Canal Regulation Work

Canal Regulation Work Points : canal regulation work, regulation works of canal, functions of distributary head regulator, meter and non meter falls, necessity and location of falls: Regulation works of canal: Any structure constructed to regulate the discharge, full supply level or velocity in a canal is known as a regulation work. Such a structure is necessary for the efficient working and safety of an irrigation channel. The various ru1ation works may be categorized as under:
1. Canal fall.
2. Head regulator or head sluice.
3. Cross regulator.
4. Canal escape.
5. Canal outlet

Head regulator and cross-regulator regulate the supplies of the off-taking channel and the parent channel respectively. The distributary head regulation is provided at the head of the distributary and controls the supply entering the distributary. It is a necessary link the parent channel and the distributing channel. A distributary head is a regulator, a meter of supply and a silt selective structure. A cross-regulator is provided on the main canal at the d/s of the off-take to head up the water level and to enable the off taking channel to draw the required supply. Functions of distributary head regulator 1. They regulate or control the supplies to the off-taking channel.
2. They serve as a meter for measuring the discharge entering into the off-taking canal.
3. They control the silt entry in the off-taking canal.
4. They help in shutting off the supplies when not needed in the off-taking canal, or when the off taking channel is required to be closed for repairs. Meter and Non Meter Falls Meter falls are those which also measure the discharge of the canal. The non meter do not measure the discharge. For a fall to act as a meter, it must have broad weir type crest so that the discharge co-efficient is constant under variable head. Generally glacis type fall is suitable as a meter. The vertical drop fall is not suitable as a meter die to the formation of partial vacuum under the nappe. Contracted and full width falls.

A fall may either be constructed of the full channel width or it may be castrated. The contracted falls, the later type, are also known as the flumed falls. Necessity and Location of Falls: Fall is an irrigation structure constructed across a canal to lower down its water level and destroy the surplus energy liberated from the falling water which may otherwise scour the bed and banks of the canal.

That the canal requires a certain slope, depending upon the discharge, to overcome the frictional losses. This slope may vary from I in 4000 for a discharge of about 1.5 cumecs to about 1 in 8000 for a discharge of 3000 cumecs. This slope is, therefore, quite flat in comparison to the available ground slope of an average value of 5 to 20 cm per kilometre length.

1. (1 in 200 to 1 in 50). Thus the ground slope in nature is always very much steeper than the design bed slope of irrigation canal, based on the silt theories. If an irrigation canal, taking off from its head, is in cutting. it will soon meet with condition when it will be entirely in embankment.

2. It has been stated earlier in chapter 15 that if the canal is in embankment, the cost of construction and maintenance is very high and at the same time the percolation and seepage losses are excessive. Also, there is always a danger of the adjacent area being flooded if some cut or breach takes place in the canal banks. Hence the canal should never be in high embankment. However, the divergence between the gentle bed slope of canal and the steep ground slope throws the canal in embankment after a certain distance though it started in cutting at its head. To overcome this difficulty, falls are introduced at appropriate places, and the water surface of the canal is lowered. Arrangements are made to dissipate the excess energy liberated from the falling water, to

3. The Location of a fall is decided from the following considerations

4. For the canal which does not irrigate the area directly, the fall should be located from the considerations of economy in cost of excavation of the channel with regard to balancing depth and the cost of the falls itself.

5. For a canal irrigating the area directly a fall may be provided at a location where the F.S.L. outstrips the ground level, but before the bed of the canal comes into filling. After the drop, the F.S.L of the canal may be e1ow the ground level for two kilometer.

6. The location of the fall may also. be decided Prom the consideration of the possibility of combining it with a regulator or a bridge or any other masonry works.

7. A relative economy of providing large number of small falls v/s small number of big falls should be worked out. The provision of small number of big falls results in unbalanced earth-work, but there is always some saving in the cost of the fall structure.