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Top1. Introduction
The agricultural economy of India is mainly based on rainfall. A large portion of a geographical area in the country falls in arid and semi-arid areas facing high uncertainty in rainfall. The main sources of irrigation in India are – canals, tanks and wells including tube-wells. Significant progress has been made during the planned period in irrigation development in India. The net irrigated area in India was 68.38 million hectares in 2014-15 (Government of India, 2018) which had been increased from 31.10 million hectares in 1970-71. However, the importance of small-scale irrigation like tank irrigation has fallen over the years. The share of tank irrigated area in total net irrigated area in India has decreased from 13.2% in 1970-71 to 3.15% in 2014-15. Irrigation by tanks was highest in the state of Tamil Nadu at 21.3% in 2014-15 followed by Andhra Pradesh at 17% and Madhya Pradesh at 15.8% (Government of India, 2018, CWC 2010). The tube-wells irrigation has seen a tremendous growth in the last few decades in India with the share of tube-wells irrigated area increasing from 14.3% in 1970-71 to 44.8% in 2014-15 of the three main sources of irrigation. Though the growth of tank-irrigated area in India was positive for the period 1950-51 to 1960-61, since then the growth of tank-irrigated area declined consistently for three consecutive decades; however the growth rate was positive in the decade of 1990s (Narayanmoorthy and Deshpande 2003).
An assessment of the performance of irrigation systems has attracted a great deal of attention from researchers, planners and managers in the last decades (Ntantos and Karpouzos 2010). In India several rainwater harvesting structures such as check dams, farm ponds, harvesting bunds, nala bunds, percolation tanks, etc are found for irrigation purposes. These structures not only facilitate the collection and storage of runoff water but also augment the groundwater level. Village tanks in some parts of India have been one of the most important water resources on which the rural communities depend for their livelihood. A tank is a village water resource formed by constructing an earthen bund (a man-made embankment) across a shallow valley to impound runoff from its catchment area. The stored water is utilized for irrigation purposes by gravity flow to the lands situated below. There are many advantages of tank irrigation (Gulati, et al. 1994, Palanisami et al 2010, Agarwal 2001, Savva 2002, Vaidyanathan 2006,Acharya 2006, ADB 2006, Sakthivadivel et al 2006,Pain et al 2008, Reddy 2009, Tiwary 2009, Jana 2009, Jana et al 2012, Jana and Lise 2013, Jana et al 2018, Reddy et al 2018, Lise et al 2019). As small-scale irrigation systems, the tanks are easily adaptable to the system of decentralized village administration that prevailed for many years. Tank irrigation, in certain parts of India, provides a good alternative for irrigation development. Tanks can have a wider geological distribution than large-scale projects and as a result income distribution and employment generation effects are not limited to one area in case of tanks. Tank investments tend to be less capital intensive, have fewer negative environmental impacts and can better involve local communities in improvement and construction works.
As per the Fourth Minor Irrigation Census report of the Government of West Bengal, out of a total number of 0.69 million tanks in West Bengal, 14% tanks were used for irrigation purposes in 2006-07. Fig 1 presents the percentage of tanks used for irrigation purposes in West Bengal during 2006-07. From the Fig 1, it can be seen that a higher percentage of tanks is used for irrigation purposes in the districts of Purulia, Bankura, Birbhum and 24 Pgs (S) in West Bengal. However, it is factual that there is variation in the percentage of tanks used for irrigation among districts.
Figure 1. Percentages of tanks used for irrigation purpose in West Bengal. Source: GoWB, 2012, Minor Irrigation Census.