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Estimating Runoff in Urban Catchments – Monzur Imteaz
Module 5Estimation and Analysis of
Runoff from Urban Catchments
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Estimating Runoff in Urban Catchments – Monzur Imteaz
Runoff HydrographPea Runoff! " #
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Estimating Runoff in Urban Catchments – Monzur Imteaz
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 &$ears(
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Estimating Runoff in Urban Catchments – Monzur Imteaz
Urban CatchmentsA R ( R Chapter )* +,oo- Eight.
%mper/ious 0raction Most %mportant 0actor%n 1efining C 10– 1-./ 0 # 3 /! 2 1 – # 1-
%mper/ious 0raction– raction of Catchment Co+ere% in Im#er+iousSurfaces
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Australian Rainfall ( Runoff
http://www.engaust.com.au/bookshop/arr.html
http://www.engaust.com.au/bookshop/arr.htmlhttp://www.engaust.com.au/bookshop/arr.html
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Runoff Coefficient2 C 10( ) f C f C −×+×= 19.0 '1010
( )250133.01.0 101'10 −×+= yr hr I C
f Im#er+ious raction
AreaCatchment
Area Impervious f =
y F C Cy ×= 10
I = 25
I = 70
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Estimating Runoff in Urban Catchments – Monzur Imteaz
Urban 0re3uency 0actorsAR% +years. 0re3uency 0actor
F y
) !$" !$55 !45
) )!" )! 55 )!)5
) )!"
y F C Cy ×= 10
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Time of ConcentrationEstimate Tra/el Time– +er,an% ,o4 an% 5utter ,o4/erland 0lo6
– 6inematic Wa+e E7uation– )ssumes Homogeneous Surface
8 Combine *ra+e, *ime for In%i+i%ua, Homogeneous Surfaces7utter 0lo6– Manning E7uation
21
321
oS R AnQ =
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Estimating Runoff in Urban Catchments – Monzur Imteaz
/erland 0lo6
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Estimating Runoff in Urban Catchments – Monzur Imteaz
8inematic &a/e E3uation
T /erland 0lo6 Time +mins. L 0lo6 9ath :ength +m.n* ;urface Roughness Coefficient
I Rainfall %ntensity +mm
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Estimating Runoff in Urban Catchments – Monzur Imteaz
;urface Roughness Coefficients;urface Type Roughness
Coefficientn*
Concrete or Asphalt ! ) ! )>,are ;and ! ) ! )?
7ra/el ;urface ! )" ! >,are ;oil ! )" ! >>
;parse @egetation ! 5> !)>7rass 9rairie !) !"
:a6ns !)# !*$rom )ustra,ian Rainfa,, 9 Runoff! ) R 9 R &2 (
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Estimating Runoff in Urban Catchments – Monzur Imteaz
( )( )3.0.0
!.0"9.!
S I n LT =
L, n*
, S known I ??
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Estimating Runoff in Urban Catchments – Monzur Imteaz
Time of Concentration
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Estimating Runoff in Urban Catchments – Monzur Imteaz
0lo6 along the 8erb
21
321
oS R An
Q =
Most of the urbanstreets are%esigne% to carr$storm4ater runoff
as 4e,,:
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Estimating Runoff in Urban Catchments – Monzur Imteaz
TypicalUrban1rainage;ystem
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Estimating Runoff in Urban Catchments – Monzur Imteaz
Urban Drainage Systems:
;ot'house %rainage0 Pi#e% %rainage0 Surface %rainage
Street %rainage0 Pi#e %rainage0 6erb &channe,( %rainage
#en channe, %rainage
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Estimating Runoff in Urban Catchments – Monzur Imteaz
House 1rainage
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;treet 1rainage
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Estimating Runoff in Urban Catchments – Monzur Imteaz
on Homogeneous Catchment1ifferent Urban :and Uses– More than ne ;an% Use *$#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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Estimating Runoff in Urban Catchments – Monzur Imteaz
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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Estimating Runoff in Urban Catchments – Monzur Imteaz
Minor and Ma or 1rainage ;ystems
ig: 1:3! Aoo BIII! )ustra,ian Rainfa,, 9 Runoff &2 (
Mi d M
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Estimating Runoff in Urban Catchments – Monzur Imteaz
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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Estimating Runoff in Urban Catchments – Monzur Imteaz
,ypass 0lo6
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Estimating Runoff in Urban Catchments – Monzur Imteaz
9it Capture Rate
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Estimating Runoff in Urban Catchments – Monzur Imteaz
%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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Estimating Runoff in Urban Catchments – Monzur Imteaz
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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