INTRODUCTION

A barrage is a type of low-head, diversion dam which 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. The
gates are set between flanking piers which are responsible for supporting the water load of the pool
created. The term barrage is borrowed from the French word "barrer" meaning "to bar

LITRATURE REVIEW
COMPONENTS OF A BARRAGE

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 Definition
The only difference between a weir and a barrage is of gates that is the flow in barrage is regulated
by gates and that in weirs, by its crest height.
Barrages are costlier than weirs.
Weirs and barrages are constructed mostly in plain areas. The heading up of water is affected by
gates put across the river. The crest level in the barrage (top of solid obstruction) is kept at low
level.
During flood, gates are raised to clear of the high flood level. As a result there is less silting and
provide better regulation and control than the weir.
Components of barrage
Main Barrage Portion
1. Main body of the barrage, normal RCC slab which supports the steel gate. In the X-Section it
consists of:
2. Upstream concrete floor, to lengthen the path of seepage and to project the middle portion where
the pier, gates and bridge are located.
3. A crest at the required height above the floor on which the gates rest in their closed position.
4. Upstream glacis of suitable slope and shape. This joins the crest to the downstream floor level.
The hydraulic jump forms on the glacis since it is more stable than on the horizontal floor, this
reduces length of concrete work on downstream side.
5. Downstream floor is built of concrete and is constructed so as to contain the hydraulic jump.
Thus it takes care of turbulence which would otherwise cause erosion. It is also provided with
friction blocks of suitable shape and at a distance determined through the hydraulic model
experiment in order to increase friction and destroy the residual kinetic energy.
Divide Wall
 A wall constructed at right angle to the axis of the weir separating the weir proper from the
under sluices (to keep heavy turbulence at the nose of the wall, well away from upstream protection
of the sluices)
 It extends upstream beyond the beginning of canal HR. Downstream it extends up to the end of
loose protection of under sluices launching apron)
 This is to cover the hydraulic jump and the resulting turbulence.
The fish ladder:
 For movement of fish (negotiate the artificial barrier in either direction)
 Difference of level on the upstream and downstream sides on the weir is split up into water steps
by means of baffle walls constructed across the inclined chute of fish ladder.

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 Velocity in chute must not be more than 3m/s
 Grooved gate at upstream and downstream – for effective control.
 Optimum velocity 6-8 ft/s
Sheet piles:
Made of mild steel, each portion being 1/2′ to 2′ in width and 1/2″ thick and of the required length,
having groove to link with other sheet piles.
Upstream piles:
Situated at the upstream end of the upstream concrete floor driven into the soil beyond the
maximum possible scour that may occur.
Functions:
1. Protect barrage structure from scour
2. Reduce uplift pressure on barrage
3. To hold the sand compacted and densified between two sheet piles in order to increase the
bearing capacity when barrage floor is designed as raft.
Intermediate sheet piles:
 Situated at the end of upstream and downstream glacis. Protection to the main structure of
barrage (pier carrying the gates, road bridge and the service bridge) in the event of the upstream and
downstream sheet piles collapsing due to advancing scour or undermining. They also help lengthen
the seepage path and reduce uplift pressure.
 Downstream sheet piles: Placed at the end of downstream concrete floor. Their main funtion is
to check the exit gradient. Their depth should be greater than the possible scour.
Inverted filter:
 provided between the downstream sheet piles and the flexible protection. Typically 6″ sand, 9″
coarse sand and 9″ gravel. Filter may vary with size of particles forming the river bed. It is
protected by placing over it concrete blocks of sufficient weight and size. Slits are left between the
blocks to allow the water to escape.
 Length should be 2 x downstream depth of sheet.
Functions:
 Check the escape of fine soil particles in the seepage water.
Flexible apron:
 Placed downstream of the filter
 Consists of boulder large enough not to be washed away by the highest likely velocity
 The protection provided is enough as to cover the slope of scour of 1 1/2 x depth of scour as the
upstream side of 2 x depth of scour on the downstream side at the slope of 3.

