1. A diversion headwork is a weir or barrage constructed across a river to divert water into a canal. It regulates water flow into the canal through a head regulator. 2. A barrage differs from a weir in that it uses large gates that can be opened and closed to directly control water levels, whereas a weir uses fixed crest heights. 3. The main purpose of a barrage is to stabilize river water levels for uses like irrigation while still allowing easy control over flow, unlike a dam which relies on water levels behind the full wall height.

1.  Any hydraulic structure which supplies water to the off-taking
canal is called a headwork.
Headwork may be divided into two
 1. Storage headwork. 2. Diversion headwork.
 1. Storage head works--- Dam is constructed across a river
valley to form storage reservoir, known as storage head works.
 Water is supplied to the canal from this reservoir through canal
regulator.
 These serves for multipurpose function like hydro- electric
power generation, flood control, fishery.
 2. Diversion head works---Weir or barrage is constructed across
a perennial river to raise water level and to divert the water to
canal, is known as diversion head work.
 Flow of water in the canal is controlled by canal head
regulator.
Headwork

2.  Raises the water level in the river so that the commanded area
is increased.
 Regulates the supply of water into the canal.
 Controls the entry of silt into the canal.
 Provide some storage of water for a short period.
 Controls the vagaries of river.
Functions of Diversion Head works

5.  Weir or Barrage.
 Divide wall or divide groyne.
 Fish ladder.
 Under-sluices or scouring sluices.
 Silt excluder.
 Canal head regulator.
 River training works such as Marginal bunds and
Guide bunds.
components of diversion head works

6.  A weir or low head dam is a barrier or the crest wall of concrete
or masonry across the width of a river that alters the flow
characteristics of water and usually results in a change in the
height of the river level.
 Used to control the flow of water for outlets of lakes, ponds,
and reservoirs.
 Weir alignment should be at right angles to the direction of
flow.
Weir

7.  A barrage is a type of low-head, diversion dam, consists of a
number of large gates that can be opened or closed to
control the amount of water passing through.
 This allows the structure to regulate and stabilize river water
elevation upstream for use in irrigation and other systems.
 Barrage provides a better control over river flow by a suitable
manipulation of gates.
 Current trend is to construct a barrage.
Barrage

8. Barrage Weir
Low set crest High set crest
Ponding by gates Ponding against raised crest
Gated over entire length Shutters in part length
Perfect control on river flow No control
Gates of greater height Shutters of small height, 2m
High floods can be passed with
min afflux
Excessive afflux in high floods
Less silting U/S due to set crest Raised crest causes silting U/S
Longer construction period Shorter construction period
Costly structure Cheaper structure
Silt removal through under-
sluices
No means of silt disposal
Difference between barrage & weir

9. Narrow and well-defined river section.
River should have high, in erodible and non-submersible banks
so that the cost of river training works is minimum.
Good foundation.
Easily accessible by road or rail.
Minimum project Cost.
Construction material should be available near the site.
Suitable arrangement for diversion of river during construction.
DHW should not submerge costly land & property on its U/S.
Suitable locations for components of DHW .
Canals taking-off from DHW should be economical with large
CA.
Length of weir should be minimum.
Site selection for diversion head work

10.  High initial low
Disadvantages---
 Large afflux during floods causes large submergence.
 Crest is high , there is great silting problem.
 Raising & lowering of shuttering on the crest is not
convenient, requires more time & labour.
Advantages of weir

11.  Good control on the river during floods. The outflow can be
easily regulated by gates.
 The afflux during floods is small , submerged area is less.
 Good control over silt entry into the canal.
 Good control over flow conditions, shoal formations & cross
currents on the U/S of the barrage.
 Better facilities for inspection & repair of various structures.
 A roadway can be conveniently provided over the structure at
a little additional cost.
Disadvantages---
 Initial cost is quite high.
Advantages of barrage

12.  1. Vertical drop weirs
Types of weirs

13.  2.Rockfill weirs

14.  3. Concrete glacis or sloping

15.  To form a still water pocket in front of the canal head so that
the suspended silt can be settled down which then later be
cleaned through the scouring sluices from time to time.
 It controls the eddy current or cross current in front of the
canal head
Divide wall

16. Divide wall

17.  It 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.
 The fish ladder is provided just by the side of the divide wall
for the free movement of fishes.
Fish ladder

20.  i) Preserve a clear and defined river channel
approaching the regulator.
 ii) Control the silt entry into the canal.
 iii) Pass the low floods without dropping the shutter
of the main weir.
 iv) Provide greater water-way for floods, thus
lowering the flood level
Sluice gates

22.  are a type of silt control device which functions to exclude
silt from water to entering the canal.
 These devices are particularly provided on the river bed in
front of the head regulator.
 A silt excluder usually consists of a number of rectangular
tunnels resting on the floor of the undersluice pocket
Silt excluders

