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HYDROLOGY LAB MANUAL 2020
The University of Lahore Department of CivilEngineering Technology Page 1
LABORATORY MANUAL
HYDROLOGY (CET03302)
Submitted To: Engr. Hafiz Shehzad Aslam
Submitted By: Syed Kasher Ali
Registration No: BSCET0118314
Section: CV5-C

PREFACE
This course is designed to provide Civil Engineering Technology undergraduates with basic
understanding of the theory and practice of Hdrology. Students will apply the knowledge gained
from theoretical to practical application. Lab works covered in this manual include Equipment used in
Hydrology, Velocity and Discharge by using current meter, Study of Barometer, Study of Rainfall
gauges, Measurement of Wind Velocity, Elevation by using GPS etc. Procedures outlining each
fieldwork have been comprehensively covered. It is hoped that students will gain valuable insight
into engineering after completion of this course, which will also help them in their professional lives.

ACKNOWLEDGMENT
The author is highly indebted to his HOD and colleagues for their constant support and guidance
during the course of preparing this manual. In addition thanks to the students for the pictures were
collected from the laboratory.

TABLE OF CONTENTS
EXPERIMENT NO-1
 LAB LAYOUT
EXPERIMENT NO-2
 EQUIPMENT USED IN HYDROLOGY
EXPERIMENT NO-3
 TO PLOT A GRAPH FOR THE GIVEN DATA OF THE TEMPERATURE “T” AND THE
SATURATED VAPOUR PRESSURE “ES” OF AIR SHOWING THAT THE SATURATED
VAPOUR PRESSURE IS FUNCTION OF THE TEMPERATURE. ALSO FIND THE
FOLLOWING FOR THE GIVEN CONDITIONS:
1) SATURATION DEFICIT (ES –E)
2) RELATIVE HUMIDITY (F)
3) DEW POINT TEMPERATURE (TD)
EXPERIMENT NO-4
 DETERMINATION OF FLOOD ANALYSIS
EXPERIMENT NO-5
 FLOOD FREQUENCY ANALYSIS
EXPERIMENT NO-6
 DETERMINATION OF VELOCITY AND DISCHARGE BY USING CURRENT METER
EXPERIMENT NO-7
 DETERMINATION OF VELOCITY AND DISCHARGE BY USING FLOATS
EXPERIMENT NO-8
 STUDY OF BAROMETER
EXPERIMENT NO-9
 STUDY OF RAINFALL GAUGES
EXPERIMENT NO-10
 MEASUREMENT OF WIND VELOCITY
EXPERIMENT NO-11
 MEASUREMENT OF ATOMOSPHERE TEMPERATURE
EXPERIMENT NO-12
• STUDY AND USES OF GPS (GLOBAL POSITIONING SYSTEM )
EXPERIMENT NO-13
 DETERMINATION OF ELEVATION BY USING GPS
EXPERIMENT NO-14
 STUDY OF SPILLWAYS AND ITS TYPES

TABLE OF FIGURES
__________________________________________________________________
FIGURE NO 1.1: WIND VANE………………………………………………………….09
FIGURE NO 1.2: Plate Anemometer…………………………………………….……….10
FIGURE NO 1.3: Digital Anemometer…………………………………………..……….10
FIGURE NO 1.4: Hygrometer…………………………………………………………….11
FIGURE NO 1.5: Digital Thermometer……………………………………………….….12
FIGURE NO 1.6: Adjustable Bed Flow…………………………………………………..12
FIGURE NO 1.7: Basic Hydrology System…………………………………...………….12
FIGURE NO 1.8: Sediment Transport …………………………………………………...13
FIGURE NO 1.9: Tipping Bucket rain gauge…………………………………………….14
FIGURE NO 1.10 Weighing Precipitation Rain Gauge……………………………...……14
FIGURE NO 3.1: Current Meter ……………………………………………………...….16
FIGURE NO 4.1: Cross-Section of a Stream…………………………………………….22
FIGURE NO 4.2: Stream………………………………………………………………….30
FIGURE NO 5.1: Effect of Weather on Air-Pressure………………………………….…32
FIGURE NO 5.2: Water based Barometer …………………………………………….…35
FIGURE NO 5.3: Mercury Barometer………………………………………………...….36
FIGURE NO 5.4: Aneroid Barometer……………………………………………….……36
FIGURE NO 5.5: Barograph…………………………………………………………...…39
FIGURE NO 5.6: The Fortin Barometer………………………………………….………40
FIGURE NO 5.7: Chart of variation in Pressure ………………………………...……….43
FIGURE NO 5.8: Rain………………………………………………………………...….43
FIGURE NO 5.9: Better Air Pressure ……………………………………………………44
FIGURE NO 5.10: Fine Water …………………………………………………………….44
FIGURE NO 6.1: Symon’s Rain Guage…………………………………………….….…47
FIGURE NO 6.2: Standard Rain Gauge……………………………………………..……48
FIGURE NO 6.3: Weighing Bucket Rain gauge ………………………………........……49
FIGURE NO 6.4: Tipping Bucket Rain Gauge ……………………………………..……49
FIGURE NO 6.5: Floating Rain Gauge …………………………………………….....….50
FIGURE NO 6.6: Optical Rain gauge…………………………………………...……..….51
FIGURE NO 6.7: Acoustic Rain Gauge ………………………………………………..…51
FIGURE NO 6.8: Location for installing Rain gauge…………………………………..…54
FIGURE NO 7.1: Anemometer ………………………………………………………...…56
FIGURE NO 8.1: Humidity Measuring scale ………………………………………….…64
FIGURE NO 9.1: Thermometer………………………………………………………...…69
FIGURE NO 9.2: Analogue Thermometer …………………………………………….…70
FIGURE NO 9.3: Dual Sensor Thermometer …………………………………….………70
FIGURE NO 9.4: K-type Thermocouple……………………………………………….…72

FIGURE NO 9.5: Infrared Thermometer …………………………………………………72
FIGURE NO 10.1: Simple GPS………………………………………………………….…74
FIGURE NO 12.1: Spill Way …………………………………………………………..….77
FIGURE NO 12.2: Over Fall Spill way ……………………………………………………77
FIGURE NO 12.3: Saddle Spill Way ……………………………………………..….……78
FIGURE NO 12.4: Shaft Spill Way ………………………………………………………78
FIGURE NO 12.5: Side Channel Spill Way ………………………………...……………79
FIGURE NO 12.6: Emergency Spill Way …………………………………………..……79
FIGURE NO 12.7: Siphon Spill Way …………………………………………………….80
FIGURE NO 14.1: Schematic Diagram of Indus River ……………………….………….82
FIGURE NO 15.1: Basic Hydrology System ……………………………………………..84

LIST OF TABLES
__________________________________________________________________
TABLE NO 3.1: Coefficient for Standard Vertical –Velocity Curve………………………...19
TABLE NO 3.2: Mean vertical velocity ……………………………………………………..23
TABLE NO 3.3: Calculations and Observations ……………………………………...……...…26
TABLE NO 7.1: Wind Speed and Description …………………………………………...….57
TABLE NO 8.1: Relative Humidity Determination Based on Water Vapor Content ……..…65
TABLE NO 8.2: Relative Humidity Determinations Using Dry &Wet Bulb Thermometer…66
TABLE NO 13.1: Observation and calculation of Flow Duration…………………………….….81
TABLE NO 15.1: Observation and Calculation of Ponding Time ……………………………….85

EXPERIMENT NO-1
LAYOUT OF HYDROLOGY LAB
PURPOSE:
 To get familiar with the different types of instruments, apparatus & their respective locations in
laboratory of Hydrology.
 To get an idea about different experiments & their purpose, to be performed in the lab

EXPERIMENT NO-2
EQUIPMENT USED IN HYDROLOGY
WIND VANE:
Objective:
A wind vane is an instrument for showing the direction of the wind.
Introduction:
Wind vane consist of an asymmetrically shaped object mounted at the center of gravity about a vertical axis.
The end, which offers the greater resistance to the motion of air, moves to the downwind position and
subsequently, the direction of the wind is determined by reference to an attached compass rose.
Figure 1.1: Wind Vane
Uses:
 Research.
 Air quality.
 General purpose meteorological application.
 Wind profiles.
ANEMOMETER:
Objective:
An anemometer is a device used for measuring wind speed, and is a common weather station instrument.
The term is derived from the Greek word anemos, which means wind, and is used to describe any wind
speed measurement instrument used in meteorology. The first known description of an anemometer was
given by Leon Battista Alberti in 1450.
Introduction:
Most anemometer consist of 3 or 4 cups that catch the wind and spin. The rotations per minutes or RPM is
translated to wind speed.

Types:
Velocity Anemometer
 Cup anemometer
 Windmill anemometer
 Hot-wire anemometer
 Laser Doppler anemometer
 Sonic anemometer
Pressure Anemometer
 Plate anemometer
 Tube anemometer
 Digital anemometer
Figure 1.2: Plate Anemometer Figure 1.3: Digital Anemometer
HYGROMETER:
Objective:
Hygrometer is used for measuring temperature and humidity.
Figure 1.4: Hygrometer

Uses:
 At greenhouses, industrial units, incubators and museums.
 To aid humidity control in residential settings.
Types:
 Metal/pulp coil type
 Hair tension
 Electronic hygrometer
Ranges:
 For temperature (-10 to 60 ̊C)
 For Humidity (0 % to 100 %)
ADJUSTABLE BED FLOW:
Objective:
This laboratory instrument is used to:
 Study the uniform and non-uniform flow through channels.
 Measure the local or point velocity of flow at a point.
 Measure the depth of flow at various sections.
Figure 1.6: Adjustable Bed Flow
BASIC HYDROLOGY SYSTEM:
Objective:
This Hydrology system is used for experimental rainfall runoff modelling and to determine the runoff
coefficient.
Figure 1.7: Basic Hydrology System

THERMOMETER:
Objective:
Thermometer is used for measuring temperature of anything i.e. materials like asphalt, cement, sand etc.
Figure 1.5: Digital Thermometer
Range:
 For temperature (-50 to 200 ̊C)
 For temperature (-58 to 392 ̊F)
SEDIMENT TRANSPORT:
Objective:
Sediment transport system is used to:
Investigate the effect of velocity of flow on height and length of ripple.
 The Threshold for incipient motion for
 Plane bed
 Ripple bed
 Measure the bed load transport rate and investigate the effect of velocity on it.
Figure 1.8: Sediment Transport
DIFFERENT TYPES OF RAIN GAUGES:
It is used by meteorologists and hydrologists to collect and measure the quantity of precipitation (rain)
during a set period of time.
Measurement:
 Most rain gauges generally measure the precipitation in millimeters.
 The level of rainfall is sometimes reported as inches or centimeters.

