8/16/2019 7.Modeling Baseflow

1/4

Buku Ebook  

B.Ing.18-(HEC-HMS) TechRefManualMar2000

Ch 7 Modelng Ba!eflo"# $near Re!er%or Model

MODELING BASEFLOW

T"o d!&ngu!ha'le coonen&! of a !&reaflo" h*drograh are (1) drec +uc, runoff of rec&a&on#and (2) 'a!eflo". Ba!eflo" ! &he !u!&aned or far-"ea&her runoff of ror rec&a&on &ha& "a! !&ored

&eorarl* n &he "a&er!hed# lu! &he dela*ed !u'!urface runoff fro &he curren& !&or. Soe conce&ual

odel! of "a&er!hed roce!!e! accoun& elc&l* for &h! !&orage and for &he !u'!urface o%een&.

Ho"e%er &h! accoun&ng ! no& nece!!ar* &o ro%de &he nfora&on for an* "a&er re!ource! !&ude!.

The rogra nclude! &hree al&erna&%e odel! of 'a!eflo"/

Con!&an on&hl*-%ar*ng %alue.

Eonen&al rece!!on odel.

$near-re!er%or %olue accoun&ng odel.

Basic Concepts and Implementation

Constant, Montl!"#a$!in% Base&lo'

Th! ! &he !le!& 'a!eflo" odel ncluded n &he rogra. I& rere!en&! 'a!eflo" a! a con!&an& flo"

&h! a* %ar* on&hl*. Th! u!er-!ecfed flo" ! added &o &he drec& runoff cou&ed fro ranfall for 

each &e !&e of &he !ula&on.

E(ponential )ecession Model

The rogra nclude! a eonen&al rece!!on odel &o rere!en& "a&er!hed 'a!eflo" (Cho"# Maden

and Ma*!# 188). The rece!!on odel ha! 'een u!ed of&en &o elan &he dranage fro na&ural !&orage n a

"a&er!hed ($n!le* e& al# 182). I& defne! &he rela&on!h of &he 'a!eflo" a& an* &e &o an n&al

%alue a!/Qt =Q0 k 

t 

(37)

"here 0 4 n&al 'a!eflo" (a& &e 5ero) and , 4 an eonen&al deca* con!&an&. The 'a!eflo" &hu!

cou&ed ! llu!&ra&ed n 6gure 22. The !haded regon rere!en&! 'a!eflo" n &h! fgure &he con&r'u&on

deca*! eonen&all* fro &he !&ar&ng flo". To&al flo" ! &he !u of &he 'a!eflo" and &he drec& !urface

runoff.

! leen&ed n &he rogra# , ! defned a! &he ra&o of &he 'a!eflo" a& &e & &o &he 'a!eflo" one da*

earler. The !&ar&ng 'a!eflo" %alue# 0# ! an n&al cond&on of &he odel. I& a* 'e !ecfed a! a flo"

ra&e (9! or cf!)# or & a* 'e !ecfed a! a flo" er un& area (9!9,2 or cf!9!+ ).

8/16/2019 7.Modeling Baseflow

2/4

6gure 22. In&al 'a!eflo" rece!!on.

The rece!!on 'a!eflo" odel ! aled 'o&h a& &he !&ar& of !ula&on of a !&or e%en and la&er n &he

e%en& a! &he dela*ed !u'!urface flo" reache! &he "a&er!hed channel!# a! llu!&ra&ed n 6gure 2. Here# af&er 

&he ea, of &he drec& runoff# a u!er-!ecfed &hre!hold flo" defne! &he &e a& "hch &he rece!!on odel

of E+ua&on 37 defne! &he &o&al flo". Tha& &hre!hold a* 'e !ecfed a! a flo" ra&e or a! a ra&o &o &he

cou&ed ea, flo". 6or eale# f &he &hre!hold ! !ecfed a! a ra&o-&o-ea, of 0.10# and &he cou&ed ea, ! 1000 9!# &hen &he &hre!hold flo" ! 100 9!. Su'!e+uen& &o&al flo"! are cou&ed "&h E+ua&on

37# "&h 0 4 &he !ecfed &hre!hold %alue.

6gure 2. Ba!eflo" odel llu!&ra&on.

& &he &hre!hold flo"# 'a!eflo" ! defned '* &he n&al 'a!eflo" rece!!on. Thereaf&er# 'a!eflo" ! no&

cou&ed drec&l*# 'u& ! defned a! &he rece!!on flo" le!! &he drec&-!urface-runoff. :hen &he drec&-

!urface runoff e%en&uall* reache! 5ero (all ranfall ha! run off &he "a&er!hed)# &he &o&al flo" and 'a!eflo"

are den&cal.

f&er &he &hre!hold flo" occur!# &he !&reaflo" h*drograh ordna&e! are defned '* &he rece!!on odel

alone# unle!! &he drec& runoff lu! n&al 'a!eflo" rece!!on con&r'u&on eceed! &he &hre!hold. Th! a*

 'e &he ca!e f !u'!e+uen& rec&a&on cau!e! a !econd r!e n &he h*drograh# a! llu!&ra&ed n 6gure 2;. In

&ha& ca!e# ordna&e! on &he !econd r!ng l' are cou&ed '* addng drec& runoff &o &he n&al rece!!on#

a! llu!&ra&ed.

