In this article we will discuss about:- 1. Introduction to Irrigation 2. Meaning of Irrigation 3. Types 4. Why Irrigation is Necessary 5. Functions 6. Advantages or Benefits 7. Disadvantages or Ill-Effects 8. Development 9. Irrigation Potential in India.
Contents:
- Introduction to Irrigation
- Meaning of Irrigation
- Types of Irrigation Systems
- Why Irrigation is Necessary
- Functions of Irrigation Water
- Advantages or Benefits of Irrigation
- Disadvantages or Ill-Effects of Irrigation
- Development of Irrigation in India
- Irrigation Potential in India
1. Introduction to Irrigation:
Water is the greatest natural gift to the mankind. All the human beings and plant life thrive on the earth only because of water. All the early civilisations flourished along great rivers, because man had realised in the very beginning that water is essential for life. Today, out of total water consumed for human needs in the world, about 80 per cent is used for raising the crops.
The use of water for raising the crops is known as irrigation. Irrigation has assumed prominence throughout the world as it is the only way by which food production may be augmented for the ever increasing population of the world. Crops are raised by rains also in most parts of the world, but uncertainty of rains, and amount of rains are uncontrollable features.
There may not be any rains or there may be insufficient rain when it is most required by the crop. This aspect affects the yield of the crop. Hence the only way of supplying required amount of water to the crop, when it is most required, is by way of irrigation.
The sources of water may be divided under two heads — namely—surface sources and ground sources. Streams, lakes etc., are the surface sources whereas wells, infiltration galleries, and springs are examples of ground sources. Harnessing these sources and delivering water to the fields for raising crops is known as irrigation.
At present it is estimated that only about 15% of the agriculturable land of the world is receiving assured irrigation facilities whereas present sources of water are enough to provide irrigation to about 50% of the irrigable area of the world.
Hence it can be said that there is a lot of scope to bring about improvements in irrigation methods. To supplement the food requirements of fast increasing population, new technologies like sea water desalination and even weather modification may have to be evolved.
2. Meaning of Irrigation:
Artificial application of water to the soil for raising crops is known as irrigation. It is a science which pertains to the planning, designing, controlling and maintenance of irrigation works so that available water resources may be used in the best possible manner.
Irrigation works involve construction of dams, reservoirs, canals, headworks, cross-drainage works, river training works etc. Methods of application of water to crops, measures to prevent water logging and generation of hydroelectric power also come under the purview of irrigation.
3. Types of Irrigation Systems:
For irrigation purposes both ground and surface water resources are utilized.
Irrigation systems may broadly be divided under two heads:
1. Flow irrigation or gravity irrigation, and
2. Lift irrigation or pumped irrigation.
1. Flow Irrigation:
In this system of irrigation the water is conveyed to the fields by gravity only. In this system irrigation water to be used for irrigation is supplied at such an elevation that it reaches the fields under gravity through a system of canals and connected works.
Flow irrigation may further be sub-divided into following two classes:
(i) Perennial irrigation, and
(ii) Flood or inundation irrigation.
In case of perennial irrigation water is supplied to the fields throughout the crop period at the controlled rate. If water is available for growing two crops then water is supplied to the fields throughout the year. This system of irrigation thus requires some storage works in form of dam, barrage or storage weir so as to store the excess flood water. The stored water is released when regular flow in the stream falls short of the requirements for crops.
Inundation or flood irrigation is also sometimes known as tidal irrigation. In this case the area is not irrigated by controlled irrigation water but inundated during monsoons when rivers are in spate. There is no control over the water. Fields once inundated retain moisture for considerable time and bring the crops sown in them to maturity by no more watering or by one or two minor waterings. Natural rains may even eliminate possibilities of minor waterings also.
Depending upon the source from which the canals draw their water flow, irrigation can be further sub-divided into two types as follows:
(a) Direct irrigation, and
(b) Storage irrigation.
(a) Direct Irrigation:
In this system an obstruction in form of low weir or barrage is constructed across the river to raise the water level to such an elevation that the flow is diverted to the off taking canal. This system is also known as run-of-the river scheme. It is also sometimes named as river canal irrigation. In this case there is practically no storage of water.
