Uniform Flow in Open Channel

1. HYDRAULICS
UNIFORM FLOW IN OPEN CHANNELS
By
Erni Syuhada Bt Mazwil Ishan

2. HYDRAULICS ENGINEERING
• A scientific fluid flow particularly in water
thoroughly in pipe, open channel, orifice and
embankment, including the problem related
to energy and pressure.
• Related to water or fluid in dynamic condition.

3. CONTENT
 What is Open Channel
 Types of Open Channel
Types of flowing water and control
Solution of uniform flow in Open Channel

4. OPEN CHANNEL
An open channel :
a)The stream not completely enclosed by solid
boundaries
b)It has free surface subjected only to
atmospheric pressure.
c)Referred as free-surface flow or gravity flow

5. Open Channel
TYPES OF OPEN CHANNEL
Natural Channel
Irregular shape
i.e : river, hillsides
rivulets, tidal etuaries
Artificial Channel
Regular shape
i.e : drains, culverts,
sewer, tunnels

6. TYPES OF OPEN CHANNEL

7. TYPES OF FLOWING WATER AND ITS
CONTROL
Rapidly
Varied Flow
i.e : hydraulic
jump
Non-Uniform Flow
≠ 0
Uniform Flow
= 0
Gradually
Varied flow
i.e : upstream
of obstruction
Open
Channel
Steady Flow
= 0
Open Channel
Unsteady Flow
≠ 0

8. TYPES OF FLOWING WATER AND ITS
CONTROL
Steady
• y (depth of water) and v (velocity) remain constant
with respect to time
Unsteady Flow
• y and v change with time

9. TYPES OF FLOWING WATER AND ITS
CONTROL
Uniform
• y (depth of water) and v (velocity) remain constant
along the channel. Figure 2.0
Non - uniform Flow
• y and v change along the length of the
channel
Figure 2.0

10. • Flow Classifications
1) Depending on the Reynolds number, Re
– Laminar Flow (if Re < 500): very slow and shallow
flowing water in very smooth open channels.
– Turbulent Flow (if Re > 1000): ordinary flow in
ordinary open channels.
– Transition Flow (if 500 < Re < 1000)
TYPES OF FLOWING WATER AND ITS
CONTROL
V = average channel velocity
L = length of channel
v = kinematic viscosity of fluid

11. 2) Depending on Froude number, Fr
– Fr = 1 : Critical Flow
– Fr < 1 : Subcritical Flow – slow flowing water
– Fr > 1 : Supercritical Flow – fast flowing water
TYPES OF FLOWING WATER AND ITS
CONTROL
V = average channel velocity
g = gravity acceralation
D = hydraulics water depth

12. TURBULENT
LAMINAR

15. TYPES OF FLOWING WATER AND ITS
CONTROL
Critical Section (In uniform and non-uniform flow)
1) If So < Sc, y > yc : Subcritical flow
2) If So = Sc, y = yc : Critical flow
3) If So > Sc, y < yc : Supercritical flow
Figure 3.0

16. Bernoulli’s Equation
Lhz
g
Vp
z
g
Vp
+++=++ 2
2
22
1
2
11
22 γγ

17. Open Channel
GEOMETRIC PROPERTIES OF OPEN
CHANNELS
RECTANGULAR CHANNEL TRAPEZOIDAL CHANNEL

18. • The terminology of geometric elements
y : depth of flow T : top width b : bottom channel width
m : side slope So : channel bottom slope v : average flow density
Fr : Froude number Re : Reynold number L : length of channel
Q : flow rates , Q = AV A : area of the flow P : wetted perimeter
R: hydraulic radius at cross
section
D : hydraulics water depth V : volume
ν : velocity E : specific energy ∆z : weir height
θ : flow temperature q = discharge over width
(m)
GEOMETRIC PROPERTIES OF OPEN
CHANNELS

19. Type of
channel
TOP WIDTH,
T
AREA, A WETTED
PERIMETER, P
RECTANGULAR B By B + 2y
TRAPEZOIDAL B+2my By + my2
B+2y √ 1+m2
GEOMETRIC PROPERTIES OF OPEN
CHANNELS
Where,

20. UNIFORM FLOW IN OPEN CHANNEL
Uniform flow is an equilibrium condition that flow
tends to if the channel :
a)constant slope
b)constant cross section
c)constant roughness
d)depth, water area, velocity and discharge at every
section of channel are constant
e)channel bed, water surface and energy line are
parallel, So = Sw = S
f)y1 = y2 , V1 = V2

21. • CHEZY FORMULA :
UNIFORM FLOW IN OPEN CHANNEL
Where ; V = mean velocity (m/s)
C = Chezy’s factor of flow resistance (m1/2
/s)
R = hydraulic radius
So = slope of energy line
Q = Discharge (m3
/s)
• MANNING FORMULA :
Where ; V = mean velocity (m/s)
n = Manning’s coefficient of roughness (s/m1/3
)
R = hydraulic radius
So = slope of energy line
Q = Discharge (m3
/s)

22. UNIFORM FLOW IN OPEN CHANNEL
Closed conduits flowing partly full
Corrugated metal storm drains 0.010
Concrete culvert 0.024
Unfinished concrete 0.013
Clay drain tile 0.014
Lined or built up channels
Unpainted steel 0.012
Planed wood 0.012
Unplaned wood 0.013
Trowel – finished concrete 0.013
Rough concrete 0.017
Glazed brick 0.020
Brick in cement mortar 0.013
Excavated channels
Clean earth (straight channel) 0.022
Earth with weeds (winding channel) 0.030
Natural streams
Clean and straight 0.030
Weedy reaches, deep pools 0.100
Typical values of Manning’s coefficient, n

23. SOLUTION IN OPEN CHANNEL
• Conveyor Factor
From eq
We obtain ;
For Chezy
For Manning

24. • Section Factor, Z
For Chezy ;
For Manning;
SOLUTION IN OPEN CHANNEL
• Thus, normal depth, yo can be obtain by using
trial and error method

25. SOLUTION IN OPEN CHANNEL
• Example :
Given trapezoidal channel 10m wide with side
slope of 1:1.5. Bed slope is 0.0003. The
channel with concrete lining, n = 0.012.
Calculate the velocity, V and flow rate, Q
when the flow depth is 3.0m. If the flow rate
is 50m/s, determine the slope, So of channel.