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ENDORESMENT

TABLE OF CONTENT

Title Page

1.

FLOW OVER A SHARP CRESTED WEIR

Introduction

2

2. Objective 2

3. Apparatus 2

4. Procedure 2

5. Result 3

6.

FLOW OVER A VENTURI

Introduction

4

7. Objective 4

8. Apparatus 4

9. Procedure 5

10 Result 6

11

.

Discussion/Analysis 7-16

12.

Conclusion 17-21

13

.

References & Appendices 22

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3/23

FLOW OVER A SHARP CRESTED WEIR

INTRODUCTION

The sharp crested weir is frequently used as a device for measuring discharge in a

channel. It is simple to install and provided that it conforms to prescribe requirement, it

may be used with confident in conjunction with standard calibration data. In this

experiment, establish the relationship between head over the weir and discharge.

OBJECTIVE

To establish relationship between head over the weir for a sharp crested weir

APPARATUS

Sharp crested weir with air vent

Dial Vernier depth gauge

Steel rule

Stop watch

PROCEDURE

1. Setting the channel horizontal using screw jack checked by depth gauges at both end.

2. Measure height of weir by steel rule.

3. Place weir vertically in the channel approximately 0.5m upstream of the outlet.

4. Rest a depth gauge on the weir crest and use the reading as references.

5. Admit water to the channel using control valve until a convenient maximum flow is

obtained.

6. The discharge is then measured by timing collection of a know weight of the water.

7. During the timed interval, the head over the weir is measured using the depth gauge at

distance of 0.3m upstream of the weir.

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4/23

8. The flow is then reduced in stages where the discharge rate and the head above the

weir is measured at each stages with weir head ranging from 50mm to 25mm

RESULT

Height of crest above channel bed, a = 50 mmWidth of channel, B = 75 mm

Head, H

(mm)

Weight of

Water (kgf)

Time (s) Discharge

(L/s)

C H/a

24 15 21 0.714 0.053 0.48

30 15 14 1.071 0.067 0.60

40 15 10 1.500 0.076 0.80

52 15 8 1.875 0.078 1.04

53 15 7 2.143 0.088 1.06

C = Q

2/3 x B x (2gh3/2)1/2

= 1.071

2/3 x 75 x (2x9.81x243/2)1/2

= 0.067

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5/23

FLOW OVER A VENTURI

INTRODUCTION

The Venturi flume is formed by a smooth contraction in the cross-section of a channel,

along which the accelerates to a throat, followed by a smooth expansion back to the

original cross-section. In the expanding section the water may continues to accelerate n a

supercritical flow in the expanding section, the condition at the throat must be critical.

This feature permits the flume to be used as measuring device needing only measurement

of head to obtain the discharge. Compared with the weir it is usually more expensive tobuild, but it has advantages of utilizing a lower head than required by a weir and of being

effectively self-cleaning.

OBJECTIVE

To observe the use of the venture flume as a measuring device through measurement of

upstream head to obtained discharge.

APPARATUS

1) Venturi flume

2) Depth gauge

3) Internal caliper

4) Steel rule

5) Pitot tube

6) Sluice gate

7) Stop watch

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6/23

PROCEDURES

1) One set channel for a mild slope of 1/1500

2) Venturi Flume must be set carefully in position at a station approximately 2 meter

upstream of the outlet from the channel

3) The leading edge of the contraction must be place at convenient point of the scale

4) Measure the throat of the flume and the width of the channel

5) Set depth gauge so that it reads zero just as it touches the channel bed

6) The pitot tube must be set so that the division which are marked at 10mm

intervals represent 10mm step from the channel bed

7) Water must be fill into the channel by opening the control valve and observe the

flow through the flume

8) Reducing the sluice gate opening at the outlet, observe the following, a standing

wave is produced between the Venturi Flume outlet and the sluice gate. When the

standing wave advances to the throat, the flow there ceases to be critical and the

upstream level will then rise

9) The experiment must be start with the maximum flow, collect the discharge of

supercritical flow over a timed interval and measure the depth at a point 0.3m

upstream10) Reduce the flow in steps and time the collected discharge and depth at 0.3m

upstream

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7/23

RESULT

Width of channel, B = 75 mm

Width of Venturi flume throat, Bc = 49 mm

Depth

Upstream,y1(mm)

Weight

Collected,W (kgf)

Time, T

(s)

Discharge,

Q (L/s)

Velocity

Upstream,V1 ,

(10-4m/s)

Specific

Energy, E(mm)

C

20 15 22 0.6818 1.818 20 0.079

30 15 14 1.0714 4.290 30 0.095

40 15 10 1.5000 8.000 40 0.110

50 15 8 1.8750 12.000 50 0.118

55 15 7 2.1429 15.710 55 0.127

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8/23

DISCUSSION/ANALYSIS

NAME: MOHD FARID BIN JAAFAR

ID NUMBER: AB05019

Sharp Crested Weir

The experiment objective is to establish the relationship between head over the

weir and discharge for a sharp crested weir. An open channel is conduit in which water

flows with a free surface. The classification of open channel flow is made according to

the change in flow respect to time and space. Open channel flow is uniform if the depth

of flow is the same at every section of the channel.

