memberfiles.freewebs.com · web viewit deals with precipitation, evaporation, infiltration, ground...

ADEEL RAFIQ (BSCE01103167)

ADEEL RAFIQBSCE01103167

2012

Hydrology and water management lab copy

Design Exercise NO 1:Purpose:

TO PLOT A GRAPH FOR GIVEN DATA FOR TEMPRATURE “I”AND THE SATURATED VAPOUR PRESSURE “es” OF AIR SHOWING THAT THE SATURATED VAPOUR PRESSURE IS A FUNCTION OF THE TEMPRATURE.AND ALSO FIND THE FOLLOWIN FOR THE GIVEN CONDATIONS:

1. SATURATED DEFICIT (es-e)

2. RELATIVE HUMIDITY (f)

3. DEW POINT TEMPRATURE (Td)

RELATED THEORY:

Hydrology: Hydrology is the science of the water 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 the hydrological cycle.

The hydrological cycle involves evaporation, transpiration, interception, infiltration, runoff, seepage and precipitation. Due to solar radiation, water from ocean , river, lakes or may other body on earth surface evaporates in gaseous form.

Engineering hydrology:

It includes that segment of the field pertinent to planning, design and operation of engineering for the control and use of water.

Significance of hydrology:

Study of water is extremely necessary as:

1. It is the basic need for human life over the planet.

2. To cope with extreme hydrological events (for example: floods, droughts, etc.)

3. To determine input data for the design and operation of hydraulic structures like dams, reservoirs, storm drainage system, water supply schemes, etc.

Metrology:


It is the science of atmosphere which is gaseous envelope surrounding the earth.

Climatic Factors:

Metrology of the region is affected by certain climatic factors:

1. Amount of distribution of precipitation.

2. The occurrence of snow and ice.

3. Wind velocity

4. Temperatures

5. Humidity

IMPORTANCE OF KNOWLEDGE OF METEOROLOGY:

1. Cloud formation

2. Occurrence of precipitation.

3. Thunder storm formation.

4. Movement of rainstorms.

5. Weather forecast.

6. Flood warnings and forecasts.

Atmosphere:It is the gaseous envelope around the earth surface .it consists of many gases like nitrogen, oxygen, carbon di oxide, etc.

1. Troposphere2. Stratosphere3. Mesosphere4. 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 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 vapours, ice crystals, clouds and precipitating particles etc.

Vaporization:

It is the process of transformation of water from liquid state to vapour state.

Vapour pressure “e”:

Pressure exerted by the water vapours in air is known as Vapour pressure .The commonly used units are mm of Hg.

Saturation Vapour Pressure “ es ”:

It is the vapour pressure when air is fully saturated at a given temperature. It is the measure of moisture holding the capacity of air which increases with increase in the air temperature.

It 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 50 to 55°C by the use of following equation:

es ≈ 3.38639[(0.00738T+0.8072)8-0.000019(1.8T+48)+0.001316]

SATURATION DAFICIT:

The difference between the saturation vapor pressure and the vapor pressure the air at the given temperature is known as Saturation Deficit.

HUMIDITY: It is the pressure of moisture in the air. Humidity in the atmosphere can be

assessed by vapor pressure of air.

RELETIVE 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 TEMPRATURE”Td”:


It can be defined as a temperature at which the air mass just becomes saturated if cooled at constant pressure with moisture neither added nor removed.

PROCEDURE:1. Plot a graph between saturated vapor pressure and temperature.2. Plot condition 1 for given value of “e” and “T” on es~ T graph.3. For point 1 draw a vertical line passing through the point up to the saturation line.4. Measure distance between saturation line, it is the saturation vapor pressure for

point 1.5. Measure vertical distance between point 1 and saturated line, It is saturation deficit.6. Compute relative humidity by using the equation.7. 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.

8. Repeat steps 2 to 5 for other points as well.

Calculations:Table for plotting saturation curve:

Table of Calculation:

Sr. # Air temperature

Vapor pres.e(mm of

Sat.V.Pressurees(mm of Hg)

Sat. deficit “es-e”

Relative humidity

Dew point temp.


Sr. # Air Temperature =T ( ͦC)

Saturated Vapor Pressure = es

(mm of Hg)1 -4 4.322 -2 4.903 0 5.514 2 6.355 4 7.366 6 8.277 8 9.328 10 10.419 12 11.7310 14 13.2511 16 1512 18 16.8713 20 18.9114 22 21.1015 24 23.7516 26 26.6017 28 29.9518 30 34.40

‘T’ Hg) =e/esx100 Td

1 11 9 11.1 2.1 81.08 7.42 17 9.5 15.7 6.2 60.51 8.43 21 14 20 6 70.0 14.84 26 18 26.6 8.6 67.67 19.2

Results and comments:1. All values are given to us for calculations.2. As temperature increasing the dew point temperature is increasing.3. As vapor pressure increasing the relative humidity is decreasing.4. As relative humidity decreasing the dew point temperature is increasing

Design exercise no: 2


ANNUAL PRECIPITATION AT RAIN GUAGE “X “AND THE AVERAGE ANNUAL PRECIPITATION AT 25 SURROUNDING RAIN GUAGES ARE LISTED IN THE FOLLOWING TABLE.

