This document describes an experiment to observe changes in a free water surface when subjected to changes in an open channel bed. Students will measure water surface elevations upstream, above, and downstream of an obstruction in the channel for two different flow rates. They will analyze the data by plotting water surface profiles and constructing specific energy diagrams to compare theoretical and experimental results. The goal is to comment on flow behavior for different situations and analyze how the water surface might differ if flow entered the obstruction supercritically rather than subcritically.

1. SPECIFIC ENERGY

2. WE ARE BOISHAK
 Md. Rafuqul Islam
ID : CEN-00505242
 Md. Ridwan Ali
ID : CEN-00505243
 Md. Rakibul Hasan Bhuiyan
ID : CEN-00505244
 Imtiajul Islam
ID : CEN-00505252
 Nasmin Akter
ID : CEN-00505213
 Md. Alauddin Masud
ID : CEN-00505225

3. Objective
To observ the changes in the
behaivor of the free surface when
subjected to change in the channel
bed.

4. Principle
2
2
1
2
22 












g
V
yz
g
V
yz 2
22
22 gy
q
y
g
V
yH 
zHH  21

5. Principle
2
2
2gy
q
yH 
zHH  21

6. Apparatus-Flume
hQ  04.2

7. Apparatus - Obstruction
7.786.965.875
0.24
ybump (ft)
x (ft)
For x 5 ybump = 0
For 5 < x 5.87 ybump = 0.276x – 1.38
For 5.87 < x 6.96 ybump = 0.24
For 6.96 < x 7.78 ybump = 2.28 - 0.293x
For x > 7.78 ybump = 0

8. What are we going to do?
We are going to measure the water
surface elevation along a open channel.

9. Procedures
 Establish a stabilized discharge in the system
 Measrure the water level difference on the
differential manometer for computing discharge.
 Measure the water surface elevation upsttrpeateam,
above and downstream of the obstruction.
 Change the flow rate and repeat step 2 and 3 for
another flow condition.
 Observe the ripples formed at the tip of the point
gage.

10. Data Sheet
Flow Situation I Flow Situation II
h = (ft); Q = (cfs); yc1 = (ft) h = (ft); Q = (cfs); yc1 = (ft)
Track
(ft)
Water
Surface
Elevation
(ft)
Bump
Geome
try (ft)
Actual
depth
(ft)
Track
(ft)
Water
Surface
Elevation
(ft)
Bump
Geome
try (ft)
Actual
depth
(ft)

11. Analysis
 Plot the water surface elevation in the vicinity
of the channel transition.
 Construct the specific energy diagram using
the measured data.
 Compare theoretical specific energy diagrams
with the experimental curves.
 Comment on the flow behavior in the two flow
situation.

12. Sample Result – water surface
profile.
Waterelevationthroughchanneltransition
Flumetrack(m)
Flowdepth(m)
11.711.811.912.012.112.212.312.412.512.612.712.812.913.013.113.213.3
0.00
0.05
0.10
0.15
0.20
ycy1
y2
Measurementsq2
>q1
Channelbed
Measurementsq1

13. Sample Result – Specific Energy
Diagram.
Depth(m)
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0.18
0.20
yc
(unit discharge) =0.057m
yc(data) =0.056m
y1 ( subcr it ical)
y2 ( super cr it ical)
Measurements q2 >q1
Theoretical diagram q2
Theoretical diagram q1
Measurements q1
Specific energy diagram

14. Further Considerations
 What are the main assumption associated with
the use of the specific energy diagram?
 Comment on the differences noticed on the
ripples produced by the point gage upstream
and downstream the obstruction.
 Analyze the water surface behavior for the
same unit discharge used in your experiment
hypothesizing the flow enters in the
obstruction as supercritical flow.

15. THANK YOU