Irrigation is mainly practised in areas where there is insufficient rainfall like in Egypt and Sudan (Nile Basin) which make use of water from the River Nile, and in Mali, Northern Nigeria (Niger Basin) which make use of water from River Niger.
These countries, especially Egypt and Sudan are in the desert, hence the need for irrigation agriculture.
Need or reasons for irrigation
These are some of the reasons for the need for irrigation in both the Nile Basin and the Niger Basin:
- Rainfall is low and unreliable
- High rate of evaporation creates water deficit in the soil
- Both areas are dry and arid
FACTORS WHICH FAVOUR IRRIGATION AGRICULTURE
- Presence of river like River Nile in Egypt and Sudan, and Niger in West Africa
- Presence of fertile alluvial soils (or plain).
- Incidence of low rain fall or unreliable rainfall
- Incidence of high rate of evaporation
- Resourcefulness of people
- Presence of large population and the need for increased food production
- The need for agricultural raw materials
- The need to control flooding
IMPORTANCE OF IRRIGATION
- It makes farmers to be less dependent on rainfall
- Irrigation makes early planting possible
- It enables farmers to cultivate one crop twice or thrice on the same piece of land in a year.
- It increases the yield of crops
- It helps to reduce salt concentration in the soil by diluting and dissolving some out of the soil.
Areas covered by irrigation
The areas covered by irrigation schemes or where irrigation agriculture is practised are:
- In the Nile Basin are:
- Lower Nile valley from the Aswan Dam to the Delta in Egypt
- Sennar (sudan)
- Middle Nile valley in the Sudan
- Kenena (Sudan)
- kasm-el-Girba area long the Atbara in Eastern Sudan
- Gezira district between the white and blue Nile in the Sudan
- Lake shores
- Khasimel Girba (Egypt)
- In the Niger Basinare
- Inland Niger Delta (in Mali)
- The Niger valley
- The lake shores e.g. Kainji Lake
Similarities Between the Nile and Niger Irrigation Practises
- Both the Nile and the Niger irrigation practises depend on large dams.
- Both practise perennial irrigation i.e. building of dams and barrages.
- Both use canals to channel water to the farm.
- Manual method is also used in both areas
- They both grow food crops, e.g. cereals and vegetables
- Both have small and large farms
- Irrigation farms in both areas are owned by government and individuals
- They both grow cash crops, e.g. sugar cane on the Niger and cotton on the Nile.
Reasons why irrigation is more important in the Nile Basin than the Niger basin
- The Nile basin occupies a desert area, especially in Egypt. It supplies virtually all the water requirements while the Niger areas receive more rainfall.
- Presence of richer alluvial flood plains in the Nile which is better for agriculture than in the Niger basin
- There is higher population in the Nile Basin than in the Niger basin. This leads to greater demand for food production
- The Nile basin is used more for cash crop production than in the Niger basin
- There is more intensive use of land on the Nile basin than on the Niger basin
METHODS OF IRRIGATION IN USE
This methods employed in both the Nile and Niger basins are the same and they include:
- Shaduf method: This involves a hand-operated lever lifting buckets of water from the river and tipping, or dropping them into narrow channels running along the ridges or patches of cultivation
- Perennial method
- Mostly, modern methods of irrigation are used in the Nile valley
- Dams and barrages are built across the Nile
- Dams hold back some of the Nile water during the floods
- Water stored behind the dams is released, especially when the level of the river is low
- Water is allowed to flow by gravity to be cultivated land below the dam
- By releasing the water, farming takes place throughout year
- The most important of these dams is the Aswan Dam
- Some other dams in this areas are Jebel, Aulia, Sennar, etc.
- Basin irrigation method: This occurs during the flooding of the rivers. When flood occurs, water is held back by building up some embankments or barriers. This water is later released during dry season
- Use of pumps: It involves the use of generators or pumping machines to get water out from rivers or wells to farmlands. This at times is also referred to as sprinkler irrigation
- Manual method (use of buckets): This involves the fetching of water with buckets from rivers and wells and getting them to farmlands.
- In the Nile Basin: Crops cultivated include cotton, sugar cane, millet, wheat, maize and rice, barley and groundnut
- In t he Niger Basin: Crops cultivated include ground-nut, maize, guinea corn, onions, sugar cane and rice.
Contributions of irrigation schemes to economic development
- Provision of food
- Establishment of farm projects
- Water is provided for small scale farming
- Revenue to government
- Enables continuous cropping throughout the year
- Growth of settlement
- Employment opportunities
- Foreign exchange earning
- Raw materials for industries
- Encourages research
- Tourist attraction
Specific problems created by Irrigation in the Nile Valley
- Irrigation uses up the water which otherwise could have been used for other demands such as hydroelectric power generation, transportation.
- The creation of the Nasser Lake by the Aswan Dam led to the submergence of several settlements and displacement of over 50,000 persons who had to be resettled in the Kasm-el-Girba area in the Sudan.
- The holding back of some silt and other sediments by the lakes and dams has prevented them from reaching the lower Nile valley in Egypt and were deposited there.
- The reduction in the seditment load of the lower Nile has decreased the rate at which sand banks are being built up in the delta. The result of this is that the Mediterranean sea has flooded over 400,000 hectares of fertile farmlands
- Fluctuation in the volume of water
- Social problems of displaced people (resettlement)
- Collapse of dams
- Retained water in dams creates diseases e.g. bilharzias, river blindness
- Growth of water weeds
- Decrease in the amount of fresh water has led to decline of fishing industry in Egypt.
GENERAL PROBLEMS OF IRRIGATION
Problems usually associated with irrigation include:
- The construction of dams has led to the displacement of people from their original homes and lands. This leads to high cost of resettlement
- Fluctuation in the volume of water in rivers also result in low yield of crops
- Irrigation equipment is expensive to purchase and maintain
- Lack of technical know-how on the establishment and operations of irrigation scheme
- Excessive dissolution of salts in irrigated area or increase in salinity prevents proper growth crps
- There is the problem of silting of dams
- There are social problems arising from the displacement of people or settlement
- Most dam may collapse
- Breeding can occur as a result of flooding
- It can result in the growth of water weeds.
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