CANAL IRRIGATION

A canal is an artificial channel that is constructed to carry water to the fields to perform irrigation. The water is taken either from the river, tank or reservoirs. The canals can be constructed either by means of concrete, stone, brick or any sort of flexible membrane which solves the durability issues like seepage and erosion. The distribution system in a canal irrigation system, canal alignment, curves and certain features of canal irrigation are briefly explained in this article. 

Distribution System for Canal Irrigation System

The figure-1 below shows the general layout of a canal distribution system depicting the different networks of canals constituting a canal irrigation system. Whatever be the irrigation scheme i.e direct irrigation using weir or a barrage and storage irrigation scheme like dams or reservoir, both demand a network of irrigation canals of various sizes and capacities. Hence the canal system comprises of:

1. Main Canal
2. Branch Canal
3. Distributaries or major distributaries
4. Minors or minor distributaries
5. Watercourses

Canal Alignment

The canal alignment is selected based on the following considerations:

1. Canal alignment must be chosen such that the maximum area is served with the least length. It also must minimize the use of cross-drainage works.
2. If the length of the canal is short, there is less head loss, seepage loss, and evaporation loss. This also brings additional areas for irrigation.
3. Following a straight alignment helps to reduce the loss.
4. Always a canal alignment with less cross-drainage work must be chosen.
5. The canal must not pass through forest, town, village or costly areas reducing the chance of giving heavy compensation.
6. Among different canals, ridge canals help to irrigate either side of the canal.
7. It must help reduce heavy cutting and filling i.e costly embankment construction must be avoided.
8. It is recommended to attain a balance in depth of cutting and depth of filling.
9. The selection of alignment over brackish, rocky or cracked strata must be avoided.

Curves in Canals

It is always recommended to align the canals without curves. Curves result in disturbance of flow. This scours the outer side of the canals and results in silting in the inner curves.In order to avoid, scouring in the concave side, it is required to provided pitching. The canal curves must be more gentle and posses more radius in order to take large discharges.

Advantages of Canal Irrigation

The main advantages of canal irrigation are:

1. Development of un-irrigated wasteland.
2. Dangerous droughts can be avoided that expedite economic development.
3. The water requirement of crops during fluctuation in rainfall intensity can be met by having a proper irrigation system.
4. Compared to conventional watering, higher productivity per hectare land is obtained due to canals.
5. The canals constructed are permanent that require regular maintenance.
6. Canal irrigation does not let the water table level go down. It only helps to increase the water level thus facilitating the digging of wells.
7. Canals also serve the purpose of hydroelectricity, drinking water supply, fishery development, and navigation.

Disadvantages of Canal Irrigation

The major disadvantages of canal irrigation are:

1. Any imbalance in the water distribution process results in a scarcity of water in some areas and water clogging in other areas. This hence makes the soil unproductive due to the movement of harmful underground salts and alkalies to the surface level.
2. Water present stationary in the canal results in the growth of worms, mosquitoes, and insects.
3. Improper maintenance results in the collection of sediments in the canals that in turn affects the capacity of the canal.
4. Canal construction demands economic investment and time. Hence, this is not a solution for all irrigation.