Download 26-11-2015 Hydrology

26-11-2015
Hydrology
Hydrology
Evaporation and infiltration : measurement
and estimation of evaporation from land and
water surfaces.
surfaces. Infiltration, factors affecting
infiltration..
infiltration
Hydrograph analyses : Surface runoff,
overland flow, factors affecting runoff
runoff..
Rational formula
formula.. Hydrograph analyses, Unit
hydrograph, channel and storage routing.
routing.
Hydrology and Applied
Hydraulics
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Applied Hydraulics
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Urban Storm Drainage : Introduction to drainage
problems in difficult climates. Planning concepts,
Rainfall intensityintensity-duration –frequency curves.
Design of drainage system elements, control of
storm water pollution.
Water and wastewater pumping : Classification,
selection, installation, operation and maintenance
of pumps for water and wastewater pumping,
electrical motors, choice and installation, starters
and other accessories.
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What is Hydrology?
A good understanding of the hydrologic
processes is important for the assessment
of the water resources, their management
and conservation on global and regional
scales.
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Water is vital for all living organisms on Earth.
Earth.
For centuries, people have been investigating
where water comes from and where it goes, why
some of it is salty and some is fresh, why
sometimes there is not enough and sometimes too
much
much.. All questions and answers related to water
have been grouped together into a discipline
discipline..
The name of the discipline is hydrology and is
formed by two Greek words:
words: "hydro" and "logos"
meaning "water" and "science"
"science"..
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Need for the Hydrologic
Studies
In general sense engineering
hydrology deals with
– It is a science of water.
– It is the science that deals with the
occurrence, circulation and distribution of
water of the earth and earth’s atmosphere.
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Basic Hydrology Concept
Applied Hydraulics
Water Distribution System:
System: General design
requirements.. Methods of analyses, control of
requirements
water hammer in long distance transmission
transmission..
Introduction to optimization of water
distribution system.
system.
Sewerage system design : General design
principles of sewers, Recent development in
sewerage system design
design..
Fundamentals of ground water flow :
Occurrence of Ground Water, Vertical
Distribution of Ground Water, Darcy’s law,
Permeability, Porosity, Anisotropic Aquifers,
Differential equations of Ground water flow
flow..
Ground
Water
Development
:
Well
development, Artificial recharge, Salinity of
Ground water, Ground water pollution,
Infiltration Galleries.
Galleries.
– Estimation of water resources
– The study of processes such as
precipitation,, evapotranspiration
precipitation
evapotranspiration,, runoff
and their interaction
– The study of problems such as floods
and droughts and strategies to combat
them
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The need of the hydrologic studies
arises from the following problems:
– Uncertainty of precipitation and its
seasonal occurrence
– Seasonal flow of rivers, and
– Population growth and rising standards of
living
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Need for the Hydrologic Studies
Necessary because of the
– Increased population and
– Rising standards of living have greatly
increased
– Hydrologic studies
importance
for
are of utmost
planning
and
development of water resources to meet
these demands
demands..
Importance of Hydrology in Civil
Engineering
Analysis of Data
Analysis of hydrologic data includes checking it for
consistency and
Homogeneity as well as finding its various statistical
parameters..
parameters
Prediction
Prediction means finding design values and
maximum possible floods and droughts.
droughts. Various
approaches for prediction of hydrologic values are:
are:
Statistical Approach
Physical Approach
Deterministic Approach (Model or approach that does not consider
randomness, given input will always produce the same output) 13
Major Hydrologic Projects
Prediction and Forecasting of:
of:
Contamination effects on rivers and lakes
Contamination propagation in groundwater
Effect of drainage on flood flows
Environmental impact of water resources
projects
Environmental impact of deforestation
Environmental impact of urbanization
Environmental impact of chemical leaks
from tanks
Environmental impact of global climate
change
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The main jobs of a hydrologist are
collection and analysis of data, and
making predictions out of this analysis.
Important role in
Design and Operation of water resources
engineering projects like
– Irrigation
– Flood control
– Water supply schemes
– Hydropower projects and
– Navigation
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Major Aspects of Hydrology
Major Aspects of Hydrology
– Collection of Data
The hydrologic data comprises (few are
mentioned below as for example):
a. Rainfall Data
b. Snowfall Data (and snow melt data)
c. Runoff Data (Catchment Runoff and
Stream Flows), and
d. Groundwater Data
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Continued….
Major Hydrologic Projects
Sciences Involved
Hydrology is a very broad subject and it
needs support from allied sciences such as
– Physics,
– Mathematics,
– Geology,
– Geography,
– Meteorology,
– Forestry,
– Agriculture and
– Hydraulics.
