004_4. Hydraulic Structures

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29 HYDRAULIC STRUCTURES

29.1 INTRODUCTION...............................................................................................29-1

29.2 EROSION AND SCOUR PROTECTION......................................................................29-1

29.3 ENERGY DISSIPATORS........................................................................................29-2

29.3.1 Riprap Basins for Condi! O!"#!s............................................................. 29-3

29.3.2 S!i""in$ Basins.........................................................................................29-3

29.3.3 Si%p"# En#r$&-Dissipa!in$ '#ad(a""s ..........................................................29-)

29.3.* D#si$n Cri!#ria and Pra+!i+#s.....................................................................29-)

29.* DROP STRUCTURES..........................................................................................29-)

29.) STOR,ATER DRAIN OUTA//S...........................................................................29-10

29. TRANSITIONS AND CONSTRICTIONS.....................................................................29-13

29..1 Transi!ion Ana"&sis ............................................................................... 29-13

29..2 Cons!ri+!ion Ana"&sis............................................................................. 29-13

29. BENDS AND CON/UENCES.................................................................................29-1)

29..1 B#nds..................................................................................................29-1)

29..2 Conf"#n+#s..........................................................................................29-1

29. SIDE-O4ER/O EIRS...................................................................................29-1

29..1 D#si$n Consid#ra!ions .............................................................................29-1

29..2 D#si$n Pra+!i+#s................................................................................... 29-1

29.9 /O SP/ITTER..............................................................................................29-19

29.9.1 D#si$n Consid#ra!ion............................................................................ 29-20

29.9.2 D#si$n Cri!#ria .................................................................................... 29-20

29.10 /O SPREADER...............................................................................................29-20

29.10.1 G#n#ra" D#si$n Cri!#ria ......................................................................... 29-20

29.10.2 D#si$n Cri!#ria for "o( Spr#adin$ Op!ions...................................................29-21

29.11 SIP'ONS..........................................................................................................29-2*

29.11.1 Sin$"#-Barr#" Sip5ons..............................................................................29-2)

29.11.2 ,"!i-Barr#" Sip5ons ...............................................................................29-2)

29.11.3 D#si$n Cri!#ria and Pra+!i+#s.....................................................................29-2)

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Hydraulic Structures

29.1 INTRODUCTION

'&dra"i+ s!r+!r#s ar# s#d !o posi!i6#"& +on!ro" (a!#r

f"o( 6#"o+i!i#s7 dir#+!ions and d#p!5s7 !5# #"#6a!ion and

s"op# of !5# s!r#a% 8#d7 and !5# $#n#ra" +onfi$ra!ion of a

(a!#r(a& in+"din$ i!s s!a8i"i!& and %ain!#nan+#

+5a ra+!#ris!i+s.

,an& of !5#r# s!r+!r#s app#ar as sp#+ia"s and ar#

#p#nsi6#7 (5i+5 r#:ir# +ar#f" and !5oro$5 5&dra"i+

#n$in##rin$ ;d$#%#n!. Prop#r app"i+a!ion of 5&dra"i+

s!r+!r#s +an r#d+# ini!ia" and f!r# %ain!#nan+# +os!s

8& +5an$in$ !5# +5ara+!#r of !5# f"o( !o fi! !5# n##ds of a

par!i+"ar pro;#+!7 and 8& r#d+in$ !5# sias s5o(n in i$r# 29.*? s5o"d 8# as fo""o(s@-

3D7 0.**7 for T. D02 >29.3?

and

3700 **7 for T D02 >29.*?

T5# (id!5 of !5# apron a! !5# +"6#r! o!"#! s5o"d 8#

a! "#as! 3 !i%#s !5# +"6#r! (id!5.

On !5# +on!rar&7 (5#r# !5#r# is a (#""-d#fin#d +5ann#"

do(ns!r#a% of !5# apron7 !5# 8o!!o% (id!5 of !5#

apron s5o"d 8# a! "#as! #:a" !o !5# 8o!!o% (id!5 of

!5# +5ann#" and !5# "inin$ s5o"d #!#nd a! "#as! on#

foo! a8o !5# !ai"(a!#r #"#6a!ion and a! "#as! !(o-

!5irds of !5# 6#r!i+a" +ondi! di%#nsion a8o !5#

in6#r!.

T5# sid# s"op#s s5o"d 8# 2@1 or f"a!!#r.

T5# 8o!!o% $rad# s5o"d 8# "#6#".

T5#r# s5o"d 8# an o6#rfa"" a! !5# #nd of !5# apron or

+"6#r!.

>ii? Apron ,a!#ria"s

T5# %#dian s!on# dia%#!#r7 d)0is d#!#r%in#d fro%

!5# fo""o(in$ #:a!ion@

0.0>F?*3

d)0 - T>D0?>29.)?

Eis!in$ s+or 5o"#s %a& 8# s#d (5#r# fa! aprons

ar# i%pra+!i+a". i$r# 29.) s5o(s !5# $#n#ra" d#si$n

of a s+or 5o"#. T5# s!on# dia%#!#r is d#!#r%in#d

sin$ !5# fo""o(in$ #:a!ons@

>i? Apron Di%#nsions

T5# "#n$!5 of an apron (La) is d#!#r%in#d sin$ !5#

fo""o(in$ #%piri+a" r#"a!ions5ips !5a! (#r# d#6#"op#d for

!5# U.S. En6iron%#n!a" Pro!#+!ion A$#n+& >19?@ La=

__________+ 7 D, for T D02

3.2FDa3 2 >29.1?

and

).**FLa_______+7 D, for T H D02 >29.2?D032

where Aprons +ons!r+!#d of %an %ad# %a!#ria"s ar# of!#n a

D, = %ai%% insid# +"6#r! dia%#!#r >%? 6ia8"# a"!#rna!i6#. R#f#r !o !5# a8o dis+ssion of! = pip# dis+5ar$# >+%#+? %an-%ad# %a!#ria"s for d#si$n +onsid#ra!ion.

"#= !ai"(a!#r d#p!5 >%?

0.0*1>F?*13 )0 - T>Do?

for Y D02 >29.?

0.027(Q)4/3dso= for Y Do

"#$Do%

>29.?

a"so

(5#r# Y d#p!5 of s+or 5o"# 8#"o( +"6#r! in6#r!.

O!5#r riprap or $a8ion r#:ir#%#n!s ar# as

indi+a!#d in !5# pr#6ios s#+!ions for +5ann#" "inin$.

Urban Stormwater Management Manual 29-1


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i$r# 29.1 Confi$ra!ion of Condi! O!"#! Pro!#+!ion >U.S. EPA7 19?

fro% sp#r+ri!i+a" !o s8+ri!i+a"7 or (5#r# !5# f"o( is sp#r+ri!i+a" and !5# !ra+!i6# for+#s or f"o( 6#"o+i!i#s ar# 5i$5#r !5an

!5# %ai%% a""o(a8"# 6a"#s. T5# 8asi+ 5&dra"i+ para%#!#r !5a!

id#n!ifi#s !5# f"o( r#$i%#7 and is s#d in +onn#+!ion (i!5 #n#r$& dissipa!#rs in

$#n#ra"7 and (i!5 5&dra"i+ ;%p dissipa!#rs in par!i+"ar7 is !5# rod# n%8#r

>C5ap!#r 12?.

T5# rod# n%8#r is a ra!io of !5# f"o( 6#"o+i!& and (a6# +#"#ri!&. In

r#+!an$"ar +5ann#"s7 !5# #:a!ion %a& 8# r#(ri!!#n in !5# fo""o(in$ for%@

A

/a/a

3D0 0.*/ a> Tai"(a!#r H 0.)Do?

3D0 0.*1J o

> Tai"(a!#r 0.)Do?

/AN

n3 om

z

1

3D0 "on3

>a?

i$r# 29.2 Pr#for%#d S+or 'o"# >ASCE7 19)?

29.3 ENERGY DISSIPATORS

En#r$& dissipa!#rs ar# r#:ir#d in !5# i%%#dia!# 6i+ini!& of

5&dra"i+ s!r+!r#s (5#r# 5i$5 i%pa+! "oads7 #rosi6#

for+#s7 and s#6#r# s+or ar# #p#+!#d. In o!5#r (ords7

!5#& ar# sa""& r#:ir#d (5#r# !5# f"o( r#$i%# +5an$#s

F2- n'___3& d)

>29.?

(5#r#7

& = (id!5 of +5ann#" >%?

! dis+5ar$# >%3s?

g = a++#"#ra!ion d# !o $ra6i!& >9.1 %s2?

dm= 5&dra"i+ %#an d#p!5 >%?

En#r$& dissipa!ion s!r+!r#s a+! as !ransi!ions7 (5i+5

r#d+# 5i$5 f"o( 6#"o+i!i#s !5a! %a& #is! nd#r a ran$# of

f"o(s. En#r$& dissipa!#rs "o+a"is# 5&dra"i+ ;%ps and a+!

as s!i""in$ 8asins. T5# s# of #n#r$& dissipa!#rs is 6#r&

+o%%on do(ns!r#a% of 5&dra"i+ s!r+!r#s (5#r#

+o%%on +5ann#" pro!#+!ion +anno! 8# s#d a"on# 8#+as#of po!#n!ia" da%a$#. If riprap or o!5#r pro!#+!ion is s#d

SECTION

>8?

3 JJJJJJJJJJJJJJJJJ4ari#s3

1 Y

(

Do

29-2 Urban Stormwater Management Manual


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for #n#r$& dissipa!ion7 i! s5o"d 8# +onfin#d in a 8asin and

s#+r#d in p"a+# (i!5 $ro! or %#s5.

T5# pri%ar& diff#r#n+# 8#!(##n #n#r$& dissipa!#rs in

$#n#ra" and drop s!r+!r#s is !5a! !5# for%#r ar# s#d !o

r#d+# 5i$5 6#"o+i!i#s a! +ri!i+a" "o+a!ions 8& 5&dra"i+

;%ps7 (5i"# !5# "a!!#r ar# 6#r!i+a" s!r+!r#s s#d for

+on!ro""in$ 6#"o+i!i#s in +5ann#" r#a+5#s 8& r#d+in$+5ann#" s"op#s. B#+as# of 6arios appr!#nan+#s s+5 as

si""s7 8aff"#s7 and (#irs7 and 8#+as# of 6aria!ions in !5#

$#o%#!r& of s!i""in$ 8asins7 a (id# 6ari#!& of #n#r$&

dissipa!#rs %a& 8# s#d.

29.3.1 Riprap Basins for Condi! O!"#!s

T5# %os! +o%%on"& s#d #n#r$& dissipa!#rs ar# riprap

8asins >i$r# 29.3?. T5#ir ad6an!a$#s in+"d# si%p"i+i!&7

"o( +os!7 and (id# app"i+a!ion.

T5# riprap p"a+#d in !5# 8asin %s! 8# insp#+!#d and

r#pair#d7 if n#+#ssar&7 a"!#r %a;or s!or%s. T5# %#dian

s!on# dia%#!#r +an 8# #s!i%a!#d 8as#d on !5# #i! 6#"o+i!&

of !5# pip# or +"6#r! as s5o(n in ,+/a$5"in a!#r

En$in##rs >19? and !5# AAS'TO Draina$# 'and8oo=

>19?. T5# "#n$!5 of !5# 8asin is #s!i%a!#d 8as#d on !5#

(id!5 or dia%#!#r of !5# +ondi!. T5# d#p!5 of !5# 8asin is

8as#d on !5# %#dian s!on# dia%#!#r.

