Lecture Hydrologic Cycle

8/20/2019 Lecture Hydrologic Cycle

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Universiti Teknologi Petronas VAB2063 HydrologyChapter-1: Hydrologic Cycle

Topic 1:

Hydrologic Cycle




Lesson Outcome

On completion of this chapter you will be able to

understand and / or identify and / or quantify

What is hydrology? Why we need to study hydrology?

What is a hydrologic cycle?

Components of hydrologic cycle World water quantities




Hydrology

Hydrology means the science of water and it

deals with the

• Occurrence

• Circulation &

• Distribution

of water of the earth and earth’s atmosphere




Hydrology

In general hydrology is a very broad subject of aninter-disciplinary nature drawing support fromallied sciences such as:

• Meteorology• Geology

• Statistics

• Chemistry

• Physics &

• Fluid mechanics




Application of Engineering

Hydrology

• Estimation of water resources

• Study of processes such as:

– Precipitation

– Runoff

– Evapotranspiration & their interaction

• Study of problems such as:

– Floods & droughts

– Strategies to combat them




Application of Engineering

Hydrology

• Design & operation of water resources

engineering projects such as:

– Irrigation

– Water supply – Flood control

– Water power &

– Navigation




Hydrologic Cycle

Water occurs on the earth in all three states

(liquid, solid and gaseous) and in various degree

of motion. Some example of dynamic aspects of

water are: – Evaporation of water from water bodies

(oceans, lakes)

– Formation and movement of clouds, rain

and snowfall

– Stream flow & groundwater movement




Hydrologic Cycle

The various aspects of water related to the earth

can be explained in terms of a cycle known as

the Hydrologic Cycl e




Components of

Hydrological Cycle:

• Precipitation

• Evaporation

• Transpiration

• Interception• Infiltration

• Runoff / Stream flow

• Interflow / Base flow

• Groundwater flow




Schematic representation

of Hydrologic Cycle

0 = Evaporation from ocean

1 = Raindrop evaporation

2 = Interception

3 = Transpiration

4 = Evaporation from land

5 = Evaporation from water bodies

6 = Surface runoff / Stream flow

7 = Infiltration

CloudsSun

Precipitation

Precipitation

Snow

Evaporation

from ocean

Pervious material

Groundwater (8)

Rock

1

0

2

34

56

7

9

8 8

8

6

8 = Ground water

9 = Deep percolation




Importance of Hydrological

Cycle

One Possible Answer:

– Helps to study the science of

hydrology in a systematic way

Can you think of a few more possible

importance of hydrological cycle?:




Water-Budget Equation

(Hydrologic Equation)

The continuity equation for water in various

phases is expressed as:

S o i

storagemassinChangeoutflowMassinflowMass




Expression of water budget

equation for a catchment:

ΔS T E G R P

where P = Precipitation

R = Surface runoff

G = Net groundwater flow out of the catchment

E = Evaporation

T = Transpiration and

S = Change in storage




Expression of water budget

equation for a catchment:

Note:

• The infiltration does not occur explicitly in the water

budget equation as the infiltration which is a loss to

the runoff processes is a gain to the ground watersystem

• All terms in the water budget equation must have

consistent units (volume or depth over the catchment

area)• In hydrologic calculations volumes are often

expressed as average depths over the catchment area




Residence time

The average duration of a particle of water to

pass through a phase of the hydrologic cycle is

known as the residence time of that phase

Residence time for a phase:

phasetheinrateflow Average

phaseainw ater of Volumer T




Estimated World Water

QuantitiesEstimated World Water Quantities

Item Area(M km

2)

Volume(M km

3)

% totalwater

% freshwater

Ocean 361.3 1338.0 96.5 -Ground water

(a) Fresh(b) Saline

134.8134.8

10.53012.870

0.760.93

30.1-

Soil moisture 82.0 0.0165 0.0012 0.05Polar ice 16.0 24.0235 1.7 68.6Other ice and snow 0.3 0.3406 0.025 1.0Lakes

(a) Fresh(b) Saline

1.20.8

0.09100.0854

0.0070.006

0.26-

Marshes 2.7 0.01147 0.0008 0.03Rivers 148.8 0.00212 0.0002 0.006

Biological water 510.0 0.00112 0.0001 0.003 Atmospheric water 510.0 0.01290 0.001 0.04

