urban runoff estimation

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HES3112 – Urban Water Resources

Estimating Runoff in Urban Catchments – Monzur Imteaz

Module 5Estimation and Analysis of

Runoff from Urban Catchments


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Runoff HydrographPea Runoff! " #


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The Rational MethodQ y = !"#$ C y % Tc y A

&here'– " $ Pea %ischarge &m3's(

– C $ Runoff coefficient & $ $ear )RI(

– I *c $ )+erage rainfa,, intensit$ &mm'h(

– ) Catchment area & m2(– $ )RI &$ears(


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Urban CatchmentsA R ( R Chapter )* +,oo- Eight.

%mper/ious 0raction Most %mportant 0actor%n 1efining C 10– 1-./ 0 # 3 /! 2 1 – # 1-

%mper/ious 0raction– raction of Catchment Co+ere% in Im#er+iousSurfaces


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Australian Rainfall ( Runoff

http://www.engaust.com.au/bookshop/arr.html

http://www.engaust.com.au/bookshop/arr.htmlhttp://www.engaust.com.au/bookshop/arr.html


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Runoff Coefficient2 C 10( ) f C f C −×+×= 19.0 '1010

( )250133.01.0 101'10 −×+= yr hr I C

f Im#er+ious raction

AreaCatchment

Area Impervious f =

y F C Cy ×= 10

I = 25

I = 70


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Urban 0re3uency 0actorsAR% +years. 0re3uency 0actor

F y

) !$" !$55 !45

) )!" )! 55 )!)5

) )!"

y F C Cy ×= 10


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Time of ConcentrationEstimate Tra/el Time– +er,an% ,o4 an% 5utter ,o4/erland 0lo6

– 6inematic Wa+e E7uation– )ssumes Homogeneous Surface

8 Combine *ra+e, *ime for In%i+i%ua, Homogeneous Surfaces7utter 0lo6– Manning E7uation

21

321

oS R AnQ =


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/erland 0lo6


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8inematic &a/e E3uation

T /erland 0lo6 Time +mins. L 0lo6 9ath :ength +m.n* ;urface Roughness Coefficient

I Rainfall %ntensity +mm


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;urface Roughness Coefficients;urface Type Roughness

Coefficientn*

Concrete or Asphalt ! ) ! )>,are ;and ! ) ! )?

7ra/el ;urface ! )" ! >,are ;oil ! )" ! >>

;parse @egetation ! 5> !)>7rass 9rairie !) !"

:a6ns !)# !*$rom )ustra,ian Rainfa,, 9 Runoff! ) R 9 R &2 (


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( )( )3.0.0

!.0"9.!

S I n LT =

L, n*

, S known I ??


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Time of Concentration


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0lo6 along the 8erb

21

321

oS R An

Q =

Most of the urbanstreets are%esigne% to carr$storm4ater runoff

as 4e,,:


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TypicalUrban1rainage;ystem


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Urban Drainage Systems:

;ot'house %rainage0 Pi#e% %rainage0 Surface %rainage

Street %rainage0 Pi#e %rainage0 6erb &channe,( %rainage

#en channe, %rainage


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House 1rainage


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;treet 1rainage


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on Homogeneous Catchment1ifferent Urban :and Uses– More than ne ;an% Use *$#e in Catchment

E3ui/alent %mper/ious Area– or Each ;an% Use *$#e

8 Measure )rea of Each ;an% Use! Ai

8


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on Homogeneous Catchment1ifferent Tra/el Times in Each :and Use * T c is *ra+e, *ime to Catchment ut,et

1epends on 1rainage et6or-– Where )reas


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9artial Area Effect

Must Chec- ,oth ;torm 1urations– ;onger Storm


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E ample of 9artial Area EffectAn urban catchment has an area of >!"5 -m "! netributary drains an area of )!" -m "2 6ith a fractionimper/ious of $5D and a tra/el time of )# minutes!The second tributary has a fraction imper/ious of )5D6ith a tra/el time of 5 minutes!

Calculate the 9ea- runoff for the ) year AR% 6hen I 10yr,17min = ? mm"! mm


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9ipe 1rainage 1esignUnderground ;treet 1rainage 9ipes– Minor $ear )RI(;treets and 1rainage Reser/es– Ma?or


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Minor and Ma or 1rainage ;ystems

ig: 1:3! Aoo BIII! )ustra,ian Rainfa,, 9 Runoff &2 (

Mi d M


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Minor and Ma or1rainage ;ystems

ig: 1:2! Aoo BIII!)ustra,ian Rainfa,, 9 Runoff&2 (


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/erland 0lo6path


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1esignChart


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Analysis of Urban Drainage System

• +re,-e elope-•

+ost,-e elope-


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%ocat ng + ts


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Estimating Runoff in Urban Catchments – Monzur Imteaz%ocat ng + ts

es gn ra n all ntens t & I = 90 mm/hr )uno co,e c ent& = 0.45 %ong tu- nal slope = 2( llowable street low w -th = 2.1 m

6rom chart& allowable = 0.04 cumec

= .I. /3!0 = 0.458908 58% 0/10&000 /3!0

= 0.00095!% 0 %0 = 4 m

;s ng )at onal 6ormula,


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8erb 0lo6 1esign Chart


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,ypass 0lo6


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9it Capture Rate


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%ocat ng + ts

ssume& rst p t has a capture rate o 7!(

< pass low = 1 , 0.7! $0.04 = 0.019 cumec llowable low rom secon- sub,catchment =

0.04 , 0.019 = 0.0!1 cumec

= .I. /3!0 = 0.458908 58% 1/10&000 /3!0 0.0!1 = 0.00095!% 1 %1 = ! m

;s ng )at onal 6ormula,


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9it


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0lo6 9aths


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9it design in a car par-


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9


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9ostde/eloped

1rainage


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1etention ,asin


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HES3112 – Urban Water Resources 1etention ,asin

urban runoff estimation

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