L32– Urban Drainage System

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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 2

Ur ba n D r a in a ge Syst e m

1 1 1 1

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L32



Urban flooding, disast er risk

m anagem ent , Urban drainage syst em ,

design requirem ent s Roadside

design requirem ent s, Roadside

drainage design



Keywords:

Urban flooding, drainage syst em Urban flooding, drainage syst em design, risk m anagem ent , roadside drain.

design, risk m anagem ent , roadside drain.

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Causes of Urban Flooding



Why urban flooding?. –

large increase in concret e/ im pervious

– large increase in concret e/ im pervious

surface?.

– Unplanned usage of urban land?

– Unplanned usage of urban land?.

– Lack of proper drainage?.

Loss of wet lands?

Mum bai on Jul 26 27 05

– Loss of wet lands?.

– Less groundwat er usage / recharge?.

Tidal effect s?

Mum bai on Jul 26, 27, 05

– Tidal effect s?.

– Very heavy st orm s – cloud burst ?.

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Urban Flood Disast er Risk Managem ent

 Developing appropriat e coping st rat egies & disast er risk

reduct ion plans, along wit h great er awareness of how t o

reduct ion plans, along wit h great er awareness of how t o reduce risks, is t he high priorit y agenda

 St rat egies: Enhancing nat ional, st at e and local scale

advocacy part nerships and knowledge m anagem ent advocacy part nerships and knowledge m anagem ent

 St andardizing hazard risk m anagem ent t ools,

m et hodologies and pract ices

 Developing int egrat ed and coordinat ed approaches  I ncorporat ing ‘Learning by Doing’ m ode of operat ions

P i h diff i / d i f b i

 Prom ot ing t he diffusion/ docum ent at ion of best pract ices  Building appropriat e com m unicat ion prot ocols facilit at ing

m ult i- plat form and m ult i- lingual dissem inat ion

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u p a o a d u gua d sse a o

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Urban Flood Disast er Risk Managem ent

 Analyzing & present ing inform at ion in an easily

underst andable form , for wider use by decision m akers, underst andable form , for wider use by decision m akers,

 Encouraging int egrat ed approaches of proj ect

im plem ent at ion based on Mast er Plan,

d d l h

 Encouraging st at es t o accord t op priorit y t o deal w it h

recurring urban flooding

 Urban flood m anagem ent – difficult iesUrban flood m anagem ent difficult ies

 Com prehensive risk assessm ent , Fact oring risks in

developm ent planning, Coordinat ion am ong different inst it ut ions Lack of inform at ion sharing Disint egrat ed inst it ut ions, Lack of inform at ion sharing, Disint egrat ed invest m ent decisions, Lack of consult at ion wit h

st akeholders et c.

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Wat ershed Based

Wat ershed Based -- Urban Flood Managem ent

Urban Flood Managem ent

A l i f ff i b fl d h

 Any planning for effect ive urban flood m anagem ent has

t o t ake int o t he considerat ion of ent ire wat ershed.

 I dent ify problem s, causes & rem ediat ionde y p ob e s, causes & e ed a o  Preparedness and m it igat ion,

 Early warning and com m unicat ion,  Response,

 Awareness generat ion,

 Com m unit y capacit y developm ent  Com m unit y capacit y developm ent .

 Vulnerabilit y & risk assessm ent – reduce vulnerabilit y

 Hazard m apping: flood level m apping, ident ify dam ages, pp g pp g, y g ,

insurance & risk t ransfer

 Spat ial Decision Support Syst em

U b I f t i S t

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 Urban I nform at ion Syst em

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Ur ba n D r a in a ge Syst e m

 Drainage syst em s cat egorized as m aj or & m inor syst em s.  Maj or drainage syst em - com prises of open nallahs/ and

t l f d i t nat ural surface drains, et c.

 Minor syst em - net work of underground pipes & channels.  Minor syst em cat egorized int o t wo t ypes: separat e &

 Minor syst em cat egorized int o t wo t ypes: separat e &

com bined.

