This article provides a paragraph on well irrigation.
The amount of water stored in the earth’s crust is estimated to be around 8 billion cubic kilometres, half of which is at depths less than 800 metres. This volume of water is about 35 times the combined storage of all the world’s rivers, fresh water lakes, reservoirs and inland seas. Ground water is that part of the subsurface water which occurs within the saturated zone of the earth’s crust where all voids (or pores) are filled with water.
The estimate of the present ground water resources in India is of the order of 650 cubic km (as against 1780 cubic km for surface water resources) out of which utilisable ground water is assessed at around 420 cubic km (as against 690 cubic km for surface water resources).
In view of the large amount of utilisable ground water, its quality and also better agricultural yields with well irrigation, it is only logical to develop ground water resources for irrigation and other activities. A hole or shaft, usually vertical, is excavated in the earth to lift ground water to the earth’s surface and is termed a well.
Following are the main requirements for the success of well irrigation:
(i) Presence of a suitable aquifer which can yield good quality water in sufficient quantity.
(ii) Availability of energy preferably electric power for pumps.
(iii) Well distributed demand for irrigation throughout the year.
(iv) Suitable configuration of command area with the highest ground around the centre of the command area.
In general, well irrigation is more efficient than canal irrigation.
Following are the comparative features of the two types of irrigation:
(i) In canal irrigation system, major structures, such as head-works, main and branch canals, etc., must be constructed prior to the start of proportionate agricultural activity which grows gradually because of the availability of irrigation facility. But wells can be constructed gradually to keep pace with the development of the agricultural activities in the area.
(ii) Transit losses in well irrigation are much less than in canal irrigation system.
(iii) Isolated patches of high lands can be better served by well irrigation.
(iv) Well irrigation offers an effective anti-waterlogging measure for the affected lands, and reduces the chances of waterlogging of canal- irrigated lands.
(v) Well irrigation ensures relatively more reliable supply of water at the time of need. This results in better yield. Besides, farmers can switch over to more remunerative crops due to the availability of the assured supply.
(vi) Well irrigation needs energy for pumping. Installation and maintenance of pumps and the cost of running the pumps make well irrigation relatively costlier.
(vii) Failure of power supply at the time of the keenest demand may adversely affect the yield in case of well irrigation systems.
It is, thus, obvious that both irrigation systems have advantages as well as disadvantages. Therefore, both must be used in a judicious manner (Conjunctive use) to obtain maximum benefits such that there is no waterlogging and the ground water resource can be maintained indefinitely.