inroduction unit 1

1. ENGINEERING HYDROLOGY

2. CHAPTERS
1. INTRODUCTION
2. PRECIPITATION
3. INFILTRATION AND RUNOFF
4. HYDROGRAPH ANALYSIS
5. GROUND WATER

3. UNIT – 1
INTRODUCTION
ENGINEERING HYDROLOGY - hydrology means science
in which we study about water, where “Hydro” means water
and word “logy” means science, which is directly derived
from Greek language
So Hydrology means the science of water. it is the science
which deals with the occurrence, distribution and circulation
of water in earth and earth’s atmosphere

4. L
SURFACE WATER HYDROLOGY - is a field that
encompasses all surface waters of the globe (surface
flows, rivers, lakes, wetlands, estuaries, oceans, etc.).
This a subset of the hydrologic cycle that does not
include atmospheric, and ground waters
GROUND WATER HYDROLOGY - it is a field that
includes underground water and water in depth in earth’s
surface it is also called sub surface water as water in
wells and under ground cavities

5. APPLICATION IN HYDROLOGY
 To find out maximum probable flood at proposed sites e.g.
Dams.
 The expected flood flows over a spillway, at a highway
Culvert, or in an urban storm drainage system can be known
by this very subject.
 It helps us to know the required reservoir capacity to assure
adequate water for irrigation or municipal water supply in
droughts condition.

6.  Hydrology is used for city water supply design which is
based on catchments area, amount of rainfall, dry
period, storage capacity, runoff evaporation and
transpiration.
 Hydrology is an imperative tool in planning and building
hydraulic structures.

7. HYDROLOGICAL CYCLE

8. HYDROLOGICAL PROCESS
 PRECIPITATION: In form of rain, drizzle, snow and hail
 EVAPORATION : Vaporization of water all sort of fluids
 INFILTRATION: Process of entering surface water in to the
ground.
 RUNOFF : after soil saturation remaining precipitation on
the surface is called runoff
it has also two phase – a) surface runoff
b) subsurface or ground water
runoff
 CONDENSATION : Formation of water in form of rain drops

9. HYDOLOGICAL WATER DISTRIBUTION
COMPONENT VOLUM
E
1000
KM^3
% OF TOTAL
WATER
ATMOSPHERIC WATER 13 0.001
SURFACE WATER
•SALT WATER IN OCEANS
•SALT WATER IN LAKES
•FRESH WATER IN LAKES
•FRESH WATER IN STREAM CHANNELS
•FRESH WATER IN ICE CAPS &
GLACERIES
•WATER IN BIOMASS
1320000
104
125
1.25
29000
50
97.2
0.008
0.009
0.0001
2.15
0.004
SUBSURFACE WATER
• WATER ABSORBED BY SOIL
•G/W WITH IN DEPTH OF 0.8 KM
67
4200
4200
0.005
0.31

10. GLOBAL RESOURCE OF WATER
 The ocean covers 71% of the surface area of earth and
which have an average depth of 3.8 km hold as large as
97% of earth water while 2% is frozen in ice capes, the deep
ground water accounts for 0.31%, these 99.31% of water is
of no use to human being. The remaining 0.69% represents
fresh water resources which the man has to deal
 0.69% of water = 4.374*10^6 km^3 water

11. WATER BUDGET EQUATION
 A water budget is an accounting of the water stored in and water exchanged
between the atmosphere, land surface, and subsurface. Inflows minus outflows
equal the change in storage over a specified period of time within a specified
volume.
 The quantities of water going through various individual path in the
hydrological cycle in a given system can be described by continuity principle
also known as water budget equation or hydrologic equation
 Water Budget Equation:
For a given area ,say a catchment, in an interval of time ∆t , the continuity
equation for water in various phases is written as
V1 - V0 = ∆s

12. In applying this continuity equation to the paths of hydrological cycle
involving change of state, the volumes considered are the equivalent
volumes of water at a reference temperature
P – R – G – E – T = ∆S
P=precipitation ∆S = ∆Ss+ ∆Ssm+ ∆Sg
R=surface runoff ∆Ss =change in standing volume of water
G=net ground water flow ∆Ssm =change in ground water volume of unsaturated zone
E=evaporation ∆Sg =change in ground water volume of saturated zone
T=transpiration
S=surface water storage
In terms of rainfall runoff relationship above equation can be expressed as
R = P – L
WHERE R=Runoff, P=Precipitation, L=losses

