Environmental Engineering Reference
In-Depth Information
Estuarine and Ocean Circulation Dynamics
in the Niger Delta, Nigeria: Implications for Oil
Spill and Pollution Management
Larry Awosika and Regina Folorunsho
Abstract
The Niger Delta is a fan-shaped sedimentary environment located between the Benin River in
the west and the Imo River in the east (longitudes 5
o
4
0
00
00
E and 7
o
40
0
00
00
E), extending a few
kilometres south of the village of Aboh at the point where the Niger bifurcates into several
rivers with estuaries opening into the Gulf of Guinea. Within the estuaries, circulation
patterns are dictated mainly by the tidal regimes and fluvial flows superimposed on the ebb
and flood currents. The ebb tidal currents are usually stronger than the flood tidal currents,
with water fluxes during the ebb tide almost twice those of the flood tides. Offshore
circulation is predominantly along-shelf and is oscillatory in nature with a fortnightly
component. The across-shelf circulation, which is more subdued, is both tide and wind
dependent. Understanding the circulation patterns both in the estuaries and in the open ocean
has implications for oil spill management and the resulting health of the estuaries, which
serve as breeding grounds for a wide variety of fish and floral species.
Keywords
Bathymetry
Continental shelf
Gulf of Guinea
Longshore currents
Littoral drift
Ocean currents
Niger Delta
Nigeria
Oil spill
Oscillating currents
Introduction
Allen (
1965
) recognized 20 major barrier islands in the
Niger Delta separated by deep tidal channels (estuaries).
The widths of the barrier islands range from a few 100 m to
12 km with lengths varying from about 5-37 km (Allen
1965
). The Niger Delta is composed of seven major envi-
ronments (Table
1
). The flood plain of freshwater swamp
ecological zone extends from the Forcados-Nun bifurcation
of the Niger to the levee-indented margin of the mangrove
swamp zone. River channel deposits, point bars, levees,
back swamp and cut-off channel deposits develop in this
zone (Whiteman
1982
).
The barrier islands separate the mangrove swamps from
the open sea. In the central part of the delta, the mangrove
swamps are 8-16 km across which interlace with lower
freshwater swamps. On the flanks of the delta, the mangrove
swamps are 32-40 km wide. The mangrove swamp ecolog-
ical zone is characterized by mudflats, tidal saline and
The Niger Delta is a fan-shaped sedimentary environment
located between the Benin River in the west and the Imo
River in the east (longitudes 5
o
4
0
00
00
E and 7
o
40
0
00
00
E),
extending a few kilometres south of the village of Aboh at
the point where the Niger bifurcates into the Nun and
Forcados Rivers (Fig.
1
). Barrier islands with beach ridges
rim the seaward margin of the Delta for about 480 km.
77
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