Geography [2 Mark Question Answer]

Tamil Nadu is the state where tank irrigation in important.
The disadvantages of tanks:
(i) They occupy large areas of land which could be used for cultivation.
(ii) There is also a lot of evaporation as these tanks are usually shallow.
(iii) Construction entails much expenditure.

Tanks are mostly used in peninsular India. This is because
(i) Peninsular India consists of hard impervious rocks which favours the storage of water.
(ii) Depression in the plateau region can be used as Natural tanks.

Advantages: Tube wells do not result in evaporation of water like suface wells. It irrigates large area (400 hectares).
Disadvantage: However tube wells are only possible in areas where the groundwater level is not too low power is needed to drain water.

The float switch is an innovative device mounted on the tank which automatically controls the water supply. If the rain water tank is full it will automatically pump the rain water for use in the garden or washing machine. If the rain water tank is empty or when there is a dry spell and water in the tank falls to the minimum level, the floating switch triggers the use of the normal mains water.

It is a downspout rain water diverter which simplifies the collection of rain water. It has advantages over other rain water collection systems in that it is installed in minutes and deactivates in seconds during winter when stored water is not needed. As it is kept underground or in low visibility locations more containers can be added (linked) or filled by simply moving a hose pipe.

(i) The rivers are perennial as they are fed by the melting snows,
(ii) The surface of the land is almost flat and soft. Hence it is easy to dig canals,
(iii) The demand for irrigation is very great in North India as a variety of crops are grown,
(iv) Type of cultivation is intensive.

The conditions necessary for tube wells are:
(a) Sufficient ground water.
(b) Cheap electric power must be made available.

(a) Tube-wells can irrigate a larger area about 400 hectares,
(b) They are definitely better in times of drought when surface wells dry up.
(c) The process of irrigation is quicker and more convenient.

Advantages: (a) easy to dig and construct, (b) cheap
Disadvantages:
(a) wells can irrigate a very small area about half an hectare of land.
(b) In times of drought they run dry. (c) Besides there is strain on the animals.

The prevailing methods are the Persian Wheel, Mhote and the Picotin.
The Persian wheel: It is also known as ‘Rehat’ and is worked by bullocks, buffaloes or camels.
Mhote: It is also worked by bullocks moving up a sloping ramp to pull up a big leather bucket.
Picotin: In this device a vertical pole is employed for balancing the bucket and the equivalent load fixed on either ends. It is also known as ‘Dhenkuli’.

Two methods of water harvesting in India are:
(a) Collecting of rain water on the roof top and directing to any tanks.
(b) Watershed is defined as a geographic area through which water flows across the land and drains into common body of water such as stream, river, lake, ocean, etc.

(i) Indian rainfall is periodic: Most of the rain falls in four months from June to September. The remaining eight months are dry.
(ii) Rainfall is not well-distributed during the rainy season: During the four months of the monsoon, there are spells of dry weather.

South India is very favourable for tanks as there are a number of natural depressions. The underlying rocks of the southern plateau are hard, impervious, which check the percolation of water underneath. The rivers of Peninsular India flow through narrow gorges where it is easier to construct dams across the river channels for impounding the water. Besides the surface is hard, sloppy, making it difficult to construct wells or canals.

Water scarcity occurs because:
(i) Seasonal rainfall
(ii) More demand due to increase in Population and Polluted water.