29.3.2 S!i""in$ Basins

If a 5&dra"i+ ;%p is s#d for #n#r$& dissipa!ion7 i! s5o"d

8# +onfin#d !o a 5#a6i"&-ar%or#d +5ann#" r#a+57 !5#

8o!!o% of (5i+5 is pro!#+!#d 8& a so"id srfa+# s+5 as

+on+r#!# !o r#sis! s+orin$. Sin+# !5# +os! of +on+r#!#

s!r+!r#s is r#"a!i6#"& 5i$57 !5# "#n$!5 of !5# 5&dra"i+

;%p is sa""& +on!ro""#d 8& a++#ssori#s !5a! no! on"&

s!a8i"is# !5# ;%p a+!ion and in+r#as# !5# fa+!or of saf#!&7

8! a"so r#d+# !5# +os! of !5# s!r+!r#.

$a% Design 'onsiderations

T5#r# ar# s#6#ra" +onsid#ra!ions !5a! s5o"d 8# in+"d#d in

d#si$nin$ 5&dra"i+ ;%ps and s!i""in$ 8asins >C5o(7 19)9K

US DOT7 193?@

() *um osition T5#r# ar# !5r## posi!ions or

a"!#rna!i6# pa!!#rns !5a! a""o( a 5&dra"i+ ;%p !o

for% do(ns!r#a% of !5# !ransi!ion in !5# +5ann#".

T5#s# posi!ions ar# +on!ro""#d 8& !ai"(a!#r.

-) "ailwater 'onditions Tai"(a!#r f"+!a!ions d# !o+5an$#s in dis+5ar$# +o%p"i+a!# !5# d#si$n pro+#dr#.

T5#& s5o"d 8# !a=#n in!o a++on! 8& +"assifi+a!ion of

!ai"(a!#r +ondi!ions sin$ !ai"(a!#r and 5&dra"i+ ;%p

ra!in$ +r6#s.

.) *um "yes 4arios !&p#s of 5&dra"i+ ;%ps !5a!%a& o++r ar# s%%aris#d in i$r# 29.*. Os+i""a!in$

;%ps in a rod# n%8#r ran$# of 2.) !o *.) ar# 8#s!

a6oid#d n"#ss sp#+ia""& d#si$n#d (a6# sppr#ss#rs

ar# s#d !o r#d+# (a6# i%pa+!.

T5# $r#a!#r !5# rod# n%8#r7 !5# 5i$5#r is !5# #ff#+! of

!ai"(a!#r on !5# ;%p. T5#r#for#7 for a rod# n%8#r as

"o( as 7 !5# !ai"(a!#r d#p!5 s5o"d 8# $r#a!#r !5an !5#

s#:#n! d#p!5 do(ns!r#a% of !5# ;%p so !5a! !5# ;%p

(i"" s!a& on !5# apron. 5#n !5# rod# n%8#r is

$r#a!#r !5an 107 !5# +o%%on s!i""in$ 8asin dissipa!#r %a&

no! 8# as +os!-#ff#+!i6# as a sp#+ia" 8+=#! !&p# dissipa!#r

>s## P#!#r=a7 19)?.

$b% 'ontro l o/ *ums

L%ps +an 8# +on!ro""#d 8& s#6#ra" !&p#s of appr!#nan+#s

s+5 as si""s7 +5!# 8"o+=s and 8aff"# pi#rs. T5# prpos# of

a si"" "o+a!#d a! !5# #nd of a s!i""in$ 8asin is !o ind+# ;%p

for%a!ion and !o +on!ro" i!s posi!ion nd#r %os! pro8a8"#

op#ra!in$ +ondi!ions. S5arp +r#s!#d or 8road +r#s!#d (#irs

+an 8# s#d !o s!a8i"is# and +on!ro" !5# ;%p.

C5!# 8"o+=s ar# s#d a! !5# #n!ran+# !o !5# s!i""in$ 8asin.

T5#ir fn+!ion is !o frro( !5# in+o%in$ ;#! and "if! apor!ion of i! fro% !5# f"oor7 prod+in$ a s5or!#r "#n$!5 of

;%p !5an (o"d o++r (i!5o! !5#%.

Baff"# pi#rs ar# 8"o+=s p"a+#d in in!#r%#dia!# posi!ions

a+ross !5# 8asin f"oor for dissipa!in$ #n#r$& %os!"& 8&

dir#+! i%pa+! a+!ion. T5#& ar# s#f" for s%a"" s!r+!r#s

(i!5 "o( f"o( 6#"o+i!i#s. 'i$5 f"o( 6#"o+i!i#s %a& r#s"! in

+a6i!a!ion a+!ion on !5# pi#rs and 8asin f"oor do(ns!r#a%.

$ c % & a s i n ' a t e g o r i e s

T5# fo""o(in$ !5r## %a;or +a!#$ori#s of 8asins ar# s#d for

a ran$# of 5&dra"i+ +ondi!ions. D#si$n d#!ai"s +an 8#

fond in !5# AAS'TO Draina$# 'and8oo= >19?7 C5o(

>19)9?7 and US DOT >193?.

"he S01 $2St) 0nthony 1aiis2 Stilling &asin% $ C5o(19)9? @ T5is 8asin7 s5o(n in i$r# 29.)7 is

r#+o%%#nd#d for s# on s%a"" s!r+!r#s s+5 as

spi""(a&s and o!"#! (or=s (5#r# !5# rod# n%8#r

6ar#s 8#!(##n 1. and 1. T5# appr!#nan+#s s#d

for !5is dissipa!#r +an r#d+# !5# "#n$!5 of !5# 8asin

8& approi%a!#"& 0M. T5is d#si$n 5as $r#a!

po!#n!ia" in r8an s!or%(a!#r s&s!#%s 8#+as# of i!s

app"i+a8i"i!& !o s%a"" s!r+!r#s. S!i""in$ Basin IIId#6#"op#d 8& !5# US Br#a of R#+"a%a!ion >UBSR? is

si%i"ar !o !5# SA 8asin7 8! i! 5as a 5i$5#r fa+!or of

saf#!&.

"he U&S3 Stilling &asin 44 T5is 8asin7 s5o(n ini$r# 29.7 is r#+o%%#nd#d for s# (i!5 ;%ps (i!5

rod# n%8#rs $r#a!#r !5an *.) a! "ar$# spi""(a&s

and +5ann#"s. T5is 8asin %a& r#d+# !5# "#n$!5 of

!5# ;%p 8& a !5ird and is s#d for 5i$5-da% and

#ar!5-da% spi""(a&s. Appr!#nan+#s s#d in !5is 8asin

in+"d# +5!# 8"o+=s a! !5# ps!r#a% #nd of !5# 8asin

and a d#n!a!#d s!i"" a! !5# do(ns!r#a% #nd. No 8aff"#

pi#rs ar# s#d in !5is 8asin 8#+as# of !5# +a6i!a!ion

po!#n!ia".



5/33


300 %% r## Board,ini%%

Dissipa!or Poo"

10 Ds or 3 o,in

Top of B#r% Top ofRiprap

Apron

-)5sor o,in

No!# A

No!# B

Top of Na!ra" C5ann#"

illtOh.- - .., .1.--'Mb ......... +.11 Ihr ;::

..... . .%.,& ' . , % ( - . 1 . . r . % . . . . . . ..... fe . de .11 - . . . . . .).......T1 'N I.'1 ......*

...+ "&,. ( $o. 1". #. . ,.( *o ...-.( '1 .%(.( ......t . . . . . . . 2 . . . . p/ . . .1 . . . / i+0... II .

"1,-. .m. ". . . IP . . ./. ((( .

3*0or 2d ,a

1.) ,in

2d)0 or 2+1)0 or

1.)d ,a 1.5d ,a

>a? C#n!r#"in# S#+!ion

T5i+=#n#d or s"opin$ To# op!iona" -Cons!r+! if do(ns!r#a% +5ann#"d#$rada!ion is an!i+ipa!#d

D 1.# 0.pra9

No!# B

, - - - - 7.)1-o!#'1'' 01

-\c'4' ----,

4 9 + K - ...7-. N egea!#" --)-J.--..7 KIN ---------11

' ',11 -- - 3

Culvert 11N i 2:1,_Horizontalil !._i D . . . . - - '+

>8? 'a"f-p"an

i$r# 29.3 T&pi+a" Riprap Basin@ >a? +#n!r#"in# s#+!ion and >8? 5a"f p"an@ 0 dia%#!#r

for pip# +"6#r!7 8arr#" (id!5 for 8o +"6#r!7 or span of pip#-ar+5 +"6#r!

>US #d#ra" 'i$5(a& Ad%inis!ra!ion7 193?.

No!#s for i$r# 29.3@

>1? If a %ai%% a""o(a8"# #i! 6#"o+i!&7 Ve7 fro% !5# 8asin is sp#+ifi#d7 #!#nd !5# 8asin as r#:ir#d !o o8!ain sffi+i#n!

+ross-s#+!iona" ar#a a! s#+!ion A-A >i.#. AAJA !4 5e% for !5# sp#+ifi#d 6#"o+i!&

>2? arp !5# 8asin !o +onfor% !o !5# na!ra" s!r#a% +5ann#". T5# !op of !5# riprap in !5# 8asin f"oor s5o"d 8# a! !5#sa%# #"#6a!ion or "o(#r !5an !5# na!ra" +5ann#" 8o!!o% a! s#+!ion A-A

Apron2:1

S&%%#!ri+a" A8o!C#n!r# /in#

B#r% as r#:ir#d

2+1s0 or 1.)d%a !o S or! Ri ra

E+a6a!# !o !5is /in#Ba+=fi"" i!5 Riprap

!e" C-C

No!#

Na!ra" C5ann#"

e" -

2d) or 1.)d%a

E+a6a!# !o !5is "in#8a+=fi"" (i!5 Riprap

e" -

B#r% as r#:ir#d!o Sppor! Riprap

2d) or 1.)d%a

e" -

29-* Urban Stormwater Management Manual


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Os+i""a!in$ L#!

Ro""#r

7

// / / / / / / / / / / / /

1 - 1. Und"ar L%p l 2.) - *.) Os+i""a!in$ L%p

/ / / / / / / / / / / / //

/!/

l 1. - 2.) #a= L%p 1 *.) - 9.0 S!#ad& L%p

111111111"# %#

,E, E ,E& & &

,E,I E E E& & & &

L%p L%p S!#ad& L%pL%p

P#rfor%an+# ro$5srfa+# +ondi!ions-

i$r# 29.* /#n$!5s and T&p#s of '&dra"i+L%ps in 'oriBrad"#& and P#!#r=a7 19)K C5o(7 19)9?

6 "he U&S3 Stilling &asin 45 T5is 8asin7 s5o(n ini$r# 29.7 is s#d (5#r# ;%ps ar# i%p#rf#+! or

(5#r# os+i""a!in$ (a6#s o++r (i!5 rod# n%8#rs

8#!(##n 2.) *.). T5is d#si$n r#d+#s #+#ssi6#

(a6#s 8& #"i%ina!in$ !5# (a6# a! i!s sor+# !5ro$5

d#f"#+!ion of dir#+!iona" ;#!s sin$ +5!# 8"o+=s. 5#n

a 5oridrop spi""(a&s? or !ransi!ions 8#!(##n op#n +5ann#"s and

+"os#d +ondi!s >drop s5af!s?.