 Separat e drainage syst em s consist of t wo conveyance

net o ks sanit a se e s ( s all nde g o nd pipes) net w orks: sanit ary sew ers ( usually underground pipes) conveying wast ewat er from hom es & businesses t o a discharge point , while t he st orm drains ( underground pipes or channels) collect wat er from t he rainfall runoff and convey it t o a discharge point

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St or m w a t e r D r a in a ge Syst e m

 Tot al st orm wat er syst em – m aj or & m inor – invent ory of t he

syst em for bet t er m anagem ent – GI S plat form .y g p

 I nvent ory w ill be bot h w at ershed based t o enable proper

hydrologic & hydraulic analysis & w ard based t o enable coordinat ed adm inist rat ive m anagem entg

 Minor syst em s should be m apped clearly show ing t he

int erconnect ions w it h m aj or syst em besides t he cross connect ions w it h sew er lines

co ect o s t se e es

 Maj or syst em s - be m apped clearly w it h delineat ion,

dem arcat ion & det ails of cross- sect ions, slopes, drain crossings including nat ural form at ions & m an m ade crossings including nat ural form at ions & m an m ade st ruct ures

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Ur ba n D r a in a ge D e sign - Re qu ir e m e n t s

 Developm ent of an adequat e & funct ioning drainage

syst em based on sound hydrologic & hydraulic design syst em based on sound hydrologic & hydraulic design principles.

 Design of an urban drainage syst em requires

knowledge of t he cat chm ent area and t opography knowledge of t he cat chm ent area and t opography, urbanizat ion det ails, rainfall int ensit y, hydrology, hydraulics, et c.

 Wat ershed/ Cat chm ent as basis of urban drainage

design

 Cont ours are necessary for det erm ining t he  Cont ours are necessary for det erm ining t he

boundaries of a wat ershed/ cat chm ent & for com put ing direct ions of flow.

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Ur ba n D r a in a ge D e sign - Re qu ir e m e n t s

 Rainfall dat a: For design of a drainage syst em, t he

convent ional pract ice is t o choose an appropriat e, p pp p st at ist ically relevant design st orm t o est ablish t he

st orm wat er flows t o be conveyed, based on exist ing nat ional & int ernat ional pract ices.

 Design st orm s can be est im at ed from rainfall dat a records

w here available.

 Up t o dat e Up t o dat e I DF ( I nt ensit y Durat ion Frequency)( t e s t y u at o eque cy) relat ionships e at o s ps

need t o be used t o m aint ain design st andards for new syst em s & ret rofit t ing/ replacem ent of old urban drainage syst em s.y

 I DF curves should be developed for each cit y, based on

ext ract ion of dat a from t he raw dat a chart s at m in.

15-m inut es resolut ion 1 0 0

H y t o g r a p h o f K a l a m b o l i r a i n f a l l

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

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Ur ba n D r a in a ge D e sign Con side r a t ion s

 Frequency of t hunderst orm s - addit ional considerat ion

for planning fut ure urban drainage syst em s. for planning fut ure urban drainage syst em s.

 Design flow: To prot ect urban areas, safe

m anagem ent & passage of wat er, result ing from

frequent st orm event s ( hydrologic design aspect s) & frequent st orm event s ( hydrologic design aspect s) & adequat e capacit y ( hydraulic design aspect s) m ust be considered.

 Urban Drainage Design: m ain obj ect ives of hydrologic

analysis & design are t o est im at e peak flow rat es &/ or flow hydrographs for t he adequat e sizing & design of flow hydrographs for t he adequat e sizing & design of conveyance & quant it y cont rol facilit ies

 To est im at e peak flow rat es, knowledge of t he rainfall

int ensit y it s durat ion & frequency is required H y t o g r a p h o f K a l a m b o l i r a i n f a l l

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int ensit y, it s durat ion & frequency is required

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Ur ba n D r a in a ge D e sign - Pr oble m s

 I ncreasing rainfall int ensit ies induced by clim at e

change, urban heat islands and ot her fact ors, will ibl lt i i t i d f i

possibly result in varying ret urn periods for a given int ensit y of rainfall.

 Rainfall int ensit yy t o be used for design will also g

depend on t he t im e of concent rat ion.

 Higher t he cat chm ent area, higher will be t he t im e of

concent rat ion & lower will be t he design rainfall concent rat ion & lower will be t he design rainfall int ensit y, ot her fact ors rem aining t he sam e.

 Peak flow rat es can be est im at ed using Rat ional

Met hod Q = C I A.

 Approxim at ions based on runoff coefficient , rainfall

int ensit y & area of cat chm ent . H y t o g r a p h o f K a l a m b o l i r a i n f a l l

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int ensit y & area of cat chm ent .

