CANAL IRRIGATION

PRESENTED BY Er. Brijlata

Sharma
Assistant professor
JECRC,Jaipur
 DEFINITION
An artificial channel filled with water and designed
for navigation , or irrigating land, etc.
An artificial water course or extensively modified
natural channel used for inland water transport
and/or the control and diversion of water for
drainage or irrigation
 TYPES OF CANAL
(BASED ON USE)

 There are two types of canals:

Aqueduct: water supply canals that are used for the
conveyance and delivery of portable for human
consumption, municipal uses , and agriculture
irrigation
Water ways : navigable transportation canals used
for carrying ships and boats shipping goods and
conveying people.
 TYPES OF CANALS
(BASED ON DISCHARGES)

MAIN CANAL
BRANCH CANAL
MAJOR DISTRIBUTORY CANAL
MINOR DISTRIBUTORY CANAL
WATER COURSE OR FIELD CHANNEL
 MAIN CANALS
Main canal takes of directly from the
upstream side of weir head works or dam.

Usually no direct cultivation is proposed.

 BRANCH CANAL
All off takes from main canal with head discharge of
14-15 cumecs and above are termed as branch
canals.

Acts as feeder channel for major distributaries.

 MAJOR DISTRIDUTARY:
 All off takes from main canal or branch canal with head
discharge from 0.028 to 15 cumecs are termed as major
distributaries .
 MINOR DISTRIBUTARY:
 All off takes taking off from a measure distributary carrying
discharge less than 0.25 cumec are termed as minor
distributaries.
 WATER COURSE
 Small channels which carry water from the outlets of a major
or minor distributary or a branch channel to the fields to be
irrigated.
 TYPES OF CANALS
(Based on lining being provided or not)
1.Lined canals

2. Unlined canals
SHAPES OF CANAL

1. CIRCULAR SHAPE
2. TRIANGULAR SHAPE
3. TRIPEZOIDAL SHAPE
4. PARABOLIC SHAPE
5. RECTANGULAR SHAPE
 LINED CANAL
A Lined canals is provided with a lining of
imprevious material on its bed and banks to
prevent the seepage of water.
 Types of canal lining
1. Concrete lining
2. Short crete lining
3. Brick or burnt clay tile lining
4. Boulder lining
 Unlined canal
An unlined canal is the one which as it bed
and banks made of natural soil through which
it is constructed and not provided with a lining
of imprevious material.
 Disadvantages of unlined canal
• Water velocities higher then 0.7m/sec or not tolerable
because of erosion . The low operating velocities requires
large cross-section area.
• High seepage and conveyance water losses result in water
logging of adjacent land.
• Danger of canal bank breakage caused by overtopping ,
erosion and animal burrowing.
• Profuse growth of aquatic weeds retards the flow and causes
heavy maintenances cost.
 ILL-EFFECT OF WATER LOGGING
• Water seeping from canal down to the soil below may , head
times , raise the ground water very close to the ground level .
• This may result in blocking all the voids in the soil and
obstructing the plant roots to breathe.
• Normal cultivation operations , such as tilling , ploughing, etc.
cannot be easily carried out in wet soils.
 Irrigation canal layout
• As for a possible, curves should be avoided in the alignment
of canals.
• The curves lead to disturbance of flow and a tendency to silt
on the inner bend and scour the toe of the outer bend.
• If curves have to be provided ;they should be as gentle as
possible.
• The permissible minimum radius of curvature for a channel
curve is shorter for lined canals than unlined ones
• The alignment should be such that the cutting and filling of
earth rock should be balanced , as far as possible.
 TYPES OF DRAINAGE SYSTEM
 Surface drainage
These constitute open ditches , field drains,
proper land grading and related structures.
Land grading , or properly sloping the land
towards the field drains, is an important
method for effecting surface drainage.
 TYPES OF DRAINAGE SYSTEM
 Sub surface drainage
These are installed to lower the water table
Consist of underground pipes which collect
water and remove it through a network of
such pipes.
UNLINED CANAL DESIGN
 Canal Design Types
Canal Design