The discharge, Q in L/s is obtained simply by dividing W in kgf by t in s, since

the weight of one liter of water is one kgf. To obtain the value C, we see that:

C = Q

2/3 x B x (2gh3/2)1/2

In this test, we get the graph specific energy against discharge. From the graph

specific energy against discharge that we had plotted, we get the straight line. If the

specific energy increases, the discharge also increases. Specific energy and discharge are

related each other in this experiment to measuring the flow in the open channel.

The head over the weir directly proportional with the discharge of water. If the head

over the weir is high, the discharge of water also high. This maybe happens because

when the discharge of water is high, the water friction at the sharp crested weir is high

and that why the head of over weir is also high.

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9/23

When carry out this experiment there will have any mistake and this can affect the

result, for example:

- Mistake while use the stop watch.

- Mistake while take a reading

- Error while take the level of water

This mistake or error maybe cause the result we get not accuracy. Use the good

condition of all apparatus also can give the accuracy result.

Venturi Flume

The Venturi Flume is formed by a smooth contraction in the cross-section of a

channel, along which the water accelerates to a throat, followed by a smooth expansion

back to accelerate in a supercritical flow, or it decelerate in a subcritical flow. In this case

the velocity upstream V1 is obtained simply by dividing Q by the cross sectional area of

the flow upstream, and to obtain the results in m/s we use SI units.

The objective of this experiment is to observe the use of the venturi flume as a

measuring device through measurement of the upstream head to obtained discharge. Its

because when the discharge of water is high, the water friction at the venturi is highbecause the area of channel is change from big to small.

We also get a good result for this test. From the graph upstream depth against

discharge, we get the straight line. When the upstream depth increases, the discharge also

increases. Flumes are usually designed to achieve critical depth in the narrowest section

(the throat) while also giving a very small afflux.

We have a several suggestions to improve this experiment. The suggestions are:

1. Weirs are often seen used in clarifiers, grit chambers and other treatment

plant units to reduce velocity or control depth in the unit.

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10/23

2. Water flowing over any weir must fall free of the weir plate (not dribble

down the side) for good accuracy. If it doesnt fall free, a weir with smaller

notch should be used.

3. They can be permanently installed, but solids carried by the water will

catch on the lip or V notch and decrease measurement accuracy. Frequent

maintenance must be planned where weirs are in used.

Water flowing over a V notch weir must stay within the notch for accurate measurement.

If it doesnt, a larger V notch or a rectangular weir should be used.

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11/23

NAME: MUHAMAD AIZAT BIN LENGAH

ID NUMBER: AB05030

An open channel is conduit in which water flows with a free surface. The

classification of open channel flow is made according to the change in flow respect to

time and space. Open channel flow is uniform if the depth of flow is the same at every

section of the channel. A uniform flow may theoretically be steady or unsteady,

depending on whether or not the depth changes with time.

OPEN CHANNEL: Flow over a Sharp Crested Weir

In this test, we get a good result because the graph is a straight line.

From the graph head against discharge that we had plotted, we get the straight line

and across the point.

If the head increases, the discharge also increases.

So, the specific energy and discharge are related to measuring the flow.

OPEN CHANNEL: Flow over a Venturi Flume

This test also is a straight line.

From the graph specific energy against discharge, we also get the straight line.

If the specific energy increases, the discharge also increases.

Flumes are usually designed to achieve critical depth in the narrowest section (the

throat) while also giving a very small afflux.

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12/23

NAME: MOHD FARHAN IZZAUDDEN BIN ABU TAIB

ID NUMBER: AB05073

From our observation, with the open channel system test we found that we that

there have a hydraulic jump happen in the tank. Hydraulic jump is the most commonly

encountered varied flow phenomenon in an open channel in which a rapid change occurs

from a high velocity low depth super critical state of flow to a low velocity large depth

subcritical state. The flow of water in an open channel is a familiar sight, whether in a

natural channel like that of a river, or an artificial channel like that of an irrigation ditch.

Its movment is a difficult problem when everything is considered, especially with the

variability of natural channels, but in many cases the major features can be expressed in

terms of only a few variables, whose behavior can be described adequately by a simpletheory. The principal forces at work are those of inertia, gravity and viscosity, each of

which plays an important role.

