Environmental Engineering Reference
In-Depth Information
Fig. 1
Nigeria coastal area geomorphologic zones (Awosika et al.
2000
)
semidiurnal tidal regimes with tidal amplitude of about
1.2 m and higher ebb flow velocities than flood flow. For
example, ebb flow velocity in excess of about 5,000 m
3
/sec
above flood flow was recorded at the Bonny River (NE-
DECO
1961
). The geomorphic unit has 21 major river
mouths/tidal inlets that intersect the coast, breaking it up
into a series of barrier islands of which 16 are within the
arcuate delta region. This natural delta receives its sedi-
ments, which mainly comprise medium to coarse uncon-
solidated sands, silt, clay, shale, and peat, from the
suspended and traction load of the Niger and Benue Rivers
and their tributaries.
The Niger Delta is characterized by a sandy shoreline
backed by extensive mangrove swamp and Barrier Island
separated by tidal channels. This region has the longest
barrier island of about 35 km (Ramos-Dodo Island), of
which the widest is Focados-Ramos Island which is 10 km
wide. In the eastern flank, the barrier islands are narrower
and appear as remnants of beach ridges, due to wave action
and tidal erosion in and around the associated creek net-
work. The barrier islands on the delta are generally
15-20 km in length and 3-5 km wide and are better
developed on the western than on the eastern flank. Based
on the shoreline morphology deposition (Fig.
3
), the delta
region is vulnerable to sandy coast erosion and horizontal
recession due to the white beach sand and sandy ridge
substrates
Box 2: Nigerian Coastal Region
• Nigeria coastline region covers a total length of
approximately 859 km.
• Nigerian coastal region is divided into four main
geomorphic zones (from east to west) namely the
stranded coast/estuary complex, the Niger Delta,
the transgressive Mahin mud coast, and the barrier
beach lagoon coast complex.
• Nigerian coast is semidiurnal and from a south-
westerly direction with two inequalities.
Based on large- and small-scale geomorphic differences
and numerous physical characteristics (i.e. beach sediment
grain size and coastal processes), the coastline was classi-
fied into six geomorphic units (Fig.
2
). The Niger Delta
consists of the western delta flank, arcuate delta, and eastern
flank categories.
The Niger Delta is a vast sedimentary basin with a
complex river network and a fragile ecology in which fresh
and saline water ecosystems maintain a dynamic equilib-
rium. The delta covers about 50 % of the total length of the
Nigerian coastline, stretching from the Benin River estuary
for about 450 km eastward, and terminates at the mouth of
the Imo River estuary. The region has a delta flank coast
(western and eastern flank) on either side accounting for
115 km
with
grades
of
fine-
to
very
fine-grained,
of
Nigerian
coastline
and
characterized
by
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