somendra sah Hydrology Report PDF.

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Engineering Hydrology (EG 664 CE)

Civil III/II-065 Batch

1

ACKNOWLEDGEMENT

We would like to acknowledge our obligation to Janakpur Engineering

College,Department of Civil Engineering for initating and faciliting one day

field tour of Engineering Hydrology. This Report is the outcome of field

visit in Engineering Hydrology carried by the Department of Civil

Engineering, IOE, Janakpur Engineering College,Tinkune Kathmandu. The

Purpose of this field visit was to make the each Student Independent to

carry out the work in real problem. We think, the purpose is fruitful and

which make us to produce the report of the fieldwork in time.

We are sincerely indebted to Department of Civil Engineering, Janakpur

Engineering College,. We would like to express our sincere gratitude to our

Field visit Coordinater Er.Ambikesh Kumar Jha, for his helpful suggestion

and instruction, during the fieldwork, without which it was very difficult to

do the work in the field and to produce the report, friendly behavior and

guiding any time during the whole work and also providing prompt

comments and rectification necessary before finalization of the report.We

cannot proceed further without thanking our Camp vice Coordinator Er.

Bir Bahadur Bohra, without whose valuable instruction we cannot finish

the work in such a worth manner.We are very thankful to our own College

that helped in lots of manner to make the field visit Successful.

At last, we would like to express our gratitude to everyone who

helped us and involved directly or indirectly for the execution of the

project.

Thank you

SUBMITTED BY:

1. Somendra Sah (065/BCE/44)


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2

INTRODUCTION

Engineering Hydrology

Hydrology means the science of water on the earth. It deals with the

occurrence, circulation, and distribution of water of the earth and earth's

atmosphere.Hydrology is an interdisciplinary science for investigation,

draws support from allied sciences such as meteorology, geology, fluid

mechanics, physics, Chemistry and statistics.

In a general sense engineering hydrology deals with:-

Estimation of water resources.The study of processes such as precipitation,

runoff,evapotranspiration and their interaction

The study of problem such as floods and droughts and strategic to combat

them.

Hydrology is classified as:-

1. Scientific Hydrology: which is concerned with academic aspects.

2. Engineering Hydrology: This is concerned with its engineering

applications.

Sources of data

The main components of hydrological cycle are rainfall, evaporation,

Transpiration, Infiltration, Runoff and Ground water. Depending upon the

problems in hand, a hydrologist would require data relating to the variousrelevant data such as:

Weather records e.g.Temp, Humidity, wind velocity Precipitation data Stream flow records Evaporation and transpiration data Infiltration characteristics of area Ground water characteristics Physical and geological characteristics of area


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3

General Knowledge of the measurement and reading of these data and the

instruments used for their measurement is of great importance in

Engineering Hydrology.

INTRODUCTION TO STUDY AREA:-

Rusi Khola is name of khola which is situated in Panauti.Panauti is 30 Km.

from Kathmandu.It lies in Kavre District &Bagmati Zone.

Other observation area is Cenral Weather Department which is situated in

Tribhuwan International Airport,Kathmandu.It lies Bagmati District &

Bagmati Zone.It is capital of Nepal.

Fig. Students at Roshi Khola


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OBJECTIVE OF FIELD TRIP

The main objective behind the offering field trip onEngineering Hydrology is to consolidate and updates the theoretical

and practical knowledge of engineering in their actual field so that

one can build upone's confidence and experiences in the related

field.In addition to this ,it develops a kind of team sprit and co-

operation for the long-term works with the environment.

The main objective of field trip are summarized below:

To provide an access to flow of water in river.To enhace the study of meterological stationTo practise the weather record,stream flow measurement,

precipitation data

To measure discharge of river.To know about the discharge measurement of equipment.Know about the how to measure rainfall, snowfall,temperature

,wind velocity ,evaporation in one day.

To know how to get information about weather of our country& other country.

To know about the application of hydrological knowledge inthe field of civil engineering.

Stream Flow Measurement

A stream can be defined as a flow channel into which the surface

runoff from a specified basin drains. A stream flow is measured in unit ofdischarge (m3/s) occurring at a specified time and constitute historical

data. The measurement of discharge in a stream forms an important

branch of hydrometer.

Discharge Measurement

The measurement of discharge in stream forms an important branch

of Hydrometry, the science of water measurement. In the hydrologicalcycle, streamflow is the only part which can be measured accurately. A


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stream is a flow channel into which surface runoff from a specified basin

drains.Firstly. We went to Roshi Khola Kavre Panauti for Stream

discharge measurement.

Discharge measurement was done by velocity area method. Floatationmethod was also done for velocity determination.

