combined sewer overflows example

8/9/2019 Combined Sewer Overflows Example

1/21

Example 8STORM WATER MANAGEMENT MODEL

APPLICATIONS MANUAL

Combined Sewer Overflows

This example demonstrates how to model systems that convey both sanitary wastewater

and stormwater through the same pipe. Systems like the one simulated here are referred as

combined sewer system, and the overflows caused during periods of moderate to heavy rainfallare known as Combined Sewer Overflows (CSOs. CSOs discharges can cause serious water

pollution problems, especially in old communities and cities, where combined sewer system are

more common. Contaminants from CSOs discharges can include conventional pollutants,

pathogens, toxic chemicals and debris.

The ob!ective of this example is to provide guidance in the application of S"## to

represent combined sewer systems and the flow regulators controlling the flow between

collection sewers, interceptors and the water body. $dditionally, this example demonstrates how

to design a pump station to pump the intercepted flows through a force main line.

8.1 Problem Statement

The ob!ective of this example is to model a combined sewer system developed for the %&

acre urban watershed presented in 'xample %, and evaluate its performance using the water

uality storm defined in 'xample ) (*.%) in. and the %+yr storm (*.& in.. Combined sewerpipes conveying wastewater and stormwater flows generated at different sewersheds (or areas

that contribute wastewater flows to a single point will be added to the model. The wastewater

discharges (or dry+weather flows will be considered to be constant and computed based on anaverage discharge rate per capita. The design will consider an interceptor si-ed to control

wastewater discharges plus a portion of the stormwater, and convey them to a pump station that

pumps these discharges through a force main line to a constant head outfall at a higher

elevation, representing the entrance condition at a wastewater treatment plant (""T. $

combination of orifices, weirs and pipes is used to represent the five flow regulators that transferwastewater into the interceptor. The Combined Sewer Overflows (CSOs that cannot be diverted

by these devices will discharge directly into the stream running through the site/s park area. The

schematic representation of the combined sewer system to be simulated in this example is shownin 0igure +1. The representation includes the combined sewer pipes (in green draining the

subcatchments (or sewersheds S1, S2, S3, S4 and S5, the stream (in blue, the interceptor (in

brown, the flow regulators (red box, and the pump station.


2/21


3/21

Figure 8-*: S+,e!ai+ re$resenai&n & +&!'ine se)er &.er%&)s /CSO0 in a +&!'ine( se)er syse! S&ur+e:

Fie%( an( Tauri /12340

Dry-Wea,er %&)s

2n S"##, combined sewer systems can be modeled easily by combining the stormwater

runoff discharges and dry water flows (wastewater flows defined in as many nodes as necessary

using the dry weather tool available in the 2nflow 'ditor property.


4/21

5epresentation of 4ry "eather 0lows in S"##

This example reuires the definition of dry weather flows to represent the

wastewater discharges into the combined sewer system. The Dry Wea,erpage ofthe In%&)E(i&ris used to specify a continuous source of dry weather flow or any

pollutant entering a node of the drainage system. The In%&) E(i&r is accessed

through the Pr&$eries Ta'%eof the node in which the flow is defined. 4ry "eather0lows in S"## are characteri-ed by an average (or baseline value and time

patterns (T that represent monthly, daily and hourly variations. 6p to four

different types of patterns can be assigned. $s with other time series in S"##,

one can either create the pattern directly from the 'ditor or select a previouslydefined pattern. 4ry weather flows are then computed as shown below7

Dry )ea,er %&) a i!e t5 /a.erage .a%ue06/TP 106/TP *067

8ased on this formulation, if no time pattern is defined, the average value

becomes a constant dry weather flow entering to the node. This definition is used inthis example to represent constant flows. The 2nflow 'ditor for dry weather flows

and the Time attern 'ditors are shown below.

F%&) Regu%ai&n Sru+ures

Flow regulators (or diversion structures are used in this example to control the flowbetween collection sewers and the interceptor. These regulators allow the conveyance of

wastewater to treatment facilities during dry weather conditions. 4uring "et "eather 0low

(""0 conditions the regulators divert flows away from the interceptor to water course to avoidsurcharge and flooding of the combined sewer systems. Typical flow regulators include side

weirs, leaping weirs, transverse weirs, orifices and relief siphons. #etcalf 9 'ddy, 2nc. (1&&1presents a detailed description of these different types of regulators. 2n particular in this exampleflow regulators of the type transverse weir with orifice, illustrated in 0igure +), are used. 2n this

regulator there is a weir or a small plate placed directly across the sewer perpendicular to the line

of flow. :ow flows are diverted to the interceptor through an orifice located upstream the weir.2ncrease of flow during wet weathers results in flow overtopping the weir and discharging to the

overflow outlet, conducting into the stream.


