A presentation on Irrigation Canals, discussing about their classification, regulation work employed, typical cross sections , lining etc.

1. CANALS
ANIRUDHAN K M
LECTURER IN CIVIL ENGINEERING

2. CANALS
• Canal is an artificial Structure, generally trapezoidal
in shape constructed on the ground to carry water to
fields either from river or from tank or reservoir

3. Classification
• Based on discharge and its relative importance irrigation
net work canals
–Main Canal
• Main Canal takes off directly from the upstream side of weir head works or
dam.
• Usually no direct supply to fields or Water courses
• Feeds Branch Canals and Major Distributaries
–Branch Canal
• Offtakes from main canal
• Discharge of 5 cumecs or more
• Feeds Major and Minor Distributaries
• No Direct Irrigation in General
–Major Distributaries (Rajbha)
• Lesser discharge than Branch canals
• Takes off from Branch Canals or Main Canals
• Discharge between 5 cumecs and 0.25 cumecs

4. Classification
• Based on discharge and its relative importance
irrigation net work canals
–Minor Distributaries (Minors)
• Lesser discharge than Major Distributaries
• Takes off from Branch Canals or Distributaries
• Discharge below 0.25 cumecs
–Water Courses
• Small Channels
• Feeds the Fields
• Takes off from Distributaries (Sometimes from Branch Canal for
nearby fields)

5. Classification
• Based on discharge and its relative importance
irrigation net work canals

6. Classification
• Based on financial output
– Productive Canals
• Yield a net revenue to the nation after full development
of irrigation in an area
– Protective Canals
• Relief work for protecting a Famine affected region

7. Classification
• Based on the function
– Irrigation Canal
• Carries water from its source to agricultural fields.
– Carrier Canal
• Feeds another canal.
– Feeder Canal
• Feeds two or more canals.
– Navigation Canal
• Used for transport of goods.
– Power Canal
• Used to carry water for generation of hydroelectricity.

8. Classification
• Based on source of supply
– Perinnial Canal
• Continuous source of water supply.
– Inundation Canal
• Draws its supplies from a river only during the high
stages of the river.

9. Classification
• Based on boundary surface of canal
– Alluvial Canals
• The canals when excavated through Alluvial soils, Such
as Silts are called alluvial canals
– Non Alluvial Canals
• Excavated through Non Alluvial Soils like Loam Clay,
Hard Soil, Murram, Rock etc.
– Rigid Boundary Canals
• Rigid sides and base
• Lined canals

10. Classification
• Based on alignment
– Contour Canal
• The ridge line (watershed) may above the river, Canal could takeof
only as Contour Canal Initially
• A contour canal irrigates only on one side because the area on the
other side is higher.
– Ridge Canal
• The dividing ridge line between the catchment areas of two
streams(drains) is called the watershed or ridge Line.
• The canal which is aligned along any natural watershed (ridge line)
is called a watershed canal, or a ridge canal
• Aligning a canal (main canal or branch canal or distributary) on the
ridge ensures gravity irrigation on both sides of the canal.
– Side Slope Canal
• A side slope canal is that which is aligned roughly at right angles to
the contours
• Canal runs parallel to the natural drainage flow - does not
intercept drainage channels – No cross-drainage structures.

11. Classification
• Based on alignment
– Ridge Canal

12. Classification
• Based on alignment
– Contour Canal

13. Classification
• Based on alignment
– Side Slope Canal

14. Canal Allignment

15. Typical Cross Sections

16. Typical Cross Sections

17. Typical Cross Sections

18. Components of Cross- Section
• Side slope
• Berm
• Freeboard
• Bank
• Service road
• Back Berm or Counter Berm
• Spoil Bank
• Borrow Pit

19. Side Slope
• The side slopes should be such that they are stable,
depending upon the type of the soil.
• A comparatively steeper slope can be provided in cutting
rather than in filling, as the soil in the former case shall be
more stable.

