Classification of Canals

1. 08. Classification of Canals
B.Sc. Civil Engineering 8th Semester
Muhammad Ajmal (PhD)
Lecturer
Agri. Engg. Deptt.
CE-402 Irrigation Engineering
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2. Classification of Canals
 Canal
❖ It is an artificial cross secrtion constructed on the ground to carry water to the
field either from a reservoir, tank or river.
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3. Types of Canals
(BASED ON SOURCE OF SUPPLY)
Permanent or Perennial
Canal
Non-Perennial Canal
Inundation Canal
Those canals which get continuous supplies by
permanent source of supply like a river or reservoir are
called as permanent canals or perennial canals. These
irrigate the field throughout the year with equitable rate
of flow.
These are the canals which irrigate the field for only
one part of the year usually during summer season or at
the beginning and end of winter season, called as non-
perennial canals. These canals take-off from rivers
which do not have assured supply throughout the year.
Draws its supplies from a river only during the high stages of
the river. No regulator is provided at the head of such canal.
This draws lot of quantity of silt which is really beneficial for
the crops.
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4. Types of Canals
(BASED ON FUNCTION)
• Carries water from its source to agricultural fields.
Irrigation Canal
• Used for transport of goods. Sometimes these are also
used for irrigation purposes.
Navigation Canal
• Used to carry water for generation of hydroelectricity.
Power Canal
• Feeds two or more canals.
Feeder Canal
Note: A canal can serve more than one purpose 4

5. Types of Canals
(BASED ON ALIGNMENT)
Watershed Canal or Ridge Canal
Contour Canal
Side Slope Canal
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6. Watershed canal or Ridge canal
Fig. Canal Alignment
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7. Watershed canal or Ridge canal
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8. Watershed canal or Ridge canal (Contd.)
➢ 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.
➢ Thus between two major streams, there is the main watershed (ridge line), which
divides the drainage area of the two streams.
➢ Since the drainage flows away from the ridge, no drainage can cross a canal aligned on
the ridge. Thus, a canal aligned on the watershed saves the cost of construction of cross-
drainage works.
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9. Contour Canal
 A contour canal is an artificially-dug
navigable canal which closely follows the
contour line of the land it traverses in order
to avoid costly engineering works such as
boring a tunnel through higher ground,
building an embankment over lower
ground, or constructing a canal lock (or
series of locks) to change the level.
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10. Contour Canal
➢ Watershed canal along the ridge line are not found economical in hill areas where the
river flows in the valley well below the watershed.
➢ In fact, the ridge line (watershed) may be hundred of meters above the river. It therefore
becomes virtually impossible to take the canal on top of such a higher ridge line.
➢ In such conditions, contour canals are usually constructed.
➢ A contour canal irrigates only on one side because the area on the other side is higher.
➢ As the drainage flow is always at right angles to the ground contour. Such a channel
would definitely have to cross natural drains and streams, necessitating construction of
cross drainage structures.
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11. Side Slope Canal
 A side slope canal is that which is aligned at
right angles to the contours; i.e. along the
side slopes.
 Since such a canal runs parallel to the
natural drainage flow, it usually does not
intercept drainage channels, thus avoiding the
construction of cross-drainage structures.
 It is a canal which is aligned roughly at right
angle to contours of the country but not on
watershed or valley.
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12. Types of Canals
(BASED ON DISCHARGE)
Main Canal
Branch Canal
Major Distributary
Minor Distributary
Water Course
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Source: Lecture Notes
Prof. Dr. M. R. Kabir