Figure 1.9: Tipping Bucket Rain Gauge Figure 1.10: Weighing Precipitation Rain Gauge
TYPES OF RAIN GAUGES:
 Standard rain gauge
 Tipping bucket rain gauge
 Optical rain gauge
 Acoustic rain gauge
 Weighing precipitation gauge
Comments:

Design Exercise No. 3
TO PLOT A GRAPH FOR THE GIVEN DATA OF THE TEMPERATURE “T” AND
THE SATURATED VAPOUR PRESSURE “ES” OF AIR SHOWING THAT THE
SATURATED VAPOUR PRESSURE IS FUNCTION OF THE TEMPERATURE. ALSO
FIND THE FOLLOWING FOR THE GIVEN CONDITIONS:
1. SATURATION DEFICIT (ES –E)
2. RELATIVE HUMIDITY(F)
3. DEW POINT TEMPERATURE (TD)
Condition Air Temperature (T) (◦C) Vapor Pressure (mm of Hg)
1 11 7.9
2 17 10.8
3 21 13
4 25 18.4
RELATED THEORY:
HYDROLOGY
Hydrology is the science of waters of the earth, their occurrence, circulation and distribution over
the globe, their physical and chemical properties and their reaction / interaction with the physical
and biological environment.
It deals with precipitation, evaporation, infiltration, ground water flow, runoff, stream flow
and the transport of substances dissolved or suspended in the flowing water. So, it is the
scientific study of hydrological cycle. The hydrological cycle involves evaporation, transpiration,
interception, infiltration, run-off, seepage and precipitation. Due to solar radiation, water from
ocean, river, lakes or any other body on earth surface evaporates in gaseous form.

ENGINEERING HYDROLOGY
It includes those segments of the field pertinent to planning, design and operation of
engineering projects for the control and u se of water.
SIGNIFICANCE OF HYDROLOGY
Study of water is extremely necessary as:
i. It is the basic need for human life over the planet.
ii. To cope with extreme hydrological events (For examples: Floods, droughts, etc)
iii. To determine input data for the design and operation of hydraulic structures like
dams, reservoirs, storm drainage system, water supply schemes, etc.
METEOROLOGY
It is the science of atmosphere which is gaseous envelope surrounding the earth.

CLIMATIC FACTORS
Meteorology of the region is affected by certain climatic factors:
i. Amount and distribution of precipitation
ii. The occurrence of snow and ice
iii. Wind velocity
iv. Temperature
v. Humidity
IMPORTANCE OF KNOWLEDGE OF METEOROLOGY
i. Cloud formation
ii. Occurrence of precipitation
iii. Thunder storm formation
iv. Movement of rainstorms
v. Weather forecast
vi. Flood warnings and forecasts
ATMOSPHERE
It is the gaseous envelope around the earth surface. It consists of many gases like nitrogen,
oxygen, carbon dioxide, etc.
Different layers of atmosphere are:
i. Troposphere
ii. Stratosphere
iii. Mesosphere

iv. Thermosphere
TROPOSPHERE / HYDROSPHERE
It is the layer of atmosphere adjacent to the surface of earth which contains about 99% of the total
atmospheric water. Its average thickness is about 8-12km.
It is the most important layer with reference to the Civil Engineering as all the hydrological
processes takes place in this layer.
ATMOSPHERIC WATER
It is the water available in the atmosphere in the form of water vapors, ice crystals, clouds and
precipitating particles etc.
VAPORIZATION
It is the process of transformation of water from liquid state to vapor state.
VAPOR PRESSURE “e”
Pressure exerted by the water vapors in air is known as Vapor pressure. The commonly used units are
mm of Hg.

SATURATION VPOR PRESSURE “es”
It is the vapor pressure when air is fully saturated at a given temperature. It is the measure of moisture
holding capacity of air which increases with the increase in the air temperature.
Its values can be obtained from the Psychometric tables.
It can also be obtained (within 1%range) from the value of temperature in the range of - 500C
to 55oC by the use of following equation:
es ≈3.38639 [ (0.00738T + 0.8072)8
– 0.000019( 1.8T + 48 ) + 0.001316]
SATURATION DEFICIT
The difference between the saturation vapor pressure and the vapor pressure of the air at the given
temperature is known as the Saturation deficit.
HUMIDITY
It is the presence of moisture in the air. Humidity in the atmosphere can be assessed by vapor
pressure of air.
RELATIVE HUMIDITY
It is the ratio between the vapor pressure and the saturation vapor pressure of the air at a given
temperature. It is usually expressed in percentage. It is represented as “f”.
f = (e / es) * 100
DEW POINT TEMPERTURE “Td”
It can be defined as the temperature at which the air mass just becomes saturated if cooled at
Constant pressure with moisture neither added nor remo ved. When air is cooled to this
Temperature, dew drops are formed.
PROCEDURE
i. Plot a graph between saturated vapor pressure and air temperature.
ii. Plot condition 1 for given value of “e” and “T” on es~T graph.
iii. For point 1 draw a vertical line passing through the point up to the saturation line

iv. Measure distance between saturation line, it is the saturation vapor pressure for point 1.
v. Measure vertical distance between point 1 and saturated line, it is saturation deficit.
vi. Compute relative humidity by using the equation.
vii. Draw a horizontal line point 1 to the left; it may intersect with the saturation curve.
Note down the temperature for the intersection point, it is the dew point temperature.
viii. Repeat steps ii to vii for other points as well.

CALCULATIONS:
Table for plotting the Saturation curve:
Sr. No.
Air Temperature
( 0 C)
Saturated vapor pressure
(mm of Hg)
1 -4 4.32
2 -2 4.90
3 0 5.61
4 2 6.35
5 4 7.36
6 6 8.27
7 8 9.32
8 10 10.41
9 12 11.73
10 14 13.25
11 16 15
12 18 16.87
13 20 18.91
14 22 21.10
15 24 23.75
16 26 26.60
17 28 29.95
18 30 34.40

Plot of saturated vapor pressure as a function ofair temperature showing the status offour conditions

Table ofCalculations
. No.
Air
Temperatur
e “T” (~C)
Vapor
Pressure
“e” (mm of
Hg)
Saturatd
vapor
pressure
“es”
mm of Hg)
Saturatio
n deficit
“es-e”
(mm of Hg)
Relative
humidity
f=(e/es)*100
%
Dew point
temperatue
“Td”
(~C)
1 11 7.9 11 3.1 71.82 5
2 17 10.8 17 5.2 63.53 10.5
3 21 13 21 7 61.9 13.7
4 25 18.4 25 6.6 73.6 19.5
RESULTS AND COMMENTS:

DESIGN EXERCISE NO.4
DETERMINATION OF FLOOD DISCHARGE ANALYSIS
RELATED THEORY:
PRECIPITATION:
Precipitation is defined as all types of moisture reaching to the surface of earth from the atmosphere. The
precipitation on the land surface is about one third of the total global precipitation.
Precipitation is the basic input for a hydrological system.
FORMS OF PRECIPITATION
Precipitation may be in the form of one or more than one of the following forms:
i. Drizzle / Mist
ii. Rain
iii. Snow
iv. Sleet
v. Glaze
vi. Hail
vii. Fogs
viii. Frost
ix. Trace

MECHANISM TO FORM PRECIPITATION
Following mechanisms are necessarily required for precipitation to occur over an area:
i. Lifting mechanism
ii. Formation of cloud droplets / Ice crystals
iii. Growth of cloud droplets / ice crystals
iv. Sufficient accumulation of moisture over an area
RAIN GAUGE
Rain gauge is an instrument used to measure the amount of rainfall or the intensity of rainfall at
any place.
AMOUNT OF PRECIPITATION
It is the total amount of rainfall over an area usually in one day. It is measured in the units of
mm or inches.
INTENSITY OF PRECIPITATION
It is the amount of precipitation at a place per unit time. It is usually expressed in mm/hr or
inches/hr.
TYPES OF STORM
ISOLATED STORM
When subsequent storm does not occur before the runoff of the previous storm ceases, that
storm is called isolated storm
COMPLEX STORM
When subsequent storm occurs before the runoff of the previous storm ceases, such
combined storms are called complex storm.

HYDROGRAPH OF AN ISOLATED STORM:
1. SIMPLE JUDGEMENT:
Table 1
T T+4 Discharge 1cm/h 2cm/h 3cm/h 4cm/h
Q+4
0 4 0 4 8 12 16
1 5 6 10 20 30 40
2 6 13 17 34 51 68
3 7 22 26 52 78 104
4 8 16 20 40 60 80
5 9 11 15 30 45 60
6 10 7 11 22 33 44
7 11 4 8 16 24 32
8 12 2 6 12 18 24
9 13 1 5 10 15 20
10 14 0 4 8 12 16
(Graph of Simple Judgment Method)

2. S HYDROGRAPH METHOD:
Table 2
Time
Discharge Discharge
Combined
(m3/sec) (m3/sec +8)
0 0 0 0
1 6 0 6 6 0
2 13 6 0 19 13 6
3 22 13 6 0 41 22 13
4 16 22 13 6 0 57 16 22
5 11 16 22 13 6 0 68 11 16
6 7 11 16 22 13 6 0 75 7 11
7 4 7 11 16 22 13 6 0 79 4 7
8 2 4 7 11 16 22 13 6 0 81 2 4
9 1 2 4 7 11 16 22 13 6 0 82 1 2
10 0 1 2 4 7 11 16 22 13 6 82 0 1
11 0 1 2 4 7 11 16 22 13 76 0
(Graph of S Hydrograph Method)

COMMENS:
DESIGN EXERCISE NO - 5
FLOOD FREQUENCYANALYSIS
RELATED THEORY
PRECIPITATION
Precipitation is defined as all types of moisture reaching to the surface of earth from the atmosphere. The
precipitation on the land surface is about one third of the total global precipitation.
Precipitation is the basic input for a hydrological system.
PROBABILITY PLOTTING
Arrange the available discharge (say “n” in total) in descending order. Let the serial order of this specific
discharge “m”. This serial order m is called rank or order of the observation. The recurrence interval and the
probability of the specific discharge Q in the series can be calculated by the following methods.
CALIFORNIA FORMULA
Tr =
𝒏
𝒎
HAZEN’S FORMULA
Tr =
𝒏
𝒎 − 𝟎.𝟓

WEIBULL’S FORMULA
Tr =
𝒏 + 𝟏
𝒎
GUMBELL’S FORMULA
Tr =
𝒏
𝒎 + 𝑪 − 𝟏
Here, C is called gumbell’s correction. Its value depends on m and n as given in the following table.