1. EXAMIN THE CONSISTENCY OF STATIONN “ X “2. WHEN DID THE CHANGE IN THE REGIME OCCUR?3. ADJUST DATA THE DATA AND DETERMINE WHAT DIFFERENCE THIS MAKES TO

THE 36 YEARS ANNUAL PRECIPITION “X “.

RELATED THEORY:

PRECIPITION:Precipitation is defined as all type 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.

1. DRIZZLE / MIST2. Rain3. Snow4. Steel5. Glaze6. Hail7. Fogs8. Frost9. Trance

MECHANISM TO FORM PRECIPITATION:Following mechanisms are necessarily required for precipitation to occur over an area:

1. Lifting Mechanism2. Formation of Cloud droplets / Ice Crystals.3. Growth of cloud droplet / Ice Crystal4. Sufficient accumulation of moisture over an area.


RAIN GUAGE: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 unit of mm or inches.

INTENSITY OF PRECIPITATION:It is the amount of precipitation per unit time. It is usually expressed in mm/hr. or inches/hr.

MEAN/AVEARAGE RAINFALL FOR “N “YEARS:It is the arithmetic average of annual precipitation for “N “years over a rain gauging station.Mathematically,

Pavg = ∑❑ (Pi )N

Where:Pavg: Average PrecipitationPi: Annual precipitation for the ith year.N: Total number of year ⅀(Pi): Summation of annual precipitation for N years

ANNUAL RAIN FALL:It is the total amount of the rain fall in one year at a place. It can be calculated by taking the summation of the daily precipitation at any place for the whole year.

AVERAGE RAIN FALL OVER AN AREA:It is the total amount of precipitation which can be assumed as uniform for the area. It is calculate by using different approaches. By Arithmetic mean, it is calculate as:

Pavg =⅀ (Pi)/N

WherePavg: Areal average precipitationPi: Average annual precipitation for the ith stationN: Summation of annual precipitation for N station.⅀ (Pi): Summation of annual precipitation for N stations


CONSISTENCY OF PRECIPITATION DATA RECORD:It is the behavior of data record of a station as compared to the average of all the surrounding stations.

DOUBLE MASS ANAYLSIS/CURVE:At any station “X “, consistency of the data record is checked by plotting the Double mass curve. The variable on the y-axis is the Accumulated annual precipitation of the station “ X “ and on x-axis is the average of accumulated annual precipitation of the neighboring station “ N “ . Consistency is checked by the slope of the curve being single or more slopes.If the slopes of the curve remain constant, the precipitation data record is constant and if the slope doesn’t remains constant, data record is inconsistent.

REASONS OF INCONSISTENCY IN PRECIPITATION DATA RECORD:Precipitation data record may be inconsistent due to the following reasons:

1. Change in location of a rain gauge.2. Change of the instrument.3. Change in the observational procedure.4. Change in the vicinity of station, e.g. Construction, Landslide, frost, Flood,

Earthquake, etc.5. Faulty rain gauge for a certain period.

PROCEDURE:

1. Calculate cumulative annual precipitation for station “X “.2. Calculate cumulative average annual precipitation of “N “surrounding

stations.3. Plot scatter diagram between cumulative annual precipitation of Station

“X” And cumulative average annual precipitation of “N” surrounding station.

4. Join the points with straight lines and note down the intersection points.5. Determine slope of the curves.6. Compute ratio of the slopes.7. Adjust average annual precipitation of the station “X” after the change

has occurred.


Results:

slope1=6075

=0.80

slope2=120100

=1.2

correction factor=0.81.2

=0.667

%age differance=3953−33653953 = 14.87%

Comments:By calculation and draw the graph we found that the data is not consistence at X station by other 25 stations.

I have a lot of %age difference because in my manual graph I found 1954 as a change year but the actual change year was 1952.