Continued….
Engineering Hydrology provides hydrologic data
essentially required for a variety of projects, such as:
as:
– Hydraulic Structures like
Dams, Bridges,
HeadHead-works,
Spillways and
Culverts etc.
etc.
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– Hydroelectric Power Generation
– Flood Control Projects
– Irrigation Projects
– Environmental Pollution Control, and
– Planning and Execution of Water Resources
Development Projects
Continued….
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World Water Budget
Application in Engineering
Hydrology finds its greatest application
in the design and operation of water
resources engineering projects
– The capacity of storage structures such as
reservoir
– The magnitude of flood flows to enable safe
disposal of the excess flow
– The minimum flow and quantity of flow
available at various seasons
– The interaction of the flood wave and
hydraulic structures, such as levees,
reservoirs, barrages and bridges
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Total quantity of water in the world is
estimated as 1386 M km3
– 1337.5 M km3 of water is contained in
oceans as saline water
– The rest 48.5 M km3 is land water
13.8 M km3 is again saline
34.7 M km3 is fresh water
– 10.6 M km3 is both liquid and fresh
– 24.1 M km3 is a frozen ice and glaciers in the
polar regions and mountain tops
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Global annual water balance
SN
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Item
Area (km2)
Precipitation (km3/year)
(mm/year)
Evaporation (km3/year)
(mm/year)
Runoff to ocean
Ocean
361.3
458,000
1270
505,000
1400
Hydrologic Cycle
Land
148.8
119,000
800
72,000
484
Rivers (km3/year)
Groundwater (km3/year)
44,700
2,200
Total Runoff (km3/year)
(mm/year)
47,000
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Hydrologic cycle….
Water exists on the earth in all its three
states, viz. liquid, solid, gaseous and in
various degrees of motion.
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Hydrologic cycle….
Hydrologic cycle….
Evaporation of water from water bodies, such as
oceans and lakes, formation and movement of
clouds, rain and snowfall, stream flow and ground
water movement are some examples of the dynamic
aspects of water.
water.
Evaporation from
water bodies
Water vapour
moves upwards
Cloud formation
Condensation
Precipitate
Interception
Transpiration
Infiltration
Runoff
Runoff–
–streamflow
Deep percolation
Ground water flow
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Evapo transpiration
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and back to the earth and ultimately to the ocean
Stream flow
(Runoff)
through
the
processes
of
evaporation,
precipitation, percolation, runoff and return to the
ocean is called hydrologic cycle
cycle..
Inter flow
Infiltration
The hydrologic cycle can be broadly divided into
two phases –
land phase, and
Base flow
Groundwater flow
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Hydrologic cycle.
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Hydrologic cycle….
The hydrologic cycle has importance
influence in a variety of fields agriculture,
forestry, geography, economics, sociology,
and political scene.
scene.
Engineering application of the knowledge are
found in the design and operation of the
projects dealing with water supply,
hydropower, irrigation & drainage, flood
control, navigation, coastal work, various
hydraulic structure works, salinity control
and recreational use of water.
water.
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VOCABULARY
Hydrologic Cycle
Journey of water from the ocean to atmosphere
Precipitation
The dynamic nature of water, the
existence of water in various state with
different hydrological process result in
a very important natural phenomenon
called
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Components of hydrologic cycle
Water, irrespective of different states,
involves dynamic aspect in nature.
atmospheric phase
phase..
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Continued….
EVAPORATION is when the sun heats up water droplets
that are in a body of water and turns them into vapor
or steam.
TRANSPIRATION is loss of water from leaves of plants
from their pores.
CONDENSATION happens when water vapor in the air
gets cold and changes back into liquid, forming clouds.
PRECIPATION occurs when water falls from the sky to
the ground in some form. There are many different
forms of precipitation. (Rain, snow, sleet, hail etc)
RUNOFF
is portion of precipitation that is not
evaporated.
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Hydrologic Cycle
Hydrologic Cycle
Infiltration
– Precipitation falling on the ground is, to some
extent, absorbed by the land
land.. This absorption
of precipitation water by land from the surface
of earth is called infiltration
infiltration..
Interception
– A part of the precipitation is obstructed by
vegetation and temporarily remains there.
there. This
process is called interception
interception.. Later the
intercepted water is either evaporated or
infiltrated..
infiltrated
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Hydrologic Cycle
Hydrologic Cycle
Depression Storage
– A part of precipitation is stored in depressions on
the catchment area.
area. This is called depression
storage.
storage.