23.  is a structure constructed in the bed of a river, u/s of a head
regulator to attack the river bed water and divert the same
into the d/s of the river.
 Its main function is to prevent the entry of silt into the canal
Silt excluder

24.  Silt ejectors, also called silt extractors, are those devices which
extract the silt from the canal water after the silted water has
travelled a certain distance in the off-take canal.
 These works are, therefore, constructed on the bed of the
canal, and little distance downstream from the head regulator.
Silt Ejectors

26.  Silt ejector is the hydraulic structure located in the canal
headreach such that sediment can be preiodically flushed back
into the river.
 It remove the water from the bottom layers of the canal
through tunnels spanning the whole width of the canal and
discharges it into some nearby drain or back to river.
Silt ejector

27.  The total length of the river may be divided into following four stages:
 1. Mountainous Stage:
The first length of the river originating from hills is known as mountainous
stage of the river.
 The longitudinal slope in this stage is very steep and velocity of flow of
water, very fast.
 The width of the river in this region is generally very small.
 This region is found most suitable for the construction of storage works
like high dams.
 Large storages are possible as very deep valleys are easily available here.
Moreover the length of the dam is also relatively small. Materials of
construction are locally available.
 This stage is however not suitable for diversion works.
Location of Diversion Head Works:

28.  The bed and banks of the river in this stage are made of gravel.
 The velocity of flow is considerable though smaller than first
stage.
 The river water contains lot of silt load. The river generally
does not flow in a single channel, but is form of small several
channels.
 Longitudinal slope is less than first stage but still considerable.
 Diversion works can be located in this region of the river.
2. Sub-Mountainous Stage:

29.  This length of the river is in plains.
 The section of the river is made of alluvial soils or silt.
 The longitudinal slope of the river is small and velocity of flow
moderate.
 This length of the river is the largest of all other lengths.
Diversion works are mostly located in this length.
 The area to be irrigated lies very near to this length and thus
reduces the overall length of the canal network.
3. Alluvial or Trough Stage.

30.  This is the last length of the river before it falls into the sea.
 This length of river is only a few kilometres long. Here velocity of
flow is very small and silting rate very high. Because of high rate of
silting, the rivers frequently change their course.
 No diversion work is constructed in this region. Secondly available
command area near this region is also small.
 Canals cannot be taken from mountainous stage, as lot of cuttings
and fillings are involved and thus canal construction becomes very
costly.
 Lot of falls will have to be constructed adding still more to the cost.
4. Delta Stage:

31.  (i) All the construction materials should be available in the vicinity.
(ii) In order to keep the length of the canal minimum, diversion head works should be
located as near the area to be irrigated as possible.
 (iii) The elevation of the water in the river should be such that water may flow to the
area under gravity. If level of water is low, the position of the head works should be
shifted a few kilometres upstream so that increased elevation of water is available.
 (iv) The canal should run in such a way that canal is partly in cutting and partly in
filling.
 (v) The river at site of diversion, should be neither too wide nor too narrow. The river
should neither be scouring nor silting.
 (vi) The river should be straight and flowing in one channel. Its bed and banks should
be stable.
 (vii) The canal alignment should be such that minimum streams cross it. This will
reduce the number of cross-drainage works to be constructed.
 (viii) The canal should take off, either at 90° or greater than 90° with the river. Canal
should not run parallel to the river. In such circumstances the canal may be eroded
during floods.

32.  Weir or barrage is constructed across a perennial river to raise
water level and to divert the water to canal, is known as
diversion head work.
 Flow of water in the canal is controlled by canal head
regulator.
 It regulates the supply of water into canals
Diversion head works

33.  Earthen embankments which are provided to confine the
flood water from the river within an allowable cross-section
and in between the embankments.
 Thus the spreading of flood water beyond these marginal
bunds is prevented
Marginal bunds or levees

34.  serves the following purposes:
 It protects the barrage from the effect of scouring and
erosion.
 It provides a straight approach towards the barrage.
 It controls the tendency of changing the course of the river.
 It controls the velocity of flow near the structure.
Guide bank

35.  A barrage is a type of dam; however, instead of being a massive concrete
wall that the water can’t flow over, the barrage is full of gates.
 These gates are opened and closed to directly control the amount of water
that passes through it. Having a barrage instead of a dam means that the
flow of water can be kept stable for its intended purpose, such as irrigation
to nearby cities, towns, or farmlands. Unlike a dam, the water stored behind
a barrage depends on the height of its gates and not the height of the entire
wall. The flow and level of water are easily monitored because the gates can
be easily manipulated.
 A barrage is constructed when water doesn’t need to be stored but rather
diverted. For this reason, the barrage is usually built across a flat and
relatively slow-moving river. Unlike a dam, which will raise waters nearly to
its height, a barrage will only raise the water level by a few feet. This is also
useful for navigation, because a barrage can increase the depth of a river by
a few feet.