The document discusses the design and function of canal falls, which are irrigation structures used to lower water levels in canals and manage energy from falling water. It highlights various types of falls, considerations for their placement, and the balance between the number and size of falls for economic efficiency. Additionally, it includes design calculations and specifications for a Sarda type fall for a specific discharge scenario.

1. Canal Falls & Types of Falls
Cistern Design for Simple Vertical
Drop Fall
Design of Sarda Type Fall
Design of a Straight Glacis Fall
Alignment of the off-taking Canal
Cross Regulator
Canal Head Regulator
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PREPARED BY KHOKHANI VIDHI H.
ASSISTANT PROFESSOR, DIET

2. A canal fall is an irrigation
structure constructed across a
canal to lower down its Water level
and destroy the surplus energy
liberated from the falling water
which may othervise scour the bed
and banks of the canal.
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ASSISTANT PROFESSOR, DIET

3. The canal falls are required when the
natural slope of the ground along the
canal alignment is steeper than the bed
slope of the canal.
The canal bed slope may vary from 1 in
4000 for a discharge of about 1.5 cumecs
to about 1 in 8000 for a discharge of 5000
cumecs.
The average ground slope is about 1 in 200
to 1 in 50.
The difference of the slopes is adjusted by
providing vertical falls in the bed of the
canal at suitable intervals.
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ASSISTANT PROFESSOR, DIET

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ASSISTANT PROFESSOR, DIET

5. As far as possible the canal should be
kept in the balanced depth of cutting.
If the fall is not provided, the canal
would go in excessive filling, which is
not desirable from the consideration
of the economy of earthwork and the
maintenance of the canal.
For a canal irrigating the area
directly, a fall may be provided at a
location where the F.S.L. of the canal
outstrips the ground level but before
the bed of the can comes into filling.
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ASSISTANT PROFESSOR, DIET

6. The site for the fall in the case of
distributaries from which direct
irrigation done, is usually decided in
such a way that the command is not
sacrificed the process of lowering of
the water level. After the fall, the
F.S.L. of the canal may be below the
ground level for to kilometer.
The location of a fall may also be
decided from the consideration of the
possibility, of combining it with a
cross regulator or a road bridge to
effect economy and to have better
regulation.
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ASSISTANT PROFESSOR, DIET

7. A relative economy of providing a
large number of small falls or small
number of large falls should also be
worked out. The provision of small
number of big falls results in
unbalanced earthwork, but there is
always some saving in the cost of
the fall structure.
Sometimes it may be necessary to
provide fewer falls of large drops to
enable hydropower generation at
these falls.
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ASSISTANT PROFESSOR, DIET

8. The various types of falls are :
1. Ogee fall
2. Rapid fall
3. Stepped fall
4. Notch fall
5. Vertical drop fall
6. Glacis fall
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ASSISTANT PROFESSOR, DIET

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15

16. u/s pile depth
u/s floor length
Top width of fall
Bottom width of fall
Height of fall
Length of cistern
Depth of cistern
Thickness of floor
d/s floor length
Depth of intermediate and d/s pile
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ASSISTANT PROFESSOR, DIET

17. Design a 1.5 m Sarda type fall
for a canal having a discharge
of 12 cumecs with the following
data :
Bed level of u/s - 103.0 m
Side slopes of channel- 1 : 1
Bed level of d/s - 101.5 m
Full supply level u/s - 104.5 m
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ASSISTANT PROFESSOR, DIET

18. Bed width u/s and d/s - 10.0 m
Assume Bligh's coefficient - 6
Use Bligh's creep theory.
Soil - Good loam
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ASSISTANT PROFESSOR, DIET

19. Rectangle
Q< 14
cumec
Trepezoidal
Q>14
cumec
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ASSISTANT PROFESSOR, DIET

20. Top
width
Bottom
width
Height
of fall
CISTERN LENGTH
HEIGHT OF
CISTERN
Head over crest
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ASSISTANT PROFESSOR, DIET

21. Rectangle
Q< 14
cumec
Trepezoidal
Q>14
cumec
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22. As the discharge Q = 12 cumecs < 14
cumecs, a rectangular crest wall is
provided.
1. Length of crest = d/s bed width
L = 10 m
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ASSISTANT PROFESSOR, DIET

23. Assume, crest width (B) = 0.8 m
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25. D1
HEAD
U/S FSL
D/S FSL
D/S TEL
U/S TEL
V2 /2g
DEPTH OF
FALL (d)
CREST
OF
FALL
E
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ASSISTANT PROFESSOR, DIET

26. Height of crest above d/s bed,
d = crest level - d/s bed level
R.L. of the crest = u/s FSL – H
OR
R.L. of crest = u/s TEL - E
u/s TEL = u/s FSL + velocity head
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ASSISTANT PROFESSOR, DIET

27. depth of water = 104.5 - 103.0 = 1.5 m
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28. in this case H = E
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30. For masonry, G = 2
h = H - H0 = 0.755 – 0.025 = 0.73 m
The top of the crest wall shall be capped
with 20 cm thick 1 : 2 : 4 concrete.
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ASSISTANT PROFESSOR, DIET

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32. 1.5 M
0.85 M
D = 2.25 m
5.5. m
0.3 m
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ASSISTANT PROFESSOR, DIET
101.5
101.2
103.77