Environmental Engineering Reference
In-Depth Information
Coastal Processes, Physical Alterations,
and Habitat Modifications
(b) The North Equatorial Countercurrent flowing eastward
from the central Atlantic;
(c) The Guinea Current, fed by the North Equatorial
Countercurrent, involving warm waters flowing east-
ward and southeastward along the coast of the Gulf of
Guinea (Sherman and Hempel
2008
); and
(d) The South Equatorial Current, which flows at some
distance from the coast, between 10S and the Equator.
The Canary Current itself transports cool waters toward
the Equator and has current speeds of approximately 20 cm/s.
It is an essentially wind-driven current linked to the same
regional wind systems responsible for the upwelling phe-
nomenon that dominates the coastal waters up to several tens
of kilometers offshore. The cool and richer upwelling waters
prevail along the northwestern part from November to April/
May and along limited parts of the northern parts of the Gulf
of Guinea (Sherman and Hempel
2008
).
High precipitation and numerous rivers on the central
West African coast generate large masses of warm (above
24 C) and low-salinity (less than 35%) waters, the so-
called Guinea waters.
In terms of coastal morphology, the succession consists
of the following:
(a) Sandy arid coastal and plains bordered by eolian dunes
(Mauritania and North coasts of Senegal);
(b) More-or-less sandy alluvial marshes with estuaries and
deltas, colonized by mangrove vegetation (South of
Senegal, Guinea-Bissau and Guinea, and Sierra Leone);
(c) Rocky scarps and sandy beaches with barrier islands,
alternating with mangrove vegetation (Sierra Leone,
Liberia, and eastern Nigeria to Gabon);
(d) Low
Coastal erosion clearly constitutes the most serious coastal
process problem in many West African countries. The rate
of the coastal retreat can average several meters per year
(e.g., in Fajara, Serekunda in the Gambia; in Keta, Ghana;
and in the south coast of Dakar, Senegal). Although the
coastline is very sensitive to natural erosion and sedimen-
tation processes attributable to high wave energy, strong
littoral drift transport, etc., human activities have signifi-
cantly intensified coastal erosion, notably through sand
mining, disturbance of the hydrological cycles, river dam-
ming, port construction, dredging, and mangrove defores-
tation, to cite a few examples. These examples are
particularly relevant for the western part of Africa and
mainly for the coastal countries in the Gulf of Guinea
(Benin, Côte d'Ivoire, Ghana, Nigeria, and Togo).
Ecosystem Goods and Services and Species
Diversity
A large variety of ecosystems and habitats exist along the
western
and
central
coasts
of
Africa,
including
the
following:
(a) Wetland habitats, particularly those containing mangrove
swamps and forests in a series of deltaic and estuarine
formations, are the most apparent features. They extend
more than 15,000 km
2
from Senegal to Congo, with the
areas of highest mangrove concentration being located
along the coasts south of Senegal, Guinea and Guinea-
Bissau, Sierra Leone, and mainly in the Niger Delta (with
more than 6,500 km
2
). Although these mangrove forests
are less diverse in terms of species than those in East
Africa, they cover large surfaces and constitute the most
extensive mangrove forests in Africa (see chapters
sandy
coastal
plains,
alternating
with
coastal
lagoons
along
the
Gulf
of
Guinea
(Côte
d'Ivoire,
Ghana, Togo, Benin, and Congo estuary); and
(e) Huge marshy areas formed by the Niger Delta, with
mangroves and rapidly growing Nypa Palms, indented
by fluvial channels subject to tidal influences.
Further, a number of islands and archipelagos are located
in the Atlantic Ocean offshore of the West Africa coasts
(Canary and the Cape Verde Islands; Bissagos archipelago)
and in the eastern part of the Gulf of Guinea (Sao Tome and
Principe and Annabon in Equatorial Guinea, among others).
The tidal ranges along these west and central coasts are
wide, exceeding 5 m in places, with the average for the
whole coastal area being studied in the order of 1 m (See
chapter ''
West African Coastal Area: Challenges and
are in Guinea-Bissau, Guinea, and Sierra Leone (from 2.
8-4.7 m to 2.8 m; see Fig
2
; Table
1
).
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