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Hydrology is the science which deals with the occurance,distribution and disposal of water on the earth !oisture is constantly in circulationbetween the land and ocean and the s"y The unending #oisture cycle is "nown as Hydrologic cycle

Di$erent phases of hydrologic cycle are as follows%&

' ()aporation and transpiration*(+-recipitation*-+

. Run o$*R+

(/0-OR0TION 0ND TR0N1-IR0TION%& In2ltration for con)enience, e)aporation and transpiration are co#bined intoe)apotranspiration*(T+ It is the total water loss fro# a crop area due to e)aporation fro# the and transpiration by the plants

In2ltration is the entry of water into the soil surface -(RCI-IT0TION%& It #ay be de2ne as the fall of #oisture fro# the at#osphere to the earth surface in any fro# Run o$ is that portion of

precipitation that is not e)aporated 3hen #oisture falls to the earth4s surface as precipitation, a part of i t is e)aporated fro# the watersurface , soil and )egetation and through transpiration by plant, and re#ainder point is a)ailable as run o$ which ulti#ately runs to theocean through surface or sub&surface ocean The run o$ of a catch#ent area is any speci2ed period is the total 5uantity of water draining

into a strea# or into reser)oir in that period This can be e6pressed as *I+ centi#eter of water o)er a catch#ent or *ii+The total water incubic& #eter or hectare #eters

The rainfall is disposed 7$ in the f7llowing #anner %' 8asin Recharge

Direct Run o$. -ercolation down to ground water9 ()aporation' 801IN R(CH0R:(%& *i+ Rain intercepted by lea)es and strea# of )egetation*ii+ 1oil #oisture held as capillary water in pore spacer of soil or as hygroscopic water absorbed on the surface of soil particles

DIR(CT RUN OFF%& Direct Run 7$ is that water which reaches the strea# shortly after it falls as rain It consists of*i+O)erland ;ow*ii+ Inter;owO)erland ;ow is that portion of water which tra)el across the ground surface to the nearest strea# If the soil is per#eable, water percolates

intact and when it beco#e saturated ;ows laterally in the surface soil to a strea# channel The condition for inter;ow is that the surface soil is per#eable but the sub&soil is relati)ely i#per#eable so that water does not percolate

deep to #eet the ground water. -(RCO&()aporation is the process in which li5uid changes state to )apour It can occur at any te#perature up to the boiling point of the li5uid

%

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F0CTOR 0FF(CTIN: RUN OFF' -ercipitation characteristic

1hape and si?e of the catch#ent. Topography

9 :eological characteristics@ !etrological characteristics

A Character of the catch#ent surfaceB 1torage characteristics

' -(RCI-IT0TION CH0R0CT(RI1TIC1%& The #ore rainfall, #ore will be the run o$ Run o$ depends on the type of the stor# causing precipitation, and alsoupon the duration Run o$ increases with the intensity is )ery less ,it rain as light slower, #uch of the water will be lost in in2ltration and e)aporation etc

and the run o$ will be less

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1H0-( 0ND 1I ( OF TH( C0TCH!(NT%&The run o$ fro# a catch#ent also depends upon the si?e shape and location of the catch#ent The entire area of a ri)er basin whose surface run o$ drains into the ri)er in the basin is considered as a hydrologic unit, and is called drainage basin water shed or catch#ent area There are two type of catch#ent&

' F0N shape catch#entF(RN shape catch#ent

Fig no *'+

2g no * +

0 fan shape catch#ent produce greater ;ood intensity 1ince all the tributaries are nearly of the sa#e length and hence the ti#e of concentration is sa#e and is lesswhen as in the fern shape catch#ent the ti#e of concentration is #ore and discharge is distributed o)er a long period

0 strea# collecting water fro# a s#all catch#ent area is li"ely to gi)e greater run o$ intensity per unit area Than the larger strea# where as the unifor# rain seldo# falls o)er the entire area, that only )ery few tributaries of the strea# feed water to #ain strea# during a particular stor#. TO-O:R0-H %&The run o$ depends upon whether the surface is s#ooth or rugged If the surface slope is steep water will ;ow 5uic"ly, e)aporation will be less resulting in greater run o$ If the catch#ent is #ountainous, and is on the windward direction the intensity of rainfall will be #ore where run o$ will also be #ore

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@ !(T(ORO

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A CH0R0CT(R OF TH( C0TCH!(NT 1URF0C(%&The run o$ also depends upon thesurface condition& 3hether the surface is drained or un&drained, natural or

culti)ated, it is bare or )egetati)e land etc It the surface has n7 natural drainage,absorption loss will be #ore If the #ore area of a catch#ent is culti)ated, surface

run o$ will be less The )egetati)e land reduces run o$

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B 1TOR0:( CH0R0CT(RI1TIC1 OF TH( C0TCH!(NT%&The arti2cial storage such asda#s ,weirs etc and natural storage such as la"es, pond etc ,to reduce pea" ;ow ()aporation losses ta"es place If the tributaries of a ri)ers discharges into a la"e,

and the ri)er o$ fro# the la"e, the point pea" ;oods in the ri)er will be reduced The

storage into the per)ious surface soil and sub soil tends to reduce the pea" ;ow andtend to regulari?e the ;ow of a strea#

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(1TI!0TION OF RUNOFF

' (#pirical for#ulae,cur)es andtablesIn2ltration #ethod

. Rational #ethod9 O)erland ;ow hydrograph

@ Unit hydrograph #ethod