Sr No
Discharge
(m3/sec)
Discharge
(m3/sec)
in descending
order
Return Period (Tr)
California
Formula
(=n/m)
Hazzen's
Formula
(=n/m-0.5)
Weibul’s
formula
(=n+1/m)
m/n C
Gumbell’s
formula
(=n/m+C-1)
1 395 887 32.00 64.00 33.00 0.03 0.26 123.08
2 619 814 16.00 21.33 16.50 0.06 0.32 24.24
3 766 766 10.67 12.80 11.00 0.09 0.38 13.45
4 422 726 8.00 9.14 8.25 0.13 0.43 9.33
5 282 721 6.40 7.11 6.60 0.16 0.47 7.16
6 887 705 5.33 5.82 5.50 0.19 0.49 5.83
7 705 697 4.57 4.92 4.71 0.22 0.53 4.90
8 528 696 4.00 4.27 4.13 0.25 0.56 4.23
9 520 634 3.56 3.76 3.67 0.28 0.58 3.73
10 436 632 3.20 3.37 3.30 0.31 0.60 3.33
11 697 624 2.91 3.05 3.00 0.34 0.62 3.01
12 624 619 2.67 2.78 2.75 0.38 0.66 2.74
13 496 598 2.46 2.56 2.54 0.41 0.69 2.52
14 489 528 2.29 2.37 2.36 0.44 0.70 2.34
15 598 527 2.13 2.21 2.20 0.47 0.72 2.17
16 359 520 2.00 2.06 2.06 0.50 0.73 2.03
17 696 496 1.88 1.94 1.94 0.53 0.74 1.91
18 726 489 1.78 1.83 1.83 0.56 0.76 1.80
19 527 464 1.68 1.73 1.74 0.59 0.77 1.70
20 310 459 1.60 1.64 1.65 0.63 0.80 1.62
21 408 440 1.52 1.56 1.57 0.66 0.82 1.54
22 721 436 1.45 1.49 1.50 0.69 0.84 1.47
23 814 422 1.39 1.42 1.43 0.72 0.85 1.40
24 459 408 1.33 1.36 1.38 0.75 0.86 1.34
25 440 395 1.28 1.31 1.32 0.78 0.87 1.29
26 632 373 1.23 1.25 1.27 0.81 0.89 1.24
27 343 371 1.19 1.21 1.22 0.84 0.91 1.19
28 634 359 1.14 1.16 1.18 0.88 0.94 1.15
29 464 343 1.10 1.12 1.14 0.91 0.96 1.10
30 373 310 1.07 1.08 1.10 0.94 0.97 1.07
31 289 289 1.03 1.05 1.06 0.97 0.99 1.03
32 371 282 1.00 1.02 1.03 1.00 1.00 1.00
n = Total no of year (32) , m = No of year

Graphs:
1.
2.
0
100
200
300
400
500
600
700
800
900
1000
0.00 20.00 40.00 60.00 80.00
Hazzen'sFormula
Hazzen's Formula = n/m-
0.5
0
100
200
300
400
500
600
700
800
900
1000
0.00 10.00 20.00 30.00 40.00
CaliforniaFormula
California Formula = n/m

3.
4.
COMMENS:
0
100
200
300
400
500
600
700
800
900
1000
0.00 10.00 20.00 30.00 40.00
Weibul’s formula
Weibul’s formula =
n+1/m
0
100
200
300
400
500
600
700
800
900
1000
0.00 50.00 100.00 150.00
Gumbell’s formula
Gumbell’s formula =
n/m+C-1

DESIGN EXERCISE NO-6
DETERMINATIONOF VELOCITYAND DISCHARGE USING CURRENTMETER
OBJECTIVES:
The objective of this experiment is to review the techniques and instruments used to measure stream velocity and
to calculate stream discharge. We review the methods for determining the vertically averaged velocity at a point
and the factors affecting the accuracy of discharge measurement.
APPARATUS:
 Current meter
 Wading rod
 Sounding Weights and Accessories
 Sonic Sounder
 Width Measuring Equipment
RELATED THEORY:
Stream Flow Discharge:
Stream flow discharge is defined as the volume rate of flow of water that includes any substances dissolved or
suspended in the water. Discharge is usually expressed in units of cubic feet per second (cfs or ft3
/sec). If the mean
water velocity normal to the direction of flow (V) and the cross sectional area (A) of water flow is known, then the
discharge (Q) can be computed as:
Q=VA.
Current Meter
A current meter is an instrument that measures the velocity of flowing water. The current meter is based on
the principle that the velocity of water is proportional to the angular velocity of the meter's rotor. The
velocity of water at a given point can be determined by counting the number of revolutions of the rotor
during a specified or measured interval of time.
Figure 3.1: Current Meter

TYPES OF CURRENT METER:
Current meters are classified according to their rotors.
 Vertical Axis Current Meter:
The most common vertical axis current meter used by the U.S. Geological Survey is the Price Meter, type
AA. The rotor is 5 inches in diameter and 2 inches high with six cone shaped cups mounted on a stainless
steel shaft. A type AA meter is also available for low velocities. The low velocity is normally rated from 0.2
to 2.5 cfs. It is recommended for use in streams where the mean velocity at a cross section is less than 1 cfs.
 Horizontal Axis Current Meter:
Horizontal axis current meters are the Ott, Neyrpic, Haskell, Hoff, and Braystoke. The Ott meter is made in
Germany, the Neyrpic, in France; both are used extensively in Europe. The Haskell and Hoff meters, both
developed in the United States, are used in a limited extent. The Braystoke meter is used extensively in the
United Kingdom. The Ott meter is not widely used in the United States because of a lack of durability under
extreme conditions.
 Optical Current Meter:
The U.S. Geological Survey has developed an optical current meter. It is designed to measure surface water
velocities in open channel without requiring submersion of the equipment. Its primary advantages are for
stream environments where the velocities are too high to be measured by a conventional meter, i.e. floods,
or where there is significant debris flow that would be hazardous to a current meter.
 Acoustic Doppler Current Meters:
Acoustic Doppler current meters determine stream velocity by measuring the change in sound energy
reflected from particles or gas bubbles suspended in the water. Acoustic Doppler velocimeters (ADV)
provide point estimates of water velocity, while Acoustic Doppler current profilers (ADCP) provide velocity
estimates in a vertical series of "cells" or "layers" in the water column.
WADING ROD
There are two types of wading rods used for determining depth in a stream.
 Top wading rod:
The top setting rod has the advantage of convenience in setting the meter at the proper depth; the hydrographer also
keeps his hands dry in the process. The top setting rod has a 1/2 inch hexagonal main rod for measuring the depth and
a 3/8 inch diameter round rod for setting the position of the current meter . This rod also has a number of design
features that assist in setting the current meter at specific fractions (0.2, 0.4, 0.6, and 0.8) of the water depth.
 Round wading rod:
The round wading rod has a base plate, lower section, three or four intermediate sections, and a sliding support and a
rod end. The round rod is used typically in ice measurements. The most convenient length for an ice rod is
approximately three feet.

SOUNDING WEIGHTS AND ACCESSORIES:
In streams that are swiftly flowing and too deep to wade, a current meter is suspended in the water by a
cable attached to a boat, bridge, or cableway. A sounding weight is suspended below the meter to keep it
stationary in the water. The weight also minimizes the damage to the meter when it is lowered to the
streambed. The sounding weights are the Columbus weights or C type weights.
SONIC SOUNDER:
An alternative method of determining stream depth is with a portable sonic sounder. The USGS uses
commercially available portable depth sounders with a narrow beam angle to minimize the errors on
inclined streambeds and permits the hydrograph to work close to obstructions and piers.
WIDTH MEASURING EQUIPMENT:
The distance to any point in a stream's cross-section is measured from an initial point on the stream bank.
Discharge measurements are marked at 2, 5, 10, or 20 feet intervals for cableways and bridges. Distance
between the markings is estimated or measured with a rule or pocket tape.
Measurements made by wading, in boats or on unmarked bridges. Steel or metallic tapes or tag lines are
commonly used measuring devices.
VERTICALLY AVERAGED VELOCITY DETERMINATION:
Current meters measure velocity at a point in the stream cross section. Discharge measurement requires
determining the mean velocity in each of the selected verticals. The mean velocity in a vertical cross section
can be approximated by making several velocity observations at different depths and then using a known
relationship between these velocities and the vertical mean velocity.
MEAN VELOCITY METHODS:
 Vertical Velocity Curve Method:
In this methodology, a series of velocity observations are made at points distributed between the water
surface and the streambed. Normally observations are taken at 0.1 depth increments between 0.1 and 0.9 of
the total depth. Observations are always taken at 0.2, 0.6 and 0.8 of the depth to facilitate comparison with
other velocity methods.
Coefficients for the standard vertical velocity curve are shown in Table.

