124 MODERN SEWER DESIGN - CSPI - Volume · PDF fileThese design aids do ... 126 MODERN SEWER DESIGN Q A 5.2) ... Hydro-logical computations have been made and preliminary design for

124 MODERN SEWER DESIGN

Fabricated fittings are hydraulically superior.

1255. HYDRAULIC DESIGN OF STORM SEWERS

CHAPTER 5

The hydraulic design of a sewer system may have to take into account theeffect of backwater (the limiting effect on flows that a downstream sewerhas on upstream sewers), surcharging, inlet capacity and all energy lossesin the system. Whether each, or all, of these factors have to be considereddepends on the complexity of the sewer system and the objectives of theanalysis (i.e., is the sizing of the system preliminary or final?). Further-more, the degree of analysis will also depend on the potential impact shouldthe sewer system capacity be exceeded. For example, would surchargingresult in damages to private property due to the foundation drains beingconnected to the system or is the depth of flooding on a roadway importantbecause emergency vehicles depend on safe access along the street. Bydefining the above factors the user may then select the level of analysiswhich is required.

This section will outline two methods using hand calculations. Both meth-ods assume that all flows enter the sewer system, i.e., that the inlet capac-ity of the system is not a limiting factor. In addition, a listing of variouscomputer models which may be used in the analysis or design of sewersystems is provided.

Flow charts and nomographs such as those presented in Chapter 4 pro-vide quick answers for the friction head losses in a given run of straightconduit between structures (manholes, junctions). These design aids donot consider the additional head losses associated with other structures andappurtenances common in sewer systems.

In most instances, when designing with common friction flow formulaesuch as the Manning equation, the hydraulic grade is assumed to be equalto the pipe slope at an elevation equal to the crown of the pipe. Considera-tion must therefore also be given to the changes in hydraulic grade line dueto pressure changes, elevation changes, manholes and junctions. The de-sign should then not only be based on the pipe slope, but on the hydraulicgrade line.

A comprehensive storm sewer design must therefore proceed on the ba-sis of one run of conduit or channel at a time, working methodically throughthe system. Only in this way can the free flow conditions be known and thehydraulic grade controlled, thus assuring performance of the system.

Making such an analysis requires backwater calculations for each run ofconduit. This is a detailed process which is demonstrated on the followingpages. However, it is recognized that a reasonable, conservative “estimate”or “shortcut” will sometimes be required. This can be done and is alsodemonstrated on pages 134 through 138.

When using the backwater curve approach the designer should first es-tablish the type of flow (sub-critical or supercritical) in order to determinethe direction his calculations are to proceed.— Super critical flow - designer works downstream with flow.— Sub-critical flow - designer works against the flow.— Hydraulic jump may form if there is super and sub-critical flow in the

same sewer.

BACKWATER ANALYSISGiven is a flow profile of a storm drainage system (see Figures 5.1 and

of Storm SewersHydraulic Design


QA

5.2) where the hydraulic grade is set at the crown of the outlet pipe. Hydro-logical computations have been made and preliminary design for the ini-tial pipe sizing has been completed.

In order to demonstrate the significance of form losses in sewer design,a backwater calculation will be performed in this example with helical cor-rugated steel pipe.

Solution1) Draw a plan and surface profile of trunk storm sewer.2) Design discharges, Q are known; Areas, A are known; Diameters of

pipe, D have been calculated in preliminary design.3) Calculate the first section of sewer line. Note: Normal depth is greater

than critical depth, yn > y

c; therefore, calculations to begin at outfall

working upstream. At “point of control” set design conditions on pro-file and calculations sheet:

Station 0 + 00 (outfall)Design discharge Q = 7.0 m3/s (9)Invert of pipe = 28.2 m (2)Diameter D = l800 mm (3)Hydraulic grade elevation H.G. = 30 m (4)Area of pipe A = 2.54 m2 (6)Velocity = V = 2.8 m/s (8)

Note: (1) Numbers in parentheses refer to the columns on Table 5.2.

Compute:a) ‘K’ value (7): K = (2g) n2 (Derived from Manning-Chezy Formula)

b) ‘Sf’ value (12): S

f = K R4/3

The friction slope (Sf) may also be estimated from Table 5.1 for a given

diameter of pipe and with a known ‘n’ value for the expected flow Q.S

f (12) is a “point slope” at each station set forth by the designer. There-

fore, the friction slope (Avg. Sf) (13) for each reach of pipe L (14), is the

average of the two point slopes Sf being considered.

c) Velocity Head (l0): Hv =

d) Energy grade point, E. G. (11) is equal to H. G. (4) plus the velocityhead (10).

e) Friction loss (15): Multiply Avg. Sf (13) by length of sewer section, L

(14) = Hf (15).

f) Calculate energy losses: Hb, H

j, H

m, H

t, using formulae in text.

g) Compute new H. G. (4) by adding all energy loss columns, (15) thru(19) to previous H. G.Note: If sewer system is designed under pressure (surcharging) thenenergy losses must be added (or subtracted, depending on whether youare working upstream or downstream) to the energy grade line, E. G.

h) Set new E. G. (20) equal to E. G. (11)

V2

2g

[ ]/V2

2g


To fi

nd e

nerg

y lo

ss in

pip

e fri

ctio

n fo

r a g

iven

Q, m

ultip

ly Q

2 by

the

figur

e un

der t

he p

rope

r val

ue o

f n.

Man

ning

Flo

w E

quat

ion:

Q =

(AR2/

3 ) x S1/

2En

ergy

Los

s =

S =

Q2 ( n

)2

n A

R2/3

Tabl

e 5.

1E

nerg

y-lo

ss s

olut

ion

by M

anni

ng’s

form

ula

for

pipe

flow

ing

full

Area

Hydr

aulic

Diam

eter

(m2 )

Radi

us (m

)(m

m)

AR

R2/3

AR2/

3n

= 0.

012

n =

0.01

5n

= 0.

019

n =

0.02

1n

= 0.

024

150

0.02

0.03

80.

112

0.00

236

7757

4692

1911

262

1471

020

00.

030.

050

0.13

60.

004

793

1239

1988

2428

3172

250

0.05

0.06

30.

157

0.00

821

437

760

573

996

530

00.

070.

075

0.17

80.

013

91.2

143

229

279

365

400

0.13

0.10

00.

215

0.02

719

.730

.749

.360

.278

.750

00.

200.

125

0.25

00.

049

5.98

9.35

15.0

018

.32

23.9

360

00.