6gure 2;. Rece!!on "&h ul&le runoff ea,!.

Linea$ )ese$*oi$ Model

The lnear-re!er%or 'a!eflo" odel ! u!ed n con

8/16/2019 7.Modeling Baseflow

3/4

Ma&hea&call*# &h! ! den&cal &o &he anner n "hch Clar,>! ?H odel rere!en&! "a&er!hed runoff# a!

de!cr'ed n Cha&er 3.

The ou&flo" fro ground"a&er la*er 1 of &he SM ! nflo" &o one lnear re!er%or# and &he ou&flo" fro

ground"a&er la*er 2 of &he SM ! nflo" &o ano&her. The ou&flo" fro &he &"o lnear re!er%or! !

co'ned &o cou&e &he &o&al 'a!eflo" for &he "a&er!hed.

Estimatin% Base&lo' Model +a$amete$s

Constant , Montl!"#a$!in% Base&lo'

The arae&er! of &h! odel are &he on&hl* 'a!eflo"!. The!e are 'e!& e!&a&ed ercall*# "&h

ea!ureen&! of channel flo" "hen !&or runoff ! no& occurrng. In &he a'!ence of !uch record!# feld

n!ec&on a* hel e!&a'l!h &he a%erage flo". 6or large "a&er!hed! "&h con&r'u&on fro ground"a&er 

flo" and for "a&er!hed! "&h *ear-round rec&a&on# &he con&r'u&on a* 'e !gnfcan& and !hould no&

 'e gnored. @n &he o&her hand# for o!& ur'an channel! and for !aller !&rea! n &he "e!&ern and

!ou&h"e!&ern ?S# &he 'a!eflo" con&r'u&on a* 'e neglg'le.

E(ponential )ecession Model

The arae&er! of &h! odel nclude &he n&al flo"# &he rece!!on ra&o# and &he &hre!hold flo". ! no&ed#&he n&al flo" ! an n&al cond&on. 6or anal*!! of h*o&he&cal !&or runoff# n&al flo" !hould 'e

!elec&ed a! a l,el* a%erage flo" &ha& "ould occur a& &he !&ar& of &he !&or runoff. 6or fre+uen& e%en&!# &he

n&al flo" gh& 'e &he a%erage annual flo" n &he channel. 6eld n!ec&on a* hel e!&a'l!h &h!. !

"&h &he con!&an on&hl*-%ar*ng 'a!eflo"# for o!& ur'an channel! and for !aller !&rea! n &he

"e!&ern and !ou&h"e!&ern ?S# &h! a* "ell 'e 5ero# a! &he 'a!eflo" con&r'u&on ! neglg'le.

The rece!!on con!&an ,# deend! uon &he !ource of 'a!eflo". If , 4 1.00# &he 'a!eflo" con&r'u&on "ll

 'e con!&an "&h all &  4 0. @&her"!e &o odel &he eonen&al deca* &*cal of na&ural unde%eloed

"a&er!hed!# , u!& 'e le!! &han 1.00. Ta'le 13 !ho"! &*cal %alue! roo!ed '* Algr and Corder*

(12) for 'a!n! rangng n !5e fro 00 &o 13#000 ,2 (120 &o 3=00 !+uare le!) n &he ?S# ea!&ern

u!&rala# and !e%eral o&her regon!. $arge "a&er!hed! a* ha%e , %alue! a& &he uer end of &he range#

"hle !aller "a&er!hed! "ll ha%e %alue! a& &he lo"er end.

Ta'le 13. T*cal rece!!on con!&an& %alue!

Flo' Component )ecession Constant, Dail!

round"a&er 0.=

In&erflo" 0.8-0.

Surface runoff 0.-0.8

The rece!!on con!&an& can 'e e!&a&ed f gaged flo" da&a are a%ala'le. 6lo"! ror &o &he !&ar& of drec&

runoff can 'e lo&&ed# and an a%erage of ra&o! of ordna&e! !aced one da* aar& can 'e cou&ed. Th! !!lfed f a logar&hc a! ! u!ed for &he flo"!# a! &he rece!!on odel "ll lo& a! a !&ragh& lne.

The &hre!hold %alue can 'e e!&a&ed al!o fro eana&on of a grah of o'!er%ed flo"! %er!u! &e. The

flo" a& "hch &he rece!!on l' ! aroa&ed "ell '* a !&ragh& lne defne! &he &hre!hold %alue.

Linea$ )ese$*oi$ Model

The lnear re!er%or odel ! u!ed "&h !ol-o!&ure accoun&ng odel. I& ! 'e!& cal'ra&ed u!ng

 rocedure! con!!&en& "&h &ho!e u!ed &o cal'ra&e &ha& odel.

8/16/2019 7.Modeling Baseflow

4/4

MODELING BASEFLOW-

Ba!c Conce&! and Ileen&a&on............................................................................................................1

Con!&an Mon&hl*-ar*ng Ba!eflo"......................................................................................................1

Eonen&al Rece!!on Model..................................................................................................................1$near Re!er%or Model............................................................................................................................2

E!&a&ng Ba!eflo" Model Aarae&er!......................................................................................................

Con!&an& # Mon&hl*-ar*ng Ba!eflo".....................................................................................................

Eonen&al Rece!!on Model..................................................................................................................

$near Re!er%or Model............................................................................................................................