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Yivitesh Sookun
National Diploma in Civil Engineering, Cohort
! "ull#Time
The $auritius %nstitute of Trainingand Development
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&iterature review The management of water resources is control by the Ministry of
Energy and Public Utilities in Mauritius. This power has been delegated
to the Water Resources Unit founded in May 199! which is responsible
for the assessment! management! de"elopment and conser"ation of
water resources. #n the past two subsidiary bodies ha"e been
established in Mauritius! the $entral Water %uthority &$W%' responsible
for portable water distribution and the Wastewater Management
%uthority &WM%'! responsible for managing waste water.
The 'astewater $anagement Authorit(Mauritius had its (ewerage Master Plan prepared in the nineties and
then the Wastewater management %uthority &WM%' was proclaimed on
the )th %ugust *))1 in the aim of being responsible for all matters
relating to the collection! treatment and the disposal of wastewater
throughout Mauritius! under the Wastewater Management %ct *)))
and it operates under the wing of the Ministry of Energy and Public
Utilities. (ince the creation of the Wastewater Management %uthority!
it is now called to manage the public wastewater system which
consists of +91 ,m of sewer networ,! -* pumping stations and 1)treatment plants including main treatment plants which are located
at (t Martin! /rand 0aie! 0aie du Tombeau and Montagne ac2uot.
The duties of the 'astewater $anagement Authorit( )'$A*+ To maintain and mange all e3isting public sewer and wastewater
sewer in Mauritius. Regulate the construction of pri"ate sewers! enforce their
maintenance according to standard as may be prescribed and
pro"ide for their inspection. $ontrol and monitor pollution! pri"ate sewers and use of
e2uipment in relation to wastewater systems. To ma,e sure that no storm drainage is connected or get mi3ed
up with the wastewater system.
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$ontrol and monitor the pollution discharged to wastewater
system by any person. $onduct and underta,e research and studies for the
implementation and de"elopment of pro4ects relating to
wastewater sector. Promoting the treatment and reuse wastewater.
Ensure the generation of su5cient resources from tari6 to
7nance the operation! maintenance and depreciation cost of
wastewater system! sewerage and sewage treatment
installations.
revious works and pro-e.ts The 8ational (ewerage Master Plan &8(MP' was accomplished in the
year 199. The principal aim of this 8ational (ewerage Master Plan
was to pro"ide public sewerage co"erage mainly in the urban areas
about +) of the population by *)1) and :) by the year *)*). The
8(MP goal is to target 1)) connection to the sewerage system by
*)).
(ince 199 the /o"ernment has started implementing the master plan
&8(MP' and has been 7nancing the following pro4ects;
The laines 'ilhems sewerage network
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increasing >ow! hence the Master Plan suggested in pro"iding a new
sewer trun, in the year *))=. The total cost of the new sewer trun,
was Rs .= billion and directing all the >ow to (t Martin treatment
plant.
Baie du Tom/eau sewerage pro-e.t The 0aie du Tombeau sewerage pro4ect consists of two areas;
1. 8orthern Port ?ouis*. 0aie du Tombeau
The aim of this pro4ect was to rehabilitate the 8orthern wor,! collection
of wastewater from the area also including *1)) house connections
and pumping the sewage >ows into the new wastewater treatment
plant.
$ontagne 0a.1uot sewerage pro-e.t This pro4ect consists of transportation! treatment and disposal of
:!))) m3
per day of wastewater from the area of southern Port
?ouis! lower 0eau 0assin and $oromandel also including the industrial
waste of Plaine ?au@an! la Tour Aoenig and Pailles.
"a.ts and 2gures on pu/li. sewer s(stem in $auritius
The per.entage .onne.tion to pu/li. sewer#n *)1)! about *9 number of people were connected to the sewer
system and the remaining -1 uses on site wastewater disposal
system.
The volume of wastewater treated /( pu/li. treatment stationBrom *))1 to *)1)! there has been an increase in the "olume of
wastewater treated by the treatment stations.
