Hydrology Flashcards
What is sink in Catchment Area?
In closed catchment the water converges to a
single point inside the basin, known as a Sink,
which may be a permanent lake, dry lake, or a
point where surface water is lost underground
What are isochrones?
lsochrones are imaginary lines across the
catchment from where water particles traveling
downward take the same time to reach the
catchment outlet.
What is hydrometeorology?
Hydrometeorology is a special branch of
hydrology that deals with the study of the
atmospheric and land phase of hydrological
cycles with the emphasis on the interrelation
involved between them
What is water shed divide?
The line which divides the surface runoff between
two adjacent river basins is called the
topographic water divide or the watershed
divide, or simply the divide.
What Is the difference between absolute
humidity and relative humidity?
The total weight of moisture content (water
vapour) per unit volume of air at a definite
temperature is cal led absolute humidity.
Absolute humidity in indirectly expressed as
vapour pressure.
Relative humidity is defined as a ratio of the
amount of water vapour actually present in the
air having definite volume and temperature (i.e.,
absolute humidity) to the maximum amount the.
air can hold (i.e., humidity capacity).
What is hydrometeorology?
Hydrometeorology is a special branch of
hydrology that deals with the study of the
atmospheric and land phase of hydrological
cycles with the emphasis on the interrelation
involved between them
State the significance of relative humidity
Relative humidity has a great climatic
significance because the possibility of
precipitation depends on it. High and low relative
humidity is indicative of the possibility of wet
(precipitation) and dry conditions respectively.
The amount of evaporation also depends on
relative humidity. Evaporation decreases with
high relative humidity while it increases with low
relative humidity.
What is the use of Depth Area Duration
(DAD) curve?
Depth of rainfall at a raingauge station is called
point rainfall. To convert the point rainfall data
to areal rainfall data, (i.e., to find out how muctl
of rainfall will occur over various areas) Depth
Area Duration curve is used.
What is normal precipitation?
The normal rainfall is the average value of rainfall
of a particular date, moment or year over a
specified 30 year period. Normal rainfall is used
to find out the missing data of certain
raingauges
What is different between infiltration and·
percolation?
The percolation is the downward flow of wate~
through the zone of aeration towards the water ·
table and infiltration is the entry of water through~
the surface layers of the soil.
How do we measure rainfall?
Rainfall is measured from a device called
raingauge. Raingauge is also known by other
names as ombrometer, pluviorneter, hyetometer
etc.
How will you dlff9rentlate between fi·Index
and W-lndex
The~ir”‘dox Is the average rainfall above whlch
the ratnfn~l volume is equal to the runoff volurno.
W-index ts the avaroge Infiltration rato or tho
infiltration capacity averaged over the whole
storm period.
What are the characteristics of precipitation
in India?
(ESE 2007
(a) South west monsoon (June-September)
(b) Post monsoon (October-November)
(c) Winter (December-February)
(d) Summer (March-May)
What is the IS Code for Water Resources?
There are many IS codes on water resources
and one of them is IS 4987-1968
Recommendations for Establishing Network of
Raingauge Stations.
What Is hydrology?
ESE 2012, 2013, 2017
It implies that branch of engineering which
deals with occurrence, circulation and
distribution of water on earth and earth’s
atmosphere. It is concerned with water available
-. in streams, lakes, oceans and snowfall, rain,
storm and the water occurring below the ground
SUrface.ln fact, Hydrology Is an Interdisciplinary
· science that take.s support from other sciences as well as like chemistry, physics, flulo mechanics, statistics, .Geology, metrologY etc
What is precipitation?
ESE 2008
All forms of water that reach the earth from the
atmosphere.
1.18 ·What ls.lsohytet method? ‘ . -· (ESE 2012)
read from pdf
What are the obligatory points?
ESE 2013
Obligatory points: These are the control points
which govern the alignment of highway and can
be classed as:
(a) Obligatory points through which alignment
has to pass.
(b) Points through which alignment should not
pass.
