In plateau surface of the ground, irrigation is done by tanks where water can be retained on the ground for a long time. In such areas rivers do not flow for the whole year and water is available only during monsoon season through rainfall. Here, water springs are temporary and canals and wells cannot be constructed due to the hilly region. Rainwater needs to be stored for irrigation in such areas.
Tanks are created automatically by storage of rain water in a wide pit on the surface of the earth. These pits are deeper than the nearby ground level. They are excavated from time to time and for increasing their capacity, banks are raised to make a boundary. Tanks excavated artificially for meeting local needs are called artificial tanks. At some places where it is difficult to dig a well because groundwater is very deep, construction of tank is considered necessary.
Advantages of Irrigation by Tanks:
1. It is a cheap and popular method of irrigation.
2. It maintains level of groundwater.
3. Where construction of wells is very costly due to hard rock surface, irrigation by tank is cheaper.
4. Expenditure is much less as compared to canals.
5. Use of additional water from rainfall is possible through tanks.
Disadvantages of Irrigation by Tanks:
1. Source of water in tanks is only from rainfall. If there is variation in rainfall, it has adverse effects on agriculture.
2. Rain water flowing towards tanks carries sediments also which reduces the depth of tanks. It requires de-silting from time to time, which is very costly,
3. Taking water from tanks for irrigation is very costly.
4. Tanks occupy large space because many natural tanks are very extensive.
Other sources of water for irrigation include lakes, earthen check dams, anicuts, check dams etc. In hilly areas, for conservation of rain water, anicuts and check dams are constructed. Similarly, natural and artificial lakes and earthen check dams are mainly constructed for local needs of water.