RELIEF AND DRAINAGE OF WEST AFRICA
The relief of West Africa can be grouped into three classes as follows:
1. The lowlands: These areas are below 300m above the sea-level and are made up of sedimentary rocks. The lowlands are further sub-divided into two:
- The interior lowlands: These are found in the inland delta (Mali), Chad basin and Niger-Benue trough (both in Nigeria), and the Volta basin (Ghana).
- Coastal lowlands: These are found near the coasts of some countries like Mauritania, the Gambia, Cote d’ivoire, Nigeria, Senegal, Sierra Leone, Liberia, Togo, Benin and Ghana.
2. The interior plateau: The average height of these areas range between 300-900m and are made up of basement complex rocks. Areas of interior plateau include:
- North central plateau of Nigeria.
- Southern Mali
- Northern Burkina Faso
- The Akwapin-Togo ranges
3. The high mountains and plateaux: These are areas above 900m in height and are made up of basement complex rocks found in:
- Futa Djalon plateau
- Jos Plateau
- Mandara mountains
- The Adamawa-Bamenda highlands.
- Most of the rivers in West Africa have their sources from these highlands.
In West Africa, there are five different types of coastline. These are:
- The smooth sandy coastline: This is found between Cape Blanco and Dakar. This coast is characterized by the presence of sand deposition along the coast.
- Ria coastline: This is found between Dakar and Sierra Leone. It is the best coastline suitable for natural harbour.
- Cliff coastline: This is found in Monrovia in Liberia and Takoradi in Ghana where high cliffs exist along the coast.
- The lagoon coastline: This is found in Ghana (River Volta), Togo, Benin and the western coast of Nigeria where numerous lagoons exist.
- The Delta coast: This is found in the mouth of Rivers Volta (Ghana) and Niger (Nigeria) where materials carried down by the rivers are deposited, resulting in distributaries that flow into the sea.
West Africa is drained by three major groups of rivers which are:
- The long rivers
- The short rivers
- The inland drainage rivers
1. The long rivers: These Rivers flow through many countries before they empty their water into the sea. They are not restricted to one country. These rivers include Rivers Niger, Volta, Gambia and Senegal.
- River Niger: River Niger, the longest river in West Africa and the third longest in Africa is about 4,160km long. It has its source from Guinea highlands and flows through Guinea, Niger, Mali, Niger and finally ends in Nigeria where it empties its water into the sea.
- Along its course, it has inland delta in Mali where the river is braided, forms tiny lakes, later rejoins and flows away. It has an important artificial lake in Nigeria called the Kainji Lake.
- River Volta: This river, the second longest in West Africa is about 1,600km long. It has its source in the plateau of Burkina Faso and flows through Ghana to the sea. It is Ghana’s most important river and has important artificial (man-made) lake called Volta Lake.
- River Senegal: This river has its source from Guinea highlands, flow through Mali and finally through Senegal to the sea.
- River Gambia: It has its source in Fouta Djalion highland, flows through Guinea, Senegal and finally through Gambia where it flows into the sea.
2. The Short rivers: These Rivers are short, slow flowing and empty their water into the sea.
Short rivers in West Africa include:
- The Cross and Ogun rivers (Nigeria)
- The Sassandra (in Cote d’ivoire)
- The Pra and Tano (in Ghana)
- The Rokel (in Sierra Leone)
- The Konkoure (in Guinea)
3. The inland drainage rivers: These rivers flow into Lake Chad and have no visible outlet to the sea. These rivers are Hadeija, Yedeseram, Logone, Yobe and Shari. These rivers are called rivers of inland drainage and the lake (Lake Chad) which they flow into is called the lake of inland drainage.
CHARACTERISTICS OF WEST AFRICAN RIVERS
- Most West African rivers do have lots of debris like water weeds, dead leaves, mud, wood, e.t.c as they flow through forest.
- The volume of water increases during the rainy season and decreases during the dry season.
- Most rivers are very shallow and full of silt associated with high evaporation and seepage of water into the soil.
- The rivers have muddy and dirty colour during rainy season but remain clear and clean during dry season.
- Most rivers have rapids and cataracts which impede or disturb inland navigation.
IMPORTANCE OF WEST AFRICAN RIVERS
- Many rivers are dammed in areas of water fall and rapids for the purpose of generating electricity.
- Rivers especially the large ones serve as medium of transportation from one place to another.
- Water from rivers is used for various domestic purposes such as cooking, washing, bathing and drinking.
- Formation of flood plains by rivers also provides fertile soil for agricultural activities.
- Rivers are known to provide food for man in form of fish, prawns, crayfish, crab, e.t.c.
- Some rivers are centers of tourist attraction and may generate foreign exchange for the nation.
- Water from rivers is used for irrigation purposes (i.e irrigation agriculture), especially in areas of low rainfall to aid crop cultivation.
LAKES IN WEST AFRICA
The lakes in West Africa include:
- Lake Chad: (natural and the largest) lake in West Africa. It is an inland drainage found in North eastern part of Nigeria.
- Lake Kainji on River Niger (Nigeria).
- Lake Volta on River Volta (Ghana).
- Lake Kossou on River Sassandra (Cote d’ivoire).