What Is Canal Irrigation?
A canal is an artificial channel, generally trapezoidal, constructed to convey water from rivers, reservoirs, etc. for several purposes like irrigation, power generation, navigation, etc.
Canals utilized for irrigation are the primary waterway that brings the water for irrigation from the main source to the areas to be irrigated.
These artificial channels are constructed with stone, concrete, brick, or a flexible membrane to prevent seepage and erosion. Irrigation canals or water channels is an open waterway whose main function is to convey water from one place to another and are referred to as main waterways supplying water to one or more farms.
The system of irrigation through artificial channels is a traditional method and more convenient for agricultural activities at less cost. There are different types of systems for irrigation that have been found and used for the cultivation of crops for many years.
Types of Canal Irrigation
Irrigation canals are classified into different types of canal irrigation based on various factors which are as follows:
- Based on the Nature of the Supply
- Based on the Functions
- Based on the Type of Surface Soil
- Based on the Canal Alignment
- Based on Financial Output
- Based on Discharge
Based on the Nature of the Supply
1. Permanent Canal
A permanent canal is a type of irrigation canal in which water is obtainable throughout the year. This type of canal is mostly directed from a permanent source of water bodies.
There are many permanent hydraulic structures that are built into the permanent canal for water regulation & distribution. A permanent canal is also called a perennial canal.
2. Inundation Canal
It is a type of canal in which water is obtainable only during the flood or monsoon season. Inundation canals are taken off from rivers to control the water level during the flooding period. A canal head regulator is provided to control & regulate the flow into the canal.
Based on the Functions
3. Irrigation Canal
A canal built along the boundaries of cultivatable soils to supply water for agriculture is called to be an irrigation canal.
4. Power Canal
A canal built especially for the generation of hydroelectric power is termed a power canal.
5. Feeder Canal
As the name suggests, the feeder canal is constructed to provide water to two or more other canals or branch canals.
6. Carrier Canal
A carrier canal is a multi-function canal that serves the purposes of both irrigations canal and feeder canal.
7. Navigation Canal
A canal that is built especially for navigation functions is known navigation canal.
The requirement of water in a navigation canal is commonly a lot higher to accommodate large ships and vessels.
Based on the Type of Surface Soil
8. Alluvial Canal
This type of canal is excavated and constructed in alluvial soils such as silt, sand, gravel, etc. then it is termed an alluvial canal.
9. Non-Alluvial Canal
If the soil of the boundary surface of the canal is of non-alluvial soil such as loam, clay, rock, etc. then it’s called to be a non-alluvial canal.
10. Rigid Surface Canal
It is also termed a non-alluvial channel but here the boundary surface of the canal is artificially lined with a hard layer of lining with material such as cement, concrete, stones, etc.
Based on Canal Alignment
11. Ridge Canal
If the alignment of the irrigation canal is aligned along the ridgeline or watershed line of an area is said to be a ridge canal or watershed canal. Since it is running at a higher water level, irrigation on both sides of the canal up to a larger extent of the area is possible.
In a ridge irrigation canal, no cross-drainage works are necessary for this type of canal.
12. Contour Canal
A canal which aligned nearly parallel to the contours of that area is called a contour canal. The contour canal can be constructed in hilly regions. This canal has to pass the drainage & hence cross-drainage works are necessary to be provided.
13. Side-Slope Canal
A canal aligned perpendicular to the contour of the area is called a side-slope canal. It is not located on the ridgeline or not on the valley line but is approximately in between them.
The Side-slope canal is parallel to the natural drainage line & hence no cross-drainage works are necessary. The slope of the bed level of the side-slope canal is very steep.
Based on Financial Output
14. Protective Canal
This canal is utilized as a relief project which is constructed to protect a particular area from the shortage of water. The main purpose of a protective canal is to fulfill the requirements of farmers during the period of famine.
15. Productive Canal
This canal will give enough revenue in return for their maintenance & running costs and also recover the initial investment made on the construction of the canal. It is said to be good if it recovers 6% of its initial investment per annum.
Based on Discharge
16. Main Canal
Because of carrying excessive water flow through the main canal, it isn’t recommended to do direct irrigation from it. The primary channel takes off directly from a river or reservoir. It carries water in big amounts to feed the branch and distributary channel.
17. Branch Canal
The branch canal takes off from the main canals at a regular period. These canals carry water to major & minor distributary channels. The total water discharge of the branch channel is about 5m3/sec. In the case of branch canals also, direct irrigation from the canal isn’t recommended unless their water-carrying capacity is very low.
18. Major Distributary Canal
In a major distributary, channel water takes off from the branch channel or in some cases from the primary canal. They distribute water to minor distributaries & field channels. A canal is termed a major distributary when its discharge varies between 0.25 to 5 m3 /sec.
19. Minor distributary Canal
In minor distributaries, channel water takes off from major distributaries & sometimes directly from branch canals depending upon the discharge of canals. Their discharge is generally below 0.25 m3/sec. These channels distribute water to the field channels.
20. Field Channels
Field channels are also called watercourses which are excavated by farmers in the irrigation field. In these canals, water is fed by the distributary canals and branch canals through canal outlets.
Alignment of Irrigation Canal
A final canal alignment should be aligned in such a way that it encloses the entire area proposed to be irrigated, with the shortest possible length, and at the same time, it’s the cost including the cost of drainage work is minimum.
Precautions to be taken while finalizing the alignment of the irrigation canal:
The canal should be aligned on the ridgeline or in such a way as to obtain maximum command.
As far as possible the alignment of the canal should be kept in the center of the commanded area. The canal should be aligned in such a way that the total length of the irrigation canal is minimum as far as possible.
The alignment has to avoid inhabited places, roads, railways, residencies, location of worship, etc. The canal should be taken through the area where subsoil formation is favorable. Waterlogged, alkali, saline, and rocky soil create troubles.
The alignment should be straight throughout as far as possible. Where alignment is not straight simple circular curves of the large radius should be provided.
To make sure the economy of the alignment of the irrigation canal should be such that more cuttings & fillings are not essential. The canal alignment shouldn’t cross hills or depressions. While finalizing the alignment for the canal, the total cost of the land to be acquired should be taken into consideration.
The cost of the alignment should be in proportion to the total cost of the project. The canal alignment should cross a minimum number of drainages.
Advantages of Canal Irrigation
The followings are the main advantages of an irrigation canal:
- Unirrigated lands can be developed by providing canal irrigation, which would increase the quantity of production of the crop in the area.
- By avoiding a dangerous situation like droughts, economic development can be expedited. Dependence on rainfall can be minimized through the development of canal irrigation.
- Canals are fed through rainwater received by rivers or reservoirs, and the water is utilized for irrigation. Production of crops needing extra water is also possible through canals.
- An irrigation canal system is a permanent hydraulic structure, hence only maintenance is necessary for getting its benefits for a long period.
- While compared with un-irrigated soils, higher productivity per hectare is also achieved due to irrigation from the canals.
- Canals can be used for multi-purpose where apart from irrigation hydroelectricity generation, navigation, drinking water supply, and fishery development is also done simultaneously
- Groundwater level doesn’t lower on account of canal irrigation, but on the contrary water level increases, which facilitates digging of wells.
- Canals are also becoming a source of tourism attraction nowadays.
Disadvantages of Canal Irrigation
- It makes the soil unfertile or unproductive as harmful underground slats & alkalis come to the surface level due to waterlogging & land can also become marshy there.
- Many infections are caused due to spread of mosquitoes, warms, and insects on account of stationary water in canals.
- Due to the imbalance in the distribution of canal water, a situation of scarcity in some areas and waterlogging in other areas is caused due to the collection of water there.
- Because of the scarcity of water in inundation canals, crops are destroyed for want of water for irrigation.
- If regular preservation and maintenance of the canal are not properly done, due to which sediments are collected which resulting in the reduction of capacity of canals.
- Construction of canals also takes more time and due to excessive economic investment, it is not possible to provide canal irrigation to all regions.
The following table shows various canal irrigation types,
|Type of Canal Irrigation||Description|
|Main Canal||The primary channel that conveys water from the source to the distribution system.|
|Branch Canal||Distributes water from the main canal to smaller areas, providing a secondary network.|
|Minors or Lateral Canals||Deliver water from branch canals to individual fields or plots.|
|Permanent Canal||Operates year-round, providing a continuous water supply for agriculture.|
|Seasonal Canal||Active only during specific seasons or crop-growing periods.|
|Inundation Canal||Fills up during the flood season, allowing fields to be inundated naturally.|
|Collector Canal||Gathers water from various sources and directs it into the main canal.|
|Distributary Canal||Distributes water from the main canal to various outlets for irrigation.|
|Watercourse||The final segment delivering water directly to individual farms or fields.|
|Conveyance Canal||Transports water over longer distances from the source to distribution points.|
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