Drop s!r+!r#s s5o"d 8# +ons!r+!#d of +on+r#!# 8#+as#of !5# for+#s in6o"6#dK 5o(#6#r7 riprap or $a8ion s!i""in$

8asins %a& 8# s#d (5#r# p5&si+a"7 #+ono%i+7 and o!5#r

+ondi!ions p#r%i!.

y

X 7 7 7

/ )Y2

*

0 1 2 3 * ) 9 10 11 12 13 1* 1) 1 1 1 19 20

.1 417$&i

1


7/33

Urban Stormwater Management Manual


8/33


()* +raezo ia l !t il ling $ain /levation+raezoial !tilling $ain 0e"tangular !tilling $ain

%ontream !e"tion

("*Centre l ine !e"t ion i$r# 29.)

Propor!ions of !5# SA Basin >C5o(7 19)9?.

29- Urban Stormwater Management Manual

&

(a*0e"tangular !tilling $ain Hal-

lan !ie 3all

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9/33


i$r# 29. Propor!ions of !5# USBR Basin II >C5o(7 19)9?

ra+!iona" Spa+#

(( ,ai%% Too!5 id!5 D1Sa/ Spa+# 2.)(

i$r# 29. Propor!ions of !5# USBR Basin I4 >C5o(719)9?

Condi!i$r# 29. S!andard En#r$& Dissipa!in$ '#ad(a"" T&p# I >C5o(7 19)9?

D#n!a!#d Si""

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Urban Stormwater Management Manual 29-

300 %% S:ar# So"id Con+r#!# B"o+= or%#dand Por#d in P"a+#7 R#infor+#d 8&

R R#-8ars Disp#rs#d E6#r& 100 %% T5ro$5o!

E

300 %% 300 %% 300 %%R R#- ar

300 %% 300 %%300 %rn"7

)0 00 .00

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>a? P"an


10/33


i$r# 29.9 S!andard En#r$& Dissipa!in$ '#ad(a""7 T&p# II >ASCE7 1992?

(#) F%*+t l#ti*+

/ 200 "" +t% ! ! %c#t *+c%t

25 "" i+i""

0.56

0.256

450 "" () 8i l#ti*+

i$r# 29.10 S!andard En#r$& Dissipa!in$ '#ad(a""7 T&p# III >ASCE7 1992?

NOTE@

'#i$5! of En#r$& Dissipa!orss5o"d 8# 0.) D

'#ad(a""

300 %%

R a! 300 %%C#n!r#s

300 %% ,ini%%

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29- Urban Stormwater Management Manual


11/33


Ta8"# 29.1 Dissipa!#r Cri!#ria >U.S. D#par!%#n! of Transpor!a!ion7 193?

Dissipa!#r T&p#

rod# N%8#r

1

A""o(a8"# D#8risTai"(a!#r

"#

Sp#+ia"

Consid#ra!ions

Si"! and

SandBo"d#rs "oa!in$

r## '&dra"i+ L%p H 1

2

O

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1

-

1

O

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1

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CSU Ri$id Bondar& 3

T%8"in$ "o( H 1 *M .)17 2)M

In+r#as#d R#sis!an+# C5#+= O!"#!

Con!ro" H#

USBR T&p# II * !o 1* R#:ir#d

USBR T&p# III *.) !o 1 R#:ir#d

UBSR T&p# I4 2.) !o *.) R#:ir#d

SA 1. !o 1 R#:ir#dCon!ra Cos! 3

1 O

0.)D

'oo= 1. !o 3

USBR T&p# 4I D#sira8"# !8 11 %3s7

or#s! S#r6i+# D#sira8"# & 900 %%

Drop S!r+!r# 1 R#:ir#d Drop ) %

,anifo"d D#sira8"#

Corps S!i""in$ #"" D#sira8"#

Riprap 3

No!#@ N non#7 / "o(7 , %od#ra!#7 ' 5#a6&

Drop s!r+!r#s in op#n +5ann#"s +5an$# !5# +5ann#" s"op#

fro% s!##p !o %i"d 8& +o%8inin$ a s#ri#s of $#n!"# s"op#s

and 6#r!i+a" drops. "o( 6#"o+i!i#s ar# r#d+#d !o non-

#rosi6# 6#"o+i!i#s7 (5i"# !5# =in#!i+ #n#r$& or f"o( 6#"o+i!&

$ain#d 8& !5# (a!#r as i! drops o6#r !5# +r#s! of #a+5

spi""(a& is dissipa!#d 8& an apron or s!i""in$ 8asin.

= dis+5ar$# p#r ni! (id!5 of +r#s! o6#rfa"" >%3s%?

= a++#"#ra!ion d# !o $ra6i!& >9.1 %s2?

h= 5#i$5! of drop >%?

T5# drop fn+!ions ar#@

Op#n +5ann#" drop s!r+!r#s $#n#ra""& r#:ir# a#ra!#dnapp#s and s8+ri!i+a" f"o( +ondi!ions a! 8o!5 !5#

ps!r#a% and do(ns!r#a% s#+!ion of !5# drop. T5# s!i""in$ 8asin

+an 6ar& fro% a si%p"# +on+r#!# apron !o 8aff"# 8"o+=s or

si""s as d#s+ri8#d pr#6ios"&.

i$r# 29.11 s5o(s !5# f"o( $#o%#!r& and i%por!an!

6aria8"#s a! a 6#r!i+a" >s!rai$5!? drop s!r+!r#. T5# f"o(

$#o%#!r& a! s+5 drops +an 8# d#s+ri8#d 8& !5# drop

n%8#r7 D9, (5i+5 is d#fin#d >C5o( 19)9? as@

92D9

h3>29.9?

(5#r#7

= *.30 D9 0.2

: = 1.00 D9 0.22

;i 0.)* D9 0.*2)h

;2 1.%?

>29.10a?

>29.108?

>29.10+?

>29.10d?



12/33


&l !5# d#p!5 of !5# !o# of napp# >%?

Y2 6 !ai"(a!#r d#p!5 s#:#n! !o &l>%?

or a $i6#n drop 5#i$5!7 h, and dis+5ar$#7 a++ordin$ !o !5# US D#par!%#n! of Transpor!a!ion 193?

!o pro6id# #i!5#r >1? an apron a! !5# 8#d "#6#" and a si"" or

8aff"#s7 or >2? an apron 8#"o( !5# do(ns!r#a% 8#d "#6#"

and an #nd si"".

T5# +5oi+# of a d#si$n !&p# and di%#nsions d#p#nds on

!5# ni! dis+5ar$#7 o6#rf"o( +r#s!? "#n$!5 is "#ss !5an !5# (id!5 of !5#

approa+5 +5ann#"7 !5# approa+5 +5ann#" %s! 8# d#si$n#d

prop#r"& !o r#d+# !5# #ff#+! of !5# #nd +on!ra+!ions !o

a6oid s+or.

T5# !(o %os! +o%%on 6#r!i+a" op#n +5ann#" drops ar# !5#

s!rai$5! drop s!r+!r# and !5# 8o in"#! drop s!r+!r#.

$a% Straight Dro Structure

i$r# 29.12 s5o(s !5# "a&o! of a !&pi+a" s!rai$5! drop

s!r+!r# and 5&dra"i+ d#si$n +ri!#ria d#6#"op#d 8& US Soi"

Cons#r6a!ion S#r6i+#. ,+/a$5"in a!#r En$in##rs >193?

pro6id#s sp#+ifi+ +ri!#ria and r#6i#(s d#si$n +onsid#ra!ions

r#"a!#d !o !5# 5&dra"i+7 $#o!#+5ni+a"7 and s!r+!ra"

d#si$n of drop s!r+!r#s.

$b% &o 4nlet Dro Structure

T5# 8o in"#! drop s!r+!r# is a r#+!an$"ar 8o op#n a!

!5# !op and do(ns!r#a% #nd as s5o(n in i$r# 29.13.

a!#r is dir#+!#d !o !5# +r#s! of !5# 8o in"#! 8& #ar!5

di=#s and a 5#ad(a"". "o( #n!#rs o6#r !5# ps!r#a% #nd

and !(o sid#s. T5# "on$ +r#s! of !5# 8o in"#! p#r%i!s

"ar$# f"o(s !o pass a! r#"a!i6#"& "o( 5#ads. T5# (id!5 of!5# s!r+!r# s5o"d no! 8# $r#a!#r !5an !5# do(ns!r#a%

+5ann#". Bo in"#! drop s!r+!r#s ar# app"i+a8"# !o drops

fro% 0. !o 3. %.

D#si$n da!a and +ri!#ria for !5#s# s!r+!r#s7 8as#d on

US Soi" Cons#r6a!ion S#r6i+#s and S!. An!5on& a""s

'&dra"i+ /a8ora!or&7 ar# a6ai"a8"# >US D#par!%#n! of

Transpor!a!ion 193K B"aisd#"" and Donn#"& 19)?. T5#

para%#!#rs !o +onsid#r for !5# 5&dra"i+ d#si$n of !5# drop

ar#@

s#+!ion >"#n$!5? of !5# +r#as# of !5# 8o in"#!

op#nin$ of !5# 5#ad(a""s dis+5ar$#7 dis+5ar$# +o#ffi+i#n!s7 and f"o( r#$i%#

+5an$#s

8o in"#! "#n$!5 and d#p!5

%ini%% "#n$!5 and (id!5 of s!i""in$ 8asin

29.7 STOR8-ATER DRAIN OUTALLS

A"" s!or%(a!#r drains of a "o+a"i!& 5a6# an o!"#! (5#r#

f"o( fro% !5# "o+a" draina$# s&s!#% is dis+5ar$#d. T5#

dis+5ar$# poin!7 or o!fa""7 +an 8# #i!5#r a na!ra" ri6#r or

s!r#a%7 or an #is!in$ or propos#d s!or%(a!#r drain or

+5ann#". T5# pro+#dr# for +a"+"a!in$ !5# 5&dra"i+ $rad#

"in# !5ro$5 a s!or% draina$# s&s!#% 8#$ins a! !5# o!fa"".

T5#r#for#7 +onsid#ra!ion of !5# o!fa"" +ondi!ions is an

i%por!an! par! of s!or% drain d#si$n.

i$r# 29.11 "o( G#o%#!r& of a S!rai$5! Drop Spi""(a& >C5o(7 19)9?

: 2=

$ 5

:1>>>>t5>>>>>

A#ra!#d

P :

SS

_______ Ld L Y



13/33


3

SB 300 %%

>1200 %%,ini%%? T

S

C >1200 %% ,ini%%?

1)0 %% i""#!s

>a? S#+!ion on C#n!r#"in#

1)0 %% E

'#ad(a"" E!#nsion

'#ad(a""

in$ a""_7

>8? Do(ns!r#a% E"#6a!ion

>+? P"an

E ,ini%% "#n$!5 of 5#ad(a"" #!#nsion 350.1 or 1.) (5i+5#6#r is $r#a!#r

3 '#i$5! of (in$ (a"" and sid#(a"" a! ;n+!ion 25 or 5s-> / $= 0.13?or !1(5i+5#6#r is $r#a!#r 4 2

/B /#n$!5 of 8asin >2.2 h 0. )2?

, 2 > 1.3 5-3?

>/$ 0.13?- ,

>d? Cri!#ria

i$r# 29.12 T&pi+a" Drop Spi""(a& and So%# '&dra"i+ D#si$n Cri!#ria >US Soi" Cons#r6a!ion S#r6i+#7 19)*?.

>

2

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100 %%

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14/33


2- -

JJJJJJJ/1_ /2__________ >JJJJJJJJJJ/3_

>8? S#+!ion on C#n!r#"in#

i$r# 29.13 Bo In"#! Drop S!r+!r# >US D#p!. of Transpor!a!ion7 193?

