Watershed management_Lecture 31-35

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M odu le 8 – ( L3 1 – L3 4 ) : “St or m

l

d

”

W a t e r & Flood M a n a ge m e n t

”:

St or m w a t e r m a n a ge m e n t , de sign of dr a in a ge syst e m , flood r ou t in g t h r ou gh ch a n n e ls a n d r e se r voir flood con t r ol a n d r ou t in g t h r ou gh ch a n n e ls a n d r e se r voir , flood con t r ol a n d r e se r voir ope r a t ion , ca se st u die s.

3 3

Flood Rou t in g

1 1 1 1

1

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L33



Flood rout ing t hough channels, Reservoir

rout ing Hydrologic rout ing Hydraulic

rout ing, Hydrologic rout ing, Hydraulic

rout ing, Lum ped flow rout ing, Muskingum

h d S V

i

h d S V

i

m et hod, St . Venant equat ions



Keywords:

y

Flood rout ing, Channel, Reservoir, Flood rout ing, Channel, Reservoir, gg Hydrologic & hydraulic rout ing.

Hydrologic & hydraulic rout ing.

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What is Flood Rout ing?



Wat ershed –

receives rainfall as

input

-produces runoff as

out put

– out flow

h d

h

diff

i h

d

t i

&

hydrograph – differs in shape, durat ion &

m agnit ude – at t ribut e t o st orage propert ies of

wat ershed syst em

wat ershed syst em .



Flood ( Flow ) rout ing

– procedure t o com put e

out put hydrograph w hen input hydrograph &

physical dim ensions of t he st orage are know n.



Used for

flood forecast ing, design of spillw ays,

g,

g

p

y ,

reservoirs & flood prot ect ion w orks et c.

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Flood Rout ing

Flood Rout ing -- Mot ivat ion

Mot ivat ion

 1 ) Floods

 predict flood propagat ion  prot ect ion

 w arning  2 ) D e sign  2 ) D e sign

 wat er conveyance syst em s  prot ect ive m easuresp

 hydrosyst em operat ion  3 ) W a t e r dyn a m ics  ungauged rivers

 peak flow est im at ion  river- aquifer int eract ion

4 4

 river- aquifer int eract ion.

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Flood Rout ing

Flood Rout ing -- Classificat ion

Classificat ion

 i) Re se r voir Rou t in g – considers m odulat ion effect s on

a flood wave when it passes t hrough a wat er reservoir – result s in out flow hydrographs wit h at t enuat ed peaks & result s in out flow hydrographs wit h at t enuat ed peaks & enlarged t im e bases .

– Variat ions in reservoir elevat ion & out flow can be predict ed wit h t im e when relat ionships bet ween elevat ion & volum e are known.

 ii) Ch a n n e l Rou t in g – considers changes in t he shape  ii) Ch a n n e l Rou t in g considers changes in t he shape

of input hydrograph while flood waves pass t hrough a channel downst ream .

Flood hydrographs at various sect ions predict ed when – Flood hydrographs at various sect ions predict ed when

input hydrographs & channel charact erist ics are know n.

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Flood Rout ing

Flood Rout ing –

– Procedure

Procedure

 Flood rout ing m et hods can be classified as hydraulic

-in which bot h cont -inuit y and dynam ic equat ions are used - or hydrologic, which generally uses t he cont inuit y or hydrologic, which generally uses t he cont inuit y

equat ion alone

d l h d f

 Hydrologic rout ing m et hods - Equat ion of cont inuit y  Hydraulic rout ing m et hods – St . Venant equat ions  Flood rout ing Applicat ions:

 Flood rout ing Applicat ions:

- Flood forecast ing - Flood prot ect ion - Reservoir design

- Design of spillway and out let st ruct ures

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Flood Rout ing Technique

 Flood r ou t in g- t echnique

of det erm ining t he flood hydrograph at a sect ion of

Di upst ream sect ions

Disc part icular locat ion

Tim e

Acc

Accum ul _{R l}

p

 D ist r ibu t e d flow r ou t in g:

Flow is a funct ion of space and t im e t hrough out t he Chow et .al( 1988)

7 7 Prof. T I Eldho, Department of Civil Engineering, IIT Bombay

Tim e

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Lum ped Flow Rout ing



Basic equat ion for hydrologic rout ing: Cont inuit y

equat ion



Specific form of st orage funct ion depending on

t

f

t

Prof. T I Eldho, Department of Civil Engineering, IIT Bombay

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Lum ped Flow Rout ing - Met hods

Based on st orage funct ion



Level pool reservoir rout ing

- St orage is a

li

f

t i

f Q

l

S f( Q)

nonlinear funct ion of Q only. S = f( Q)



Muskingum m et hod

for flow rout ing in

channels

St orage is linearly relat ed t o I & Q

channels – St orage is linearly relat ed t o I & Q



Linear reservoir m odels

– St orage is a linear

funct ion of Q and it s t im e derivat ives

 Effect of reservoir st orage is t o redist ribut e t he

hydrograph by shift ing t he cent roid of t he inflow hydrograph t o t he posit ion of t hat of t he out flow hydrograph in t im e

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Lum ped Flow Rout ing - Met hods

 Ca se 1 : I n va r ia ble r e la t ion sh ip be t w e e n S & Q

 St orage & out flow are funct ions of wat er surface elevat ion

- w hen reservoir has a horizont al wat er surface elevat ion

 S = f ( Q) – com binat ion of t hese t wo funct ions

 Peak out flow occurs at int ersect ion of inflow hydrograph

and out flow hydrograph and out flow hydrograph

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Lum ped Flow Rout ing - Met hods

Ca se 2: V a r ia ble r e la t ion sh ip be t w e e n S & Q

 Applies t o long, narrow reservoirs & open _{Ou t}

Channels

 Wat er surface profile curved due t o back wat er

Eff t

flow

Effect s

 Peak out flow occurs lat er t han point of int ersect ion

t im e

St or a ge

 Replacem ent of loop wit h dashed line – w hen back

wat er effect is not significant

Ou t fl I n

-flow Based on Chow et .al( 1988)

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Re se r voir Rou t in g

 Procedure for calculat ing t he out flow

hydrograph from a reservoir wit h a

h i t l t f a

horizont al w at er surface

 Flow of flood waves from rivers/

st ream s keeps on changing t he head oir Prof. T I Eldho, Department of Civil Engineering, IIT Bombay

2 2

   

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Re se r voir Rou t in g

For reservoir rout ing t he following dat a should be known

 Elevat ion vs St orage

Elevat ion vs out flow discharge and hence st orage vs

 Elevat ion vs out flow discharge and hence st orage vs

out flow discharge

 I nflow hydrograph, and

 I nit ial values of inflow, out flow Q, and st orage S at

t im e t = 0.

∆t must be shorter than the time of transit of the flood wave through the reach

Variety of methods- for reservoir routing

Pul’s method and Goodrich’s method

I n flow

Ou t flow

Disc har ge

Pul s method and Goodrich s method

Tim e Based on Chow et .al( 1988)

Tim e

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Re se r voir Rou t in g – Pu l’s M e t h od

 Procedure is repeat ed for full inflow

hydrograph

RR

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Re se r voir Rou t in g – Goodr ich M e t h od

R d i i ( 2) 2S  2S 

 Rearranged equat ion is ( 2)

 Preparat ion of graphs for h vs LHS and hence RHS are known

Q t   _ 

 

LHS and hence RHS are known

 Value of out flow Q for

subsequent rout ing periods

RR

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Channel Rout ing-

Muskingum Met hod

 Hydrologic rout ing m et hod for handling variable discharge

– st orage relat ionship.