Table: 3.1 Coefficients for standard vertical-velocity curve.
Typical velocity curve
Fraction of total water
depth
Ratio of point velocity to mean vertical velocity
0.05 1.160
0.1 1.160
0.2 1.149
0.3 1.130
0.4 1.108
0.5 1.067
0.6 1.020
0.7 0.953
0.8 0.871
0.9 0.746
0.95 0.648

 Three-Point Method:
The three point method is a combination of the two-point and the six-tenths depth methods and utilizes
velocity measurements at 0.2, 0.6 and 0.8 of the depth. The mean velocity is determined by averaging the
0.2 and 0.8 depths; the result is then average with the 0.6 depth observation. In equation form, this is
Vmean = (V0.2 + V0.8)/4 + (V0.6)/2
 Two-Point Method:
The two point methodology uses velocity observations at 0.2 and 0.8 of the depth below the surface. The
average of these two observations is the mean velocity in the vertical.
 Six-Tenths Depth Method:
This approach presumes that a velocity observation made in the vertical at 0.6 of the depth below the
surface is the mean vertical velocity. Observational data and mathematical models have shown that the 0.6
depth produces reliable results.
The U.S. Geological Survey used the 0.6 depth method under the following conditions:
 The depth is between 0.4 and 1.5 feet (Price pygmy meter) or 1.5 and 2.5 feet (Price type AA)
 Large amounts of slush ice or debris make it impracticable to observe the velocity at the 0.2 depth
 The distance between the meter and the sounding weight is too great to place the meter at the 0.8 depth
 The stream stage is changing rapidly and a measurement must be quickly made.
 Two-Tenths Depth Method:
In the two-tenths depth method, the velocity is observed at 0.2 of the depth of the surface; a coefficient is
then applied to the observed velocity to obtain the vertical mean velocity. The two-tenths depth method is
not as reliable as either the two-point or the six-tenths depth methods, but it is used in situations where it is
not possible to obtain depth sounding or position the current meter at the 0.6 or 0.8 depths.
 Subsurface Velocity Method:
In this methodology, the velocity is observed at an arbitrary depth below the water surface. The observed
depth should be at least 2 feet below the surface. The method has application when stream stage is available
and sounding and depth data cannot be estimated reliably.
 Surface Velocity Method:
The surface velocity method is preferable to the subsurface velocity method provided an optical current
meter which accurately measures surface velocities is available. In natural channels, a surface velocity
coefficient of 0.85 or 0.86 is used to compute the mean velocity. In a smooth channel, the coefficient is 0.90.
 Integration Method:
In this methodology, the current meter is lowered in the vertical to the streambed and then raised to the
surface at a uniform rate. During this time, the total number of revolutions and the total elapsed time are
used in conjunction with the current meter rating table to estimate the mean vertical velocity.
 Five-Point Method:

Another rarely used method in the United States is the five-point method. Observations are make in each
vertical at 0.2, 0.6, and 0.8 of the depth below the water surface. Observations are also taken as close to the
surface and the streambed as practical. The velocity observations are used to compute the mean vertical
velocity, Vmean, using the equation,
Vmean = 0.1( Vsurface + 3V0.2 + 3V0.6 + 2V0.8 + Vbed)
 Six-Point Method:
The six-point method is also rarely used in the United States. Data points are collected at 0.2, 0.4, 0.6 and
0.8 of the depth below the water surface. The data are supplemented with observations close to the surface
and the streambed. The mean velocity is computed from the equation,
Vmean = 0.1( Vsurface + 2V0.2 + 2V0.4 + 2V0.6 + 2V0.8 + Vbed)
DISCHARGE MEASURING METHODS
 Midsection Method:
The USGS currently uses the midsection method of computing stream discharge using current meter
velocity measurements. In this method, the stream cross section is divided into rectangular subsections as
shown in Figure 2.2. At the center of each of these subsections (called a vertical), a depth and velocity
measurement is made, and the distance from a datum point on the shore is determined. The total discharge
can be determined using the procedure outlines.

Figure 3.2: Midsection Method
Velocity at an end vertical has to be adjusted as a percentage of the adjacent vertical, since it is not possible to
measure the velocity accurately with the current meter close to a boundary. Laboratory data summarized in the table
below suggest that the mean vertical velocity in the vicinity of a smooth wall of an idealized rectangular channel is
related to the mean vertical velocity at a distance from the wall equal to the depth (Vd).
Table: 3.2 Mean vertical velocity near a well as a function of velocity at one channel depth from the well.
Distance from Wall Mean Vertical Velocity
(Ratio of Depth) (fraction of Vd)
0.00 0.65
0.25 0.90
0.50 0.95
1.00 1.00

 Mean section Method:
The mean section method was used by the U.S. Geological Survey prior to 1950. In this older method,
discharges are computed for subsections between successive observation verticals. The velocities and depths
at successive verticals are each averaged; each subsection extends laterally from one observation vertical to
the next. The subsection discharge is the product of the average of two mean velocities, the average of two
depths, and the distance between observation verticals.
The total discharge is again given by Equation. Young (1950) determined that the midsection method is
simpler to compute and is slightly more accurate than the mean section method.
ASSUMPTION IN DISCHARGE MEASUREMENT
Carter and Anderson (1963) performed statistical studies that analyzed discharge measurement error in
natural streams under average conditions. Four assumptions were evaluated:
 The rating of the current meter is applicable to the measurement conditions.
 The observed velocity is a true time-average velocity.
 The ratio is known between the velocity of selected points in the vertical and the mean velocity in the vertical.
 The depth measurements are correct; the velocity and depth are a linear function of the distance between the
verticals.
PROCEDURE:
1. The first step in making a conventional current-meter measurement of discharge is to select a
measurement cross section of desirable qualities.
2. After the cross section has been selected, the width of the stream is determined. A tag line or measuring
tape is strung across the measurement section for measurements made by wading, from a boat, from ice
cover, or from an unmarked bridge.
3. Then find the depth of the each section using depth measuring device.
4. Next the spacing of the verticals is determined to provide about 25 to 30 subsections.
5. The verticals should be so spaced that no subsection has more than 10 percent of the total discharge.
6. After the stationing of the observation verticals has been determined, the appropriate equipment for the
current-meter measurement is assembled and the measurement note sheets for recording observations
are prepared.
7. The following information will be recorded for each discharge measurement: 1. Name of stream and
location to correctly identify the established gaging station; or name of stream and exact location of site
for a miscellaneous measurement.
8. Date, party, type of meter suspension, and meter number. 3. Time measurement was started using
military time (24-hr clock system). 4. Bank of stream that was the starting point. 5. Control conditions.
6. Gage heights and corresponding times. 7. Water temperature.
9. Assemble the current meter
10. The meter should balance on the hanger used and should spin freely;
11. The stopwatch should check satisfactorily in a comparison with the hydrographer’s watch.

12. Depth (if any) at the edge of water is measured and recorded. The depth determines the method of
velocity measurement to be used, normally the two-point method or the 0.6-depth method.
13. After the meter is placed at the proper depth and pointed into the current, the rotation of the rotor is
permitted to become adjusted to the speed of the current before the velocity observation is started.
14. The stopwatch is started simultaneously with the first signal or click, which is counted as “zero,” and not
“one.” The count is ended on a convenient number coinciding with one of those given in the column
headings of the meter rating table. The stopwatch is stopped on that count and is read to the nearest
second or to the nearest even second if the hand of the stopwatch is on a half-second mark. That number
of seconds and the number of revolutions are then recorded.
15. After the meter has become adjusted to the current, the number of revolutions made by the rotor is
counted for a period of 40 to 70 s.
16. The hydro-grapher moves to each of the observation verticals and repeats the above procedure until the
entire cross section has been traversed.
17. Number of revolution corresponding to the velocity of the water.
18. Then area of the section is multiply with the velocity to determine the discharge of channel.
Calculations and Observations:
1 2 3 4 5 6 7 8
Section
Flow Velocity (m/s)
Depth
(m)
Width
(m)
Area (m2)
Flow
(m/s)
0.2D 0.8D Mean
1 0.6 0.4 0.5 1.3 2.0 2.6 1.30
2 0.8 0.6 0.7 1.7 1.0 1.7 1.19
3 0.9 0.6 0.75 2.0 1.0 2.0 1.50
4 1.1 0.7 0.9 2.2 1.0 2.2 1.98
5 1.0 0.6 0.8 1.8 1.0 1.8 1.44

FACTORS AFFECTING THE ACCURACY OF A DISCHARGE MEASUREMENT:
1. The measurement of discharge is affected by several issues that can bias, distort, and impact the stage
discharge relationship. Accurate measurement requires that the measurement equipment be properly
assembled and maintained. This is especially critical for current meters which are susceptible to damage.
2. The underlying characteristics of the measurement section also affects measurement accuracy. Ideally, a
cross section lies within a straight reach resulting in streamlines that are parallel to each other. Velocities
should be greater than 0.5 feet per second and depths should exceed 0.5 feet. The streambed should also
be relatively uniform and free of slack water, eddies, and excessive turbulence. Finally, the measurement
section should be located relatively close to the gaging station. Each of these conditions will impact the
accuracy of the measurement data.
3. The spacing of the observation verticals also impacts the measurement accuracy. Ideally, 25 to 30
verticals should be used; the verticals should be spaced so that each subsection will have approximately
equal discharge.
4. Inaccuracies in sounding and the placement of current meters are most likely to occur in those sections
that have great depths and velocities. As a result, heavy sounding weights should be used to reduce the
vertical angle made by the sounding weight.
5. Wind also affects the accuracy of discharge measurements.
6. Measurements during freezing winter conditions can be especially challenging.
Comments:

EXPERIMENT NO-7
DETERMINATION OF VELOCITY AND DISCHARGE USING FLOATS
OBJECTIVE:
To Measure volumetric flow rate (Q) and mean velocity (v) of a stream.
INTRODUCTION:
Stream flow or volumetric flow rate/discharge is defined as the volume rate of flow of water (including any
sediment or other solids that may be dissolved or mixed with it) (Buchanan and Somers, 1969). Hundreds of
thousands of stream flow measurements are done every year. They can be done on a wide array of water
body discharges, from still waters to floods. Since the flow velocity varies at different points in a stream
cross section, calculating the average velocity at many points within that cross section is highly
recommended.
APPARATUS:
 Tape measure
 Watch or stop-watch
 Rod, yard or meter stick to measure depth
 Buoyant objects such as a weighted block of wood or oranges (objects that float immersed at the water
surface).
 Stakes for anchoring tape measure to stream banks
 Waders
RELATED THEORY:
Discharge:
In hydrology, discharge is the volume rate of water flow that is transported through a given cross-sectional
area. It includes any suspended solids (e.g. sediment), dissolved chemicals (e.g. CaCO3 (aq)), or biologic
material (e.g. diatoms) in addition to the water itself.
Stream velocity:
Stream velocity is the speed of the water in the stream. Units are distance per time (e.g., meters per second
or feet per second). Stream velocity is greatest in midstream near the surface and is slowest along
the stream bed and banks due to friction.
Reach:
For the float method, measure out some convenient distance along the stream bank (try at least 30 meters).In
hydrology, this is called a "reach".