S#6#ra" asp#+!s of o!fa"" d#si$n %s! 8# $i6#n s#rios

+onsid#ra!ion. T5#s# in+"d# !5# f"o("in# or in6#r! >insid#

8o!!o%? #"#6a!ion of !5# propos#d s!or%(a!#r drain o!"#!7

!ai"(a!#r #"#6a!ions7 !5# n##d for #n#r$& dissipa!ion7 and!5# ori#n!a!ion of !5# o!"#! s!r+!r#.

T5# f"o("in# or in6#r! #"#6a!ion of !5# propos#d o!"#!

s5o"d 8# #:a" !o or 5i$5#r !5an !5# f"o("in# of !5#

o!fa"". If !5is is no! !5# +as#7 !5#r# %a& 8# a n##d !o

p%p or o!5#r(is# "if! !5# (a!#r !o !5# #"#6a!ion of !5#

o!fa"" >s## C5ap!#r *?.

T5# !ai"(a!#r d#p!5 or #"#6a!ion in !5# s!or% drain o!fa""

%s! 8# +onsid#r#d +ar#f""&. E6a"a!ion of !5# 5&dra"i+

$rad# "in# for a s!or% draina$# s&s!#% 8#$ins a! !5#

s&s!#% o!fa"" (i!5 !5# !ai"(a!#r #"#6a!ion. or %os!

d#si$n app"i+a!ions7 !5# !ai"(a!#r (i"" #i!5#r 8# a8o !5#

+ro(n of !5# o!"#! or +an 8# +onsid#r#d !o 8# 8#!(##n

!5# +ro(n and +ri!i+a" d#p!5 of !5# o!"#!. T5# !ai"(a!#r

%a& a"so o++r 8#!(##n !5# +ri!i+a" d#p!5 and !5# in6#r! of

!5# o!"#!K 5o(#6#r7 !5# s!ar!in$ poin! for !5# 5&dra"i+

$rad# "in# d#!#r%ina!ion s5o"d 8# #i!5#r !5# d#si$n

!ai"(a!#r #"#6a!ion7 or $c>c+ D?27 (5i+5#6#r is 5i$5#r.

An #+#p!ion !o !5# a8o r"# (o"d 8# for a 6#r& "ar$#

o!fa"" (i!5 "o( !ai"(a!#r (5#r# a (a!#r srfa+# profi"#

+a"+"a!ion (o"d 8# r#:ir#d !o d#!#r%in# !5# "o+a!ion

(5#r# !5# (a!#r srfa+# (i"" in!#rs#+! !5# !op of !5# 8arr#"and f"" f"o( +a"+"a!ions +an 8#$in. In !5is +as#7 !5#

do(ns!r#a% (a!#r srfa+# #"#6a!ion (o"d 8# 8as#d on

+ri!i+a" d#p!5 or !5# d#si$n !ai"(a!#r #"#6a!ion7 (5i+5#6#r

(as 5i$5#r.

If !5# o!fa"" +5ann#" is a ri6#r or s!r#a%7 i! %a& 8#

n#+#ssar& !o +onsid#r !5# ;oin! or +oin+id#n!a" pro8a8i"i!&

of !(o 5&dro"o$i+ #6#n!s o++rrin$ a! !5# sa%# !i%# !o

ad#:a!#"& d#!#r%in# !5# #"#6a!ion of !5# !ai"(a!#r in !5#

r#+#i6in$ s!r#a% >s## +5ap!#r *..2 for d#!ai"s?.

En#r$& dissipa!ion %a& 8# r#:ir#d !o pro!#+! !5# s!or%

drain o!"#!. T5is is !o pr#6#n! #rosion of !5# o!fa"" 8#d

and 8an=s. Riprap aprons or #n#r$& dissipa!#rs s5o"d 8#

pro6id#d if 5i$5 6#"o+i!i#s ar# #p#+!#d.

T5#r# %a& 8# ins!an+#s in (5i+5 an #+#ssi6# !ai"(a!#r

+as#s f"o( !o 8a+= p !5# s!or% draina$# s&s!#% and o!

of in"#!s and %an5o"#s7 +r#a!in$ n#p#+!#d and p#r5aps

5a


15/33


o!"#! +an so%#!i%#s a""#6ia!# !5is +ondi!ion >s## +5ap!#r

*?K o!5#r(is#7 i! %a& 8# n#+#ssar& !o iso"a!# !5# s!or%

drain fro% !5# o!fa"" 8& s# of a p%p s!a!ion >s##

C5ap!#r *?.

T5# ori#n!a!ion of !5# o!fa"" is ano!5#r i%por!an! d#si$n

+onsid#ra!ion. 5#r# pra+!i+a"7 !5# o!"#! of !5# s!or%

drain s5o"d 8# posi!ion#d in !5# o!fa"" +5ann#" so !5a! i!is poin!#d in a do(ns!r#a% dir#+!ion. T5is (i"" r#d+#

!r8"#n+# and !5# po!#n!ia" for #+#ssi6# #rosion. If !5#

o!fa"" s!r+!r# +anno! 8# ori#n!#d in a do(ns!r#a%

dir#+!ion7 !5# po!#n!ia" for o!"#! s+or %s! 8# +onsid#r#d.

or #a%p"#7 (5#r# a s!or% drain o!fa"" dis+5ar$#s

p#rp#ndi+"ar !o !5# dir#+!ion of f"o( of !5# r#+#i6in$

+5ann#"7 +ar# %s! 8# !a=#n !o a6oid #rosion on !5#

opposi!# +5ann#" 8an=. If #rosion po!#n!ia" #is!s7 a

+5ann#" 8an= "inin$ of riprap or o!5#r si!a8"# %a!#ria"

s5o"d 8# ins!a""#d on !5# 8an=. A"!#rna!i6#"&7 an #n#r$&

dissipa!#r s!r+!r# +o"d 8# s#d a! !5# s!or% drain

o!"#!.

29.; TRANSITIONS AND CONSTRICTIONS

C5ann#" !ransi!ions >i$r# 29.1? ar# !&pi+a""& s#d !o

a"!#r !5# +ross-s#+!iona" $#o%#!r&7 !o a""o( !5# (a!#r(a&

!o fi! (i!5in a %or# +onfin#d ri$5!-of-(a&7 or !o prpos#"&

a++#"#ra!# !5# f"o( !o 8# +arri#d 8& a sp#+ia"is#d 5i$5

6#"o+i!& +on6#&an+#. Cons!ri+!ions +an appr#+ia8"& r#s!ri+!

and r#d+# !5# +on6#&an+# in a %ann#r (5i+5 is #i!5#r

d#!ri%#n!a" or 8#n#fi+ia". or #a%p"#7 a 8rid$#7 8o

+"6#r!7 or o!5#r +ons!ri+!ion %a& in+r#as# ps!r#a%

f"oodin$ 8& #n+roa+5in$ !oo far in!o !5# f"oodp"ain+on6#&an+#7 (5#r#as in ano!5#r si!a!ion7 a 5&dra"i+

+on!ro" s!r+!r# +an 8# #%p"od !o prpos#"& ind+# an

ps!r#a% spi"" in!o a s!ora$# fa+i"i!&.

T5# prpos# of !5is s#+!ion is !o 8ri#f"& o!"in# !&pi+a"

d#si$n pro+#dr#s for !ransi!ion and +ons!ri+!ion s!r+!r#s

!5a! %a& 8# r#:ir#d for #n$in##r#d (a!#r(a&s.

29.;.1 Transi!ion Ana"sis

$a% Subcritical "ransitions

Transi!ions for s8+ri!i+a" f"o( fr#:#n!"& in6o"6# "o+a"is#d

or 8an= "inin$ +onfi$ra!ions (5i+5 a""o( +5an$# in !5#

+ross s#+!ion and prod+# a (a!#r srfa+# profi"# 8as#d on

$rada""& 6ari#d f"o(. T5# #n#r$& "os! !5ro$5 a !ransi!ion

is a fn+!ion of !5# fri+!ion7 #dd& +rr#n!s7 and !r8"#n+#.

T5# in!#n! is of!#n !o %ini%is# fri+!ion "oss#s andor T5#

in!#n! is of!#n !o %ini%is# fri+!ion "oss#ss andor #rosion

!#nd#n+i#s. Ea%p"#s in+"d# !ransi!ions 8#!(##n

!rap#fro% ps!r#a% !o do(ns!r#a% "o+a!ions?. i$r# 29.1*

i""s!ra!#s so%# of !5#s# !ransi!ions. /oss +o#ffi+i#n!s

s5o(n in Ta8"# 29. ar# app"i#d !o !5# diff#r#n+# in !5#

6#"o+i!& 5#ad7 as s5o(n is E:a!ion 29.11.

Ta8"# 29.2 S8+ri!i+a" Transi!ion En#r$& /oss Co#ffi+i#n!s

Con!ra+!ion Epansion

/#ss !5an 100 %% 8#!(##n

0.00 0.00

/#ss !5an 12.)V 8#!(##n+#n!r#"in# and !an$#n! "in#s

O !o 0.10 O !o 0.10

arp#d T&p# 0.10 0.20

C&"indri+a" Fadran! T&p# 0.1) 0.2)

,od#s! Transi!ions 0.30 0.)0S!rai$5! Un# T&p# 0.30 0.)0

S:ar# End#d T&p# 0.30 0.)

Ana"&sis of !ransi!ions r#:ir#s +ar#f" (a!#r srfa+# profi"#

ana"&sis in+"din$ 6#rifi+a!ion of #ff#+!i6# +5ann#" 5&dra"i+

+on!ro"s. I! is no! n+o%%on !o 5a6# a !ransi!ion (5i+5 is

firs! !5o$5! !o 8# p#rfor%in$ in a s8+ri!i+a" %od#7 8!

s8s#:#n!"& fond !o prod+# a sp#r+ri!i+a" profi"# (i!5 a

5&dra"i+ ;%p.

En#r$& /oss >%? Co#ffi+i#n! >171 772? >29.11?

(5#r#7

>771 h?-%=

f"o(6#"o+i!& ps!r#a% of !ransi!ion

1* f"o( 6#"o+i!& do(ns!r#a% of !ransi!ion

$b% Suercritical "ransition 0nalysis

Sp#r+ri!i+a" !ransi!ions ar# 8#&ond !5# s+op# of !5is

%ana" and r#:ir# sp#+ia" ana"&sis (5#n s#d. T5#

+onfi$ra!ion of a sp#r+ri!i+a" !ransi!ion is #n!ir#"&

diff#r#n! fro% s8+ri!i+a" !ransi!ions. I%prop#r"& d#si$n#d

and +onfi$r#d sp#r+ri!i+a" !ransi!ions +an prod+# s5o+=

(a6# pa!!#rns (5i+5 r#s"! in +5ann#" o6#r!oppin$ and

o!5#r 5&dra"i+ and s!r+!ra" pro8"#%s.

29.;.2 Cons!ri5!ion Ana"sis

$a% 'onstriction with Ustream Subcritical 1low

T5#r# ar# a 6ari#!& of s!r+!r#s !5a! ar# +ons!ri+!ions.

T5#& +an in+"d# 8rid$#s7 +"6#r!s7 drop s!r+!r#s7 andf"o( %#asr#%#n! d#6i+#s. Cons!ri+!ions of 6arios !&p#s

ar# s#d in!#n!iona""& !o +on!ro" 8#d s!a8i"i!& and ps!r#a%

122

2$ 2$



16/33


(a!#r srfa+# profi"#s. or #a%p"#7 a +ons!ri+!ion %a& 8#

s#d !o +as# (a!#r !o 8a+= p or o6#rf"o( in!o a

d#!#n!ion 8asin.