If discharge in the river is more than the off taking canal capacity, the excess water is allowed to flow down the river. If discharge in the river is less than the capacity of the off taking canal, the canal can be run with full discharge only for a day or two as there is no storage to augment the supplies for longer times.
Hence canal will thereafter run with reduced discharge which is available from the river. Sarda Canal System and Ganga Canal System of U.P., are the examples of direct irrigation schemes. Direct irrigation projects are generally of smaller magnitude as there is no rigid control over the supplies.
(b) Storage Irrigation System:
In this case a solid barrier such as dam or a storage weir is constructed across the river and excess flood water is stored behind it. A large storage reservoir or an artificial lake is formed behind the dam. The stored water is used to run the canals full of water when discharge in the river falls short of the canal capacity.
This system involves construction of a dam and as such proves to be costly. To make them economical, these schemes are usually planned as multipurpose schemes. Generally more than one canal is taken off and also hydro-electric-power is generated.
Bhakra Dam Scheme of Punjab and Ramganga Scheme of U.P. are the examples of storage schemes. In such schemes, since lot of storage is developed behind the darn, therefore considerable land property gets submerged upstream of the dam.
Direct irrigation system is adopted when river is perennial and carries enough discharge during lean months, to run the canal full. Storage scheme is adopted when river either is not perennial or flows with insufficient discharge during lean months.
2. Lift Irrigation or Pumped Irrigation:
Lift irrigation may be classified as –
(i) Life irrigation from surface water, and
(ii) Lift irrigation from ground water.
In case of lift irrigation from surface water, lift canals are taken either from river directly or from parent gravity flow canal. In this case water is lifted with the help of big pumps and thrown into the lift canal. The water in the lift canal flows under gravity. When lift canal, after some run of length again comes in cutting, the water may again be lifted. In lift canals water may be lifted in stages depending upon the total lift required. Lifted water flows under gravity in the canal.
In the case of lift irrigation from ground water, water is lifted from deep tube wells. Tube well is bored in the field where its water is to be used. Tube well is fitted with pump which is run either with the help of electric motor or diesel engine. This method is the most economical method of utilizing ground water resources.
4. Why Irrigation is Necessary:
Irrigation of crops becomes necessary under the following circumstances:
1. When Rainfall is Very Small:
In such a case rainfall is not sufficient to mature the crops. Water has to be supplied to the crops artificially. In such a case irrigation works are constructed at far places where water for irrigation is available.
This water is then conveyed to the deficient areas through a system of canals and used for irrigation purposes. Rajasthan Canal is an example of such an irrigation system. This canal carries surplus waters of Punjab Rivers to and zones of Rajasthan where rainfall is very scanty.
2. When Rainfall is not Distributed over the Crop Period:
There are certain areas where overall annual rainfall statistics speak of sufficient rainfall for growing crops. But rainfall not being uniformly distributed for the crop period, it is not possible to mature the crops by rainfall alone.
Rainfall may be sufficient or even excessive, during early periods of the crop, and later on, there may be no rains or very little rains to cause the proper maturity of the crop. The ultimate result of such a condition is that either crops may die altogether or their yield is affected.
In such areas excess water during excessive rainfalls is collected and used for irrigation purposes when rainfall is very scanty. In India rainfall is very small during winters. Most of the irrigation projects in India are based on this concept.
Excessive rain water during heavy rains is kept stored in form of reservoirs by constructing dams and weirs. This stored water is not used during monsoons but used during winter for growing second crop i.e. Rabi crop.
3. For Growing Cash and Other Commercial Crops:
Irrigation also becomes necessary where it is proposed to grow cash crops and other commercial crops, which generally require very large amount of water and that too at fixed intervals.
Overall rainfall data may be appealing not to install any irrigation system, but requirements of water of cash crops at fixed intervals which cannot be assured by rainfall alone may warrant the necessity of installation of an irrigation system.
5. Functions of Irrigation Water:
Water when applied to fields performs the following functions:
1. It supplies moisture to the soil which is essential for the life of bacteria favourable to the plant growth.
2. It lowers the temperature of the soil during summer and thus provides more favourable conditions for plant growth.
3. It saves the plants from the harmful effects of frost during intensive colds.
4. It is essential for the chemical action within the plant leading to its growth.
5. It supplies moisture or water to the soil at fixed interval so as to replenish the moisture content of the soil.
6. Tillage of the fields becomes easy as irrigation water renders the fields soft.
7. It also reduces the concentration of the harmful salts in the soil. Harmful salts get washed out or diluted by irrigation water.
