ce-341 evapotranspiration & rwh

7/24/2019 CE-341 Evapotranspiration & RWH

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EVAPOTRANSPIRATION


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Measurement of Evapotranspiration

1. Lysimeters

2. Field Plots

(invoking water budget equation)


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a) PENMN!" E#$%&'N

based on energybalane and mass tran*er

PET = daily potential evaporation in mm/day

A = saturation vapour pressure gradient with temperature at mean air temp

mm of Hg/oC

Hn = net radiation in mm of water/day

Ea = f(wind velocity & vapour pressure deficit

= pshychrometric constant = !"#$ mm of Hg/o

C

Estimation of Evapotranspiration


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Saturation vapour pressure of water and pressure gradient

Estimation o*


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( ) ( )

+

+=

N

neT

N

nbarHH aaan 90.010.0092.056.01 4

Estimation o* +n

Ha = incident solar radiation in mm of water/day f( latitude% period of year

a = !"$ cos(latitude in degree

' = !"

) = ma*imum possi'le hours of 'right sunshine

f(latitutde

n = actual hour of sunshine

r = reflection coefficient (al'edo

f(water/land surface


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Estimation o* Ea

+ = wind velocity at m a'ove the ground in ,m/day

es = saturation vapour pressure at water temp" in mm of Hg

ea = actual vapour pressure at air temp" in mm of Hg

( )asa eeV

E

+=160

135.0 2


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Mean monthly solar radiation at top of atmosphere, Hain mm of

water/day

Estimation o* +a


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Mean mont,ly values o* -ossible suns,ine ,ours N

Estimation o* N


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b) /LNE0&33LE E#$%&'N

Empirical e-uation 'ased of data from arid western .

Evapotranspiration in crop season in cm

100/

54.2

=

=

fh

T

TPF

KFE

ET = PET in a crop season in cm

0 = f (crop type

Ph = monthly percent of annual day1time hours2 f (latitutde

= mean monthly temp" in o3fT


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4alues o* 5 *or seleted ro-s


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Monthly daytime hours percentage Pafor use in Blaney-Criddle

Euation


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!"#$%"&E! H"!'ES$(!"#$%"&E! H"!'ES$(


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%hat is !ainwater harvesting)

onsious olletion and storage o* rainwater to

ater to demands o* water *or drinking

domesti -ur-ose 6 irrigation is termed as

ainwater +arvesting7


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%hy harvest rainwater )

&here are many reasons *ut following are some of the important

ones+

4&o arrest ground water decline and augment ground water ta*le

4&o improve water uality in auifers

4&o conserve surface water runoff during monsoon

4&o reduce soil erosion

4&o inculcate a culture of water conservation


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How to harvest rainwater

Broadly there are two ways of harvesting rainwater

i. Surface runoff harvesting

ii. !oof top rainwater harvesting


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Components of the roof top rainwater

harvesting system

Components of the roof top rainwater harvesting system

Catchment

&ransportation

irst flush

ilter


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Sand (ravel ilter


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Charcoal ilter


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P'C- Pipe filter+


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ME&H01S 0 !00 &0P !"#$%"&E! H"!'ES$(

Storage of 1irect use

!echarging ground water auifers

a. !echarging of *ore wells*. !echarging of dug wells+

c. !echarge pits

d. !echarge &renches

e. Soa2 ways or !echarge Shafts

f. Percolation &an2s


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!echarging of *ore wells


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!echarge Pits


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Soa2 away or !echarge Shafts


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!echarging of dug wells


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!echarge &renches

ce-341 evapotranspiration & rwh

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