MethodologyArea-Velocity method:

This method of discharge measurement consists essentially of measuring

the area of cross-section of the river at a selected section called gauging site

and measuring the velocity of flow through the cross sectional area. This

method is the most practical method of measuring stream discharge.

In this method, the width of the stream is divided into a number of

increments. The following are some of the guidelines to select the number

of segments:

1. The segment width should not be greater than 1/15 to 1/20 of the

width of the river.

2. The discharge in each segment should be less than 10% of the total

discharge.

3. The difference in velocities in adjacent segments should not be

more than 20%

But most of the time all of these conditions cannot be fulfilled so we musttake steps according to the site condition.

For velocity measurement, for shallow sections, it is measured at 0.6 of the

distance from the water surface to streambed whereas for deep sections,

the average velocity is taken by measuring velocities at 0.2 and 0.8 of the

distance from the water surface to streambed.

The product of velocity, depth and width of the section gives sectional

discharge. The total sum of the sectional discharge is the total discharge ofthe stream.


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Q= A x V

Where; Q = discharge (m3/sec)

A = sectional area ( m2

)

V = velocity (m/s)

To measure depth, for shallow streams, height-calibrated rod can be used

whereas for deep streams and for accurate depth measurements

electroacoustic instrument called echo-depth recorder is used. Velocity is

measured using current-meter so this method is also sometimes called

standard current meter method.

1. Current Meter:

The most commonly used instrument used in hygrometry to measure

velocity is a current meter. It consists essentially of a rotating element

which rotates due to the reaction of the stream current with an angular

velocity proportional to stream velocity.

There are two types of current meter

1. VERTICAL AXIS CURRENT METER

The vertical axis meter consists of a series of conical cups a vertical axis.

The cups rotate in a horizontal plane and a cam attached to the vertical

axial spindle records generated signals proportional to the revolutions of

the cup assembly. The disadvantage of such meters is that these are useless

in situations where there are appreciable vertical components of velocities.

The accuracy is higher in higher velocities than in smaller ones.

2. HORIZONTAL AXIS CURRENT METER

The horizontal axis meters consist of a propeller mounted at the end of

horizontal shaft and these rotate in vertical plane w.r.t. horizontal axis.

These meters are fairly rugged and are not affected by oblique flows of as

much as 15.The accuracy of the instrument is about 1% at the threshold

value and is about 0.25% at a velocity of 0.3m/s and above.

The current meter is so designed that its rotational speed varies linearly

with the stream velocity at the location of the instrument. A typical

relationship is given by,


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V = aNs+ b

Where,

V = velocity of flow in m/s

Ns = no. of revolution per sec of the current meter

a and b are meter constants given by the manufacturer, or generally

determined by experiments. We used vertical axis current meter for

velocity measurements.

Current meter in the field atRoshi Khola

Fig.current meter

Procedure:

Suitable section of stream was first selected so that the reach isstraight and is free from obstacles such as boulders, plants, etc.

The width of the stream is divided into a number of segments, eachsegment usually containing no more than 10% of the total discharge.

For each incremental width, stream depth is measured.The current meter is placed at a depth where average velocity is

expected to occur (0.6 times the total depth from surface).This

procedure is known as thesingle point observation method.


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The total no. of revolutions in 30 seconds of time wasnoted from the digital counter.

The process was repeated for other width increments.

Observations and Calculations

FOR AREA VELOCITY METHOD:-

Distance from

left

Depth(Y) Number Of

Rev.

Rev./10Sec(N.

S.)

1 0.46 10

2 0.56 11

3 0.45 8

4 0.36 7

5 0.1 2

Width of river=5.25m

FOR FLOAT METHOD:-

Width Of River=4.0m

Distance=20m

S.N. Time(t)sec Velocity(v)m/sec

1. 22 0.909

2. 20 1

3. 18 1.111

4. 19 1.052

5. 21 0.952

6. 21 0.952

7. 29 0.65

8. 28 0.714

9. 19 1.05310. 21 0.952


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11. 18 1.11

12. 26 0.769

sum=11.224

CALCULATION & OUTCOME RESULT:-

FOR AREA & VELOCITY METHUD:-

1st Left

average width(w)=1.5m

Last Right

average width=1.75m

Other remaining

average width=1m

Distanc

e from

left

Average

width(

w) m.

Depth(

y)

m.

Ns=Rev/s

ec

Velocity

V=0.51Ns+0.