Actually the hydraulic jump can happen in so many ways such as :

a)At the foot of an overflow spillway dam

b)Behind a dam on a steep slope

c)Below a regulating sluice

d)When a steep slope channel suddenly turns flat.

Open channel flow is defined as flow in any channel where the liquid flows with a

free surface. Open channel flow is not under pressure; gravity is the only force that can

cause flow in open channels and a progressive decline in water surface elevation always

occurs as the flow moves downstream (BOR, 1997). Examples of open channel flow at

mine sites include: rivers, streams, creeks, discharges from tailings ponds, and other

uncovered conduits. Closed channels, such as adits, tunnels, and ventilation shafts, can betreated as open channels when flowing partially full and not under pressure.

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13/23

Open channel flow occurs under one of three possible flow conditions: sub-

critical; critical; or super-critical. Three basic relationships govern open channel flow:

the continuity equation, the momentum equation, and the energy equation. Each of the

relationships is briefly described in the following sub-sections. The reader is

encouraged to consult some of the hydrology and hydraulic engineering texts listed in

the reference section for more information.

We found that the hydraulic jump have some uses in our life :

1. To dissipate excessive energy.

2. To increase the water level on the downstream side.

3. To reduce the net uplift force by increasing the weight, i.e., due toincreased depth.

4. To increase the discharge from a sluice gate by increasing the effective

head causing flow.

5. To Provide a control section.

6. For thorough mixing of chemicals in water.

7. For aeration of drinking water.

8. For removing air pockets in a pipe line

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14/23

NAME: AMRYANA BINTI POHAN

ID NUMBER: AB05004

Open channel flow is defined as flow in any channel where the liquid flows with a

free surface. Open channel flow is not under pressure; gravity is the only force

that can cause flow in open channels and a progressive decline in water surface

elevation always occurs as the flow moves downstream.

Examples of open channel flow at mine sites include: rivers, streams, creeks,

discharges from tailings ponds, and other uncovered conduits. Closed channels,

such as adits, tunnels, and ventilation shafts, can be treated as open channels when

flowing partially full and not under pressure.

Flume

Flumes are used to measure flowrate (discharge) in open channels. Flumes,

compared to weirs, have the advantage of less head loss through the device, yet

are more complicated to construct and more difficult to analyze.

Head is measured in the flume upstream of the throat - in the so-called "approach

channel". For Parshall flumes, head is measured upstream from the throat adistance of 2/3 of the length of the approach channel (x=length of approach

channel in the above diagram). For the other three flumes, head is measured

upstream from the throat a distance of 3 to 4 times the maximum expected head.

This location is somewhat arbitrary because the head does not vary too much with

position, so the exact location of the head measurement is not as important as for

a Parshall flume. Since the rectangular, trapezoidal, and U flumes can have a

raised throat (a hump), it is important to note that head is measured from the top

of the hump rather than from the bottom of the approach channel

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15/23

Weir

Weirs are typically installed in open channels such as streams to determine discharge

(flowrate). The basic principle is that discharge is directly related to the water depth

(h) in the figure above; h is known as the "head." Rectangular weirs can be

"suppressed," "partially contracted," or "fully contracted." Suppressed means there

are no contractions. A suppressed weir's notch width (b) is equal to the channel width

(B); thus, there really isn't a notch - the weir is flat all the way along the top. For a

weir to be fully contracted, (B-b) must be greater than 4hmax, where hmax is the

maximum expected head on the weir. A partially contracted weir has B-b between 0

and 4hmax. Weir contractions cause the water flow lines to converge through the

notch.

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16/23

Effective use of water for crop irrigation requires that flow rates and volumes be

measured and expressed quantitatively. Measurement of flow rates in open channels

is difficult because of non uniform channel dimensions and variations in velocities

across the channel. Weirs allow water to be routed through a structure of known

dimensions, permitting flow rates to be measured as a function of depth of flow

through the structure. Thus, one of the simplest and most accurate methods of

measuring water flow in open channels is by the use of weirs.

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17/23

NAME: NUR FAREZZA BINTI JASMI

ID NUMBER: AB05047

The experiment objective is to establish the relationship between head over the

weir and discharge for a sharp crested weir.

In this experiment, we can prove the objective. The head over the weir directly

proportional with the discharge of water.

A uniform flow may theoretically be steady or unsteady, depending on whether or

not the depth changes with time.

An open channel is conduit in which water flows with a free surface. The

classification of open channel flow is made according to the change in flow respect to

time and space.

A uniform flow may theoretically be steady or unsteady, depending on whether or

not the depth changes with time. The establishment of unsteady uniform flow requires

that the water surface fluctuate with time while remaining parallel to the channel bottom.

