L8 unit hydrograph

Hydrology_unit hydrograph

1. L O G O .

2. Cov e rage Flo o d p i c torial v i e w s H y drog r a ph - R e v iew Uni t H y drog r a ph Uni t H y drog r a p h . Why ? A s sumption s For UH T erm i nol o gy for UH C r e atin g Uni t H y drog r a ph A p p l i c atio ns of U n it H

3. F L OOD PIC T ORIAL VIEWS

4. C li ck to ad d T e x t C li c k to ad d T e x t C li c k to ad d T e x t Con t ents

5. C li ck to ad d T e x t C li c k to ad d T e x t C li c k to ad d T e x t Con t ents

6. C li ck to ad d T e x t C li c k to ad d T e x t C li c k to ad d T e x t Con t ents

7. C li ck to ad d T e x t C li c k to ad d T e x t C li c k to ad d T e x t Con t ents

8. C li ck to ad d T e x t C li c k to ad d T e x t C li c k to ad d T e x t Con t ents

9. C li ck to ad d T e x t C li c k to ad d T e x t C li c k to ad d T e x t Con t ents

10. C li ck to ad d T e x t C li c k to ad d T e x t C li c k to ad d T e x t Con t ents

11. C li ck to ad d T e x t C li c k to ad d T e x t C li c k to ad d T e x t Con t ents

12. C li ck to ad d T e x t C li c k to ad d T e x t C li c k to ad d T e x t Con t ents

13. C li ck to ad d T e x t C li c k to ad d T e x t C li c k to ad d T e x t Con t ents

14. C li ck to ad d T e x t C li c k to ad d T e x t C li c k to ad d T e x t Con t ents

15. C li ck to ad d T e x t C li c k to ad d T e x t C li c k to ad d T e x t Con t ents

16. C li ck to ad d T e x t C li c k to ad d T e x t C li c k to ad d T e x t Con t ents

17. C li ck to ad d T e x t C li c k to ad d T e x t C li c k to ad d T e x t Con t ents

18. C li ck to ad d T e x t C li c k to ad d T e x t C li c k to ad d T e x t Con t ents

19. C li ck to ad d T e x t C li c k to ad d T e x t C li c k to ad d T e x t Con t ents

20. C li ck to ad d T e C li c k to ad d T e C li c k to ad d T e Con t ents x t x t x t

21. C li ck to ad d T e x t C li c k to ad d T e x t C li c k to ad d T e x t Con t ents

22. C li ck to ad d T e x t C li c k to ad d T e x t C li c k to ad d T e x t Con t ents

23. C li ck to ad d T e x t C li c k to ad d T e x t C li c k to ad d T e x t Con t ents

24. C li ck to ad d T e x t C li c k to ad d T e x t C li c k to ad d T e x t Con t ents

25. Con t ents C li ck to ad d T C li c k to ad d T C li c k to ad d T e x t e x t e x t

26. Prediction The onl y hydrograp h that pred i cts the behav i or o f a fl o o d f ro m a s tor m o f a n y duration

27. Why Cons t ruc t & Ana l yse Hydro g raph s ? To find out discharge p atterns of a particul a r dra inage b a s i n Hel p predict floo d in g ev e nts, therefore influ e nce implementation of flo o d prev e ntio n me a s u res

28. 28 Hydrograp h Theory

29. Hydrograph G r aphical r epre s entati o n of ti m e (hour s ) v ersus disc h ar g e ( c fs or a cms ) at a part i cul a r p oint on strea m o r channel the w a t e r she d area w h i ch drains

30. Peak D i scharge ?

31. ------------------------ - YES ? Then we will be a ble to Manage the Storm wate r . Ident i fy the F l oo d Pla n s o n d o wn strea m s i de. T o p l ace the Hydrau l i c structure s a t s afe level. E f fici e n t U rban Storm wate r manag emen t p l an. De s i gn th e D i f fere n t types o f Hy dra u l i c structures. M in i m iz e the e f fects of Flo od s.