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The under sluices: scouring sluices
Maintaining a deep channel in front of the Head regulator on the downstream side.
Functions:
1. As the bed of under sluice is not lower level than rest of the weir, most of the day, whether flow
unit will flow toward this pocket => easy diversion to channel through Head regulator
2. Control sil entry into channel
3. Scour the silt (silt excavated and removed)
4. High velocity currents due to high differential head.
5. Pass the low floods without dropping
6. The shutter of the main weir, the raising of which entails good deal of labor and time.
7. Capacity of under sluices:
8. For sufficient scouring capacity, its discharging capacity should be at least double the canal
discharge.
9. Should be able to pass the dry weather flow and low flood, without dropping the weir shutter.
10. Capable of discharging 10 to 15% of high flood discharge
River training works
To ensure smooth and axial flow of water, to prevent the river from out ——the works due to
change in its course.
River Training Works
Guide banks:
Earthen embankments => stone pitching
Force the river into restricted channel, to ensure almost axial flow near the weir site. (Embankments
in continuation of G-Banks. To contain flood within flood plains)
Marginal Bunds:
Provided on the upstream in order to protect the area from submergence due to rise in HFL, caused
by afflux.
Groans or spurs:
 Embankment type structures constructed transverse to river flood, extending from the banks into
the river (also transverse dykes)
 Protect the bank from which they are extended by deflecting the current away from the bank.

METHODOLOGY/PROCEDURE

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The Barrage and the Head Regulators of feeder channels and appurtenant structures will be
designed on the basis of standard design criteria established for other barrages and allied structures,
already constructed on the Indus River and its tributaries. The design criteria, including formulae,
coefficients and constants will be used in all hydraulic designs as applicable.
There are two aspects of the design of a barrage i.e:
1. Surface flow / Overflow consideration
2. Safety against subsoil flow i.e. (by Bligh’s creep theory, Lane’s weighted creep theory and
Khosla’s theory)
1. Surface Flow / Overflow Consideration:
Following items have to be estimated / designed in case of overflow considerations:
1. Estimation of design flood.
2. Length of barrage i.e. (Width between abutments)
3. Retrogression
4. Barrage profile i.e. upstream floor level, D/S floor level, crest level
1. Estimation of design flood:
The design flood (maximum flood) is estimated for which the barrage is to be designed depending
upon the life of structure. The design flood estimation may be for 50 years, 100 years etc.
2. Length of Barrage (Width b/w Abutments):
Lacey’s formula can be used for fixing the length of barrage i.e. Pw = 4.75 Q
Where, Pw = Wetted perimeter Q = Maximum flood discharge
From t the length of barrage can be evaluated as, Length of barrage = L.L.C x Pw
Where, L.L.C = Lacey’s looseness coefficient Take L.L.C = 1.8, if not mentioned
3. Retrogression:
It is a temporary phenomenon which occurs after the construction of barrage in the river flowing
through alluvial soil. As a result of back water effect and increase in the depth, the velocity of water
decreases resulting in deposition of sedimentation load. The water flowing through the barrage have
less silt, so water picks up silt from downstream bed. This results in lowering d/s river bed to a few
miles. This is known as retrogression.
It may occur for the first few years and bed levels often recover their previous level. Within a few
years, water flowing over the weir has a normal silt load and this cycle reverses. Then due to
greater depth, silt is deposited and d/s bed recovers to equilibrium. Retrogression value is minimum
for flood discharge and maximum for low discharge. The values vary (2 - 8.5) ft.