5/21

Figure 8-4: Trans.erse )eir %&) regu%a&r

Transverse flow regulator can be represented in S"## using weir and orifice elements

available in the model. 8ecause these elements correspond to hydraulic links, the use of therepresentation proposed here reuires the definition of additional !unctions. $ schematic

representation of two possible definitions of a transverse flow regulator in S"##is shown in

0igure +; (a and b, in addition to a third representation that operates with the same principleshown in 0igure +), but no weirs or orifices are used (0igure +; c. These three representations

are implemented in this example. Two of them consider the weir shown in 0igure +), but there

is a difference in the definition of the diversion to the interceptor. The definition in (a considersa bottom orifice to conduct flows from the combined sewer into the interceptor, while the

definition in (b considers a pipe instead of a bottom orifice. 0inally, the third definition (0igure

+; c considers neither a weir nor an orifice to divert flows into the interceptor and the stream.The control here is defined through different inlet offsets for the pipes that convey flows to the

interceptor and the stream. The first pipe has an inlet offset of -ero while the pipe linked to thestream has a larger invert elevation.

Several alternative representations are illustrated in this example to show differentapproaches in defining regulators. articular configurations in real applications will depend on

the specific conditions in the field. Some of the hydraulic phenomena that can be artificially

introduced into the model by these representations include surcharged weirs, instabilities caused

by short pipes and excessive storage associated with large pipes.


6/21

J

J

O

W

J

Combinedsewer flow

Tointerceptor

To stream

J

J

W

J

Combined

sewer flowTointerceptor

To stream

(a) (b)

W

O

J

Transverse Weir

Bottom Orifice

Junction

Combined sewer

Interceptor

Stream

J

J

J

Combined


To stream

(c)

Regular conduit

ifferent

inlet offset

J

J

O

W

J

Combinedsewer flow

Tointerceptor

To stream

J

J

W

J

Combined


To stream

(a) (b)

W

O

J

Transverse Weir

Bottom Orifice

Junction

Combined sewer

Interceptor

Stream

J

J

J

Combined


To stream

(c)

Regular conduit

ifferent

inlet offset

Figure 8-: A%ernai.e &r re$resening rans.erse )eir %&) regu%a&r in SWMM

Pu!$ Sai&ns

umps are links used to lift water to higher elevations. They are defined in the model

between two nodes and can be in+line or off+line. The principal input parameters for a pump

include the identification of the inlet and outlet nodes, its pump curve, initial on


7/21

C&!'ine( Se)er Syse!

0igure +> shows the system to be modeled in this example. 'xample ? (Example 7.inpis the starting point for the model setup, although ma!or changes are reuired. @utter elements

will be removed as will the pipes along the stream running through the parkA the pipes will be

replaced with an interceptor located at the north side of the stream, as illustrated in 0igure +1.The interceptor conveys wastewater flows to a pump station comprising a storage unit, whichrepresents the wet well, and a pump. The pump discharges through a force main line to a

constant head outfall (O2 representing the inlet to a hypothetical ""T. The pipes representing

the line will be defined as well as the nodes connecting them. These nodes will represent simpleconnections and not manholesA thus, the property Bsurcharge depth will be used to specify a

maximum possible pressure along the line. Dew pipes representing the combined sewer system

need to be defined as well as several weirs and orifices to define the flow regulators. The readermay notice that the bed of the stream is assumed to be = ft lower than the stream bottom

elevations used in 'xample %. The reason for this is so that backwater from the stream will not

flood the regulators in the combined sewer system.