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million cubic metres. The "olume rises up to appro3imately +.))
million cubic metres between *))= and *))-.
llustration of 3re(water and Bla.kwater from a household
Consumption of water dail( /( a person(ince water is essential for a human being! they ma,e use of it for
"arious acti"ities in their daily life. %ccording to WCD &World Cealth
Draganisation'! a person uses appro3imately 1+) to 1=) litres of water
daily. Their daily acti"ity consists drin,ing! coo,ing! personal washing!
washing clothes and cleaning home.
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4sage of water dail( per person in terms of gallons
A.tivities per
person
3allons used
Page =
5 gallons per 6ush
! gallons per da(
Total 7 58! 7 9: gallons
9 minutes of shower
; gallons per da(
Total 7 98; 7 ; gallons
gallons per da(
: glasses of water
9 gallon per da(
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Conversion of gallons to litres
Total usage of water daily per person = 18 + 20+ 2.5+ 1= 41.5 gallons1 gallon = 3.78541 litres
41.5 gallons= 41.5 x 3.78541= 157 litres
?euse of treated wastewater
The reuse of treated wastewater ha"e been a common practice for
de"eloping countries such as %sia and %frica o"er the past few years
and it is now recei"ing particular attention due to rapid urbani@ation.
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'astewater treatment
#n order to reuse wastewater! it is important to treat raw wastewater to
meet speci7c needs and public safety. The wastewater treatment
processes are classi7ed as such;
1. Primary treatment*. (econdary treatment. Tertiary treatment
rimar( treatment Treatment in"ol"es sedimentation &sometimes preceded by screening
and grit remo"al' to remo"e gross and settleable solids. The remaining
settled solids! referred to as sludge! are remo"ed and treated
separately.
Se.ondar( treatment/enerally! a le"el of treatment that remo"es :+ of 0iological D3ygen
occulation and 7ltration.
'astewater treatment pro.ess
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'astewater reuse areas of appli.ation
Categor( of reuse E8ample of appli.ation
• 4r/an reuse )unrestri.ted*
• @ther
&ands.ape irrigation of
parks, pla(ground, s.hool
(ards, golf .ourse
"ire prote.tion,
Constru.tion
• Agri.ultural "ood .rops
Non food .rop
%rrigation of food .rop for
human .onsumption
%rrigation of 6owers, 2/ers,
fodders= Seed .rops,
pasture .ommer.ial
nurseries, sod farms
• Environment enhan.ement Arti2.ial wetland .reation
• %ndustrial reuse Cooling water s(stem,pro.ess water, /oiler feed
water, toilets, laundr(,
.onstru.tion wash#down
water, air .onditioning
Agri.ultural wastewater reuse
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&Rice farming with treated wastewater in apan!
Aumamoto'
'astewater produ.tion and reuse of treated wastewater in
$auritius#n Mauritius! the rate of consumption of freshwater is high and the
agricultural sector is one of the largest users of water for irrigation
purpose. %lternati"e sources of water supply ha"e been found and it
consists of using treated wastewater and this concept ha"e been using
worldwide and Mauritius should not be an e3ception. The rate of
wastewater is increasing and it is generated from domestic!
commercial and industrial acti"ities. #n *)1* the "olume treated was
9.1 M m3
and it is e3pected to rise about -9.9 Mm3
in *).
'astewater treated and reuse for irrigation purpose
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The irrigation authority signed an agreement with the Wastewater
Management %uthority for the reuse of treated wastewater to tertiary
le"el using UK light in the year *))=. %n e3pected total "olume of
)!))) m3
Iday tertiary treated eNuent is deli"ered by the (t Martin
Wastewater Treatment Plant to the West $oast canal system to irrigate
=)) hectares of sugarcane plantation. The 73ed price charged to
farmers for treated water was :) centsI m3
! but this price was not
a6ordable by the farmers. %fter the e3piration of the agreement in
*))9! the irrigation authority had no alternati"e not to renew the
contract. ?ater the /o"ernment analyse the situation and drop to aconclusion where the price of treated water charged to farmers was
73ed to -) centsI m3
! but again farmers ha"e disagreed and the
Ministry of Energy and Public Utilities had to re"iew the pricing
structure.