280.

150

0.28

20.

080

2.26

23.

535

5.67

26.

929

9.04

970

00.

380.

175

0.31

30.

120

0.99

41.

554

2.49

33.

045

3.97

780

00.

500.

200

0.34

20.

172

0.48

80.

762

1.22

31.

494

1.95

190

00.

640.

225

0.37

00.

235

0.26

00.

407

0.65

20.

797

1.04

110

000.

790.

250

0.39

70.

312

0.14

80.

232

0.37

20.

454

0.59

411

000.

950.

275

0.42

30.

402

0.08

90.

139

0.22

40.

273

0.35

712

001.

130.

300

0.44

80.

507

0.05

60.

088

0.14

10.

172

0.22

413

001.

330.

325

0.47

30.

627

0.03

70.

057

0.09

20.

112

0.14

614

001.

540.

350

0.49

70.

764

0.02

50.

039

0.06

20.

076

0.09

915

001.

770.

375

0.52

00.

918

0.01

70.

027

0.04

30.

052

0.06

816

002.

010.

400

0.54

31.

091

0.01

20.

019

0.03

00.

037

0.04

817

002.

270.

425

0.56

51.

282

0.00

90.

014

0.02

20.

027

0.03

518

002.

540.

450

0.58

71.

494

0.00

60.

010

0.01

60.

020

0.02

619

002.

830.

475

0.60

91.

725

0.00

50.

008

0.01

20.

015

0.01

920

003.

140.

500

0.63

01.

978

0.00

40.

006

0.00

90.

011

0.01

522

003.

800.

550

0.67

12.

550

0.00

20.

003

0.00

60.

007

0.00

924

004.

520.

600

0.71

13.

217

0.00

140.

002

0.00

30.

004

0.00

627

005.

720.

675

0.76

94.

404

0.00

070.

0012

0.00

190.

0023

0.00

3030

007.

070.

750

0.82

55.

832

0.00

040.

0007

0.00

110.

0013

0.00

1733

008.

550.

825

0.88

07.

520

0.00

030.

0004

0.00

0 60.

0008

0.00

1036

0010

.17

0.90

00.

932

9.48

40.

0002

0.00

030.

0004

0.00

050.

0006

( n )2 x

10-2

AR

2/3


Tabl

e 5.

2 H

ydra

ulic

cal

cula

tion

shee

t

12

34

56

78

910

1 112

1314

1516

1718

1920

Inve

rtD

H.G.

Sec-

AK

VQ

V2E.

G.S f

Avg.

Sf

LH f

H bH j

H mH t

E.G.

Stat

ion

mm

mm

tion

m2

m/s

m3 /s

2gm

m/m

m/m

mm

mm

mm

m

0 +

000.

000

28.2

0018

0030

.000

02.

540.

0113

02.

87.

00.

3930

.390

0.01

270.

0 127

33.5

0.42

430

.390

0 +

033.

528

28.6

2418

0030

.424

2.54

0.01

130

2.8

7.0

0.39

30.8

140.

0127

0.01

274.

70.

059

0.05

630

.814

0 +

038.

222

28.7

4018

0030

.540

2.54

0.01

130

2.8

7.0

0.39

30.9

300.

0127

0.0 1

2737

.40.

473

30.9

300

+ 07

5.59

029

.212

1800

31.0

122.

540.

0113

02.

87.

00.

3931

.402

0.01

270.

0266

12.3

0.06

10.

132

31.4

020

+ 07

7.87

629

.805

1400

31.2

051.

540.

0095

04.

57.

01.

0532

.255

0.04

060.

0406

30.5

1.23

832

.255

0 +

108.

356

31.0

4314

0032

.443

1.54

0.00

950

4.5

7.0

1.05

33.4

930.

0406

0.04

0630

.51.

238

0.05

333

.493

0 +

138.

836

32.3

3414

0033

.734

1.54

0.00

950

4.5

7.0

1.05

34.7

840.

0406

0.02

9913

.10.

092

1.08

534

.784

0 +

141.

900

33.7

1112

0034

.911

1.13

0.00

785

3.1

3.5

0.49

35.4

010.

0191

0.01

9135

.00.

669

35.4

010

+ 17

6.90

034

.380

1200

35.5

801.

130.

0078

53.

13.

50.

4936

.070

0.01

910.

0351

13.5

0.12

31.

299

36.0

700

+ 18

0.42

136

.402

1600

37.0

020.

280.

0063

63.

51.

00.

6437

.492

0.05

110.

0511

35.5

1.81

40.

032

37.4

920

+ 21

5.89

238

.248

1600

38.8

480

0.28

0.00

636

3.5

1.0

0.64

39.3

380.

0511

39.3

38

n =

Varia

ble

K =

2g(n

2 )S f =

K (

V2 ) /R

4/3

2

g�

H frict

ion =

6.1

91

�H fo

rm =

2.6

57


i) Determine conduit invert (2). In the example we are designing for fullflow conditions; therefore, H. G. (4) is at crown of pipe and invert (2) isset by subtracting, D (3) from H. G. (4).

j) Continue to follow the above procedure taking into account all formhead losses.

k)Complete profile drawing; showing line, grade and pipe sizes. This savestime and usually helps in spotting any design errors.

Energy LossesStation 0 + 033.528 to 0 + 038.222 (Bend)

Hb = K

b , where K

b = 0.25

, central angle of bend = 30o

Kb = 0.25 = 0.1443

Hb = 0.1433 (0.39) = 0.056 m

Station 0 + 075.590 to 0 + 077.876 (Transition)

Ht = 0.2

= 0.2 (1.05 - 0.39)= 0.132 m

Station 0 + 108.356 (man hole)

Hm = 0.05

= 0.05 (1.05) = 0.053mStation 0 + 138.836 to 0 + 141.900 (Junction)

30o

1

3

2

Q1 = 3.5 cms

A1 = 1.13 m2

D1 = 1200 mm

Q2 = 7.0 cms

A2 = 1.54 m2

D2 = 1400 mm

Q3 = 3.5 cms

A3 = 1.13 m2

D3 = 1200 mm

= 30oI 0I 0

3090

[ ]V2

2g

[ ]V12

2g

V22

2g ,

Expansion

V1 > V

2

0

90I

[ ]V2

2g


( )( )

3.52 cos 30o

1.13 (9.81)3.52

1.13 (9.81)

1.13 + 1.542

( )Hj + D

1 — D

2 = — —( )A

1 + A

2

2Q

22

A2g

Q1

2

A1g

Q32 cos

A3g

I 0

(Hj + 1.2 — 1.4) =

(7.0)2

(1.54) (9.81)

( )1.335 H

j — 0.2 (1.335) = 3.243 — 1.105 — 0.957

1.335 Hj — 0.267 = 1.181

Hj = 1.085 m

• P = • M (Pressure plus momentum laws)

Fittings and elbows are easily fabricated in all sizes.


