Alignment of Canals - Canal Irrigation

The alignment of the irrigation canals can be in three ways, normally watershed canals, contour canals, and side-slope canals. These three canals are briefly explained in the article below. 

1. Watershed Canals

The watershed canals are also called as ridge canals. A ridge or a water-shed is the dividing line between the catchment area as shown in figure-1. The canals that are aligned along the natural watershed or ridge line is called as a watershed canal or a ridge canal.

The two main advantages of having watershed canals are:

· The drainage water does not cross the canals and interrupt the canal flow. Hence it does not demand cross-drainage works. This saves the cost of having cross-drainage work.

· As either side of the ridge canal is descending downwards, the field areas present either side of the ridge canal can be irrigated by gravity.

2. Contour Canals

Contour canals are canals that are constructed or aligned parallel to the contour lines of that area or country. The figure-2 below shows the construction of canals parallel to the contours. These canals require a single bund, as one of the sides is at a higher elevation compared to another side. Hence this is also called single bund canals. 

From the figure, it is clear that during precipitation or rain, the water flows across the canals. So a pathway is provided for the movement of drain water, by means of cross-drainage works. The construction of cross-drainage works makes the construction more costly.
A contour canal provides irrigation water to one side of the canal as the other side is in a higher contour.

3. Side Slope Canals

A side slope canal is aligned in a perpendicular direction to the contours along the side slopes. As the canal is constructed parallel to the drainage flow, there is no interruption to the drainage channels, hence eliminating the need for cross-drainage works. 

These as flows from high altitude to low altitude, there is a need for protection for the canal inner layers along with bunds on either side. Hence, the side slope canals are also called as double bund canals. 

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