Since it is impossible for this condition to occur within a channel, steady uniform

flows are the fundamental type of flow treated in open channel hydraulics.

Figure 1 . The most common types of sharp-crested weirs are rectangular, trapezoidal(Cipolletti), and 90? V-notch weirs. These are shown in Figure 2

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18/23

CONCLUSION

NAME: MOHD FARID BIN JAAFAR

ID NUMBER: AB05019

Sharp Crested Weir

The objective given are achieve and we make this experiment is successfully. In

this experiment, we know the relationship between head over weir with discharge of

water and can prove the objective of test. From the graph we plot, all the graph we get is

a straight line. From the result we get, the value of the time to full 5 liter water increased

when the depth decreased. So, with doing this experiment, we can learn in more about

open channel and how to apply in civil engineering field. This experiment is also

important in the hydraulics construction such as dam, canal and others. This experiment

used to know the characteristic of the construction.

Venturi Flume

We do this experiment successfully. We achieve the objective this test accurately.

This experiment is also important in the construction field. After do this experiment, we

can prove the objective of test and know the relationship between upstream head with

discharge of water. This experiment is also important to know the high of the head must

be design before make the dam. This also can apply to the construction of the drainage

for the area always happen flood.

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19/23

NAME: MUHAMAD AIZAT BIN LENGAH

ID NUMBER: AB05030

OPEN CHANNEL: Flow over a Sharp Crested Weir

After do this experiment, we can prove the objective of test and know the

relationship between head over weir with discharge of water. This experiment is also

important in the construction field. For example in the hydro construction such as dam,

.canal and others. This experiment used to design the type of this construction

OPEN CHANNEL: Flow over a Venturi Flume

After do this experiment, we can prove the objective of test and know the

relationship between upstream head with discharge of water. This experiment is also

important in the construction field.

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20/23

NAME: MOHD FARHAN IZZAUDDEN BIN ABU TAIB

ID NUMBER: AB05073

As a conclusion, we found that the Open-channel flows are a special class of

boundary-layer flows that are confined to a channel form. There are some point that we

can says Why are open-channel flows important?

1 - Many natural systems responsible for the transport of sediment are channelized,

2 in both subaerial and subaqueous environments.

3 - Nearly all of the modeling performed on the entrainment and transport of

4 sediment is either in open channels or in 1-D boundary layers.

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21/23

NAME: AMRYANA BINTI POHAN

ID NUMBER: AB05004

As a conclusion, these tests were important to examine the fundamental

characteristics of flow over two sharp-crested weirs and to measure the coefficient

discharge values. It is also important to determine the relationship between upstream

head and flow-rate for water flowing over a sharp crested weir and to calculate the

discharge coefficient and to observe the flow patterns obtained.

Weirs provide a simple and accurate method of measuring flow rates in open

channels. Rectangular, Cipolletti, and 90 V-notch weirs were described, and calibration

tables were given for each. Also, procedures for the construction and placement of weirs

to ensure greatest accuracy were discussed.

A venturi flume has a special shaped open channel flow section which may be

installed in a ditch, canal, or lateral to measure the flow rate. The Parshall flume is a

particular form of venturi flume.

Types of flumes:

Parshall

Palmer-Bowlus Trapezoidal

HS/H/HL-Type

Cutthroat

RBC

Montana

SANIIRI

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22/23

NAME: NUR FAREZZA BINTI JASMI

ID NUMBER: AB05047

In this experiment, we know the relationship between head over weir withdischarge of water and can prove the objective of test.

This experiment is also important in the construction. For example in the hydro

construction such as dam, canal and others. This experiment used to know the

characteristic of the construction

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23/23

REFERENCES & APPENDICES

http://www.engineering.usu.edu/classes/cee/3500/openchannel.htmhttp://www.fluent.com/solutions/examples/x172.htm

http://herkules.oulu.fi/isbn9514259777/html/chapter3_4.html

http://www.jfccivilengineer.com/broad_crested_weir.htm

From books:

Engineering Laboratory Manual: Hydraulic& Hydrology Laboratory: OpenChannel
http://www.engineering.usu.edu/classes/cee/3500/openchannel.htmhttp://www.fluent.com/solutions/examples/x172.htmhttp://herkules.oulu.fi/isbn9514259777/html/chapter3_4.htmlhttp://www.jfccivilengineer.com/broad_crested_weir.htmhttp://www.engineering.usu.edu/classes/cee/3500/openchannel.htmhttp://www.fluent.com/solutions/examples/x172.htmhttp://herkules.oulu.fi/isbn9514259777/html/chapter3_4.htmlhttp://www.jfccivilengineer.com/broad_crested_weir.htm

10.open channel

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