Calculations:Year Annual precipitation (cm) Cumulative ppt(cm) Adjusted annual ppt at

station X( )Station X

Average of 25 surrounding stations

Station X

Average of 25 surrounding stations

1976 74 104 74 104 741975 73 90 147 194 731974 122 152 269 346 1221973 116 117 385 463 1161972 82 112 467 575 821971 113 138 580 713 1131970 72 93 652 806 721969 120 146 772 952 1201968 90 92 862 1044 901967 85 114 947 1158 851966 88 111 1035 1269 881965 80 97 1115 1366 801964 112 104 1227 1470 1121963 116 131 1343 1601 1161962 81 91 1424 1692 811961 106 92 1536 1784 106


1960 95 142 1625 1926 951959 112 123 1737 2049 1121958 88 142 1825 2191 881957 68 92 1893 2283 681956 111 131 2004 2414 1111955 86 93 2090 2507 861954 97 99 2187 2606 971953 112 112 2299 2718 74.71952 190 142 2489 2860 126.731951 126 111 2615 2971 84.041950 108 107 2723 3078 72.041949 127 108 2850 3186 84.711948 172 119 3022 3305 114.721947 153 138 3175 3443 102.051946 120 90 3295 3533 80.041945 126 123 3421 3656 84.041944 129 111 3550 3767 86.041943 121 124 3671 3891 80.701942 119 111 3790 4002 79.371941 163 135 3953 4137 108.72 ∑=3953 ∑=3364.9

Design Exercise No:3Tittle: The name, location, by longitude and latitude means annual precipitation for certain weather stations within and outside the catchment’s area are given below:-

Name of Station Longitude----ͦ ----‘

Latitude----ͦ ----‘

Mean annual ppt.(mm)


A 101 45 22 57 128.30B 101 09 21 54 136.73C 102 03 21 15 113.03D 102 06 20 27 123.77E 102 45 22 54 150.41F 104 09 22 39 186.51G 104 51 22 54 225.85H 102 51 21 57 126.51I 102 51 21 33 108.84J 103 42 20 27 141.40K 104 42 22 03 151.33L 104 54 22 45 161.46

Estimate the average rain fall over basin area by using following three methods

1. Arithmetical mean method

2. Thiessen polygon method

3. Isohyetal method

The boundary of watershed is rectangular and is defined by the following coordinates:-

A’ (101 ͦ 30’ ,23 ͦ 00’ )

B’ (104 ͦ 45’ ,23 ͦ 00’ )

C’ (104 ͦ 45’ ,20 ͦ 30’ )

D’ (101 ͦ 30’ ,20 ͦ 30’ )

RELATED THEORY: AVERAGE PRECIPITATION AND ITS SIGNIFICANCE:Average precipitation is defined as the amount of rain fall that can be assumed uniform for the whole basin area.With the help of average precipitation data, total volume of the rainfall over an area can be calculated by simply multiplying the basin area with the average precipitation over that area.

METHODS OF CALCULATING AVERAGE PRACIPITATION OVER AN AREA:

The methods mostly used for calculating average precipitation over an area are:


1. Arithmetic mean method2. Thiessen polygon method3. Isohyetal method

1. ARITHMETIC MEAN METHOD:It is an approximate method to calculate the average precipitation over an area. In this method, precipitation is averaged for different stations when the gauging stations area approximately equally spaced and also the amount of precipitation is recorded at these stations doesn’t vary much.

Pavg =⅀(Pi)/NWhere:Pavg: Average precipitation area over an area⅀Pi:: Sum of mean precipitation at N stationsN: Number of gauging stations

2. THIESSEN POLYGON METHOD:This method consists of weighing the value of precipitation at each station by a suitable proportion of the basin area.By this method:

Pavg=⅀(PiAi)/⅀(Ai)Where:Pavg=Average precipitation over an areaPi=Mean precipitation for the ith polygonAi=Area of the ith polygon

3. ISOHYETAL METHOD:It is defined as the line representing the same amount of precipitation. In this method, area between two isohyets is determined. Weighted average for these isohyets is determined and then average precipitation for the whole basin area is computed.

Pavg=⅀(PiAi)/⅀(Ai)Pavg=Average precipitation over an areaPi=Mean precipitation for the ith stripAi=Area of the ith strip

PROCEDURE:

FOR ARITHMETIC MEAN METHOD:1. Note down the annual precipitation for all the gauging stations.2. Sum of mean precipitation at all of the gauging stations.


3. Divide by the total number of stations to get average precipitation for the whole basin area.

Pavg=⅀Pi/N= (P1+P2+P3 +. . . . . . . +PN)/NWhere:Pavg= Average precipitation for the whole basin areaPi= Annual precipitation at the ith stationN= Number of gauging stations

FOR THIESSEN POLYGON METHOD:1. Select suitable and same scale for the both axes depending upon the boundary

limits for the catchment area.2. Plot catchment boundary and gauging stations locations.3. Plot polygons around each strength by each connecting closest stations by

straight dash lines and drawing perpendicular bisectors to make the sides of the polygons.