Station 0 + 176.900 to 0 + 180.421 (Junction)

70o

70o

1 2

3

4

In this example, the head losses at junctions and transition could also havebeen accommodated by either increasing the pipe diameter or increasingthe slope of the pipe.

This backwater example was designed under full flow conditions butcould also have been designed under pressure; allowing surcharging in themanholes, which would have reduced the pipe sizes. Storm sewer systems,in many cases, can be designed under pressure to surcharge to a tolerablelevel.

0.705 Hj — 0.6 (0.705) = 1.105 — 0.364 — 0.123 — 0.125

0.705 Hj — 0.423 = 0.493

Hj = 1.299 m

Station 0 + 215.892 (manhole)

Hm = .05 = 0.5 (0.64)

= 0.032 m

Total friction Hf throughout the system = 6.191 m

Total form losses = 2.657 m

Q42 cos 0

4

A4g

Q32 cos 0

3

A3g

Q1 = 1.0 m3/s

A1 = 0.28 m2

D1 = 600 mm

Q4 = 1.0

A4 = 0.28

D4 = 600

04 = 70o

Q2 = 3.5

A2 = 1.13

D2 = 1200

Q3 = 1.5

A3 = 0.64

D3 = 900

03 = 70ϒ

(Hj + D

1 — D

2)

=( )A

1 + A

2

2Q

22

A2g

Q1

2

A1g

(Hj + 0.6 — 1.2)

= (1.0)2

(0.28) (9.81)(3.5)2

(1.13) (9.81)

(1.0)2 cos 70o

(0.28) (9.81)(1.5)2 cos 70o

(0.64) (9.81)

( )0.28 + 1.132

( )V2

2g


Flow

Channel

0 +

000.

000

0 +

033.

528

BC

FLO

W

7.0

m3 /

s7.

0 m

3 /s

0 +

180.

421

0 + 215.892

M.H.

0 + 108.356

M.H.

0 + 077.876

0 + 075.590

0 + 038.222 EC

1.5 m3/s

3.5 m3/s

0 + 138.836

0 + 141.900

1.0 m3/s

1.0

m3 /

s 70

o

3.5

m3 /

s 30

o

Fig

ure

5.1

Pla

n a

nd

pro

file

fo

r st

orm

se

we

r


0 + 215.892

M.H.

0 + 108.356

M.H.

0 + 180.421

0 + 176.900

0 + 141.900

0 + 138.836

0 + 077.876

0 + 075.590

0 + 038.222

0 + 033.528

0 + 000.00

E.G

.

GR

OU

ND

SU

RFA

CE

H.G

.L. a

tC

row

n

H.G

. 00

+ 03

50

+ 07

0Tr

ansi

tion

junc

tion

junc

tion

0 +

105

0 +

140

0 +

175

0 +

210

0 +

245

.37

m

.30

m

.23

m

600

mm

CPS

1400

mm

CPS

1800

mm

CPS

1200

mm

CPS

Fig

ure

5.2

Pla

n a

nd

pro

file

fo

r st

orm

se

we

r


[ ]

= +

13 n2 LQ2 (16)2g ≠2 D16/3

Hf = = for K

f = 2n2

METHODS OF DETERMINING EQUIVALENT HYDRAULICALTERNATIVESA method has been developed to aid the designer in quickly determiningequivalent pipe sizes for alternative material, rather than computing thebackwater profiles for each material.

The derivation shown below allows the designer to assign representativevalues for loss coefficients in the junctions and length of average reachbetween the junctions, and develop a relationship for pipes of differentroughness coefficients. In this manner the designer need only perform adetailed hydraulic analysis for one material, and then relatively quicklydetermine conduit sizes required for alternative materials. The relation-ships for hydraulic equivalent alternatives in storm sewer design may bederived from the friction loss equation.

The total head loss in a sewer system is comprised of junction losses andfriction losses:

where: Hj = K

j

V2

2g

Q2

A2 2g

HT = H

j + H

f

= Kj

Q2 16≠2 D4 2g

= Kj

where:

2n2 LV2

R4/3 2g

HT = H

j + H

f

13 n2 LQ2 (16)2g ≠2 D16/3

16Q2 Kj

2g ≠2 D4

= 8Q2

g ≠2

Kj D4/3 + 13 n2 L

D16/3


Thus, for comparison of concrete and steel:

The flow Q for each conduit will be the same, therefore the relationshipsimplifies to:

Average values for conduit length between manholes (L), and junctionloss coefficient (K

j), must next be selected. Representative values may be

derived for the hydraulic calculations that will have already been performedfor one of the materials.

In this example the average conduit length is 90 metres with an averagejunction loss coefficient of 1.0. With the selected L, n and K

j values the

equations are determined for a series of pipe diameters. The results areshown in Table 5.3. These figures are then plotted on semi-log paper, fromwhich hydraulically equivalent materials may be easily be selected. (Fig-ures 5.3 and 5.4)

[ ]8Q2

g≠

Combination increaser, manhole and elbow in one length of pipe.

=8Q2

g≠K

j (D

c)4/3 + 13(n

c)2 L

(Dc)16/3 [ ]K

j (D

s)4/3 + 13(n

s)2 L

(Ds)16/3

Kj (D

c)4/3 + 13(n

c)2 L

(Dc)16/3

Kj (D

s)4/3 + 13(n

s)2 L

(Ds)16/3=


Table 5.3 Methods of determining equivalent alternatives

Junction and Friction Losses

Kj = 1.0 L = 90m

Smooth Pipe Annular CSP Pipe Helical CSP Pipen = 0.012 n = 0.024 n var. (see Table 4.9)

Diameter D4/3 + 0.168 D4/3 + 0.674 D4/3 + 1170 n2

(mm) D16/3 D16/3 D16/3

n values200 1525.30 4226.21 1525.30 0.012250 529.86 1351.46 486.12 0.011300 227.03 537.74 245.01 0.013400 61.39 128.38 95.04 0.019500 22.79 43.17 26.61 0.015600 10.28 17.99 13.50 0.018700 5.29 8.68 6.71 0.018800 3.00 4.66 3.98 0.02900 1.82 2.71 2.43 0.021

1000 1.17 1.67 1.52 0.0211200 0.55 0.74 0.68 0.0211400 0.29 0.37 0.35 0.0211600 0.17 0.21 0.19 0.0211800 0.10 0.12 0.12 0.0212000 0.07 0.08 0.08 0.0212200 0.05 0.05 0.05 0.0212400 0.03 0.04 0.03 0.021

Note: Pipe diameter in metres in above equations.