Drainage Irrigation
Channel Channel
Design Design
 Design Parameters
 The design considerations naturally vary
according to the type of soil.
 Velocity of flow in the canal should be critical.
 Design of canals which are known as
‘Kennedy’s theory’ and ‘Lacey’s theory’ are
based on the characteristics of sediment load
(i.e. silt) in canal water
 Important Terms Related to Canal
Design
Alluvial soil
Non-alluvial soil
Silt factor
Co-efficient of rugosity
Mean velocity
Critical velocity
Critical velocity ratio (C.V.R.), m
Regime channel
Hydraulic mean depth (R)
Full supply Level
Economical section
 Alluvial Soil
The soil which is formed by the continuous deposition of
silt is known as alluvial soil. The river carries heavy
charge of silt in rainy season. When the river overflows
its banks during the flood, the silt particles get
deposited on the adjoining areas. This deposition of silt
continues year after year. This type of soil is found in
deltaic region of a river. This soil is permeable and soft
and very fertile. The river passing through this type of
soil has a tendency to change its course.
 Non-alluvial Soil

The soil which is formed by the disintegration of

rock formations is known as non-alluvial soil. It
is found in the mountainous region of a river.
The soil is hard and impermeable in nature. This
is not fertile. The river passing through this type
of soil has no tendency to change its course.
Silt Factor
During the investigations works in various canals in alluvial
soil, Gerald Lacey established the effect of silt on the
determination of discharge and the canal section. So, Lacey
introduced a factor which is known as ‘silt factor’.
It depends on the mean particle size of silt. It is denoted by ‘f’. The
silt factor is determined by the expression,

f = 1.76 dmm
where dmm = mean particle size of silt inmm

Particle Particle size (in mm) Silt factor

Very fine Silt 0.05 0.40
Fine Silt 0.12 0.60
Medium Silt 0.23 0.85
Coarse Silt 0.32 1.00
Coefficient of Rugosity (n)
The roughness of the canal bed affects the velocity of
flow. The roughness is caused due to the ripples formed
on the bed of the canal. So, a coefficient was
introduced by R.G Kennedy for calculating the mean
velocity of flow. This coefficient is known as coefficient
of rugosity and it is denoted by ‘n’. The value of ‘n’
depends on the type of bed materials of the canal.
Materials Value of n
Earth 0.0225
Masonry 0.02
Concrete 0.13 to 0.018
Mean Velocity
It is found by observations that the velocity at a depth
0.6D represents the mean velocity (V), where ‘D’ is
the depth of water in the canal or river.
Mean Depth

D
0.6 D

(a) Mean Velocity By Chezy’s Expression:

V= C√RS
(b) Mean Velocity By Manning’s Expression:
V=(1/n)x(R^⅔)x(S^ ⅟₂)
 Critical Velocity
When the velocity of flow is such that there is no
silting or scouring action in the canal bed, then that
velocity is known as critical velocity. It is denoted by
‘Vo’. The value of Vo was given by Kennedy according to
the following expression,
Vo = 0.546 D0.64
; where, D = Depth of water

D
 Critical Velocity Ratio
(C.V.R.)
The ratio of mean velocity ‘V’ to the critical velocity ‘V₀’
is known as critical velocity ratio (C.V.R.). It is denoted
by ‘m’ i.e.
C.V.R. (m)=V/V₀
When m = 1, there will be no silting or scouring
When m > 1, scouring will occur
When m < 1, silting will occur

So , by finding the value of m, the condition of the canal

can be predicted whether it will have silting or scouring
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.
Hydraulic Mean Depth
The ratio of the cross-sectional area of flow to
the wetted perimeter of the channel is known
as hydraulic mean depth. It is generally denoted
by R.
R = A/P
Where,
A = Cross-sectional area
P = Wetted perimeter
 Full Supply Level
The maximum capacity of the canal for which it is
designed, is known as full supply discharge. The
water level of the canal corresponding to the full
supply discharge is known as full supply level
(F.S.L).
FSL
 Economical Section
If a canal section is such that the earth obtained from cutting (i.e.
excavation) can be fully utilized in forming the banks, then that
section is known as economical section. Again, the discharge will be
maximum with minimum cross-section area. Here, no extra earth is
required from borrow pit and no earth is in excess to form the spoil
bank. This condition can only arise in case of partial cutting and
partial banking. Sometimes, this condition is designated as
balancing of cutting and banking. Here, the depth of cutting is
called balancing depth.
Filling Area