St i f t i f b t h t fl & i fl di h

 St orage is a funct ion of bot h out flow & inflow discharges  Wat er surface in a channel reach is not only parallel t o t he

channel bot t om but also varies wit h t im e

 Models st orage in channel- com binat ion of wedge & prism  Pr ism st or a ge: Volum e t hat would exist if uniform flow

o ed at t he do nst eam dept h occurred at t he dow nst ream dept h

 W e dge st or a ge : Wedge like volum e form ed bet ween

act ual wat er surface profile & t op surface of prism st oragep p p g

I n flow t o ch a n n e l

W e dge st or a ge

B d Ch t l( 1988)

16 16

Ou t flow fr om ch a n n e l Pr ism st or a ge

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Channel Rout ing-

Muskingum Met hod

 During t he advance of flood wave, inflow exceeds out flow –

Posit ive wedge Posit ive wedge

 During recession, out flow exceeds inflow –Negat ive wedge  Assum pt ion: Cross sect ional area of t he flood flow sect ion is

d l l h d h h

direct ly proport ional t o t he discharge at t he sect ion

 Volum e of prism st orage is equal t o KO

 Volum e of t he wedge st orage is equal t o KX( I - O)  Volum e of t he wedge st orage is equal t o KX( I O)

 K – proport ionalit y coefficient , X - weighing fact or having

t he range 0 < X < 0.5

W e dge st or a ge = KX ( I - O)

Based on Chow et .al( 1988)

I n flow t o ch a n n e l

17 17 Prof. T I Eldho, Department of Civil Engineering, IIT Bombay_{Pr ism}

st or a ge = KO

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Channel Rout ing-

Muskingum Met hod

 Tot al st orage: - - - - Muskingum

st orage equat iong q

 Linear m odel for rout ing flow in st ream s

 Value of X depends on shape of m odeled wedge st orage  X = 0 for level pool st orage ( S = KO) ; X = 0 5 for a full  X = 0 for level pool st orage ( S = KO) ; X = 0.5 for a full

wedge

 K- Tim e of t ravel of flood wave t hrough channel reaches

l f d b

 Values of st orage at t im e j and j + 1 can be writ t en as

 Change in st orage over t im e int erval t is

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Channel Rout ing-

Muskingum Met hod

F h i i i

 From t he cont inuit y equat ion

 Equat ing t hese t wo equat ions  Equat ing t hese t wo equat ions

 Sim plifying….

- - - Muskingum ’s rout ing equat ion

rout ing equat ion Where

Chow et al( 1988)

19 19

Chow et .al( 1988)

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Channel Rout ing-

Muskingum Met hod

 ∆ t should be so chosen t hat K > t > 2KX ….. For best

result s

 If ∆ t < 2KX ……. Coefficient C₁ will be negat ive

Required input for Muskingum rout ing

 I nflow hydrograph t hrough a channel reach,  I nflow hydrograph t hrough a channel reach,  Values of K and X for t he reach

 Value of t he out flow Oj from t he reach at t he st art

F i h l h K & X t k

 For a given channel reach, K & X are t aken as

const ant

 K is det erm ined em pirically ( eg. Clark’s m et hod:

0 5

K= cL/ s0.5_{; c – const ant ; L – lengt h of st ream ,; s –}

m ean slope of channel) or graphically.

 X is det erm ined by t rial and error procedure

20 20

y p

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Muskingum Met hod - Procedure

Rou t in g Pr oce du r e :

 Knowing K and X, select an appropriat e value of ∆ t

 Calculat e C1, C2, and C3

S f h l d k fl

 St art ing from t he init ial condit ions know n inflow ,

out flow, calculat e t he out flow for t he next t im e st ep

 Repeat t he calculat ions for t he ent ire inflow

hydrograph

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Flood Rout ing by St . Venant Equat ions

 Physically based t heory of flood propagat ion - from

t he Saint Venant equat ions for gradually varying flow t he Saint Venant equat ions for gradually varying flow in open channels.

 Hydraulic rout ing m et hod

l fl d ll d fl d

 Flow as 1 D flow – Gradually varied flow condit ion  Conservat ion of m ass- cont inuit y equat ion

 Conservat ion of m om ent um – Dynam ic w ave equat ion  Conservat ion of m om ent um Dynam ic w ave equat ion

22 22

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Gov. Equat ion for Flow Rout ing

Equat ion of cont inuit y

0

S_f frict ion slope of channel.