$ethodolog(
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retrie"e data needed for the design and construction of sewers
but to record pertinent information about the local conditions
before construction begins and these information are;
1. Maps and other drawing of area
*. ?ocations of streets! alleys! stream! drainage ditches andother features that may a6ect the sewer system
. % bench mar, on each bloc, of street
. ?ocal rainfall and runo6 data
+. $ondition of the soil where sewers will be constructed
?eview design .onsideration and sele.t /asi. design dataand .riteria
Design the sewers
repare .ontra.t drawings and spe.i2.ations
"low of pro.edures in planning, designing and .onstru.tion of
sewers
Stages of sewer design pro.edures The design procedures are composed of + stages and they are as such;
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Stage 9# reliminar( site investigation, data .olle.tion and
anal(sis
#denti7cation of area to be ser"ed or de"eloped
$ollect topographic map and geographic data
/ather information about local conditions such as;9= Possible contours at suitable inter"als! high and low
changes on surface slope.;= #ndustry or other utilities5= Physical feature &e3ample; ri"er'= Road layout>= ?ocal rainfall and runo6 data
Underta,e site in"estigation and include sur"eys to identify
potential con>ict with other ser"ices.
Stage ;# reliminar( horiontal la(out of sewers
&a(out of sewers
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The minimum diameter of manholes should be 1*)) mm &:
in' largerdiameters are preferable for large diameter sewers. %
minimum accessdiameter of =1) mm &* in' should be pro"ided.
Stage 5# Design sewer siing
ow rates for each section in the system
(elect pipe si@es! slopes! and in"erts. Perform the hydraulicdesign of the system. Re"ise selections until the design criteria
are met.
Stage # Cost estimation $omplete cost estimate for the design and alternate designs.
$arefully re"iew all designs! along with assumptions! alternates!
and costs.
Stage ># ?evision of design $omplete the plan and pro7le construction drawings and prepare
the speci7cations and other bid documents.
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The manning e2uation was de"eloped to estimate the a"erage
"elocities of >ow rate in open channel.
Where!
K O mean "elocity &mIs'
s O hydraulic gradient &energy loss per unit length'
n O Mannings roughness coe5cient
R O hydraulic radius &m'
?7 Area of liquid (m2)
Wetted perimeter (m)
Determining the minimum and ma8imum velo.ities in
sewer#n this particular section # will gi"e procedures of how to determine the
minimum and ma3imum of sewers. /enerally! "arious formulas are
a"ailable to determine the >ow rate in sewers. ow in both open
and closed conduits.
$inimum velo.it(Ma,ing reference to 0( E8 -+*; *)):! it states that to achie"e the self
cleansing of small diameter sewers! the "elocity should be at least ).-
mIs. % minimum "elocity allows the sewage >ow to self cleanse
amount of silt to be carry through sewers! and help to minimi@e sewer
obstruction. Bor larger diameter sewers up to 9))mm! the minimum
"elocity should be of 1.) mIs to achie"e self cleansing$a8imum velo.it(
The occurring of fast >ow is obtained when the sewer is laid at steepgradient and >ow may become supercritical. Bast >ow is not stable and
will gi"e rise to scouring and ca"itation when pipe surface is not
smooth. The ma3imum "elocity at pea, >ow shall be to mIs.
Page 1=
71n = R
2 /3
= S1/2
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(ometimes due to the topography of the land! sewers with steep
gradient are una"oidable. Cence! to reduce the ma3imum "elocity!
?aying of sewers with >atten gradient with the installation of bac,drop
manhole is re2uired.
The manning e2uation was de"eloped to estimate the a"erage
"elocities of >ow rate in open channel.