20. Berms
• Berm is the horizontal distance left at ground
level between the toe of the bank and the top
edge of cutting.
• The berm is provided in such a way that the
bed line and the bank line remain parallel.
• If s1: 1 is the slope in cutting and s2:1 in filling,
then the initial berm width = (s2 – s1) d1.
• When water flows in the canal at FSL (Full
Supply Level), silt particles are deposited on
the berms and make the final side slope to
1.5:1

21. Berms
• Purposes of Berms
– They help the channel to attain regime conditions.
– They give additional strength to the banks and provide
protection against erosion and breaches.
– They protect the banks from erosion due to wave action.
– They provide a scope for future widening of the canal.

22. Free Board
• The margin between FSL and bank level is known as
freeboard.
• The amount of freeboard depends upon the discharge of the
channel.

23. Bank
• The primary purpose of banks in to remain water.
• The can be used as means of communication and as
inspection paths.
• They should be wide enough, so that a minimum cover of 0.50
m is available above the saturation line.

24. Service Roads
• Service roads are provided on canals for inspection purposes, and may
simultaneously serve as the means of communication in remote areas.
• They are provided 0.4 m to 1.0 m above FSL, depending upon the size of
the channel.
• Dowla:
– As a measure of safety in driving, dowlas 0.3 m high and 0.3 to 0.6 m
wide at top, with side slopes of 1.5: 1 to 2:1, are provided along the
banks.
– They also help in preventing slope erosion due to rains etc.

25. Counter Berms Back Berms
• Even after providing sufficient section for bank embankment,
the saturation gradient line may cut the downstream end of
the bank.
• In such a case, the saturation line can be kept covered at least
by 0.5 m with the help of counter berms as shown in figure
below.

26. Spoil banks
• When the earthwork in excavation exceeds earthworks in filling, even
after providing maximum width of bank embankments, the extra earth
has to be disposed of economically.
• To dispose of this earth by mechanical transport, etc. may become very
costly, and an economical mode of its disposal may be found in the form
of collecting this soil on the edge of the bank embankment itself.

27. Burrow Pits
• When earthwork in filling exceeds the earthwork in
excavation, the earth has to be brought from somewhere.
• The pits, which are dug for bringing earth, are known as
borrow pits.

28. Burrow Pits
• If such pits are excavated outside the channel, they are
known as external borrow pits
• If they are excavated somewhere within the channel, they
are known as internal borrow pits.
• Internal borrow pits are more preferred than external one.
• The inside borrow pit may be located at the centre of canal.
• The idea behind this is that the borrow pits will act as water
pockets where the silt will be deposited and ultimately the
canal bed will get levelled up

29. Balancing Depth
• Economic Canal is possible only if, ƩCut = Ʃ Fill
• If the amount of Cutting and filling are equal, then no
need of Spoil Bank or Burrow pit
• For a cross section there is only one depth ‘d’ of
canal which enables, ƩCut = Ʃ Fill
• This depth is called Balancing Depth
Cutting Area = Total Filling area

30. Balancing Depth
From figure
Equating both
Usual Values of Side slope in filling is 1:1, ie., z=1 Usual value for Side slope in
Cutting is 1.5:1, ie n=1.5
Then,

31. Regime Channel
• When the character of the bed and bank
materials of the channel are same as that of
the transported materials and when the silt
charge and silt grade are constant, then the
channel is said to be in its regime and the
channel is called regime channel.
• This ideal condition is not practically possible.

32. Canal Lining
• Necessity
– Preventing Seepage Losses
– Increased Velocity by reduced friction – Increased
Discharge
– Prevention of Erosion of bed in high velocities
– Retard growth of weeds
– Reduction in Maintenance

33. Canal Lining
• Advantages
– Water conservation – Preventing Seepage Losses
– Avoiding Water-Logging in adjoining
– Rugosity Co-efficient is reduced, by increased smoothness
– Increased velocity – decreased losses due to evaporation
– Only a Narrow Cross section is needed as the velocity is
increased (to keep constant discharge)
– Higher velocity offers flatter hydraulic gradient or bed
slope – Better command is obtained
– Higher velocity prevents silting
– More stable banks
– Reduced maintenance and possibility of breaching due to
increased stability
– Reduced weed growth
– Increased head availability – flatter gradient
– Assures economical water distribution
– Avoids contact of water with harmful salts

