The Western and Central Africa Land–Sea Interface: A Vulnerable, Threatened, and Important Coastal Zone Within a Changing Environment - The Land/Ocean Interactions in the Coastal Zone of West and Central Africa - page 3

Fig. 1 Map of the coast of West Africa with main rivers and marine currents

river systems draining the entire coastline from Senegal to
Congo. The most important rivers include the Niger, which
drains an area of over 1 million km 2 ; the Volta, with a
drainage basin of 390,000 km 2 (World Bank Africa 1994 );
and the Congo river, with the second largest mean annual
runoff and catchment area in the world, freshwater and sedi-
ment discharge estimated to be 30-80 tons/km 2 . For purposes
of energy production, irrigation, and flood control, however,
most of these rivers have been dammed, consequently sig-
nificantly altering their hydrology and sediment flows, thereby
causing inevitable downstream impacts and accelerating
coastal erosion processes (see chapter ' ' Management of a
Tropical River: Impacts on the Resilience of the Senegal River
Estuary ' '). The coastal basins, particularly along the Niger
Delta, are gradually subsiding because of the geology of the
area, as well as such human activities as oil mining and natural
gas exploitation. On the other hand, the existing agrochemical
and agricultural runoff within the Niger River basin, as well as
the sediment load and urban and industrial wastewaters, have
caused notable groundwater contamination and water quality
degradation. These pollutant discharges directly affect the

coastal ecosystems of the countries located along the coast.
Regarding coastal concerns, the potential sea level rise and its
impacts also are important, including shoreline retreat and
coastal erosion, an increased frequency of coastal wetland
submergence and saltwater intrusion into estuaries and coastal
lagoons and aquifers.

General Oceanography, Coastal Morphology,
and Processes

Four distinct and relatively persistent oceanic current sys-
tems are of importance off the shores of Western and
Central African coasts (Fig. 1 ) in regard to the transport of
substances, water temperature, meteorology, and biological
conditions. They are as follows:
(a) The cold Canary Current, flowing southwestward along
the coast in the northern part of the Western and Central
African region (Mauritania, Senegal, Gambia, Guinea,
etc.). It feeds the North Equatorial Countercurrent and
the Guinea Current (Fig. 1 );