03

m/sec

Area

(A)

m2

Segmental

discharge

Q(m3/se

c)

1 1.5 0.46 1 0.54 0.345 0.186

2 1 0.56 1.1 0.591 0.56 0.33

3 1 0.45 0.8 0.438 0.45 0.197

4 1 0.36 0.70 0.387 0.36 0.139

5 1.75 0.1 0.2 0.132 0.0875

0.011

TOTAL DISCHARGE(Q)=0.863m3/sec

FOR FLOAT METHOD :

Total X-sectional of River=1.08 m2

Average velocity=11.224/12=0.935 m/sec

TOTAL DISCHARGE(Q)=1.009 m3/sec


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2. Float Method

A floating object on the surface of the stream when timed can yield the

surface velocity by the relation.

Vs = S/t

Where, S =distance travelled in time t.

This obtained velocity Vs when multiplied by the cross sectional area A of

the stream along the mid point of the S distance gives the discharge Q using

the relation:

Q = Vs*A

This method of finding velocity and hence discharge finds applications in

special circumstances although is primitive method: ( I ) a small stream in

flood ( II ) a small stream with rapidly changing water surface and (III)

preliminary surveys and also for checking purposes.

There may be surface floats (simple float moving on the stream) or there

can also be the Rod Float, in which a cylindrical rod is weighed so that it

can float vertically.

Field Procedure:

After fixing the gauging site, a distance of 15 m. both upstream anddownstream was measured along the centre line of the river. Two

people stood at the two extreme points of the 30 m. length.

Then a surface float was allowed to flow through the above marked30 m. and the time taken to do so was measured using a stop watch.

The process was repeated as per required.

FIELD VISIT OF METEOROLOGICAL STATION AT AIRPORT

SINAMANGAL

The study of hydrology necessitates the collection of data on humidity,

temperature, precipitation, radiation, and evapotranspiration and wind

velocity. For the collection of these meteodata, number of meteostations is

fixed around the country. Around 400 meteorological stations are presentlyoperating in our country.


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This meteorological station operates under Department of Hydrology and

Meteorology, Nepal. The various equipments and instruments we studied

at this station were:

1, Rain gauge

Symonss Gauge (Non-recording Type)Tipping Bucket (Recording Type)

2. Campbell Sunshine Recorder

3. Anemometer

4. Steven Box

5. Evaporimeter

Steven Box (Psychrometer) - Thermometers for measuring Min & Max

temp. And Relative Humidity.

1. Rain Gauge

The precipitation is measured by an instrument called rain gauge.Rain

gauge is also known as hyetometer,ombrometer or pluviometer.Rainfall isexpressed in terms of the depth to which rainfall water would stand on an

area if the rainfall was collected in it. The rainfall is collected and measured

in a rain gauge.

A rain gauge essentially consists of a cylindrical vessel assembly kept in the

open to collect rain. Rain Gauge is broadly classified as:

i. Non recording Rain gauge

ii. Recording Rain gauge

( I ) Symonss Gauge ( Non-recording Gauge)

Symonss Gauge consists of a circular collecting area of about 12 cm

diameter connected to a funnel. The funnel discharges the rainfall catch

into a receiving vessel. The funnel and receiving vessel are housed in a

container. Water contained in the receiving vessel is measured by suitably

graduated measuring glass with accuracy unto 0.1 mm.The non recording

rain gauge gives the amount of rainfall only.


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They cannot provide the information regarding when exactly the rainfall

commenced.

(ii) Tipping Bucket rain Gauge (Recording Type)

Recording type rain gauges are those rain gauges,which can give

permanent automatic rainfall record without any bottle reading.Recording

gauge produce a continuous plot of rainfall against time and provide

valuable data intensity and duration of rainfall for hydrological analysis of

stroms. There is mechanical and electrical arrangement by which the total

amount of rain fallen gets recorded automatically on a graph paper. The

gauge thus produces a record of cumulative rain vs. time in the form of a

graph which is known as mass curve rainfall.

Rain water is first caught in a collector and is funnelled into a two

compartmental bucket of 0.25mm each. These buckets are so balanced that

when 0.25mm of rainfall collects in one bucket, it cannot withstand more

and tips round to bring the adjacent one in collecting position. The water

from tipping bucket can be collected. Further while tipping it actuates an

electrically driven pen to trace a record on clockwork driven chart. This

instrument can also digitize the output signal as seen to the automatic data

logger.

Fig.Rain gauge


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2. Campbell Sunshine Recorder:

Campbell Sunshine recorder is used to measure the duration of bright

sunshine hours which mainly depends on the latitude of the place and

environment. The main principle of Campbell Sunshine recorder is thatwhen bright sun rays are converged using a lens into a paper it gets burnt.

The special paper used is known as Campbell Sunshine card.

