hydraulics and irrigation engineering lab...

Lab Manual Book

HYDRAULICS AND IRRIGATION ENGINEERING

NAME OF STUDENT

REGISTRATION #

SECTION

INSTRUCTOR’S NAME

CIVIL ENGINEERING DEPARTMENT

Hydraulics and Irrigation Engineering Lab Manual

THE UNIVERSITY OF LAHORE

LIST OF EXPERIMENTS

1. To establish steady uniform flow conditions in the laboratory flume and to determine Chezy’s coefficient “C” and Manning’s roughness coefficient “n”.

2. To investigate the relationship between specific energy (E) and depth of flow (Y) in a rectangular channel.

3. To study the flow characteristics over a hump/weir.

4. To study the characteristics of hydraulic jump developed in the laboratory flume.

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PREFACE

This Laboratory Manual is intended to provide undergraduate engineering students an understanding of the basic principles of Hydraulics and Irrigation Engineering and its machinery covering all experiments related to the final year level of the B.Sc. Civil Engineering.

In this text, related theory is discussed with help of the photographs of apparatuses and machines to quickly grasp the basic concepts .To further elaborate the theory, blank spaces are provided for observations. It also contains brief procedure for the experiment, precautions, self-explanatory table of observations and calculations, blanks spaces for writing results and finally comments on the results. As practiced university, SI units are also used in this manual .However, wherever felt necessary, values in alternate units are also provided to facilitate students.

In this Laboratory manually, totally four experiment are covered. Experiment number 1 is to determine Manning’s roughness coefficient ‘n’ and Chezy’s coefficient ‘c’ in a laboratory flume. Experiment number 2 refers to investigate the relationship between specific energy and depth of flow, experiment number 3 is to study the flow characteristics over a hump/weir and experiment number 4 is to study the flow characteristics of hydraulic jump developed in the laboratory flume.

Any comments/ suggestions by the teachers / students will be highly appreciated.

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ACKNOWLEDGEMENT

We would like to thank CH. Karamat Ali (Assistant Professor), Head of Water Sector and Prof. Dr. Zulfiqar Ali Khan, Head of Civil Engineering Department, The University of Lahore for reviewing the manuscript and offering many helpful suggestions for the manual in particular and many other colleagues and students in general.

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EXPERIMENT NO. 1

To Determine Manning’s Roughness Coefficient ‘n’ And Chezy’s Coefficient ‘c’ in a Laboratory Flume

OBJECTIVES:

Physical measurement of n & c. To study the variation of n & c as a function of velocity of flow in the flume. To investigate the relationship between n & c.

APPARATUS:

(S-6) glass sided tilting Flume with manometer, slope adjusting scale and flow arrangement

Hook/Point gauge (to measure depth of water)

Figure 1.1: Flume Apparatus

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RELATED THEORY:

FLUME:

Laboratory Open channel supported above the ground/ elevated open channel. TYPES OF FLUME:

According to shape, Flume may have following types. Rectangular Flume Trapezoidal Flume U Flume Parshall Flume

Figure 1.2: Different types of Flume

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S6 (GLASS SIDED) TILTING FLUME APPARATUS:

A glass sided tilting flume apparatus is fabricated with stainless steel with manometric flow arrangement and slope adjusting scale which use in laboratory to perform the various experiments. It is a function of the shape of the pipe, channel, or river in which the water is flowing. Our laboratory flume is 0.3 m wide, 0.45 m deep with working length of 4.30 m.

HOOK/POINT GAUGE:

It is used to measure the depth of flowing flow in tilting flume at different points of section.

UNIFORM FLOW:

A uniform flow is one in which flow parameters and channel parameters remain same with respect to distance between two sections. This flow is only possible in prismatic flow.

NON UNIFORM FLOW:

A uniform flow is one in which flow parameters and channel parameters do not remain same with respect to distance between two sections. This flow is not possible in prismatic flow.