13. Types of Canals
(Based on lining provided or not)
• Bed and banks made up of natural soil.
• Water velocities higher than 0.7 m/s are not tolerable.
• High seepage and conveyance water losses.
• Profuse growth of aquatic weeds retards the flow
Unlined
Canal
• Lining of impervious material on its bed and banks to
prevent the seepage of water.
• Different types of lining used e.g. concrete, brick or
burnt clay tile, boulder, etc.
Lined
Canal
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14. AN UNLINED CANAL
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15. A LINED CANAL
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16. Types of Canals
(Based on Financial output)
• Those canals which yield a net revenue to the nation
after full development of irrigation in the area.
• Profuse growth of aquatic weeds retards the flow
Productive
canals
• Those canals which apply water to a low income
community for irrigation purposes to protect community
from famine.
Protective
canals
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17. Types of Irrigation Canals
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 In irrigation canal design two important factors has to be counted (i) quantity of silt carried by canal
and (ii) type of boundary of canal. There are three types of channel based on factors. They are (a)
Alluvial (b) Non-alluvial and (c) Rigid Boundary or Lined
(a) Alluvial channels: are those which are excavated in alluvial soil, and carry sufficient silt in water.
The boundary of such canal is of silt known as alluvium. The silt content in canal depend on the
velocity of flow. At high velocity more silt scouring at bottom of canal occurs, while at low velocity
minimum silt deposition occurs. To design a channel in such area a non silting nor scouring velocity
has to be adopted.
(b) Non alluvial channels: These channel are excavated in non alluvial soil like, rock, loam or clay.
Such channels usually have no silting problem as water flow with non silting velocity
(c) Rigid Boundary channels: Those channels which have sides and bottom of rigid materials. Lined
channels are rigid boundary channels.

18. Cross Section of Irrigation Canal
 This section is partly in cutting and partly in filling and aims in balancing the quantity of
earth work in excavation with that in filling.
 When the NSL is above the top of the bank, the entire canal section will have to be in
cutting, and it shall be called ‘canal in cutting’.
 Similarly, when the NSL is lower than the bed level of the canal, the entire canal section
will have to be built in filling, and it is called ‘canal in filling’.
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FSL= Full Supply Level
NSL=Natural Surface Level

19. Components of Cross- Section
 Side slope
 Berm
 Freeboard
 Bank
 Service road
 Back Berm or Counter Berm
 Spoil Bank
 Borrow Pit
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20. 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.
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Sr. No. Type of Soil Slope in Cutting Slope in Filling
1 Clayey Soil 1.5 : 1 2 : 1
2 Sandy Soil 3 : 1 4 : 1
3 Loamy Soil 1.5 : 1 2 : 1
4 Gravel Soil 0.75 : 1 1.25 : 1
5 Hard Rock 0.25 : 1 ----
6 Soft Rock 0.5 : 1 ----

21. Berm
 Berm is the horizontal distance left at ground level between the toe of the bank and the
top edge of cutting.
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 Purposes of Berms
❖ They give additional strength to the banks and provide protection against erosion and breaches.
❖ They provide a scope for future widening of the canal.

22. Freeboard
❖ The margin between FSL and bank level is known as freeboard.
❖ The amount of freeboard depends upon the discharge of the channel.
❖ Recommended minimum freeboard = 0.5 m
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23. Bank
 The primary purpose of banks is to retain water.
 This can be used as means of communication and as inspection paths.
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24. Service Road
 These are provided on canals for inspection purposes, and may simultaneously serve
as the means of communication in remote areas.
Dowla: As a measure of safety in driving, dowlas with side slopes of 1.5: 1 to 2:1, are provided
along the banks.
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25. Back Berm or Counter Berm
 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.
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26. Spoil Bank
 When the earthwork in excavation exceeds earthworks in filling, the extra earth has to be
disposed of economically.
 Economical mode of its disposal may be collecting this soil on the edge of the bank
embankment itself.
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27. Borrow Pit
 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.
 If such pits are excavated outside the channel, they are known as external borrow pits, and if
they are excavated somewhere within the channel, they are known as internal borrow pits.
 Internal borrow pits are more preferred than external one.
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 The inside borrow pit may be located at the center 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.