4. Determine area of each polygon by counting the numbers of squares.5. Compute product ( PiAi) and sum up all the products.6. Compute average precipitation using the following formula:

Pavg= (P1A1 +P2A2 +P3A3 . . . . . . . . . . . . . +PNAN)/ (A1+A2+A3+. . . . . . . +AN)Where:N: number of polygon within catchmentPi: mean annual precipitation for the Ith

polygonAi: area of the ith polygon

FOR THE ISOHYETAL METHOD:1. Select suitable and same scale for both X and Y axis.2. Plot catchments boundary and station locations.3. Maintain precipitation amount on each station.4. Select suitable counter interval and number of Isohyets.5. Draw Isohyets by linear interpolation between the stations.6. Compute product ( PiAi) and sum up all the products.7. Compute average precipitation using the following formula:

Pavg= (P1A1 +P2A2 +P3A3 . . . . . . . . . . . . . +PNAN)/ (A1+A2+A3+. . . . . . . +AN)

Where: N: Number of strip / segment within catchment

Pi : mean annual precipitation for the Ith strip. Ai: area of the ith strip


For Arithmetic mean method:

∑=1754.14

Pavg= 1754.1412

=146.14 %


Sr.No Name of station

Annual PrecipitationPi(………..)

1 A 128.302 B 136.733 C 113.034 D 123.775 E 150.416 F 186.517 G 225.858 H 126.519 I 108.8410 J 141.4011 K 151.3312 L 161.46

Table of calculations for Thiessen polygon method:

Sr.No Gauging Station

Observed annual

precipitation pi(mm)

Area of polygonAi(min²)

ProductP

iAi(mm.min²)

1 A 128.30 1700 2181102 B 136.73 2400 3281523 C 113.03 2900 3277874 D 123.77 1500 1856555 E 150.41 2500 3760256 F 186.51 1400 2611147 G 225.85 200 451708 H 126.51 2800 3542289 I 108.84 3300 35917210 J 141.40 4000 56560011 K 151.33 5900 89284712 L 161.46 200 32292

∑=28000 ∑=3946152

Pavg =3946152

28000=140.93 %


Table of calculations for Isohyetal method:

Sr.No Isohyetal precipitatio

npi(……….)

Mean precipitatio

npi(……….)

Area of strip

Ai(…………..

)

ProductPiAi(…….)

1 108.84110 4600 506000

2 130 13300 1729000

3 150 7700 1155000

4 170 2300 391000

5 190 1000 190000

6 210 600 126000

∑=29500 ∑=4097000

Pavg=4097000/29500 =138.88mm

Results and Comments:

DESIGN EXERCISE NO: 4

TO PLOT RATING CURVE FOR A STATION AND TO EXTEND THE RELATION TO ESTIMATE THE FLOW AT THE REQUIRED STAGE BY LOGARITHMIC AND CHEZY’S METHODS

4.1RELATED THEORY:

4.1.1 STAGE:


120

200

180

160

140

220

It is defined as the height of the water surface above any arbitrary datum (reference

surface). It is usually represented as “H”.

4.1.2 STAGE GAUGE AND ITS TYPES:

Stage gauge is the instrument which is used to observe / measure stage at any

gauging station.

Types of stage gauges used are:

i. NON-RECORDING STAGE GAUGE:These are the stage gauges that do not record the value of stage

automatically. Most commonly employed types are Staff stage gauge

and Wire weigh gauge.

ii. RECORDING STAGE GAUGE:These stage gauges automatically keep the record of the stages

recorded for a particular duration of time. Float type stage gauge is one

of the examples.

4.1.3 RATING CURVE AND ITS SIGNIFICANCE:

Rating curve is the graphical representation between Stage and Discharge at a

particular stream gauging station.

Rating curve is useful in:

i. Estimating discharge values corresponding to any stage value.

ii. Determining stage values corresponding to various flows for the

construction of hydraulic structures.

4.1.4 ESTABLISHMENT OF RATING CURVE AT A SITE:

At a particular section in the stream, stage and discharge are simultaneously

observed and with the help of this data, rating curve is plotted. The cross-sectional

area of flow is divided in a number of segments, assigning that in a particular

segment, velocity remains uniform in width. Velocity is determined in each segment

with the help of current-meter. With the help of velocity and cross-sectional area,


discharge is calculated for that particular segment and then total discharge is

calculated by integrating it for the whole cross-section.

4.1.5 EXTENSION OF RATING CURVE:

Rating curve is established at a particular section on the basis of the data collected

for the stages and discharges observed in the stream. A flood magnitude (of higher

return period) is expected in the future greater than the highest observed in the past.

For this flood magnitude stage, the available rating curve becomes useless and

hence for the stages higher than the observed, extension of the rating curve

becomes essential.

Following methods can be used to extend the rating curve:

i. LOGARITHMIC METHOD:If the cross section of stream at the gauging station is of regular shape,

then this method will be used.