Figure 8-: S+,e!ai+ re$resenai&n & ,e +&!'ine( se)er syse!s

The first modification is to remove !unctionsAux1andAux2as well as conduits C2a, C2,

C_Aux1, C_Aux2, C_Aux1to2,P5,P,P!andP". Then, the elevations of the nodes are changedas well as the inlet and outlet offsets of the links defining the stream in the park. The new invert

elevations of the nodes in the stream (Aux3, #3, #4, #5, #, #", #$, #1%, #11and outlet O1 are

shown in Table +1. Eunction in the stream that are not connected to the other conduits will havea ;er& depth (thus, the depth of these !unctions is given by the maximum depth of the stream

conduit connected to the !unction, while the other ones will have a depth eual to the ground

elevation minus the invert elevation of the !unction. The stream is shown in blue color in 0igure

+1 and 0igure +>.


8/21

The next step is to define the combined sewer pipes, shown in green on 0igure +> and

identified with the letterP.$ll of them have a roughness coefficient of & ;.% E1) ;&> ;.

E%a ;&>>.? ; $ux) ;&>.= *

E% ;&>= ; E21 ;&= 1>

E) ;&> * E2% ;&=? 1=.

E; ;&>> * E2) ;&== 1>

E= ;&>;. * E2; ;&=% 1;

E> ;&>; * E2= ;&=* 1>E? ;&>* 1% E2> ;&>? ?.%

E ;&>1.= * E2? ;&>? >

E& ;&=&. * E2 ;&>% >.%

E1* ;&=. * E2& ;&>* =.%

E11 ;&= * O1% ;&=? +

E1% ;&> ;.% "ell ;&;= 1;1C&%&rs in(i+ae ),e,er ,e n&(es 'e%&ng & ,e srea! /'%ue0" ,e se)er $i$es /green0" ,e iner+e$&r

/'r&)n0 &r ,ey are ,e (i.ersi&n =un+i&n /grey0*O1 5 Ou%e =un+i&n &r ,e srea!" !a#i!u! (e$, n& (eine(4O* 5 Ou%e =un+i&n & ,e )ase)aer rea!en $%an" i#e( sage & 23<

"ith the sewer pipes entered in the model, it is necessary now to redefine the outlets of

the different subcatchment. These outlets will receive the stormwater runoff generated by the

subcatchments as well as the flows corresponding to the wastewater flows, defined later in thissection. 2n other words, the subcatchments used for drainage are also defined as sewersheds in

this example. Do other changes to the properties of the subcatchments are reuired. Table +%

shows the new subcatchments/ outlets.

The next step is to define the interceptor running along the north side of the stream thatconveys the wastewater flows to the pump station located at the east side of the watershed. 2ts

pipes are identified with the letter Iand brown color, as shown in 0igure +>. Conduits&1,&2,&3,

&4and&$are the main pipes of the interceptor. The new nodes belonging to the interceptor are

identified with the letters#&. roperties of the nodes and pipes of the interceptor are summari-edin Table +1 and +).

Ta'%e 8-*: Su'+a+,!ens> &u%es

Su'+a+,!en Ou%e n&(e

S1 E1

S% E%a

S) $ux)

S; E1)