13. PRACTICAL APPLICATION OF HYDROLOGY
 DESIGN OF HYDRAULIC STRUCTURE : The design of any structure
related to water such as spillway, dam, culvert, highway bridge and
railway bridge etc may be considered to consist of these parts
a) hydrologic design-The term hydrology, as used in the design of storm
drains, is the study and application of past rainfall records and runoff data to
a method of predicting future rainfall and runoff.
these involved in the design of drainage and storm water facilities and consideration
for natural passage of water resulting from storm events using instruments as rain
gauge
b) hydraulic design-Hydraulic design provides the best suitable shape and section
of the structure according to quantity of water estimated.
In the context of hydraulic design, hydrologic analysis provides estimates of flood
magnitudes as a result of precipitation. These estimates consider processes in a
watershed that transform precipitation to runoff and that transport water through the
system to a project’s location.ex-dam hydraulic opening gates.

14. c) Structural design-the structural design ensures the
stability and safety of chosen section against water
pressure and other pressures.
Various design of hydraulic components require base
foundation and systematic distribution of load and
allocation, so this sort of design arranges such system
in safe and systematic manner.
2) Municipal and industrial water supply-The availability
of water is often the most important factor in locating the
major industries & it has considerable effect on growth
of municipalities.
3) Irrigation- The irrigation projects are directly based on
hydrological variables such as infiltration,runoff and
evaporation.
The rainfall data and hydrogarph fixes the storage
capacity of any reservoir
4) Hydro power- Hydrological studies are essensial for
planning and hydro power development.To determine
the hydro power output we have to know first reliable
flow duration curve,because minimum flow decides
prime capacity of plant.
5) Flood control-flood contol measures become effective
when they are associated with flood forecasts.
6) Erosion and sediment control- excessive erosion in
catchment feeds sediment to runoff and tons of top
fertile soil will be removed.
7) Navigation -

15. HYDROMETEOROLOGY
 HYDROMETEOROLOGY-In the hydrologic cycle
water is transported in the air over the land and below
the surface of the earth, but meteorology deals with
atmospheric portion of hydrological cycle, with the
transportation of water in the air, for this reason
meteorology always defined as science of
atmosphere phenomenon.
 Hydrometeorology is defined as the study of the
atmospheric process which affects the water
resources of the earth and are interest to hydraulic
engineers.

16. CONSTITUENTS OF ATMOSPHERE
 CONSTITUENTS OF THE ATMOSPHERE-The
permanent constituents of atmosphere by volume
are N2-78%, O2-21% and the rest inert gasses. the
variable constituents may be in solid, liquid and
gaseous form, it is invisible and referred as
humidity and when it is in the form of minute drops,
formed up on condensation, it is called fog or cloud.

17. VERTICAL STRUCTURE OF ATMOSPHERE
 VERTICAL STRUCTURE OF
ATMOSPHERE - The lowest layer which
contains about 75% of mass and almost all
the moisture and dust of the atmosphere is
called troposphere
 The top of the troposphere is called
tropopause. The height of the tropopause
varies from about 8 km over the poles and 16
km near the equator.

18. TROPOSPHERE
STRATOSPHERE
MESOSPHERE
IONOSPHEREA
L
T
I
T
U
D
E

19. LAYERS OF EARTH ATMOSPHERE

20. LAPSE RATE
 In general, a lapse rate is the
negative of the rate of temperature
change with altitude change, thus:
 where γ is the lapse rate given
in units of temperature divided by
units of altitude, T = temperature,
and z = altitude. Average lapse rate is
about 2°C/1000ft
 The lapse rate is defined as the rate of decrease with
height for an atmospheric variable. The variable
involved is temperature unless specified otherwise.
 The terminology arises from the word lapse in the
sense of a decrease or decline; thus, the lapse rate is
the rate of decrease with height and not simply the
rate of change. While most often applied to Earth's
atmosphere.
Altitude(m)
Temperature (C)

21.  In the troposphere temperature decreases
with elevation with an average rate of 6.5
degree C/km. this is known as lapse rate.
Above the tropopause is the stratosphere.
 Troposphere is the zone in which the
weather phenomenon and atmospheric
turbulence are most marked. Because of
their effect on mass transport and & energy
transport