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D e sign Con side r a t ion s

 Sim ple channel design: Manning’s equat ion:

Q = AR2/ 3_S1/ 2_{/ n}

F t t i f t l l fil i t h d i

 For com put at ion of w at er level profiles in t he drainage

syst em s or channels/ rivers, suit able soft ware for flood rout ing should be used.

 Public dom ain soft ware - HEC- HMS for hydrologic

m odelling of t he wat ershed, HEC- RAS for river

m odeling, SWMM ( St orm wat er Managem ent Model) m odeling, SWMM ( St orm wat er Managem ent Model) for sewer/ drainage design

 All fut ure st orm wat er drainage syst em s m ay be

designed t aking int o considerat ion a runoff coefficient designed t aking int o considerat ion a runoff coefficient of upt o C = 0.95 for est im at ing peak discharge using t he rat ional m et hod

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UD S – Ope r a t ion & M a in t e n a n ce

 Proper operat ions and m aint enance ( O&M) are crucial

for any syst em t o be funct ional t o t he designed for any syst em t o be funct ional t o t he designed capacit y & for it s durabilit y as well.

 Pre- m onsoon desilt ing - a m aj or O&M act ivit y.

d f l f d h ld b k d

 Periodicit y of cleaning of drains should be worked out ,

based on t he local condit ions.

 Rem oval solid wast e: Suit able int ervent ions in t he Rem oval solid wast e: Suit able int ervent ions in t he

drainage syst em like t raps, t rash racks can reduce t he am ount of solid wast e going int o t he st orm sewers

Rem oval of sedim ent

 Rem oval of sedim ent  Drain inlet connect ivit y

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UD S – Spe cia l Con side r a t ion s

 Low- lying areas should be reserved for parks and

ot her low - im pact hum an act ivit ies, ot her low im pact hum an act ivit ies,

 Wherever unavoidable, buildings in low lying areas

should be const ruct ed on st ilt s above t he High Flood Level ( HFL) / Full Tank Level ( FTL)

Level ( HFL) / Full Tank Level ( FTL)

 For chronic flooding spot s, alt ernat e locat ions m ay be

explored for accom m odat ing people st aying t here

 Buildings should be const ruct ed on st ilt s aft er t aking

int o account t he st abilit y of slopes, and

St orm wat er drainage syst em s for coast al cit ies have

 St orm wat er drainage syst em s for coast al cit ies have

t o be designed t aking int o account t he t idal variat ions.

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Roa d Side D r a in a ge



Road side drain:

I nt egral part of urban

drainage syst em

g

y

– St or m D r a in a ge

 Collect st orm wat er runoff

– Away from st ruct ures

 Through roadway and/

w at erw ay w at erw ay

 Right - of- way  Obj ect ives

– Appropriat e design – Hydrologic & hydraulic considerat ions

– Minim ize t he flooding and erosion t o propert ies

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Prof. T I Eldho, Department of

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Roa d Side D r a in a ge – D e sign St e ps

• Design Problem and design crit eria specificat ion

 Type specific localit y  Type, specific localit y

– Syst em drainage area definit ion and prelim inary layout

 St reet layout , t ot al drainage area t o be handled

– Field and office dat a collect ion

Make field visit sit e specific problem s ( no widt h

 Make field visit , sit e specific problem s ( no widt h,

t rees, out crops, ut ilit y locat ions, et c. – Syst em layout

 Final layout , all dit ches, wat erways, inlet s,

m anholes, m ains, lat erals, culvert s, flow direct ion, et c

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et c.

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Roa d Side D r a in a ge – D e sign St e ps

g

p

– Hydrologic calculat ions

 Flow est im at ion for t he designed frequency

– St reet flow

 Flow and spread calculat ions, m axim um spread,

gut t ers flow gut t ers flow

– I nlet spacing and layout

 Locat ion and t ype of inlet , size, ext ra inlet , et c.yp , , ,

– Hydraulic calculat ions

 Size of t he drain, perm issible velocit y, slopes,

t et c.