9/21

S= E1%

S> E11

S? E1*

Ta'%e 8-4: Su!!ary & ,e +&n(uis1

Pi$e ID S,a$e In%eN&(e

Ou%eN&(e

Leng,/0

, &r (/0 *

R&ug,C&e

'/0

4 ?1 ?* 9 In%eOse /0Ou%e

Ose /0

C) Circular E) E; 1*.&> %.%= *.*1> * * * * *

C; Trape-oidal E; E= 1)).* ) *.*= = = = * *

C= Trape-oidal E= E> %*?.;= ) *.*= = = = * *

C> Trape-oidal E? E> 1)&.&& ) *.*= = = = = *

C? Circular E> E &=.;) ).= *.*1> * * * * *

C Trape-oidal E E& 1>=. ) *.*= = = = * *

C& Trape-oidal E& E1* )%*.)% ) *.*= = = = * *

C1* Trape-oidal E1* E11 1;%.>* ) *.*= = = = * *

C11 Circular E11 O1 &*.1* ;.?= *.*1> * * * * *

CF$ux) Trape-oidal $ux) E) ;;;.?= ) *.*= = = = > *

1 Circular E1 E2? 1>*.?= 1.)) *.*1> * * * * *

% Circular E%a E% 1=?.; 1.= *.*1> * * * * *

) Circular E% E2& ;&?.%= 1.= *.*1> * * * * *

; Circular $ux) E2> =&=.%& 1.>? *.*1> * * * * *

= Circular E1) E? )??.?> 1.>? *.*1> * * * * *

> Circular E1% E2 ;&.;% 1.>? *.*1> * * * * *

21 Circular E21 E2% 1=*.)> 1 *.*1> * * * * *

2% Circular E2% E2) %)*.) 1 *.*1> * * * * *

2) Circular E2) E2; =?.%? 1.= *.*1> * * * * *

2; Circular E2; E2= 1%;.;= 1.= *.*1> * * * * *

2= Circular E2? E2% 1*.>= *.)) *.*1> * * * * *

2> Circular E? E2) 1=).*% *.>> *.*1> * * * * *

2? Circular E2 E2; )%. *.= *.*1> * * * * *

2 Circular E2& E2= ;?.?% *.= *.*1> * * * * *2& Circular E2= "ell 1** % *.*1> * * * * ;

1C&%&rs in(i+ae ),e,er ,e $i$es 'e%&ng & ,e srea! /'%ue0" ,e se)er $i$es /green0 &r ,e iner+e$&r

/'r&)n0* , &r ( +&rres$&n(s & ,e (e$, /Tra$e;&i(a% s,a$e0 &r (ia!eer /Cir+u%ar s,a$e0

4 ' +&rres$&n(s & ,e '&&! )i(, /Tra$e;&i(a% s,a$e0

" 9 ?1 an( ?* +&rres$&n( & ,e %e an( rig, s%&$e /Tra$e;&i(a% s,a$e0

The flow regulation structures are the next elements to be represented in the model. 0ive

flow regulators identified with the letter Rwill be defined to control the flows from the fivecombined sewers (P1, P3, P4,P5andP into the interceptor. These identifiers ('1,G,'5 are

given only for reference purposes in the textA in the actual model regulators are not defined as

elements directly, but rather through a combination of orifices, weirs and pipes (i.e, in the modelthere is not an element named '1, as seen in 0igure +>. 5egulators '2, '4 and'5will be

simulated using a rans.erse )eir and a pipe (0igure +; b. 5egulator '1will be simulated

using a rans.erse )eirand a '&&! &rii+e(0igure +;a, and regulator'3will be representedas two conduits with different inlet offsets (0igure +;c, with conduit C, connected to the

stream, being 9 higher than conduit&, connected to the interceptor. Thus, discharges to the

stream will not occur until the water depth at !unction E? is greater than = ft. $s mentionedbefore, different representations are used to illustrate different possible approaches in modeling


10/21

regulators in combined sewer systems. 2n actual applications, the final representation will depend

on the particular characteristics of the regulator to be modeled. $ll the orifices and weirs have

discharge coefficients of "1 >.= ) *.; E; Orifice Or1 *.= E21

5% 1 E2? "% =.= = *.)) E= ipe 2= See Table +)

5) = E? C> ipe, see Table +) ipe 2> See Table +)

5; > E2 ") = ; *.; E1* ipe 2? See Table +)

5= ) E2& "; ;.= ; *.)= E11 ipe 2 See Table +)

Pu!$ sai&n" &r+e !ain %ine an( &u%e

0inally the pump station is defined at the downstream end of the interceptor. $ wet well

whose bottom elevation is 29 is defined as the outlet node of conduit &$ The well is

represented using a storage unit with a constant surface area of 4


11/21

downstream end of pipe&13is outfall O2, a Fi#e(constant head outfall with an invert elevation

of 28 , and a fixed stage at 23< 8oth elevations are defined in the roperty 'ditor of the

outfall. Table += summari-es the force main line information, and 0igure +? shows its thedetails.

Ta'%e 8-9: Su!!ary & ,e &r+e !ain %ine

Pi$e ID S,a$e In%e N&(e1 Ou%e N&(e1Leng,

/0

Dia!eer

/0

R&ug,

C&e

In%e

Ose /0

Ou%e

Ose /0

21* Circular E21* (;&;? ft E211 =** % *.*1> * *

211 Circular E211 (;&=;. ft E21% =** % *.*1> * *

21% Circular E21% (;&>%.> ft E21) =** % *.*1> * *

21) Circular E21) (;&?*.; ft O% (;&> =** ; *.*1> * *1Nu!'er in $aren,esis in(i+aes ,e in.er e%e.ai&n & ,e n&(e

4efining a force main line

$ force main line can be defined in S"## by using a

set of pipes connected by nodes with a maximum depth

of -ero and an arbitrary highsurcharge de-th. "hen thenode/s maximum depth is defined as -ero, the depth of

the node is euivalent to the distance from its bottom to

the top of the highest conduit connected to it. Therefore,the node does not work as a manhole but a simple

connection. $ high surcharge depth is assigned to avoid

flooding when the main line works under surchargedconditions. 2n the case of the nodes defined for the line in

this example, a value of 9< for the surcharge depth is

used, as shown in the figure at the right.