T5# 5&dra"i+ dis!in+!ion of +ons!ri+!ions is !5a! !5#& +an

+as# rapid"& 6ari#d f"o(. T5# ps!r#a% !ransi!ion "oss

+o#ffi+i#n!s in Ta8"# 2.9 app"&7 8! o!5#r fa+!ors +o%#

in!o p"a&. Si$nifi+an! #ddi#s +an for% ps!r#a% anddo(ns!r#a% of !5# +ons!ri+!ion d#p#ndin$ pon !5#

$#o%#!r&. "o( s#para!ion (i"" s!ar! a! !5# ps!r#a% #d$#

of !5# +ons!ri+!ion7 !5#n !5# f"o( +on!ra+!s !o 8# narro(#r

!5an !5# op#nin$ (id!5. T&pi+a""&7 !5# (id!5 of +on!ra+!ion

is 10M of !5# d#p!5 a! !5# +ons!ri+!ion for #a+5 sid#

8ondar&. or #a%p"#7 a! a !&pi+a" drop (i!5 an a8rp!

+r#s! +on!ra+!ion and ass%in$ +ri!i+a" d#p!5 of 1.0 %7 !5#

+ons!ri+!ion on #a+5 sid# (o"d 8# 100 %%7 or 200 %%

!o!a" +on!ra+!ion fro% !5# op#nin$ (id!5. Bas#d on !5is

+on!ra+!#d (id!5 and an ass%p!ion of +ri!i+a" +ondi!ions

a! !5a! "o+a!ion7 !5# ps!r#a% (a!#r srfa+# profi"# %a& 8#

+o%p!#d.

In +#r!ain +as#s7 !5# f"o( r#$i%# (i"" r#%ain s8+ri!i+a"

!5ro$5 !5# +ons!ri+!ion. C5o(7 19)97 pr#s#n!s $id#"in#s

d#6#"op#d 8& !5# USGS for +ons!ri+!ions (5#r# !5# rod#

n%8#r in !5# +on!ra+!#d s#+!ion do#s no! #+##d 0..

T5#s# +as#s ar# $#n#ra""& %i"d +ons!ri+!ions.

A p5#no%#non of a8rp! +on!ra+!ions >and a8rp!

#pansions? is !5a! !5# 6#"o+i!i#s +an 8# %+5 5i$5#r in

!5# +#n!r# and +5an$# si$nifi+an!"& a+ross !5# +ons!ri+!ion

!5roa! s#+!ion. T5is r#s"!s in a "ar$# #n#r$& +o#ffi+i#n!

and a fr!5#r drop in (a!#r srfa+# o6#r (5a! is firs!

an!i+ipa!#d. T5is +ondi!ion +an prod+# s!ron$ #dd&

+rr#n!s (i!5 a 5i$5 #rosion po!#n!ia". A +ons!ri+!ion in an

op#n +5ann#" n##ds !o 8# +ar#f""& #6a"a!#d for 6#"o+i!&7

s+or7 (a!#r srfa+#7 and r#"a!#d pro8"#%s.

$.

C&"indri+a" Fardran! S!rai$5! /in#

ar #d A8r !

i!B

B#d$#

A8rp!

i$r# 29.1* Transi!ion T&p#s >UDCD7 199?

29-1* Urban Stormwater Management Manual


17/33


Cons!ri+!ions s#d for f"o( d#p!5 +on!ro" or f"o(

%#asr#%#n! d#6i+#s r#:ir# a 5i$5 d#$r## of a++ra+&.

T5# d#si$n infor%a!ion a6ai"a8"# !5a! +an 8# s#d for

#nsrin$ a 5i$5 d#$r## of a++ra+& is "i%i!#d. I! is

ad6isa8"# !o s# %od#"s !#s!#d or pro6#n pro!o!&p#

"a&o!s. As a s#+ondar& op!ion7 ad;s!a8"# #d$# p"a!#s or

o!5#r +o%pon#n!s +an 8# pro6id#d !o a""o( "a!#r +5an$#s

a! %ini%a" +os! if !5# +ons!r+!#d fa+i"i!i#s s5o"d n##d

r#fin#%#n!.

$b% 'onstriction with Ustream Suercritical 1low

T5is si!a!ion is 5i$5"& +o%p"# and 8#&ond !5# s+op# of

!5is %ana". Possi8"# s5o+= (a6#s or +5o=#d f"o( +asin$

5i$5 ps!r#a% 8a+=(a!#r or a 5&dra"i+ ;%p ar# %a;or

+on+#rns. T5# si!a!ion is !o 8# a6oid#d in r8an draina$#

8#+as# of in5#r#n! ins!a8i"i!i#s.

29.7 BENDS AND ON!L"ENES

G#n#ra" +onsid#ra!ions for "in#d +5ann#"s and +ondi!s ar#

dis+ss#d in C5ap!#rs 2 and 2). Addi!iona" #%p5asis is

add#d 5#r#in for +#r!ain si!a!ions. C5ann#"s and +ondi!s

!5a! prod+# sp#r+ri!i+a" f"o( %a& r#:ir# sp#+ia"

s!r+!ra" or d#si$n +onsid#ra!ions. T5is dis+ssion is

"i%i!#d sin+# !5#s# !&p#s of s!r+!r#s ar# asso+ia!#d (i!5

5&dra"i+ p#rfor%an+# !5a! $#n#ra""& #+##ds !5#

r#+o%%#nd#d +ri!#ria for %os! #n$in##r#d (a!#r(a&s.

E!#nsi6# s!d&7 sp#+ia"is#d %od#""in$7 andor ana"&sis %a&

8# r#:ir#d for !5#s# si!a!ions.

C5ann#" +onf"#n+#s ar# +o%%on"& #n+on!#r#d in d#si$n.

"o( ra!#s +an 6ar& dispropor!iona!#"& (i!5 !i%# so !5a!

5i$5 f"o(s fro% ps!r#a% +5ann#" +an dis+5ar$# in!o

do(ns!r#a% +5ann#" (5#n i! is a! 5i$5 or "o( "#6#".

D#p#ndin$ on !5# $#o%#!r& of !5# +onf"#n+#7 #i!5#r

+ondi!ion +an 5a6# i%por!an! +ons#:#n+#s7 s+5 as

sp#r+ri!i+a" f"o( and 5&dra"i+ ;%p +ondi!ions7 and r#s"!

in !5# n##d for s!r+!r#s.

T5# %ain #%p5asis in !5is s#+!ion is on s8+ri!i+a" f"o(

+ondi!ions. Sin+# sp#r+ri!i+a" +ondi!ions +an o++r in

6arios si!a!ions7 so%# +ondi!ions ar# $#n#ra""& r#6i#(#dK

5o(#6#r7 sp#r+ri!i+a" f"o( ana"&sis is no! d#s+ri8#d in

d#!ai".

29.).1 B#nds

$a% Subcritical &ends

S8+ri!i+a" 8#nds ar# r#:ir#d !o 5a6# +#r!ain %ini%%

+r6a!r#s d#s+ri8#d in C5ap!#rs 2) and 2. I! is

i%por!an! !5a! !5# d#si$n#r r#+o$nis# !5# +ons#:#n+#s of

approa+5in$ and #+##din$ !5#s# +ri!#ria. C5o(7 19)97

Ros#7 19*97 and o!5#rs i""s!ra!# f"o( pa!!#rns7

sp#r#"#6a!ion7 and 8a+=(a!#r or f"o( r#sis!an+#

+5ara+!#ris!i+s. Sp#r#"#6a!ion r#f#rs !o a ris# in !5# (a!#r

srfa+# on !5# o!#r sid# of !5# 8#nd. Eff#+!i6#"&7 !5#

8#nd +an 8#5a6# "i=# a +on!ra+!ion7 +asin$ 8a+=(a!#r

ps!r#a% and in a++#"#ra!#d 6#"o+i!& 9.1 %s2?

r = +5ann#" +#n!r#"in# radis >%?

$b% Suercritical &ends

As (i!5 sp#r+ri!i+a" !ransi!ions7 !5# 5&dra"i+s for

sp#r+ri!i+a" 8#nds ar# +o%p"#!#"& diff#r#n! fro% !5#

5&dra"i+s for s8+ri!i+a" 8#nds. Sp#r+ri!i+a" +5ann#"s ar#

$#n#ra""& no! d#sira8"# in r8an draina$#. 'o(#6#r7

sp#+ia" si!a!ions %a& o++r (5#r# sp#r+ri!i+a" f"o(s #n!#r

a +r6#d +5ann#"7 for #a%p"#@

a! +onf"#n+#s (5#r# on# +5ann#" is "ar$#"& #%p!&7

and !5# #n!#rin$ f"o( #pands and 8#+o%#s

sp#r+ri!i+a"

a! a s5arp 8#nd in a +ondi! (5os# s"op# in5#r#n!"&

"#ads !o sp#r+ri!i+a" +ondi!ions

a! a +5ann#" drop !5a! na6oida8"& #nds p on a +r6#

T5# =#& p5#no%#non !o 8# a(ar# of is s5o+= (a6#s7 of

(5i+5 !5#r# ar# !(o !&p#s7 posi!i6# and n#$a!i6#. On !5#

o!sid# of an an$"ar 8#nd7 a posi!i6# s5o+= (a6# (i""

o++r (5i+5 r#s"!s in a ris# in !5# (a!#r srfa+#. T5#(a6# is s!a!ionar& and +ross#s !o !5# insid# of !5# +5ann#"7

and !5#n +an +on!in# !o r#f"#+! 8a+= and for!5. 5#r#

!5# f"o( pass#s !5# insid# an$"ar 8#nd7 a s#para!ion (i""

o++r and a n#$a!i6# s5o+= (a6# or drop in !5# (a!#r

srfa+# (i"" o++r. T5is s!a!ionar& n#$a!i6# s5o+= (a6# (i""

+ross !o !5# o!sid# of !5# +5ann#". Bo!5 s5o+= (a6#s (i""

+on!in# !o r#f"#+! off !5# (a""s7 r#s"!in$ in a 6#r&

dis!r8#d f"o( pa!!#rn.

A 8asi+ +on!ro" !#+5ni:# is !o s#! p 8#nd $#o%#!r& !o

+as# !5# posi!i6# s5o+= (a6# !o in!#rs#+! !5# poin! (5#r#

!5# n#$a!i6# (a6# is propa$a!#d. A 8#nd sa""& r#:ir#s

!(o d#f"#+!ions on !5# o!sid# and on# 8#nd on !5# insid#.

A 8#n#fi+ia" asp#+! of !5# s5o+= (a6# is !5a! i! !rns !5#

Urban Stormwater Management Manual 29-1)


18/33


f"o( in a pr#di+!a8"# pa!!#rn7 and !5s !5# +5ann#" (a""s

5a6# no %or# for+# i%pos#d on !5#% o!5#r !5an !5a!

+as#d 8& !5# in+r#as#d >or d#+r#as#d? d#p!5s. T5is

!#+5ni:# is d#s+ri8#d 8& Ipp#n >Ros#7 19*9 and Corps of

En$in##rs7 190? and is a"so r#por!#d 8& C5o(7 19)9.

O!5#r +on!ro" !#+5ni:#s in+"d# 6#r& $rada" 8#nds7 sp#r

#"#6a!#d f"oors7 and +on!ro"s si""s7 8! !5#s# %#!5ods ar#$#n#ra""& "#ss #ffi+i#n!. T5#r# is "i%i!#d da!a on +5ann#"s

(i!5 s"opin$ sid# 8an=s7 8! i! is +"#ar !5#r# is a $r#a!