Total:(a) All kinds of water(b) Fresh water

510.0148.8

1386.035.0

100.02.5 100.0

Source: World Water Balance & Water Resources Of The Earth. UNESCO 1975




Global Annual Water

BalanceGlobal Annual Water Balance

Item Ocean Land

Area (M km2) 361.30 148.8

Precipitation

(km3/year)

(mm/year)

458,000

1270

119,000

800Evaporation

(km3/year)

(mm/year)

505,000

1400

72,000

484

Runoff to ocean

Rivers (km3/year)

Groundwater (km3/year)

Total runoff(km

3/year)

(mm/year)

44,700

2,200

47,000

316





Water Balance of

Continents

Water Balance of Continents (mm/year)

Continent Area(M km

2)

PrecipitationP

Totalrunoff

Runoff as% of P

Evapor ation

Africa 30.3 686 139 20 547

Asia 45.0 726 293 40 433

Australia 8.7 736 226 30 510

Europe 9.8 734 319 43 415

N. America 20.7 670 287 43 383

S. America 17.8 1648 583 34 1065





Water Balance of Oceans

Water Balance of Oceans (mm/year)

Ocean Area

(M km2)

Precpt. Inflow from

adjacent

continents

Evapo. Water

exchange

with other

oceans

Atlantic 107 780 200 1040 -60

Arctic 12 240 230 120 350

Indian 75 1010 70 1380 -300

Pacific 167 1210 60 1140 130





Hydrological Data

• Weather records (temperature, humidity & wind speed)

• Precipitation data

• Evaporation & transpiration data

• Stream-flow records• Infiltration characteristics of an area / catchment

• Groundwater characteristics

• Physical & geological characteristics of the area




References

• Elizabeth M. Shaw (1989). Engineering Hydrology

Techniques in Practice. John Wiley & Sons.

• Ray K., Linsley, Jr., Max A. Hohler. (1988). Hydrology for

Engineers. Mc Graw Hill.

• Roberson, JA. Cassidy, JJ. Chaudhry MH. (1998).

Hydraulic Engineering. John Wiley & Sons.

• Richard H. McCune (1998). Hydraulic Analysis and

Design. Prentice Hall.

• Subramanya K. (1996). Engineering Hydrology. Tata

McGraw-Hill.




Exercise 1:

A lake has a water surface elevation of 103.2 m above datum at thebeginning of a certain month. In that month the lake received an

average inflow of 6.0 m3/s from surface runoff sources.

In the same period the outflow from the lake had an average value of

6.5m3/s. Further in that month, the lake received a rainfall of 145 mm

and the evaporation from the lake surface was estimated as 6.10 cm.

Write the water budget equation for the lake and calculate the water

surface elevation of the lake at the end of the month. The average

lake surface area can be taken as 5000 ha. Assume that there is no

contribution to or from the ground water storage.




Solution 1:

For a time period t the water budget for the lake can be written as:

Input volume – Output volume = Change in storage

ΔS A E t Q A P t I

Where:

I = average inflow rate

Q = average outflow rate

P = precipitation

E = evaporation A = surface are of the lake

S = change in lake storage volume

t = time




Solution 1: (contd.)

Here, t = 1 month

= 30 x 24 x (60 x 60)

= 2.592 x 106 s

= 2.592 Ms

Inflow volume = I t = 6.0 x 2.592 = 15.552 Mm3

Outflow volume =

Input due to precipitation PA =

In one month:

Qt = 6.5 x 2.592 = 16.848 Mm3

100

14.5 x 5000 x 100 x 100

= 7.25 Mm3

106




Solution 1: (contd.)

Outflow due to Evaporation EA = 100

5000 x 100 x 100

= 3.05 Mm3

106

6.10

x

Hence, S = (15.552 + 7.25)

– (16.848 + 3.05)

= 2.904 Mm3

Change in elevation z = A

2.904 x 106

5000 x 100 x 100

S

=

= 0.058 m (+ve)New water surface elevation

at the end of the month

(above datum)

= 103.2m + 0.058m

= 103.258 m (Ans)

Lecture Hydrologic Cycle

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