Canal falls are structures constructed across canals to lower the bed level to maintain the designed slope when there is a change in ground level. The main types of canal falls are ogee falls, stepped falls, vertical falls, rapid falls, and straight glacis falls. Canal escapes are side channels that remove surplus water from canals into natural drains. The main types are surplus escapes, tail escapes, and scouring escapes. Cross drainage works include structures like aqueducts and siphon aqueducts to allow canals to pass over drainages when their bed levels differ.

1. Canal Regulation
&
Cross Drainage Works
Unit-V
BTCI09007

2. Syllabus
• Canal Regulation Works
• Canal Fall- Necessity and Location- Types of
Falls- Cross Regulator and Distributory Head
Regulator- Their Functions, Silt Control
Devices, Canal Escapes- Types of Escapes.
• Cross Drainage Works: Types- selection of
suitable type of CD works- aqueduct and
Siphon aqueduct

3. What is Canal Fall?
• Whenever the available natural ground slope
is steep than the designed bed slope of the
channel, the difference is adjusted by
constructing vertical ‘falls’ or ‘drops’ in the canal
bed at suitable intervals, as shown in figure
below. Such a drop in a natural canal bed will not
be stable and, therefore, in order to retain this
drop, a masonry structure is constructed. Such a
structure is called a Canal Fall or a Canal drop.

4. Canal Fall

5. Canal Fall
Irrigation canals are designed for a prescribed bed slope
so that velocity becomes non silting or non scouring.
But if the ground topography is such that in order to
maintain the canal designed slope, indefinite filling
from falling ground level is to be made. This indefinite
filling is avoided by constructing a hydraulic structure
in the place of sudden bed level. This hydraulic
structure is called canal fall or drop. Beyond the canal
fall, canal again maintains its designed slope.

6. Canal Fall
• Thus, a canal fall or drop is an irrigation structure
constructed across a canal to lower down its bed level
to maintain the designed slope when there is a change
of ground level to maintain the designed slope when
there is change of ground level. This falling water at
the fall has some surplus energy. The fall is
constructed in such a way that it can destroy this
surplus energy.

7. Necessity of Canal Falls
• 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

8. Necessity of Canal Falls

9. Necessity of Canal Falls
• When the slope of the ground is more or
less uniform and the slope is greater than the
permissible bed slope of canal.

10. Necessity of Canal Falls
• In cross-drainage works, when the difference
between bed level of canal and that of
drainage is small or when the F.S.L of the
canal is above the bed level of drainage
then the canal fall is necessary to carry the
canal water below the stream or drainage.

11. Necessity of Canal Falls

12. Types of Canal Fall
• Depending on the ground level conditions and shape of
the fall the various types of fall are:
Ogee Fall
• The ogee fall was constructed by Sir Proby Cautley on
the Ganga Canal. This type of fall has gradual convex
and concave surfaces i.e. in the ogee form. The gradual
convex and concave surface is provided with an aim to
provide smooth transition and to reduce disturbance
and impact. A hydraulic jump is formed which
dissipates a part of kinetic energy. Upstream and
downstream of the fall is provided by Stone Pitching.

13. Ogee Fall

14. Types of Canal Fall
Stepped Fall
• It consists of a series of vertical drops in the form of
steps. This steps is suitable in places where sloping
ground is very long and require a long glacis to connect
the higher bed level u/s with lower bed level d/s. it is
practically a modification of rapid fall. The sloping
glacis is divided into a number drops to bring down the
canal bed step by step to protect the canal bed and sides
from damage by erosion. Brick walls are provided at
each drop. The bed of the canal within the fall is
protected by rubble masonry with surface finishing by
rich cement mortar.

15. Stepped Fall

16. Types of Canal Fall
Vertical Fall (Sarda Fall)
• In the simple type, canal u/s bed is on the level of
upstream curtain wall, canal u/s bed level is
below the crest of curtain wall. In both the
cases, a cistern is formed to act as water cushion.
Floor is made of concrete u/s and d/s side stone
pitching with cement grouting is provided. This
type of fall is used in Sarda Canal UP and
therefore, it is also called Sarda Fall.