What Is Drizzle?
Drizzle Is a fine sprinkle of water droplets of
size less than 0.5 mm and Intensity less than 1
mm/hr. The drops of drizzle appear to float n
air.
What Is Theissen Polygon method?
(ESE 2013
It is a method of estimating the mean rainfall
over an area on the basis of weightage of area
closest to the rain gauge station. If the
catchment Is divided into n areas of area A1,
A2, … An with respective precipitation as P1,
p2, … Pn then mean precipitation is given by,
What is stochastic hydrology?
ESE 2013
While dealing with hydrological systems, there
always remain an element of error due to spatial
variation of hydrological data, uncertainty
involved in data collection, temporal variability
etc. Stochastic hydrology not only uses models
to predict hydrological variables but also tries
to quantify the errors in the model outcome.
What is Transpiration System?
ESE 2016
In transpiration system, uninterrupted supply
of water and solutes takes place from root of
plants to leaves via the xylem from where water
evaporate into the air. In some plants
transpiration is driven by capillary action and
in some plants it is driven by root pressure
What is hydrological cycle?
ESE 2013, 2016, 2017
On Earth, water occurs in all the three physical
states viz. solid (in the form of ice), liquid and
gas (steam). Evaporation of water from water
bodies like oceans, lakes, rivers etc. take place
which rise above leading to the formation of
clouds. As the clouds rise further, they
condense and water comes back on to the Earth
in the form of rains, snowfall etc. All these
aspects of water constitute a cycle known as
hydrologic cycle.
Working principal of telemetering rain gauge.
ESE 2016
Telemetring rain gauge is a recording type of
rain gauge which contains electronic units to
transmit the rainfall data to the base station.
Tipping bucket type rain gauge is usually
adopted for this purpose.
What are the different types of clouds?
ESE 2016
Cirrocumulus , cirrus, cirrostratus,
cumulonimbus, altocumulus, altostratus, stratus,
cumulus and stratocumulus
Why do we use the term •average annual
rainfall’?
(ESE 2017)
Average annual rainfall for a place is generally ns.
calculated by averaging the last 30 years of
What are isohyets?
ESE 2017, 2016
A line on a map connecting points having the
same amount of rainfall in a given period
What is a Hyetograph?
(ESE 2017, 2018)’
A hyetograph is a graphical representationot
the distribution of rainfall intensity over time.
Why do we use the term •average annual
rainfall’?
(ESE 2017)
Average annual rainfall for a place is generally ns.
calculated by averaging the last 30 years of annual rainfall. Annual rainfall is the sum of daily
rainfall that can be calculated from raingaug.. .
records.
Mention the differences between arithmalic
mean and Theissen polygon method.
(ESE 2011)
In Arithmetic Mean method, average
precipitation over the catchment area is taken
as the arithmetic mean of the station values.
In Theissen Polygon method, the rainfal
recorded at each station is given a weightaQt
on the basis of the area closest to the station
What are the various types of Rain Gauges?
ESE20U
Measuring cylinder rain gauge
Tipping-bucket rain gauge
Weighing rain gauge
Optical rain gauge
1.34 What is NOMA and NDRF?
read from pdf
Explain the following terms: • Evaporation • Precipitation • Interception • Infiltration • Transpiration • Percolation • Storage • Runof
Evaporation Is the transfer of water from a
liquid state to a gaseous state i.e., it is the
conversion of liquid to the vapour phase.
• Precipitation is the disposition of water on
the earth’s surface in the from of rain, snow,
hail, frost and so on.
• Interception Is the short-term retention of
rainfall by the tollage of vegetation.
• Infiltration is the movement of water into
the soil of the earth’s surface.
• Transpiration is the soil moisture taken up
through the roots of a plant and discharged
Into the atmosphere through the tollage by
evaporation.
• Percolation is the movement of water from
one soli zone to a lower soil zone.
• Storage Is the volume of water which gets
stored In natural depressions of a basin.
• Runoff is he volume of water drained by a
river at the outlet of a catchment.