Detention Storage
– When the precipitation occurs for a longer
duration and at a rate greater than the rate of
infiltration some water is collected on the surface
of the earth up to a certain depth
depth.. On attaining a
certain depth, the action of gravity makes this
water flow.
flow. Before it starts flowing, the water
stored on the surface of earth is called detention
storage.
storage.
Runoff
– After the detention storage is built up, as
explained above, the water will start flowing
over the ground and is called runoff.
runoff.
Inter Flow
– The part of infiltrated water which moves
laterally through the upper soil layers above
the groundwater level and soon joins the
stream is called inter flow.
flow.
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Continued….
Continued….
Hydrologic Cycle
Total Runoff
A part of infiltrated water moves in the form of inter
flow which soon joins the stream, the remaining
portion of infiltrated water percolates to deeper layers
of the ground and is stored as groundwater
groundwater.. This
groundwater sometimes also joins the stream flow
through springs and seepage process.
process.
The stream flow is then called the total runoff i.e. it is
sum of all the components of precipitation water.
water.
Direct runoff plus the losses gives total runoff.
runoff.
The runoff can be expressed in depth units for a
certain area or it can be expressed in volume units
units.. It
can also be expressed in discharge units for a
specified time.
time.
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Continued….
CLOUDS
Atmospheric Phase of Hydrologic Cycle
Clouds are masses of small water droplets or tiny ice
crystals that float in the air.
Clouds are classified into three main groups:
lower, middle and higher level clouds.
Lower level clouds have ever-changing structure
due to turbulent motions.
Lower level clouds: cumulus, cumulo-nimbus, stratus,
stratocumulus, nimbostratus and fog.
– Atmospheric phase of hydrologic cycle starts with the formation
of clouds after vaporization from water bodies and ends after
the occurrence of precipitation
precipitation..
Land Phase of Hydrologic Cycle
– After occurrence of precipitation, water comes in contact with
the earth surface and hydrologic cycle enters the land phase
phase..
Part of precipitation is infiltrated and a part of it, depending
upon circumstances, is intercepted by trees and vegetation.
vegetation. If
there are depressions in the surface upon which precipitation
falls, a part of precipitation will be stored in the depressions in
the form of depression storage.
storage. All of these parts are liable to
vaporization.. Rainwater stands on the surface of earth where it
vaporization
falls, after various losses, depending upon the rate of rainfall
when the depth of standing water becomes sufficient it starts
flowing over the ground surface in the form of surface runoff.
runoff.
Middle level clouds: altocumulus, altostratus
Higher level clouds: cirrus, cirrostratus and cirrocumulus
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Continued….
World Precipitation and Average
Rainfall
Precipitation
PRECIPITATION
CYCLONIC: Results from lifting of air masses converging into low
pressure of cyclone.
• FRONTAL : A border region between two adjacent air masses with
different temp. & humidity is a FRONT.
• When a flow of warm and moist air masses from south meets cold
air mass of polar region, cause precipitation.
• NON-FRONTAL: Moist warm air mass is stationary and moving
cold air mass meets it
Precipitation plays a major role in determining
the climate of an area.
Rainfall is critical as it replenishes ground water
and supplies both natural watershed systems and
irrigation channels.
Worldwide rainfall averages vary greatly from
region to region
Areas that receive
Single strongest variable driving hydrologic
processes
Formed by water vapor in the atmosphere
As air cools its ability to ‘hold’ water
decreases and some turns to liquid or ice
(snow)
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– less than 250 mm (10 in) of rain each year are
deserts,
– more than 2000 mm (80 in) are equatorial or tropic.
CONVECTIVE:
• Caused by Natural rising of warmer lighter air in colder, denser
surroundings.
• Spotty, intensity varies from light showers to cloud bursts.
OROGRAPHIC:
• Lifting of warm moisture laden air mass due to topographic barriers
(mountains)
TURBULANT ASCENT
• Air mass forced to rise up due to increased turbulence & friction.
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Causes of Precipitation
FORMS OF PRECIPITATION
RAINFALL MEASUREMENT
Drizzle Size of water droplet under 0.5 mm, intensity is <0.01
mm/hour.
Rain Size of water droplet >0.5 mm, Upper size of water drop
6.25 mm, drops > then this break up as they fall
Glaze When Drizzle or rain freezes as it comes in contact with
cold objects.
Sleet Frozen air drops cooled to ice stage while falling through
air at sub-freezing temperature.
Snow Precipitation in form of ice-crystals resulting from
sublimations (water vapour directly changes to ice)
Snow flakes No. of ice crystals fused together from snow flakes.