4. Accretion:

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It is the reverse of retrogression and normally occurs upstream, although it may occur d/s after the
retrogression cycle is complete.There is no accurate method for calculating the values of
retrogression and accretion but the values which have been calculated from different barrages can
be used as a guideline.
5. Barrage profile:
• Crest level:The crest level is fixed by the total head required to pass the design flood over the
crest. The pond level is taken as the H.F.L.Maximum scour depth can be calculated from Lacey’s
scour formula,
R = 1.35 (q2f)1/3 (M.K.S) R = 0.9 (q2f) 1/3 (F.P.S)
Discharge per unit width,q = QLVelocity of Approach, V = qRVelocity head = v22g And discharge
can be found using discharge formula, Q = CLH 3/2
Where C = Coefficient of discharge Taken as 2.03 (M.K.S), Q = Flood Discharge, L = Length of
barrage crest, H=Total Energy Head = v22g + h•

Estimation of Design Flood

Basis of Estimation
The design flood for any given return period is usually estimated by the frequency analysis method.
Appropriate type of frequency distribution will be selected from among the following:
1. Pearson & Log Pearson Type III distributions
2. Gumbel's Extreme Value distributions
3. Normal & Log Normal distributions
It is pertinent to point out that Log Pearson Type III distribution has been adopted by United States
Federal Agencies whereas Gumbel distribution has generally been found to be suitable for most of
the streams in Pakistan including river Indus and its tributaries.

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Design Return Period
A return period of 100 years is generally adopted in the design of important and costly barrage
structures where possible consequences of failure are very serious. Accordingly, the estimation of
design flood will be carried out for various return periods of 100 years, 200 and 500 years subject
to Client's concurrence. However, the actual recorded peak flood discharge will be reviewed for
design if it exceeds the discharge calculated for the concerned return period.
Hydraulic Units
The dimensions and units of properties used in solving hydraulic problems are expressed in three
fundamental quantities of Mass (M), Length (L), and time (T). All analyses and designs will be
carried out in the Foot-Pound-Second system of units and conversion to S.I Units will be made only
of important results as necessary.
Width of Barrage
Three considerations govern the width of a barrage. They are the design flood, the Lacey design
width and the looseness factor. It is generally thought that by limiting the waterway, the shoal
formation upstream can be eliminated. However, it increases the intensity of discharge and
consequently the section of the structure becomes heavier with excessive gate heights and cost
increases, though the length of the structure is reduced.
The design flood is discussed in section 2.2 and the other two considerations are discussed in the
following sections.
Lacey's Design Width
The Lacey's Design or Stable width for single channel is expressed as:
W = 2.67 v Q
Where Q is the Design Discharge in cusecs (ft3/sec).
The Barrage is designed for a width exceeding W, partly to accommodate the floodplain discharge
and partly to take advantage of the dispersion of the channel flow induced by the obstruction caused
by the barrage itself.
The Looseness Factor
The ratio of actual width to the regime width is the "looseness factor", the third parameter affecting
the barrage width. The values used have varied from 1.9 to 0.9, the larger factor being applied in
the earlier design. Generally it varies from 1.1 to 1.5. From the performance of these structures, a
feeling arises in certain quarters that with high Looseness Factor, there is a tendency for shoal
formation upstream of the structures, which causes damages and maintenance problems. The
Consultants will use the most appropriate looseness factor to provide reasonable flexibility keeping
the ill effects to the minimum.

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Afflux
The rise in maximum flood level of the river upstream of the barrage as a result of its construction
is defined as Afflux. Afflux, though confined in the beginning to a short length of the river above
the barrage, extends gradually very far up till the final slope of the river upstream of the barrage is
established.
In the design of barrages/weirs founded on alluvial sands, the afflux is limited to between 3 and 4
feet - more commonly 3 feet. The amount of afflux will determine the top levels of guide banks and
their lengths, and the top levels and sections of flood protection bunds. It will govern the dynamic
action, as greater the afflux or fall of levels from upstream to downstream the greater will be the
action. It will also control the depth and location of the standing wave. By providing a high afflux
the width of the barrage can be narrowed but the cost of training works will go up and the risk of
failure by out flanking will increase. Selection and adoption of a realistic medium value is
imperative.
Tail Water Rating Curve
Tail water rating curve for the barrages will be established through analysis of gauge discharge
data. The proposed tail water levels for new designs will be established by subtracting the designed
retrogression values from the existing average tail water levels.
Crest Levels
Fixation of crest level is clearly related with the permissible looseness factor and the discharge
intensity in terms of discharge per foot of the overflow section of the barrage. After considering all
the relevant factors and the experience on similar structures the crest levels will be fixed in order to
pass the design flood at the normal pond level with all the gates fully open.
Discharges through a Barrage (Free Flow Conditions)
The discharge through a Barrage under free flow conditions shall be obtained from the following
formula:
Q = C. L. H3/2....... (1)
Where,
Q = discharge in cusecs
C = Coefficient of Discharge
L = Clear waterway of the Barrage (ft)
H = Total Head causing the flow in ft
The value of C is generally taken as 3.09, but may approach a maximum value of 3.8 for modular
weir operation (Gibson). However to design a new barrage it will be determined by physical model
studies.