How can the rate of reservoir silting be
reduced?
By venting the density currents by properly
locating and operating the outlets and sluice
gates. Density currents may be· ‘defined as the
gravitational flow of one fluid under another fluid of approximately equal density
How the flow of river can be measured?
ESE 2013
River flow can be measured by any of he following methods: (i) Direct determination of the stream discharge (a) Area velocity method (b) Dilution techniques (c) Ultra sonic method (d) Electromagnetic method (il) Indirect determination of stream discharge (a) Hydraulic structures like weir. flumes. gated structures etc. (b) Slope area method
What is the average discharge o1 Ganges
river?
(ESE 2013
Ganges is the third largest river with an average
discharge of 38120 m3
/sec.
What Is evapotranspiration?
ESE 2016
The process by which water is transferred from
land to the atmosphere by evaporation from soil
and other surfaces and by transpiration from
plants.
What are the factors on which evaporation
depends?
(ESE 2016)
- Temperature
- Surface area
- Humidity
- Wind speed
How do you measure velocity of Ganga
river?
Velocity of the Ganga river can be measured by
using a current meter
What are the methods tor measuring
evapotranspiration?
Lysimeter
Field experiment
Soil moisture depletion study
Water balance method
2.12 What is working principle of wind
anemometer?
(ESE 2017)
The stronger the wind blows, the faster the rod
spins. The anemometer counts the number of
rotations, or turns, which is used to calculate
wind speed. Because wind speeds are not
consistent wind speed is usually averaged over
a short period of time.
Who is responsible for measuring discharge
of river?
(ESE 2017)
Central water commission is responsible for
measuring discharge of river.
How to measure the discharge of river?
ESE 2017
Methods to measure the discharge of river:
(i) Timed Gravimetric
(ii) Tracer-Dilution
(iii) Area-Velocity
(iv) Manning’s Equation I (Gauckler-ManningStrickler Formula)
(v) Hydraulic Structures (Flumes &Weirs)
How do you calculate evaporation losses?
(ESE 2017
Measurement of evaporation losses done by:
• Using evaporimeters
• Using empirical equations
• By analytical methods
What is the use and principle of Penman’s
method?
Penman’s equation is used to determine the
consumptive use of different areas or different
segments of a basin
What are the effects of silting of power
reservoirs?
If sufficient water required for power generatiCO
remains available, the reservoir’s efficiencY
remains unaffected by silting. But due to silted
water, the abrasion of the blades of turbines maY
occur very soon and power production maY be
stopped over considerable length of time
What is the nature of inflow mass curve?
It is a continuously rising curve as it is the plot
of accumulated inflow v/s time
What is Instantaneous Unit Hydrograph
(IUH)?
A unit hydrograph of infinitesimal duration is
called instantaneous unit hydrograph.
Why runoff is not maximum, even when the·
duration of the rain is more than the time of
concentration?
Because in such case the intensity of rain
reduces with the increase ln Its duration.
What is the significance of time of
concentration?
The runoff resulting due to a rainfall having a
duration lesser than the time of concentration
will not be maximum, as the entire area will not
contribute to the runoff.
When maximum runoff Is obtained?
It will be obtained from the rain having a duration
equal to the time of concentration and this is
called the critical rainfall duration.
Which have more time of concentration leaf
shape or circular basin?
Leaf shaped basin will have more time of
concentration as compared to circular basin
Should hydrograph be symmetric?
Hydrograph not necessarily be symmetric as
the shape of rising limb depends on the intensity
of rainfall while the shape of recession limb
depends on the infiltration characteristics of the
catchment.
What is unit hydrograph and when a channel
is said to be in regime?
(ESE 2012, 2013)
Unit hydrograph is the direct runoff hydrograph
resulting from unit depth of rainfall excess over
the catchment.
