Canal headworks are hydraulic structures constructed across rivers to divert water into canals. They raise the river water level and regulate flows. There are two main types - diversion and storage headworks. Diversion headworks like weirs and barrages divert water without storage, while dams form storage reservoirs. Key components include weirs/barrages, divide walls, fish ladders, under sluices, silt excluders, and head regulators. Location depends on river characteristics, and sites must be accessible with suitable foundations. Failure can occur through subsurface piping/uplift or surface scouring during floods. Precautions include reducing exit gradients, providing sheet piles, ensuring floor thickness, using filters and energy

1. CANAL HEADWORKS
PRESENTED BY:
KHLAINBORLANG MALNGIANG(B14CE013)
ATUL HAJONG (B14CE014)
ABISHEK KUMAR (B14CE016)
SHATRUGHAN SHIRA(B14CE017)
NEERAJ KUMAR YADAV(B14CE019)

2. CANAL HEADWORKS
–Any Hydraulic Structures/works constructed across river
and supplies water to the off taking canal is called canal
headwork.
Canal head works
Diversion headworks
Weir or barrage is constructed
across a perennial river to raise
water level and divert the
required quantity.
Storage head works
Dam is constructed across a
river valley to form storage
reservoir divert the required
quantity.

4. TYPES OF HEADWORKS
Fig1: DIVERSION HEADWORK Fig 2: STORAGE HEADWORK

5. CANAL HEADWORKS
 Purposes:
– Raises water level in the river
– Regulates supply of water into the canal
– Controls the entry of silt into the canal
– Provides some storage for a short period
– Reduces the fluctuations in the level of supply in river

6. TYPES OF DIVERSION HEAD WORKS
 1. Temporary diversion head works
– Consists of a bund constructed across river to raise the
water level in the river and will be damaged by floods.
 2. Permanent diversion head works
– Consists of a permanent structure such as a weir or
barrage constructed across river to raise water level in
the river.

8. LOCATION OF CANAL HEAD WORKS
 Depends on the stages of flow (reaches) of river
 (i) Rocky stage
 (ii) Boulder stage
 (iii) Trough stage or alluvial stage
 (iv) Delta stage
 Both rocky and delta stages are not suitable for
location of diversion head works

9. ROCKY STAGE
In this stage river is in the hills. The bed slope and velocities are high. It is generally
not suitable for the location of a diversion headworks.
Advantages:
• A sound rocky foundation is usually available at the site.
• Due to high velocities of flow no silting problem.
• High heads are available for hydroelectric work.
Disadvantages:
• The land in the hilly area is not suitable for agriculture.
• The discharge in the river is low because of small catchment.

10. BOULDER STAGE
In this stage the bed and banks of the river are composed of boulders and gravels.
Advantages:
• Length of weir is generally shorter in boulder stage.
• Construction materials such as stone, aggregates, sand, gravel are locally available.
Disadvantages:
• Seepage losses are high.
• Demand of irrigation water is low because the land is not fertile.

11. TROUGH OR ALLUVIAL STAGE
In this stage the cross section of river is made up of alluvial sand and silt. The bed
slope and velocity are small.
Advantages:
• Demand of irrigation water is high.
• Seepage losses are less in the canal.
• The water contains silt which has manurial value.
Disadvantages:
• Construction material is usually not available locally.
• Cost of headworks is usually more due to poor foundation.
• Problem of silt in the canal.

12. DELTA STAGE
The river passese on to the delta stage as it approaches the ocean.
The bed slope and velocities are reduce so much that it is unable to carry its
sediments load.
It drops down the sediments and gets divided into channels on either sides of the
deposit resulting in the formation of a delta.
Not Suitable for location of a diversion headworks because the river section is
excessively wide.

14. SITE SELECTION FOR DIVERSION HEAD WORK
• River section at the site should be narrow and well-defined.
• Should have a large commanded area.
• Site should be such that the weir (or barrage) can be aligned at right angles to the
direction of flow in the river.
• Good foundation should be available at the site.
• Site should be easily accessible by road or rail.
• Overall cost of the project should be a minimum.

15. COMPONENTS OF DIVERSION HEADWORKS

16.  1. Weir or Barrage
 2. Divide wall or divide groyne
 3. Fish ladder
 4. Pocket or approach channel
 5. Under sluices or scouring sluices
 6. Silt excluder
 7. canal head regulator
 8. River training works such as marginal bunds
and guide bunds
COMPONENTS OF DIVERSION HEADWORKS

17. WEIR OR BARRAGE
Weir is a structure constructed across river to raise the
water level and divert the water into the canal .Weir
aligned at right angle to the direction flow. Shutters are
provided at the crest of the weir so that part of raising
up of water is carried out by shutters.