!#nd#n+& for s5o+= (a6#s !o propa$a!# p sid# s"op#s and

di6#r! f"o( o! of !5# +5ann#".

C5o(7 19)9 s5o(s s#6#ra" $ood p5o!o$rap5s of !5#s#

pro8"#%s. SCS7 19 pr#s#n!s a do+%#n!a" r#por! of a

+r6#d spi""(a& on a %od#s! f"ood +on!ro" s!ora$#.

Drin$ an o6#rf"o( #6#n!7 a s5o+= (a6# pa!!#rn (as

prod+#d !5a! r#s"!#d in no f"o( on on# sid# of !5#

spi""(a& and $r#a! d#p!5s on !5# opposi!#.

A sp#+ia" pro8"#% (i!5 "on$ +ondi!s s#d for f"ood +on!ro"7

par!i+"ar"& "ar$# 8o +"6#r!s7 is !5a! !5#& (i"" 5a6# an

in5#r#n! !#nd#n+& !o(ards sp#r+ri!i+a" f"o( +ondi!ions a!

"#ss !5an f"" +apa+i!&. 5#n !5# f"o( #n+on!#rs 8#nds7

s5o+= (a6#s +an o++r (5i+5 5i! !5# +#i"in$ and +an

"#ad !o #i!5#r pr#ssris#d +ondi!ions andor ns!a8"#

+ondi!ions (5#r# !5# f"o( f"+!a!#s 8#!(##n

sp#r+ri! i+a" and pr#ssr# +ondi!ions7 of!#n #a+#r8a!#d

8& sr$in$7 air f"o(7 and o!5#r pro8"#%s. 4#r& $rada"

8#nds and air 6#n! pro6isions ar# d#sira8"# and !5#

d#si$n#r s5o"d s# +a!ion an&!i%# s5o"d

sp#r+ri!i+a" f"o( #n+on!#r a 8#nd.

29.).2 Conf"#n5#s

On# of !5# %os! diffi+"! pro8"#%s !o d#a" (i!5 is

+onf"#n+#s (5#r# !5# diff#r#n+# in f"o( +5ara+!#ris!i+s

%a& 8# $r#a!. 5#n #n!#rin$ !5# +o%8in#d +5ann#"7 !5#

f"o( +an di6#r$# and drop in "#6#" if !5# f"o( +apa+i!& is

sdd#n"& in+r#as#d. T5is +an r#s"! in 5i$5 6#"o+i!& or

ns!a8"# sp#r+ri!i+a" f"o( +ondi!ions (i!5 a 5i$5 #rosion

po!#n!ia". 5#n si$nifi+an! s#di%#n! f"o(s #is!7

a$$rada!ion +an o++r a! !5# +onf"#n+#7 r#s"!in$ in !5#

"oss of +apa+i!& in on# or 8o!5 ps!r#a% +5ann#"s.

$a% Subcritical 1low 'on/luence Design

T5# d#si$n of +5ann#" ;n+!ions is +o%p"i+a!#d 8& %an&

6aria8"#s s+5 as !5# an$"# of in!#rs#+!ion7 s5ap# and

(id!5 of !5# +5ann#"s7 f"o( ra!#s7 and !&p# of f"o(. T5#

d#si$n of "ar$# +o%p"# ;n+!ions s5o"d 8# 6#rifi#d 8&

%od#" !#s!s.

i$r# 29.1) i""s!ra!#s !(o !&p#s of ;n+!ions. T5#

fo""o(in$ ass%p!ions ar# %ad# for +o%8inin$ s8+ri!i+a"

f"o(s@

1. T5# sid# +5ann#" +ross-s#+!ion is !5# sa%# s5ap# as!5# %ain +5ann#" +ross-s#+!ion

2. T5# 8o!!o% s"op#s ar# #:a" for !5# %ain +5ann#" and

sid# +5ann#"

3. "o(s ar# para""#" !o !5# +5ann#" (a""s i%%#dia!#"&

a8o and 8#"o( !5# ;n+!ion

*. T5# d#p!5s ar# #:a" i%%#dia!#"& a8o !5# ;n+!ion

in 8o!5 !5# sid# and %ain +5ann#"

). T5# 6#"o+i!& is nifor% o6#r !5# +ross-s#+!ions

i%%#dia!#"& a8o and 8#"o( !5# ;n+!ion

Ass%p!ion No. 3 i%p"i#s !5a! 5&dros!a!i+ pr#ssr#

dis!ri8!ions +an 8# ass%#d7 and ass%p!ion No. )

s$$#s!s !5a! !5# %o%#n!% +orr#+!ion fa+!ors 8#

#:a" !o #a+5 o!5#r a! !5# r#f#r#n+# s#+!ions.

T5# #:a!ion $o6#rnin$ f"o( +ondi!ions for a 6#r!i+a"

(a""#d +5ann#"7 (i!5 !5# %ain +5ann#" (id!5 8#in$

+ons!an!7 is >i$r# 29.1)>a??@(A22 12

+cos@c >29.13a?

Or for a 6#r!i+a" (a""#d +5ann#"K %ain +5ann#" (id!5 6ar#s

>i$r# 29.1)>8??@

12 2 213 *.b ,2 F1 i$r# 29.1)>a??@

*11 32 A &362 F12

= 2 Q 3 3g 0l+ cos@ '- +A:(B.dg 0. g0- 2 3

>29.13+?

Or for a !rap#


19/33


19*9?. In s8+ri!i+a" f "o(7 8a+=(a!#r #ff#+!s ar#propa$a!#d ps!r#a% !5#r#8& !#ndin$ !o #:a"is# !5# f"o(

d#p!5s in !5# %ain and sid# +5ann#"s. 'o(#6#r7

8a+=(a!#r +anno! 8# propa$a!#d ps!r#a% in sp#r+ri!i+a"

f"o( and f"o( d#p!5s in !5# %ain and sid# +5ann#"s +anno!

$#n#ra""& 8# #p#+!#d !o 8# #:a". Ln+!ions for rapid

f"o(s and 6#r& s%a"" ;n+!ion an$"#s ar# d#si$n#d

ass%in$ #:a" (a!#r srfa+# #"#6a!ions in !5# sid# and

%ain +5ann#"s.

S!andin$ (a6#s >Ipp#n7 19)1? in sp#r+ri!i+a" f"o( a! op#n

+5ann#" ;n+!ions +o%p"i+a!# f"o( +ondi!ions. T5#s# (a6#s

%a& n#+#ssi!a!# in+r#as#d (a"" 5#i$5!s in !5# 6i+ini!& of !5#

;n+!ion. T5# s!di#s 8& Bo(#rs7 19)0 indi+a!# !5a! a

5&dra"i+ ;%p %a& for% in on# or 8o!5 of !5# in"#!

+5ann#"s7 d#p#ndin$ on !5# f"o( +ondi!ions. B#5"=#7 19

+o%p"#!#d a %od#" s!d& and pr#s#n!#d d#si$n

$id#"in#s !o addr#ss !5#s# pro8"#%s.

a6# +ondi!ions !5a! %a& 8# prod+#d 8& rapid f"o( inand do(ns!r#a% of a !&pi+a" ;n+!ion ar# s5o(n in

i$r# 29.19. On# ar#a of %ai%% (a6# 5#i$5! +an

o++r on !5# sid# +5ann#" (a"" opposi!# !5# ;n+!ion poin!

and ano!5#r on !5# %ain +5ann#" ri$5! (a"" do(ns!r#a%

fro% !5# ;n+!ion. B#5"=#7 19 5as +ond+!#d a s#ri#s of

"a8ora!or& !#s!s (5i+5 indi+a!# !5a! (a6# pi"#p a$ains!

!5# +5ann#" (a""s +an 8# p !o s#6#n !i%#s !5# ini!ia" d#p!5

for a f"o( rod# n%8#r of for. T5# d#si$n of (a""s !o

+on!ain !5#s# (a6# 5#i$5!s o6#r "on$ +5ann#" dis!an+#s is

sa""& no! #+ono%i+a". T5# pra+!i+a? r#%#d& is !o

r#d+# or %ini%is# s!andin$ (a6#s.

P#a= f"o(s fro% !5# sid# +5ann#" %a& no! o++r

si%"!an#os"& (i!5 p#a= f"o(s in !5# %ain +5ann#".

/a8ora!or& !#s!s 8& B#5"=#7 19 indi+a!# !5a! !5#

o++rr#n+# of d#si$n f"o( in on# of !5# +5ann#"s (i!5 ra192?7 !5# fa""in$profi"# r#s"!s if !5# ra!io of !5# 5#i$5! of !5# (#ir7 c, !o!5# +5ann#" sp#+ifi+ #n#r$&7 ,E r#f#r#n+#d !o !5# !opof !5# (#ir7 is "#ss !5an 0..

29.i$r# 29.1?.

29.%? c = 5#i$5!

of (#ir >%? w = +5ann#"

sp#+ifi+ #n#r$& >%?

and7

>29.1*?

Urban Stormwater Management Manual 2A-1C


20/33


47.1. O A1

# .

>a? P"an - Cons!an! id!5

vi83

$43

81W 83

>8? P"an - Un#:a" id!5

i$r# 29.1) C5ann#" Ln+!ion D#fini!ion S=#!+5#s

Ar#a

,ain C5ann#"

vi

Y1y

Possi8"#a6# ron!s 7

5 1 r#i 3:..?

/ Y 7

3DR#f"#+!#da6#s

\

$*

2

) 9.1 %s2)

a' pr#ssr#-5#ad +orr#+!ion

Kin nor%a" d#p!5 of f"o( in approa+5 +5ann#" >%?

c = 5#i$5! of !5# (#ir a8o !5# +5ann#" 8o!!o% >%?

4a"#s for a and a' of 1.2 and 1.0 r#sp#+!i6#"& +an 8#

s#d in !5# approa+5 +5ann#"7 (5i"# a! !5# "o(#r #nd of

!5# (#ir 6a"#s of 1.* and 0.9) +an 8# s#d for a and a'

r#sp#+!i6#"&.

(b) 3ising #ater Sur/ace

T5# ana"&sis for #s!i%a!in$ !5# (#ir "#n$!5 for !5# risin$

(a!#r srfa+# profi"# is 8as#d on !5# !5#or#!i+a" #:a!ions

d#6#"op#d 8& D#,ar+5i >Co""in$# 19)?@

L = ' L F G : -

(5#r#7

/ONGITUDINA/ SECTION

L "#n$!5 of (#ir >%?

@ = +5ann#" (id!5 >%?

' = +ons!an! >0.3) for a fr## napp#?

0 : 6ari#d f"o( fn+!ion >i$r# 37 Co""in$# 19)?E

.>- = d#p!5 in +5ann#" >%?

E = sp#+ifi+ #n#r$& >%?

E:a!ion 29.1 is r#+o%%#nd#d for s# on"& in !5# +as#

of a risin$ (a!#r srfa+# profi"#. ,#!+a"f and Edd& In+.

>192? indi+a!#s !5a! !5is #:a!ion (or=s 8#s! (5#n !5#

rod# n%8#r is 8#!(##n Q 0.3 - 0.92.

29.9 !LO# SPLITTER

A f"o( sp"i!!#r is a sp#+ia" s!r+!r# d#si$n#d !o di6id# a

sin$"# f"o( and di6#r! !5# par!s in!o !(o or %or#

do(ns!r#a% +5ann#"s. A f"o( sp"i!!#r +an s#r6# !5r##

fn+!ions.