32. Micro Hydr o Projects

33. Uni t Hydrograph A conce p tual di r e c t runo f f h y drograph resu l ting f ro m a rai n fall exces s o f un i t depth a n d constan t intensity for a pa r ticul a r w a t e rshe d i s c al le d a un i t h y drograph

34. Th e u n it calcu l ate hydrog r a ph m e thod i s employe d to t h e d irect runo f f hydrogra p h a t the w ater shed outl et give n the rainf a ll excess produce d b y a stor m event . Th i s m etho d i s categorized a s a l umpe d model i n whic h the hydrolog i c characteristics o f the entir e watershe d ar e com b i ne d an d typified by on e o r more p arame t ers , s impl e mat hematical e x press i o n s, o r graph s .

35. Th e Uni t hydrogr a p h i s a usefu l t o o l i n the proces s of pred i cting the imp a ct o f prec i p i tation o n stream flo w . Th e Uni t d ept h i s 1 cm i n the S I un it sy s t e m an d 1i n c h i n the U . S . syste m. It i s us u a l l y a b brev i at e a s a U h c . Th e subscript “ c ” i n dica t e the D uratio n o f t h e rainf a ll e x ces s .

36. For ins t a nce , the d i r ect runo f f hyd r o g r a p h produce d by a r ainfa l l e x c e ss that has a d urat i o n o f 3 h r an d co n s t a n t intens i ty o f 1 /3 in./ h r is d e n oted by UH 3 an d d e pth o f the ra i nfa l l exces s is (1 /3 i n ./hr) (3 hr) = 1 in

37. W e can dev e l o p a uni t hydrogr a p h for a gag e d w ater shed b y an a lyzing the simu l ta n eo u s rainfa l l an d run o f f records . U nfor tunate l y , m ost s m al l , urban/rural w ater she d s ar e ungag e d . H o weve r , there are sever a l av a ila b le unga g ed synthetic un it hydro g raph met h o ds t o devel o p a uni t hydrog r a ph f o r watersh ed s e. g . Es p e y T e n -M i n ute U n i t H y drogra p h .

38. U N IT H Y D R O G R A P H — W H Y ? S i mplify i n g ou r task / w o rk / procedures . Giv e s u s a b a se l i n e for a sp e cif i e d w a tershe d . Stand a rdize the hydrograp h for d i f fer en t w ater shed s . Gives u s in f or m atio n t h a t ho w the flow o f a st rea m w i ll b e a f fect e d ov e r time b y the a d d itio n o f on e uni t of runo f f.

39. Th e role o f U n i t Hyd ro gr a p h the o ry i n the flood pre d ict i on proc e ss i s to prov i d e a n estimat e o f s t ream flow g i v en an d amoun t precip i tat i o n . Once w e know ho w much rain f a l l o r s n o wm e l t h as occurred , o r i s li k el y t o occu r , an d w e h ave a n ide a of h ow much o f this w i ll tur n i nto runo f f, w e still nee d to know h ow the flow o f a st rea m wil l b e a f fect e d ove r time b y that runo f f . Th e uni t hydrogra p h provid e u s wit h a w a y to estima t e this, a n d i s a n i n tegral part o f ma n y hydrol o g i cal model i n g system s .

40. C li ck to ad d T e x t C li c k to ad d T e x t C li c k to ad d T e x t Con t ents

41. A S SU M P T IONS The p r im a r y assu m ptio n of uni t hy d rogr a p h t he o ry is that t h e ra in f al l has u nifo r m di s t rib u tio n , b o th i n sp a c e - wit h minimal variations ac r os s the b a si n - an d i n ti m e; in oth e r wor d s, the ra in f al l ra t e di d not v a r y m u ch d u ring the event . I n re alit y , precipitatio n e ven t s a re r a re l y unif o r m in s p a ce a n d t im e. O f ten, one p o rtion of the b asin experienc e s high er int e n s i ty p recipita t io n t h a n an o t h er portio n.

42. The ba s e du r atio n of dir e ct ru no f f hydrog r ap h due t o an e f fecti v e rainfall of uni t duratio n i s con s tan t . The o r dinate s of DRH a re dir e ctly p r opo r tion a l t o the to t a l amount of DR of ea c h hydrog r ap h (prin c iple s of linea r it y , s u pe r posi t ion, and p r opo r tionali t y) For a give n ba s in , the ru no f f hydrog r ap h due t o a give n pe r io d of ra infal l reflects al l the c o mbined physi c a l c h a r a c te r istic s of ba s in (tim e - inva r ia n t)

43. C li ck to ad d T e C li c k to ad d T e C li c k to ad d T e Con t ents x t x t x t

44. C li ck to ad d T e x t C li c k to ad d T e x t C li c k to ad d T e x t Con t ents

45. B A SI N - A V E RA G ED RAIN F ALL I n t y pi c a l n o n - sn o w s it u a t ion s , w e b eg i n the h y d ro l ogi c p r o c es s with ra infal l. I n p ar t ic u la r , w e st a rt wit h a b a si n - av e raged r ainfal l. This simply tells us how much ra i n fe l l , or i s f o rec a st t o fall, on a give n b a sin and t y picall y tak e s the f o rm of a rainfall d e pt h p e r t i m e . I n uni t h y d r o gr a ph the o r y , we a ssume t h a t t hi s ra in f al l has fallen uni f or m l y a c r os s the ba s in

46. C li ck to ad d T e x t C li c k to ad d T e x t C li c k to ad d T e x t Con t ents

47. B A SI N - A V E RA G ED E X CE S S RAIN F ALL From a v e ra g e d rainfall, we n e e d t o know h o w m uc h of the b asi n - aver a ge d ra i nfal l wi l l be c o me ru n o f f . I n uni t hyd r o g raph th e o r y , r u no f f is of t e n r e fe r red t o as “e x ce s s p recipita t ion” o r “ex c ess ra infal l . ” R ainfall ru n o f f m ode l s wil l t y pi c a l l y p r ovid e an e s ti m at e of w h a t b ecom e s e x ce s s rainfal l . So, f o r ex am ple , i f 25% of o u r 4 . 00 c m ba s i n - av e ra g e d ra infall becom e s exc e ss r ainfall , then we h av e a b a s i n ave r age d e xcess ra infal l of 1 . 00 cm

48. Th e u n i t h y dr o gr a p h re p res e nt s the e x cess p r C e c o i p n i t t e a n ti o t s n o r q u i ck – res p o n se ru n o f f C li ck to ad d T e x t C li c k to ad d T e x t C li c k to ad d T e x t D ir ec t Runo ff

49. TER M INOLOGY - UH D u rati o n R i si n g L i mb R e cess i o n L i mb (fal l i n g l i m b ) P e a k Fl o w T im e to Pe a k (rise tim e ) T im e o f C o nc e ntra tion R e cess i o n C u rve B a se fl o w S e p a rati o n l i ne B a se flow Quick R e sp o ns e R u n o f f P o i n t o f i n flecti o n

50. U H C o mpon e nts / T ermi n olo g y

51. CR E A TING U.HY D RO G RAPH From Stream fl o w D ata S y nthe t ically Espey T e n-M i nute Uni t H y drograph Sn y der SCS U nit H y drograph T i m e- Are a Uni t H y dro g raph(Clar k, 194 5) Gam m a Function Uni t H y drograph “ Fit t ed” D is t ribu t ions G e omorp h ologic My Conc e rn

52. S T E P S F O C R o n D t e E n R t s I V ING T H E U NI T H Y D R OGRA P H flow hydr o grap h a t a g i ven stre a m gau g e l o cat io n a l o n g w i th the follow i n g i n format i o n: Th e B a sin Area Th e B a si n - average d rainfa l l de pth Th e durat i o n ove r whi c h th e e x cess pre c ipita t ion - C li ck to ad d T e x t C li c k to ad d T e x t C li c k to ad d T e x t A u n i t hydrogra p h c a n b e de r ive d f ro m a t o t a l st ream occurred.

53. When der iving a un it hydrogra p h i t i s importan t to start w i th a n arch i v ed hy d rograph i n whic h the q u ick -res p ons e r u no f f portio n i s from on e sing l e stor m ev en t. I n ad d ition, that stor m sh o ul d ha ve produ c e d it s e x c e ss prec i pi t atio n wit h n e ar l y un ifor m coverage i n space an d time ove r the basin Sel e ct Ap p ropriate Pre c ipitatio n E v e nt Ste p -1

54. Remo v e Base f l ow Con t rib ut i on Ste p -2

55. The t o tal volume o f wa t e r f rom t h e q ui c k - respo n se runo f f ne e d s t o b e c a lc u la t e d . Th i s i s d on e by su m ming t h e ar e a s un d e r t h e QRR Hydr o g r ap h for ea c h ti m e step, i n this c a s e , hou r l y . Cal c u l ate Qui c k – Re s p o n s e V o l ume Ste p -3

56. D eter mine E x cess P P T Dept h f ro m B a sin Ste p -4

57. D eter mine E x cess P P T Dept h f ro m B a sin Ste p - 4 For ex a mple, assu m e we hav e a b a s i n a r e a of 100 s q u ar e k m , whi c h i s 1 00 , 000 , 000 sq . m and calc u la t e d v olum e of qui ck - res p on s e t o be 2 , 000 , 000 c u m-then the dept h wil l be

58. Adj u st the Quic k -R e s pons e H y dr o gr a ph Ste p -5 The e x cess p p t d ept h p ro b abl y w o n `t be ex a ctly one uni t a s unit hydr o grap h re q uire s. So, w e hav e t o adj u st the QRR hydrog r ap h t o s h o w w h a t the r e s p o n s e from one uni t w o ul d be.

59. Adj u st the Quic k -R e s pons e H y dr o gr a ph Ste p -5 O n ce we m ultipl y ea c h poin t on t h e hy d ro g raph by o u r adju s t ment f a c t o r of . 5 , o u r r esul t in g u ni t hy d rogr a p h i s f o r exactl y 1 c m of exce s s p r e c ipita t ion

60. Det ermin e Dur ati o n o f UH Ste p -6 The du r at i o n of a un i t hydro g raph refers to a c o nt i nu o us time pe ri od du ri ng wh ic h one un i t o f exce s s ppt o c c urre d . If it took 6 ho urs for t h e one un i t of exce s s t o o c c u r , we hav e a 6 - hr un i t h y drogra p h . Re m e mb e r , the un i t hydro g raph du r at i o n d o e s not ref e r to the du r a tio n of the stream flo w res po n s e .

61. The d i f fic u lt pa rt of de t e r mini n g the du r at i o n of a un i t hydro g raph is e stimati n g whi c h po rtio n of t h e en t ire prec i p itat i o n even t a c tua l l y c o ntr i bu t e s to exce s s ppt. Re c a ll that the wate r t ha t infi l trat e s & pe rco lates i nto deeper st ora g e and ba s e flo w is not pa rt of exce s s ppt. W e can es t i m ate this port i o n of the ppt. by ap p lying a c o n stant l oss fu n c t i o n to the ra i nfa l l . Re c a ll that w e hav e a l r ea d y c alc u l ated the d e pth of the exce s s ppt to be 2.0 c m . N o w , w e need to k n ow how l o n g it took for that exce s s to o c c u r .

62. S o w e move this l o s s function l in e such that the amoun t o f pp t . ab o ve the l i n e i s equ a l t o the de pth o f e x cess pp t . that w e a l re a d y calcu l ate d for the bas i n . Bel o w that l i n e the pp t . goe s t o long - ter m s tor age . A b ov e the l i n e i s the e x cess pp t .

63. Now w e hav e a n exce s s prec i p itat i o n bar gra p h of 6-h r . Noti c e that the a m o u nts fr o m h ou r to ho u r on this gra p h are not tr u l y un i form. Th i s is typic a l . For pu r p o s e s of c a lc ul a t i ng a un i t hydro graph d u rat i on, how ev e r , w e a s s u me that a ll exce s s ppt o c c urred un iformly in time.

64. Fin a l U n i t H y dro g raph At the end o f these st e p s, w e h a ve a 6- h r un i t h ydro g rap h . It s h ow the stream flo w res po n se to 6 hrs of exce s s ppt th a t pro du c e d one un i t of de pth.

65. Appli c at i o n o f Un i t H y d r o g r a ph

66. The U H me t ho d is ba s e d on the a s su m pt i o n of a l i ne ar relationsh i p betwe en t h e rainfall exces s and the DR rates. More s p e c if i c al l y , the method a s s u mes that The ba s e t i me of the D R H res u lti n g fr o m a r a i nfa ll exce s s of a g iven du r at i o n is c o n st a n t regard l e s s of the amoun t of the rainfall exces s, and The ord i n a t e s of a D R H res u l t i n g fr o m a ra i n f a ll exce s s of a g iven du r at i o n are d irectly pro po rti o nal to the tota l amou nt of ra i nfa l l exce s s

