2. The perennial canals are those which are taken out from the perennial rivers by constructing a barrage or weir to regulate the flow of water. Most of the canals in our country belong to this group.

Canal irrigation is widely practiced in the Northern Plains of India, where Uttar Pradesh, Punjab, Haryana, Bihar and Rajasthan account for about half of the total canal irrigated area in India. In the peninsular region, canals have been built in the lower valleys and deltas of rivers.

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Some of the important irrigation canals are Upper Ganga, Lower Ganga, Sarda, Agra canals in Uttar Pradesh; Sirkhind, Bhakra, Bist doab and Western Yamuna canals in Punjab and Haryana; Sone, Kosi and Gandak canals in Bihar; Indira Gandhi Canal in Rajasthan. Canals have been taken out from the reservoirs of the multi-purpose river valley projects in almost all the states.

Merits of Canals Irrigation:

i. Most of the canals provide perennial irrigation and save the crops from drought conditions.

ii. The sediments brought by the canals are deposited in the fields. They add to the fertility of the soils.

iii. The canals, which are parts of multipurpose river valley projects, provide cheap source of irrigation.

iv. Although the initial expenditure is very high, but it is quite cheap in the long run.

Demerits of Canal Irrigation:

i. Canals generally lead to water-logging along the canal-route due to seepage of water.

ii. Excessive flow of water in the fields raises the level of the groundwater. This can cause the problem of reh, i.e. high concentration of salt.

iii. The marshy area near the canals is breeding grounds for mosquitoes.

iv. During the rainy season, the canals can overflow and cause floods.

v. Canal irrigation can be practiced in plain areas only.