4209186190

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Majalah Ilmiah UKHUWAH

Volume 4No.2 April - Juni 2009 J

K AJ IA N B EB ER AP A M ETO O E E VA PO TR AN VIR AS I

01 K RE UN G A CE H

O l.e h : F lrd a us * )

Abst rak

L eb ih d an s ep aru h c ura h h uja n y an g m e nc ap ai p en nu ka an ta na h a ka n s i k em b alik an k ea tm o sfir s eb ag ai

a kib at d an p ro se s e va po tra ns vira siy an g te rja di.s eh in gg a s ala h s atu fa kto r y an g s an ga t m em pe ng aru hi d ala m

p en ye dia an k eb utu ha n a ir p ad a s ua tu a re al p erta nia an a da la h b es ar k ec iln ya e va po tra ns fira si y an g te Jja di.

P ad a ka jie m in i, d ip erfiitu ng kan n Ua i h ide ks e va po tra nsp ira si m en ggu na ka n e liip at p erh itu nga n, ya itu

dengan m enggun~kan m etode penm an , m e tode ha~ reaves , m e tode b laney ~ ridd le yang d im od ifikas i dan

m e to de th om h w aite .s hin gg a d en ga n m e ng gu na ka e m pa t m e to de in i, p erk ira an n ila i in de ks e va po tra np ira si I

ya ng t er ja d i p a d a d ae ra h irig as i la ng au d an p a y a 1 0 0 0 0 0 b a n ga pa t m e nd ek ati d en ga n k ajia n y an g s e b e n a m y a .D ari has il a na lia s da ta dengan m enggunakan keem pa t m etode te rsebu t d ipe ro leh bahw a n ila i in deks

e va po rtan sp ira si ya ng te rb esa r d id ap at d an h as il p erh itu ng an d en ga n m en gg una ka n m eto de H arg re ave s,

s ed an gk an u ntu k n ila i in de ks e va po tra ns vira si y an g te rk ec il d id ap at d en ga n m e n gg un ak an m e to de p erh iu ng an

penman .

PENDAHULUAN

1 .L .a ta rbe lakang

Leb ih dan sepa ruh cu rah hu jan yang

menca ! }a i p e rm u k a a n t a n a h a k a n d ik e m b a l i k a n k e

a tm ospe r sebaga i ak iba t da r i p ro ses

e va po ra ns pira si y an g te rje di s eh in gg a s ala h s atu

fa k to r yang sanga t m em penga ruh i da lam

penyed ian kebu than a ir pada sua tu .a rea l

p re ta nia n a da la h b es ar k ec iln ya e va po tra ns pira si

y a n g t er ja d i.

P erh itu ng an n ila i in de ks e va po tra ns pira si

dengan m enggunakan sa tu m etode saja t idak lah~

cukup un tuk dapa t m em pe rk ira kan seca ra tepa t

besam ya evapo transp iras i yam g te rjad i, m aka

d ipe rlu kan bebe rapa m e tode un tuk

m em pe rk ira ka n. D e ng an d em ik ia n p erk ira an n ila i

in deks evapo transp ira s i yang te rjad i pada a rea l

') D o se n F T. J ur. S ip il. U N ID A i B . Aceh .

pe rtan ian te rsebu t dapa t m endeka ti dengan

k e ja d ia n y a ng s e be n amya .

2 . T uju an P en ulis an

Tu juan da ri p e n u l i s a n in i ada lah un ttik

m e ng ka ji n ila i e va po tra ns pira si y an g te rja di p ad a

d ae ra h K re un g A c eh .

METODOLOG I ·

M etode yang d igunakan ada lah dengan

m e la ku kan s tu di k ep us ta ka an ya itu tin ja ua n d an

be rbaga i pus ta ka yang m enyangku t ten tang

evapotransp i ras i .

