The monsoonal rainfall in India is concentrated only in four months and more than 50% of the net sown area is rainfed only. Irrigation is thus essential to overcome spatial and temporal variation of rainfall.

Archaeological and historical records show that from ancient times we have been constructing sophisticated hydraulic structures like dams built of stone rubble, reservoirs or lakes, embankments and canals for irrigation. Not surprisingly, we have continued this tradition in modern India by building dams in most of our river basins. Before we look at these methods of irrigation in detail, let’s have a look at some of the hydraulic structures used in ancient India!

Some Hydraulic Structures used in Ancient India:

• In the first century BC, Sringaverapura near Allahabad had sophisticated water harvesting system channelling the flood water of the river Ganga.
• During the time of Chandragupta Maurya, dams, lakes and irrigation systems were extensively built.
• Evidences of sophisticated irrigation works have also been found in Kalinga (Orissa), Nagarjunakonda (Andhra Pradesh), Bennur (Karnataka), Kolhapur (Maharashtra), etc.
• In the eleventh century, Bhopal Lake, one of the largest artificial lakes of its time was built.
• In the 14^th century, the tank in Hauz Khas, Delhi was constructed by Iltutmish for supplying water to the Siri Fort Area.

Coming back to irrigation in the present day India, let’s look at some important facts and figures before we move forward:

Some important facts and figures:

• The net irrigated area = 66.1 million hectares.
• Total/Gross Irrigated Area = 92.6 million hectares.
• Irrigation Intensity in India = (Gross Irrigated Area ÷Gross Sown Area) * 100

= (92.6 ÷ 194.4) *100

= 47.6%

More than 50% of the country’s cropped area depends exclusively on rainfall, most of which is concentrated in a few months of the year. Even where the annual overall precipitation is high, the available moisture is not adequate to support multiple cropping.

Ultimate Irrigation Potential:

As seen in the above figures, only about 66mha i.e. 47.6% of the net sown area is estimated to be irrigated. There is a need to bring more cropped area under assured irrigation so as to increase agricultural productivity and production.

The total ultimate irrigation potential of the country has been estimated as 140mha, with about 76 mha from surface water sources and about 64mha from groundwater sources.

Irrigation – Sources and Methods

The main sources of irrigation in India are:

• Canals
• Wells (and tubewells)
• Tanks

The relative importance of these has been changing from time to time. Let’s look at these in detail:

1. Canal Irrigation:

• A canal is an artificial watercourse constructed for water supply and irrigation.

• There are two types of canals:
  1. Inundation Canals – These are taken out from the rivers without any regulating system like weirs etc at their head. Such canals are useful only during the rainy season
  2. Perennial Canals – These are those which are taken off from perennial rivers by constructing a barrage across the river. Most of the canals at present in India are perennial.
• Canals can be an effective source of irrigation in areas of low relief, deep fertile soils, perennial source of water and an extensive command area. Therefore the main concentration of canal irrigation is in the northern plains.
• The canals are practically absent from the peninsular plateau region because of rocky terrain. However, the coastal and the delta regions in South India have some canals for irrigation.

Canal Irrigation in India

• The percentage of canal irrigation area to total irrigated area in the country has fallen from about 40% in 1950-51 to less than 25% at present.
• The states UP, Punjab, Haryana, Rajasthan and Bihar account for about 60% of the canal irrigated area in the country.
• Merits of canal irrigation:
  1. Perennial Source
  2. Provides safety from droughts
  3. Brings fertile sediments to the fields
  4. Economical to serve a large area

• Demerits:
  1. Canal water soaks into the ground and leads to water logging, increases salinization, and leads to marshy conditions leading to malaria and flooding
  2. Wastage of water.

2. Wells (and Tube Wells)

• A well is a hole dug in the ground to obtain the subsoil water. An ordinary well is about 3-5 metres deep but deeper wells up to 15 metres are also dug.
• This method of irrigation has been used in India from time immemorial. Various methods are used to lift the ground water from the well. Some of the widely used methods are the persian wheel, reht, charas or mot, and dhinghly (lever) etc.
• A tube well is a deeper well (generally over 15 metres deep) from which water is lifted with the help of a pumping set operated by an electric motor or a diesel engine.

A Tubewell

• Well irrigation is gradually giving way to energized tube wells. But there are many wells still in use where electricity is not available or the farmers are too poor t0 afford diesel oil.
• This method of irrigation is popular in those areas where sufficient sweet ground water is available.
• It is particularly suitable in areas with permeable rock structure which allows accumulation of ground water through percolation. Therefore wells are seen more in areas with alluvial soil, regur soil, etc. and less seen in rocky terrain or mountainous regions.
• These areas include a large part of the great northern plains, the deltaic regions of the Mahanadi, the Godavari, the Krishna and the Cauvery, parts of the Narmada and the Tapi valleys and the weathered layers of the Deccan trap and crystalline rocks and the sedimentary zones of the peninsula
• However, the greater part of peninsular India is not suitable for well irrigation due to rocky structure, uneven surface and lack of underground water.
• Large dry tracts of Rajasthan, the adjoining parts of Punjab, Haryana and Gujarat and some parts of Up have brackish ground water which is not fit for irrigation and human consumption and hence unsuitable for well irrigation
• At present irrigation from wells and tubewells accounts for more than 60% of the net irrigated area in the country.
• UP has the largest area under well irrigation which accounts for 28% of the well irrigated area of the country. U.P., Rajasthan, Punjab, Madhya Pradesh, Gujarat, Bihar and Andhra Pradesh account for about three-fourths of the total well-irrigated area

Source

• Merits of well irrigation
  • Simplest
  • Cheapest
  • Well is an independent source of irrigation and can be used as and when the necessity arises. Canal irrigation, on the other hand, is controlled by other agencies and cannot be used at will.
  • Some ground water salts are useful for crops
  • Does not lead to salinization and flooding problems
  • There is a limit to the extent of canal irrigation beyond the tail end of the canal while a well can be dug at any convenient place.
• Demerits
  • Only limited area can be irrigated. Normally, a well can irrigate 1 to 8 hectares of land.
  • Not suitable for dry regions
  • Overuse may lead to lowering of water table

3. Tank irrigation

• A tank is a reservoir for irrigation, a small lake or pool made by damming the valley of a stream to retain the monsoon rain for later use.

A Tank in Tamil Nadu

• It accounts for approximately 3% of the net irrigated area in India.
• Tank Irrigation is popular in the peninsular plateau area where Andhra Pradesh and Tamil Nadu are the leading states.
• Andhra Pradesh has the largest area (29%) of tank irrigation in India followed by Tamil nadu (23%).

Tank Irrigation in India

• It is practised mainly in the peninsular region due to the following reasons:
  • The undulating relief and hard rocks make it difficult to dig canals and wells
  • There is little percolation of water due to hard rock structure and ground water is not available in large quantities.
  • Most of the rivers are seasonal; there are many streams which become torrential during the rainy season – so the only way to use this water is to impound it by constructing bunds and building tanks. Also, it is easy to collect rainwater in natural or artificial pits because of impermeable rocks.
  • Scattered nature of agricultural fields
• Merits
  • Most of the tanks are natural and do not involve cost for their construction
  • Independent source for an individual farmer or a small group of farmers
  • longer life span
  • can be used for fishing also
• Demerits
  • Depends on rain and these tanks may dry up during the dry season
  • Silting of their beds
  • Require large areas
  • Evaporation losses
  • Sometimes there might be a need to lift the water to take it to the field