Philadelphia Airport, 16 x 26mm fiber-bonded, full bituminous coated and full pavedCSP with semi-corrugated bands with O-ring gaskets, provides storm drainage forairport— 5800 m of 2000mm, 2200mm, 2400mm, 2700mm diameters, 14 - 16 gauge,2 - 3m of cover.


00.

20.

40.

60.

81.

01.

21 .

41.

61.

82.

02.

2

1000

0

1000 10

0 10 1

0.1

0.01

Dia

met

re in

met

res

Fig

ure

5.3

E

quiv

alen

t alte

rnat

ives

with

ann

ular

CS

P w

here

C =

13n

2L

Sm

ooth

pip

e

CS

P

EX

AM

PLE

:G

iven

: 0.8

m d

iam

eter

CS

P,

hydr

aulic

ally

equ

ival

ent t

o 0.

7m

di

amet

er s

moo

th p

ipe

D4/3 + CD16/3


00.

20.

40.

60.

81.

01.

21.

41.

61.

82.

02.

2

1000

0

1000 100 10 1

0.1

0.01

Dia

met

res

in m

etre

s

Fig

ure

5.4

E

quiv

alen

t alte

rnat

ives

with

hel

ical

CS

P (

n va

riabl

e) w

here

C =

13n

2L

EX

AM

PLE

:G

iven

: 0.9

m d

iam

eter

CS

P,

hydr

aulic

ally

equ

ival

ent t

o 0.

8m

di

amet

er s

moo

th p

ipe

D4/3 + CD16/3

Sm

ooth

pip

e

CS

P


DESIGN OF STORM DRAINAGE FACILITIES

System LayoutThe storm drainage system layout should be made in accordance with theurban drainage objectives, following the natural topography as closely aspossible. Existing natural drainage paths and watercourses such as streamsand creeks should be incorporated into the storm drainage system. Thusthe storm design should be undertaken prior to finalization of the streetlayout in order to effectively incorporate the major-minor drainage con-cepts.

Topographic maps, aerial photographs, and drawings of existing serv-ices are required before a thorough storm drainage design may be under-taken.

Existing outfalls within the proposed development and adjacent landsfor both the minor and major system should be located. Allowances shouldbe made for external lands draining through the proposed development bothfor present conditions and future developments.

The design flows used in sizing the facilities that will comprise the drain-age network are based on a number of assumptions. Flows that will occurunder actual conditions will thus be different from those estimated at thedesign stage; “the designer must not be tempted by the inherent limitationsof the basic flow data to become sloppy in the hydraulic design.”(1) Alsothe designer should not limit his investigation to system performance un-der the design storm conditions, but should assure that in cases where sewercapacities are exceeded such incidents will not create excessive damage.

This requirement can only be practically achieved if the designer real-izes that a dual drainage system exists, comprised of the minor system andthe major system. Utilizing both systems, the pipe system may be providedfor smaller, more frequent rainfall events, and an overland system for ex-treme rainfall events.

In the layout of an effective storm drainage system, the most importantfactor is to assure that a drainage path both for the minor and major sys-tems be provided to avoid flooding and ponding in undesirable locations.

Minor SystemThe minor system consists chiefly of the storm sewer comprised of inlets,conduits, manholes and other appurtenances designed to collect and con-vey into a satisfactory system outfall, storm runoff for frequently occur-ring storms (2 to 5 year design).

Storm sewers are usually located in rights-of-way such as roadways andeasements for ease of access during repair or maintenance operations.

Major SystemThe major drainage system will come into operation when the minor sys-tem’s capacity is exceeded or when inlet capacities significantly controldischarge to the minor system. Thus, in developments where the majorsystem has been planned, the streets will act as open channels draining theexcess storm water. The depth of flow on the streets should be kept withinreasonable limits for reasons of safety and convenience. Considerationshould be given to the area of flooding and its impact on various streetclassifications and to public and private property.

Typical design considerations are given in Table 5.4.


Multiple inline storage installation.

Table 5.4 Typical maximum flow depths

Storm Return Frequency (Years)

Location* 5 25 40

Walkways, Minor surface flow As required for As required forOpen spaces up to 25mm deep overland flow outlets overland flow outlets

on walkways

Minor, Local and 1m wide in gutters or 100mm above crown 200mm above crownFeeder Roads 100mm deep at low

point catch basins

Collector and Minor surface flow up to crown 100mm above crownIndustrial Roads (25mm)

Arterial Roads Minor Surface flow 1 lane clear up to crown(25mm)

*In addition to the above, residential buildings, public, commercial and industrial buildingsshould not be inundated at the ground line for the 100 year storm, unless buildings areflood-proofed.

To prevent the flooding of basement garages, driveways will have tomeet or exceed the elevations corresponding to the maximum flow depthat the street.

The flow capacity of the streets may be calculated from the Manningequation, or Figure 5.5 may be used to estimate street flows.

When designing the major system it should be done in consideration ofthe minor system, with the sum of their capacities being the total system’scapacity. The minor system should be first designed to handle a selectedhigh frequency storm, (i.e., 2-year) next the major system is designated fora low frequency of flood storm, (i.e., 100-year). If the roadway cannothandle the excess flow, the minor system should be enlarged accordingly.


4

3.5 3

2.5 2

1 .5 1

0 .5 0

010

2030

4 050

60

Cap

acit

y –

(m3 /

s)

Slope – percent

Fig

ure

5.5

H

ydra

ulic

cap

acity

of r

oadw

ays

Not

e: B

lvd.

= B

oule

vard

Streetline

Streetline

150m

mBl

vd.

n =

0.0

5B

lvd.

n =

0. 0

13P

avem

ent

W.L

.Maj

or s

yste

m

15mrightofway-8mPavement(2%Blvd)





20m

right

ofway

-9mPav

emen

t(6%

Blvd)


HYDRAULIC DESIGN EXAMPLE OF MINOR-MAJOR SYSTEM

Description of SiteThe site for this design example is shown on Figure 5.6.