Float:
To move or cause to move buoyantly, lightly, or freely across a surfaceor through air, water,etc.
Types:
 Surface floats:
Surface floats are small, light bodies, such as wood or wax, which float on the surface of the water and can
readily be seen from the shore. Measurement by this means is rapid hut the velocities obtained may be
greatly in error, due to the action of wind on the float.
 Double floats:
The double float consists of a light surface float and a subsurface float somewhat heavier than water
connected to it t>y a cord or a small rope. The office of the upper float is to support the lower float and
indicate its position. The connecting cord can be lengthened at will and the lower float be placed at any
desired depth.
 Float rod:
Professor Cabeoc was the first to use the float rod for measuring velocity. This was in 1646. The rod is of
wood or tin, from 1 to 2 inches in diameter, weighted at the lower end so as to float vertically. Its lower end
should nearly touch the bottom and its upper end project a few inches above the surface of the water, so as
to be visible.
 Float frame.
For obtaining velocity, a light frame of wood which nearly filled the cross section of the channel, but there
are practical difficulty in the way of the use of this instrument.
CONDITIONS FOR FLOATING MEASUREMENT:
The following are favorable conditions for float measurements:
 The river channel must be straight with more or less uniform cross-section along the entire reach.
 The length of the reach must be from 50 m to 100 m.
 There must be steady flow along the entire reach.
 The stream channel should have no under-water surface obstructions that would disturb the flow of
water, and consequently the stream velocity.

PROCEDURE:
The following procedure outlines the methods to follow in making discharge measurements:
1. Reconnaissance is conducted along a segment of the stream to find a convenient site of observation.
2. When a favourable site is selected, the selected length of reach is measured, say 50 meters, marking the
ends with a stake.
3. If possible, travel time should exceed 20 seconds.
4. A range line through each stake is constructed. Both range lines are made perpendicular to the axis of
the stream by using the 3–4–5 triangle method of erecting perpendiculars, or by the compass or other
means.
Figure 4.1: Cross-section of a Stream
5. The width of the stream at the upper and lower ends are measured with a tape if the stream is narrow,
and by the triangulation method if the stream is wide.
6. Tag lines, each spanning the stream at the upper end and at the lower end are laid. Similar tags are
placed at the first, mid and third quarter points. The depths are measured at the upper and lower end tag
lines.
7. Members of the survey team do the following:
 One observer at the upper end with a signal flag.
 One member of the team acts as a recorder.
 One observer at the lower end with a stop watch.
 One observer further upstream to release the float.
 One member of the team to retrieve the float.

8. The chief of the survey team signals for the beginning of observations. The float is then released further
upstream. Once the float passes the upper end tag line, upper end observer drips down his flag. The
lower end observer receives the signal by taking note of the time with the stop watch.
9. When the float passes at the lower end tag line, the lower end observer again takes note of the time the
float has travelled and then recorded. The float is retrieved.
10. Average your cross-sectional areas (A) to compute Q.
11. The above procedure is being repeated at the first, mid and third quarter points.
Optional steps:
If increased accuracy is desired and the stream is wide enough, you can divide the stream into 3 or more
sections or float lanes, and measure surface velocities in each lane.
Figure 4.2: Stream
OBSERVATIONS AND CALCULATIONS:
Vsurface = travel distance/ travel time = d/t
Because surface velocities are typically higher than mean or average velocities
V mean = k Vsurface where k is a coefficient that generally ranges from 0.8 for rough beds to 0.9 for smooth
beds (0.85 is a commonly used value)

V = d/t Q = VA
Where:
V = Stream velocity
D = distance of float travelled (m)
Q = rate of discharge
A = [Width of the river (m)] × [average depth of water (m)]
T = time (minutes)
FACTORS CONTROLLING ACCURACY OF STREAM MEASUREMENT.
 The accuracy of a stream measurement depends largely upon the accuracy with which the cross-
sectional area and the velocity are measured.
 The accuracy of a discharge measurement also depends much upon the physical features of the stream at
the discharge section or point of measurement. When possible, this section should be on a straight reach
and far enough from a bend t6 be out of its influence, the bed should be permanent and not stony, and
the slope and wetted perimeter such that at high and low stages of the stream, the velocity in all parts of
the section will he easily measureable.
 Rapid fluctuations of the water surface or river height during measurement and the condition of the
velocity-measuring instrument are other factors which affect the accuracy of a stream measurement.
Comments:

EXPERIMENT NO-8
STUDYOF BAROMETER
OBJECTIVE:
To learn about this device, called barometer. Find out the history behind its discovery and how it functions.
INTRODUCTION:
A barometer is a scientific instrument used in meteorology to measure atmospheric pressure. Pressure
tendency can forecast short term changes in the weather. Numerous measurements of air pressure are used
within surface weather analysis to help find surface troughs, high pressure systems and frontal boundaries.
A BRIEF HISTORY OF THE BAROMETER:
The first barometer is thought to have been built sometime between 1640 and 1643 by Gasparo Berti,
however, Evangelista Torricelli who is generally credited with inventing the barometer built the first
barometer with mercury in 1643. It was not until around 1675 that barometers were used domestically for
weather prediction. The stick barometer was the first made as a scientific instrument. As the popularity of
the barometer grew so did their decoration and attractiveness and were considered prize pieces of furniture
as well as being useful. The wheel barometer was devised around 1663 but gained popularity in the 1770’s.
A problem with these mercury barometers was that they were not easily portable without spillage. By 1843
Vide had invented a barometer without mercury, an aneroid barometer, which consisted of a chamber being
connected to the pointer by levers to enhance movement and thus more portable and used by scientists to
measure heights of hills or at sea.
WHAT IS ATMOSPHERIC PRESSURE?
The atmospheric pressure is the force exerted by the weight of the Earth's atmosphere, expressed per unit
area in a given horizontal cross-section. Thus, the atmospheric pressure is equal to the weight of a vertical
column of air above the Earth's surface, extending to the outer limits of the atmosphere.
HOW WEATHER AFFECTS AIR PRESSURE:
One of things you see most frequently in weather forecasts is big “H” and “L” signs moving across a map.
These are large swaths usually many hundreds of miles across of high or low pressure. There’s no number
which indicates high or low; it’s merely a relative term an area of high pressure is higher than what is
around it.An area of high pressure i.e. more downward force pushes air down. As the air descends, it warms,
which inhibits the formation of clouds and storm systems. So high pressure is almost always a sign of good
or fair weather.

Figure 5.1: Effect of Weather on Air-Pressure
TYPES OF BAROMETER:
 Water-based barometers:
The water barometer consisted of a 30’ long vertical glass tube that was sealed at the top; the open bottom
was immersed in a cistern of water. As the atmospheric pressure increased, the level of the water in the
column rose, falling again as the atmospheric pressure decreased.
Figure 5.2: Water-based Barometer
 Mercury Barometer:
The standard mercury barometer design is the same as the water one only the glass tube is 29.92 inch high
containing mercury.

As a storm approaches, the atmospheric pressure drops and the level of the column of mercury also falls.
Once the storm passes and high pressure returns, the height of the column of mercury rises with the
increasing atmospheric pressure.
Figure 5.3: Mercury Barometer
HANDLING PRECAUTIONS FOR MERCURY:
High-purity distilled and refined mercury is used in mercury barometers. When the mercury surface
oxidizes, the interface between the surface and the ivory pointer becomes unclear. Heavily contaminated
mercury surface requires cleaning. Since mercury is a toxic substance, it is necessary to pay attention to the
following when handling mercury.
 A container of mercury must be sealed tightly to prevent leakage and breakage. Do not put mercury into
any metal containers as mercury reacts and amalgamates almost all metals except for iron.
 The floor of the room where mercury is stored or used in large amounts should be shielded and laid with
an impervious covering. It must not be stored together with other chemicals, especially with ammonia or
acetylene.
 Mercury has a relatively low boiling point of 357 °C, and produces dangerous poisonous gas if on fire. It
must not be stored close to a heat source.
 Check the mercury handling room and personnel periodically to make sure that the amount of mercury
does not exceed the dangerous limit. (The environmental regulation on water contamination affecting
personal health limits the total amount of mercury to 0.0005 mg/l.)

Correction of barometer readings:
The mercury barometer’s reading should be corrected to the one and the standard condition. Standard
condition is defined as a temperature of 0 °C, where the density of mercury is 13.5951 g/cm3 and a gravity
acceleration of 980.665 cm/s2. During actual observation, the reading should be corrected for the index
error, temperature correction, and gravity acceleration as follows:
Corrections on index error:
Individual mercury barometers include index errors (difference between the value indicated by an individual
instrument and that of the standard). The index error is found by comparison with the standard, and the
value is stated on a "comparison certificate".
Corrections for temperature:
The temperature correction means to correct a barometric reading, obtained at a certain temperature, to a
value when mercury and graduation temperatures are 0 °C. The temperature of the attached thermometer is
used for this purpose. The height of the mercury column varies with temperature, even the atmospheric
pressure is unchanged. The graduation of the barometer is engraved so that the correct pressure is indicated
when temperature is 0 °C. In a case that when temperature is above 0°C, the graduation expands and the
measured value will be smaller than the true value. This effect of temperature must be corrected from these
two aspects collectively Correction for the expansion and contraction of mercury is much larger than that for
the expansion and contraction of the graduation. The correction value for temperature Ct is expressed as
follows: where: H hPa is the barometric reading after the correction for index error. t °C is the temperature
indicated by the attached thermometer.  is the volume expansion coefficient of mercury.  is the linear
expansion coefficient of the tube. There is a small difference in absolute values for correction between
temperatures below and above 0 °C. The values for correction at temperatures above 0 °C are negative and
those below 0 °C are positive.