A channel is said to be in regime if the channel
flow is such that there occurs neither the silting
nor scouring. Such regime conditions are not
easily possible in streams/rivers but in artificial
channels, it can be achieved. The underlying
concept of designing such a regime channel is
that whatever silt has entered into the channel
at its head is kept in suspension so that it does
not settle down at the channel bottom. Also the
flow velocity in the channel should be such that
It does not produce any local slit by erosion of
the channel bed material and from the erosion
of channel side slopes
What are· the various assumptions Involved
·In Unit Hydrograph?
Assumptions involved in UH theory are
(a) Time lnvarlance : It means that the direct
runoff response to a given effective rainfall
in a catchment is time-invariant
(b) Linear Response : The direct-runoff
response to the rainfall excess is assumed
to be linear.
What is direct runoff hydrograph?
ESE 2013
It is the hydrograph that results from surface
runoff hydrograph obtained after the base flow
separation.
What is catchment area?
{ESE 2013, 2016)
It is that area of land that contributes its drainage
water into a stream or a water course. It is also
called as drainage area or the drainage basin.
What Is Rational Formula for runoff?
ESE 2016
Rational formula: The rational formula is expressed as: Q =CiA p where QP = Peak discharge C = Coefficient of runoff ; = Mean intensity of precipitation A= Drainage area
What is hydrograph? What are uses of it?
(ESE 2014, 2016, 2018}
It is a graphical representation of rate of flow
(discharge) versus time in a river, channel or
conduit carrying flow.
The uses of hydrograph are:
1. Development of flood hydrographs for
extreme rainfall magnitudes
2. Extension of flood flow records based on
rainfall records.
3. Development of flood forecasting and
warming system based on rainfall.
What Is catchment? Difference between
watershed and catchment?
(ESE 2016)
Watershed: A watershed is the land area that
drains into a lake, river or stream. It is an area
covered by a system of surface and subsurface water flowing to a common point of
disposal. A watershed divides one drainage
basin from the other.
Catchment area: A river drains the area
collected from a specific area which is called
as catchment area.
How to relate hydrograph of one catchment
to another?
By synthetic unit hydrograph.
Do rivers feed groundwater or groundwater
feed rivers?
(ESE 2016)
Both the statements are correct. When the bed
of river is below the groundwater table, during
periods of low flow in the stream, the water
surface may go dc;>wn below the general water
table elevation and the groundwater contributes
to the flow in stream. Such streams are called
as effluent streams. Perennial rivers are of this
kind.
But when the water table is below the river bed,
the stream water percolates below the ground
towards the groundwater storage. Such streams
are called as influent streams. intermittent rivers
and the rivers which go dry during long periods
of dry weather are of this kind.
Rational formula and significance.
ESE 2016
Rational formula: The rational formula is
expressed as:
QP =CiA
where QP = Peak discharge
C = Coefficient of runoff
i = Mean intensity of precipitation
A = Drainage area
• This formula is quite suitable for use in the
peak flow prediction in small catchments
of area up to 50 km2.
• This formula also has great significance in
the design of urban drains and in the design
of small culverts and bridges.
What do you know about interflow?
ESE 2017
lnterflow is the lateral movement of water in the
unsaturated zone, or vadose zone, that first
returns to the surface or enters a stream pri()( to
becoming groundwater.
How can we measure Infiltration rate? ·.
We can measure infiltration rate by:
(i) lnfiltrometer
(il) Horton’s equation
(iii) Phillips equation
(iv) Kostiakov equation
(v) Holtans equation
What is Instantaneous Unit Hydrograph?
ESE 2016, 2017
An instantaneous unit hydrograph may be
defined as a hydrograph of direct runoff resulting
from a unit depth of effective rainfall generated
uniformly over a watershed in an infinitesimally
small period of time.
What is a Synthetic Unit Hydrograph?
ESE 2017
A synthetic unit hydrograph retains all the
features of the unit hydrograph, but does not
require rainfall-runoff data. A synthetic unit
hydrograph is derived from theory and
experience, and its purpose is to simulate basin
diffusion by estimating the basin lag based on
a certain formula or procedure. Example: Snyder
synthetic hydrograph
What is the stage-discharge graph?
