These are constructed by building earthen walls built across a depression or valley behind which rain water collects. This is later used in the dry summer months.
Conditions Required for Tank Irrigation
1. There should be hard rocks or impervious layer below so that water does not seep in.
2. There should be some means of filling up again.
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It allows the surplus water during monsoons to be stored and used later.
It is easy and economical to construct.
It helps to raise the underground water level.
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Disadvantages of Tank Irrigation
1. Tanks use up large areas of land which could be used for agriculture.
2. They dry up in summer and are not of much use.
3. A lot of water evaporates as they are very shallow.
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4. It is difficult to carry water to the fields due to rocky terrain.
The tanks are popular in the Deccan because
1. Natural depressions are found here so they are cheaper to build
2. Non Porous rocks found here prevent seepage of water
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3. A number of streams are found here, which overflow during the rainy season. So water which would have got wasted is utilized.
4: The population and agricultural fields are scattered so tank irrigation is well suited.