2. CANAL REGULATION
Introduction:
Canal regulation is the process of regulating water from a reservoir or diversion
head works through a canal system for a dependable supply of water for irrigation
requirement.
The canal system plays a key role in regulating the irrigation water.
The major components of a permanent canal system are discussed below.
Components of a permanent canal system
Main canal
Branch canal
Distributaries
Water courses
3. Components……
Main Canal (M):
This canal takes off from the river and derives water through a regulator. For a certain
length in the beginning the canal may be in full cutting.
Obviously direct flow irrigation from such a channel is not possible as its water surface
is below the general ground surface.
The main function of the canal is to take the required amount of irrigation water at the
head and to deliver it in the canal system below.
Branch Canals (B):
After the main canal comes in the tract which is to be irrigated by the canal system,
water is distributed over the entire commanded area.
For this purpose the main canal is branched to cover the whole area. The bifurcated
canals are called branch canals or simply branches.
4. Components…
From the branches also direct irrigation is very rarely done.
The main function of the branches is to make the water available in different parts of the
tract for further distribution. The section of a branch canal is smaller than the main canal.
Distributaries:
They can be subdivided into:
i. Major distributaries, and
ii. Minor distributaries or minors.
Major Distributaries (D):
They are also named Rajbaha. Major distributaries are smaller in section than the branches.
They are taken off mainly from the branches to distribute the water to various parts for
direct irrigation purposes.
5. Components…
Sometimes major distributaries may take off directly from the main canal.
The distributaries provide water to field channels through outlets for irrigation.
Minor Distributaries (M):
They are smaller in section than the major distributaries. The main purpose of these
distributaries is to reduce the length of the field channels.
They are taken off from the major distributaries and sometimes from the branch
canals.
When the length of the field channels is more than 3 km the minor distributaries
are introduced to reduce the length.
They are also called minors.
6. Components…
Water Courses:
They are also named as guls or field channels. They are the channels which take
irrigation water to the fields.
The water courses derive their supply from the distributaries through outlets.
An outlet is a simple and a small irrigation structure constructed on the distributaries.
It may be a simple pipe outlet or any other type provided to allow flow of water into
the water courses.
Irrigation department is responsible for construction and maintenance of the canal
system up to minor distributaries.
The field channels are constructed by cultivators themselves as per the alignment
sanctioned by the department.
7. Components…
Nowadays the field channels are also constructed by irrigation department for
cultivators.
The job of maintenance of field channels is left entirely to the cultivators. The length
of a water course should not exceed 3 km in any case.
It generally serves an area of 40 to 50 hectares. The upper limit of discharge in a
watercourse ranges between 0.08 to 0.06 m3/sec.
8.
9. Canal Regulation Works
These are structures constructed to regulate the flow rate and volume of water
Necessary for the efficient working and safety of an irrigation channel
Important Regulators
Head regulator or head sluice
Cross regulator
Canal outlet
Regulators are normally aligned at 90 degree to weir.
10. Head Regulator
Regulators Constructed at the off taking point are called head
regulators.
When it is constructed at the head of main canal it is known as canal
head regulator.
And when it is constructed at the head of distributary, it is called
distributary head regulator.
Function:
To control the entry of water either from the reservoir or from
the main canal.
Tocontrol the entry of silt into off taking or main canal.
Toserve as a meter for measuring discharge of water.
11. Head Regulator
Construction: The components of head regulator depends upon
the size of canal and location of head regulator.
It consists of one or more gated research openings with barrels
running through the bank.
For large canals head regulators are flumed to facilitate the
measurement of discharge.
13. Cross Regulator
Cross Regulator
ARegulator Constructed in the main canal or parent canal downstream of an
off take canal is called cross- regulator.
It is generally constructed at a distance of 9 to 12 km along the main canal and
6 to 10 km along branch canal.
Functions:
(i) ToControl the flow of water in canal system
(ii) Tofeed the off taking Canals
(iii) Toenable closing of the canal breaches
(iv) Toprovide roadway for vehicular traffic
14. Cross Regulator
The sill of regulation is kept little higher than the u/s bed level of
canal across which it is constructed.
Construction: For Cross Regulators abutments with grooves and
piers are constructed parallel to the parent canal.
Vertical lift gates are fitted in the grooves. The gates can be
operate from the road.
18. Types of Regulator
Still pond regulation
Open flow regulation
Silt control devices
19. Still pond regulation:
Canal draws water from still pond
Water in excess of canal requirements is not allowed to escape under the
sluice gates.
Velocity of water in the pocket is very much reduced; silt is deposited in
the pocket
When the silt has a level about 1/2 to 1m below the crest level of Head
Regulator, supply in the canal is shut off and sluice gates are opened to
scour the deposited silt.
20.