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Discharge through a Barrage (Submerged Flow Conditions)
The flow over the weir is modular when it is independent of variations in downstream water level.
For this to occur, the downstream energy head over crest (E 2) must not rise beyond eighty (80)
percent of the upstream energy head over crest (E1). The ratio (E2/E1) is the "modular ratio" and the
"modular limit" is the value (E2/E1 = 0.80) of the modular ratio at which flow ceases to be free.
Fane's Curve
For submerged (non - modular) flow the discharge coefficient in equation (1) above should be
multiplied by a reduction factor. The reduction factor depends on the modular ratio (E2/E1) and the
values of reduction factor (Cr) given in the table below are from Fane's curve (Ref: 2.3) which is
applicable to weirs having upstream ramp and sloping downstream with slope 2H:1V or flatter:
"E2/E1 " Value of "Cr"
0.80 0.99
0.85 0.99
0.90 0.98
0.92 0.96
0.94 0.90
0.95 0.84
0.96 0.77
0.97 0.71
0.98 0.61
The submerged discharge is given by the equation:
Q = 3.09. Cr.b .E11.5
Gibson Curve
Q = C'bE1.5
Where:
Q = submerged discharge over crest (cusecs)
C' = submerged discharge coefficient
B = width of weir (ft)
E1 = upstream energy head above crest
= h1 + v12/2g (ft)
For submerged discharges the free flow discharge coefficient (C=3.80) is multiplied by a reduction
factor (C'/C). The coefficient factor depends on the modular ratio (h/E), where his downstream
depth of flow above crest. The values of reduction factor "C'/C" given in the table below are from
Gibson curve applicable to the broad crested weirs:

h/E C'/C C'

0.70 0.86 3.27

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0.80 0.78 2.96
0.90 0.62 2.36

CALCULATIONS AS PER GIVEN DATA

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 RESULTS
A barrage that are set in consideration of surface flow, subsurface flow and nature of the
foundation soil by Hydraulic Jump theory and Khosla’s theory. It solves the uplifting pressure head
distribution on the structure using regression from Khosla’s pressure curves, allowing for the
approximately perfect design of structures built on anisotropic and shallow as well as isotropic and
deep permeable media with and without consideration of concentration and retrogression. The app
also provides the hydraulic design parameters for the Canal Head Regulator provided at the head of
the off-taking canal.
CONCLUSIONS
The different parameters of the components of a diversion structure are interrelated. Their optimum
combination is dependent on the cost of construction of the elements at a particular site. The
practical situation in the construction of water work structures is that the cost of material and
construction vary; making an optimum design at one point in time (while in design stage) to be
obsolete at other (during construction).
This particular study focused on developing an application that would solve the surface and
subsurface flow problems for diversion structure with a sloping apron and founded on porous
media. Little or no effort is made to include the structural design of gates, piers and some other

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component structures that need special structural design considerations in the computer program.
Moreover, there is a need to develop the procedure of optimization for least cost design, i.e.
consideration of permissible afflux, water- way width, wing walls and the top levels of aprons.
REFERENCES
 Construction of Concrete Barrages - Code of Practice, Bureau of Indian Standards, 1993.
 Hydraulic Design of Barrages and Weirs, Bureau of Indian Standards, 1966.
 The Practical Design of Irrigation Works, Constable, London, 1912.
 The Theory of Ground water flow Beneath Hydro Technical Structures, Petersburg, 1922.

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