chapter 1 of Advanced Open channel hydraulics by Ven Te Chow

1. 1

2. ADVANCED OPEN CHANNEL
HYDRAULICS (CHAPTER NO 1)
REFERENCE BOOK: OPEN CHANNEL HYDRAULICS BY “VEN TE CHOW”
2
Presented By: Hadiqa Qadir
2k22-MS-HIE-02
Civil Engineering Department (CED), UCE&T, BZU, Multan

3. CHAPTER 1: OPEN CHANNEL FLOW & ITS CLASSIFICATIONS
Content:
1. Description/Introduction
2. Types Of Flow
3. State Of Flow
4. Regimes Of Flow
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4. 1. NTRODUCTION
Hydraulics: The word “hydraulics’’ originates from the Greek word (hydraulikos) which in turn originates
from (hydro, Greek for water) and (aulos, meaning pipe). So hydraulics means flow of water.
Therefore,
The branch of science that deals with the flow/velocity and the flow mechanism of fluids/water is called
hydraulics.
It is widely applied in many civil and environmental engineering system such as
water resources, water management, flood defense, harbors and port, bridge, building,
hydropower,irrigation, ecosystem,pumps,turbines, etc.
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5. INTRODUCTION (CONT.)
 Flow of a liquid may take place either as open channel flow or pressure flow.Pressure
flow takes place in a closed conduit such as a pipe, and pressure is the primary driving
force for the flow.
 For open channel flow,on the other hand the flowing liquid has a free surface at
atmospheric pressure and the driving force is gravity.Open channel flow takes place
in natural channels like rivers and streams.
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Figure1.0: Open Channel Flow Examples: A River and an Irrigation Canal
(Artificial Channel)

6. (2) Pipe flow : it is also a conduit
flow having no free surface
Types of flow
two
types
(1) Open channel flow (2) Pipe flow
(1) Open channel Flow : Open
channel flow is a conduit flow
having open surface
Flow
Figr. Pipe Flow
Figr.- Open Channel Flow
Flow
FLOW OFWATER
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The movement of water through conduit
either by the action of gravitational
force or atmospheric pressure or
artificial force or conjugation of all is
called flow of water.

7. DIFFERENCE BETWEEN OPEN CHANNEL FLOW(OCF) AND PIPE
FLOW
Open Channel Flow Pipe Flow
1. .Defines as a passage in which liquid flows
with its upper surface exposed to atmosphere.
1.A pipe is a closed conduit . Pipe has no such
free surface since water must fill the whole
conduit
2.Open channel flow caused by gravitational and
atmospheric pressure
2. No direct atmospheric pressure
but hydraulic pressure only.
3.Hydraulic grade line coincides
with the water surface
3.Hydraulic grade line does not
coincides with the water surface.
4.The maximum velocity occurs
at a little distance below the water surface.
4.The maximum velocity
occurring at the pipe centre. 7

8. Figure : 1 Comparison between pipe flow and open channel flow
1 2
1
V 2 /2g
y1
z1
v1
v2
hf
2
v 2/2g
y2
z2
Datum line
C/L
Figure : 1-1(b) Open channel flow
Figure :1-1(a) Pipe Flow
3
v 2/2g
y
3
z3
hf
4
v 2/2g
y4
z4
Channelbed
v3
v4
Datum line
3
4
Parallel to Datum
DIFFERENCE BETWEEN OPEN CHANNEL FLOW(OCF) AND PIPE
FLOW
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9. DIFFERENCE BETWEEN OPEN CHANNEL FLOW(OCF) AND PIPE
FLOW
5.The shape of the velocity profile is dependent
on the channel roughness
5.Velocity Distribution is symmetrical about
the pipe axis
6.There are variable cross sections and shape-
from circular to the irregular forms of natural
streams.
6.In pipe flow the cross section of flow is fixed,
since it is completely defined by the geometry of
the conduit.
Generally the cross section is round.
7.The roughness in an open channel varies
with the position of the free surface.
7.The roughness in pipes depends on the interior
surface ranges from that of new smooth brass or
wooden-stave pipes, corroded iron or old steel
pipes.
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10. 2.TYPES OF OPEN CHANNEL FLOW
Open channel flow conditions can be characterised with respect to space (uniform or non-uniform flows) and time
(steady or unsteady flows).
 Space - how do the flow conditions change along the reach of an open channel system.
a. Uniform flow - depth of flow is the same at every section of
the flow dy/dx = 0
b. Non-uniform flow - depth of flow varies along the flow dy/dx  0
Time - how do the flow conditions change over time at a specific section in an open channel system.
c. Steady flow - depth of flow does not change/ constant during the
time interval under consideration dy/dt = 0
d. Unsteady flow - depth of flow changes with time dy/dt  0 10