21. Open flow regulation
Sluice gates are opened and allow excess of the canal requirement
Top water passes into the canal
Bottom water maintain certain velocity in the pocket to keep the silt to
remain in suspension
Canal is not closed for scouring the silt.
22. Silt Control Devices
Scouring Sluices or Under sluices, silt pocket and silt excluders
The above three components are employed for silt control at the head work.
Divide wall creates a silt pocket.
Silt excluder consists of a number undertunnels resting on the floor pocket. Top
floor of the tunnel is at the level of sill of the head regulator.
Various tunnels of different lengths are made. The tunnel near the head
regulator is of same length of head regulator and successive tunnels towards
the divide wall are short.
Velocity near the silt laden water is disposed downstream through tunnels and
under sluices.
23. Silt Control Devices
Silt Excluder: The silt excluder is located on the u/s of diversion weir and in
front of the head regulator.
The object is to remove silt that has entered in the stilling basin through
scouring sluices.
Silt Ejector: Silt Ejector is located in the canal take off from the diversion weir at
6 to 10 km in the canal reach. It ejects the silt that has entered in the canal
24.
25.
26.
27. Installing silt excluders
Making entry of clear top water by Providing raised sill in the canal
Lower sill level of scouring sluices
Wide head regulator reduces velocity of water at intake
Smooth entry to avoid unsteady flow
Handling careful the regulation of weir
Disturbance is kept at minimum in weirs
28. Silt excluder:
Silt is excluded from water entering the canal, constructed in the bed
infront of head regulator - excludes silt from water entering the canal
Designed such that the top and bottom layers of flow are separated with
the least possible disturbance
Top water to canal - bottom, silt laden through under sluices
No of tunnels resting on the floor of the pocket of different lengths
The tunnel near the head regulator being of same length as that of the
width of head regulator - tunnel of different length.
Capacity of tunnel is about 20% of canal discharge
29. Minimum velocity 2 to 3 m/s to avoid deposition in tunnel is kept the
same as sill level of head regulator
From discharge and scouring velocity the total waterway required for
under water tunnels can be determined
Silt extractor or silt ejector:
Device by which the silt, after it has entered the canal is extracted or
thrown out.
Constructed on the canal some distance away from head regulator
Horizontal diaphragm above the canal bed
anal bed slightly depressed below the diaphragm 0.5 to 2.8m
30. Under diaphragm, tunnel which extent the highly silted bottom water
tunnel.
There should be no disturbance of flow at the entry.
Sediment - laden are diverted by curved vanes
Forwards the escape chamber: steep slope to escape channel is provided.
The streamlined vane passage accelerate the flow through them, thus
avoiding deposition (decreasing section area increases the flow velocity)
The tunnel discharge by gate at the outlet end (escape channel)
31. Location:
If near head regulator, silt will be in suspension
If too far away than result in silting of canal.
32. Classification of Regulators:
I – According to purpose:
1- Regulation of Discharge “Q”
2- Regulation of Water slopes (and velocity)
3- Measurement of Discharge “Q”
4- Division or Diversion of Discharge
5- Change in bed slope
33. II – According to location
1- Head Regulator
2- Intermediate Regulator
3- Escape Regulator
4- Diversion Regulator
III – According to Material (Type of Construction)
1- Masonry Arch Regulator
2- Mixed Type Regulator (masonry + RC)
3- RC Regulator
34. Location of regulators
Should always be located at straight reaches (position “a”)
Never located within curves in waterways (either silting or scouring is
liable to occur causing destruction of the regulator (position “b”)
At diversion; location should be chosen 50-200m DS the point of
“c”
Should always be located at straight reaches (position “a”)
35.
36. Advantages of Regulators to weirs
Regulator may be fully opened at flood time giving enough water way
area to avoid excess heading up
both US & DS water levels are controlled
minimize silting at US
37.
38. Principles of Design
Hydraulic Design
To get the area of water way
Discharge is considered for fully opened
Regulator
Determination of heading up
Check the velocity through regulator vents
39. Floor design
To determine the floor length
To cover the floor length by regulator floor
To check the percolation length
To determine the floor thickness
To make adequate precautions against
undesired percolation
40. Structural Design
To determine the dimensions and check the stability of the structural
elements which are: Piers; Abutments; wing walls Roadway (bridge);
gates Cranes and lifting devices
41. Main Elements of Regulators
1- The water area of vents (S*dw)
2- The bridge
3- The piers between the regulator vents
4- The abutments
5- The floor
6- The gates
42.
43. Forces acting on Regulator
Pu - Upstream water pressure
PD - Downstream water pressure acting on the DS emergency
groove
PL - Water pressure in lateral direction when one vent is
for repair
PW - Wind pressure on exposed surface (if any)
W1 - Weight of bridge + live load (for worst case of loading)
W2 - Own weight of pier
W3 - Own weight of gates + lifting apparatus (if any