Hydrology Flashcards

Question

What are the different types of clouds? | ESE 2016

Answer 1

Cirrocumulus , cirrus, cirrostratus, cumulonimbus, altocumulus, altostratus, stratus, cumulus and stratocumulus

Answer 2

Average annual rainfall for a place is generally ns. | calculated by averaging the last 30 years of

Answer 3

A line on a map connecting points having the | same amount of rainfall in a given period

Answer 4

A hyetograph is a graphical representationot | the distribution of rainfall intensity over time.

Answer 5

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.

Answer 6

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

Answer 7

Measuring cylinder rain gauge Tipping-bucket rain gauge Weighing rain gauge Optical rain gauge

Answer 8

read from pdf

Answer 9

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.

Answer 10

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

Answer 11

``` 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 ```

Answer 12

Ganges is the third largest river with an average discharge of 38120 m3 /sec.

Answer 13

The process by which water is transferred from land to the atmosphere by evaporation from soil and other surfaces and by transpiration from plants.

Answer 14

* Temperature * Surface area * Humidity * Wind speed

Answer 15

Velocity of the Ganga river can be measured by | using a current meter

Answer 16

Lysimeter Field experiment Soil moisture depletion study Water balance method

Answer 17

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.

Answer 18

Central water commission is responsible for | measuring discharge of river.

Answer 19

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)

Answer 20

Measurement of evaporation losses done by: • Using evaporimeters • Using empirical equations • By analytical methods

Answer 21

Penman's equation is used to determine the consumptive use of different areas or different segments of a basin

Answer 22

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

Answer 23

It is a continuously rising curve as it is the plot | of accumulated inflow v/s time

Answer 24

A unit hydrograph of infinitesimal duration is | called instantaneous unit hydrograph.

Answer 25

Because in such case the intensity of rain | reduces with the increase ln Its duration.

Answer 26

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.

Answer 27

It will be obtained from the rain having a duration equal to the time of concentration and this is called the critical rainfall duration.

Answer 28

Leaf shaped basin will have more time of | concentration as compared to circular basin

Answer 29

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.

Answer 30

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

Answer 31

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.

Answer 32

It is the hydrograph that results from surface runoff hydrograph obtained after the base flow separation.

Answer 33

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.

Answer 34

``` 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 ```

Answer 35

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.

Answer 36

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.

Answer 37

By synthetic unit hydrograph.

Answer 38

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.

Answer 39

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.

Answer 40

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.

Answer 41

We can measure infiltration rate by: (i) lnfiltrometer (il) Horton's equation (iii) Phillips equation (iv) Kostiakov equation (v) Holtans equation

Answer 42

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.

Answer 43

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

Answer 44

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.

Answer 45

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

Answer 46

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.

Answer 47

Stage is the elevation of water surface measured | from a datum

Answer 48

(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

Answer 49

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

Answer 50

1. Structural methods: (i) Storage and detention reservoirs. (ii) Leaves (flood embankments) (iii) Channel {Improvement). (iv) Rood ways (new channels) (v) Soil conservation 2. Non-structural methods: (i) Flood plain zoning (ii) Rood warning, evacuation and relocation

Answer 51

The maximum flood that any structure can safely | pass is called the design flood.

Answer 52

ndex of wetness = . . · Actual raifall in given year / (Normal rrumall at that place.) It indicates the deficiency of rain or excess of rain.

Answer 53

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.

Answer 54

River valley at the dam site should be narrow but should open out upstream to provide a large basin for a reservoir

Answer 55

It involves starting and stopping of pumping intermittently to produce relatively rapid changes in the head of the well

Answer 56

These are smaller dams and trap large amounts | of coarser sediments

Answer 57

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…

Answer 58

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.

Answer 59

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

Answer 60

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.

Answer 61

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

Answer 62

Flood for bridges in a river can be estimated bY | the use of rational formula.

Answer 63

The entry of sediment can be prevented by constructing Silt Excluders on the bed of the river, upstream of head regulator

Answer 64

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.

Answer 65

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.

Answer 66

Flooding or flood is the unusually high stage in the river such that the river overflows its banks and inundates the surrounding areas.

Answer 67

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.

Answer 68

Design flood is the flood adopted in the design | of structure.

Answer 69

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

Answer 70

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.

Answer 71

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.

Answer 72

The specific capacity of a well is defined as the | well yield per unit of drawdown.

Answer 73

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.

Answer 74

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

Answer 75

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

Answer 76

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

Answer 77

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