Equation used in this method is:

logQ=logK+n log(H –a)

ii. CHEZY’S METHOD:The basic concept behind this method is the Chezy’s equation:

Q=AC √RSBy simplifying:

Q=AC √R√SWhere:

A = Cross-sectional area of flow

C = Chezy’s co-efficient

R = Hydraulic radius = Areaof flow

Wetted Perimeter = BD

(B+2D) = D

(As B>>D for a very wide channel so D can be neglected)

S = Slope of the energy line

So,

Q=A (C√S )√DQ=(C√ S)A√D

Q∞ A√D


So the graph between these two quantities gives a straight line which

can be extended up to the required point.

4.2 PROCEDURE:

4.2.1 FOR CHEZY’S METHOD:

i. Calculate the values of “A√D ” corresponding to the given data.

ii. Select suitable scale and plot the graph between “Q” and “A√D ”.

iii. On the same graph paper, plot the graph between “H” and “A√D ”.iv. Locate the point for which the value of discharge is to be calculated on

the curve H~A√D.

v. Take offset from this point to the Q ~A√D curve and then to the Q-

axis. Read the value from the scale for the required reading of the

stage.

4.2.2 FOR LOGARITHMIC METHOD:i. Assume any value of “a” (Normally in the range of 0.1-0.6).

ii. Corresponding to this value of a, calculate the value of log (H-a).

iii. Plot the graph between log (H-a) and logQ.

iv. Depending upon the curvature of graph, assume different values of ‘a’

and repeat the same procedure again. (In case of downward curvature,

decrease the value of ‘a’ and vice versa).

v. Keep on assuming different values of ‘a’ till a single slope is obtained.

vi. Calculate the value of log (H-a) at the required value of ‘H’ for the value

of ‘a’ at which graph is of single slope.

vii. Take offset from point log (H-a) to the curve, calculate the value of

logQ and then determine the value of ‘Q’.

CALCULATIONS:

Sr.

No.

Stage

H ( )

Depth

D ( )

Area

A ( )

Discharge

Q ( )

A√D( )

Log Q Log (H-a)

a= a= a= a= a=


DESIGN EXERCISE NO: 5

GIVEN ARE THE ORDINATES OF A STORM HYDROGRAPH FOR A RIVER DRAINING CATCHMENT AREA OF . . . . . (……) DUE TO … HOURS ISOLATED STORM. DERIVE THE ORDIANTES OF … HOURS UNIT HYDROGRAPH FOR THE CATCHMENT.


5.1RELATED THEORY:

5.1.1 HYDROGRAPH:

It is the graphical representation of flow against time for a particular section of the

stream/river. Flow discharge is plotted on y-axis and time is plotted on x-axis.

5.1.2 PARTS OF HYDROGRAPH:

Four important parts of hydrograph are:

i. Ground water recession curve

ii. Rising limb

iii. Peak

iv. Recession or falling limb.

5.1.3 COMPONENTS OF HYDROGRAPH:i. Direct runoff (DRO)

ii. Base flow

5.1.4 FACTORS AFFECTING THE SHAPE OF HYDROGRAPH:

Factors affecting the shape of hydrograph are:

i. Climatic factors (Amount of rainfall, intensity and duration of rainfall,

etc)

ii. Physiographical factors (Shape of basin, slope of watershed, surface

conditions of the catchment, soil type in the catchment, etc)

5.1.5 HYDROGRAPH SEPERATION AND METHODS OF SEPERATION OF HYDROGRAPH:

Splitting of hydrograph ordinates in two parts (Direct runoff and Base

flow ordinates) is known as hydrograph separation.


Methods used for the separation of hydrograph are:

i. Straight line methoda) Horizontal straight line method:

A horizontal line is drawn from the point of rise. Area below line is

Base flow. Line is drawn on assumption that a constant amount of

base flow is maintained during the storm runoff.

b) Inclined straight line method:

Inclined line is obtained by joining the points at which the runoff

enters and the runoff ceases. DRO ceases after N days from the

peak discharge and is obtained as:

N=K (A )0.2

Where:

N = Time in days after which DRO ceases from the peak and

depends on the basin characteristics.

A = Area of the water shed

K = Co-efficient (=1 for A in mi2 and = 0.8 for A in km2)

ii. Fixed base length method

In this method, a line AB is drawn in the extension of ground water

recession curve ending at peak of hydrograph (B). Another line BC is drawn from

point B to C where DRO ceases at a distance of N days from the peak of

hydrograph. The area of hydrograph above curve ABC is DRO and below is base

flow.

5.1.6 UNIT HYDROGRAPH AND ITS APPLICATION:

Unit hydrograph is the direct runoff hydrograph with unit effective

precipitation spread uniformly in space and time over the entire watershed for

a given duration.


Unit hydrograph is used for the prediction of flood peak and time to

peak in the stream at a particular section due to any amount of effective

precipitation over the watershed.