34. Canal Lining
• Disadvantages
– Heavy initial cost.
– Difficulty in providing outlets
– Difficulty in Maintenance
– Absence of berm – absence in additional stability
for vehicular and pedestrian traffic

35. Canal Lining
• Types of Lining
Hard Surface
Lining
• Cement concrete
Lining
• Shotcrete lining
• Precast Concrete
Lining
• Cement Mortar
Lining
• Brick Lining
• Stone Blocks
Lining
• Asphaltic Lining
Earth Type Lining
• Soil Cement
Lining
• Clay puddle
• Sodium
Carbonate Lining
Buried and Protected
Membrane type
Lining
• Prefabricated Light
membrane Lining
(Geo-membrane)
• Bentonite soil and
Clay membrane
lining
(Geosynthetic Clay
Liner - GCL)
• Road Oil Lining

36. Canal Lining
• Cement Concrete Lining
– It has high initial cost so its use is limited.
– It has excellent hydraulic properties
– Thickness varies from 5-10cm for M 15 concrete
and 7.5 to 15cm for M 10 concrete.
– A subgrade is prepared and compacted.
– Subgrade is saturated to a depth of 30cm in sandy
soil and15cm in other soils.
– Lay a base coat of 1:4 cement and sand slurry on
the subgrade.
– Spread oil paper/crude oil on the subgrade.
– The concrete is usually laid in alternate blocks.

37. Canal Lining
• Shotcrete Lining
– Shotcrete consumes large amount of cement.
– Cement and Sand in the ratio (1:4) is shot at the
subgrade through a nozzle.
– Thickness of this type of lining varies from 2.5 to
6.5 cm.
– Shotcrete is also used for repair of old but sound
concrete lining.

38. Canal Lining
• Precast Concrete Lining
– This consists of precast slabs usually 90cm x 30cm
in size.
– Thickness of each slab varies from 5 to 6.5 cm.
– Blocks are manufactured with an interlocking
arrangement.
– Slabs are laid on well prepared and compacted
subgrade.

39. Canal Maintenance
• Problems associated with
Canals
– Silting of Canals
– Breaching of Canal due to
Weak Banks
– Weed Growth
– Over flow of Canal Banks
Maintenance
• Silt Removal
– Flushing
– Silt Scouring Fleet
– Bundle of throny bushes
– Iron Rakes
– Reduction in Area of by Flow
– Stirring of Silt by Water Jets
– Dredging
– Excavation
• Strengthening of Canal Banks
– External Silting System
– Internal Silting System
– Formation of Berm by Internal Silting
– Formation of Back Berm
• Weed Control

40. Canal Regulation
• Canal Falls
• Head Regulator or Head Sluice
• Cross Regulator
• Canal Escape
• Canal Outlet

41. Falls or Drops
• A structure designed to secure lowering of the water
surface in a canal and to dissipate safely the surplus
energy so liberated, which otherwise scour the bed
and banks of the canal

42. Falls or Drops
Necessity:
• Velocity in a canal is a function of the slope of the canal.
There is a limit for the velocity, so that the canal bed can
neither be scoured nor silted up. Hence there is a limiting
surface slope in the canal.
• The slope of the country, where the canal system has to run
will naturally be steeper than the surface slope the canal
system that has to come up. To bring the velocity with in the
permissible velocities, falls or drops are introduced at
suitable locations.
• Falls are combined with regulators, bridges, and escapes.

43. Falls or Drops
• When the slope of the ground suddenly changes to steeper
slope, the permissible bed slope can not be maintained.
• It requires excessive earthwork in filling to maintain the slope.
• In such a case falls are provided to avoid excessive earth work
in filling

44. Falls or Drops

45. Falls or Drops
• Types of Canal Falls
– Ogee Fall
– Rapid Fall
– Stepped Fall
– Notch Fall
– Vertical Drop fall
– Glacis Type Fall
• Inglis Fall
• Montague Type Fall