11. Types of Open Channel Flows
a. Uniform flow
b. Non-uniform flow
c. Steady flow
d. Unsteady flow
y
y
y1
y2
y
Time = t1
y
Time = t2
y1
Time = t1
y1
Time = t2
y
t3
t2
t1
y
t3
t2
t1
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12. (2) Unsteady Flow
(2) Non-uniform
flow
(1) Uniform flow
(1)Steady Flow
(2) Rapidly
varied flow
(1) Gradually
varied flow
(1) Rapidly
varied unsteady
flow
(2) Gradually
varied unsteady
flow
(1) Unsteady uniform flow
(2) Unsteady Non-uniform
flow
Classification of open channel flow in a flow diagram
Space as the criteria
Time as the criteria
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13. TYPE OF OPEN CHANNEL FLOW (CONT.)
 The flow is rapidly varied if the depth changes abruptly over a comparatively short distance. Examples
of rapidly varied flow (RVF) are hydraulic jump, hydraulic drop, flow over weir and flow under a sluice
gate.
 The flow is gradually varied if the depth changes slowly over a comparatively long distance. Examples
of gradually varied flow (GVF) are flow over a mild slope and the backing up of flow (backwater).
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14. RVF GVF RVF GVF RVF GVF RVF
Sluice gate
Contraction
below the gate
Hydraulic
jump Flow over Weir
Hydraulic Drop
Bed profile
Varied flow Showing Hydraulic jump and Hydraulic drop
Bed profile
Fig – 1-3(d) : Rapidly
varied flow (RVF)
Depth change rapidly
Weir
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15. The state or behaviour of open-channel flow is governed basically by the viscosity and
gravity effects relative to the inertial forces of the flow.
Effect of viscosity - depending on the effect of viscosity relative to inertial forces, the
flow may be in laminar, turbulent, or transitional state.
- Reynolds number represents the effect of viscosity relative to inertia,
3. STATE OF FLOW

VR
=
Re
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where V is the velocity, R is the hydraulic radius of a conduit and  is the kinematic viscosity (for water
at 20C,  = 1.004  10−6 m2/s, dynamic viscosity  = 1.002  10−3 Ns/m2 and density  = 998.2 kg/m3).

16. Re < 500 , the flow is laminar
500 < Re < 12500, the flow is transitional
Re > 12500 , the flow is turbulent
The flow is laminar if the viscous forces are dominant relative to inertia.
Viscosity will determine the flow behaviour. In laminar flow, water particles
move in definite smooth paths.

VR
=
Re
The flow is turbulent if the inertial forces are dominant than the viscous
force. In turbulent flow, water particles move in irregular paths which are
not smooth.
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17. Effect of gravity - depending on the effect of gravity forces relative to inertial forces, the
flow may be subcritical, critical and supercritical.
- Froude number represents the ratio of inertial forces to gravity forces,
STATE OF FLOW (CONT.)
gD
V
=
Fr
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gD
V 
→
where V is the velocity, D is the hydraulic depth of a conduit and g is the gravity
acceleration (g = 9.81 m/s2).
Fr < 1 , the flow is in subcritical state
Fr = 1 , the flow is in critical state
Fr > 1 , the flow is in supercritical state
gD
V =
→
gD
V 
→

18. A combined effect of viscosity and gravity may produce any one of the following four regimes of
flow in an open channel:
a. subcritical - laminar , when Fr < 1 and Re < 500
b. supercritical - laminar , when Fr > 1 and Re < 500
c. supercritical – turbulent , when Fr > 1 and Re > 12500
d. subcritical - turbulent , when Fr < 1 and Re > 12500
4. REGIMES OF FLOW
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