Friday, February 8, 2013

Sources of Irrigation

Sources of Irrigation Depending upon the availability of surface or groundwater, topogra­phy, soil, rainfall conditions and rivers, various types of irrigation are practised in India.

Tank irrigation:
Mostly prevalent in uneven and relatively rocky plateau of peninsular India, tanks are the most popular method of irrigation in the states of Tamil Nadu, Karnataka, Andhra Pradesh and Maharashtra. In India most of the tanks are small in size and built by individuals or groups of farmers by raising bunds across seasonal streams. About 11 to 14 per cent of the net irrigated area in the country is normally under tank irrigation. Tank irrigation in the Deccan and South India is highly developed compared to tank irrigation in other regions because the land is rocky and the soil is not porous. Rainwater cannot sink into the ground, making it difficult to dig wells. The dig­ging of canals is also difficult and expensive on the rocky surface of the peninsular plateau. As the rivers of South India are seasonal, the construction of perennial canals is not feasible. The hard rocks of the region do not allow the water of tanks to seep through. Hence tank irrigation has been successful there. But there are drawbacks in tank­irrigation: tanks cover large areas of cultivable land; evaporation of water is relatively rapid due to large expanse of shallow water in the tanks; tanks do not ensure a perennial supply of water.

Well irrigation is an important source ofirrigation. The water in wells is obtained from the subsoil and has to be lifted by suitable devices, e.g., manual or animal labour or by pumping sets run by power. Wells (including tubewells) account for more than 30 million acres (more than 55 per cent of total irrigated area). Well irrigation is most common in alluvial plain areas where the water table is fairly high. Owing to the soft nature of the soil, wells are easy to dig and the yield of crops from the land after irrigation is rewarding. The states with 50 per cent or more of the irrigated area under wells and tube-wells are Punjab, Uttar Pradesh, Rajasthan, Gujarat, Maharashtra. Madhya Pradesh and Tamil Nadu also have a sizeable area under well irrigation. The major changes in respect of well irrigation during the last few decades include change from dug-wells to tube­wells and large scale replacement of animal power with commercial power (electricity or diesel) for lifting water. Tamil Nadu has the largest number of electrified pumpsets. Now, waterpumps running on solar energy are also being encouraged.

Canal irrigation is also an important source of irriga­tion accounting for above 30 per cent of the net irrigated area. Canal irrigation is possible in areas which are exten­sive plains and are drained by well distributed perennial rivers, such as the northern plains, coastal plains, deltas (where even the distributaries can act as canals), and the broad valleys of the peninsula. Inundation canals are those which are taken out without constructing dams or 'bunds' and get water only when the main stream is flooded-thus, they have limited validity. Now, the efforts are on to convert them to perennial systems. The post-independence period saw the construction of canals as a part of the multi-purpose projects, e.g., Bhakra-Nangal (Punjab), Damodar Valley Gharkhand and West Bengal) and the Nagarjunasagar (Karnataka) projects. The initial costs of constructing canals is high, but once constructed, the operational cost is minimum, which makes them a cheap source of irrigation in the long run. Canal irrigation is important in Punjab, Haryana, western Uttar Pradesh, Assam, West Bengal, coastal Orissa and coastal Andhra Pradesh. The canals are almost absent in hilly states like Kerala and the North-East.

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