Environmental Engineering Reference
In-Depth Information
Morphological Characteristics of the Bonny
and Cross River (Calabar) Estuaries
in Nigeria: Implications for Navigation
and Environmental Hazards
Regina Folorunsho and Larry Awosika
Abstract
The Bonny and Cross River estuaries are two major estuaries along the eastern coast of
Nigeria. These estuaries are characterized by deep and shallow channels with semi-diurnal
tides that generate tidal currents in phase with the tidal directions. The mouths of these
estuaries are used extensively by a wide range of vessels and boats with varying sizes ranging
from small dinghies and powerboats to merchant ships and commercial fishing boats. The
morphology of these estuaries is being shaped by high tidal oscillations superimposed on
waves and high volumes of sediment brought in by the rivers and creeks that flow into their
drainage basins. The estuaries serve as navigational ways to the Bonny, Onne, Port Harcourt,
Okrika and Calabar ports which are of high socio-economic importance to Nigeria.
Navigational and environmental problems facing these estuaries include strong currents,
occurrence of sandbars or shoals around the mouth, and erosion.
Keywords
Estuary
River discharge
Tides
Niger Delta
Ports
Climate
Introduction
The Bonny and Cross River estuaries, like other estuaries in
the Niger Delta, are affected by the Intertropical Conver-
gence Zone (ITCZ), generally referred to as the Intertrop-
ical Discontinuity (ITD). This frontal zone is related to the
northward and southward movement of the sun. Associated
with the movement of the ITCZ are the warm humid
maritime Tropical (mT) air mass with its south-westerly
winds and the hot and dry continental (cT) air mass with its
north-easterly winds. These air masses determine the
dominant seasons (rainy and dry) during any given time and
are responsible for the different factors that govern the
climate.
Wind speeds during the dry season are generally subdued
with a mean monthly speed of between 2 and 4 m/s. Wind
directions along the coast are predominantly south-westerly.
However, the north-easterly dust-laden harmattan winds
affect the coast especially in December and January. During
The Bonny and Cross River estuaries are two major estuaries
along the eastern coast of Nigeria (Fig.
1
). In particular, the
Bonny River estuary is within the Niger Delta while the Cross
River estuary is within the Strand coast of Nigeria (Fig.
2
). These
estuaries are strongly influenced by currents, tides and storms
surges. The mouths of these estuaries are used extensively by a
wide range of vessels and boats with varying sizes ranging from
small dinghies and powerboats to merchant ships and com-
mercial fishing boats to the five major ports in the eastern
Nigeria. These ports (Bonny, Onne, Port Harcourt, Okrika and
Calabar) are essential for economic development in Nigeria.
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