17. Vertical Fall

18. Types of Canal Fall
Rapid Fall
• When the natural ground level is even and
rapid, this rapid fall is suitable. It consists of
long sloping glacis. Curtain walls are provided
on both u/s and d/s sides. Rubble masonry with
cement grouting is provided from u/s curtain
wall to d/s curtain wall. Masonry surface is
finished with a rich cement mortar.

19. Rapid Fall

20. Types of Canal Fall
Straight Glacis Fall
• It consists of a straight glacis provided with a
crest wall. For dissipation of energy of flowing
water, a water cushion is provided. Curtain
walls are provided at toe and heel. Stone
pitching is required at upstream and
downstream of the fall.

21. Straight Glacis Fall

22. Types of Canal Fall
Trapezoidal Notch Fall
• It was designed by Reid in 1894. In this type a
body or foundation wall across the channel
consisting of several trapezoidal notches between
side pier and intermediate pier is constructed. The
sill of the notches are kept at upstream bed level
of the canal. The body wall is made of concrete.
An impervious floor is provided to resist the
scouring effect of falling water. Upstream and
downstream side of the fall is protected by stone
pitching finished with cement grouting

23. Trapezoidal Notch Fall

24. Types of Canal Fall
Well or Cylinder Notch Fall
• In this type, water of canal from higher level is
thrown in a well or a cylinder from where it
escapes from bottom. Energy is dissipated in
the well in turbulence. They are suitable for
low discharges and are economical also.

25. Types of Canal Fall
Montague Type Fall
• In the straight glacis type profile, energy
dissipation is not complete. Therefore,
montague developed this type of profile where
energy dissipation takes place. His profile is
parabolic and is given by the following
equation,

26. Montague Type Fall

27. Types of Canal Fall
Inglis or Baffle Fall
• Here glacis is straight and sloping, but baffle
wall provided on the downstream floor
dissipate the energy. Main body of glacis is
made of concrete. Curtain walls both at toe and
heel are provided. Stone pitching are essential
both at u/s and d/s ends

28. Inglis or Baffle Fall

29. Canal Escape
• It is a side channel constructed to remove surplus
water from an irrigation channel (main canal,
branch canal, or distributary etc.) into a natural
drain.
• The water in the irrigation channel may become
surplus due to -
• Mistake
• Difficulty in regulation at the head
• Excessive rainfall in the upper reaches
• Outlets being closed by cultivators as they find
the demand of water is over

30. Canal Escape
• It is the structure required to dispose of surplus or
excess water from canal from time to time. Thus, a
canal escape serves as safety valve for canal system. It
provides protection to the canal from possible damage
due to excess supply which may be due to mistake in
releasing water at head regulator or heavy rainfall that
makes sudden regular demand of water. The excess
supply makes the canal banks vulnerable to failure due
to overtopping or dangerous leaks. Therefore, provision
for disposing this surplus water in form of canal
escapes at suitable intervals along the canal is essential.
Moreover emptying canal for repair and maintenance
and removal of sediment deposited in the canal can also
be achieved with the help of canal escapes.

31. Escapes are usually of the following
three types.
Surplus Escape
• It is also called regulator type. In this type sill
of the escape is kept at canal bed level and the
flow is controlled by a gate. This type of
escapes are preferred now-a-days as they give
better control and can be used for employing
the canal for maintenance.

32. Surplus Escape

33. Surplus Escape

34. Escapes are usually of the following
three types.
Tail Escape
• A tail escape is provided at the tail end of the
canal and is useful in maintaining the required
FSL in the tail reaches of the canal and
hence, they are called tail escape.