20. Types of weirs:
1.Masonry weirs with vertical drops
2.Rock fill weirs with slopping apron.
3.Concrete weirs with d/s glacis

22. DIVIDE WALL
Long wall constructed at right angles in the weir or barrage,with stone masonry or
cement concrete.
On the upstream side, the wall is extended just to cover the canal head regulator and
on the downstream side, it is extended up to the launching apron.
Functions of the divide wall are as follows:
Form a still water pocket in front of the canal head in which helps in settling of silt.
Controls the eddy current or cross current in front of the canal head.
Provides a straight approach in front of the canal head.
It resists the overturning effect on the weir or barrage caused by the pressure of the
impounding water.

23. FISH LADDER
Consists of an inclined channel with a slope not exceeding 1 in 10.
The compartment of bays of fish ladder should be sufficiently large so that the
fish do not collide with the sides of the bay when ascending.
Grooved gates are provided at the entrance and at the exit of the fish ladder for
closing it.
The water supply to the fish ladder should be adequate for the fish to travel at all
times.

24. UNDER SLUICES
Functions of under sluices:
Maintain a clear and well defined river channel in front of the headregulator.
Used to scour away the silt deposited in front of the head regulator.
They pass low floods without dropping the weir crest shutters.
They control the silt entry into the canal.
They provide greater waterway for floods, thus lowering the flood levels.

25. SILT EXCLUDER
 Device to exclude silt from water entering the canal.
Consists of a number of rectangular tunnels
The tunnels are of different lengths.
The length of the tunnels gradually decreases as the distance of the head regulator.

26. CANAL HEAD REGULATOR
Functions of Canal Head Regulator:
 It regulates the supply of water entering the canal.
 It prevents the river-floods from entering the canal
 The entry of silt into the canal is controlled
 Silt gets deposited in the pocket, and only the clear water enters the regulator
bays.

27. CANAL HEAD REGULATOR
Constructed at the head of canal to regulate flow.
Consists of a number of piers which divide the total width of the canal
into a number of spans which are known as bays.
The piers consist of number tiers on which the adjustable gates are
placed.
The gates are operated form the top by suitable mechanical device.

29. Causes of Failure of weir or barrage on permeable foundation
The combined effect of surface flow and surface flow may cause the failure of the weir or
barrage.
1. Failure due to subsurface flow :
(a) By piping or undermining:
The water from the upstream side
continuously percolates through the bottom
of the foundation and emerges at the
downstream end of the weir or barrage floor.
 The force of percolating water removes the
soil particles by scouring at the point of
emergence as a result depression is formed
through the bottom of the foundation.
A hollow pipe like formation thus develops
under the foundation due to which the weir
or barrage may fail.

30. Undermining or piping

31. 1. Failure due to subsurface flow
(b)By uplift Pressure:
The percolating water exerts
upward pressure on the
foundation of the weir or
barrage. If this uplift is not
counterbalanced by the self
weight of the structure, it may
fail by rapture.

32. (a) By Hydraulic Jump:
When the water flows with a
very high velocity over the
crust of the weir then hydraulic
jump develops. This hydraulic
jump causes a suction pressure
or negative pressure on the
downstream side which acts in
the direction of uplift pressure.
If the thickness of the
impervious floor is not
sufficient, then the structure
fails by rapture.
2. Failure by Surface Flow:

33. (b) By Scouring During floods: The
gates of the barrage are kept open
and the water flows with high
velocity. The water may also flow with
very high velocity over the crest of
the weir. Both the cases can result in
scouring effect on the downstream
and on the upstream side of the
structure. Due to scouring effect on
the downstream and on the
side of the structure, its stability gets
endangered by shearing.
2. Failure by Surface Flow:

34. Precautions Against Failure
Length should be carefully designed to reduce the exit gradient.
Sheet piles should be provided on the upstream side and the downstream
side to reduce the uplift pressure considerable.
Thickness of the impervious floor should be sufficient to counterbalance
the uplift pressure.
Inverted filter should be provided with concrete blocks on the top so that
the percolating water does not wash out the soil particles.
Energy dissipater blocks like friction blocks, impact blocks, should be
provided.

35. Energy Dissipater Blocks

36. Reference
 Linked slide shared.
 Irrigation engineering and Hydraulic. .structured.
 www.civilenggforall.com