The document discusses the design of fall structures for irrigation canals. It begins with an introduction to fall structures and their purposes. It then discusses the classification and types of falls. The document outlines the steps involved in the hydraulic design of falls, including determining crest parameters, transition designs, energy dissipation, and other checks. It provides a literature review on previous research conducted on topics like flow regimes and failure cases. The methodology section describes the process used for the design, including calculations for crest levels, scour depth, cutoff levels, basin design, and other structural dimensions. Drawings and diagrams of the general profile and arrangements are also included.

1. DESIGN
Muhammad Fahim Aslam

2. PRESENTATION LAYOUT
o Fall Structures
o Purpose of Falls
o Types of Falls
o Steps for Design of Fall Structures
o Literature Review
o Methodology
o Results
o Profile
o Drawings
o Conclusion
o References

3. FALL STRUCTURES
 A canal fall or drop is an irrigation structure constructed across a
canal to lower down its bed level to maintain the designed slope
when there is a change of ground level to maintain the designed
slope when there is change of ground level.
 Fall structures are also necessary on canals to provide flatter
longitudinal bed slope to the canals when the average natural slope
of land is steeper than required longitudinal slope to design stable

4. PURPOSE OF PROVIDING FALLS
 It conveys water from a higher to a lower elevation
 Dissipates excess energy
 Helps to save earthwork
 Helps to Improve command and regulation of canal

5. Classification of Falls:
Meter Falls:
Measure the discharge of the canal
Non meter Falls
Do not measure discharge
For a fall to act like meter, it must have broad weir type crest so that
the discharge coefficient is constant under variable head.
Generally glacis type fall is suitable as a meter whereas vertical
drop is not suitable due to formation of partial vacuum under the
nappe.

6.  Flumed Falls
The contracted falls are called flumed falls
 Unflumed Falls
while full channel width falls are the unflumed falls

7. Types of Falls:
 Vertical Fall
 Glacis Fall
 Rapids
 Trapezoidal notch falls
 Chute Fall
 Inglis Fall
 Montague type fall

8. STEPS INVOLVED IN HYDRAULIC DESIGN
OF FALLS
Known Data
Decision
About Type of
Fall
Determination
of Crest
Parameters
Defining Type
of U/S & D/S
Transition
Design of
Energy
Dissipation
System
Check For
Scour
Check For
Exit Gradient
Check For
Apron
Thickness
against Uplift
Pressures

9. LITERATURE REVIEW
 Masoume et al. (2018) performed a comprehensive set of experiments on grid
drop-type dissipators in a rectangular open channel.
The adjustment and boundaries of different flow regimes
The variation of flow hydraulic characteristics downstream of a grid drop-type
dissipator, caused by the gradual alteration of the tail-water depth.
Results indicated that two key flow regimes, namely “bubble impinging jet flow
regime” and “surface flow regime” arise because of the changes made
in the tail-water depth.
 Jyh-jong et al. (2015) presents failure cases of low-head drop structures in
bedrock channel.
Three processes include,
1. Local scour in channel bed and bank toe downstream the vertical drop structure.
2. Scour at structure edges of the transition interface between artificial material and
natural bedrock.
3. Damage of concrete pavement by impact of large boulders

10. LITERATURE REVIEW (Cont.)
Lin et al. (2010) investigated the characteristics of flows over a
vertical drop experimentally using laser Doppler velocimetry for detailed
quantitative velocity measurements and a flow visualization technique
for qualitative study of flow pattern.
Ismail et al. (2009) investigated the flow over a drop structure placed
in a rectangular channel through an experimental program. Procedures
adopted are
1. The first procedure was physically based with an empirical
component for the estimation of the depth of the pool formed at the
base of the drop.
2. The second resulted in an equation for the direct estimation of the
downstream depth.

11. LITERATURE REVIEW (Cont.)
Rajaratnam et al. (2010) presented a critical analysis of the energy loss at drops.
Mohammad et al. (2008) experimentally studied the energy loss of the vertical drop
with subcritical flow in the upstream channel with a physical model of 0.20m drop
height.
Kabiri et al. (2016) investigated flow characteristics over vertical drops equipped
with a grid roof
The results indicate that the proposed hydraulic structure eliminates unfavorable flow
conditions and forms the basis of a more effective flow control system compared with
a plain vertical drop.
Xie et al. (1998) developed experimental hardware to perform the experiments of
drop Marangoni migration in the case of intermediate Reynolds numbers in a
microgravity environment.
Experimental results show that Marangoni migration velocity depends on the
temperature gradient and the drop diameter for fixed experimental mediums

12. LITERATURE REVIEW (Cont.)
Arturo et al. (2010) used computational fluid dynamics (CFD) models to
formulate, implement and evaluate junction and drop-shaft boundary
conditions (BCs) for one-dimensional modeling of transient flows in single-
phase conditions (pure liquid).
The results suggest that the junction and drop-shaft BCs can be used for
modeling transient free-surface, pressurized, and mixed flow conditions with
good accuracy.
Roberta et al. (2013) made an experimental campaign in order to
investigate the hydraulic features of a vertical drop shaft, also considering the
influence of a venting system consisting of a coaxial vertical pipe, projecting
within the drop shaft with different plunging rates.