>a? R#d+!ion in (a!#r srfa+# #"#6a!ion X B& di6idin$ !5#

f"o( fro% a "ar$# pip# in!o %"!ip"# +ondi!s7 !5#

5#i$5! of f"o( >%#asr#d fro% !5# f"o( "in# !o !5#

(a!#r srfa+# >or for pip#s f"o(in$ f""7 !5# insid#

dia%#!#r? +an 8# r#d+#d. T5is %a& 8# n#+#ssar& !o

ro!# f"o(s nd#r i%%o6a8"# o8s!r+!ions.

A

/ala!#r profi"#

51 r

En#r$& Grad# /in#

E66++ 42= ++ d

2$

6+H.

C5ann#" In6#r!

O!r-6--1& F . G,#!+a"f Edd&7 192?

>29.1?

cc 4n2

2

1 #irn


7

/

B

A5

&

Yc


22/33


29.9.1 D#si$n Consid#ra!ion

$a%Condi!ion 1

C

B c%it

>8? Condi!ion 2

J

5 Q1 1; "ritPC H +rt and /

Q'e

2d2K

>+? Condi!ion 3

i$r# 29.1 Possi8"# T&p#s of a!#r Srfa+# Profi"#s

a! a Sid#-o6#rf"o( #ir

>,#!+a"f Edd&7 192?.

29.9.2 D#si$n Cri!#ria

>8? Di6idin$ f"o(s (5#r#6#r n#+#ssar& Ea%p"#s of !5is

in+"d# di6ision of #is!in$ "ar$# sp#+ia"-d#si$n

+ondi!s7 s+5 as ar+5#s or 5ors#s5o#s7 in!o "#ss#p#nsi6# %"!ip"#-pip# +on!ina!ions and di6ision of

f"o( 8#!(##n "o( and 5i$5-f"o( +ondi!s a! !5#

in!a=# of an in6#r!#d sip5on.

>+? To r#s!ri+! f"o(s !o (a!#r :a"i!& !r#a!%#n! fa+i"i!i#s

and 8&pass !5# r#%ainin$ 5i$5#r f"o(s arond !5#

fa+i"i!i#s >off-"in#?. T5is +an 8# a++o%p"is5#d 8&

sp"i!!in$ f"o(s in #+#ss of !5# (a!#r :a"i!& d#si$n

f"o( ps!r#a% of !5# fa+i"i!& and di6#r!in$ 5i$5#r

f"o(s !o a 8&pass pip# or +5ann#". T5# 8&pass

!&pi+a""& #n!#rs a d#!#n!ion pond or !5# do(ns!r#a%

r#+#i6in$ draina$# s&s!#%. A +r+ia" fa+!or in

d#si$nin$ f"o( sp"i!!#rs is !o #nsr# !5a! "o( f"o(s ar#

d#"i6#r#d !o !5# !r#a!%#n! fa+i"i!& p !o !5# (a!#r

:a"i!& d#si$n f"o( ra!#. A8o !5is ra!#7 addi!iona"

f"o(s ar# di6#r!#d !o !5# 8&pass s&s!#% (i!5 %ini%a"

in+r#as# in 5#ad a! !5# f"o( sp"i!!in$ s!r+!r# !o

a6oid sr+5ar$in$ !5# (a!#r :a"i!& fa+i"i!& nd#r 5i$5

f"o( +ondi!ions.

i$r# 29.19 s5o(s a !&pi+a" f"o( sp"i!!#r %ad# of

%an5o"#s (i!5 +on+r#!# 8aff"#s. i$r# 29.20 s5o(s a

!&pi+a" di6#rsioniso"a!ion s!r+!r#.

T5# f"o( sp"i!!#r s5a"" 8# d#si$n#d !o +a!#r for

%on!5 ARI s!or%.

T5# !op of !5# (#ir s5a"" 8# "o+a!#d a! !5# (a!#r

srfa+# for !5# 3-%on!5 ARI (a!#r :a"i!& d#si$n

s!or%.

T5# %ai%% 5#ad o6#r !5# (#ir s5a"" 8#

%ini%is#d

for f"o( in #+#ss of !5# (a!#r :a"i!& d#si$n f"o(s.

29.1' LO- SPREADER

"o( spr#ad#rs ar# s#d !o nifor%"& spr#ad f"o(s a+ross

!5# inf"o( por!ion of (a!#r :a"i!& fa+i"i!& >#.$. sand fi"!#r78iofi"!ra!ion s(a"#7 or fi"!#r s!rip?. Op!ions A !5ro$5 C

>s## S#+!ion 29.10.2? +an 8# s#d for spr#adin$ f"o(s !5a!

5a6# a"r#ad& +on+#n!ra!#d. Op!ion D is on"& for f"o(s

!5a! ar# a"r#ad& n+on+#n!ra!#d and #n!#r a fi"!#r s!rip

or 8iofi"!ra!ion s(a"#.

29.1'.1 =#n#ra" D#si$n Cri!#ria

5#r# f"o( #n!#rs !5# spr#ad#r !5ro$5 a pip#7 i! is

r#+o%%#nd#d !5a! !5# pip# 8# s8%#r$#d !o

pra+!i+a""& dissipa!# #n#r$&.

Ro+= pro!#+!ion is r#:ir#d a! o!fa""s.

P K___

KQl

T(o %a;or +onsid#ra!ions #is! for !5# d#si$n of f"o(-

sp"i!!in$ d#6i+#s@ Q2

(a* '#ad /oss '&dra"i+ dis!r8an+#s a! !5# poin! o

f"o( di6ision r#s"! in na6oida8"# 5#ad "oss#s. T5#s#"oss#s7 5o(#6#r7 %a& 8# r#d+#d 8& !5# in+"sion of

prop#r f"o( d#f"#+!ors in !5# d#si$n of !5# s!r+!r#.

D#f"#+!ors %ini%is# f"o( s#para!ion 8& pro6idin$ a

$rada" !ransi!ion for !5# f"o(7 ra!5#r !5an 8& for+in$

a8rp! +5an$#s inf"o( dir#+!ion.

()* D#8ris In a"" !ransi!ions fro% "ar$# !o s%a""#r pip#s7 d#8ris

a++%"a!ion is a po!#n!ia" pro8"#%. Tr## "i%8s

and o!5#r d#8ris !5a! f"o( fr##"& in !5# "ar$#r pip#

%a& no! fi! in !5# s%a""#r pip#>s? and %a& r#s!ri+! f"o(.

In addi!ion7 f"o( sp"i!!#rs +as# %a;or f"o(

dis!r8an+#s r#s"!in$ in !5# r#$ions of d#+r#as#d

6#"o+i!&. T5is r#d+!ion +as#s %a!#ria" ssp#nd#d in!5# s!or%(a!#r f"o( !o s#!!"# in !5# sp"i!!#r 8o.

A"!5o$5 !5# d#f"#+!or d#si$n s5o"d %ini%is# 6#"o+i!&

r#d+!ion as %+5 as possi8"#7 !o!a" #"i%ina!ion of !5#

pro8"#% is n"i=#"&. T5#r#for#7 posi!i6# %ain!#nan+#

a++#ss %s! 8# pro6id#d. B#+as# f"o( sp"i!!in$

d#6i+#s ar# %ain!#nan+#-in!#nsi6#7 !5#ir s# s5o"d

8# ;di+ios"& +on!ro""#d 8& !5# #n$in##r.

Q2

dl LQ


23/33



24/33


29.1'.2 D#si$n Cri!#ria for "o, Spr#adin$

Op!ions

T5# fo""o(in$ pr#s#n!s !5# d#si$n +ri!#ria for #a+5 of !5#fo""o(in$ spr#adin$ op!ions@

An+5or#d p"a!# >Op!ion A?

Con+r#!# s%p 8o >Op!ion B? "a!-!opp#d no!+5#d +r8 spr#ad#r >Op!ion C?

T5ro$5-+r8 por!s >Op!ion D? $a%

tion 0 0nchored late i$r# 29.21

s5o(s !5# d#!ai"s of !5# spr#ad#r.

T5# spr#ad#r s5a"" 8# pr#+#d#d 8& a s%p 5a6in$ a

%ini%% d#p!5 of 200 %% and %ini%% (id!5 of 00

%%. T5# s%p ar#a s5a"" 8# "in#d (i!5 s!#ps !o

r#d+# #rosion and !o pro6id# #n#r$& dissipa!ion.

T5# !op of !5# f"o( spr#ad#r p"a!# s5a"" 8# "#6#"7

pro;#+!in$ a %ini%% of )0 %% a8o !5# fina"

$rad# of !5# in6#r! of !5# (a!#r :a"i!& fa+i"i!&. T5# p"a!# s5a"" #!#nd 5ori!&p.?

Inf"o(

1220 %% or Pro6id# S#para!#A++#ss !o Ei!5#r Sid# of Baff"# a""

100 %% T5i+= R#infor+#d Con+r#!#a!#r Fa"i!& D#si$n

B&pass Pip#

To a!#r Fa"i!& a+i"i!&

S%p >Op!iona"?


25/33

srfa+# >(#ir 5#i$5!?. T5# d#si$n (a!#r srfa+# s5o"d 8# s#! !o

pro6id# a %ini%% 5#ad(a!#rdia%#!#r ra!io of 2.0 on !5# o!"#! Pip#.

i$r# 29.19 T&pi+a" "o( Sp"i!!#r D#6i+#


26/33


Di6#rsion #ir

Op#n C5ann#"

/O

'IG' /O

D 200

4 A

SECTION A-A

Op#n C5ann#"Di6#rsion #ir

!o i"!ra!ion Basin

JJJ 'IG' /O

i$r# 29.20 T&pi+a" Iso"a!ionDi6#rsion S!r+!r#

$b% tion & 'oncrete Sum &o

T5is a"!#rna!i6# s#s a r#+!an$"ar +on+r#!# s%p >s##

i$r# 29.22 for d#!ai"s?

T5# (a"" of !5# do(ns!r#a% sid# of !5# +on+r#!# s%p

s5a"" #!#nd a %ini%% )0 %% a8o !5# in6#r! of

!5# !r#a!%#n! 8#d.

T5# do(ns!r#a% (a"" of !5# 8o s5a"" 5a6# r#!rns

a! 8o!5 #nds. Sid# (a""s and r#!rns s5a"" 8# s"i$5!"&

5i$5#r !5an !5# (#ir so !5a! #rosion of !5# sid#

s"op# is %ini%is#d.

$c% tion ' 1latI"oed 9otched 'urb Sreader

"a!-!opp#d no!+5#d +r8 spr#ad#r is s5o(n in

i$r# 29.23. T5# spr#ad#r s#+!ions ar# %ad# of #!rd#d

+on+r#!# "aid sid# 8& sid# and "#6#". T&pi+a""& for !##!5

p#r 1.2) % s#+!ion pro6id# $ood spa+in$. T5# spa+#

8#!(##n ad;a+#n! !##!5 for%s a 6-no!+5.

$d%tion D "hrough 'urb

D#!ai"s of !5# spr#ad#r ar# s5o(n in i$r# 29.2*.

Un+on+#n!ra!#d f"o(s fro% pa6#d ar#as #n!#rin$ fi"!#r

s!rips or +on!inos f"o( 8iofi"!ra!ion s(a"#s +an s# +r8

por!s !o a""o( f"o(s !o #n!#r !5# s!rip or s(a"#. Cr8 por!s

s# pr#fa8ri+a!#d op#nin$s !5a! a""o( +on+r#!# +r8in$

!o 8# por#d or #!rd#d +on!inos"& (5i"# s!i"" pro6idin$

an op#nin$ !5ro$5 !5# +r8 !o ad%i! (a!#r !o !5#(a!#r :a"i!& fa+i"i!&.

