water bodies as well as across artificial
obstacles like railway line or roads.
• The main structures of a canal system for
conveyance of canal flow and control of water
levels are as follows -
1. Pipe conduits (or culverts) and inverted
syphons to carry flow under railways and
highways.
2. Aqueducts, syphon aqueducts, super-passage,
canal siphon or level crossings across natural
drainage courses or other depressions.
3. Transitions at changes in cross sections.
1. Structures for crossing canals
across roads and railway lines
• These are structural elements to convey canal water
under roads or railway lines. For small roads, carrying
relatively less traffic, the pipe conduit is sufficient. A
general view of the pipe conduit is shown –
Transitions at changes in
Cross-Sections
• A transition is a local change in cross section which
produces a variation of flow from one uniform state
to another due to changes in cross sections of the
channel.
• For a well designed transition, the optimum angle
between the channel centre-line and a line joining
the channel sides at the water line between the
beginning and the end of the transition is about 14
degrees. The mentioned angle should not exceed 27.5
degrees in any case to maintain streamlined flow.
• Following are the common types of transitions
Type 2
• Similar to type 1 but the outer slopes of the
earthen canal banks are replaced by retaining
walls which reduces the length of the culvert while
the inner slopes of the canal are retained as
earthen sections
Type 3
• The normal earthen banks of the canal are
replaced by a flumed trough of concrete or
masonry
• Recommended for large streams
Note that the classification of syphon aqueducts is
also exactly in similar terms
REGULATING STRUCTURES 
1. Canal Falls - to lower the water level of
the canal by controlling the bed grade
(control of bed grade)
2. Canal Escapes - to allow release of
excess water from the canal system
(control of discharge)
3. Cross & Head Regulators - to head up
water in the parent channel & to divert
some of it through an off take channel
(control of FSL)
1. Canal Falls
• A canal has a designed longitudinal slope
but has to pass through an undulating
terrain. When a canal crosses an area that
has a larger natural surface slope, a canal
drop, also called fall in India, has to be
provided suitably at certain intervals
Vertical Drop or Sarda-Type Fall
• Falls with impact type energy dissipators
• Raised crest to head up water on the
upstream
• Water falls with an impact in a pool of
water on a depressed floor acting like a
cushion to dissipate excess energy of the
fall.
• It was first tried in Sarda Canal in UP.
APPURTENANT STRUCTURES
REQUIRED FOR SARDA & GLACIS FALL
• The floor of the fall should be able to
resist the uplift pressure
• Cut Off walls to be provided at upstream
and downstream ends of the floor
• Side protection at the upstream & the
downstream with brick pitching
• Bed protection with dry brick pitching just
upstream and downstream of the fall
Canal regulators
• These include the cross regulator (in the
parent canal) and the head regulator
(in the off-take canal) for controlling
the flow through a parent canal
• They also help to maintain the water level
in the canal on the upstream of the
regulator.
DEVICES--
Canal Outlets or Modules
• Structures at the head of a water course or field
channel.
• Supply canal (distributary) is under the control of an
irrigation authority under the State government.
• An outlet is a link connecting the government owned
distributary and the cultivator owned field channel
• It should satisfy the needs of both the groups.
• Since equitable distribution of the canal supplies is
dependent on the outlets, it must not only pass a
known and constant quantity of water, but must also
be able to measure the released water satisfactorily.
Outlet design should be easy & reliable
• Outlet should be robust enough such that it is
not easily tampered with.
• The cost of an outlet structure should be low
• It should work efficiently with a small working
head (reason - since a larger working head
would require higher water level in the
parent channel resulting in high cost of the
distribution system)
TYPES OF OUTLETS/MODULES
(a) Non-modular outlets
• These outlets operate in such a way that the flow
passing through them is a function of the difference in
water levels of the distributing channel and the
watercourse. Hence, a variation in either affects the
discharge.
• Ex – Submerged Pipe Outlet, Open Sluice Outlet
(b) Semi-modular outlets
• The discharge through these outlets depend on the
water level of the distributing channel but is
independent of the water level in the watercourse so
long as the working head required for their working
is available.
The discharge through such outlet will therefore
depend on the water level in the distributary.
Ex – Kennedy’s Gauge Module or Venturi Flume,
Crump’s Adjustable Proportional Module(APM),
Open Flume Outlet, Orifice semi-module outlet
Rigid Modules/Modular outlets
• The discharge through modular outlets is
independent of the water levels in the
distributing channel and the watercourse,
within reasonable working limits. This type of
outlets may or may not be equipped with
moving parts.
• Though modular outlets, like the Gibb’s module,
Khanna’s Module, Foote’s Module have been
designed and implemented earlier, they are not
very common in the present Indian irrigation
engineering scenario.
Criteria for Judging the
Performance of Modules
• Flexibility – It is the ratio of rate of change of
discharge of the outlet to the rate of change of
discharge of the distributary channel.
• If flexibility equals unity, the rate of change of
discharge of outlet equals the rate of change of
discharge of distributary. Such an outlet is said
to be Proportional Outlet.
• For hyper proportional outlet, F > 1
• For sub proportional outlet, F < 1
• The ratio of head on the outlet (h) to the full
supply depth of distributary (y) is known as
Setti
of change of discharge through an outlet to
the rate of change of water level of the
distributary is called as Sensitivity.
• For rigid/non-flexible modules, the discharge
is fixed and thus flexibility & sensitivity is
zero.
• Modular Limit – The modular limits are
the extreme values of any one or more
variables beyond which an outlet becomes
incapable of acting as a module or semi-
module.
The range between the extreme values of
various such factors is known as modular
range.
EMITTERS IN IRRIGATION
• In drip irrigation, emitter devices are used
• Kind of an outlet
• Should be inexpensive & compact
• Should not promote clogging
• Placed at a design spacing in the pipes
• Able to deliver light & frequent application of water
Long Path Emitter -
Flow occurs in a long flow path section.
Ensures laminar flow
Very sensitive to pressure differences in the system
Orifice Emitter -
Flow through these emitters is turbulent
Water flows through a small opening/orifice
53
Spray Emitter -
Releases water with a lot of energy beneath the
surface
Converts in the form of spray
More area is covered due to rotation
For comparatively coarser textured soil
Short path Emitter -
Behave like orifice emitters
A characteristic short tube section
Compensating Emitter -
Provides a constant discharge over a wide range of
pressure
Many short and long path emitters are available in
compensating types.
METERING FLUMES/METERS
• A structure constructed on the canal/channel for
measuring discharge
• There is excessive loss of head due to such
constructions. Hence, not used nowadays.
Types of Meter Flumes
1. VENTURI FLUME
• Open channel counterpart of venturimeter
• Gradually contracting portion, a throat & a
gradually expanding portion
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