West Bengal receives sustained rainfall due to its proximity to the Bay of Bengal yet we are unable to make full use of it due to some natural constraints. Rapid rise in demand of water in all sectors of domestic, industrial and agricultural uses during the last decade has started throwing up several problems in water resources management. So the optimal management of available Water Resources has become a major issues world over. Due to occurrence of recurrent droughts, advent of high yielding varieties and introduction of an incentive oriented agricultural pricing policy paved the way for irrigated agriculture. The Spatial and temporal variability of rainfall along high evapo-transpiration and runoff is posing a major challenge to the scientific community. As a result development of agriculture is essentially dependent on irrigation, not only in Rabi / Boro season but also in Khariff seasons in the event of drought or inadequate rainfall. Harnessing of Water Resources to meet various Sectoral requirements has been our prime concern, which is the foundation of our agricultural vis-à-vis economic growth and welfare of state. Water Resources are being utilized in the State from medium and major sized irrigation schemes whose culturable command area(C.C.A) above 2000 ha. and from minor irrigation schemes with the C.C.A up to 2000 ha. as per the criteria laid down by the Planning Commission, Govt of India.
Thus small and marginal farmers who constitute the majority of cultivators and cultivate major portion of agricultural land in West Bengal, can afford to individually invest on creation of irrigation sources. Therefore, with a view to boosting up agriculture production in a large scale and to promote rural economy, the policy of the government has been to create new sources and hand them over to the Beneficiary Committees through the Panchayat for their operation, maintenance, optimal use and overall management.
Water Resources Development Directorate is responsible for the development of existing potential of water resources available in the State through construction and maintenance of various types of MI schemes utilizing ground water as well as surface water resources.The schemes which are implemented by this directorate for development of water resources under M.I. sector may be categorized as below :-
Surface Water Development Minor irrigation Schemes:
Surface water resources are being utilized through irrigation tanks, storage, permanent and temporary diversions. Water of these detention storage reservoirs & Perennial sources are utilized for irrigation during the period of no rain. A small portion of surface water run off of each watershed is being utilized yet.
1.1)Surface Flow Irrigation Scheme:
These schemes use rainwater for irrigation purposes either by storing it or by diverting it from a stream, nala or river. Sometimes, permanent diversions are constructed for utilizing the flowing water of a stream or river. Temporary diversions are also constructed in many areas which are usually washed away during the rainy season.
These schemes aim at providing gravity flow irrigation by mere diversion of stream water supply without creating any storage. An obstruction (weir) constructed across the stream for raising and diverting water through the artificial channel.
These schemes are constructed mainly to drain water from low-lying areas which are water-logged due to tidal action of river. Reversal flow of water of the river enters into and inundates the agriculture. To control the entry of water, a sluice gate is constructed at the outlet of the natural drainage channel of the area. By way of construction of this type of scheme two-fold facilities namely (i) drainage and (ii) irrigation are obtained. According to the requirement of water for irrigation during Rabi / Boro season, a portion of water is preserved in the existing channel instead of draining it out.
Waste Water Utilization Irrigation Scheme:
Water Resources Development Directorate have implemented Surface Flow Minor Irrigation Schemes in the Districts of Hooghly using treated effluents of Tribeni Tissue Factory and Bandel Thermal Power Station benefiting 50 ha. and 120 ha. irrigation area respectively in the adjoining cultivable area of those locations instead of discharging back to the river.
Boro Bundh scheme:
Boro Bundh Schemes are taken up in some low-lying areas of Midnapore, Hooghly, and Howrah districts where no cultivation is possible during rainy season and topography and characteristics of the river do not permit to construct a permanent storage work. These schemes are temporary in nature. Earthen bundhs are constructed across the river in the month Oct-Nov every year to harvest water for utilization in boro crops. Before on-set of the monsoon these bundhs are removed to restore the natural water way.
- Diversion Schemes:
1.2)Surface Lift Irrigation Scheme:
In regions where the topography does not permit direct flow irrigation from rivers and streams, water has to be lifted into the irrigation channels. These works are similar to diversion schemes, but in addition pumps are installed and pump houses constructed.
River Lift Irrigation Schemes:
River lift irrigation Schemes are installed where topography of land does not permit to construct storage of diversion works with gravity flow irrigation schemes. Water is lifted from the river with the help of either by two number diesel engine pump-sets or two number electric driven pump-motor sets and delivered to field through underground pipe line net work. The schemes may be categorized as below :
Major River Lift Irrigation Schemes:
Water from River, Canals, Beels etc. is lifted by two pump sets each capable of discharging 200 cubic meter per hour ie. total 400 cubic meter per hour to irrigate and area of 60-80 hectares of land. Water is distributed through under ground pipe line emanating from two distribution chambers which may either be independently connected with the pump sets or may be interlinked depending upon shape and size of command area.
Medium River lift Irrigation Schemes:
Water from River, Canals, Beels etc. is lifted by two pump sets each capable of discharging 100 cubic meter per hour ie. total 200 cubic meter per hour to irrigate and area of 40 hectares of land. Water is distributed through under ground pipe line emanating from two distribution chambers which may either be independently connected with the pump sets or may be interlinked depending upon shape and size of command area.
Mini River Lift Irrigation Schemes:
Water from River, Canals, Beels etc. is lifted by two pump sets each capable of discharging 50 cubic meter per hour ie. total 100 cubic meter per hour to irrigate and area of 20 hectares of land. Water is distributed through under ground pipe line emanating from two distribution chambers which may either be independently connected with the pump sets or may be interlinked depending upon shape and size of command area. In all the schemes it is possible to have cropping intensity of 200%.