STEADY FLOW:

A steady flow is one in which the conditions (velocity, pressure and cross-section) may differ from point to point but do not change with time.

UNSTEADY FLOW:

A steady flow is one in which the conditions (velocity, pressure and cross-section) may differ from point to point but change with time.

STEADY UNIFORM FLOW:

Conditions do not change with position or with time in the stream. An example is the flow of water in a pipe of constant diameter at constant velocity.

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STEADY NON UNIFORM FLOW:

Conditions change from point to point in the stream but do not change with time. An example is flow in a tapering pipe with constant velocity at the inlet – velocity will change as you move along the length of the pipe towards the exit.

Figure 1.3: Tapering Pipe

UN STEADY UNIFORM FLOW:

At a given instant in time the conditions at every point are the same, but will change with time. An example is a pipe of constant diameter connected to a pump pumping at a constant rate which is then switched off.

UNSTEADY NON-UNIFORM FLOW:

Every condition of the flow may change from point to point and with time at every point. For example waves in a channel.

MANNING’S ROUGHNESS FORMULA:

The Manning formula states that:

WHERE,

Q is the flow [L3/T]

V is the cross-sectional average velocity [L/T]

K is a conversion factor which is 1 in SI units.

n is the Manning coefficient (also called as resistance to flow).

R is the hydraulic radius [L]

S is the slope of the water surface or the linear hydraulic head loss.

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HYDRAULICS RADIUS:

The hydraulic radius is a measure of channel flow efficiency.

WHERE,

Rh is the hydraulic radius [L]

A is the cross sectional area of flow (A= B*y). [L2]

P is wetted perimeter and is equal to B+2y. [L]

Figure 1.4: Channel dimensions

The greater the hydraulic radius, the greater the efficiency of the channel.

The hydraulic radius is greater for the deeper channels.

CHEZY’S FORMULA:The Chezy’s formula states that:

FLOW RATE (DISCHARGE):

It is the amount of water in m3 passing in one second from a point.

Q= kA√ (2g∆h)

Where,

K = roughness coefficient and here its value is 1.2

∆h = h1 – h2 [L]

h1 = head of water in one limb of the pressure tube. (It’s a greater value). [L]

h2 = head of water in other limb of the pressure tube. (It’s a lesser value). [L]

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RELATIONSHIP BETWEEN ‘n’ & ‘c’:

V = C√RS , V =

1n R2/3S1/2

Comparing these equations………..

C√RS =

1n R2/3S1/2

C=

1n

. R2/3 .S1/2

R1/2. S1/2

C =1nR1/6

PROCEDURE:

Set a particular slope of the flume. Start the pump; allow the flow in the flume to be stabilized. Determine the flow rate in the flume. Take three readings of depth of flow in flume at different points and average it for a

particular flow rate in the flume. Change the flow rate through the flume. Again allow the flow in the flume to be stabilized. Again take three readings of depth of flow in flume at different points and average it. Repeat the whole procedure (at least 5 readings) for different discharges in the flume.

PRECAUTIONS:

Depth of flow should be measure at stabilized flow. Slope in flume should be constant. In the absence of point gauge, if depth of flow is being measured with scale, then it

should be placed at 900 angles with respect to the base of flume. There should be no leakage of water from flume body while water is flowing.

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OBSERVATIONS AND CALCULATIONS:

Flume width = B = ----------- m

Value of k to find the Q = ----------

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Sr. #

Bed slope(S)

Rise of water in tubes and their difference (m)

Average Depth of flowY= (Y1+Y2+Y3)/3

(m)

Wetted Perimeter P=B+2Y

(m)

Area of flow

A= (B*Y)(m2)

Hydraulic

mean Radius

R= A/P(m)

Flow rateQ=

kA√(2g∆h)(m3/sec)

Manning’sConstant

n= AR2/3S1/2/Q

Chezy’s Constant

c=R1/6/n

h1 h2 ∆h Y1 Y2 Y3 Y

1

2

3

4

5


GRAPHICAL REPRESENTATION:

a) Graph between Q and n

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(b) Graph between Q and C

(c) Graph between n and C

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RESULTS:

COMMENTS:

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gv

yE2

2


EXPERIMENT NO. 2

TO INVESTIGATE THE RELATIONSHIP BETWEEN SPECIFIC ENERGY (E) AND

DEPTH OF FLOW (Y)

OBJECTIVES:

To study the variations in specific energy as a function of depth of flow for a given discharge in the laboratory flume.

