WEEK 3: DRAINAGE OF NIGERIACONTENT Drainage refer to water bodies like rivers and lakes.a. RIVERS IN NIGERIA Most of the country is drained by the Niger, Benue and

their tributaries. River Niger, the largest river in Nigeria ha 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 take their sources from highlands in Nigeria known as hydrological centres. These centres are:

1. Western Highlands They have rivers such as Ogun, Osun, and Osse which flow

directly into the Atlantic ocean.2. North-central Highlands The drainage pattern is clearly centrifugal or radial, with Jos

Plateau constituting the central dome. They have such rivers as Kaduna, Hadejia, Zamfara, Yobe, Gana,

Gongola, gboko, Mada and Rima which rise and flow in different directions.

3. Eastern Highlands They have rivers like Donga, Yedseram, Katsina Ala, Cross river,

Taraba and Naado river. These rivers flow into either lake Chad, river Benue or Atlantic

ocean.4. The Eastern Scarplands They have rivers like Anambra, Ajalli, Adaba, Mamu and Oji all of

which flow into river Niger.CHARACTERISTICS OF NIGERIA RIVERS The volume of the rivers changes with season: Volume increases

during rainy season and decreases during dry season. Presence of rapid and cataracts: These rapids and cataracts

impede or disturb inland navigation.

Presence of debris: Such debris include dead leaves, mud, wood etc. Short courses with high speed: Most rivers are usually very short and flow rapidly or swiftly e.g. rivers Ogun, Osun and Cross river. Specific direction of flow: 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. Shallowness: Most rivers are very shallow and full of silt associated with high evaporation and seepage of water into the soil. The colour changes with season: The rivers have muddy and dirty colour during raining season but remain clear and clean during dry season. Seasonality: Most rivers flow during rainy season but stop or reduce flowing during the dry season.

USES OR IMPORTANCE OF NIGERIA RIVERS1) Medium of transportation: Large rivers like Niger and Benue

serve as medium of transportation from one place to another.2) Rivers provide water for irrigation especially when they are

dammed.3) They help to generate hydro-electric power e.g. Kainji, Jebba

and shiroro.4) Water from rivers is used for various domestic purposes such

as cooking, washing and bathing.5) Water from rivers is also required by many industries such as

textile, brewery and chemical industries.

6. Rivers do provide employment to many people e.g. fisher men, canoe and ship building.7. Rivers are known to provide food for many in form of fish, prawns, crayfish, crab .e.t.c.8. Some rivers are centres of tourist attraction and may generate foreign exchange for a nation e.g. Argungu fishing festival in Kebbi state.9. Some rivers are good sites for the construction of river ports.10. Formation of flood plains by rivers also provides fertile soil for agricultural activities.RIVER BASIN • A river basin is an area where a river or rivers flow through . Such area are at times demarcated for the purpose of developmental planning.• River basin is also known as catchment area.• In Nigeria, there are five major river basins.• These are: (i). The Niger Basin (ii). The Benue Basin (iii). The Chad Basin(iv). The Cross River Basin (v). The South Atlantic Basin.• The rivers in these basins are grouped into three classes of :1. Long rivers with large basin: These rivers flow to the sea across

long distances through the land e.g. rivers Niger and Benue.

2. Short rivers with small basin: These rivers also flow to the sea but are very short e.g. rivers Osun, Ogun, Cross river e.t.c.3. Rivers in basins of inland drainage: These rivers do not reach the sea but rather they flow into lake Chad e.g. rivers Yobe, Hadejia, Yedseram and Gana.

IMPORTANCE OF RIVER BASINSa) Good sites for settlements: River basins are depressed

lowlands that enable people to settle and build houses.b) Suitable land for agriculture: River basins with alluvial plains

are fertile lands for agriculture purposes.c) Medium of communication: The presence of rivers enables

people to transport themselves and their goods from on place to another.

d) River basins serve as deposits for minerals e.g. petroleum in the Niger Delta area.

e) Water from rivers in the basins may be used for domestic and industrial purposes.

f) 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.

1. Man-made or artificial lakes These lakes are constructed by man. Examples include lake Kainji on river Niger and Shiroro lake on

river Kaduna.2. Natural lakes These are lakes which exist naturally. Lake Chad is the only popular example Lake Chad is also described as an inland drainage because it

receives water from many rivers such as Hadejia, Gana, Yobe, Yedseram e.t.c.

In spite of the fact that lake Chad receives water from many rivers, it is very shallow.

REASONS FOR THE SHALLOWNESS OF LAKE CHAD1) Nature of the rivers flowing into the lakeo The five rivers that supply the lake with water are shallow, flow

sluggishly and pass through semi-desert.o Hence most of the water is lost through evaporation and

percolation into soil leading to reduced flow of water in the lake.2). Tapping of some rivers by river Benueo Specific rivers like River Lagone (outside Nigeria) is being tapped

by the Benue headstream. This contributes to reduced volume of water.

3). Location of the lakeo The lake is essentially located in Sahara desert and thus it

experiences high evaporation leading to low volume of water.

4. Underground drainageo Lake Chad is experiencing underground seepage to nearby oasis. Hence, the shallowness of the lake.

ASSIGNMENTOn the outline map of Nigeria, name and locatei. River Nigerii. River Benueiii. River Kadunaiv. River Crossv. River Osunvi. River Ossevii. River Gongolaviii. River Sokotoix. Lake Chadx. Kainji damxi. Shiroro damxii. Jebba damNB: This assignment must follow the note on drainage of Nigeria.