Campbell Sunshine recorder consists of a special arrangement of

transparent spherical lens provided with hourly graduated paper

(Campbell Sunshine card). The sphere is faced directly towards the sun by

fixing the latitude of place. The card is concentrically mounted with the

sphere.

Continuous burnt line on paper represents continuous sunshine and as

paper is graduated for time in hours, the no. of hours can be determined.

The glass sphere is usually 10cm in diameter. The card is held below the

sphere in any one of the three grooves depending upon the seasons of the

year. There are different cards for different hemispheres of the earth as

well as different card for various seasons:

Fig: Campbell Sunshine Recorder Fig: Campbell Sunshine card

3. Anemometer

Anemometer is used for measuring the speed and direction of wind. The

speed of wind varies with temperatures; pressure and altitude. There are

two horizontal arms over which the instrument for measuring direction


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and magnitude are mounted. Direction of wind is usually expressed in

terms of 16 compass points (N, NNE, NE, NEE, E, SEE,)

The anemometer used was a three cup anemometer with a vertical axis of

rotation.

Anemometer converts the rotational speed of the cups into linear speed.

The speed of wind is measured in km/day in the particular anemometer. It

was placed 2m above the ground surface.

Fig.Determinination ofDirection FigMeasurement of Magnitude of wind

Fig: Anemometer

4. Steven Box:

Steven Box consists of special arrangement of 4 thermometers with a view

to determine the maximum & minimum temperatures and Relative

Humidity.

Two small clips are placed inside the thermometers to measure the

maximum and minimum temperatures. When the temperature gets to the

minimum, the mercury remains at the same position even if temperatures

rises ( In case of minimum thermometers) whereas in case of maximum

thermometers its exactly the opposite. When the mercury rises to the


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maximum temp, the mercury remains there and hence maximum and

minimum temperatures are recorded. When we visited, the maximum

temperature recorded was 180C.

For the measurement of relative Humidity, two thermometers were placedvertically. One of the thermometer's bulb was wrapped around a wet cloth

and the bulb of the other was kept dry. These two thermometers'

combination is also called psychrometer. Wet bulb loses water from the

cloth constantly due to evaporation due to which the temperature of this

thermometer is lower than dry bulb temperature. The rate of capillarity in

the cloth depends upon Relative Humidity.

Wet bulb Deficit or Wet Bulb depression is the difference in temperatures

of these two thermometers.

Fig: Steven Box

5. Evaporimeter

An Evaporimeter is used to measure the evaporation rate and hence

estimate the approximate rate of evaporation from a natural water body.

Evaporimeters are large water containing pans which are exposed to the

atmosphere. If rate of evaporation is to be determined using an

evaporimeter, other meteodata such as humidity, wind movement, air and


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water temperatures and precipitation should be noted on a regular basis as

these parameters affect evaporation significantly.

Evaporation rate = (Evaporated volume) / Time taken to reduce the depth

Evaporimeters are generally placed at a height of 15cm above the ground

so as to allow free air circulation and on wooden blocks so that heat

transfer by conduction can be checked effectively.

Evaporation pans are not the exact models of reservoirs and posses some

drawbacks.

Fig: Evaporimeter


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Conclusions and Discussions

Due to the importance given to field trip, the students were able to

updates their theoretical knowledge of engineering in their actual field.In

addition to this,it develops a kinds of team sprit and co-operation for longterms work with the environment. With this field visit, we had a chance to

be familiar with the different hydrological parameters measured in

meteostations and the instruments & equipments used to measure these

parameters.

The different hydrological parameters measured were wind velocity, R.H.

of air, Rainfall intensity, Sunshine duration, Air temperature, Evaporation,

etc.

During this visit, temperatures were the only parameters we could

measure as other parameters required ample time and due to instruments.

The automatic data logger which was supposed to record all the data was

out of order. But we had the general idea of all the instruments and their

uses in measuring of hydrological data.

Comments:

Here ,the velocity from two different method produced two different

discharges. This can be due to the fact that floatation method, although was

performed repeatedly, did not give accurate results in comparison to

velocity area method. The accuracy in determination of discharge by A-V

method depends upon the time and economy. If more accurate results are

required, small increments in depths are recorded. Also if a floating rod or

a specified object was used in floatation, it could give more accurate results.

In the field, we floated small papers, plastics, etc which may also be the

reason that the results given by two methods did match.

We believe that such educational tour will be a lot of help for us in

understanding the actual situation while undertaking any professional

tasks in the future and we hope that IOE will continue such field tours.


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BIBLOGRAPHY

1.Engineering Hydrology- K.Subramanya

2.A Course Manual on Engineering Hydrology

-Er.Narayan Prasad Subedi

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