E21*, ;&;? ft

E21), ;&?*.; ft

E21%, ;&>%.> ft

E211, ;&=;. ft

"ell

ump1

21*

21)21%

211

0ixed stage,

;&?* ft

O%, ;&> ft

Figure 8-3: F&r+e !ain %ine

$ type 3pump curve also calledPump 1will be used for the pumpA this curve relates the

pump discharges and head differences between the input node (well and the output nodes (#&1%.Table +> shows the curve for this example, which is entered following the same steps used in


12/21

the defining other curves such as a storage curve. The pump turns on when the depth at the well

reaches 9 and turns off with a water depth of * A finally, the initial status at the beginning of

the simulations will be O. $ll these properties are defined in the roperty 'ditor of the pump.

Ta'%e 8-: Pu!$ +ur.e

@ea( /01 11 1% 1) 1; 1= 1> 1? 1 1& %* %1 %% %) %;

Dis+,arge /+s0 ?.% >.& >.= >.1 =.? =.% ;.? ;.1 ).> %.& %.) 1.= *. *1 @ea( is ,e ,ea( (ieren+e 'e)een ,e s&rage uni Wellan( ,e =un+i&nJI10

Dry-Wea,er /&r )ase)aer0 %&)s

"astewater flow from the sewersheds will be simulated using the 4ry "eather 2nflow

tool in S"##, described in the sidebar B'e-resentation of ,r. /eather Flows in S/00. 4ry

weather flows are computed and defined for each subcatchment because wastewater sewershedsand drainage subcatchments are considered to be the same. $verage daily values of dry weather

inflow are used in this example for simplicity. Iowever, peak daily flows can range from two tofour times greater than the average daily flows. Therefore, if a conservative design is reuired,

variable time patterns should be used to create dry weather flows representing the maximumwastewater flows. This representation, together with continuous rainfall records, allows the

simulation of the dynamic performance of the system under extreme events.

Typical per capita domestic loading rates vary between ;* gpd for apartements and 1=*

gpd for luxury residences and estates (Dicklow et al., %**;. $SC' (1&&% defines a range ofaverage per capita domestic loading rate between =* gpd and %>= gpd. 8ased on these ranges and

an estimation of ) to = inhabitants per lot, an average domestic loading rate per lot of 4>** *.*1*S) $ux) 1* + )*** *.**;

S; E1) 1? %=* =1**J%=* *.*1%)

S= E1% + 1** 1** *.*1%=

S> E11 + + * *

S? E1* + + * *


13/21

Pre+i$iai&n (aa an( si!u%ai&n &$i&ns

The *.%) inches storm defined previously in Table =+1, 'xample =, and the %+year storm

will be used to evaluate the performance of the combined sewer system. The *.%) in. storm canbe easily incorporated in the model by creating a new time series called %23in. with the

corresponding values of time and intensity. 4ynamic wave flow routing, time steps of 19 s

(reporting, wet+weather and routing and 1 ,r (dry weather and a total duration of 1% hours willbe used in all the simulations.

$ll the information for the model has been summari-ed in Tables +1 to +?. 2t is

recommended to check the system definition one more time and compare the configuration with

that shown in 0igure +> before running the model. The input file and the study area map shouldlook like the filexa(-le "in-and the watershed configuration shown in 0igure +.

C!C"

C# C$

C%

C&

C'

C

C

C*+u,!

-

-.

-!

-"

-#

-$

II.

I!

I"

I#

I$

I%

I&I'

I

I

I. I!

-ump

Or

WW.

W!

W"

J

J.a

J.

J!

J" J#J$

J%

J&J'

J

J

J.

J!

+u,!

JIJI.

JI!

JI"

JI#

JI$JI%

JI&

JI'

JI

JI

JI.

JI!

O

O.

Well

S(

S.

S!