5.1.7 ASSUMPTIONS FOR THE UNIT HYDROGRAPH:Following assumptions are made for the development of the unit hydrograph:

i. Precipitation amount and intensity is uniform over the entire watershed.

ii. Precipitation intensity remains uniform throughout the storm.

iii. Base length of hydrograph DRO for a particular catchment resulting

from a storm of a given duration is approximately constant.

iv. Entire watershed is treated as a single unit.

PROCEDURE:

i. Plot hydrograph for the given data.

ii. Separate base flow and direct runoff.

iii. Determine volume of direct runoff in km3 or ft3.

Volumeof direct runoff=Δt ×3600×Σhi

iv. Determine volume of DRO in cm or inches (i.e. volume in terms of depth) “x”

by dividing the volume with watershed area.

v. Compute ordinates of UHG:

Ordinatesof UHG=Ordinatesof DRO / x

Where:

Ordinates of DRO is in “m3/s or ft3/s”

x is in “cm or inch”

Ordinates of UHG is in “(m3/s)/cm or (ft3/s)/inch”

vi. Plot unit hydrograph.

vii. Check area under the curve of UHG, it should be 1cm or 1in depending upon

the system of units being used.

viii. CALCULATIONS:

Time from

start ( )

Discharge

( )

Base flow

( )

Direct runoff

( )

Ordinates of unit

hydrograph (DRO /x)

( )


Volume of DRO =

Volume of DRO in terms of depth =

Area under UHG =

Area under UHG in terms of depth = (should be ≈ 1cm or 1inch)

RESULTS AND COMMENTS:


DESIGN EXERCISE NO 6

THE ORDINATES OF … HOURS UNIT HYDROGRAPH ARE GIVEN, DERIVE THE ORDINATES OF:

i. S-CURVE HYDROGRAPHii. … HOURS UNIT HYDROGRAPHiii. … HOURS UNIT HRDROGRAPH


6.1RELATED THEORY:

6.1.1 APPLICATION OF UNIT HYDROGRAPH:

Unit hydrograph is associated with definite duration of rainfall and

hence cannot be used for all durations. It is therefore necessary to derive unit

hydrograph for various durations.

Any duration unit hydrograph can be converted into long or short

duration unit hydrograph by S-curve method provided other durations are

integral multiple of the given duration.

6.1.2 S-CURVE:S-curve is a hydrograph of surface runoff, which result from an addition

of an infinite series of T hr unit hydrograph each lagged by T hours with

respect to the preceding one. The S-curve becomes constant after a period

equal to the base length of the unit hydrograph used to derive it.

6.1.3 METHODS FOR S-CURVE GENERATION:Methods used for the derivation of S-curve ordinates are:

i. Offset method

ii. S-curve addition method

PROCEDURE:

FOR OFFSET METHOD:i. Ordinates of given duration unit hydrograph are given a lag of time

equal to the duration of unit hydrograph and subsequent offsets are

recorded.

ii. Ordinates of S-curve are obtained by the addition of all ordinates for a

particular time.

FOR S-CURVE ADDITION METHOD:i. Ordinates of unit hydrograph are given a lag equal to the duration of

unit hydrograph and the ordinates of S-curve addition at a particular

time are obtained by the S-curve addition and UHG been lagged.

ii. To get the ordinates of UHG for a particular duration, S-curve addition

curve ordinates are given a lag of UHG duration and then the

difference of both columns is divided by a factor “t2/t1”


Where:

t2 = Time of required UHG

t1 = Time of given UHG

CALCULATIONS:

Derivation of S-curve ordinates by Offset method:

Time

(Hrs)

Ordinates of

… hrs UHG

(m3/sec)

Offset Ordinates of

S-curve

(m3/sec)1 2 3 4 5 6


Derivation of S-curve, …hrs UHG and …hrs UHG:

Time

(Hrs)

Ord. of

… hrs

UHG

(m3/sec)

S-curve

addition

(m3/sec)

Ord. of

S-curve

(m3/sec)

S-curve

lagged

by …

hrs

Col4

-

Col5

Ord. of

…hrs

UHG

(m3/sec)

S-curve

lagged

by …hrs

(m3/sec)

Col4

-

Col8

Ord.

of ...hrs

UHG

(m3/sec)


(m3/sec)

Col1 Col2 Col3 Col4 Col5 Col6 Col7 Col8 Col9 Col10

RESULTS AND COMMENTS:


DESIGN EXERCISE NO 7

COMPUTE THE TRANSMISSIVITY “T” AND STORATIVITY “S” FROM THE ONE DAY CONTINUOUS PUMPING DATA FOR A WELL, FULLY PENETERATING IN


AN AQUIFER, WHICH IS HORIZONTAL, CONFINED AND HOMOGENOUS ISOTROPIC

7.1RELATED THEORY

7.1.1 AQUIFER

An Aquifer is water bearing stratum or formation capable of transmitting

water in quantities sufficient to permit development.

Storage volume within an aquifer is changed whenever water is

recharged to, or discharged from, an aquifer.