Hail Lumps of bulbs of ice over 5 mm diameter formed by
alternate freezing or melting.
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•Amount of precipitation is Depth (in cm or inches) which falls
on a level surface, measured by rain gauge.
RAIN GAUGE
NON-AUTOMATIC
SYMON'S
AUTOMATIC
WEIGHING
BUCKET TYPE
TIPPING BUCKET
FLOAT TYPE
1.Precipitation characteristics
– Cm. Of water over a catchment
– Total water in m3 or hectare-metre
Rainfall is disposed off in manner– Basin Recharge
• Rain intercepted by leaves, stems.
• Water held up in surface depressions (depression storage)
• Soil moisture as capillary water in pore spaces
– Direct run-off
• Water which reaches the stream shortly after it falls as rain
• Overland flow- water which travels across the ground surface.
• Interflow-
– Percolation due to ground water
• Sub-soil is permeable, water percolates deep to meet the ground water
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– Evaporation
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5.
Geological characteristics
Type of surface soil, sub-soil, type of rock & their permeability
characteristics.
Soil & sub-soil is pervious, more seepage and reduces peak flood.
Surface is rocky, more run-off.
Fissured rocks, most of water lost by seepage, less run-off.
More intense rainfall distributed over a small area; a stream
collecting water from small catchment give greater runoff/unit area. In big catchment run-off intensity of larger
stream/area is less.
More rain fall, more run-off
Type of storm causing precipitation
Increases with intensity of rainfall, extent of storm over catchment.
Less intensity of rain fall, more loss in infiltration and evaporation,
run-off less.
2.Topography
Depends on smooth or rugged surface
Surface slope is steep, water flows quickly, less absorption &
evaporation losses and more run-off.
In mountainous catchment, and on windward side, intensity of rainfall will be more and more run-off.
3.Storage characteristics of catchment
Artificial storage (dams, weir etc) & natural storage (river, lake etc.)
tend to reduce peak flow. Gives more evaporation loss.
The storage into pervious surface soil and sub-soil reduces the peak42
flow
Evaporation & Transpiration
FACTORS AFFECTING RUN-OFF
Shape & size of catchment
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FACTORS AFFECTING RUN-OFF
RUN-OFF
RUN-OFF: Run-off of a catchment area is total quantity of water
draining into a stream or reservoir. It is expressed as –
FACTORS AFFECTING RUN-OFF
4.
•Knowledge of its amount, character, season, effects are
important to design irrigation works.
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SYMON’S RAINGAUGE
Most common type of nonautomatic type, used by
Meteorological Deptt. of Govt. of
India
Consists of cylindrical vessel 127
mm at top and 210 mm at bottom.
Top section of funnel is with a
circular brass rim of 127 mm size.
Funnel shank is inserted in the
receiving bottle of 75 to 100 mm
capacity. During heavy rainfall,
rain should be measured 3 or 4
times a day. Rim is 305 mm above
ground.
Set up in concrete block of
60x60x60 cm.
•Rainfall is source of all water used for irrigation.
• In Fan shaped catchment all tributaries are approx. of same
size. It gives more run-off since peak flood from tributaries
reach the main stream at the same time.
6.
Meteorological characteristics
In Fern leaf catchment, tributaries are of
different lengths and meet the main
tributaries at regular intervals. In such
narrow catchment peak flood intensity is
reduced since discharge is distributed
over a long period of time
7.
Character of catchment surface
Fig. 4.1
Temperature, wind, humidity
Low temperature, ground is saturated, more run-off.
High temp. & greater wind velocity, less run-off
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Surface is drained or undrained, natural or cultivated, bare or covered
with vegetation etc.
No natural drainage, more absorption loss.
More area is cultivated, less run-off.
Presence of vegetal cover reduces run-off during smaller storms.
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Water Budget Equation
Overland Flow
Water Budget Equation
Catchment area
If rainfall exceeds soil infiltration capacity:
Catchment area….
The area of land draining in to a stream
or a water course at a given location is
called catchment area / drainage area /
drainage basin / watershed.
A catchment area is separated from its
neighbouring areas by a ridge called
divide / watershed
watershed..
– Water fills surface depression then
– Water spills over downslope as overland
flow and
– Eventually to the stream
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A watershed is a geographical unit in which
the hydrological cycle and its components can
be analysed
analysed.. The equation is applied in the
form of waterwater-balance equation to a
geographical region, in order to establish the
basic hydrologic characteristics of the region
region..
Usually a watershed is defined as the area
that appears, on the basis of topography, to
contribute all the water that passes through a
given cross section of a stream.
stream.
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