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> ; :' , !: _ ; ;

: , : l ! j . . . . ,'Y ,"Majalah l lmiah UKHUWAH;, .Volume 4 No. 2April - Juni 2009

: , P E M B A H A S A N

1 . P em itu ng an E va po tr8 ns pita si

I t f e to d e P e n m a n

P e r h it u n g a n E v a p o t r a n s p i r a s i u n t u k b u l a n

ja nua ri d engan m eng9unakan m etoda penm an

a d a l a h :

a ) . O a t a - d a ta b u la n ja n u a r i :

- T em p e F c i f u t u d a r a : : 2 6 . 4 7 O C

- K e l e m b a b a n r e la t i f ( R h ) = 8 7 . 0 0 %

- K e c e p a t a n a n g in (U ) = 1 2 7 .0 1 K m J ja m

-P e n y in a ra n m a ta h a r i ( s ) = 4 9 . 7 0 %

- L a t i t u d e = 0 3 ° 4 8 ' 0 0 '

- E le v a s i s t a s i u n B e la w a n : 3 m e te r

b ) . P e rh it u n g a n r a d ia s i d a ta n g ( H i ) :

- R a = 1 4 . 3 4 m m lh a r i

- A lb e d o ( r ) = 0 . 2 5

S e h i n g g a :

H i: ( 1 - r ) } i i R a x ( a 1 + a2 5 )

H i = ( 1 -0 .2 5 ) x 1 4 . 3 4 x

( 0 .2 4 + ( 0 .4 1 x (49.70/100)) )

H i : : 4 . 7 7 m m /h a n

. 187

N b ; K o e f i s i e n d e r iv a t e m p ir i s d e n g a n h a r g a :

a 1 = 0 . 2 4

83 = 0 . 5 6

84 = 0 .0 8

a s = 0.28

86= 0.55

a7:: 0 . 2 6

S a = 1.00

8g = 0 . 0 0 6

c ) . P e rh i t u n g a n r a d ia s i p a n t u la n (H b ):

- C O " :: 1 5 . 9 9

- e a : : 3 4 . 5 9 m b a r

- ed = R h x e a = 3 0 .0 9 m b a r

- . . . J e d : : 5 . 4 9 m b a r

S e h i n g g a :

H b = c a 4 x (a 3 - (a 4 x ~ed)) x (a5 + (a6 x s )

H b = 1 5 . 9 9 x ( 0 .5 6 - ( 0 .0 8 x 5 . 4 9 ) ) x

0 . 2 8 + ( 0 .5 5 x (49.70/100)) )

r ib : 1 . 0 7 mm /h a n

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M~mahnmmhUKHuWAH

Volume 4 No.2 April- Juni 1009

d ) . P e rh i t u n g a n a e ro d i n a m i c t e rm (E a) ; S e h i n g g a

E a = ( a 7 x ( e a - ed) ) x ( a 8 + ( a 9 x U )

E a = ( 0 .2 6 x ( 3 4 . 5 9 - 3 0 .0 9 ) ) x

( 1 . 0 0 + ( 0 . 0 0 6 x 1 2 7 .0 1 ))

E a = 2 .0 S m m lh a r i

e} . P e rh i t u n g a n i n c le k s e v a p o t r a n s p ir a s i (E ta )

u n t u k b u l a n ja n u a r i a d a la h :

E t o = B x (H i - H b ) + (1 - B ) x E a

Eta = 0 .15 x (4 .11-1 .01 ) + ( 1 - 0.75) +

( 1 - 0 . 7 5 } x 2 . 0 6

E t a = 3 .2 9 m m lh a r i

E t o = 3.29 x 3 1 = 1 0 2 . 0 1 m m J b u l a n .

P e r h i t u n g a n e v a p o l r a n s p i r a s i u n t u k b u l a n

j a n u a r i d e n g a n m e n g g u n a k a n m e t o d e H a r g re a v e s

a d a l a h :

a ) . O a t a -d a ta b u la n ja n u a r i

- T e m p e r a tu r u d a r a : : ; 2 S . 4 7 ° C

M P e rs e n s in a r m a ta h a r i (s ) = 4 9 . 7 0 %

b ) , P e m i t u n g a n r a d ia s i s in a r m a t a h a r i y a n g t e r j a d i

( R s ) :

