Based on the availability of surface and ground­water relief, soils and climatic characteristics vary­ing sources of irrigation are utilised in India.

These include tanks, wells (including tube wells), canals, etc (Fig. 14.2). Of the total net irrigated area 60.85 per cent is irrigated by wells (including tube wells and pumping sets), 29.24 per cent by canals, 4.62 per cent by tanks and 5.29 per cent by other sources. Alluvial tracts of the northern plains are well suited for well and canal irrigation, while tank is the prin­cipal source of irrigation in the crystalline areas of the Deccan Plateau. Table 14.II gives an idea about the progress in respect of different sources of irriga­tion between 1950-51 and 2000-01.

While canals were the principal source of irrigation up to 1971 -72 their place was taken up by wells (including tube wells) thereafter. In recent years there has been phenomenal growth in respect of minor irrigation and farmers are going for individual pumping sets to ensure better and more reliable supply of irrigation water to the field.

Tank irrigation is very popular in the eastern part of the southern Peninsula (Fig. 14.2) where topography favours their construction by erecting dams across seasonal streams. In West Bengal, Orissa and Bihar tanks are mostly of excavated type which besides irrigation is also used for fisheries.

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Tanks play vital role in the irrigation of Tamil Nadu where 20.4 per cent of the net irrigated area is watered through tanks. Andhra Pradesh (16.1%), Kerala (13.1%), Orissa (14.6%), and Karnataka (9.9%) in the Peninsular India and West Bengal (7.4%), Bihar (4.3%) and Rajasthan (0.77%) in the northern plains have sizeable net irrigated area irrigated through tanks (Table 14.III).

Tamil Nadu has been the traditional area for tank irrigation. There are about 24,000 tanks in the state. Tank irrigation is signification in Tiruchchirappalli, Chingleput, North Arcot, South Arcot, Ramanathpuram. Madurai, Salem. Thanjavur and Coimbatore districts, irrigating about 60 lakh hec­tares of the net cropped area.

In Andhra Pradesh Nellore, Warangal districts are important for tank irrigation. Nijamsagarin Andhra Pradesh, Krishnaraj sagar in Karnataka; Jaisamand, Rajsamand and Balsamand in Rajasthan are big lakes which besides irrigation are used for providing drinking water to the neighbouring areas. According to one estimate there are about 5 lakh big and 50 lakh small tanks in the country which are used for irrigation and aquaculture.

The area under tank irrigation increased from 36.13 lakh hectares in 1950-51 to 45.61 lakh hec­tares in 1960-61. Between 1970-71 and 2000-01 it declined from 41.12 lakh hectares to a minimum of 25.24 lakh hectares. Various state governments are providing loans and subsidies for the construction of new tanks and repairof old ones. But their popularity is declining in comparison to canals and tube wells as means of irrigation.

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Tank irrigation suffers from certain inherent weaknesses. Tanks get silted up soon and regular desilting is required to make these suitable for irriga­tion. Most of the tanks are non-perennial and be­come dry during late winter and summer seasons when water is urgently required for rabi and zaid crops. At the time of failure of Monsoon these are not dependable source of irrigation. Due to large areal coverage and their shallow depth huge quantity of stored water is either evaporated or sinks under­ground without being used in the irrigation.

Tanks occupy a large fertile area which otherwise could have been utilised for growing crops. Also the lifting of water from the tanks and bringing it to the fields are strenuous and costly exercises which discourage their use amongst farmers. But even then tanks are effective means of collecting rain water and their use should be popularised for irrigation, aquaculture, and drinking water and water sports.