35. Tail Escape

36. Escapes are usually of the following
three types.
Scouring Escape
• This escape is constructed for the purpose of scouring
of excess silt deposited in the head reaches from time to
time. Hence, it is called scouring escape. Here the sill
of the regulator is kept at about 0.3 m below the canal
bed level at escape site. When deposited silt to be
scoured, a higher discharge than the FSL is allowed to
enter the canal from the head works. The gate of the
escape is raised so as to produce scouring velocity
which remove the deposited silt. This type of Escape
has become obsolete as silt ejector provided in the
canal can produce better efficiency.

37. Scouring Escape

38. 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.
• To control the entry of silt into off taking or main canal.
• To serve as a meter for measuring discharge of water.

39. 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.

40. Head Regulator

41. Cross Regulator
• Cross Regulator
• A Regulator 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) To Control the flow of water in canal system
• (ii) To feed the off taking Canals
• (iii) To enable closing of the canal breaches on the d/s
• (iv) To provide roadway for vehicular traffic

42. Cross Regulator

43. Cross Regulator
Construction: For Cross Regulators abutments
with grooves and piers are constructed parallel to
the parent canal. The sill of regulation is kept
little higher than the u/s bed level of canal across
which it is constructed. Vertical lift gates are
fitted in the grooves. The gates can be operate
from the road.

44. Canal regulators

45. Canal regulators

46. Cross Regulator

47. Head Regulator

48. 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 under tunnels
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.

49. 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

50. Silt Control Devices
Silt Excluder

51. Silt Control Devices
Silt Ejector

52. Silt Control Devices

53. Canal Outlet/modules
• A canal outlet or a module is a small
structure built at the head of the water
course so as to connect it with a minor or a
distributary channel.
• It acts as a connecting link between the
system manager and the farmers.

54. Canal Outlet/modules

55. Non-Modular Modules
• Non-modular modules are those through which the
discharge depends upon the head difference between
the distributary and the water course.
Common examples are:
(i) Open sluice
(ii) Drowned pipe outlet

56. Types of Outlet/modules
• Non-modular modules

57. Semi-Modules or Flexible
modules
• Due to construction, a super-critical velocity is ensured
in the throat and thereby allowing the formation of a
jump in the expanding flume.
• The formation of hydraulic jump makes the outlet
discharge independent of the water level in water
course, thus making it a semi module. Semi-modules or
flexible modules are those through which the discharge
is independent of the water level of the water course but
depends only upon the water level of the distributary so
long as a minimum working head is available.
• Examples are pipe outlet, open flume type etc.

58. Semi-Modules or Flexible
modules

59. Rigid Modules or Modular
Outlets
• Rigid modules or modular outlets are those through
which discharge is constant and fixed within
limits, irrespective of the fluctuations of the water
levels of either the distributary or of the water course
or both.
• An example is Gibb’s module:

60. Gibb’s Module

61. Cross Drainage Works
• Irrigational Canals while carrying water from
headworks to crop field, have to cross few natural
drainage streams, nallaha, etc.. To cross those
drainages safely by the canals, some suitable
structures are required to construct. Works
required to construct, to cross the drainage are
called Cross Drainage Works (CDWs). At the
meeting point of canals and drainages, bed levels
may not be same. Depending on their bed
levels, different structures are constructed and
accordingly they are designated by different
names.

62. Necessity of Cross Drainage Works
• The water-shed canals do not cross natural drainages.
But in actual orientation of the canal network, this ideal
condition may not be available and the obstacles like
natural drainages may be present across the canal.
So, the cross drainage works must be provided for
running the irrigation system.
• At the crossing point, the water of the canal and the
drainage get intermixed. So, for the smooth running of the
canal with its design discharge the cross drainage works are
required.
• The site condition of the crossing point may be such
that without any suitable structure, the water of the canal
and drainage can not be diverted to their natural
directions. So, the cross drainage works must be provided
to maintain their natural direction of flow.