The site is about 15 hectares in size consisting of single family and semidetached housing as well as a site for a public school. The site slopes gen-erally from west to east, where it is bounded by a major open water course.To accommodate the principles of the “minor-major’’ storm drainage sys-tems, the streets have been planned to conform as much as possible to thenatural contours of the lands. Where sags in roadways between intersec-tions could not be avoided, overflow easements or walkways have beenprovided to permit unobstructed surface runoff during major storms, asshown on Figure 5.7.

Selected Design Criteria

Minor SystemBased on a reasonable level of convenience to the public, a two-year de-sign curve is considered adequate as a design basis for the minor systemwithin this development.

Storm Sewer installation involved 1300 m of full bituminous coateded full pavedpipe arch.


Figure 5.6 Site plan with route of surface runoff

N

GreenBelt

GreenBelt

School


N

GreenBelt

Culvert

Watercourse

Culvert

School

GreenBelt

Headwall

OverflowEasement

OverflowEasement

Drainage Areaof Design Example

Storm Sewer Section

Major SystemThe major (or overflow) system will be checked together with the minorsystem against a 100-year storm intensity. The combination of these twosystems shall be able to accommodate a 100-year storm runoff.

Minor SystemFor the limited extent of area involved, designing on the principles of theminor-major drainage concept without gravity connections to foundationdrains permits considerable tolerance in the degree of accuracy of runoffcalculations such that the rational formula Q = k•C•i•A is considered ad-

Figure 5.7 Storm drainage areas


equate. The values for the two year rainfall intensity curve obtained fromlocal records are shown in Table 5.5.

The following steps should be followed in the hydraulic design of theminor system:1. A drainage area map should be prepared indicating the drainage limits

for the site, external tributary areas, location of imported minor systemand carryover flows, proposed minor-major system layout and directionof surface flow.

2. The drainage area should be divided into sub-areas tributary to the pro-posed storm sewer inlets. In this case the inlet shall be located at theupstream end of each pipe segment.

3. The coverage of each sub-area should be calculated.4. The appropriate runoff coefficient should be developed for each sub-

area. The example has been simplified in that impervious areas discharg-ing to grass areas have been given a runoff coefficient equal to the grassedarea runoff coefficient. The runoff coefficient in this example has beendetermined based on 0.20 for grassed areas and areas discharging to grasssuch as roof, patios and sidewalks) and 0.95 for impervious surfaces(streets and driveways), which for this site results in an average runoffcoefficient of 0.35 for all the sub-areas.

5. The required capacity of each inlet should be calculated using the ra-tional method, with the initial time of concentration and the corres-ponding intensity. In this example,T

c = 10 minutes.

i = 72 mm/hr (2-year storm) (Table 5.5).Inlets will be located at the upstream manhole for each length of con-duit.

Table 5.5 Rainfall intensity duration frequency

Time 2 Year Return 100 Year Return(Min) (mm/hr) (mm/hr)

5 105 26210 72 17915 57 14620 48 12225 42 10930 37 9735 34 8940 30 8145 28 7450 26 6955 24 6460 22 5965 21 5570 19 5175 18 4780 16 4485 15 4190 13 3995 12 38

100 11 33125 10 32150 9 25175 7 23200 7 22


6. Commencing at the upstream end of the system, the discharge to becarried by each successive segment in a downstream direction is calcu-lated. The initial time of concentration is 10 minutes at the most up-stream inlet. Added to this value is the required travel time in the con-duit to the next inlet. The resulting time of concentration is then used todetermine a new intensity at that point.

Also, a weighted area x C value must be determined at each succes-sive inlet.

At a confluence of two or more conduits, the longest time of con-centration is selected and the procedure continues downstream. The abovecomputations are summarized in Table 5.6.

7. With computed discharges at the upstream end of each pipe segment, atentative pipe size to accommodate friction losses only is selected usingthe friction flow charts in Chapter 4. In this design example, a helical68mm x 13mm CSP with variable roughness coefficient (Table 4.9) hasbeen selected as the conduit material. The corresponding velocities forthe expected flow are determined to calculate the pipe flow time. Thistime added to the upstream time of concentration results in the new timeof concentration for the downstream segment as described in Step 6.Design velocities in storm sewers should be a minimum of 1.0 m/s whenflowing half full to full to attain self cleaning velocities and to preventdeposition, to a maximum of 4.5 m/s to avoid erosive damage to theconduit.

Recharge trench installation showing junction box.


Culvert design technology and open-channel flow design are increasingly applied tourban storm water management. Triple structural plate pipe-arches enclose streamunder roadway, and industrial land development.

Note: If upon completion of the hydraulic design (and backwater cal-culations), the times of concentrations have varied enough to alter thedischarges, new flow values should be determined. In most cases theslight variance in the T

c will not significantly affect the peak flows.

8. As the preliminary design proceeds downstream, some account must bemade for the manhole and junction losses. Certain rules of thumb maybe used before the detailed hydraulic analysis. In this design examplethe following manhole drops were assumed:

15 mm for straight runs45 mm for 45ϒ junctions75 mm for 45ϒ to 90ϒ junctionsAlso crowns of incoming and outgoing pipes at manholes were kept

equal where the increase in downstream diameter met or exceeded theabove manhole drops.

The preliminary minor system design is shown in Table 5.6 with thetentative pipe sizes and manhole drops.

9. The hydraulic analysis should next be performed on the proposed minorsystem to ensure that it operates as expected. The hydraulic grade is setat the crown of the outlet conduit, with hydraulic calculations proceed-ing upstream. The energy loss equations shall be used following the sameprocedure as in the Hydraulic section. The detailed hydraulic calcula-tions are computed for each station, on pages 153 and 154, with theresults summarized in Table 5.7. In this example the initial pipe sizesdid not change, but rather manhole drops were adjusted to account forthe junction losses. If junction losses would have resulted in the eleva-tion of the pipe crown exceeding the minimum cover criterion, then the


hydraulic grade line may have been lowered by increasing the pipesize. The hydraulic grade line may be permitted to exceed the crownwhere some surcharging in the storm system can be tolerated.

10. The designer may now estimate the required pipe sizes for a minorsystem for an alternative conduit material or roughness coefficient.There is no need to perform a detailed hydraulic analysis for the alter-native conduit, but rather use the method of “Equivalent Alternatives”as described earlier in this chapter. In this example the average lengthof conduit is estimated to be 90m with an average manhole junctionloss coefficient of 1.0. The alternative conduit will have constant n =.012. Therefore the alternative material may be determined. The re-sults are summarized in Table 5.8.