13. Methodology
 Basic Hydraulic and geometric Data of the Canal was
available comprising of.
Discharge
Full Supply Level (FSL) of canal
Bed Levels of Canal
Berm Widths
Free Board
Flow velocity
Longitudinal Slope
Side Slope
Lacey’s Silt Factor

14. Methodology (Cont.)
 First of all crest level, crest height and crest width were calculated in order to check the
discharge carrying capacity of structure, with the help of following formulas
CL = Q/(CW)0.667
Where
CL= Crest Level
Q= Discharge in canal
C= Co-efficient of Discharge
W= Width of structure
 Measured the Lacey’s scour depth (R )
R’ =FOS × R
 Three criteria’s were used to decide the level of cutoff length. Minimum Level from following
three was decided as the cutoff level. U/S and D/S cutoff levels have been calculated through
this method
R’-(FSL- Bed Level)
(FSL-Bed Level)/2
(NSL- 1ft)
3/12
9.0 






f
q
R

15. Methodology (Cont.)
 Basin design of the fall( Length of Cistern and sill height) has been done
with the help of two approaches
 Bahadarbad Irrigation Research Institute Formula (Ref. Iqbal Ali)
 Eichvery Formula

16. Methodology (Cont.)
 Calculation of uplift pressures was done with the help of Khosla’s
Theory and accordingly the structural lengths have been calculated
ἀ =b/d
λ = (1 + √(1+α2))/2
φE =(1/π)(Cos-1(λ-2)/λ)
φD =(1/π)(Cos-1(λ-1)/λ)
 Stone protection works(Length and Thickness) on U/S and D/S side
have been calculated by using the scour levels and structural lengths
 Computation of exit gradient was done
Exit Gradient value must be below the permissible values of Exit
Gradient.





 2/1
 d
H
GE

17. Methodology (Cont.)
 Structural Lengths of the structure are calculated according to the canal cross section
Length of Wing Wall =
Hz. Length of Splay of Wing Wall =
 Computation of U/S, D/S Tail energy levels(TEL) were calculated with the help of levels and
losses.
 Energy values were read from the Blench Curves (Plates 10.1, 10.2, 10.3a, 10.3b and 11)
 Froude no. was calculated to check the type of flow over the fall.
 Levels of the Hydraulic Grade line were calculated by using the uplift pressures calculated
earlier.
 Profile of the vertical fall before and after the jump was drawn by using the dimensions of the
floor lengths, hydraulic grade line and unbalance head before and after the vertical fall.

18. GENERAL PROFILE OF FALL
640
645
650
655
660
0 5 10 15 20 25
Elevations
Floor Length
Profile of Vertical Fall at FSL
Pre-Jump Profile
Concrete Floor
Post-Jump Profile
HG Line

19. DRAWINGS (General Arrangement
Plan)

20. Longitudinal Cross Section

21. CONCLUSION
 Literature review on Vertical Fall has been done
 Most optimum design has been carried out using different
theories and criteria’s so that the best hydraulic results are
achieved from the structure without affecting the economy and
life.
 Check for exit gradient and uplift pressures by Khosla’s
Theory
 The structure is safe against piping and uplift.
 Also, the heel of the walls of the fall has been extended so
that the weight of soil shall also help to increase the weight of
the structure
 Accordingly the structure lengths have been calculated.
 Hydraulic grade line and Hydraulic Profile of the vertical fall
has been drawn by calculating the energy levels and pre/post
fall unbalance heads.

22. REFERENCES
 Masoume Sharif, Abdorreza Kabiri-Samani. (2018) Flow regimes at grid drop-type dissipators
caused by changes in tail-water depth. Journal of Hydraulic Research 0:0, pages 1-12.
 C. Lin, W.-Y. Hwung, S.-C. Hsieh, K.-A. Chang. (2007) Experimental study on mean velocity
characteristics of flow over vertical drop. Journal of Hydraulic Research 45:1, pages 33-42.
 Ismail I. Esen, Jasem M. Alhumoud, Khoanddkar A. Hannan. (2004) Energy Loss at a Drop
Structure with a Step at the Base. Water International 29:4, pages 523-529.
 N. Rajaratnam, M.R. Chamani. (1995) Energy loss at drops. Journal of Hydraulic Research 33:3,
pages 373-384.
 Mohammad R. Chamani, N. Rajaratnam, M. K. Beirami. (2008) Turbulent Jet Energy Dissipation
at Vertical Drops. Journal of Hydraulic Engineering 134:10, pages 1532-1535.
 A.R. Kabiri-Samani, E. Bakhshian, M.R. Chamani. (2017) Flow characteristics of grid drop-type
dissipators. Flow Measurement and Instrumentation 54, pages 298-306.
 Xie J., Lin H., Han J., Dong X., Hu W., Hirata A. and Sakurai M. (1998). Experimental
investigation on Marangoni drop migrations using drop shaft facility. International Journal of Heat
and Mass Transfer, 41(14), pp.2077-2081.
 Naib S.K.A. (1984) Hydraulic Research on Irrigation Canal Falls. In: Smith K.V.H. (eds) Channels
and Channel Control Structures. Springer, Berlin, Heidelberg.
 Padulano, Roberta & Del Giudice, Giuseppe & Carravetta, Armando. (2013). Experimental
Analysis of a Vertical Drop Shaft. Water. 5. 1380-1392. 10.3390/w5031380.
 Garg, Santosh. Irrigation Engineering and Hydraulic Structures. 16th ed. Delhi: Khanna
Publishers, 2002.
 Chow, Ven. Open Channel Hyraulics. Singapore: McGraw-Hill International, 1959.
 Ali, Iqbal. Irrigation and Hydraulic Structures. 2nd ed. Karachi: Farhat Iqbal, 2003.

23. Thank
you