Cutting Area Balancing depth

 Unlined Canal Design on Alluvial soil by
Kennedy’s Theory
After long investigations, R.G Kennedy arrived at a theory which states
that, the silt carried by flowing water in a channel is kept in suspension
by the vertical component of eddy current which is formed over the
entire bed width of the channel and the suspended silt rises up gently
towards the surface.
The following assumptions are made in support of his theory:
 The eddy current is developed due to the roughness of the bed.
 The quality of the suspended silt is proportional to bed width.
 It is applicable to those channels which are flowing through
the bed consisting of sandy silt or same grade of silt.
 It is applicable to those channels which are flowing through the
bed consisting of sandy silt or same grade of silt.
 He established the idea of critical velocity ‘Vo’ which will make a
channel free from silting or scouring. From, long observations, he
established a relation between the critical velocity and the full
supply depth as follows,
Vo = CDn
The values of C and n where found out as 0.546 and 0.64
respectively, thus Vo = 0.546 D0.64

Again, he realized that the critical velocity was affected by the grade
of silt. So, he introduced another factor (m) which is known as critical
velocity ratio (C.V.R).
Vo = 0.546mD0.64
 Drawbacks of Kennedy’s
Theory
The theory is limited to average regime channel only.
The design of channel is based on the trialand error method.
The value of m was fixedarbitrarily.
 Silt charge and silt grade are not considered.
 There is no equation for determining the bed slope and it
depends on Kutter’s equation only.
The ratio of ‘B’ to ‘D’ has no significance in his theory.
 Design Procedure
 Critical Velocity, Vo = 0.546 D0.64
 Mean Velocity

 B/D ratio is assumed accordingly

 Discharge, Q = A V
Where, A = Cross-section area in m2,
V = mean velocity in m/sec
 The full supply depth is fixed by trial to satisfy the value of ‘m’.
Generally, the trial depth is assumed between 1 m to 2 m. If the
condition is not satisfied within this limit, then it may be assumed
accordingly.
Unlined Canal Design on Alluvial soil by
Lacey’s Theory
Lacey’s theory is based on the concept of regime condition of
the channel. The regime condition will be satisfied if,
The channel flows uniformly in unlimited incoherent
alluvium of the same character which is transported by the
channel.
The silt grade and silt charge remains constant.
The discharge remains constant.
But in practice, all these conditions can never be satisfied.
And, therefore artificial channels can never be in ‘True
regime’.
 Initial Regime and Final Regime
When only the bed slope of a channel varies due to
dropping of silt , and its cross-section or wetted perimeter
remains unaffected, even them the channel can exhibit
‘no silting no scouring’ properties, called INITIAL REGIME.

IF there is no resistance from the sides, and all the

variables such as perimeter, depth, slope etc. are equally
free to vary and get adjusted according to discharge and
silt grade, then the channel is said to have achieved
permanent stability, called FINAL REGIME.
 Design Procedure
 Calculate the velocity from equation

Where, Q is discharge in cumecs,

V is velocity in m/s
f is silt factor
 Workout the hydraulic mean depth (R) from the equation

 Compute area(A) of channel section by using

 Compute the wetted perimeter, P

Knowing these values, the channel section is known; and finally

the bed slope (S) is determined by the equation

 B/D ratio of channel is assumed accordingly.

 Drawbacks of Lacey’s Theory
 The conceptof true regime is theoretical and con not be
achieved practically.

 The various equations are derived by considering the silt factor f

which is not at all constant.
 The concentration of silt is not taken into account.
 Silt grade and silt charge is not taken intoaccount.
 The equations are empirical and based on the available data from a
particular type of channel. So, it may not be true for a different
type of channel.
 The characteristics of regime channel may not be same for allcases.
Comparison of Kutter’s & Lacey’s Theory
Kennedy’s Theory Lacey’s Theory
It states that the silt carried by the It states that the silt carried by the
flowing water is kept in suspension by flowing water is kept in suspension
the vertical component of eddies by the vertical
which are generated from the bed of component of eddies which are
the channel. generated from the entire wetted
perimeter of thechannel.
It gives relation between ‘V’ and ‘D’. It gives relation between ‘V’ and ‘R’.
In this theory, a factor known as critical In this theory, a factor known as silt
velocity ratio ‘m’ is introduced to make factor ‘f ’ is introduced to make the
the equation applicable to different equation applicable to different
channels with different silt grades channels with different silt grades.

In this theory, Kutter’s equation is This theory gives an equation for

used for finding the meanvelocity. finding the meanvelocity.
This theory gives no equation for bed This theory gives an equation for
slope. bed slope.
In this theory, the design is based on This theory does not involve trial
trial and errormethod. anderror method.
 conclusions
 Explicit design equation and sections shape co
efficient have been present for the minimum cost
design of lined canal of triangular, rectangular
trapezoidal& circular shapes .
 These equation &co efficient have been
obtained by applying the nonlinear optimization
technique