1.0 INTRODUCTION

An open channel is a waterway, canal or conduit in which a liquid flows with a free

surface. Open channel flow describes the fluid motion in an open channel. In most

applications, the liquid is water and the air above the flow is usually at rest and at standard

atmospheric pressure. In some practical cases the pressure of the air above the flow might

become sub-atmospheric. Next to the free surface of an open channel flow some air is

entrained by friction at the free surface. That is, no slip condition at the air water interface

induces the air motion. The term ‘air boundary layer’ is sometimes used to describe the

atmospheric region where air is entrained through momentum transfer at the free surface.

In open channel flow the free surface is always at a constant absolute pressure and the

driving force of the fluid motion is gravity. In open channels the transition from a rapid flow

to a slow flow is called a hydraulic jump. The transition occurs suddenly and is characterized

by a sudden rise of the liquid surface. The forces acting on a control volume are the

hydrostatic pressure forces at each end of the control volume, the gravity forces, the invert

reaction force and the bottom friction.

Objective for open channel flow :

I. To investigate the characteristic a standing wave ( the hydraulic jump ) produced when

waters beneath an undershot weir and to observe the flow patterns obtained.

II. To understanding the usage of the hydraulics jump.

III. To know the related between upstream and downstream.

IV. To know the related between flow depth below jump and flow depth above jump and

make comprise.

Open channels may be constructed to specified criteria:

as part of the road drainage system where space within the road reserve is sufficient to

provide for open channels.

as diversion channels, especially where the road is being constructed generally along the

line of a watercourse and severs one or more meanders in the stream. Care must be

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exercised as shortening of the stream will increase the gradient and hence velocity, which

may induce scouring and also prevent the upstream passage of fish; and/or

from the outlets of culverts or drainage systems.

Examples of Open Channel Flow Examples of Open Channel Flow :

The natural water drainage through the numerous creek and river systems.

The flow of rainwater in the gutters of our houses.

The flow in canals, drainage ditches, sewers, and gutters along roads.

The flow of small rivulets, and sheets of water across fields or parking lots.

The flow in the chutes of water tides.

Variables in open-channel flows :

Variable.

Bends.

Bottom slope variation.

Character of its bounding surface.

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2.0 STUDY AREA

Information on channel location

- Behind Dewan Tunku Mahkota Ismail (DTMI)

Surrounding environment

Basically we do inside campus near Dewan Tunku Mahkota Ismail (DTMI). Infront there got

PNS building. There surrounded by student who pass by near our location. Beside our

location also there is tree for landscape purposes. There were toilet places behind our location

too.

Channel characteristics

- Depth of flow y – is the vertical measure of water depth

- Normal depth d – is measured normal to the channel bottom.

- Flow or discharge Q – is the volume of fluid passing a cross-section perpendicular to the

direction of flow per unit time.

- Mean velocity V – is the discharge divided by the cross-sectional area.

- Wetted perimeter P – is the length of channel perimeter that is wetted or covered by

flowing water.

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- Hydraulic radius R – is the ratio of the flow area A to wetted perimeter P.

- Hydraulic depth D – is the average depth or irregular cross section.

Energy in a river is determined by three factors:

1. mass of water;

2. height of the river above sea level;

3. gradient of the channel.

Not all energy is available to erode or transport sediment. Friction with the bed and banks and

turbulence reduces energy. The faster the flow of water (velocity), the greater the turbulence.

Water with a more turbulent flow can transport more sediment. Velocity is affected by three

main factors. These are channel slope, the roughness of the channel’s bed and banks and the

cross-section channel shape. The hydraulic radius is the term used to describe the shape of a

channel. It is the ratio between the length of the wetted perimeter and and the cross-section

area.

Example :

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The higher the hydraulic radius the lower the amount of water in contact with the bed and

banks which means there is less friction and water can move at a higher velocity.

Date and time of measurement

- 11TH NOVEMBER 2014

- 11.00 A.M – 11.30 A.M

On-site weather observations

- Cloudy 25˚c

Flow direction

- The flow direction is to Upstream to downstream

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5.0 CONCLUSION

In conclusion, based on the project that our group had done we understand that the flow of

water through canals for irrigation, hydraulic structure. Moreover, we know how to apply

theories of hydraulic, methods and application of hydraulic designs either experimentally or

in actual situation. We can also derive the discharge,Q is the volume of fluid passing a cross-

section perpendicular to the direction of flow per unite time. Whereas the wetted perimeter,P

is the length of channel perimeter that covered by flowing water. Then, the hydraulic radius is

mainly about the ratio of the flow area,A to wetted perimeter,P (R=A/P). On the other hand,

we also can understand about the hydraulic depth which means the average depth of irregular

cross section. Thus, we can apply all he flow parameters and geometric in our actual

situation. We can recommend that the debris around the channel need to clean to make sure

that the flow in normal state and no problem occur when the flow is move. And then the

concrete pavement got some damage around the culvert. For that we need to plastering with

concrete around the culvert to make sure that the flow will be in good state.

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References

- http://www.taiwan921.lib.ntu.edu.tw/mypdf/fluid10.pdf

- http://www.geotalk.info/#!channel-characteristics/caa3

- http://www.alevelgeography.com/?page_id=246

- http://www.acegeography.com/changing-channel-characteristics.html

- http://www.tsaad.net/docs/T.Saad%20-%20Open%20Channel%20Flow

%20(February2004).pdf

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