Corrections for gravity:
Gravity affects the height of the mercury column. After the corrections for index error and temperature, the
reading under the local acceleration of gravity has to be reduced to the one under the standard gravity
acceleration. This is called corrections for gravity. The gravity value for correction Cg is derived by: where:
g0 is the standard gravity acceleration. g is the gravity acceleration at an observing point. H is the
barometric reading after the index error and temperature corrections H0 is the value already corrected for
gravitation. The gravity acceleration used in corrections for gravity value is calculated to the fifth decimal
place, in m/s2. When the gravity acceleration at the observing point is larger than the standard gravity
acceleration, the gravity value for correction is positive. Otherwise, the value for correction is negative. To
use a barometer for regular observations at a particular location, a synthesis correction table that summarizes
values for correction for index error, temperature and gravity should be used.
ANEROID BAROMETER:
The aneroid barometer succeeded the water and mercury barometers and gives a very accurate measurement
of atmospheric pressure. It consists of a small evacuated container with a corrugated top. As the atmospheric
pressure rises, the corrugated top is pushed inwards and as the pressure decreases the top pops back up
again. A system of levers connects the corrugated top to a dial that indicates atmospheric pressure in milli-
bars.
Figure 5.4: Aneroid Barometer

 BAROGRAPH:
A barograph is a barometer that records the barometricpressure over time. The barograph is an automated
version of the aneroid barometer, except there is a pen connected by levers to the corrugated top. This pen
traces atmospheric pressures onto a barogram located on a revolving drum. Examples of barographs and
barograms are shown below;
Figure 5.5: Barograph
 Electronic Barometer:
Stable and continuous power supply is required to measure atmospheric pressure with an electronic
barometer.
 Testing vacuum in a barometer:
Greater the atmospheric pressure, greater is the vertical height of the mercury column. The space above
mercury is a vacuum. This empty space is called 'Torricellian vacuum'. This can be shown by tilting the tube
till the mercury fills the tube completely.
 The Fortin Barometer:
It is an improved version of the simple mercury barometer. It gives more accurate reading of the
atmospheric pressure because a vernier scale is used here.

Figure 5.6: The Fortin Barometer
USES OF BAROMETERS:
 Measuring Weather:
Barometers have long been used for measuring weather patterns. Air pressure from high and low pressure
fronts that move throughout the globe is useful in determining or predicting what the weather will be like at
a given time and on a given date. This is the most basic and historical use for barometers, and these devices
help determine whether it will be hot or cold, or what the likelihood of precipitation might be on any given
date.
 Pressure Reading Devices:
Other types of barometers include the pressure devices found on pressure cookers, canning utensils and
steam boilers. Any time an air pressure inside of a vessel has to be measured, a barometer is the most useful
tool to perform this measurement.
 Air Travel:
Other types of barometers include air pressure reading devices that report the air speed of an aircraft. Often
called pitot tubes, these devices are a type of barometer that senses the pressure of air moving against an
aircraft and then converts this reading into an estimated air speed indicator, allowing pilots to determine
how fast they are moving relative to the air around them.
 Altitude Measurements:
Yet another type of use for barometers on airplanes or elsewhere is as a measure of altitude. Since air gets
thinner and lighter the higher up you travel into the atmosphere, a barometer can be useful for determining
how high above sea level you are. Barometers that have this function are often called altimeters or altitude
meters.
PROCEDURE OF USING BAROMETER:
 Correct for altitude if using a stick barometer:
To accurately measure the air pressure using a stick barometer, you will need to correct for your altitude
using a conversion chart.[8] Look at the barometer at eye level and record the number next to the top of the
mercury. This is the pressure in millimeters of mercury (mmHg).
 Find your elevation and then use to the chart to find the relevant correction factor. Add the
correction factor to the reading on the barometer. This reading should match the reading of the local
weather service.
 If you are at an elevation of over 1,000 ft, stick barometers do not work.
 Set the manual hand to the current reading:
 The set hand will serve as a reference that allows you to easily tell if the pressure is steady, rising or
falling.

 Remember, this hand will only be present on an aneroid barometer. If you have an electronic
barometer, you can simply check the reading.
 If you have a mercury barometer, you will need to correct for altitude if you’re above sea level.
 Check the barometer an hour later:
Predicting weather using a barometer is all about changes in air pressure. You want to check the reading
every few hours to determine if the pressure is changing or staying the same.
 If using an aneroid or mercury barometer, gently tap the face of the barometer to release any
pressure changes stored in the mechanisms. Take the reading after the needle or mercury has stopped
moving.
 Move the set hand if the pressure has changed so the next time you check it will be obvious what
direction the air pressure is going.
 Chart the changes in pressure:
Keep a journal of all the readings you take with your barometer. Sketch a small graph for the changes in a
day to help with your forecasting. Is the pressure rising? Falling? Staying the same? This is all important
information for predicting the weather.
 Do not expect large changes in the movement of needle. Daily changes are usually between 0.02 and
0.10 of an inch using the barometer scale. Larger variations may occur in winter and are dependent
upon location and altitude.
 Take frequent readings (every few hours) and plot them on your graph.
Figure 5.7: Chart of Variation in Pressure
How Forecasting the Weather using Barometer:
 Predict rain if the air pressure is falling:
Generally, if the pressure is falling, the weather is taking a turn towards storms and rain. The starting point
of the reading is also important in the forecast. Higher readings indicate better weather even if the pressure
is falling.
 If the reading is over 30.2 inches of mercury and falling rapidly, this indicates cloudy, but warmer
weather.

 If the reading is between 29.8 and 30.2 inches of mercury and falling rapidly, rain is most likely on the
way.
 If it’s under 29.8 inches of mercury and falling slowly, rain is likely; if it’s falling rapidly, a storm is
imminent.
Figure 5.8: Rain
 Forecast improving weather when air pressure rises:
As the air pressure rises, the weather tends to improve as the high pressure systems moves through your
location.
 Readings over 30.2 inches of mercury that rise indicate that the weather will continue to be fair.
 Readings between 29.8 and 30.2 inches of mercury that rise indicate that the weather will remain
whatever it presently is.
 Readings under 29.8 inches of mercury that rise indicate that the weather is clearing, but will be
cooler.
Figure 5.9: Better Air Pressure
 Forecast fine weather when air pressure is steady:
Steady air pressure indicates long periods of nice weather and suggests that you will be experiencing
more of the same. If it’s sunny and the pressure is holding, expect more sunshine! Higher pressures
indicate warmer weather, while lower pressures indicate cooler weather.
 A strong high pressure system is around 30.4 inches of mercury. Anything above 30 is considered
high pressure.
 A typical low pressure system is around 29.5 inches of mercury. Anything below 29.9 is considered
low pressure.

Figure 5.10: Fine Weather
BAROMETRIC PRECAUTION:
 The barometric pressure graph produced by this watch can be used to obtain an idea of upcoming
weather conditions. Note that this graph provides only a rough idea of barometric pressure trends, and it
is not intended for official weather predictions or reporting activities.
 Pressure sensor readings can be affected by sudden changes in temperature. Because of this, there may
be some error in the readings produced by the watch.
Comments:

EXPERIMENT NO-9
STUDY OF THE RAINFALL GAUGES
OBJECTIVE:
To study about the rainfall gauge and different type of rainfall gauges.
HISTORY:
The first known rainfall records were kept by the Ancient Greeks, about 500 B.C.About 400 B.C. people
in India also began to record rainfall. The readings were correlated against expected growth, and used as a
basis for land taxes.
RAINFALL GAUGE:
Rain gauge is a type of instrument used by meteorologists and hydrologists to measure rainfall rate in a
certain period of time. Rain gauges are also known as udometer, pluviometer and barometer.
TYPES OF RAIN GAUGES:
There are two types of rain gauges:
1. Non-Recording Type Rain Gauge:
 Symons Rain Gauge/standard rain gauge:
Non-recording type rain gauge is most common type of rain gauge used by meteorological department. It
consists of a cylindrical vessel 127mm in diameter with a base enlarged to 210mm diameter.
At its top section, funnel is provided with circular brass rim which is 127mm exactly so that it can fit into
vessel well. This funnel shank is inserted in the neck of a receiving bottle which is 75 to 100mm high from
the base section and thinner than the cylinder, placed into it to receive rainfall.
Figure 6.1: Symon’s Rain Gauge
A Receiving bottle has capacity of 100mm and during heavy rainfall, amount of rain is frequently exceeded,
so the reading should be measured 3 to 4 times in a day. Water contained in this receiving bottle is measured

by a graduated measuring glass with accuracy up to 0. 1mm. For uniformity the rainfall is measured every
day at 8:30Am IST and is recorded as rainfall of the day. Proper care, maintenance and inspection of rain
gauge especially during dry weather is necessary to keep the instrument free form dust and dirt, so that the
readings are accurate.
 Standard rain gauge:
The standard NWS rain gauge, developed at the start of the 20th century, consists of a funnel emptying into
a graduated cylinder, 2 cm in radius, which fits inside a larger container which is 20 cm in diameter and
50 cm tall. If the rainwater overflows the graduated inner cylinder, the larger outer container will catch it.
When measurements are taken, the height of the water in the small graduated cylinder is measured, and the
excess overflow in the large container is carefully poured into another graduated cylinder and measured to
give the total rainfall. Sometimes a cone meter is used to prevent leakage that can result in alteration of the
data.
Figure 6.2: Standard Rain Gauge
2. Recording Type Rain Gauges:
There are five types of recording rain gauges
 Weighing bucket type
 Tipping bucket type
 Floating or natural syphon type rain gauge
 Optical rain gauge
 Acoustic rain gauge
 Weighing Bucket Type Rain Gauge:
Weighing bucket type rain gauge is most common self-recording rain gauge. It consists of a receiver bucket
supported by a spring or lever balance or some other weighing mechanism. The movement of bucket due to
its increasing weight is transmitted to a pen which traces record or some marking on a clock driven chart.
Weighing bucket type rain gauge instrument gives a plot of the accumulated (increased) rainfall values
against the elapsed time and the curve so formed is called the mass curve.