To plot E-Y diagram for a given discharge in the channel.

APPARATUS:



RELATED THEORY:

SPECIFIC ENERGY:

The specific energy (E) is the total energy per unit weight measured relative to the channel bed, and it is given by the sum of the depth and velocity head (assuming small bed slope and a kinetic energy correction factor of 1)

Figure 2.1: Energy Diagram

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ASSUMPTIONS:Following assumptions are being done.

Normal flow conditions exist in channel. ( Steady uniform flow )

Velocity correction factor ( α = 1 )

Bed Slope is very small. ( Practically S < 1: 10 )

Hence, the specific energy is constant along the channel having uniform flow conditions, but it varies for non-uniform flow conditions.

SPECIFIC ENERGY DIAGRAM:

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It is a plot between specific energy as a function of depth of flow.

Figure 2.2: Specific Energy DiagramBASIC TERMINOLOGY:

CRITICAL FLOW:

It is the flow that occurs when the specific energy is minimal for a given discharge. (Fr = 1)It can be seen in Fig. that a point will be reached where the specific energy is minimum and only a single depth occurs. At this point, the flow is termed as critical flow.

SUPER CRITICAL FLOW:

The flow for which the depth is less than critical is (velocity is greater than critical) is termed as supercritical flow. (Fr > 1)

SUB CRITICAL FLOW:

Flow with low velocity and larger depth. (Fr < 1)

FROUD NO:

It is the ratio of the inertial forces to the gravitational forces.Where, v = velocity of flow y = depth of flow

CRITICAL DEPTH:

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The depth of flow of water at which the specific energy is a minimum is called critical depth.

CRITICAL VELOCITY:

The velocity of flow at the critical depth is known as critical velocity.

FIGURE 2.3: SUPER AND SUB

MINMUM SPECIFIC ENERGY:

It is the specific energy at critical depth under critical velocity condition in the channel.

ALTERNATE DEPTHS:

For any value of the specific energy other than critical one, there are two depths, one greater than the critical depth and other smaller than the critical depth. These two depths for a given specific energy are called alternate depths.

PROCEDURE:

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Start the pump to maintain a constant discharge in hydraulic flume apparatus. Allow the flow in the flume to be stabilized. Take three readings of depth of flow in the flume at different points and average it. Calculate the specific energy using the following relationship:

E= y +

q2

2gy 2

Change the slope of the flume by automatic system attached to the apparatus. Again allow the flow in the flume to be stabilized. Again take three readings of depth of flow in flume at different points and average it. Repeat the whole procedure by changing the slope of the flume. Draw the specific energy curve.

PRECAUTIONS:

Tip of the hook gauge should just touch the water. Take piezometric readings when flow is ready. Take more than three readings.


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Flume width = B= -------- m

Value of k to find the Q = ----------


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Sr. #

Bed slope(S)

DischargeQ

(m3/sec)

Average Depth of flowY= (Y1+Y2+Y3)/3

(m)

Area of flowA=

(B*Y)

(m2)

V=Q/A

(m/sec)

Velocity Head

V2/2g

(m)

Specific Energy

E= y + V2/2g(m)

Y1 Y2 Y3 Y

1

2

3

4

5

6


GRAPH BETWEEN SPECIFIC ENERGY (E) AND DEPTH OF FLOW (Y)

RESULTS:

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COMMENTS:

EXPERIMENT NO. 3

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TO STUDY THE FLOW CHARACTERISTICS OVER A HUMP/WEIR

OBJECTIVE:

To study the variations in the flow with the introduction of different types of humps in the flume

APPARATUS:


Hook/Point gauge (to measure depth of water) Broad crested hump

o Round cornero Sharp corner

Sharp corner

Round corner

Figure 3.1: Humps

RELATED THEORY:

HUMP/WEIR:

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It is a streamline Construction provided at the bed of channel.