Large storm drain projects under runways at a major airport.


Increasers are easily fabricated for correct field location.

Pipe-arch sewer installation in a residential area satisfying minimum headroomrequirement; however it has adequate capacity and strength.


Leng

thTo

tal

Tota

lIn

tens

ityof

Size

Fall

M.H

.U p

Dow

nAc

tual

M.H

.M

.H.

Area

Sect

ion

Trun

kI

QPi

pePi

peSl

ope

Drop

Stre

amSt

ream

Cap.

Vel.

Sect

.Ac

cum

.Fr

omTo

(ha)

CA

x C

A x

CA

x C

(mm

/hr)

(m3 /s

)(m

)( m

m)

%(m

)(m

m)

(m)

(m)

Q(m

3 /s)

(m/s

)M

in.

Min

.

12

0.74

0.35

0.26

0.26

720.

0590

200

0.84

0.76

231.

590

230.

830

0.05

1.03

1.47

11.4

72

31.

100.

350.

390.

6567

0.12

8030

01.

301.

0475

230.

755

229.

715

0.1 2

1.71

0.77

12.2

43

41.

040.

350.

361.

0165

0.18

8140

00.

980.

7975

229.

640

228.

850

0.1 8

1.58

0.85

13.0

94

50.

830.

350.

291.

3062

0.22

9340

01.

5 01.

3075

228.

775

227.

475

0.22

1.96

0.79

13.8

8

67

1.06

0.35

0.37

0.37

720.

0790

200

1.70

1.53

231.

610

230.

080

0.07

1.47

1.04

11.0

47

8–

––

––

0.07

9020

01.

701.

5375

230.

005

228.

475

0.07

1.47

1.04

12.0

88

91.

500.

350.

530.

9066

0.16

7530

02.

201.

6545

228.

430

226.

780

0.16

2.23

0.56

12.6

4

1011

1.80

0.35

0.63

0.63

720.

1390

300

1.40

1.26

230.

360

229.

100

0.13

1.77

0.86

10.8

611

120.

710.

350.

250.

8869

0.17

8330

02.

401.

9915

229.

085

227.

095

0.17

2.32

0.60

11.4

612

130.

420.

350.

151.

0367

0.19

8140

01.

100.

8975

227.

020

226.

130

0.19

1.68

0.80

12.2

6

59

0.43

0.35

0.15

1.45

600.

2481

500

0.76

0.62

7522

7.40

022

6.78

00.

241.

470.

9214

.80

913

0.53

0.35

0.19

2.54

580.

4081

600

0.62

0.50

150

226.

630

226.

130

0.41

1.41

0.96

15.7

613

142.

280.

350.

804.

3756

0.67

150

600

1.70

2.55

7522

6.05

522

3.50

50.

682.

321.

0916

.85

1415

0.55

0.35

0.19

4.56

550.

6915

060

01.

802.

7015

223.

490

220.

790

0.70

2.39

1.06

17.9

115

162.

350.

200.

475.

0353

0.74

3570

01.

200.

4275

220.

715

220.

295

0.74

1.99

0.28

18.1

916

O

utfa

ll–

––

5.03

530.

7415

080

00.

681.

0275

220.

220

219.

200

0.74

1.61

1.58

19.7

7

Tabl

e 5.

6P

relim

inar

y st

orm

sew

er d

esig

n

Q=

Flow

A=

Area

in H

ecta

res

C=

Coef

ficie

nt o

f Run

off

I=

Inte

nsity

of R

ainf

all f

or P

erio

d in

mm

/hr

Loca

tion

R

unof

fIn

verts

Tim

e(E

ntry

: 10

Min

.)


Installing 1,800mm diameter CSP to be used as an underground detention chamberfor stormwater runoff.


Tabl

e 5.

7H

ydra

ulic

cal

cula

tion

shee

t

12

34

56

78

910

1112

1314

1516

1718

1920

Inve

rtD

H.G.

Sec-

AK

VQ

V2E.

G.S f

Avg.

Sf

LH f

H bH j

H mH t

E.G.

M.H

.m

mm

mtio

nm

2m

/sm

3 /s2g

mm

/mm

/mm

mm

mm

mm

Outle

t21

9.20

080

022

0.00

00

0.50

0.00

636

1.47

30.

740.

111

220 .

111

0.00

6022

0.11

116

220.

149

800

220.

949

00.

500.

0063

61.

473

0.74

0.11

122

1.06

00.

0060

0.00

6015

00.

900

0.03

30.

016

221.

060

1522

0.59

370

022

1.29

30

0.38

0.00

636

1.92

40.

740.

189

221 .

482

0.01

230.

0092

350.

322

0.02

222

1.48

214

223.

478

600

224.

078

00.

280.

0063

62.

442

0.69

0.30

422

4 .38

20.

0243

0.01

8315

02.

745

0.02

50.

015

224.

382

1322

7.42

860

022

8.02

80

0.28

0.00

636

2.37

10.

670.

287

228.

315

0.02

290.

0236

150

3.54

00.

034

0.37

622

8.31

59

228.

912

600

229.

512

00.

280.

0063

61.

415

0.40

0.10

222

9.61

40.

0081

0.01

5581

1.25

60.

008

0.22

022

9.61

45

229.

586

500

230.

086

00.

200.

0044

11.

223

0.24

0.07

623

0.16

20.

0054

0.00

6881

0.55

10.

007

0.01

623

0.16

2

1222

8.99

440

022

9.39

40

0.13

0.00

385

1.51

30.

190.

117

229.

511

0.00

970.

0163

811.

320

0.01

0.03

622

9.51

111

230.

798

300

231.

098

00.

070.

0033

22.

406

0.17

0.29

523

1.39

30.

0310

0.02

0483

1.68

90.

015

231.

393

1023

3.18

230

023

3.48

20

0.07

0.00

332

1.84

00.

130.

173

233.

655

0.01

820.

0246

902.

214

0.17

233.

655

823

0.57

930

023

0.87

90

0.07

0.00

332

2.26

50.

160.

261

231.

140

0.02

740.

0178

751.

335

0.03

10.

001

231.

140

723

3.92

720

023

4.12

70

0.03

0.00

283

2.22

90.

070.

253

234.

380

0.03

890.

0332

902.

988

0.26

234.

380

623

7.67

820

023

7.87

80

0.03

0.00

283

2.22

90.

070.

253

238.

131

0.03

890.