Op#nin$s in !5# +r8in$ s5a"" 8# a! r#$"ar in!#r6a"s 8! a!

"#as! #6#r& 3. >%ini%%?. T5# (id!5 of #a+5 +r8 por!

op#nin$ s5a"" 8# 2) %% %ini%%. Approi%a!#"& 1)

p#r+#n! or %or# of !5# +r8 s#+!ion "#n$!5 s5a"" 8# in op#n

por!s7 and no por! s5o"d dis+5ar$# %or# !5an a8o! 10

p#r+#n! of f"o(.

AN4 A

Di6#rsion Pip# Dia%#!#r7 D



27/33


P/AN

Ea%p"# of an+5or#d p"a!# s#d (i!5 a sand fi"!#rZ>,a& a"so 8# s#d (i!5 o!5#r (a!#r :a"i!& fa+i"i!i#s?

SECTION A-A

i$r# 29.21 /#6#" Spr#ad#r >Op!ion A?


In"#! Pip#4-No!+5#dor/#6#" P"a!# Spr#ad#r

An+5or pos!sspa+#d 1. % 0.0or a! #a+5 #ndif (id!5 1. %

Ed$# of Sand

Pond Sid# S"op#

>Sand B#d?

ZSand fi"!#r %a& s# o!5#rspr#adin$ op!ions

A

E!#nd#d in!o s"op# !o pro!#+! fro% !5#100 ar f"o( or !5# 5i$5#s! f"o(

#n!#rin$ (a!#r :a"i!& fa+i"i!&A

JJ Sand /ar

Gra6#" /ar

00 %%

A"!#rna!i6# D#si$n

Ea%p"# of Ca!+5 Basin r#+o%%#nd#d for 5i$5#r f"o( si!a!ions>G#n#ra""& 1*0 /S or $r#a!#r for 100 ar s!or%?

Eis!in Grad#/#6#" Spr#ad#r P"a!#8o"!#d !o an+5or Pos!

00 %% E%8#dd#din!o #isi!n$ $rond


28/33


P/AN

Ea%p"# of a Con+r#!# S%p "o( Spr#ad#rs#d (i!5 a 8iofi"!ra!ion s(a"#

>,a& 8# s#d (i!5 o!5#r .F. a+i"i!i#s?

SECTION A-A

NOTE@

E!#nd sid#s in!o s"op#. '#i$5! of sid# (a"" andr#!rns %s! 8# sffi+i#n! !o 5and"# !5# 100 ar f"o(

or !5# 5i$5#s! f"o( #n!#rin$ !5# a+i"i!&

i$r# 29.22 /#6#" Spr#ad#r >Op!ion B?

29.11 SIPHONS

An& +ondi! !5a! drops nd#r an o8s!r+!ion s+5 as

rai"road !ra+=s7 d#pr#ss#d road(a&s or !i"i!i#s7 and r#$ains

#"#6a!ion a! !5# do(ns!r#a% sid# of !5# o8s!r+!ion is

r#f#rr#d !o as an in6#r!#d sip5on.

B#+as# of !5# in6#r!#d 8o!!o%7 !5# sip5on s!ands f""

s!or% (a!#r #6#n (5#n !5#r# is no f"o(. So%# draina$#

dis!ri+!s dis+ora$# !5# s# of sip5ons on !5# 8asis !5a!

!5# sip5on r#:ir#s %or# fr#:#n! %ain!#nan+# in+"din$

r#%o6a" of d#8ris !5a! %a& +"o$ !5# +ondi!. N#6#r!5#"#ss7

sip5ons 5a6# +#r!ain ad6an!a$#s in par!i+"ar s#!!in$s7

sa""& in r8an ar#as (5#r# o!5#r so"!ions s+5 as f"o(

Con+r#!# S%p

O!fa"" Rip Rap Pad

In"#! Pip#

Sid# (i!5 R#!rns.>S## No!#?

S(a"# Bo!!o%

In"#! Pip#in$ a"" O!"in#

)0 %% C"#aran+#

Con+r#!# S%p>100 %% (a"" !5i+=n#ss?

[C00 %%

29-2* Urban Stormwater Management Manual


29/33


r#-ro!in$ %a& r#s"! in disrp!ions !o !raffi+ and 5i$5#r

+os!s.

Sip5ons ar# nor%a""& sin$"#-or %"!i-8arr#" and +onsis!

of an #n!ran+# s#+!ion7 drop7 d#pr#ss#d r#a+57 ris#7

and o!"#! s!r+!r#. Sip5ons r#:ir# 5&dra"i+ 5#ad !o

op#ra!# prop#r"& and !5# ad#:a+& of a6ai"a8"# 5#ad

s5o"d 8# ass#ss#d #ar"& in !5# d#si$n pro+#ss.Sip5ons +an 8# si%p"#r or sop5is!i+a!#d7 and !5# r#"a!#d

d#si$n #ffor! +an 8# no%ina" or +o%p"#. T5# fo""o(in$

#a%p"#s app"& !o "ar$#7 sop5is!i+a!#d sip5ons (i!5

%"!ip"# appr!#nan+#s so%# or (5i+5 %a& no! a"(a&s

8# n#+#ssar&.

29.11.1 Sin$"#Barr#" Sip@ons

Sin$"#-8arr#" sip5ons +an 8# s#d for +on6#&in$

s!or%(a!#r f"o(s (5#r# !5#r# ar# p#riods of no f"o(

drin$ (5i+5 %ain!#nan+# +an 8# pro6id#d.

E6#n !5o$5 so%# a$#n+i#s "i%i! !5# s"op# of !5# risin$

"#$ of !5# sip5on !o 1JM, s!##p#r s"op#s and #6#n

6#r!i+a" drops and ris#rs ar# a++#p!a8"#7 if %ain!#nan+#

+5a%8#rs (i!5 d#8ris +o""#+!ion s%ps a! !5# 8o!!o% ar#

pro6id#d a! !5# drop and ris#r of !5# sip5on7 as s5o(n in

i$r# 29.2).

S"opin$ "#$s of sip5ons >i$r# 29.2? 5a6# 8##n d#si$n#d

(i!5o! %ain!#nan+# +5a%8#rsK 5o(#6#r7 !5# +5a%8#rs

pro6id# %ain!#nan+# f"#i8i"i!& (i!5 dir#+! a++#ss !o s#r6i+#

!5# sip5on. T5# s!##p#r !5# "#$s of !5# sip5on7 !5# %or#

diffi+"! i! is !o +"#an !5# sip5on fro% s5a""o( %an5o"#s

"o+a!#d n#ar !5# $rond srfa+#7 and L##p %ain!#nan+#

+5a%8#rs r#a+5in$ !o 8arr#" in6#r!s %a& 8# r#:ir#d.

5#r# a 6#r!i+a" drop and ris#r ar# pro6id#d7 !5#& s5o"d

s#r6# as %ain!#nan+# +5a%8#rs and in+"d# a++#ss

do(n !o !5# 8arr#is and s%ps. Snnps "o+a!#d a! !5#

8o!!o% of !5# %ain!#nan+# +5a%8#rs !rap !5#

d#8ris !5a! a++%"a!#s in !5# sip5on.

29.11.2 8"!iBarr#" Sip@ons

In +5ann#"s or s#(#rs !5a! +on6#& a +on!inos f"o(7

(5#r# on# 8arr#" do#s no! 5a6# sffi+i#n! +apa+i!& and !5#f"o( 5as !o 8# di6id#d7 or (5#r# r#dndan+& is r#:ir#d 8&

"o+a" a$#n+i#s7 !5# %"!i-8arr#" sip5on is app"i+a8"#. P"an

and profi"#s of s+5 sip5ons ar# s5o(n in i$r# 29.2.

5#r# r#dndan+& is r#:ir#d for %ain!#nan+# prpos#s7

on# addi!iona" #:a" +apa+i!& 8arr#" is sffi+i#n!. To f"fi"

i!s fn+!ions7 !5# %"!i-8arr#" sip5on r#:ir#s #:ip%#n!

and s!r+!r# 7 in+"din$ $a!#s !5a! +"os# !5# 8arr#" !o 8#

nnain!ain#d (5i"# !5# o!5#r 8arr#" is op#n.

Sp#+ia" s!r+!r# %a& a"so in+"d# a f"o( dis!ri8!ion

+5a%8#r and a f"o( adap!#r +5a%8#r. T5#s# +5a%8#rs

ar# s#d !o +on!ra+! and #pand !5# f"o(s. T5#

dis!ri8!ion +5a%8#r s#r6#s !o dir#+! !5# f"o( fro% on#

s#(#r !o !5# !(o 8arr#is of !5# sip5on a"!#rna!i6#"& s#d7

(5i"# !5# f"o( adap!#r +5a%8#r s#r6#s !o dir#+! !5# f"o(

fro% !5# !(o 8arr#is of !5# sip5on !o on# +ondi!.

29.11.3 D#si$n Cri!#ria and Pra5!i5#s

On# of !5# +ri!i+a? +ri!#ria for !5# d#si$n of sip5ons is !5#

%ain!#nan+# of s#"f-+"#ansin$ 6#"o+i!i#s nd#r (id#"&

6ar&in$ f"o( +ondi!ions >ASCE 199?. Sip5ons s#d for

+on6#&in$ s!or% (a!#r ar# sa""& d#si$n#d for a

6#"o+i!& of 0.9 %s for a )-ar r#!rn in!#r6a" d#si$n

f"o(. Sip5ons (i!5 (a!#r +on!ainin$ a8rasi6#

ssp#nd#d %a!#ria"s s5o"d 8# d#si$n#d for a f"o(

6#"o+i!& "#ss !5an 3 %s.

T5# 5#ad "oss#s !5ro$5 #a+5 of !5# sip5on +o%pon#n!s%s! 8# #s!i%a!#d for !5# prpos# of p"o!!in$ !5# 5&dra"i+

$rad# "in#. Ups!r#a% sr+5ar$in$ s5o"d 8# a6oid#d7 and

!5#r#for# on# of !5# %ain d#si$n o8;#+!i6#s s5o"d 8# !o

%ini%is# !5# 5#ad "oss#s !5ro$5 !5# sip5on. T5# fri+!ion

"oss#s +an 8# #s!i%a!#d 8& sin$ !5# +o%8in#d Dar+&-

#is8a+5 - ,annin$ #:a!ion is s#f" in !5# fo""o(in$

for% >in %#!ri+ ni!s?@

hr =19.) n2L52

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4 6#"o+i!& >%s?

$ a++#"#ra!ion of $ra6i!& >%s2?

,inor "oss#s >s+5 as a! 8#nd7 +on!ra+!ion and #pansion7

and #n!ran+# and #i! "oss#s? +an 8# #s!i%a!#d as

dis+ss#d in C5ap!#r 2). I! s5o"d 8# no!#d !5a! 5#ad

"oss#s in sip5ons +an 8# si$nifi+an!7 par!i+"ar"& in fa!

+oas!a" ar#as7 (5#r# !5# "o( !#rrain do#s no! a""o( for

sr+5ar$# and !5# a6ai"a8"# pro;#+! +orridor is narro(.

T5# si


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Urban Stormwater Management Manual 2A-2J


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Documents

004_4. Hydraulic Structures