It is a structure or obstruction that is constructed across a river or stream to raise the level of water on upstream side so that it can be diverted to canals to meet the irrigation requirements.

Weirs can be gated (barrage) or un-gated.

Figure 3.2: Flow over a Hump/Weir

FLOW OVER A RAISED HUMP:

Figure 3.3: Flow over Raised Hump

CRITICAL HUMP HEIGHT:

It is the minimum height that causes critical depth (critical flow) over the hump.

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Hump

V2

Z

Y3Y1 Y2

V1


EFFECT OF HUMP HEIGHT ON DEPTH OF FLOW:

Figure 3.4: Effect of hump height on depth of flow

Damming Action:

If the height of hump is made higher than the critical hump height, critical depth is maintained over the hump and upstream depth of water is increased. This phenomenon is known as Damming Action.

PROCEDURE:

Fix the slope of the flume. Introduce round corner weir at a certain location. Set a particular discharge in the flume. Note the depth of flow at U/S, D/S and over the weir at certain points (More than one). Repeat the same for various discharges. Calculate the value of yc, y1, y2 & y3 and make their comparison. Repeat the same procedure for sharp corner weir. Plot water surface profiles.

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TYPE OF

WEIR

DISCHARGE

UNIT WIDTH

DISCHARGE

CRITICAL DEPTH

U/S DEPTH OF FLOW DEPTH OF FLOW OVER WEIR/HUMP

D/S DEPTH OF FLOW TYPE OF FLOW

m3/sec m2/sec yc y1 y2 y3 Yavg y1 y2 y3 Yavg y1 y2 y3 Yavg U/S Over Weir

D/S

m m m m

Round Corner Weir

Sharp Corner Weir


FOR WATER SURFACE PROFILE

SR NO WEIR TYPE DISCHARGE HORIZONTAL DISTANCE DEPTH OF FLOW

m3/sec X1 (m) X2 (m) X3 (m) U/s (m) Over hump (m)

D/s (m)

1Round Corner

Weir2

3

1Sharp Corner

weir2

3

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GRAPHICAL REPRESENTATION: (ROUND CORNERED WEIR)

Graph between Horizontal Distance (X) and Depth of flow (Y)


GRAPHICAL REPRESENTATION: (SHARP CORNERED WEIR)


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RESULTS:

COMMENTS:

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EXPERIMENT NO. 4

TO STUDY THE CHARACTERISTICS OF HYDRAULIC JUMP DEVELOPED IN THE

LABORATORY FLUME

OBJECTIVE:

To achieve physically, the development of hydraulic jump in the laboratory flume To measure the physical dimensions of hydraulic jump To Plot hydraulic jump for various Froude’s No. (Fn) To calculate Energy Losses through the hydraulic jump

APPARATUS:



RELATED THEORY:

HYDRAULIC JUMP:

The rise of water level which takes place due to transformation of super-critical flow to the sub-critical flow is termed as Hydraulic Jump.

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D/SU/S

Hydraulic Jump

Dam


PRACTICAL APPLICATIONS OF HYDRAULIC JUMP:

Practical applications of hydraulic jump are many, it is used

1. To dissipate energy of water flowing over dams, weirs, and other hydraulic structures and thus prevent scouring downstream of the structures.

2. To recover head or raise the water level on the downstream side of the measuring flume and thus maintain high water level in the channel for irrigation or other water distribution purpose.

3. To increase the weight on an apron and thus reduce uplift pressure under a masonry structures by raising the water depth on the apron.