67. In oth e r w o r d s, the ba s e of the D R H res u ltin g fr o m a rainfall exces s of, s a y , 1.5 in. pro d uc e d ov er af 2- hr du r at i o n is t h e s a me as that of the 2-hr UH . Al s o the ord i nate of th i s DR H are 1.5 times the ord i nates of the UH 2 at res pe ctive time s. W e c a n s i mply st ate that D R H = c UH2 D R H = 1. 5 UH2 Gen e r a l F orm

68. C li ck to add C li c k to add C li c k to add Con t ents T e x t T e x t T e x t

69. C li ck to ad d T e C li c k to ad d T e C li c k to ad d T e Con t ents x t x t x t

70. Examp l e: Two s t o r m eac h o f 6-hr d u r a ti o n an d h av i n g r ainfa l l exces s values o f 3 .0c m a n d 2.0 c m r esp e ctiv e l y occur suc c e s s i ve l y . The 2-c m ER r ai n fo l lows the 3- c m ra in . The 6-hr U H for the catchment is the sa me as g i ve n in p r e v io u s e x a m p le. Cal c u l ate the re s ul t ing DRH .

71. C li ck to ad d T e x t C li c k to ad d T e x t C li c k to ad d T e x t Con t ents

72. C li ck to ad d T ex C li c k to ad d T ex C li c k to ad d T ex Con t ents t t t

73. C li ck to ad C li c k to ad C li c k to ad Con t ents d T e x t d T e x t d T e x t

74. Uni t Hy d r o g r a p h o f Diff e r e n t Dur ati o ns Unde r condition whe r e lac k o f a d equat e d at a in dev e l o pemen t o f un it hydrograph D - h o u r u ni t hydrograp h i s u s e d t o dev e l o p u n it hy d rograp h s o f d i f f eri n g dura t ion s nD T w o met ho d ava i l a b l e : Met ho d o f superpos i tion Th e S - C u rve

75. I f a D -h uni t hydrogra p h i s av ai la b l e, an d it s de s ire d to deve l o p un it hydrograp h o f n D, it s i s eas i l y accom p l ishe d b y supe r pos i n g n uni t hydrog r ap h s with eac h grap h separated f ro m the previo u s o n b y D - h . M e th o d o f Su p er p ositi o ns

76. D = 2 - H r Uni t Hydrogr a ph Adjusted Net Rainfall one inch over basin Q p

77. Chang e U H Durat i on C o nsider 1 h r UH A d d a n d L a g t w o UH by one hour Sum and divide by 2 R e sults in 2 h r UH

78. Example Given the or d in ates of a 4- h r un i t hydrogra p h as b elo w d e r i v e the o r d i n a tes o f a 12-hr u nit hydrograp h for the sa me ca tc hm e nt T i m e (hr) 4 8 12 16 20 24 28 32 36 40 44 Ordinates of 4-hr U H 20 80 130 150 130 90 52 27 15 5

79. C li ck to ad d T e C li c k to ad d T e C li c k to ad d T e Con t ents x t x t x t

80. S - Curve A l so kno w n a s S - hydrograph Hydr o gra p h produce d b y contin o us eff e cti v e rainfa l l a t a constant rate for i n finite peri o d . C u rve obt a ine d b y summ atio n o f a n i n fi n it e series o f D -h U H spaced D -h ap ar t .

81. C li ck to ad C li c k to ad C li c k to ad Con t ents d T e x t d T e x t d T e x t

82. S - Curve s for UH

83. S - Curves Con v ert 2 h r UH to 3- hr Lag each 2-hr UH by Duration D Add to produce S -cur v e S -curve

84. Example Solve p re v i o u s e x a m p l e with S - cu rv e m etho d: Given the ordinate s o f a 4 - h r u ni t hy d rog r a p h a s be l ow deri v e the ord i nate s o f a 12 - h r un it hydrograp h for t h e same catchment T i m e (hr) 4 8 12 16 20 24 28 32 36 40 44 Ordinates of 4-hr UH 20 80 130 150 130 90 52 27 15 5

85. Con t ents

86. Hydrograp h Convolution 1 2 3 Add up the ordin a tes of all th r ee to p r o d uce st o rm h y d r o g r a ph 1 2 3 S T O R M H Y D R O Add an d Lag Met hod

87. L O G O