– Various design checks

 Discharge, Froude num ber, velocit y, slope

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 Discharge, Froude num ber, velocit y, slope

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Drainage Design

Drainage Design -- Fact ors

Fact ors

– Ret urn period of flood ( rainfall)

– Spread

– I nlet t ypes and spacing

– Longit udinal slope; Cross slope

– Curb and gut t er sect ion

– Roadside and m edian channels

id

d

k

/ fl

– Bridge decks / fly over

– Shoulder gut t er

Median barriers

– Median barriers

– St orm drains

– Det ent ion st orage; Erosion

w w w.greenhighwayspart nership.org

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– Det ent ion st orage; Erosion

– Cost

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I m port ant Design Considerat ions

1. How m uch area should be considered for a reach?

 Act ual lengt h is in- bet ween hydrologic m ount t o

draining point

mount mount

nallah nallah

2. How m uch widt h should be considered on ot her side of t he road drainage?

 I nt ernat ionally road side drain are designed t o cat er  I nt ernat ionally road side drain are designed t o cat er

“ only road runoff” , but in highly populat ed area it m ay be designed t o carry runoff from nearby area also

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I m port ant Design Considerat ions

 Act ual widt h should be based on t opographical survey

 The roads in Mum bai are very peculiar

 The act ual area cont ribut ing t o road side drain is not know n

3) Designed rainfall int ensit y? 3) Designed rainfall int ensit y?

 Generally rainfall int ensit y wit h 10 year ret urn period  For im port ant roads it should be 50 year ret urn period

 I t should be based on t im e of concent rat ion, I DF curves

 I RC ecom m ends tim e of concent at ion as

m ade

 I RC recom m ends t im e of concent rat ion as:

m ade

of t w o t im e periods:

1.Tim e required for t he

rain wat er t o flow over t he road surface and ent er

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I m port ant Design Considerat ions

 As per I RC 50: For Mum bai

t he crit ical int ensit y of rainfall is 50 m m / hr

Type of surface Range

of C

Gravel and WBM pavement 0.35-0.70 Soil covered with turf

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I m port ant Design Considerat ions

5) Manning’s Coefficient value?

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I m port ant Design Considerat ions

7) Widt h and dept h?

 The widt h is as per t he local widt h available for t he  The widt h is as per t he local widt h available for t he

const ruct ion of t he drains

 Dept h should be est im at ed based on Manning’s form ula  As far as possible rect angular

 Econom ical sect ion is b= 2d

 Som e places pipes were also used  Som e places pipes were also used

AS per I RC 50: Minim um widt h of drain should not be less

AS per I RC 50: Minim um widt h of drain should not be less t han 250 m m and incase of pipe t he m inim um diam et er should not be less t han 450 m m .

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I m port ant Design Considerat ions

8. Slope of t he drains? Longit udinal slope?

 Generally slope should not be less t han 0.3%

 But in flat t errain it can go upt o 0.2%  But in flat t errain it can go upt o 0.2%

 Slope is designed such t hat t he flow is always in

sub-crit ical flow crit ical flow

 To avoid hydraulic j um p

 As pe r I RC 5 0 , a m in im u m lon git u din a l

gr a die n t is 0 .3 %

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I m port ant Design Considerat ions

9. Free board?

 Generally for open channels a free board of 0 3 m is  Generally for open channels a free board of 0.3 m is

provided

 But Mum bai is having very flat t errain and does not

allow t o have m ore free board allow t o have m ore free board.

 I RC recom m ends t he following free boards

Bed widt h Free board Bed widt h Free board < 300 m m 10 cm

300 t o 900 m m 15 cm

900 t 1500 30

900 t o 1500 m m 30 cm

Larger size 90 cm

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Design Considerat ions

10. Type of inlet t o drains?

 Curb inlet

 Grat e

 Com bined

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Design Considerat ions

11. Junct ion box size?

 This should be designed as per t he velocit y of t he  This should be designed as per t he velocit y of t he

wat er crossing or j oining each ot her.

12. Adequacy of nallah

Level difference bet ween I L and Maxim um Wat er level in Level difference bet ween I L and Maxim um Wat er level in

nallah

 I f t he I nvert ed Level of t he drain is lower t han t he

MWL in nallah t hen nallah wat er st art s ent ering int o MWL in nallah t hen nallah wat er st art s ent ering int o t he drains

 Then slope has t o be m odified and designed such t h t t h I L f d i i b t h MWL f ll h t hat t he I L of drains is above t he MWL of nallah.

13. Connect ion bet ween t he Main drain on eit her side of t he road

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Design Considerat ions

14) Design of drain draining t o t he creek or

nallah having t idal effect .