- Major River Lift Irrigation Schemes:
Rain Water Harvesting are being done by excavating top soil and part of weathered mantle down to a shallow depth below ground level, creating a reservoir for storage of rain water as surface resources and simultaneously enriching soil moisture as well as sub-surface resources with natural percolation. Re-excavation of old tanks are made to augment their capacities for harvesting rain water during monsoon and for subsequent utilization of the same in irrigation during dry seasons. Re-excavation also augments recharge to the water basin thereby increasing availability of ground water.
Hydraulic Ram (Hydram):
An automatic device with which the energy of a quantity of water from a low head is used to lift proportionate quantity of this water to a greater height. This works on the principle of water hammer. In hilly areas use of hydram has been proposed considering steep gradient and high velocity of the streams.
- River Lift Irrigation Schemes:
- 1.1)Surface Flow Irrigation Scheme:
Ground Water Development Minor Irrigation Schemes:
2.1)Deep Tube Well:
These schemes are constructed for utilization of ground water resources in areas where irrigation is not covered through surface water resources & where water table is usually more than 7 meters below ground level and electrically operated submersible pump sets are required to be used for lifting water.
Heavy Duty Tube Well(HDTW)
These are capable of discharging 200 cubic meter per hour to irrigate and culturable command area of 40 hectares through under ground pipe lines emanating from an elevated distribution chamber. A large number of such structures are existing and are being operated by Govt. machinery. However as per policy of the State these type of structures are being handed over to the users for subsequent operation, management & maintenance.
Medium Duty tube Well(MDTW)
These are capable of discharging 100 cubic meter per hour to irrigate and culturable command area of 20 hectares through under ground pipe lines emanating from an elevated distribution chamber. A large number of such structures are existing and are being operated by Govt. machinery. However as per policy of the State these type of structures are also being handed over to the users for subsequent operation, management & maintenance.
- Heavy Duty Tube Well(HDTW)
2.2)Shallow Tube Well:
Light Duty Tube Well (LDTW):
These structures are suitable for areas where water table is usually more than 7 meters below ground level and electrically operated submersible pump sets are required to be used for lifting water. These are capable of discharging 30 cubic meter per hour to irrigate an area of 4 to 6 hectares through open channels. These structures are installed in a cluster of 5 to 6 tube wells. It has been found that such structures can be managed very efficiently and economically by the users.
Shallow Tube Wells (Diesel/Electric):
These structures are suitable for areas where water table is within 7 meters below ground level and water can be lifted with centrifugal pump sets run by electric motor set or diesel engines and thereby dependence on electricity can be avoided. These structures are suitable for the 6 Districts in the northern part of the State and part of Murshidabad District. Each of the tube well will be capable of discharging 30 cubic meter per hour to irrigate 4 to 6 hectares of culturable command area and it is possible to have 200% cropping intensity.
- Light Duty Tube Well (LDTW):
It covers ordinary open wells of varying dimension dug or sunk from the ground surface into water bearing stratum to extract water for irrigation purposes.These open dug wells are of 1.2 meters to 3.0 meters diameter for a depth of 8 to 12 meters appeox. Generally 1.2 dia. with R.C.C ring are constructed in alluvium formation and 3.0 metre dia. ODW are constructed in lateritic and hard rock formations. Water is being lifted manually and the quantum of water lifted is approx. 1.6 m³/ hour. The average culturable command area varies from 0.4 hectares to 1.5 hectares with 300 percent crop intensity of cultivable land.
- 2.1)Deep Tube Well:
Surface Water & Ground Water Development Micro Irrigation Schemes:
Much of the debate and discussion in the irrigation sector hasbeen on increasing the supply of water to agriculture and this has led to bringing of more area under surface and groundwater irrigation. However, little attention has been paid to improving the efficiency of irrigation, i.e., ensuring that there is 'more crop per drop' of water. Agriculture data still measure productivity in kilos per ha even though in many areas the scarce resource is water, not land. It is in this context that microirrigationemerges as a potential answer to the problem ofincreasing irrigated area with limited water resources available.As noted earlier, micro-irrigation comprises three technologies-drip, sprinkler irrigation and micro sprinkler irrigation. Three of them save conveyance losses and improve water application efficiency by applying water near the root-zone of the plant. Drip systems convey water in small quantities through drippers/micro-tubes while sprinklers are pressurized systems where a fountain or spray of water is released by the sprinkler connected by pipes, resulting in foliar irrigation.
These three types are:
In draught prone areas of western part of the State, economic and efficient use of irrigation water is necessary to have as much agriculture production as possible with minimum water use. In these areas pilot schemes using drip irrigation method have been proposed. Drip Irrigation system delivers water to the crop using a network of mainlines, sub—mains and lateral lines with emission points spaced along their length. Each Drip/ emitters, orifice supplies a measured, precisely controlled uniform application of water, nutrients, and other required growth substances directly into the root zone of the plan.
In vegetable producing areas of districts of northern part of the State, pilot schemes using sprinklers have been proposed on the consideration that rate of evaporation is comparatively less in those areas. Sprinkler Irrigation is a method of applying irrigation water which is similar to rainfall. Water is distributed through a system of pipes usually by pumping. It is then sprayed into air of entire soil surface through spray heads. It breaks up into small water drops which fall to the ground.
3.3)Micro Sprinkler Irrigation:
Micro sprinklers, spray jets, micro sprayers and misters can throw the water over a wide area, when low volume overhead irrigation is desired and for areas where drip emitters are not practical. Micro Sprinklers are used for irrigation of seasonal crops like vegetables, onions, potato, nurseries etc. Micro sprinklers, micro sprayers, spray jets, misters and foggers are available in a variety of styles and configurations and, like drip-emitters, operate at low-pressure from as low as 15 PSI to as high as 50 PSI.
- 3.1)Drip Irrigation: