A canal is an artificial channel constructed to convey water from rivers, reservoirs, etc. for several purposes like power generation, navigation, irrigation, etc. Canals are classified into different types based on factors such as nature of supply source, functions, type of boundary surface, financial output, discharge capacity and alignment of the canal.
Classification of Canals based on Different Factors
Canals are classified into different types based on factors which are as follows :
- Based on the nature of the supply source
- Based on functions
- Based on the type of boundary surface soil
- Based on the financial output
- Based on discharge
- Based on canal alignment
Based on the Nature of Supply Source
- Permanent Canal
- Inundation Canal
1. Permanent Canal
A Permanent canal is a type of canal in which water is available throughout the year. This type of canal is generally directed from a permanent source of supply water bodies. Several Permanent hydraulic structures are constructed in this type of canal for water regulation and distribution. A Permanent canal can also be called as a perennial canal.
Fig 4: Sirhind Feeder Canal, India
4. Carrier canal
A carrier canal is multi-function canal which serves the purposes of both irrigation canal and feeder canal. It means the carrier canal feeds the other canals as well as provides water for direct irrigation.
Fig 5: Carrier Canal
5. Navigation canal
A canal which is constructed especially for navigational purposes is known as navigation canal. The water level required in a navigation canal is generally a lot higher to accommodate large ships, vessels, etc.
Fig 6: Panama Navigation Canal, Panama
Based on Type of Boundary Surface of Canal
- Alluvial canal
- Non-alluvial canal
- Rigid Surface canal
1. Alluvial canal
If the canal is excavated in alluvial soils such as silt, sand, gravel, etc. then it is said to be an alluvial canal.
Fig 7: Alluvial Canal
2. Non-alluvial canal
If the boundary surface of the canal is of non-alluvial soils such as loam, clay, rock, etc. then it is said to be a non-alluvial canal.
Fig 8: Non-alluvial Canal
3. Rigid Surface canal
Rigid surface canals also come under non-alluvial canals but here the boundary surface of the canal is lined artificially with a hard layer of lining material such as cement, concrete, stones, etc.
Fig 9: Rigid Surface Canal or Lined Canal
Based on Financial Output
- Protective canal
- Productive canal
1. Protective Canal
Protective canals are relief work projects which are constructed to protect a particular area from the shortage of water. The main objective of a protective canal is to fulfill the requirements of cultivators during the period of famine.
Fig 10: Protective Canal
2. Productive Canal
Productive canals are those which will produce enough revenue for its maintenance and running costs and also to 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.
Fig 11: Productive Canal, South-North Water Transfer Project, China
Based on Discharge
- Main canal
- Branch canal
- Major distributary canal
- Minor distributary canal
- Field canal
Fig 12: Canal Classification based on Discharge
1. Main canal
The main canal takes off directly from a river or reservoir. It carries water in large amounts to feed the branch and distributary canals. Due to conveying of very high discharge through the main canal it is not recommended to do direct irrigation from it.
2. Branch Canal
The branch canal takes off from main canals at regular intervals. These canals supply water to major and minor distributary canals. The discharge of the branch canal is generally over 5 m3/sec. In the case of branch canals also, direct irrigation is not recommended unless their water carrying capacity is very low.
3. Major Distributary Canal
Major distributary canal takes off from the branch canal or in some cases from the main canal. They supply water to minor distributaries and field channels. A canal is said to be major distributary when its discharge lies between 0.25 to 5 m3/sec.
4. Minor Distributary Canal
Minor distributary canal takes off from major distributaries and sometimes directly from branch canals depending upon the discharge of canals. Their discharge is generally below 0.25 m3/sec. These canals supply water to the field channels.
5. Field Channels
Field channels also known as watercourses are small channels excavated by cultivators in the irrigation field. These channels are fed by the distributary canals and branch canals through canal outlets.
Based on Canal Alignment
- Ridge canal
- Contour canal
- Side-slope canal
1. Ridge Canal
A canal aligned along the ridgeline or watershed line of an area is said to be ridge canal or watershed canal. Since it is running at the peak altitude of the area, irrigation on both sides of the canal up to a larger extent of the area is possible. There is no interception of natural drains on ridge lines hence, no cross drainage works are required for this type of canal.
Fig 13; Ridge Canal
2. Contour Canal
A canal aligned roughly parallel to the contours of the area is called a contour canal. This type of canal can be seen in hilly regions. Since it is parallel to the contour line, the ground on one side of the canal is higher and hence irrigation is possible only on the other side of the canal. A contour canal has to pass the drainage and hence cross drainage works are required to be provided.
Fig 14: Contour Canal
3. Side-slope Canal
A canal aligned nearly perpendicular to the contour of the area is called a side-slope canal. It is located neither on the ridgeline nor on the valley line but is approximately in between them. It is parallel to the natural drainage line and hence no cross drainage works are required. The bed slope of side slope canal is very steep.