7.1.2 HYDRAULIC CONDUCTIVITYIt is the discharge through a porous medium for unit cross-sectional

area under unit hydraulic gradient. It is also called as co-efficient of

permeability.

K= Qi A

Where:

K = Hydraulic conductivity

Q = Flow rate

i = Hydraulic gradient

A = Cross-sectional area

7.1.3 TRANSMISSIVITYIt is defined as the rate at which water of prevailing kinematic viscosity

is transmitted through a unit width of aquifer under a unit hydraulic gradient.

It is the product of hydraulic conductivity and the layer thickness.

T=Kb

Where:

T = Transmissivity

K = Hydraulic conductivity

b = layer thickness

7.1.4 STORATIVITY:


The volume of water that an aquifer releases from or takes into storage

per unit surface area of aquifer per unit change in head normal to that surface

is called as storativity.

It is the product of specific storage “Ss” and thickness of aquifer “b”.

S=Ssb

7.1.5 UNSTEADY RADIAL FLOW IN A WELL PENETERATING A CONFINED AQUIFER:

When well in a confined aquifer starts discharging the water from the

aquifer, it results in the formation of cone of depression of the piezometric

surface. The cone gradually expands with time till equilibrium is attained. The

flow configuration from the start of the pumping till attainment of equilibrium, if

in unsteady regime, is called as unsteady radial flow in a well.

It can be described by the equation in polar co-ordinates form as

follows:

(∂2h/∂r )+(1/r )(∂h/∂r )=(S /T )(∂h /∂ t)

This equation is known as “Thiess equation”.

Where:

h = Head in observational well

r = Distance of observational well from the discharging well

S = Storativity

T = Transmissivity

t = Time since beginning of pumping

Parameters used in the solution of this equation are:

s=(Q / 4πT )∗W (u)

u=r 2 s/ (4Tt)

Where:

s = Draw-down in an observational well

Q = Well discharge

W(u) = Well function

u = Well parameter


7.1.6 THIESS METHOD FOR SOLUTION OF “T” & “S”:This method is widely used for the determination of Storativity “S” and

Transmissivity “T”.

Equations used are:

s=(Q / 4πT )∗W (u)

r 2/ t=(4T /S)u

Hence, relation between W(u) and u is similar as that of s and r2/t, as

terms within brackets are constant.

So, Thiess suggested an approximate solution for “S” and “T” based on

graphical method of Super-position.

PROCEDURE:

i. Plot a graph of “W(u)” verses “u” on logarithmic paper. This curve is

known as “Type curve”.

ii. Plot the values of draw-downs against the values of “r2/t” on logarithmic

paper of same size and scale as for the Type curve.

iii. Super impose the draw down data on the Type curve keeping the co-

ordinate axes of the two curves parallel.

iv. Adjust the super-imposed graph until a position is found by trail where

most of the plotted points of the observed data fall on a segment of

Type curve. Select any convenient point and record the co-ordinates of

this match point.


v. Determine “S” and “T” with these values of “W(u)”, “u”, “s” and “r2/t”.


CALCULATIONS:


Experiment # 1To Carry out Experimental Rainfall-Runoff Modeling

and to determine the Runoff coefficient

Apparatus1) Basic hydrology system Apparatus2) Stop watch

Related TheoryHydrological cycle:

The central theme of hydrology is that water circulates throughout the Earth through different pathways and at different rates. The most vivid image of this is in the evaporation of water from the ocean, which forms clouds. These clouds drift over the land and produce rain. The rainwater flows into lakes, rivers, or aquifers. The water in lakes, rivers, and aquifers then either evaporates back to the atmosphere or eventually flows back to the ocean, completing a cycle. Water changes its state of being several times throughout this cycle. This whole cycle of water is termed as hydrological cycle.


Figure 1: Hydrological cycle


Runoff

Runoff is the movement of land water to the oceans, chiefly in the form of rivers, lakes, and streams. Runoff consists of precipitation that neither evaporates, transpires nor penetrates the surface to become groundwater. Even the smallest streams are connected to larger rivers that carry billions of gallons of water into oceans worldwide. Excess runoff can lead to flooding, which occurs when there is too much precipitation.

Hydrograph

It is the graphical representation of flow against time for a particular section of the stream/river. Variable kept on y-axis is flow or discharge while on x-axis it is time.

Rainfall runoff modeling

A rainfall runoff model is a mathematical model describing the rainfall - runoff relations of a rainfall catchment area, drainage basin or watershed. More precisely, it produces the surface runoff hydrograph as a response to a rainfall as input. In other words, the model calculates the conversion of rainfall into runoff.

