List of canal regulation works: 1. Head Regulator and Cross-Regulator 2. Meter Flumes 3. Standing Wave Flume 4. Canal Escapes.
1. Head Regulator and Cross-Regulator:
Head Regulator (H.R.):
It is a masonry or concrete structure, constructed at the head of off-taking channel. Its main function is to admit, the regulated supplies of water in the off-taking channel.
Cross Regulator (CR):
It is a masonry or concrete structure, constructed across the parent channel just Down stream of the head-regulator of the off- taking canal. Its main function is to raise the water level the parent channel, to such a level that requisite supplies the off-taking canal may be diverted through the head regulator.
Both H.R. and C.R. cannot be used alone. They have to be used together. One exercises control over the off-taking canal and other over parent canal.
Main functions of H.R. and C.R. have been enumerated as follows:
Functions of H.Rs:
1. They exercise control over the supplies to be admitted into the off-taking canals.
2. They act as metre for measuring discharge entering the off-taking channel.
3. Silt entry into the off-taking canal is checked or controlled.
4. They can shut-off the supplies the off-taking canal as and when required.
Functions of Cross Regulator (CR):
1. Effective regulation of the canal system is impossible without cross- regulator.
2. During low discharges parent channel, the cross regulator may be partly closed and thus water level on U/S side raised which can be diverted to run off taking canal full. Off-taking canals can be run rotation.
3. Flow of water D/S of parent channel may be completely closed for the purpose of repairs etc.
4. They absorb fluctuations at various sections of the canal system and thus help in preventing the possibilities of breaches in the Tail reaches.
5. Water can be stopped, to close the breaches the D/S side of C.R.
6. Cross-regulator is generally located where some road has to cross the parent canal. In that case it acts as bridge also.
2. Meter Flumes:
It is a very good device of measuring discharge in the canals. The normal section of the canal is reduced by providing converging slope of say 1:1 to the U/S side wall. After crest the side walls are giving diverging slope from 1 in 3 to 1 in 10. Discharge passing over a flume is measured by following formula-
Q = 1.7 LH3/2
where L is the effective length of the crest and H is the head causing flow. Discharge can be actually worked by using following formula also-
where C = A constant whose value varies from 0.65 to 1.0.
A = Area of normal canal section.
a = Area at throat of the flume.
H = Depth of water in normal canal section.
h = Depth of water at throat.
3. Standing Wave Flume:
It is also a meter flume which is designed for maximum discharge and thus implies critical conditions at the throat. All the elements of a standing wave flume are shown in Fig. 21.19.
Various dimensions should be as follows:
4. Canal Escapes:
Canal escape is a head regulator type structure used to extract either only excess water which has got entered into the canal by mistake or for whole of canal water in case of breach. Escape is installed at such a location where canal happens to cross a natural drainage. The discharge from the escape is carried either to low lying areas or back to the river on D/S side with the help of a natural drain.
Following are the circumstances when escapes have to be used.
(i) When cultivators suddenly close their outlets, the excess water from the canal is extracted through escape.
(ii) During breach water from the canal has to be immediately drained off so as to decrease water pressure at the breach. It is done by escape.
(iii) By mistake or otherwise, when excess discharge than the design discharge has entered the canal.
(iv) When due to rains in upper regions, excess rain water has entered the canal.
In all the above circumstances, the main purpose of escape is to extract excess discharge from the canal.
Theoretically the discharging capacity of escape should be equal to full discharge of the canal, but on practical grounds, the capacity is limited to half the discharge of the channel at that point.
Since escape conveys water from the water shed (canal runs on water shed) to the drain, its alignment should be chosen to take advantage of low contours. The velocity of flow in the drain should however be not allowed to reach the scouring velocity.
Escapes can be classified into following three categories:
(i) Canal scouring escape
(ii) Surplus escape
(iii) Tail escape
The escape provided for the purpose of scouring the silt from the canal is known as canal scouring escape. Such escape is a gated escape. If purpose of the escape is to extract only surplus water from the canal then that escape is known as surplus escape. Surplus escape may be gated or ungated type.
Gated surplus escape has pucca head regulator type structure fitted with gates. In case of ungated type the canal bank at the escape site is depressed and made pucca. The depressed bank is then filled with soil and full-fledged bank is developed.
Under normal circumstances canal keeps on running between its banks. But whenever canal is to be emptied, the canal bank is opened. Canal bank being pucca does not get scoured and hence does not develop into a wide breach. After emptying the canal, the escape site is again filled with soil and again a safe bank is developed.
Tail escape is such an escape which is installed at the tail of the canal. Its job is to discharge off excess water from tail of the canal so as to maintain F.S.L. at the tail. The structure is weir type with its crest level at the F.S.L. of the canal at the tail.
The channel which leads the surplus water from the escape to the natural drain is known as escape channel.