Canals are most important source of irrigation from the period of 1960s, but in the 1970s, they yielded first place to wells and tube wells and now constitute the second most important source of irrigation in India. Canals are most effective techniques of irrigation in areas of low level relief, deep fertile soils, perennial source of water and extensive command area. Therefore, the main concentration of canal irrigation is in the northern plain of India, especially the areas comprising Uttar Pradesh Haryana and Punjab.
The digging of canals in stony and uneven areas is difficult and unprofitable. Thus the canals are practically absent from the Peninsular plateau area. However, the coastal and the delta regions in South India do have some canals for irrigation.
Canals in India are of two types:
1. Inundation canals, which are taken out from the rivers without any regulating system like weirs at their head. Such canals supply irrigation mainly in the rainy season when the river is in flood and there is excess water. When the rainy season is over, the flood in the river subsides, the level of water falls below the level of the canal head and the canal dries up. Some canals taken off from the Satluj in Punjab were of this type. Since irrigation from this type of canals is unsure, they have been converted in perennial canals.
2. Perennial Canals are those which are taken off from perennial rivers by constructing a barrage across the river. Most of the canals in India today are perennial.
Advantages of Canal Irrigation: Most of the canals provide perennial irrigation and supply water as and when required. This saves the crops from drought conditions and helps in increasing the farm production. Canals carry a lot of residue brought down by the rivers. This sediment is deposited in the agricultural fields which make soil more fertile. Some of the canals are parts of multipurpose projects and, therefore, provide inexpensive source of irrigation. Although the initial cost involved in canal irrigation is more, it is quite cheap in the long run.
Drawbacks or Disadvantages of Canal Irrigation: The canal water soaks into the ground and results in water-logging along the canal route. Excessive flow of water in the fields raises the ground water level. Capillary action brings alkaline salts to the surface and makes large areas unfit for agriculture. Huge areas in Panjab, Haryana and Uttar Pradesh suffer from the problem caused by canal irrigation. The muddy areas near the canals act as reproduction grounds of mosquitoes which result in widespread malaria. Many canals overflow during rainy season and flood the surrounding areas. Canal irrigation is suitable in plain areas only.