1. Why Groundwater is used? 1.Accessible to large number of users at an affordable price 2. Less capital intensive than surface water and is not dependant on mega-water project. 3. High micro biological quality due to natural protection 4. Offers better insurance against drought because of long lag between changes in recharge and responses in groundwater level and well yields. 5.More productive than surface water irrigation and provides farm irrigation ‘on demand’ which few surface system can ensure. 6. Better WUE than surface water Why efficient use of irrigation water is a necessity for crop production? Agriculture contributes to about 25% of West Bengal’s GDP. In West Bengal, monsoon brings about 1600 – 1900 mm rainfall catering to 61% of the water demand for irrigation. The population of Bengal is 83 million which accounts for 7.6% of India’s population. The states geographical area is 89,000 sq km that covers 2.7% of India’s geographical area. Agriculture is the main occupation of 70% of the population that depends on the available arable land of about 55,000 sq km. Due to limited availability of surface and groundwater resources, efficient use of water is of paramount importance for sustainable agriculture. In many areas of the mature delta of South Bengal, groundwater is highly contaminated with arsenic, making it unsuitable for irrigation. The subterranean arsenic removal technology (SAR) may provide a viable option for producing irrigation quality water at an affordable cost. Irrigation system What are the different types of irrigation system used in South Bengal? Gravity Gravity irrigation - Water conveyed to the field by gravity only. Such system consists of head works across the river and distribution system i.e. canal network. Run-off-the River Scheme – In this system, obstruction is created across the river by weir or canal so that water is raised and diverted to channel Storage Scheme – High barriers like dams constructed to store water and release as per irrigation demand Pumped Irrigation Lift irrigation: Pumps used to lift water from big rivers (surface irrigation) and distributing the water as per irrigation requirement. Tube-well irrigation : Lifting water from wells by means of pumps Tidal irrigation In this scheme, the irrigated land is inundated during monsoon when river flows are high. It is also called flood irrigation Total irrigable area 1911000 ha,out of which 37% is contributed by groundwater. The rest is supplemented by canal(38%), tank(14%) and other sources( 11%). (source : www.fao.org,1997)www.fao.org,1997 What are the disadvantages of using Groundwater? The downside of groundwater use is over-exploitation. In some areas too much groundwater has been extracted, and the effects have been catastrophic. Agriculture has collapsed-destroying people's livelihoods-and drinking water supplies have been endangered with freshwater aquifers becoming polluted with such contaminants as arsenic, fluoride, and lead. Such disasters happen because groundwater resources are largely unmanaged, and because the policy needed to deal with the problem is not yet in place. Tidal Irrigation Field to field irrigation Gravity canal irrigation Pumped Irrigation What is the water demand for crop yield ? Major crops Rice : 2100 litres/kg Wheat: 1100 litres / kg Maize : 900 litres/kg Appropriateness of SAR technology for decontaminating groundwater for irrigation purpose? Cost of producing major crops Impact of absorbing SAR technology Rice : Rs 4 /kgRice : Rs 7/kg Wheat : Rs 5/ kgWheat : Rs 6/ kg Maize : Rs 3.5/kg Maize : Rs 4.5/kg Conclusion : It is likely that SAR based groundwater treatment system can only be used for cash crops and those grain crops which fetch adequate procurement price and exert lower demand on irrigation water http://www.qub.ac.uk/tipot