22.  Hydrologist are interested in the troposphere
and the process that take place in it.
However although the weather is considered
as resulting from the interchange of the heat
energy within the troposphere process above
this layer giving ozone variations and
ionization etc may influence the weather
conditions to some extent

23.  TROPOSPHERE - The troposphere is where all
weather takes place and the thin zone between
troposphere and stratosphere is called tropopause.
 STRATOSPHERE - Above the troposphere is
the stratosphere . The thin ozone layer in the upper
stratosphere has a high concentration of ozone, a
particularly reactive form of oxygen. This layer is
primarily responsible for absorbing the ultraviolet
radiation from the Sun

24.  MESOSPHERE & IONOSPHERE - Above the stratosphere is the
mesosphere and above that is the ionosphere (or thermosphere),
where many atoms are ionized (have gained or lost electrons so they
have a net electrical charge).
 The ionosphere is very thin, but it is where aurora(polar light) take
place, and is also responsible for absorbing the most energetic
photons from the Sun, and for reflecting radio waves, thereby
making long-distance radio communication possible.
 The structure of the ionosphere is strongly influenced by the
charged particle wind from the Sun (solar wind), which is in turn
governed by the level of Solar activity. One measure of the structure
of the ionosphere is the free electron density, which is an indicator
of the degree of ionization.

25.  AIR MASS- A vast and deep body of the air in which the temperature and humidity
characteristics are relatively homogeneous at any given elevation is called an air
mass
 There are 4 general air mass classifications categorized according to the source
region.
 polar latitudes P - located poleward of 60 degrees north and south
 tropical latitudes T - located within about 25 degrees of the equator
 continental c - located over large land masses--dry
 marine m - located over the oceans----moist

26.  AIR FRONT- The surface
of contact between two
adjacent air masses or
between an air-mass and
the surrounding
atmosphere is called air
front
 There are four types of air
fronts –
(a)cold front
(b) warm front
(c) Occluded front
(d) stationary front

27.  COLD FRONTS -- A cold
front is a transition zone
where a cold air mass
replaces a warm air mass. It
is drawn as a blue line with
blue triangles pointing in the
direction the front is moving.
 The cold air mass is more
dense than the warm air
mass it replaces. As the cold
air moves into the warm air
region it forces the warm air
to rise very quickly, resulting
in deeper clouds and
heavier precipitation than we
saw with a warm front

28.  WARM FRONTS -- A warm front
is a transition zone where a
warm air mass replaces a cold
air mass. It is drawn as a red
line with red semicircles pointing
in the direction the front is
moving.
 The warm air is less dense than
the cold air and easily slides up
over top of the cold air mass
gradually pushing it out of the
way. Since warm air easily
slides upward in the vicinity of a
warm front, we generally do not
see convective precipitation.

29.  OCCLUDED FRONT --
An occluded front is a
region where the faster
moving cold front
catches up to the
slower moving warm
front. As a result the
coldest air alters the
sloping warm front
surface. These
separate newer colder
air with cool air north of
the warm front.

30.  STATIONARY FRONT -
- A stationary front is
when there is no
movement of an actual
temperature gradient,
but there is still
convergence and
forced lifting. These
front are drawn as
alternating small
segments of warm and
cold front lines.

31. CYCLONE
 CYCLONE- A cyclone is a
 more or less circular area of low
atmosphere
 winds blow spirally inwards in
counter clockwise direction in the
north hemisphere and in clockwise
direction in southern hemisphere.
 The pressure gradient exists
towards the centre of the cyclone.
.