Runoff coefficient

The percentage of precipitation that appears as runoff is termed as Runoff coefficient. The value of the coefficient is determined on the basis of climatic conditions and physiographic characteristics of the drainage area and is expressed as a constant between zero and one (Chow, 1964). Symbol C

Runoff volume= C x Rainfall volume

Factors affecting runoff coefficient are :

1. Soil type2. Vegetation3. Slope and catchment size


http://en.wikipedia.org/wiki/Hydrograph

http://en.wikipedia.org/wiki/Drainage_basin

http://en.wikipedia.org/wiki/Surface_runoff

http://en.wikipedia.org/wiki/Rainfall

http://ww2010.atmos.uiuc.edu/(Gh)/wwhlpr/precip_hyd.rxml?hret=/guides/mtr/hyd/run.rxml

http://ww2010.atmos.uiuc.edu/(Gh)/wwhlpr/groundwater.rxml?hret=/guides/mtr/hyd/run.rxml

http://ww2010.atmos.uiuc.edu/(Gh)/wwhlpr/transpiration.rxml?hret=/guides/mtr/hyd/run.rxml

http://ww2010.atmos.uiuc.edu/(Gh)/wwhlpr/evaporation.rxml?hret=/guides/mtr/hyd/run.rxml

http://ww2010.atmos.uiuc.edu/(Gh)/wwhlpr/precip_hyd.rxml?hret=/guides/mtr/hyd/run.rxml

Procedure:

1) Level the instrument.2) Select duration of rainfall (say Df = 60 sec ).3) Open the valve for certain “T” value of time for certain intensity (in terms of

discharge) of rainfall (say 6 Lit/min).4) Note the values of runoff produced at some fixed interval (say 15 sec) until the time

when runoff becomes constant.5) Repeat the same procedure for two more intensities of rainfall (e.g., Df = 120 sec &

180 sec).6) Compute the values of amount of rainfall (intensity x Df).7) Calculate the volume of runoff produced (sum of ordinates x time interval).8) Calculate Runoff coefficient “C”.

Observations and CalculationsArea = 18493.51 cm2

Table 1.1

Q Q I = Q/A Df

Runoff ValuesTim

e Ordinates

(Lit/min)

(cm3/sec)

(cm/sec) (sec) (sec

) (Lit/sec)

6 100 0.0054 60 0 0.0115 0.012530 0.01545 0.0260 0.02575 0.0390 0.032

105 0.03120 0.028135 0.021150 0.02165 0.018180 0.015195 0.015210 0.015225 0.015240 0.015255 0.015

Sum of ordinates = 0.3515


Table 1.2

Q Q I = Q/A Df

Runoff ValuesTim

e Ordinates

(Lit/min) (cm3/sec) (cm/sec) (sec) (sec) (Lit/sec)

8 133.3336 0.0072 120 0 0.01215 0.01530 0.0245 0.02860 0.0375 0.03190 0.03

105 0.038120 0.031135 0.03150 0.03165 0.028180 0.025195 0.02210 0.018225 0.018240 0.015255 0.015

- -- -- -- -- -- -- -- -



Table 1.3

Q Q I = Q/A Df

Runoff ValuesTim

e Ordinates

(Lit/min)

(cm3/sec)

(cm/sec) (sec) (sec

) (Lit/sec)

10 166.667 0.0090 180 0 0.01515 0.01530 0.0245 0.02560 0.0375 0.03190 0.032

105 0.032120 0.033135 0.032150 0.036165 0.036180 0.038195 0.038210 0.035225 0.031240 0.031255 0.028270 0.024285 0.02300 0.018315 0.015330 0.015345 0.015360 0.012375 0.012390 0.012405 0.012

- -- -- -



Table 1.4 Determination of Runoff coefficients

Sr #

I Df

Amount = I x

Df

Volume = Amount x

Area

Runoff volum = ∑ordinates x Δt C

(mm/hr) (sec) (mm) (mm3) (Litres

) (mm3) (-)

1 194.4 60 3.24 5991897.24 5.2725 5272500 -

2 259.2 120 8.64 15978392.64 6.51 6510000 -

3 324 180 16.2 29959486.2 10.095

10095000 -

Graphs:

Graphs are not exact as calculated data. These graphs are based on assumed values just to show. You can make these graphs by yourself.

0 50 100 150 200 250 3000

0.005

0.01

0.015

0.02

0.025

0.03

0.035

Hydropgraph for Table 1.1

Time (sec)

Runo

ff (L

it/se

c)


0 50 100 150 200 250 300 350 4000

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04


Time (sec)

Runo

ff (L

it/se

c)

0 50 100 150 200 250 300 350 400 450 5000

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04


Time (sec)

Runo

ff (L

it/se

c)


40 60 80 100 120 140 160 180 2000

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

f(x) = − 0.00370833333333333 x + 1.02866666666667R² = 0.963975556406545

C vs Df

Df (sec)

C

Comments:


memberfiles.freewebs.com · web viewit deals with precipitation, evaporation, infiltration, ground...

Documents