What is Canal Fall?

Canal fall is a structure which has been constructed across a channel. To permit lowering down of its water level and to dissipate the surplus energy passed by the falling water is lastly.

Location of Canal Fall:

When the natural slope of the ground is greater than the designed bed slope of the channel, it is necessary to reduce the difference between these slopes. Firstly this is done by providing the vertical falls or drops, in the bed of the channel at the suitable intervals. Following points are necessary to consider, before locating such falls or drops, in the bed of the channel.

It must be provided at a location where the F.S.L of the channel out strips  the ground level but before the end of the channel comes into filling.

Necessity:

1. A structure constructed across a canal to lower down the water level and vanishes.
2. The surplus energy developed during the falling of water which prevents scouring the bed and banks of the canal is called as fall.
3. Hence it is very essential to build the fall structure so that scouring of the bed and canal can be avoided.
4. Location of fall can be decided from the various considerations.

Selection of site:

1. So as to achieve the economy of earth work the site for the fall for the main canal and branches from which no direction irrigation is done is preferably selected.
2. A fall is preferably provided at the site where F.S.L of the canal outstrips the ground level but before the canal bed comes into the filling.
3. The site for the fall in case of distributaries from which direct irrigation is done is preferably selected such that the command is not sacrificed in the process of lowering of the water level.
4. Lastly the site for canal fall should be selected or decided where there can be the combination of various canal regulation work. This combination gives the minimum overall cost.

Classification of Fall

1. Falls designed to maintain the depth discharge relation
2. Fall designed to maintain a fixed supply level in the channel above the work.
3. Fall designed to allow the variation of the surface level above the work at the will of the operator.
4. Miscellaneous types

1. Wall fall or cylindrical fall
2. Pipe fall
3. Chute or rapids

Types of Canal fall:

1. Ogee fall
2. Rapid fall
3. Steeped fall
4. Notch fall
5. Vertical drop type of fall

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