sediment transport mechanism along 
the Nigerian coastline and is basically within the nearshore zone (1- 
5m water depth). The longshore currents have a main effect 
within the first few kilometres offshore. Velocities of longshore 
current as estimated by Allen (1965) ranged from 0.22ms'! to 1.0ms 
!. Longshore current velocities range between 18 and 41 cm/s 
during ebb tides. 
There are three main longshore drift directions along the Nigerian 
Coastline. These directions are: 
1. The west-east littoral drift along the western coastline. 
li. The littoral drift off the north western flank of the Niger Delta. 
ill. The west-east littoral drift between Akasa point and the Calabar 
estuary. 
4.5 Spreading 
When there is an oil spill on water, spreading immediately takes 
place. The gaseous and liquid components evaporate. Some get 
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