4. To indicate special flow conditions, such as the existence of super critical flow or the presence of the control section, so that a gauging station may be located.

5. To mix chemicals used for the purification of water.

DEPTH OF HYDRAULIC JUMP:

d2 = d1/2(-1 + √1+8(q²/gy3))

Or

d2 = d1/2(-1 + √1+8F1²)

EXPRESSION FOR THE LOSS OF ENERGY DUE TO HYDRAULIC JUMP:

hL = (d2-d1)³/4d1d2

LENGTH OF HYDRAULIC JUMP:

It is generally 5-7 times depth of jump for barrages.

LOCATION OF HYDRAULIC JUMP:

It depends upon:

o d2 (Depth of flow just after Hydraulic Jump)o yn (Depth of flow after Hydraulic Jump)

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The following will illustrate the location of a hydraulic jump in three typical cases.

CASE A:

Hydraulic jump will form before the toe of structure on glacis and it will be submerged and weak hydraulic jump. Preferably it is required for barrages because it is more stable. (yn> d2).

CASE B:

Hydraulic jump will form at toe of hydraulic structure. (yn= d2).

CASE C:

The jump will shift away from toe. It is avoided as for as design is concerned. It will cause more scouring so cost of protection work increases. (yn< d2)

TYPES OF HYDRAULIC JUMP:Hydraulic jumps are of several distinct types. According to the U.S. Bureau of Reclamation, these types can conveniently be classified according to the Froude’s # of the incoming flow, as follows:

For F = 1 to 1.7, the water surface shows undulations, and the jump is called as undular jump.

For F = 1.7 to 2.5, a series of small rollers develop on the surface of the jump, but the downstream water surface remains smooth. The velocity throughout is fairly uniform and the energy loss is low, this jump is called as weak jump.

For F = 2.5 to 4.5, there is an oscillating jet entering the jump bottom to the surface and back again with no periodicity. Each oscillation produces a large wave of irregular period, which, very commonly in canals, can travel for miles doing unlimited damage to earth banks and ripraps. This jump may be called as oscillating jump .

For F = 4.5 to 9.0, the downstream extremity of the surface roller and the point at which the high velocity jet tends to leave the flow occur at practically the same vertical section. The action and position of this jump are least sensitive to variation in tail water depth. The jump is well balanced and performance is at its best. The energy dissipation ranges from 45 to 70%. This jump may be called as steady jump.

For F = 9.0 and larger, the high velocity jet grabs intermittent slugs of water rolling down the front surface of the jump, generating waves downstream and a rough surface can prevail. The jump action is rough but effective since the energy dissipation may reach 85%. This jump may be called as strong jump.

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PROCEDURE:

Fix the bed slope of glass flume.

Set a particular discharge in the flume.

Develop the hydraulic jump by holding back the tail water.

Measure the depths of water. i.e. yo, y1, y2 and corresponding horizontal distances x0, x1, x2.

Repeat the procedure with varying discharges.

Plot the water surface profiles of hydraulic jump at different discharges.

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Flume width = B= -------- m

Value of k to find the Q = ----------Channel Bed Slope = _________________

SR NO.

DISCHARGE

Q

UNIT WIDTH DISCHARGE

q = Q/B

CRITICAL DEPTH

Yc=(q2/g)1/3

DEPTH OF HORIZONTAL FLOW/HORIZONTAL DISTANCE

Velocity of flow

V1=Q/A1

Velocity of flow

V2=Q/A2

Froude No.

before jump

Froude No. after

jump

Depth of

Jump

Energy Loss Type

of Jump

m3/sec m2/sec mY0 X0 Y1 X1 Y2 X2

m/sec m/sec Fr1=V1/(gD)1/2

Fr2=V2/(gD)1/2

d2 hL

m m m

1

2

3

4

5

6

*Area of Flow before Jump = A1 = Y1 ×B * Area of Flow after Jump = A2 = Y2 ×B



RESULTS:

COMMENTS:


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