Drainage refers to water bodies like rivers and lakes. Drainage of Nigeria is discussed in two parts – rivers and lakes.
- RIVERS IN NIGERIA: Nigeria is drained by two main rivers – Rivers Niger and Benue. River Niger, the largest river in Nigeria has its source from Guinea highlands in Guinea. It passes through Mali and Niger Republic to Nigeria. River Benue has its source from eastern highlands and joins the Niger at Lokoja. Because of this, Lokoja is known as a confluence town. Other rivers in Nigeria take their sources from highlands in Nigeria known as Hydrological centres. These are:
- Western Highlands: They have rivers such as Ogun, Osun and Osse which flow directly into the Atlantic Ocean.
- North-Central Highlands: They have such rivers as Kaduna, Hadeija, Zamfara, Yobe, Gana, Gongola and Rima.
- Eastern Highlands: They have rivers like Donga and Kastina-Ala.
- Eastern Scarplands: They have rivers like Anambra and Cross River.
Characteristics of Nigeria Rivers
- The volume of water increases during the rainy season and decreases during the dry season.
- Most rivers have rapids and cataracts which impede or disturb inland navigation.
- Most Nigerian rivers do have lots of debris like dead leaves, mud, wood, etc. when they flow through forest.
- Most rivers are usually very short and flow rapidly or swiftly e.g. Rivers Ogun, Osun and Cross River.
- Rivers in the south flow in the north-south direction into the sea while rivers in the north flow in a radial pattern to different directions.
- 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 flow during rainy season but stop or reduce flowing during the dry season.
Importance of Nigerian Rivers
- Rivers, especially the large ones serves as medium of transportation from one place to another.
- Many rivers are dammed in areas of water fall and rapids for the purpose of generating electricity.
- Water from rivers is used for irrigation purposes (i.e. irrigation agriculture) especially in areas of low rainfall to aid crop cultivation.
- Water from rivers is used for various domestic purposes such as cooking, washing, bathing and drinking.
- Water from rivers is also required by many industries such as textile, brewery and chemical industries.
- Rivers do provide employment to many people e.g. fishermen, canoe and ship builders.
- Rivers are known to provide food for man in form of fish, prawns, crayfish, crab, etc.
- Some rivers are centers of tourist attraction and may generate foreign exchange for a nation.
- Some rivers are good sites for the construction of seaports and river ports.
- Formation of flood plains by rivers also provides fertile soil for agricultural activities.
Problems Encountered in the utilization of Nigeria Rivers
- Seasonal fluctuation of the water volume.
- Rapids and falls on the rivers.
- Growth of water weeds.
- Narrow channels.
- River pollution.
- Inland drainage into lakes.
- Silting at river mouths.
- Shallow channels.
- Shortness of rivers.
River basin refers to the area generally drained by a river and its tributaries. In other words, river basins are naturally depressed lowland areas. River basin is also called catchment area.
In Nigeria, there are five major river basins. These are:
- The Niger Basin.
- The Benue Basin.
- The Chad Basin.
- The Cross River Basin.
- The South Atlantic Basin.
The rivers in these basins are grouped into three classes of:
- Long rivers with large basin: These Rivers flow to the sea across long distances through the land e.g. Rivers Niger and Benue.
- Short rivers with small basin: These Rivers also flow to the sea but are very short e.g. Rivers Osun, Ogun, Cross river, etc.
- Rivers in basins of inland drainage: These Rivers do not reach the sea but rather they flow into Lake Chad e.g. Rivers Yobe, Hadeija and Yedseram and Gana.
Importance of River Basins
- As a result of the fact that river basins are depressed lowlands, it enables people to settle and build houses.
- Some river basins with alluvial plains are fertile lands for agricultural purposes.
- The presence of rivers enables people to transport themselves and their goods from one place to another.
- Depressed or lowland areas do serve as deposits for minerals e.g. petroleum.
- Water from rivers in the basins may be used for domestic and industrial purposes.
- Rivers in the basins do provide or act as fishing ground for fishermen.
- LAKES IN NIGERIA: A lake is a body of water surrounded by land. The lakes in Nigeria are grouped into two major types.
- Man-made or artificial lakes: These lakes are constructed by man. Examples of such lakes are Lake Kainji on River Niger and Shiroro Lake on River Kaduna.
- Natural lakes: These are lakes which exist naturally. The only popular example is Lake Chad. Lake Chad is also described as an inland drainage because it receives water from many rivers such as Hadeija, Gana, Yobe, Yedseram. In spite of the fact that Lake Chad receives water from many rivers. It is very shallow.
Reasons for the shallowness of Inland Drainage (Lake Chad)
- Nature of the rivers flowing into the lake: The five rivers that supply the lake with water are shallow, flow sluggishly and pass through semi desert. Hence, most of the water is lost through evaporation and percolation into soil leading to reduced flow of water into the lake.
- Tapping of some rivers by river Benue: Specific Rivers like River Lagone (outside Nigeria) is being tapped by the Benue headstream. This contributes to reduced volume of water.
- Location of the lake: The Lake is essentially located in Sahara desert and thus it experiences high evaporation leading to low volume of water.
- Underground drainage: It has been suspected that Lake Chad is experiencing underground seepage to nearby oasis, hence, the shallowness of the lake.
Importance of Lakes
- Provision of food e.g. fish.
- Generation of H.E.P.
- Development of the area.
- Industrial uses.
- Domestic uses.