M R s o = 6 4 5 .0 4 L a n g le y s

R s = 0 . 1 0 x R s o x ( s ) 0 . 5

R s = 0 . 1 0 x 6 4 5 .0 4 x ( 4 9 . 7 0 ) 0 .5

R s = 4 5 4 .7 4 2 L a n g le y s

c ). P e r h it u n g a n K e b u t u h a n a ir t a n a n m a n r e fe re n s i

p o t e n s i a l (Etg) :

E t g : : 0 . 0 1 3 5 x ( T '" 1 7 . 7 8 ) x R s

Etg = 0.0135 x (26.47 + 17 .78) x 454 .72

E tg :: 27 1 .6 5 1 L a n g l e y s / h a r i

d). p e r h i t u n g a n E t p :

E t p = 1 .2 x Etg

E t p = 1 . 2 x 2 7 1 . 6 5 2

E t p = 3 2 5 . 9 8 2 L a n g l e y s /h a r i

e ) . P e r h it u n g a n El lMaman

M K co = 1 2 0

• A = 595 . -0 .5 5 xT

A = 595 . - 0 .5 5 x 26.47

A : : : 5 8 1 . 3 4 2 s k a l/ g

s e h i n g g a :

E tlalaman = K c o x s,

E t ta n M 1 8 l 1 = 1.02 x 326.982

E 1 tanaman = 332,501 L a n g l e y s / h a r i

~ t l a n aman = 3 3 2 . 5 0 1 x 1 0 : : ; 5 . 7 2 m m lh a r i

5 8 1 . 3 4 2

E l t a n a m a n = 5 . 7 2 x 3 1 : : ; 1 7 7 . 3 1 m m lb u l a n

188

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i~~'hIlmiahU K HUY l A H

· : ', '. V Q ( i l F n e4 No.2 April - Juni 2009

; ~ ; : ~ el a n e y - C r i d d le Y a n g D lm o d if i k a s ;

. . . .; ; : :> ; > ~ , P e r h i t u n g a n e v a p o t r a n s p i r a s i d e n g a n

· ', ;. , i ! M ~ n ' g g u n a k a i im e t o d e B la n e y - C r i d d l e o o a l a h :

' ; ; , ' ; < 'a .d a t a - d a t a b u l a n J a n u a r i :

i , n . : ~ T e m p e r a t l l r u d a r a (t)

< ,: i ' : : Y , _ . ' ~ K o e f i s ie n t a n a m a n b u la n a n ( K c )

~ l a t i t u d e

. . , .

, ' . , O C : : ' : · . : : ' : ; :

~ P e r s e n ta s e ja m s ia n g h a r i b u l a n a n

~ (P )

P e m i t u n g a n k o e f i s ie n t a n a m a n b u l a n a n

(K) :

K : : ; 0 . 0 3 1 1 ( 2 6 . 4 7 ) + 0 . 2 4 0

K t= 1 . 0 6 3

K ; ; ; k t x k c

K = 1 .063 x 1 .1 0= 1 .1 70

C . P e rh i t u n g a n e v a p o t r a n s p ir a s i b u la n a n (U )

u n tu k b u la n J a n u a r i a d a l a h :

U = K . P ( 4 5 .7 . t + 8 1 3 )

100

U = : 1 .1 7 0 x 8 . 3 6 3 x 4 5 . 7 x 2 6 . 4 7 + 8 1 3 )

100

U = : 1 9 7 .9 1 3 m m J b u ia n .

U 1 9 7 . 9 1 3 = 6 .3 8 m m /h a r t

3 1

U n t u k p e r h it u n g a n e v a p o t r a n s p i r a s i d e n g a n

m e n g g u n a k a n m e t o d e B la n e y - D r i d d l e u n t u k

b u la n - b u la n b e r i k u t n y a .