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Channel Flow- Diffusion &

 Boundary condit ions

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Solut ion Met hodologies

 An a lyt ica l m e t h od: sim plified

governing equat ions, boundary dit i & t l t i l condit ions & geom et ry, analyt ical solut ions can be obt ained.

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B

a

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F

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o

d

R

o

u

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M

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e

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Flood Rou t in g

Flood Rou t in g –

– Ca se st u dy

Ca se st u dy

Cat chm ent Area 847.52 Ha

Elevat ion varies from 0.5 m t o 227 m above MSL. No of subcat chm ent s 31

No of subcat chm ent s 31

Rainfall event 26/ 07/ 2005; 15/ 07/ 2009

Lengt h of channel 5271 m

FEM Li 80 Ch l l t

27 27

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Ca se St u dy: Flood Rou t in g

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Ca se St u dy: Flood Rou t in g

15July2009 15July2009

Fig Com parison of observed Fig. Com parison of observed and sim ulat ed st ages

at chainage 5121 m on 15t h July 2009

30 30

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Re fe r e n ce s

 Am erican Societ y of Civil Engineers and Wat er Environm ent

Federat ion ( ASCE and WEF) . 1998. Urban Runoff Quality

Management. WEF Manual of Pract ice No. 23, ASCE Manual and Report on Engineering Pract ice No. 87.

 http://ndma.gov.in/ndma/guidelines.html

 ht t p: / / w w w .epa.gov/ oaint rnt / st orm w at er/ index.ht m

 Subrahm anya, K( 2007) . Engineering Hydrology, Tat a McGraw- Hill,  Subrahm anya, K( 2007) . Engineering Hydrology, Tat a McGraw Hill,

New Delhi, 294- 300

 Chow , V.T., Maidm ent , D.R., and Mays, L.W. ( 1988) . Applied

Hydrology McGraw-Hill I nc New York

Hydrology, McGraw Hill,I nc., New York

 Bedient , P.B.,Huber, C.W. ( 1988) . Hydrology and Flood Plain

Analysis, Addison-Wesley Publishing Company

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Tu t or ia ls - Qu e st ion !.?.



St udy t he various flood rout ing

m et hodologies in det ails and suggest

applicat ions of each.



What are t he soft w are available for flood

rout ing?. (

www.hec.usace.army.mil

)

Evaluat e t he applicat ions for various

problem s such as reservoir rout ing/ channel

rout ing.

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Se lf Eva lu a t ion - Qu e st ion s!.



What is flood rout ing and w here it is used?

E

l i

i

t i



Explain reservoir rout ing.



Different iat e bet w een Pul’s m et hod & Goodrich

m et hod

m et hod.



Describe t he Muskingum m et hod of flood rout ing.

Describe t he prism st orage & w edge st orage in a



Describe t he prism st orage & w edge st orage in a

channel.



What are t he input dat a required for Muskingum



What are t he input dat a required for Muskingum

rout ing?.

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Assign m e n t - Qu e st ion s?.

g

Q



What are t he m ot ivat ions for flood rout ing?.



Describe different t ypes and advant ages of



Describe different t ypes and advant ages of

flood rout ing.



I llust rat e t he channel rout ing procedure



I llust rat e t he channel rout ing procedure.



Describe t he lum ped flow rout ing.

Di

h

i

ll

b

d

fl

d

t i

i



Discuss physically based flood rout ing in

channels by using St . Venant equat ions.

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Dr. T. I. Eldho Dr. T. I. Eldho Professor,

Professor,

Department of Civil Engineering,

Department of Civil Engineering, pp gg gg

Indian Institute of Technology Bombay, Indian Institute of Technology Bombay, Mumbai, India, 400 076.

Mumbai, India, 400 076.

Email:

Email: [email protected]@iitb.ac.in

35 35 Email:

Email: [email protected]@iitb.ac.in

Phone: (022)

Phone: (022) –– 25767339; Fax: 2576730225767339; Fax: 25767302

http://www.