8. It helps dissolve chemical manures and renders them effective for plant growth. Thus water acts as nutrient carrier.
9. It helps in bringing up ground water table. Higher ground water table is very helpful in the installation of tube wells. Tube wells relieve lot of irrigation pressure from canals and canal water thus saved, may be used for developing new areas.
10. Irrigation water is essential for producing nourishing food for the plants.
6. Advantages or Benefits of Irrigation:
Earlier, irrigation projects were sanctioned only if after deducting the maintenance charges, they would ensure return of minimum prescribed rate of interest on the capital outlay. Sometimes unproductive schemes were also sanctioned. Nowadays, irrigation projects are sanctioned on the basis of benefit cost ratio. This ratio should be generally more than 1.5.
Direct and indirect benefits from irrigation project have been summarised as follows:
1. Food production is increased. This helps in the solution of food problem of any country.
2. Production of other crops also increases.
3. Due to assured controlled supply of irrigation water it is possible to grow cash crops like cotton, sugarcane, tobacco etc.
4. Famine fear is eliminated forever. In a particular year if there are no rains at all the yield of the crops is bound to suffer. But suffering will not be very acute as production of the crops may not be as it should be, but some production will be there. It may not be possible to export production that year, but whatever, has been produced may be sufficient for local needs.
5. Irrigation projects are so designed that they bring some revenue to the state. This revenue adds to the income of the state, and state can undertake certain welfare measures with it.
6. It helps the country in the attainment of self-sufficiency in food production. This results in saving the lot of foreign exchange.
7. The people of the region become prosperous. This is because yield of the crops and value of land increases due to irrigation facilities.
8. Irrigation canals and reservoirs may be used as sources for domestic and industrial water supply schemes.
9. Irrigation canals provide facilities for cattle watering, boating, bathing and other recreations.
10. Large deep canals with very low velocity of flow can be used for inland navigation.
11. Major river valley projects are generally planned as multipurpose schemes. They usually provide hydro-electric power along with irrigation. Falls in the canals are also used to generate additional electricity which may be used for industrialisation of rural areas.
12. Almost all the irrigation canals are provided with inspection road on one of their banks. These roads may be used as a means of communication with the interior far flunged areas where there are no pucca roads.
13. Due to percolation of water, large strips of land along both the banks of the canals remain damp. Trees may be planted in these strips. These trees grow without any watering. These trees yield lot of timber and add in the timber wealth of the country. Rows of trees also add to the aesthetic view of the country.
14. Irrigation raises the ground water table in the area, due to constant seepage and percolation of water from canals. So long as this water table remains well below the root zone of the crops, it is beneficial. Tube well irrigation can be easily installed and the water obtained from it can be used for augmenting the irrigation or for raising the cash crops.
15. Fish industry can be developed along the banks of the reservoirs.
16. The people in irrigated areas are more civilized being more educated. Their living habits, behaviour, and way of talking are more civilized.
17. Being more civilized and educated, the people of the area become more aware of their rights and responsibilities for the nation.
18. Because of plantation along the canal banks, chances of rains in the area are improved. Plantation also prevents soil erosion.
7. Disadvantages or Ill-Effects of Irrigation:
It is the law of the nature that where something causes advantages, it will definitely cause certain disadvantages also.
Following may be the ill-effects of excess irrigation:
1. Due to careless irrigation or excess irrigation, ponds and depressions in the area get filled up with water. This may lead to creation of breeding places for mosquitoes.
2. Over irrigation may cause excessive rise in the ground water table and thus may be the cause of water logging and salt efflorescence of the area.
3. The atmosphere is generally damp, which is not good for health.
4. Presence of canals affect the drainage conditions of the area. For this lot of cross-drainage works have to be constructed, which are very costly.
5. Bridges have to be constructed on canals to pass railway lines and roads.
6. Irrigation projects are generally big projects and require lot of money and skill in their construction.
7. Deep canals may prove dangerous for people who do not know swimming.
8. The people in irrigated areas are prosperous and consider their own importance more than others. The people even kill each other on petty disputes of land and irrigation.