M e t o d e T h o r n t w a lt e

P e r h it u n g a n e v a p o t r a n s p i r a s i u n t u k b u l a n '

J a n u a r i d e n g a n m e n g g u n a k a h n i t o d e T h o m t w S i t e

a d a l a h :

: : ; 2 6 . 4 7 0C

= 1a ID a t a - d a t a b u l a n J a n u a r i :

= 0 3 0 4 8 'O O ~ T e m p e r a t u r u d a r a (t) :: 2 6 . 4 7 0 C

- l a t i t u d e = 0 3 0 4 8 ' O O ~

=8.363%

b . P e r h it u n g a n h e a t i n d e k b u l a n a n T h o r h tw a it e ( i ) :-i ( ! n ) 1 , S 1 4

5

j = ( 2 6 . 4 7 ) M 14

5

i:; 12.468

c. P e rh it u n g a n n i l a i k o e f i s ie n a :

- I = 1 2 r w 1 . 5 1 41 F 1 5

1'" ( 2 6 . 4 7 1 1 . 5 1 4 + (26.80) 1 . 5 1 4 ( 2 7 . 2 8 ) 1 , 5 1 4 1 . 5 1 4

5 5 5 5

( 2 6 , 8 3 ) 1.514 +(26.49) 1.514 +(26,54) 1.514 - +@M ) 1.514

5 5 5 5

r = 1 2 . 4 6 8 + 1 2 . 7 0 4 + 1 3 . 0 5 1 + 1 3 . 1 1 6 + 1 3 .3 4 9 + 1 3 . ' 1 0 0 +1 3 , 1 8 1 + 1 2 .8 9 9 + 1 2 . 7 2 6 +1 2 . 4 8 3 + 1 2 . 5 12 + 1 2 .7 3 3

1 = 1 5 4 ,6 2 6

-a = 0 . 0 0 0 0 0 0 6 7 5 13- 0 .O O O O 7 7 1 1 l+ 0 .0 1 7 92 1 + 0 .4 9 2 39

a = 0 .0 0 0 0 0 0 6 7 5 ( 1 5 4 . 6 2 8 )3 - 0 .0 0 0 0 7 71 ( 1 5 4 , 6 2 8 ) 2 +0 ,0 1 7 92 ( 1 54 .6 2 8 ) + 0 . ' 1 9 2 3 9

a = 3 . 9 1 5

. 189

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Maja/ah Ilmiah UKHUWAH

Volume 4No.2 April - Juni 2009

d . P e rh itungan evapobansp iras i bu lanan

s ta n da r (PET ):

PET = 1 .6 ( 10 .T ) a

L

PET = 1 .6 ( 1 0 . ( 2 6 . 4 D h . 9 1 5

154.628

- PET = 13.129cmlbu lan

e , P erh itungan evapo transp iras i bu lanan yang

te rgan tung d a n t empa t ( P E ) :

- PE = PET S . T z

3 0 x 1 2

d imana S. Tz l30 x 12 d iin te rp ola si d ari

ta be l u ntu k b ula n Ja nu ari = 1.025

seh ingga :

PE = 1 3.1 26 x 1.025 = 13 .454 cm lbu la n

PE = 134.58 mfl l ibU lan

PE = 134.540 = 4.34 mmlha r i

31

K E S I M P U L A N

Be rdasa rkan pe rh itungan n ila i inde ks

evapo tra nsp iras i, m aka n ila i inde ks

evapot ransp i ras i y an g te rb es ar d i d ap st d a n has i l

pe rh itungan dengan m enggunakan m e tode

H a r g r e a v e s sedangkan un tuk n ila i indeks

evapo transp iras i te rkec il d i dapa t dengan

m e ng gu na ka n m e to de p erh itu ng an P enm an .

DAFTAR KEPUSTAKAAN

D e pa rtem e n P e ke ~ aa n Umum D j~ e n Pe n g aira n . 1986. S ta nd ar P ere nca na an lr ig as i K P 01, Ed is i P e rtama ,

B ac la n P en erb it P U J ak arta , J ak arta .

E . H ansen V aughn , W . Is rae lsen O rson , E . S tringham G len , P ip in Te thyan Endang dan Soe ljip to . 1 992 .

D as ar - d as ar d an P ra kte k lr ig as i, E dis i K eem pa t, E rla ng ga , J ak arta .

Mar tha i r . JO yce . 1 983. M e n g e n a l D asa r - d a s a r H i d r o lo g i, W . N ova , B an dung S bs roda rsono Ir. S uyono dan

T ak ed a T en su ka , H id ro lo gi U ntu k P en ga ira n P T P ra dn ya P ara m ita , Ja ka rta .

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