What is Irrigation?
Types of Irrigation :
1. Lift Irrigation : This method of irrigation of agricultural land is done by lifting water from lower level. Water is drawn from deep wells or open wells using pumping system.
2. Surface or Flow Irrigation : This method of irrigation of agricultural land is done by supplying water from a channel located at higher elevations. In this system, the elevation of canal head should always be higher than land of irrigation.
There are two types of Flow Irrigation :
i) Inundiation Irrigation System : In this system, water is available to agricultural land in rainy season only. This system does not consist of any regulator at the head of canal to control water flow. The water flows only when the water level of the river rises above the canal bed. Thus, the flow water stops automatically when the water level of river falls below canal bed.
Therefore, this system completely depends on water level of river.
Since, there is no regulator at the head of canal, over-irrigation is possible resulting in damaging of crops.
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| Inundation Irrigation System |
ii) Perennial Irrigation System : This system works effectively when constructed across perennial river (i.e. the river which flows throughout the year in its full capacity). In this system, weirs or barrages are constructed across perennial river, so as to raise water level on the upstream side in order to form a storage reservoir. This system is provided with a regulator at the head of canal to control the flow of water through the canal towards agricultural land.
Since, water is available throughout the year, this makes the system reliable.
Perennial Irrigation systems are of two types :
a) Direct Irrigation System : In this system, weirs are constructed across the perennial river to raise the water level at upstream. Here, the water level on the upstream side will remain at a constant height and the excess water flows over the weir.
Sometimes, barrages are also constructed in this system to regulate the flow of water.
The hydraulic structure constructed in direct irrigation system is called Diversion Head Works.
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| Diversion Head Works |
b) Storage Irrigation System : In this system, dam is constructed across perennial river to form storage reservoir.
Head regulators are used in this system to control the flow of water. The storage reservoir is also known as multipurpose reservoir.
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Storage Reservoir |
Benefits of Irrigation :
1. Crop Yielding : During low rainfall or drought, the yield of crop can be increased by irrigation system.
2. Protection from scarcity : By ensuring the availability of irrigation system or facility, the food production of a country can be improved.
3. Improvement of cash crops : The cultivation of cash crops like vegetable, fruits, tobacco etc. can be improved by irrigation system.
4. Prosperity of farmers : By ensuring availability of irrigation facility to farmers, they can grow two or more crops on the same land and earn more money and improve their life.
5. Revenue Source : The water supplied to the cultivators may be lieu of some taxes, which will help to earn some revenue which can be spent on other development schemes.
6. Navigation : Irrigation canals can be used for communication and transportation of goods.
7. Power Generation : In some irrigation projects, multipurpose reservoirs are constructed where hydroelectric power system is installed along with irrigation system.
8. Water Supply : Irrigation system is the source of water supply for domestic and industrial purposes.
Drawbacks of Irrigation :
1. Rising Water Table : The water table in the surrounding area of the canal increases due to excessive seepage of water through bed and banks of canal resulting in constant saturation of root zone of crops and developing alkaline property which is harmful to the crops.
2. Formation of Marshy Land : Due to excessive seepage of water from canals lead to formation of marshy land along the course of the canals. This results in the formation of colonies of mosquitoes which may be responsible for diseases.
3. Loss of Land : Since construction of dams, reservoirs, barrages, canals etc. requires huge amount of land, thereby the valuable land is lost.