[ESE 2018]
Stage-discharge graph is the graphiC
representation of discharge in the river with the ·onol corresponding stage of the river at a sect’
the river. The stage-discharge relationship is alSO
called as rating curve.
What is a Hydrograph?
ESE 2016, 2017
A hydrograph is a graph showing the rate of
flow (discharge) versus time past a specific point
in a river, channel, or conduit carrying flow
What is base flow, runoff?
[ESE 2018]
Base flow: It is the delayed flow that reaches a
stream mostly as groundwater flow.
Run off: It is the draining or flowing off of
precipitation from a basin area through a surface
channel. It in fact represents the output from
the catchment in a given period of time.
What do you mean by the stage?
Stage is the elevation of water surface measured
from a datum
Explain different typeS of drought.
(a) Hydrological drought: Meteorologi.cal
drought, if prolonged result in hydrological
. · . . .’dr()ught with marked depletion of surface
·. · . water and groundwater. The consequ~nce
are the drying up tanks, reservoirs, streams
and rivers, cessation of springs and fall in
the groundwater level.
(b) Agricultural drought: This occurs when the
soil moisture and rainfall are inadequate
during the growth season to support
healthy crop growth to maturity. There will
be extreme crop stress and wilt conditions
Define drought.
Drought is a climate anomaly characterized by
deficit supply of moisture. This may result from
subnormal rainfall over large regions causing
below normal natural availability of water over
long periods of time
Enumerate different methods to flood
control.
- Structural methods:
(i) Storage and detention reservoirs.
(ii) Leaves (flood embankments)
(iii) Channel {Improvement).
(iv) Rood ways (new channels)
(v) Soil conservation - Non-structural methods:
(i) Flood plain zoning
(ii) Rood warning, evacuation and relocation
What is design flood?
The maximum flood that any structure can safely
pass is called the design flood.
What do you mean by index of wetness?
ndex of wetness = . . · Actual raifall in given year / (Normal rrumall at that place.)
It indicates the deficiency of rain or excess of
rain.
Where arch dams are suited?
They are best suited at sites where the dam
must be extremely high and narrow, with the
availability of very strong side walls of the
canyon.
How a river valley be selected for dam
construction?
River valley at the dam site should be narrow
but should open out upstream to provide a large
basin for a reservoir
What is Rawhiding?
It involves starting and stopping of pumping
intermittently to produce relatively rapid
changes in the head of the well
What are check dams?
These are smaller dams and trap large amounts
of coarser sediments
What Is reservoir routing?
Reservoir routing is a mathematical procedure by which the hydrograph immediately below the reservoir is determined for the given inflow hydrograph(s) of the river(s) contributing to the storage of the reservoir. The routed hydrograph is characterized by the attenuation of flood peak of the inflow hydrograph. In reservoir…
What is flood forecasting?
ESE 2013
It is the process of providing the information of
the incipient flood well in advance so that
suitable measures can be taken to mitigate the
loss of life and property that are likely to be
affected by the flood. Flood forecasting
technique may be either short range, medium
range or the long range forecasts.
What is flood routing?
Flood routing is the technique of determining
the flood hydrograph at a section of a river by
employing the data of flood flow of one or more
upstream sections
What is flood? Give recent examples related
to flood?
(ESE 2016)
A flood is an overflow originating from a river or
from some other water body which results in
overflowing of the river banks and inundation of
the surrounding areas. A river gets flooded due
to excessive rainfall or excessive melting of
glaciers.
How delta is formed?
When a river reaches a lake or the sea the water
slows down and loses the power to carry
sediment. The sediment is dropped at the mouth
of the river. Some rivers drop so much sediment
that waves and tides can’t carry it all away. It
builds up in layers forming a delta
How to estimate flood for bridges in river?
Flood for bridges in a river can be estimated bY
the use of rational formula.
How to prevent the entry of sediments in
power plants?