63. Necessity of Cross Drainage Works

64. Types of Cross Drainage Works
• Type I (Irrigation canal passes over the drainage)
• (a) Aqueduct
• (b) Siphon Aqueduct
• Type II (Drainage passes over the irrigation canal)
• (a) Super passage
• (b) Siphon super passage
• Type III (Drainage and canal intersection each other
of the same level)
• (a) Level crossing
• (b) Inlet and outlet

65. Selection of Type of Cross Drainage
Works
• Relative bed levels
• Availability of suitable foundation
• Economical consideration
• Discharge of the drainage
• Construction problems

66. Types of Cross Drainage Works
• Type-I Irrigation canal Passes over the
Drainage: This condition involves the
construction of following:
• 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.

67. Aqueduct

68. Aqueduct

69. Aqueduct

70. Siphon Aqueduct
• In a hydraulic structure where the canal is
taken over the drainage, but the drainage water
cannot pass clearly below the canal. It flows
under siphonic action. So, it is known as
siphon aqueduct. This structure is suitable
when the bed level of canal is below the
highest flood level.

71. Siphon Aqueduct

72. Siphon Aqueduct

73. Types of Cross Drainage Works
• Type-II Drainage Passes Over the irrigation
Canal.
• Super Passage
• The hydraulic structure in which the drainage
is taken over the irrigation canal is known as
super passage. The structure is suitable when
the bed level of drainage is above the full
supply level of the canal. The water of the
canal passes clearly below the drainage.

74. Super Passage

75. Super Passage

76. Siphon Super Passage
• 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.

77. Siphon Super Passage

78. Siphon Super Passage

79. Types of Cross Drainage Works
• Type III Drainage and Canal Intersect each
other at the same level.
• Level Crossings
• 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 (i) crest wall
(ii) Stream regulator (iii) Canal regulator.

80. Level Crossings

81. Level Crossing

82. Types of Cross Drainage Works
• 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.

83. Inlet and Outlet

84. Selection of Type of Cross Drainage
Work
• The following factors should be considered:
• (i) Relative Bed Level
• According to the relative bed levels of the canal and the river or
drainage, the type of cross drainage work are generally selected
which has been discussed earlier. But some problems may come at
the crossing point
• The following points should be remembered while
recommending the type of work,
• (a) The crossing should be at right angle to each other,
• (b) Well defined cross-section of the river or drainage should be
available.
• (c) At the crossing point the drainage should be straight for a
considerable length.
• (d) The width of the drainage should be narrow as far as possible.
• Considering the above points The C/s can be shifted to the
downstream or upstream.

85. Selection of Type of Cross Drainage
Work
Availability of Suitable Foundation
• For the construction of cross drainage works
suitable foundation is required. By boring
test, if suitable foundation is not
available, then the type of cross drainage work
should be selected to site Condition.

86. Selection of Type of Cross Drainage
Work
Economic Consideration
• The cost of construction of cross drainage
works should be justified with respect to the
project cost and overall benefits of the project.
So, the type of works should be selected
considering the economical point of view.

87. Selection of Type of Cross Drainage
Work
Discharge of the drainage
Practically the discharge of the drainage is very
uncertain in rainy season. So, the structure
should be carefully selected so that it may not be
destroyed due to unexpected heavy discharge of
the river or drainage.

88. Selection of Type of Cross Drainage
Work
Construction of Problems
• Different types of constructional problems may arise
at the site such as sub soil water, construction
materials, communication, availability of land etc. So
the type of works should be selected according to the
site condition.

89. Questions
• What do you understand by a fall in
canal? Why it is necessary?
• What are the functions of a canal head
regulator?
• Explain functions of cross regulator and
distributory head regulator.
• Write a S.N. on Types of Canal Falls

90. References
• Irrigation Engineering & Hydraulic Structures
– By Prof. Santosh Kumar Garg
– Khanna Publishers
• Internet Websites
• http://www.uap-bd.edu/
• Lecture Notes By: Dr. M. R. Kabir
• Professor and Head, Department of Civil Engineering
Department
• University of Asia Pacific (UAP), Dhaka

91. Thanks…