46. Falls or Drops
• Ogee Fall

47. Falls or Drops
• Ogee Fall

48. Falls or Drops
• Rapid Fall

49. Falls or Drops
• Rapid Fall

50. Falls or Drops
• Stepped Fall

51. Falls or Drops
• Notch Fall

52. Falls or Drops
• Notch Fall

53. Falls or Drops
• Vertical Drop Fall

54. Falls or Drops
• Vertical Drop Fall

55. Falls or Drops
Glacis Type Fall
Ingllis Type Fall
(Stright Glacis Fall)
Montagu Type Fall
(Parabolic Glacis Fall)

56. Falls or Drops
• Well Fall

57. Falls or Drops
• Sarda Fall

58. Sluices
• Types of Outlet
– Non-Modular
• Pipe Outlet
– Semi Modular or Flexible
• Pipe outlet discharging freely in atmosphere
• Kennedy’s Gauge Outlet
• Open Flume Outlet
• Orifice Semi-Modules
– Rigid Module
• Gibb’s Module
• Khanna’s Rigid Module
• Foote Module

59. Sluices
• Pipe Outlet

60. Escapes
• Types
– Canal Scouring Escape
– Surplus Escape
– Tail Escape

61. Escapes
Surplus Escape

62. Cross Drainage Works
i. Works Carrying Canal over Drainage
i. Aqueduct
ii. Syphon Aqueduct
ii. Works Carrying Drainage over Canal
i. Super Passage
ii. Canal Syphon
iii. Works Admitting Drainage Water into Canal
i. Level Crossing
ii. Inlet and Oulet

63. Cross Drainage Works
Works Carrying Canal over Drainage
– Aqueduct
• The hydraulic structure in which the irrigation canal is taken
over the drainage (such as river, stream etc..) is known as
aqueduct.
• This structure is suitable when bed level of canal is above the
highest flood level of drainage.
• In this case, the drainage water passes clearly below the
canal.

64. Cross Drainage Works
Works Carrying Canal over Drainage
– Aqueduct

65. Cross Drainage Works
Works Carrying Canal over Drainage
– Syphon Aqueduct
• In case of the siphon Aqueduct, the HFL of the drain is much
higher above the canal bed, and water runs under siphonic
action through the Aqueduct barrels.

66. Cross Drainage Works
Works Carrying Canal over Drainage
– Syphon Aqueduct

67. Cross Drainage Works
Works Carrying Drainage over Canal
– Super passage
•The hydraulic structure in which the drainage is passing over
the irrigation canal is known assuper passage.
•This structure is suitable when the bed level of drainage is
above the flood surface level of the canal. The water of the
canal passes clearly below the drainage
•A super passage is similar to an aqueduct, except in this case
the drain is over the canal.
•the FSL of the canal is lower than the underside of the
trough carrying drainage water. Thus, the canal water runs
under the gravity.

68. Cross Drainage Works
Works Carrying Drainage over Canal
– Super Passage

69. Cross Drainage Works
Works Carrying Drainage over Canal
– Canal Syphon
• The hydraulic structure in which the drainage
is taken over the irrigation canal, but the canal
water passes below the drainage under
siphonic action is known as siphon super
passage.
• This structure is suitable when the bed level of
drainage is below the full supply level of the
canal.

70. Cross Drainage Works
Works Carrying Drainage over Canal
– Canal Syphon

71. Cross Drainage Works
Works Admitting Drainage into Canal
– Level Crossing
• When the bed level of canal and the stream are
approximately the same and quality of water in canal and
stream is not much different, the cross drainage work
constructed is called level crossing where water of canal and
stream is allowed to mix.
• With the help of regulators both in canal and stream, water is
disposed through canal and stream in required quantity.
• Level crossing consists of following components
– Crest wall
– Stream regulator
– Canal regulator.

72. Cross Drainage Works
Works Admitting Drainage into Canal
– Level Crossing

73. Cross Drainage Works
Works Admitting Drainage into Canal
– Inlet and Outlet.
• When irrigation canal meets a small stream or drain at same
level, drain is allowed to enter the canal as in inlet.
• At some distance from this inlet point, a part of water is
allowed to drain as outlet which eventually meets the original
stream.
• Stone pitching is required at the inlet and outlet.
• The bed and banks between inlet and outlet are also
protected by stone pitching.
• This type of CDW is called Inlet and Outlet.

74. Cross Drainage Works
Works Admitting Drainage into Canal
– Inlet and Outlet.

75. THANK YOU