Types of canals
1. Based on purpose
Based on the purpose of service, the canals are designated as (a) Irrigation canal (b) Navigation canal (c) Power canal (d) Feeder canal
(a) Irrigation canal
The canal which is constructed to carry water from the source to the agricultural land for the purpose of irrigation is known as Irrigation Canal such as Bhakhra Canal, Rajasthan Canal, etc.
(b) Navigation canal
The canal which is constructed for the purpose of inland navigation is known as Navigation canal. This type of canal is also utilised for irrigation such as Ganga-Brahmaputra navigation cum irrigation canal.
(c) Power canal
The canal which is constructed to supply water with very high force to the hydroelectric power station for the purpose of moving turbines to generate electric power is known as Power Canal or Hydel Canal such as Nangal Hydel canal.
(d) Feeder canal
The canal which is constructed to feed another canal or river for the purpose of irrigation or navigation is known as feeder canal such as Farakka barrage feeder canal.
2. Based on nature of supply
Based on the nature of supply, the canals are designated as (a) Inundation canal (b) Perennial canal.
(a) Inundation canal
The canal which is excavated from the banks of the inundation river to carry water to the agricultural land in the rainy season only when the river flows to its full capacity is known as Inundation canal. No regulator is provided at the head of such a canal. The flow of water through the canal depends on the fluctuation of water level in the river. When the water level Rises above the bed level of the canal the water starts flowing through the canal. When the water level falls below the bed level of the canal, the flow of water through the canal stops.
(b) Perennial canal
The canal which can supply water to the agricultural land throughout the year is known as Perennial canal. This type of canal is taken from the upstream side of the diversion head works ( Weir or barrage) or from the storage reservoir with regulator at the head of the canal.
3. Based on discharge
According to the discharge capacity, the canals are designated as (a) Main canal (b) Branch canal (c) distributary channel (d) Field channel.
(a) Main canal
The large canal which is taken directly from the diversion head work or from storage reservoir to supply water to the network of other small canal is known as the main canal. The irrigation water is not directly supplied to the field from the main canal. The water is taken to the field through the branch canal, distributary channel and field channel. So the main canal is the backbone of the canal system.
(b) Branch canal
The Branch canals are taken from either side of the main canal at suitable points so that the whole command area can be covered by the network. The discharge capacity of the Branch canal is smaller than of the main canal. The discharge varies from 5 to 10 cumec.
(c) Distributary channels
The distributary channels are taken from the Branch canal to supply water to different sectors. The discharge capacity of these channels varies from 0.25 to 3 cumec. Again, these are designated as major distributary and minor distributary according to their function in the total net work.
(d) Field channels
These channels are taken from the outlets of the distributary channels by the cultivators to supply water to their own lands.These channels are maintained by the cultivators.
4.Based on alignment
Depending upon the alignment, the canals are designated as (a) Ridge or Watershed canal (b) Contour canal (c) Side slope canal.
(a) Ridge or watershed canal
The canal which is aligned along the ridge line ( watershed line) is known as Ridge canal or Watershed canal. The advantage of this type of canal is that it can irrigate the areas on both sides. Again there is no possibility of crossing any natural drainage and hence no cross-drainage work is necessary.
(b) Contour canal
The canal which is aligned approximately parallel to the contour lines is known as Contour canal. This canal can irrigate the areas on one side only. This canal may cross natural drainage and hence cross-drainage works are necessary.
(c) Side slope canal
The canal which is aligned approximately at right angles to the contour lines is known as the Side slope canal. It can irrigate the areas on one side only. Again, it does not cross any natural drainage and hence the cross drainage works are not necessary.
Book – Irrigation Engineering, Writer – N N Basak