Figure 6.3: Weighing Bucket Type Rain Gauge
 Tipping Bucket Type Rain Gauge:
Tipping bucket type rain gauge is a 30cm sized circular rain gauge adopted for use by US weather bureau. It
has 30cm diameter sharp edged receiver and at the end of the receiver is provided a funnel.
Pair of buckets are pivoted under this funnel in such a manner that when one bucket receives 0.25mm of
precipitation (rainfall), it tips discharging its rainfall into the container, bringing the other bucket under the
funnel.
Figure 6.4(a): Figure 6.4(b):
Tipping Bucket Type Rain Gauges
Tipping of bucket completes an electric circuit causing the movement of pen to mark on clock driven
receiving drum which carries a recorded sheet. These electric pulses generated are recorded at the control
room far away from the rain gauge station. This instrument is further suited for digitalizing the output
signal.
 Floating or Natural Syphon Type Rain Gauge:
The working of this type of rain gauge is similar to weighing bucket rain gauge. A funnel receives the water
which is collected in a rectangular container. A float is provided at the bottom of container, and this float

raises as the water level rises in the container. Its movement being recorded by a pen moving on a recording
drum actuated by a clock work.
When water rises, this float reaches to the top floating in water, then syphon comes into operation and
releases the water outwards through the connecting pipe, thus all water in box is drained out. This rain
gauge is adopted as the standard recording rain gauge in India and the curve drawn using this data is known
as mass curve of rain fall.
Figure 6.5(a) Figure 6.5(b)
Floating Type Rain Gauge

 Optical rain gauge:
These have a row of collection funnels. In an enclosed space below each is a laser diode and a photo
transistor detector. When enough water is collected to make a single drop, it drops from the bottom, falling
into the laser beam path. The sensor is set at right angles to the laser so that enough light is scattered to be
detected as a sudden flash of light. The flashes from these photo detectors are then read and transmitted or
recorded.
Figure 6.6: Optical Rain Gauge
 Acoustic rain gauge:
The acoustic disdrometer is an acoustic rain gauge. Also referred to as a hydrophone, it is able to sense the
sound signatures for each drop size as rain strikes a water surface within the gauge. Since each sound
signature is unique, it is possible to invert the underwater sound field to estimate the drop-size distribution
within the rain. Selected moments of the drop-size distribution yield rainfall rate, rainfall accumulation, and
other rainfall properties.
Figure 6.7: Acoustic Rain Gauge
SELECTION OF RAIN-GAUGING STATION:
While selecting the site for rain-gauging station following points are taken into consideration:
 The spot at which rain-gauge is to be installed should be truly representative of the area, of which it is
supposed to give depth of rainfall.
 The rain-gauging station should be easily accessible to the observer at all times.

 The gauge should be erected on level ground, not upon a slope or a terrace and never on a wall or a roof.
 All other conditions satisfied, a position sheltered from the wind is preferable to an exposed one. In
mountains and near sea coasts it is very essential to ensure that the gauge is not un-dully exposed to the
swept of wind.
 The gauge should be properly secured by a barbed wire fencing and locking arrangement.
 The rain-gauging station should not be too close to the buildings or trees etc. The nearness of such
objects affects entry of rainfall in the funnel. Its distance from other objects should not be less than twice
the height of the object above the rim of the gauge.
Network of Rain-Gauges:
The network of observation stations has to be properly designed to cover all the representative portions of
the basin area with due care to the topography, orography so as to get equitable coverage of spatial
variations in the basin. The broad guide lines set up for the required network of rain-gauge stations as per
World Meteorological Organization (WMO) is as follows: For plain areas of the basin 1 rain-gauge for
every 500 km2. For hilly areas of the basin: 1 rain-gauge for every 150 km2.
Limitations of Accuracy:
The most significant influences on the accuracy of precipitation measurement are the environment and wind
at the installation site rather than the performance of the instrument itself. Such influences are difficult to
eliminate. Additionally, because precipitation is strongly characterized by locality, it is difficult to choose
observation sites with a sufficient level of representation. Site selection without such consideration may
result in observations that have very poor accuracy.
Windshields:
Wind exerts a significant influence on the observation of precipitation with snow and rain gauges, and there
is no way to avoid its effects. However, accurate collection of precipitation in a rain gauge is possible when
the wind around the receptacle is horizontal and its speed is equal to that at ground level or when no vortices
develop near the gauge. A windshield is effective in reducing the influence of wind.
SOURCES OF ERRORS:
Observation errors in measuring precipitation are caused by the influences of the environment, instrument
errors and errors due to wetting and evaporation.
 Some initial rainwater may get lost in moistening gauge funnel and inside surface.
 Blowing wind may tilt the rain from vertical which thus brings less rain catch in the gauge.
 Vertical upward air currents may impact upward acceleration to precipitation thus brings less rain catch
in gauge.
 Mistake in reading the scale of gauge.
 Dents in collector rim may change its receiving area.
 Some rain water may get lost due to splash from the collector.
 Gauge inclined 10 ̊ from vertical will approx. cater 1.5 % less rain than it should.
 Tipping of bucket may be affected due to rusting or accumulation of dust on pivot.

HOW TO INSTALL A RAIN GAUGE:
Step#1: Location:
Find a good spot outside for your rain gauge. Look for an open area away from buildings and with nothing
overhead such as trees, electric wires, or the edge of a roof. These obstacles can direct rainwater into or
away from the opening of your gauge and cause inaccurate measurements.
Examples of Good Locations for Rain Gauges
(a) Deck Railing (b) Fence
(c) Mailbox Post (d) Middle of Yard
Figure 6.8: Location for installing rain gauge
Step#2: Mounting:
Once you've found the perfect spot, it's time to place the rain gauge. For the State Water Survey rain gauge
pictured in the upper left-hand corner of this page, there are two different mounting methods:
Ground Insertion:
Firmly push the rain gauge into the ground, pointy-end first. Remember storm winds can be strong so be
sure to push the gauge deep enough for it to stand upright in bad weather.
Surface Attachment:
The easiest way to mount the rain gauge to wood is to nail it in place using the two mounting holes located
on the bottom "stake" of the rain gauge.

 Find two nails with heads small enough to slide completely through the mounting holes. Finish nails
work well. You don't want to use screws or large-headed nails since the gauge must be removed from
the fence or post in order to dump out old rainwater.
 Holding the rain gauge in your hand, position the tube so the open top of the gauge will be an inch or
two above the wood post, fence, or stick (see pictures a, b, and c on earlier page). That way the wood
won't shelter the gauge from full rainfall.
 Test to see if your gauge can slide easily on and off the nails. If not, adjust the nails.
PRECAUTIONS TO BE CONSIDERED WHILE INSTALLING A RAIN GAUGE:
 Do not place a rain gauge under trees or roofs to avoid extra collection of water
 Prevent it from any obstruction
 Place it on a raised fixed platform to avoid splashing water from entering
 While measuring the rainfall it is required to note that rain gauge should not be inserted totally
inside the ground.
 Rain water should not be lost in the ground.
 Rain water should not be evaporated.
Comment

EXPERIMENT NO-10
MEASUREMENT OF WIND VELOCITY
OBJECTIVE:
To measurement of wind velocity using an anemometer.
APPARATUS:
 Anemometer
RELATED THEORY:
 Wind:
Wind is the horizontal movement of air.
 Wind velocity:
Wind speed is the rate or movement of air flow as it travels from high to low pressure, in relation to the
Earth. Warm air rises because it weighs less than cold air, and the cold air then moves in and replaces the
warm air.
 Anemometer:
The instrument used to measure wind speed is called an anemometer, which is an indicator that will spin in
the wind. The anemometer rotates at the same speed as the wind. It gives a direct measure of the speed of
the wind.
Figure 7.1: Anemometer

 The Beaufort Scale:
The Beaufort scale was devised by Sir Francis Beaufort from Navan, County Meath. It is a way of
estimating the wind strength according to the appearance of the sea or land.
Table 7.1 wind speed and description
Category Wind speed Description
0
< 1 km/h Calm - Smoke rises vertically.
1
1–5 km/h
Light air- Direction of wind shown by smoke but not by
wind vanes.
2
6–11 km/h Light breeze- Wind felt on face, leaves rustle.
3
12–19 km/h
Gentle breeze - Leaves and small twigs in constant
motion.
4
20–28 km/h
Moderate breeze - Raises dust and loose paper, small
branches are moved.
5
29–38 km/h
Fresh breeze - Small trees in leaf begin to sway, crested
wavelets form on inland waters.
6
39–49 km/h
Strong breeze - Large branches in motion, whistling
heard in telegraph wires, umbrella used with difficulty.
7
50–61 km/h
Near gale - Whole trees in motion, inconvenience
walking against the wind.
8
62–74 km/h
Gale - Breaks twigs off trees, generally impedes
progress
9
75–88 km/h
Strong gale- Slight structural damage occurs (chimney
pots and slates removed).
10
89–102 km/h
Storm - Seldom experienced inland, trees uprooted,
considerable structural damage occurs
11
103–117 km/h
Violent storm - Very rarely experienced, accompanied
by widespread damage.

12
≥ 118 km/h Hurricane.
FACTORS AFFECTING WIND SPEED:
 Pressure gradient:
Is a term to describe the difference in air pressure between two points in the atmosphere or on the surface of
the Earth. It is vital to wind speed, because the greater the difference in pressure, the faster the wind flows
(from the high to low pressure) to balance out the variation. The pressure gradient, when combined with
the Coriolis effect and friction, also influences wind direction.
 Rossby waves:
Are strong winds in the upper troposphere. These operate on a global scale and move from West to East
(hence being known as Westerlies). The Rossby waves are themselves a different wind speed from what we
experience in the lower troposphere.
 Local wof hurricanes, weather conditions:
Play a key role in influencing wind speed, as the formation monsoons and cyclones as freak weather
conditions can drastically affect the flow velocity of the wind.
PROCEDURE:
1. Divide the into small groups with the following roles (optional)
 One time keeper who will be responsible for timing one minute for each trial.
 One official "counter" for the day. The others may count on their own, but the counter's readings will
be the ones recorded.
 One holder who will hold the anemometer while the spins are counted; the holder should make sure
that he holds the anemometer so that the wind is unobstructed.
2. Mount or hold the anemometer in a place that has full access to the wind from all directions.
3. When the time keeper says "Go", the counter in each group will count how many times the marked cup
passes them in one minute and write it down.
4. If possible, repeat the above step four (4) times and record the average number of spins
Optional:
You can multiply the average number of spins by 60 to find out how many times the anemometer would
spin in an hour and come up with a statement such as: the speed of the wind today is about 1,000 spins per
hour.

