Environmental Engineering Reference
In-Depth Information
the major estuaries of Sine Saloum and the Gambia. This
coast is structured by rocky outcrops of sandstone and
badly deteriorated, fragile ferruginous cuirass.
• The mangrove coastlines associated with the estuaries in
the Southern Rivers region from Sine Saloum in Senegal
to the Sherbro islands in Sierra Leone.
• A coastal region highly structured into rocky headlands
and sandy coves from Liberia to the West of Coast
d'Ivoire. This same profile is also to be found in the
central part of Ghana.
• From the west of Cˆ te d'Ivoire to Benin stretches two
large sediment basins of soft coastline (Côte d'Ivoire and
Dahomey basins) also characterised by important lagoon
and channel systems parallel to the coast and situated
behind a sandbank that is very narrow in places (lidos).
These two large sediment basins are separated by the
Three Points Cape in Ghana and a few adjacent forma-
tions that are more or less rocky (sandstone) or in head-
lands, right to the mouth of the Volta.
Congolese zones (White
1983
). The extensive wetlands,
corresponding to the morphology of flat, low-lying topog-
raphy of the major part of the coast and to the interpene-
tration of fluvio-marine influences, in particular in the
estuarine areas, constitute the striking characteristics of this
maritime façade.
Major Natural Areas
There are four major, extensive, more or less protected
natural areas along this coastline: the Banc d'Arguin
National Park in Mauritania, the Delta of the River Senegal,
the Bijagos archipelago and the Sherbro-Robertsport com-
plex between Sierra Leone and Liberia.
Between these major units, some of which have already
been subject to conservation measures for some time (Ar-
guin, Bijagos), is an interspersed network of natural areas
that are still relatively preserved, some of which are subject
to local protection measures (RAMSAR sites, marine pro-
tected areas in Senegal, the national network of marine and
coastal protected areas in Guinea Bissau, etc.).
Dense Guinea-Congolese forest
The last relicts of the Guinean coastal forests (Guinea
Bissau, Guinea) are today largely deteriorated, or have
simply disappeared. However, a few dense forest areas
remain in places, in particular in Liberia, with little data
available on the actual status and distribution of these for-
mations. Secondary forests from the recolonising of plan-
tation areas that were previously artificialised are better
represented from Liberia to Ghana. Note that the dense,
evergreen Guinea-Congolese forests extend from Cap Pal-
mas to Cape Coast in Ghana, at some distance from the
coast. These formations extend to Nigeria after an inter-
ruption (Dahomey gap), due to the bioclimatic reasons from
Keta in Ghana to Benin inclusive. There is practically no
forest remaining on the actual edge of the coastal area.
These hinterland forest facies vary depending on the
edaphic conditions (rock outcrops and cuirasses, wetland
depressions, leached sand on coastal terraces), orographic
conditions (reliefs), bioclimatic conditions (duration of the
dry season) and the intensity of human intervention (fires,
conversions and secondary regrowth after
The major part of the coast in West Africa has a
high sensitivity to coastal erosion related to (i) the
nature of the materials (mobile sandy sediment or
highly altered and fractured rocks; (ii) the circulating
sediment fluxes which remain limited either due to
continental or river mouth trapping, or due to the
coastal sediment partitioning that can be observed on
coasts
that
are
more
predominantly
structured
in
headlands and coves.
The developments and infrastructures that disturb a
coastal drift that is typically parallel to the shore
create observable direct impacts: siltation upstream
and erosion downstream of the portions of the coastal
region that have undergone human artificialisation, in
particular through structures placed perpendicular to
the shore and the coastal drift current (ports of Nou-
akchott, Lomé, Cotonou, etc.).
In the stepped coasts, or in headlands and coves,
the diversity of the situations in relation to the pre-
dominant ocean waves and the coastal drift current
requires a case-by-case analysis of the sensitivity to
erosion, which is largely conditioned by the local
configuration.
plantation or
slash-and-burn).
This coastal evergreen Guinea-Congo rainforest is
recognised as exceptionally rich with a diversified flora
including a notable proportion of endemic species. Like the
dense coastal forests of Guinea, these forest entities are also
highly threatened.
Mangroves
The mangroves of West Africa are completely different
in their composition from those in East Africa. The seven
main
Biodiversity and Ecological Services
The biodiversity of the coastal ecosystems of West Africa is
directly related to the variety of types of coast and to the
steep
bioclimatic
gradient
characteristic
of
the
region,
covering
the
Saharan,
Sahelian,
Sudanese
and
Guinea-
species
they
comprise
(Rhizophora
mangle,
R.
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