8. Development of Irrigation in India:
History reveals that India, China and Egypt knew the science of irrigation from very primitive stage. In the early days of civilization irrigation works were not given any significance as population of the world at that time was not much. In the early days crops were grown on rain water only. But as the time passed on, population also went on growing and food requirements increased.
It was not possible to fulfil the food requirements from crops grown by rains only and thus man realized the importance of the rivers to increase the food output. In early stages of irrigation, banks of rivers were used to be cut and nearby areas or fields used to be inundated with river water.
In doing so sometimes cut in the river bank used to become too large and this used to submerge large areas under floods, thus causing lot of damage. Although some irrigation works were constructed earlier also but irrigation started taking shape from Mughal period in India.
Muslim rulers took keen interest in constructing canals for irrigation purposes. These canals were primarily inundation canals. There were no regulation works on these canals for exercising control on them. Later on most of these canals were converted to modern perennial canals. Inundation canals are still in existence in Sindh province of Pakistan.
Sultan Firoz Tughlaq constructed a number of canals from Yamuna and Sutlej rivers in fourteenth century. Some of these canals were later remodelled by Akbar in sixteenth century. Shah Jahan also constructed a number of new canals and remodelled some old ones.
Foundation of modern irrigation in India was laid during British period. In the early days of their rule they laid more emphasis on improvement of existing irrigation works. Western Yamuna Canal, Eastern Yamuna Canal, and Cauvery Delta systems were remodelled and put to use for modern irrigation.
Great Ganga Canal, Eastern Yamuna Canal and aqueduct over Solani river were the major works done by Sir Proby Cantley in North India. Sir Arthur Cotton worked in Southern India and was responsible for the development of Godavari and Krishna Deltas.
After independence most of the important and productive irrigation works of Punjab and Sindh went to Pakistan and India had to face very acute problem of food shortage. This fact made Indian Government aware about the importance of irrigation.
In first five year plan 27.2 per cent of the total outlay was set aside for the development of new potential of irrigation and power. In second and third five year plans this outlay was 19 per cent and 22 per cent respectively. Lists of some of the important irrigation works constructed before and after independence have been given in Tables 1.1 and 1.2.
Most of the major irrigation projects in India are multipurpose projects. They also generate hydro-electric power along with irrigation.
9. Irrigation Potential in India:
India’s total geographical area is about 328 million hectares, out of which about 200 million hectares is cultivable. At present about 50 per cent of the geographical area i.e. 164 million hectares, is under cultivation.
India is country of villages. About 75 per cent of its vast population lives in villages. The main occupation of this 75 per cent population is agriculture. Hence agriculture is the main industry of India and it will continue to be so in future for considerable times to come.
India has very large water resources, in form of ground water, large rivers, and lakes etc. India also has very large area of thirsty tracts which if provided with irrigation facilities can yield very large quantities of food and other crops.
India has water resources and the land to use them and thus there is very large scope of development of irrigation and power potential. Availability of water and land are probably the root causes that India has the pride of having some of the earliest irrigation works.
Surface water resources for India have been estimated at about 178 million hectare metres out of which only 35 per cent i.e. about 56 million hectare metres can be used for irrigation. The ground water resources have been estimated at about 22 million hectare metres.
By 1970-71, India had total area under irrigation about 39 million hectares. It has been estimated that with full utilization of available water resources only 82 million hectares will receive irrigation water. In other words only 50 per cent of the cultivable area (164 million hectares) can ultimately be irrigated.
India started its planned development of irrigation potential with the initiation of its first five year plan in 1951. At the end of fourth five year plan i.e., 1974, only 25 per cent of the total cropped area i.e. 164 million hectares had come under irrigation, and remaining 75 per cent of cropped area was still dependent upon rainfall alone.
In fifth five year plan 10 million hectares additional area also has come under irrigation. At this rate it is expected that India will attain its full irrigation potential of 82 million hectares in about coming 20 years.
Food production can be increased by following two ways:
(i) By bringing more of cultivable area under irrigation.
(ii) By increasing the production per hectare.
Water resources can irrigate up to 82 million hectares only. If after achieving this potential of irrigation still we fall short in food, then we have to depend entirely on increase in production per hectare.
Per hectare production can be increased by following measures:
(i) With assured irrigation.
(ii) Adopting multiple cropping.
(iii) Judicious use of irrigation water.