The entry of sediment can be prevented by
constructing Silt Excluders on the bed of the
river, upstream of head regulator
What is EI-Nino?
ESE 2017
El Nino Southern Oscillation refers to the cycle
of warm and cold temperatures, as measured
by sea surface temperature. SST, of the tropical
central and eastern Pacific Ocean. El Nino is
accompanied by high air pressure in the western
Pacific and low air pressure in the eastern
Pacific.
Difference between backwaters and delta.
ESE 2016
Back water: A back water is a sort of water
turned back in its course due to an obstruction
due to opposing current or flow of a tide. In other
words, a back water is the part of river in which
there is little or no flow.
Delta: A delta is a landform that forms due to
deposition of sediments carried by river and gets
deposited on the land just before the river meets
the sea.
What do you meant by flooding? Give
technical definition?
Flooding or flood is the unusually high stage in
the river such that the river overflows its banks
and inundates the surrounding areas.
What is recurrence Interval?
[ESE 2018]
Recurrence interval (also called as return period)
represents the average time interval between
the occurrences of a rainfall equal to or greater
than a specified magnitude (say X). Thus,
T :o: 1/P
where
T :o: Reccurence interval or return period
P ;:: Probability of occurrence of an event (rainfall)
of magnitude equal to or greater than X.
What is design flood?
Design flood is the flood adopted in the design
of structure.
What Ia flash flood?
(ESE 2019
It is a flood that ·normally ocours due to sudden . heavy rainfall. A flash flood is sudden influx of water into~ ,dry area usually within 6 hours
What is storage coefficient?
In case of confined aquifer, volume of water
given by unit plan area of aquifer when
piezometric surface falls by unity is called
storage coefficient. For unconfirmed aquifer,
storage coefficients is assumed to be equal to
specific yield. Storage coefficient is also called
as store coefficient.
What is storage coefficient?
In case of confined aquifer, volume of water
given by unit plan area of aquifer when
piezometric surface falls by unity is called
storage coefficient. For unconfirmed aquifer,
storage coefficients is assumed to be equal to
specific yield. Storage coefficient is also called
as store coefficient.
Define specific capacity.
The specific capacity of a well is defined as the
well yield per unit of drawdown.
Differentiate between confined aquifer and
perched aquifer?
(ESE 2012)
A perched aquifer is an aquifer that occurs
above the regional water table. in the unsaturated
zone. It occurs when there is an impermeable
layer of rock or sediment or relatively
impermeable layer above the main water table/
aquifer but below the surface of the land.
A confined aquifer is a water-bearing stratum
that is confined or overlain by a rock layer. Rock
does not transmit water in any appreciable
amount or that is impermeable.
The water inside the confined aquifer is
subjected to pressure higher than atmospheric
pressure.
What is groundwater table?
ESE 2009
Groundwater Table: It refers to the depth
below the ground level below which the voids
of the earth are saturated with water. It varies
from place to place and changes according to
pattern of groundwater exploitation at a
particular place
What is probable maximum flood?
ESE 2013, 2016, 2017
It is the extreme flood that is physically possible
in a region as a result of severe most
combinations including the rare combinations
of meteorological and hydrological factors
What do you mean by recharge of
groundwater
In general there are three methods to
recharge groundwater viz.:
(a) By spreading of water over permeable
soils from where it directly infiltrates.
(b) Through recharge well method wherein
water is injected into the bore holes called
as recharge wells.
(c) By induced infiltration method wherein
water table gradient is increased from the
source of recharge. Ranney type wells are
constructed near the river banks
What is aquifer and aquiclude?
ESE 2019
Aquifer: It is a geological formation that stores
water in significant quantity and also yields water
sufficiently. An aquifer is highly porous as well
as permeable. e.g. Unconsolidated deposits
of sand and gravel.
Aquiclude: It is a geological formation which
is porous but not permeable. Due to porosity,
it stores significant amount of water bust due
to low permeability, it yields water in very
insignificant amount. e.g. Deposit of clay