28. Balancing Depth
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 A canal section will be economical when earth work involved at a particular section has an
equal amount of cut and fill. Usually a canal section has a part in cutting and part in filling as
shown in fig.
 If the amount of cut is equal to the amount of fill, it has to be paid for once only.
Definition
 For a given C/S there is always only one depth of cutting for which the cutting and filling
will be equal. The depth is known as balancing depth.

29. If h = vertical height of top of bank
from the bed of canal.
b = bed width of the channel.
t = top width of the canal bank.
n:1 = side slope of bank in filling.
z:1 = side slope of canal in cutting.
d = full supply depth of canal.
y = depth of cutting.
Area of the cut = by + zy2 = y(b + zy)
Area of fill = 2[(h – y)t + n(h-y)2]
Balancing Depth
Equating the area of cut and fill:
y(b + z y) = 2[(h – y)t + n(h-y)2 ]
b y+ zy2 = 2th + 2nh2 – 2nhy – 2ty – 2nhy + 2ny2
y2 (2n – z) – (b + 4nh + 2t)y + 2h(t + nh) =0
From this equation the balancing depth of the canal
may be determined.
A canal is usually constructed with side slope of 1:1 in
cutting and a slope 1.5:1 in filling.
Putting n = 1.5 and z =1 in above equation.
We get;
y2 – (b/2 + 3h + t)y + h (t + 3/2 h)=0

30. Example
 Calculate the balancing depth for a channel section having a bed width equal to 18 m and side
slopes of 1:1 in cutting and 2:1 in filling. The bank embankments are kept 3.0 m higher than the
ground level (berm level) and crest width of banks is kept as 2.0 m.
Solution: Let d be the balancing depth, i.e. the depth for which excavation and filling becomes
equal.
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31. Example (Contd.)
Area of cutting = (18 + d) d m2
Area of filling = 2(2+14)/2×3 = 48 m2
Equating cutting and filling, we get
(18 + d) d = 48
or, d2 + 18d – 48 = 0
or, d = 2.35 m (neglecting –ve sign), Balancing depth = 2.35 m
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32. Canal Lining and its Advantages
➢ It is the treatment given to the canal bed and banks to make the canal section impervious.
➢ Water Conservation: Lining a canal results in reduction in water losses, as water losses in
unlined irrigation canals can be high.
➢ No seepage of water into adjacent land or roads: If canal banks are highly permeable, the
seepage of water will cause very wet or waterlogged conditions, or even standing water on
adjacent fields or roads. Lining of such a canal can solve this problem.
➢ Reduced canal dimensions: The resistance to flow of a lined canal is less than that of an
unlined canal, and thus the flow velocity will be higher in the lined canal . Therefore, with the
higher velocity, the canal cross-section for a lined canal can be smaller than that of an unlined
canal.
➢ Reduced maintenance: Maintenance costs for the following issues are eliminated using lining
of canals.
❖ Periodical removal of silt deposited on the beds and sides of canals.
❖ Removal of weeds and water canals.
❖ Minor repairs like plugging of cracks, uneven settlements of banks, etc. 32

33. Types of lining
Hard Surface Lining
Cast Insitu Cement
Concrete Lining
Shotcrete or Plastic
Lining
Cement Concrete Tile
Lining or Brick Lining
Asphaltic Concrete
Lining
Boulder Lining
Earth Type Lining
Compacted Earth
Lining
Soil Cement Lining
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34. Cast In-situ Cement Concrete Lining

35. Shotcrete & Plastic Lining

36. Canal Lining
CONCRETE LINING

37. Canal Lining
Concrete tiles canal lining

38. Canal Lining
Brick canal lining
PREFABRICATED CHANNEL
SECTION

39. Disadvantages
 Higher initial investment
 Repair is costly
 Shifting of outlet is costly because it involve dismantling and relaying of lining.
 Longer construction period
 Sophisticated construction equipment and labor is needed.

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