Diversion headworks are hydraulic structures that divert water from a river into a canal. They raise the river's water level and regulate the water and silt supply to the canal. Common types include temporary diversion weirs made of bunds and permanent structures like weirs and barrages. Weirs are built perpendicular to flow and come in masonry, rockfill, and concrete varieties. Proper design considers subsurface seepage using theories like Bligh's creep theory and Khosla's method of independent variables and curves.

1. DIVERSION HEADWORKS

2. HEADWORKS
Head Works
 Any hydraulic structure which supplies water to
the off-taking canal is called a head work.
HEAD WORKS
Diversion head works
To raise water level in
river and divert the
required quantity
Storage head works
To store water on u/s
of river and divert the
required quantity

3. DIVERSION 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

4. 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

5. 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

6. SUITABLE SITE FOR DIVERSION HEAD WORKS
 Having selected the reach of the river,
selection suitable site in accordance with
the following considerations
 1. As far as possible, a narrow, straight, well
defined channel confined between banks not
submerged by the highest flood
 2. Should be possible to align the off taking canal
in such a way that command of its area is obtained
without excessive digging

7. SUITABLE SITE FOR DIVERSION HEAD WORKS
 3. Materials of construction such as stone, sand etc.
should be available in the vicinity of the site
 4. Site should be accessible by rail or road

8. COMPONENTS OF DIVERSION HEADWORKS

9. COMPONENTS OF DIVERSION
HEADWORKS
 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

10. WEIR
 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

11. CLASSIFICATION OF WEIRS
 According to the material used for
construction and certain design features
 1. Masonry weirs with vertical drop walls
 2. Rock fill weirs with sloping aprons
 3. Concrete weirs with a downstream glacis

12. MASONRY WEIR WITH VERTICAL DROP

13. MASONRY WEIR WITH VERTICAL DROP
 Weir consists of
 Impervious horizontal floor or apron
 A masonry weir wall with either side vertical; or
both faces inclined; or u/s face vertical and d/s
face inclined
 Curtain walls or cutoffs or piles are provided at the
u/s and d/s ends of the floor
 Block protection at the u/s end and graded inverted
filter at the d/s end
 Launching aprons or pervious aprons after block
protection graded filter

14. ROCKFILL WEIRS WITH SLOPING APRONS

15. ROCKFILL WEIRS WITH SLOPING APRONS
 Weir consists of
 A masonry weir wall
 Dry packed boulders laid in the form of glacis
or sloping aprons
 Some intervening core walls

16. CONCRETE WEIRS WITH DOWNSTREAM GLACIS

17. CONCRETE WEIRS WITH DOWNSTREAM GLACIS
 Floor made of concrete
 Sheet piles of sufficient depth provided at the u/s
and d/s ends
 Sometimes intermediate piles are also provided
 Hydraulic jump is developed at the d/s slope due
to which considerable amount of energy is
dissipated
 Suitable on pervious foundations

18. BARRAGE
 Crest is kept at a low level
 Raising up of water level is accomplished by means
of gates
 During floods, these gates are raised and clear off
the high flood level

19. CAUSES OF FAILURES OF WEIRS ON PERMIABLE
FOUNDATIONS
 Causes of failures
 Due to seepage or subsurface flow
 Due to surface flow

20. CAUSES OF FAILURES OF WEIRS ON
PERMIABLE FOUNDATIONS
 Due to subsurface flow
 Piping or undermining
 By uplift pressure
 Due to surface flow
 By suction due to hydraulic jump
 By scour on the u/s and d/s of the weir

21. DESIGN OF IMPERVIOUS FLOOR FOR
SUBSURFACE FLOW
 Bligh’s creep theory
 Khosla’s theory

22. BLIGH’S CREEP THEORY
 Design of impervious floor or apron
 Directly depend on the possibilities of percolation in
the porous soil on which the apron is built
 Bligh assumed that
 Hydraulic gradient is constant throughout the
impervious length of the apron
 The percolating water creeps along the contact of
base profile of the apron with the sub-soil, losing
head enroute, proportional to the length of its travel
 Stoppage of percolation by cut off (pile) possible only
if it extends up to impermeable soil strata

23. BLIGH’S CREEP THEORY
 Bligh designated the length of travel as
‘creep length’ and is equal to the sum of
horizontal and vertical length of creep

24. BLIGH’S CREEP THEORY
 If ‘H’ is the total loss of head, loss of
head per unit length of creep,
C=H/L
 c-percolation coefficient
 Reciprocal of ‘c’ is called ‘coefficient of
creep’(C)

25. BLIGH’S CREEP THEORY
 Design criteria
(i) Safety against piping
Length of creep should be sufficient
to provide a safe hydraulic gradient
according to the type of soil
Thus, safe creep length,
Where, C= creep coefficient=1/c

26. BLIGH’S CREEP THEORY
 Design criteria
(ii) Safety against uplift pressure
Let ‘h’’ be the uplift pressure head at any point of
the apron
The uplift pressure = wh’
This uplift pressure is balanced by the weight of the
floor at this point

27. BLIGH’S CREEP THEORY
If, t =thickness of floor at this point
G = specific gravity of floor material
Weight of floor per unit area
=

28. BLIGH’S CREEP THEORY

29. LIMITATIONS OF BLIGH’S THEORY
 Bligh made no distinction between horizontal and
vertical creep.
 Did not explain the idea of exit gradient - safety
against undermining cannot simply be obtained by
considering a flat average gradient but by keeping
this gradient will be low critical.
 No distinction between outer and inner faces of
sheet piles or the intermediate sheet piles, whereas
from investigation it is clear, that the outer faces of
the end sheet piles are much more effective than
inner ones.