0389

903.

501

0.25

238.

131

423

0.70

840

023

1.10

80

0.13

0.00

385

1.75

20.

220.

156

231.

264

0.01

290.

0092

930.

856

0.16

623

1.26

43

231.

593

400

231.

993

00.

130.

0038

51.

433

0.18

0.10

523

2.09

80.

0087

0.01

0881

0.87

50.

0123

2.09

82

232.

737

300

233.

037

00.

070.

0033

21.

700

0.12

0.14

723

3.18

40.

0154

0.01

2180

0.96

80.

074

0.00

223

3.18

41

234.

551

200

234.

751

00.

030.

0028

31.

592

0.05

0.12

923

4.88

00.

0198

0.01

7690

1.58

40.

1323

4.88

0

n =

Varia

ble

S f = K

(V2 ) /R

4/3

K =

2g(n

2 )

2g


( )

(Hj + 0.5 — 0.6) = —

Kb = 0.25 = 0.117

M.H. 16 0 = 45ϒ From Figure 4.13 K = 0.3

Hb = K = 0.3 x 0.11 = 0.033m

Ht = 0.2 — = 0.2 x (.19 — .11) = 0.016m

M.H. 15

M.H. 14 Kb = 0.25 = 0.083

( )V1

2

2gV

22

2g

Ht = 0.2 — = 0.2 (.30 — .19) = 0.022m( )V

12

2gV

22

2g

Hb = K

b = 0.083 x .30 = 0.025m

Hm = 0.05 = 0.05 x .30 = 0.015m

( )V2

2g

V2

2g( )M.H. 13

Hb = K

b = 0.117 x (.29) = 0.034m( )V2

2g

0 = 90ϒ cos 90ϒ = 0

(Hj + 0.6 — 0.6) = —

Hj = 0.376m

(Hj + D

1 — D

2) = — — cos 0( )A

1 + A

2

2Q

2 2

gA2

Q1

2

gA1

Q3

2

gA3

( )0.28 + 0.282

(0.67) 2

9.81 (0.28)

Hj = 0.220m

M.H. 9 Hb = K

b = x 0.10 = 0.008mV 2

2g1090

0 = 90ϒ cos 90ϒ = 0

( )0.20 + 0.282

( )V2

2g

1090

2090

0 = 90ϒM.H. 5

(0.4) 2

9.81 (0.28)

(0.4) 2

9.81 (0.28)

(0.24) 2

9.81 (0.20)

Detailed Hydraulic Calculations for Step No 10 in Minor System Design

0.25( )


( )

( )

V2

2

2gH

m = 0.1 — = 0.1 (.26 — .25) = 0.001m( )

Hb = K

b = x 0.08 = 0.007m

Ht = 0.2 — = 0.2 (.16 — .08) = 0.016m

V2

2g ( )

( )V1

2

2gV

22

2g

1090

M.H. 12

Ht = 0.2 (.3 — .12) = 0.036m

Hm = 0.05 = 0.05 (.3) = 0.015m( )V2

2gM.H. 11

K = 1.0M.H. 10

Hm = K

= 1.0 (.17) = 0.17mV2

2g

Hb = (.26) = 0.031m20

90M.H. 8

V1

2

2g

0 = 90ϒM.H. 7

From Figure 4.13 K = 1.04

Hb = 1.04 (.25) = 0.260m

K = 1.0M.H. 6

Hm = K = 1.0 (.25) = 0.250m

0 = 90ϒM.H. 4


Hb = 1.04 (.16) = 0.166m

( )V2

2

2gH

t = 0.2 — = 0.2 (.15 — .10) = 0.010m

V1

2

2gM.H. 3

0 = 60ϒM.H. 2


Hb = 0.49 (.15) = 0.074m

( )V2

2

2gH

t = 0.1 — = 0.002m

V1

2

2g

K = 1.0M.H. 1

Hm = K = 1.0 x 0.13 = 0.13

( )

( )

( )V2

2g

( )V2

2g

0.25 1090

0.25Hb = x .12 = 0.010m

0.25


Major SystemVarious manual methods can be used to estimate the major system flows.As a preliminary estimate, designers often apply the Rational formula, us-ing the rainfall intensity for a 100 year storm and a C factor 60 percent to85 percent higher than what would be used for a 2-year or 5-year storm.The increase in value is basically to allow for a change in the antecedentmoisture condition. Except in special circumstances, a C factor above 0.85need not be used.

In this design example the C factor of 0.35 used for the design of theminor system will be increased to 0.60, an increase of about 70 percent.The results are shown in Table 5.9.

In cases where this method results in flows in excess of the acceptableroadway capacity, a more detailed method should be applied, such as theSCS Graphical Method or a suitable hydrological computer model.

If properly laid out the major system can tolerate the variability in flowsestimated by the various methods. A minor increase in the depth of surfaceflow will greatly increase the capacity of the major system, without neces-sarily causing serious flooding. The designer must also consider the re-maining overland flow accumulated at the downstream end of the develop-ment; adequate consideration must be given for its conveyance to the re-ceiving water body. This may involve increasing the minor system andinlet capacities or providing adequate drainage swales.

Table 5.8 Equivalent alternative n = .012

Location

M.H. M.H. Pipe SizeStreet From To mm

1 2 2002 3 3003 4 4004 5 4006 7 2007 8 2008 9 300

10 11 30011 12 30012 13 4005 9 5009 13 600

13 14 60014 15 60015 16 70016 Outfall 800


Tabl

e 5.

9 M

ajor

sys

tem

flow

s fo

r 10

0 ye

ar s

torm

Runo

ffTo

tal

Tim

e of

Inte

nsity

Tota

l Run

off

Sew

er*

Maj

or S

yste

mRo

adSu

rface

Loca

tion

Area

Sect

ion

Conc

entra

tion

IQ

Capa

city

(ove

rland

flow

)Gr

ade

Capa

city

**M

H to

MH

(ha)

CA

x C

A x

Cm

in.

(mm

/hr)

(m3 /s

)(m

3 /s)

(m3 /s

)%

(m3 /s

)

1-2

0.74

0.60

0.44

0.44

10.0

179

0.22

0.07

0.15

2.00

5.15

2-3

1.10

0.60

0.66

1.10

11.5

174

0.5 3

0.11

0.42

2.00

5.15

3-4

1.04

0.60

0 .62

1.72

12.8

160

0.76

0.14

0.63

2.00

5.15

4-5

0.83

0.60

0.50

2.22

14.2

151

0.93

0.14

0.79

1.90

5.09

6-7

1.06

0.60

0.64

0.64

10.0

179

0.31

0.11

0.21

2.00

5.15

7-8

––

––

11.5

169

0.00

0.00

0.00

2.20

5.41

8-9

1.50

0.60

0.90

1.54

13.0

159

0.67

0.14

0.53

2.00

5.15

10-1

11.