I f t he out let point of t he drain is t o a creek or

a nallah whose wat er level rises according t o

t he t ide level

h

f h

d

h

ld b

b

h



The I L of t he drains should be above t he high

t ide level, else sea w at er ent ers t he drain

I f

ibl l

i

d

i

b



I f possible a large size drains m ay be

const ruct ed w hich can act as holding pong

unt il t he high t ide level

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unt il t he high t ide level.

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D a t a N e e de d for t h e de sign

 I Rainfall int ensit y

 Runoff coefficient

 Area cont ribut ing t o drains ( lengt h and widt h)  Cross- sect ional param et ers of t he road

 RL of t he hydraulic m ount  RL of t he hydraulic m ount

 RL of t he ground level, I L of t he drains

I I . KEY PLAN OF TH E W ORK

t he lengt h

locat ion of nallah

size, I L of drains at st art ing point and draining point Slope bet ween t he sect ions

Ot her m aj or drainage work nearby/ or river nearby

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Ot her m aj or drainage work nearby/ or river nearby

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D a t a N e e de d for t h e de sign

I I I . D ETAI LED PLAN OF TH E ROAD

– Lengt h ( in t erm s of chainage)

– Locat ion of point sources and t heir discharge – Hydrologic m ount

– RL of ground levels at chainage point s and ot her – RL of ground levels at chainage point s and ot her

im port ant point s

– Arrows showing t he flow direct ion of st orm wat er in t he drains

– Locat ion of draining nallah

– Locat ion and size of cross drainage work – Locat ion and size of cross drainage work – Locat ion of m an holes and t heir sizes

– Any ot her it em relevant t o t he sit e specific design ( t o

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y p g (

be highlight ed)

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D a t a N e e de d for t h e de sign

I V . LON GI TUD I N AL SECTI ON D RAW I N G

– Finished Road Level

– RL of exist ing ground level

– I L of drains

– Bed levels, w at er levels of nallah

– Locat ion of curb inlet point s

– Locat ion and size of ot her point

sources j oining t he drain

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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 Qualit y

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

 ht t p: / / ndm a.gov.in/ ndm a/ guidelines.ht m l

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

 Mark O Weesakul S Apirum anekul C Aroonnet S B

 Mark, O., Weesakul, S., Apirum anekul, C., Aroonnet , S.B.,

Dj ordj evic, S. ( 2004) . “ Pot ent ial and Lim it at ions of 1D Modelling of Urban Flooding.” J.Hydrology, 299, 284- 299

 Nat ional Disast er Managem ent Guidelines ( 2010) Managem net  Nat ional Disast er Managem ent Guidelines ( 2010) – Managem net

of urban flooding, Gov. of I ndia, New Delhi.

 Nat ional Research Council of t he Nat ional Academ ies ( NRC) . 2008.

“ Urban St orm wat er Managem ent in t he Unit es St at es ” The

36 36 36 36

Urban St orm wat er Managem ent in t he Unit es St at es. The Nat ional Academ ies Press. Washingt on, DC.

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



Crit ically st udy t he urban drainage

design m et hodology adopt ed in

I ndia?.

h t t p:/ / n dm a gov in / n dm a / gu ide lin e s h t m l h t t p:/ / n dm a .gov.in / n dm a / gu ide lin e s.h t m l



Com pare t he urban drainage design



Com pare t he urban drainage design

pract ices in USA, UK and I ndia and

propose bet t er m anagem ent pract ices

for I ndian Cit ies.

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

 What are t he im port ant causes of urban flooding?

 What are t he difficult ies in urban flood m anagem ent ?  What are t he difficult ies in urban flood m anagem ent ?  Discuss wat ershed based urban flood m anagem ent .  Describe t he invent ories t o be t aken for st orm wat er  Describe t he invent ories t o be t aken for st orm wat er

drainage syst em .

 What are t he im port ant design considerat ions for urban

drainage syst em s?.

 What are t he im port ant dat a t o be considered for

roadside drainage design? roadside drainage design?.

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

g

Q

 What are t he im port ant st rat egies for urban flood

disast er risk m anagem ent ?.

 I llust rat e various urban drainage syst em s.



What are t he im port ant design requirem ent s

for urban drainage syst em s?.



Discuss t he im port ant design considerat ions

for roadside drainage design?.



What are t he im port ant fact ors t o be

considered for roadside drainage design?.

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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: eldho@iitb.ac.ineldho@iitb.ac.in

40 40 Email:

Email: eldho@iitb.ac.ineldho@iitb.ac.in

Phone: (022)

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

http://www.