30. LIMITATIONS OF BLIGH’S THEORY
 Losses of head does not take place in the same
proportions as the creep length. Also the uplift
pressure distribution is not linear but follow a
sine curve.
 Bligh did not specify the absolute necessity of
providing a cutoff at the d/s end.

31. LANE’S WEIGHTED CREEP THEORY
 An improvement over Bligh’s theory
 Made distinction between horizontal and
vertical creep
 Horizontal creep is less effective in reducing
uplift than vertical creep
 Proposed a weightage factor of 1/3 for
horizontal creep as against the 1 for vertical
creep

32. KHOSLA’S THEORY
Dr. A. N. Khosla and his associates done investigations on
structures designed based on Bligh’s theory and following
conclusions were made
 The outer faces of sheet piles are much more effective
than inner ones and the horizontal length of floor.
 The intermediate sheet piles, if smaller in length than the
outer ones were ineffective.
 Undermining of floors started from the tail end. If
hydraulic gradient at exit is more than the critical
gradient, soil particles will move with water and leads to
failure.
 It is absolutely essential to have reasonably deep vertical
cutoff at the d/s end to prevent undermining.

33. KHOSLA’S THEORY
Khosla and his associates carried out further research to
find out a solution to the problem of subsurface flow
and provided a solution
 Considered the flow pattern below the impervious
base of hydraulic structures on pervious foundations
to find the distribution of uplift pressure on the base
of the structure and the exit gradient.
 A composite weir section is split up into a number of
simple standard forms.

34. SPECIFIC CASES OR THE STANDARD FORMS
 (i) Straight horizontal floor of negligible thickness
with pile either at u/s end or at d/s end
 (ii) Straight horizontal floor of negligible thickness
with pile at some intermediate point
 (iii) Straight horizontal floor depressed below the bed,
but with no cutoff

35. The standard forms
(a) A straight horizontal floor of negligible thickness with a
sheet pile either at the u/s end or at the d/s end of the floor

36. The standard forms
(b) A straight horizontal floor of negligible thickness with a
sheet pile at some intermediate point

37. The standard forms
(c) A straight horizontal floor depressed below the bed but
with no vertical cutoff

38. KHOSLA’S METHOD
These standard cases were analyzed by Khosla and his
associates and expressions were derived for determining the
residual seepage head (uplift pressure) at key points .
key points are
 the junction points of pile and floor
 bottom point of pile and bottom corners of depressed
floor

39.  The curves gives the values of Φ (the ratio of
residual seepage head and total seepage head) at
key points.
 The directions for reading the curves are given on
the curves itself.
KHOSLA’S CURVES

40. KHOSLA’S CURVES FOR CUTOFF AT D/S END OR U/S END,
DEPRESSED FLOOR

41. KHOSLA’S CURVES FOR INTERMEDIATE SHEET PILE

42. KHOSLA’S CURVES FOR EXIT GRADIENT

43. METHOD OF INDEPENDENT VARIABLES
 The curves are for specific cases only
 In actual practice
 consider the assembled profile with piles at
u/s end, d/s end, intermediate point, floor
has some thickness and slope
 combination of simple profiles needs to be
considered
 Corrections need to be applied

44.  (i) Straight floor of negligible thickness with pile at
u/s end
 (ii) Straight floor of negligible thickness with pile at
some intermediate point
 (iii) Straight floor of negligible thickness with pile at
d/s end
METHOD OF INDEPENDENT VARIABLES

45.  The pressure obtained at the key points from
curves are then corrected for
o (i) Thickness of floor
o (ii) Interference of piles
o (iii) Sloping floor
METHOD OF INDEPENDENT VARIABLES

46. CORRECTION FOR THICKNESS OF FLOOR
 Pressure at actual points C1 and E1 can be computed
by considering linear variation of pressure between
point D and points E and C
 When pile is at u/s end,
 Correction for Pressure at
 Pressure at C1

47. CORRECTION FOR THICKNESS OF FLOOR
For the intermediate pile,
Correction for
 Correction for
When pile at d/s end,
 Correction for

48. CORRECTION FOR MUTUAL INTERFERENCE OF PILES
 Percentage correction for mutual interference of piles (C)
 d- depth of pile on which the effect of another pile of
depth D is required to be determined
 D- depth of pile whose effect is to be determined on the
neighboring pile of depth d

49. CORRECTION FOR MUTUAL INTERFERENCE OF PILES
 This correction is positive for points in the rear and
subtractive for points in the forward direction of flow
 For example, if we want to find the interference of pile
no. 2 on pile no.1, the correction will be positive as
point C is on rear side of pile 2

50. CORRECTION FOR SLOPE
 The % pressure under a floor sloping down is greater than
that under a horizontal floor
 The % pressure under a floor sloping up is less than that
under a horizontal floor
 Correction is plus for down slopes and minus for up slopes
Slope (vertical/horizontal) Correction (%)
1 in 1 11.2
1 in 2 6.5
1 in 3 4.5
1 in 4 3.3
1 in 5 2.8
1 in 6 2.5
1 in 7 2.3
1 in 8 2.0

51. CORRECTION FOR SLOPE
 The corrections given table are to be further multiplied by
the proportion of horizontal length of slope to the distance
between the two pile lines in between which the sloping
floor is located
 The slope correction is applicable only to that key points
of pile line which is fixed at the beginning or end of the
slope