Well irrigation is more popular in those regions where ground water is in ample and where there are few canals. These areas include a large part of the Great Northern Plain, the deltaic regions of the Mahanadi, the Godavari, the Krishna and the Cauvery, parts of the Narmada and the Tapi valleys and the weathered layers of the Deccan Trap and crystalline rocks and the sedimentary zones of the Peninsula. However, the greater part of the Penisnular India is not appropriate for well irrigation due to stony structure, rough surface and lack of underground water. Large dry tracts of Rajasthan, the adjacent parts of Punjab, Haryana, and Gujarat and some parts of Uttar Pradesh have salty ground water which is not suitable for irrigation and human use and hence inappropriate for well irrigation.
A well is a hole dug in the ground to get the subsoil water. Normal well is about 3-5 metres deep but deeper wells up-to 15 metres are also dug. This system of irrigation has been used in India from ancient time. Various methods are used to lift the ground water from the well for irrigation, drinking, bathing and for other purposes.
Tube well: A tube well is a deeper well (generally over 15 metres deep) from which water is lifted with the help of a pumping set operated by an electric motor, a diesel engine or solar power. A tube well cannot be constructed in all places and requires some geographical conditions favouring its installation. The main factors for Tube well construction are:
- There should be enough quantity of ground water because a tube well can generally irrigate 2 hectares per day against 0.2 hectares per day irrigated by an ordinary well.
- The water level should be nearly 15 metres. If the water table is more than 50 metres deep the cost of pumping out water from the tube well becomes uneconomic.
- There should be normal supply of cheap electricity or diesel so that water from the tube well can be taken out at the hour of need.
- The soil in the immediate neighbourhood of the tube-well should be productive so that there is demand for irrigation and the cost involved in the construction and operation of the tube well can be recovered by the increased farm production.
Advantages of Well and Tube Well Irrigation:
Well is simplest and cost effective source of irrigation and the poor Indian farmer can easily afford it. Well is an independent source of irrigation and can be used as and when the necessity arises. Several chemicals such as nitrate, chloride, sulphate, etc. are generally found mixed in well water. They make soil fertility when they reach the agricultural field along with well water. It is more reliable during periods of famine when surface water dries up.
Disadvantages of well and Tube Well Irrigation:
With these methods, only limited area can be irrigated. Normally, a well can irrigate 1 to 8 hectares of land. The well may dry up and may be rendered ineffective for irrigation if excessive water is taken out. In the drought situation, the ground water level falls and enough water is not available in the well when it is needed the most.
Tube wells can draw a lot of groundwater from its neighbouring areas and make the ground dry and not suitable for agriculture. Well and tube well irrigation is not possible in areas of salty groundwater.