800.

601.

081.

0810

.017

90.

530.

130.

411.

854.

9611

-12

0.71

0.60

0.43

1.51

11.5

169

0.70

0.14

0.57

2.00

5.15

12-1

30.

420.

600.

251.

7612

.016

00.

780.

120.

662.

205.

41

5-9

0.43

0.60

0 .26

2.48

15.7

142

0.98

0.12

0.85

2.00

7.79

9-1

30.

530.

600.

323.

6217

.113

61.

360.

121.

242.

007.

7913

-14

2.28

0.60

1.37

6.75

18.4

130

2.41

0.22

2.19

2.50

8.78

14-1

50.

550.

600.

337.

0820

.912

02.

340.

232.

112.

007.

7915

-16

2.35

0.60

1.41

8.49

23.4

113

2.65

0.23

2.43

0.50

3.96

16-O

utfa

ll–

––

8.49

24.0

112

2.62

0.23

2.39

0.50

3.96

*As

sum

ing

suffi

cien

t inl

et c

apac

ity**

Refe

r to

Figu

re 5

.5


Foundation DrainsTo establish the groundwater level, piezometer measurements over a 12month period were taken, indicating the groundwater table would be safelybelow the footing elevations for the proposed buildings, minimizing theamount of inflow that can be expected into the foundation drains.

The municipal requirements include detailed lot grading control, thusfurther reducing the possibility of surface water entering the foundationdrains. Accordingly a flow value of 7.65 x 10-5 m3/s per basement is used.See the discussion on Foundation Drains in Chapter 2 of this text. For de-tailed calculations see Table 5.10.

Computer ModelsThere is a wide range of computer models now available for analyzingsewer networks. The complexity of the models varies from straightforwardmodels which use the rational method to estimate the peak flow to compre-hensive models which are based on the continuity and momentum equa-tions and are capable of modeling surcharge, backwater, orifices, weirsand other sewer components.

Table 5.11 lists several of these models and their capabilities.

Smooth-lined CSP storm sewer being installed.


Tabl

e 5.

10 F

ound

atio

n dr

ain

colle

ctor

des

ign

shee

t Unit

Flow

Tota

lFr

omTo

Area

Dens

ityTo

tal

Cum

.Pe

r Uni

tFl

owLe

ngth

Grad

ient

Pipe

Dia

.Ca

paci

tyVe

loci

tyLo

catio

nM

.H.

M.H

.(h

a)(p

er h

a)Un

itsUn

its(m

3 /sx1

0-5 )

(m3 /s

x10-

3 )(m

)%

(mm

)(m

3 /s)

(m/s

)

Cres

cent

‘G’

1A2A

1.20

218

187.

65 1

.38

119

0.98

200

0.03

11.

12Cr

esce

nt ‘G

’2A

3A0.

722

1129

7.65

2.2

294

1.51

200

0.03

71.

37Cr

esce

nt ‘G

’3A

4A1.

492

2251

7.65

3.9

015

20.

5020

00.

022

0.79

Cres

cent

‘G’

4A5A

0.60

29

607.

65 4

.59

930.

5520

00.

023

0.82

Cres

cent

‘G’

1A6A

1.52

223

237.

65 1

.76

152

1.39

200

0.03

61.

28Cr

esce

nt ‘G

’6A

7A0.

932

1437

7.65

2.8

390

2.25

200

0.04

01.

67Cr

esce

nt ‘G

’7A

8A0.

582

946

7.65

3.5

210

51.

3120

00.

035

1.28

Stre

et ‘F

’9A

10A

1.54

330

307.

65 2

.30

137

1.20

200

0.03

41.

21St

reet

‘F’

10A

11A

0.85

317

477.

65 3

.60

133

1.20

200

0.03

41.

21

Stre

et ‘A

’5A

8A0.

633

1310

67.

65 8

.11

821.

8120

00.

041

1.52

Stre

et ‘A

’8A

11A

0.51

310

116

7.65

8.8

775

4.34

200

0.06

32.

31St

reet

‘A’

11A

13A

0.94

319

135

7.65

10.3

013

31.

4220

00.

036

1.34

Sour

ce: P

aul T

heil

Asso

ciat

es L

td.


Table 5.11 Computer models – Sewer system design and analysis

Model Characteristics

Model Purpose:Hydraulic Design • • • •Evaluation/Prediction • • • •

Model Capabilities:Pipe Sizing • • • •Weirs/Overflows • • • •Surcharging • • •Pumping Stations • • •Storage • • •

Hydraulic Equations:Linear Kinematic Wave • •Non-Linear Kinematic Wave • •St. Venant’s – Explicit •St. Venant’s – Implicit •

Ease of Use:High • •Low • • • •

1. Wright, K.K., Urban Storm Drainage Crite-ria Manual, Volume 1, Wright-McLaughlinEngineers, Denver, Colorado, 1969.

2. Dept. of the Army, CE Storm Users Manual,Construction Engineering Research Labora-tory, Champaign, Illinois, 1985.

3. Hydrograph Volume Method of Sewer Sys-tem Analysis, HVM Manual, Dorsch ConsultLimited, Federal Republic of Germany, 1987.

4. Terstriep, M.L., Stall, J.B., Illinois UrbanDrainage Area Simulator (ILLUDAS), Illi-nois State Water Survey, Bulletin 58, Urbana,Illinois, 1974.

5. Huber, W.C. Heaney, J.P. and Cunningham,B.A., Stormwater Management Model (SWMMVersion IV) Users Manual, U.S.Envioronmental Protection Agency, 1986.

6. Wallingford Storm Sewer Package (WASSP),Users Guide, Hydraulics Research Laboratory,Wellingford, UK, 1984.

REFERENCES

HV

M D

orsc

h3

CE

Sto

rm2

ILLU

DA

S4

SW

MM

-Ext

ran5

SW

MM

-Tra

nspo

rt5

WA

SS

P-S

IM6

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124 MODERN SEWER DESIGN - CSPI - Volume · PDF fileThese design aids do ... 126 MODERN SEWER DESIGN Q A 5.2) ... Hydro-logical computations have been made and preliminary design for