PROCEDURE FOR DIGITAL ANEMOMETER:
1. Turn the instrument ON by pushing and holding the MODE button for 4 seconds. Release the MODE
button after turn ON.
2. Set the instrument into Manual Mode by holding the MODE button for 6 seconds. You will see a
flashing group of letter on the right.
3. Push the Plus (+) key until the m/s is displayed then release the MODE button. The display will default
to measuring wind speed in meters per second (m/s) in about 6 seconds.
4. Blow on the impeller mechanism for a few seconds and verify that the display indicates wind speed
measured in meters per second. The last wind speed reading will remain on the screen until the next
reading is taken.
5. Turn the floor fan ON to the highest speed setting.
6. Place the anemometer’s impeller at various points in front of the moving air from the fan – left, right and
middle – and note the readings you obtain.
7. Place the anemometer’s impeller closer to and away from the moving air and note the reading you
obtain.
8. Find the spot where you obtain the highest wind speed and note that position as the spot to place the
Wind Pitch wind turbine in subsequent experiments.
9. The bar graph on the left side of the LCD that moves up and to the right is the Beaufort Wind Scale
reading (bft). It shows in relative terms the general nature of the wind speed based on generalized
weather conditions. The actual wind speed number and the Beaufort numbers are different. For example,
a wind speed of 5.8 m/s will generate a bft of 4. Refer to the Table above for wind speed and bft ranges.
SAFETY PRECAUTION USING ANEMOMETER:
1. The use of the environment:
 It is forbidden to use an anemometer in a flammable gas environment.
 It is forbidden to place the anemometer probe in a flammable gas. Failure to do so may result in fire
or even explosion.
2. Note:
 Do not disassemble or modify the anemometer. Failure to do so may result in electric shock or fire.
 In use, if the anemometer emits an unusual smell, sound or smoke, or if liquid flows into the interior
of the anemometer, Please turn off the battery immediately to remove the battery.
3. MAINTENANCE:
 Do not expose the probe and anemometer body to rain. Otherwise, there may be electric shock, fire
and personal injury. Do not touch the internal sensor area of the probe.
 When the anemometer is not used for a long time, please take out the internal battery. Otherwise, the
battery may leak, causing damage to the anemometer.

 Do not place the anemometer in a place with high temperature, high humidity, dust and direct
sunlight. Failure to do so may result in damage to internal components or deterioration of
anemometer performance.
 Do not wipe the anemometer with volatile liquid. Otherwise, the anemometer housing may be
deformed and discolored. When the surface of the anemometer is stained, it can be wiped with a soft
fabric and a neutral detergent.
 Do not drop or press the anemometer. Failure to do so will result in malfunction or damage to the
anemometer.
 Instructions for use: Please use the anemometer correctly according to the requirements of the
instruction manual. Improper use can result in electric shock, fire, and damage to the sensor.
 Do not touch the sensor part of the probe while the anemometer is energized. Otherwise, it will
affect the measurement results or cause damage to the internal circuit of the anemometer.
Comments:

EXPERIMENT NO-11
MEASUREMENT OF ATMOSPHERIC TEMPERATURE
OBJECTIVE:
Upon completion of this unit of instruction, student aviators and flight officers will demonstrate knowledge
of meteorological theory enabling them to make intelligent decisions when confronted with various weather
phenomena and hazards.
INTRODUCTION:
The purpose of this assignment sheet is to introduce the student to the general composition and structure of
the atmosphere, the properties of temperature and atmospheric pressure, and their effect on aircraft
altimeters. This lesson will discuss the basic building blocks of the atmosphere, beginning with the lower
layers in which most flight activity occurs. These layers have particular temperature characteristics affecting
many aspects of weather and are important to the understanding of later chapters.
APPARATUS:
 A mercury thermometer
 A radiator
 An ice pack
 A notepad
 A pen
 Graph-paper
RELATED THEORY:
Temperature refers to how hot or cold the atmosphere is as measured by a thermometer in Celsius (C) or
Fahrenheit (F) Kelvin (K).A traditional thermometer consists of mercury red sprite or green sprite in a glass
tube and operates on the principal that the liquid expands more that the glass does when heated.
HOW DO I CONVERT READINGS FROM CELSIUS TO FAHRENHEIT?
To convert between the two, we use the following equations:
TC = (TF − 32) ÷ 1.8
When the temperature is given in TF and need to convert it into Celsius
TF = (TC × 9/5) + 32
When the temperature is given in TC and need to convert it into TF
TC= Means temperature in Celsius.
TF= Means temperature in Fahrenheit.
Thermometer:
A thermometer measures the air temperature. Most thermometers are closed glass tube containing liquids
such as alcohol or mercury. When air around the tube heats the liquid, the liquid expands and move up the

tube.
Figure 9.1: Thermometer
Types of Thermometer:
 Analogue Thermometers
 DualSensorThermometers (Indoor Outdoor)
 Temperature Labels
 K-typeThermocouples (K-typeThermometers)
 InfraredThermometers
 Probe Thermometers.
Analogue Thermometers:
Analogue thermometers are often one the cheapest and most popular types of thermometer. They are ideal
for use in the home or in non-specialist environments where traceable accuracy is not required. Most people
associate analogue with liquid filled devices. But the term is inclusive of a range of Bi-Metal devices that
operate using mechanical components. The visual display is often a dial or pointer or scale.
Figure 9.2: Analogue Thermometer
Dual Sensor Thermometers (Indoor Outdoor):
Indoor outdoor thermometers are unique due to how they record and display data. Unlike many other
devices they contain two probes. These probes come in a variety of forms. The most common arrangement

is an internal probe within the unit itself and an external probe sometimes connect via a wire. The external
probe can be placed a long distance away from the unit. Some external probes can be wireless for a longer
range. The display shows both readings at the same time allowing direct comparisons. A common use is as
fridge freezer thermometers. They are also common in storage areas and classrooms. They are an
inexpensive but more durable alternative to analogue devices.
Figure 9.3:Dual Sensor Thermometers (Indoor Outdoor)
Temperature Labels:
Temperature indicator labels are not strictly a type of thermometer but boy are they useful. These labels are
self-adhesive temperature proofing foils. They are ideal for use in processes which need to reach specific
temperature values such as sterilization. Labels are great for a clear indication of when temperature values
are exceeded. We sell a great deal of these to breweries for monitoring tanks during brewing. Each foil
segment on a label is sensitive to a different temperature and when exposed to its rating will turn black. The
most common models are irreversible meaning they are a one-time use once activated
Figure 9.4:Temperature Labels
K-type Thermocouples (K-type Thermometers):
K-Type thermocouples are one of the more specialized and niche types of thermometer. They deal with
extreme temperatures and are most common in laboratories and industry. This type of device caters for
applications that need high precision. Their most notable feature is the ability to facilitate a range of
interchangeable plug in probes. ‘K-type’ actually refers to the probe metal composition. We still refer to the
unit as a K-Type as it is the most common type of probe. Each probe has a specific purpose. Models with
multiple sensors allow comparative readings. We recommend you check out our thermocouple probes

before purchasing. Due to the high precision needed with these devices we always recommend calibration.
Figure 9.5:K-type Thermocouples (K-type Thermometers)
Infrared Thermometers:
Infrared thermometers are one the go-to types of thermometer for non-contact measurement. The non-
contact feature makes them the best tool for measuring extremely high or low surface temperatures. It is
common for them to include a laser targeting system designed to show the Centre of the measurement area.
Out of all thermometers, they can be the most complex to use due to complexities such as spot-size and
emissivity. We recommend you visit our Infrared page to learn more about them. They find use in places
such as the automotive trade and air conditioning systems.
Figure 9.6:Infrared Thermometers
PROCEDURE:
 Find a place outside to keep the thermometer.
 At the same time every day (for example 10.00 a.m.), record the temperature at this place.
 Repeat this every day for a month.
 Record the data on the notepad.
 Choose one month in winter and one in summer to show differences.
 After a month of recording, draw a graph to represent the data.
 Plot the days along the horizontal axis and the temperatures along the vertical axis.

 Join the dots.
Analyzing results:
Ask the following questions:
1. Has the temperature has changed over the month?
 Are there any differences between winter and summer months?
 What was the coldest reading (minimum temperature)?
 What was the hottest reading (maximum temperature)?
1. Calculate the average (mean) temperature for the month by adding up the temperature recorded on
each day and dividing your result by the total number of days in the month.
Comments:

EXPERIMENT NO-12
STUDY AND USES OF GPS (GLOBAL POSITIONING SYSTEM )
OBJECTIVES:
The Global Positioning System (GPS) tells you where you are on Earth. GPS is the only system today that
can show your exact position on the Earth anytime, in any weather, no matter where you are! It also tells the
elevation from the sea level.
GPS HAS THREE ‘SEGMENTS’:
1. The space segment now consists of 28 satellites, each in its own orbit about 11,000 nautical miles
above the Earth.
2. The user segment consists of receivers, which you can hold in your hand or mount in your car.
3. The control segment consists of ground stations (five of them, located around the world) that make
sure the satellites are working properly.
Figure 10.1: A simple GPS
Comments:

EXPERIMENT NO-13
DETERMINATION OF ELEVATION BY USING GPS
OBJECTIVES:
When the elevation is not on the level ground like slope and mountains. Then we take two readings of
elevation
Elevation 1 and Elevation 2.then we subtract smaller value from the greater one and we divide it by the
distance between these two points.
Elevation 1
Elevation 2
Distance
=
𝐸𝑙𝑒𝑣𝑎𝑡𝑖𝑜𝑛 2 – 𝐸𝑙𝑒𝑣𝑎𝑡𝑖𝑜𝑛 1
𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒
Comments:

EXPERIMENT NO-14
STUDY OF SPILLWAYS AND ITS TYPES
SPILL WAY:
When the water in the reservoir increases the large amount of reservoir increases the large amount of water
in dangers the stability of dam structure to avoid this a structure is provided in the body of dam or near the
dam this structure is called spill way.
OR
A spill way is a structure used to provide the controlled released of flow from a dam in a downstream area.
Figure 10.1:spill way
TYPES OF SPILL WAYS:
i. Over fall spill way:
It allows water to pass over it crust widely used on gravity arch and buttruss dam this is a simplest type
of spillway.
Figure 10.2:over fall spillway
ii. Saddle spill way:

This type is mainly used when other types are not favorable in some basins formed by a dam there may
be one or more natural depressions or saddle in the rim of the basin which can be used as spill way.
Figure 10.3:saddle spillway
iii. Shaft spill way:
This shape is just like a funnel water drops through a vertical shaft in a foundation material to
horizontal conduit that conveys the water passed the dam.
Figure 10.4:shaft spillway
iv. Side channel spill way:
When the Dam in not rigid and it is undesirable to passed flood water over the dam this type of spill
way is used.
Figure 10.5: side channel spillway

v. Emergency spill way:
It is design to safely pass the inflow design flood routed though the reservoirs if the flow is controlled
by gates it is a controlled spill way and if the flow is not controlled by gates then it is called an
uncontrolled spill way.
Figure 10.6:over fall spillway
vi. Siphon spill way:
It is designed by the principal of a siphon when water rises over the FRL (full reservoir level) then
water starts spilling.
Figure 10.7:siphon spillway
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