32. ANTICYCLONE
 ANTICYCLONE- Anticyclone
are the high pressure areas
generally elliptical in shape
 It is covering very large area
 the wind blow spirally
outward in clockwise direction
in the northern hemisphere
and in counter clockwise
direction in southern
hemisphere
 Pressure gradient exist
towards the circumference of
cyclone

33. CYCLONE & ANTICYCLONE

34. FORMATION OF PRECIPITATION
There are four basic conditions which are to be
satisfied for the precipitation to occur
 Accumulation of moisture of sufficient intensity to
account for the observed rates of precipitation
 Cooling of air to the dew point temperature to
produce saturation condition
 Condensation
 Growth of small water droplets to percepitable size

35. FORMS OF PRECIPITATION
 DRIZZLE – It is the fine
sprinkle of very small
uniform water drops with
diameter between 0.1 to
0.5 mm. the drops are so
small that they seems to
float in air
 RAIN – it is the
precipitation of liquid water
in which the drops are
generally larger than 0.5
mm in size

36.  GLAZE –The ice coating on land
when rain or drizzle, freezes as it
comes in contact with cold objects at
the ground is called glaze.
 FOG - Fog is a visible mass
consisting of cloud water droplets or
ice crystals suspended in the air at or
near the Earth's surface.[Fog can be
considered a type of low-
lying cloud and is heavily influenced
by nearby bodies of
water, topography, and wind
conditions. In turn, fog has affected
many human activities, such as
shipping, travel, and warfare.
 SLEET – When rain drops are
frozen while falling through a layer
of subfreezing air near the earth
surface it is called sleet.
 HAIL – precipitation in the form of
irregular balls of ice over 5 mm in
diameter is called hail.

37. METEOROLOGICAL OBSERVATIONS
 METEOROLOGICAL OBSERVATIONS –
Periodical measurements on meteorological
parameters such as atmospheric pressure ,
wind direction, temperature, humidity,
precipitation and evaporation are the essential
for the understanding of atmospheric
phenomenon.
 Indian Meteorological Department(IMD)
generally take observations twice a day that is
at 08:30 and at 17:30

38. CLIMATE AND WEATHER
 CLIMATE AND WEATHER – The state of
atmosphere with respect to the temperature,
humidity, wind, cloudiness etc at any given time
is generally referred to as the weather. The
climate of a region is the aggregate of the
weather.
Weather is the condition of the atmosphere at a
particular place over a short period
climate refers to the weather pattern of a place
over a long period, usually thirty years and more

39.  In India the year may be divided into 4
weather seasons –
 Cold weather season(Dec to Feb)
 Hot weather season(March to May)
 South west monsoon season(June to sep)
 Retreating south west monsoon season(Oct
to Nov)

40.  Cold weather season(winter) --
occurring from December to early
April. The year's coldest months are
December and January, when
temperatures average around 10–15
°C (50–59 °F) in the northwest;
temperatures rise as one proceeds
towards the equator, peaking around
20–25 °C (68–77 °F) in mainland
India's southeast.
 Hot weather season(summer) --
Summer or pre-monsoon season,
lasting from April to June (April to
July in northwestern India). In
western and southern regions, the
hottest month is April; for northern
regions, May is the hottest month.
Temperatures average around 32–45
°C in most of the areas.

41.  SOUTH WEST MONSOON
SEASON (RAINY) --
Monsoon or rainy season, lasting
from June to September. The season
is dominated by the humid southwest
summer monsoon, which slowly
sweeps across the country beginning
in late May or early June. Monsoon
rains begin to recede from North
India at the beginning of October.
South India typically receives more
rainfall.
 RETREATING SOUTH WEST
MONSOON SEASON -- Post-
monsoon season, lasting from
October to December. In
northwestern India, October and
November are usually cloudless.
Tamil Nadu receives most of its
annual precipitation in the northeast
monsoon season.

42. MONSOON
MONSOON is referred to a season in which wind system reverses completely
Monsoons are experienced in tropical areas roughly between 200 N to 200 S.
Latest atmospheric conditions influence the monsoon wind are-
a) Differential heating and cooling of land and water in which low pressure is created in land areas where
high pressure is created in sea zone in day time but this process is reversed in night.

43.  Shift of the position of inter tropical convergence zone
(ITCZ)
 In summer the equitorial draft that is normally present at 5o north of the equator moves over
the Ganga plane as a result monsoon trough(convergence zone) is created in monsoon
season.

44. TIBETAN PLATEAU GETS INSTANTLY HEATED
 Tibetan plateau gets instantly heated so a high pressure
zone is created above Tibetan plateau up to 9 km above
mean sea level.

45. SOUTHERN OSCILLATION
Southern oscillation Between Indian ocean and pacific ocean due to
pressure difference

46.  Monsoon start to end

47. RETREATING MONSOON