West African Coastal Area: Challenges and Outlook - The Land/Ocean Interactions in the Coastal Zone of West and Central Africa - page 13

Fig. 2 Proportion of length of
shoreline according to the
different coastal facies (SDLAO,
UEMOA-IUCN 2011 ). Note the
high proportion of mangrove
coasts, also related to the highly
fractal dimension that
characterises the shoreline in
these milieus

extend their capacity, or will do so in the near future. The
increasing penetration of the private sector in the manage-
ment and even building of ports (for ore ports) should act as
an incentive to the States to be vigilant in taking into
account the environmental and coastal impacts of these new
facilities.

• Relict of sandstone or hardpan spared by erosion (sand-
stone on the Senegalese Petite Côte, the Bijagos and
around the periphery of Accra).
• Granites and metamorphic rocks presents on all of
Liberia, Western Côte d'Ivoire and the central part of the
coast of Ghana.
The remainder of the coast line is composed of:
Unstable and/or very dynamic coasts
• Sand banks, estuaries, river mouths, spits and islets by
nature also very unstable and dynamic (12 %).
• Mangroves, continuously evolving (48 %).
• Sandy formations of lidos, thin sandy rim between a
lagoon

A Fragile, Dynamic Coastline

On the coasts constituted of sedimentary accumulation, which
are by far the most common in West Africa, the mobility of the
shoreline largely depends on the local balance of supply and
removal in the sediment budget. Removal operates under the
action of natural agents (coastal drift, ocean waves, wind, etc.),
which are also partly responsible for sediment supply. Removal
may also be the result of human activity, either directly
(extraction from the beaches of raw materials for building
activities, for instance), or indirectly (the creation of surfaces
that reflect wave energy or installations that disrupt the oper-
ation and the exchanges between the different sediment com-
partments of the beaches or that disturb the coastal drift parallel
to the shore). The dams situated on the catchment areas also
constitute traps for continental sediment which no longer
reaches the coast, increasing the sediment deficit, particularly at
the level of the estuaries and mouths of rivers.

and the sea shore, also unstable and highly

changing (7 %).
Less dynamic coasts, but still subject to natural episodes
of erosion and accretion outside of human intervention.
• More or less straight sandy coasts, fashioned by the
coastal drift currents, relatively stable but subject to
cyclical phases of erosion and accretion, also very sen-
sitive to nay disruptions of the coastal drift (16 %).
• Stepped coasts or headlands and coves, where the coves
are compartments more or less separated by rock out-
crops or less soft. Their stability strongly depends on the
orientation in relation to the ocean waves and currents
(14 %). The sediment stocks here are often very limited
(Fig. 2 ).

Of the estimated less than 6,000 km of coastline (at a scale
of 1:75,000) from Mauritania to Benin, rocky coasts repre-
sent fewer than 3 % of the coast line. These coasts are made
of rock that is often altered and fractured, subject to land-
slides and erosion. There are, however, a few rock outcrops
that structure this coast in headlands that are less soft but
often fractured and fragile, and especially few in number:
• Basalts and other rocky formations on the Cape Verde
Peninsula (Senegal).
• Rock outcrops at Cap Verga and the Conakry peninsula
(Guinea).
• Breakwater at Freetown (Sierra Leone).

The whole of this coastal system is first of all
conditioned by the sediment legacies dating from the
last transgressions and remobilised by the morpho-
genic agents (currents, winds and ocean waves).
Continental fluxes, whether aeolian or fluviatile, only
partially contribute to maintaining the legacy stocks.
This is nonetheless a hypothesis which has not yet
been confirmed.