S"

S#

S$

S%

Figure 8-8: Fina% !&(e%" )aers,e( +&nigurai&n

8.# Res"lts


14/21

and shutoff depth are shown with blue lines. The water depth in the well at the beginning of the

simulation is ) ft and the pump initial status is off (oint 1. The pump starts working once the

startup threshold depth of = ft is reached (oint %. The incoming discharges are large enough sothat the pump continues working and water depth in the well does not reach the shutoff elevation.

The water depth reaches a maximum (oint ) and starts decreasing until reaching % ft, depth at

which the pump stops operating (oint ;. $fter % hours, only wastewater flows are dischargedinto the well, and the water depth increases slowly again until reaching the startup depth (oint

=A the pump turns on but rapidly stops when the shutoff depth is reached (oint >. 0rom

hereafter pumped discharges fluctuate between the startup and shutoff limits


15/21


16/21

0igure +1* shows the water elevation profile of the force main line, from the well to the

outlet O2, at =% minutes of simulation. 2t is possible to observe the almost constant head and the

energy losses caused by friction along the system.

Figure 8-1, theonly conduits of the stream receiving direct contribution from the subcatchments are C1%(through !unction #1%, outlet of subcatchment S! and C11 (through !unction #11, outlet of

subcatchment S. 0lows simulated in any other conduit representing the stream would imply

that CSOs are occurring somewhere in the system. 0igure +11 shows that this is not the case andno overflows from the sewer pipes are reaching the stream. 0lows are not observed in conduit

C1* because no runoff is generated by the pervious subcatchment S!.

1* 9 $4

E21*


17/21


18/21

Figure 8-1*: F%&) (is+,arges in (ieren $&ri&ns & ,e iner+e$&r"


19/21


20/21

CSOs are smaller than those of the discharges into the interceptorA however, the peak discharge is

larger.

Figure 8-1: F%&) (is+,arges si!u%ae( in %&) regu%a&rsR1an(R4un(er ,e *-yr s&r!

Table + compares the main results for the *.%) in. and %+yr storms. 2n addition, results

obtained using the 1*+yr storm are also included for reference. Do CSOs occur for the *.%) in.

storm and all the wastewater flows are diverted into the interceptor. 0or the %+ and 1*+yr storms,

all the regulators are releasing discharges into the stream. Dote how the occurrence of CSOs isreflected in the drastic increase of the peak discharge simulated at the stream outfall O1. The

peak discharge changes from *. cfs for the *.%) in. storm to %*.1) cfs for the %+yr storm and;>.;> cfs for the 1*+yr storm. Table + also shows that the maximum discharge conveyed by the

interceptor barely changes with the magnitude of the storm once all the regulators are

discharging CSOs to the stream. The maximum water depth in the well is practically the same for

the %+ and 1*+ year storm. This result clearly shows that flow regulators work in a way such thatall the flows above the diversion capacity are directly discharged into the water body.

Ta'%e 8-8: Su!!ary & ,e !ain resu%s &r (ieren s&r! e.ens

N&(e ID


21/21

#ax. discharge /3(cfs, regulator 5; * &.) 1).;>

#ax. discharge /4(cfs, regulator 5= * >.>& .&

8.$ S"mmary

This example illustrated how to represent combined sewer systems composed of

combined sewer pipes, flow regulators, a pump station and a force main line. The model buildwas used to simulate the performance of the system using different storms and the occurrence of

Combined Sewer Overflows (CSOs. The key points illustrated in this example were7

1. Combined sewer systems and their main components can be easily modeled using the

hydraulic features available in S"##. 0low regulators work in a way such that all the flowsabove the diversion capacity are directly discharged into the water body.

%. 4ry weather flows can be directly defined in nodes using the dry weather tool available in the2nflow 'ditor available in the roperty Table. These flows can be specified using constant

values or time patterns.

). 0low regulators in S"## can be represented using a combination of pipes, orifices andweirs. The final modeling of these regulators should consider the local conditions in the

combined sewer systems under analysis.

;. $ wet+well pump station in S"## can be modeled using a storage unit representing the

well and a pump. The operation of the pump is defined through the pump curve and otheroperation rules that include the initial status and the startup and shutoff elevations.

=. $ force main line can be defined in S"## by using a set of pipes connected by nodes with

a maximum depth of -ero and an arbitrary highsurcharge de-th, defined to avoid floodingwhen the main line works under surcharged conditions.

combined sewer overflows example

Documents