"low @pen .hannelDpen channel >ow must ha"e a free surface! where normally free
water surface is sub4ected to atmospheric pressure! which remains
relati"ely constant throughout the entire length of the channel. Types
of >ow in open channel are as follows;
Stead( 6ow 'hen dis.harge )* does not
.hange with time
4niform 6ow 'hen depth of 6uid does not.hange for a sele.ted length or
se.tion of .hannel4niform stead( 6ow 'hen dis.harge does not .hange
with time and depth remains
.onstant for sele.ted se.tionaried stead( 6ow Depth .hanges /ut dis.harge
remains .onstantaried unstead( 6ow Both depth and dis.harge .hange
along a .hannel se.tion
?apid var(ing 6ow Depth .hange is rapid
3raduall( var(ing 6ow Depth .harge is gradual
$anning roughness .oe.ient, )n*When using the manning e2uation in the design of sanitary sewer! the
manning roughness coe5cient "aries due to the following factors;
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1. The types of material use for the design*. The material being transported
The carrying capacity of sewers are mainly reduced by house
connection! 4oints which do not line up properly! deposits in sewers and
coating inside the pipe. Bor such reason when designing sanitary
sewers! assumption ha"e been made where manning roughness
coe5cient are considered to be greater than that which would occur if
clear water carried in a straight and well aligned sewer.
$anning roughness .oe.ient .ommonl( used in sewer design
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Determining the .apa.it( of sewer pipe
Brom them Manning E2uation
71
n = R2 /3
= S1/2
K O Mean "elocity &mIs'
Where!nO Manning coe5cient( O (lope of energy line
When the "alue of K &mean "elocity' is obtained! using the continuity
e2uation to 7nd the discharge in pipe.
Where!Q O ow rate in pipeK O Mean "elocity% O $ross sectional area of >ow
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Determining minimum and ma8imum grade#n this section # will be gi"ing procedures of how # will proceed to
calculate gradient of sewer pipe.
#n the design of drainage or sanitary sewer pipe! it should be laid to an
ade2uate gradient where the design will wor, accurately and
functional. #f the gradient of the selected pipe is too steep! the li2uid
may run faster than the solids and thus lea"ing the solids stranded and
could bloc, the pipe. Dn the other hand! if gradient is not too steep
enough! it may also bloc, the pipe as solids may slow down and
become stranded.
/radient may be de7ned as fall di"ided by distance.
&(ection of a pipe'
Basi. formula to .al.ulate gradient for sewer pipe
Where!
1. Ball in a pipe may be de7ned as the "ertical amount by which the
pipe drops o"er a distance*. The distance can be between sections of pipe or between to
manholes.
Page *)
3radient 7 Fall
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Determining grades for sewer pipe
Cal.ulating falls and gradient for pipe To determine the gradient of pipe!
Where!MC 1; Manhole 1MC *; Manhole *
The abo"e formula can be rearranged to 7nd fall if the gradient is
already a"ailable
Cal.ulating invert levels
Consider the se.tion of a pre.ast manhole
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3radient 7
"all 7 3radient 8
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To 2nd the invert level of sewer pipe the /elow .al.ulation is
use to determine it,
'here,3round elevation in
)m*
Cover in )mm*
Diameter of pipe in
)mm*
Page **
%nvert level of pipe 7 3round elevation F Cover F
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Data Colle.tion%t this stage of my pro4ect # will gi"e an o"er"iew of my data collection.
The 7rst part of my data collection consists of the collection a hard
copy of the location plan of the Anowledge 0ased Training $entre from
the administration department itself.
Dnce # obtain the location plan from the administration o5ce! the
second part of my data collection are as follows;1. To carry out a site in"estigation! to collect data about the local
conditions of the location! whether any structure &manmade or
natural' and ser"ices will a6ect the propose sewer design.*. #dentify potential con>icts with other ser"ices &$W% and $E0' on
location.. To carry out sur"ey to gather information about the topography
of the location.. $ollect speci7cations about di6erent types of sewer pipe
a"ailable on mar,et.
Brom the sur"ey # conducted on the site! the data obtain are as such;
&o.ation plan
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Data o/tained after .ondu.tion surve( on site The pin, line on the location plan shows the propose sewer line for my
design! and after # conducted my sur"ey on site the data obtain are
shown in the table below.
Page *
oi
nt
Ba.k#sight "ore#sight : 99=:: 9=; A to B
9=9:
C 9=>5> 9=!G 99=GH 9=;9 B to C
>=;
D 9=GH5 9=!9 99=H5; 9=95H C to D
>H=
E 9=!H 9=!> 99=H59 9=;:; D to E
9G=G>
" 9=!H 9=;5G E to "
9;=!
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Where!
C.#; Ceight of #nstrument
R.?; Reduced ?e"el
&o.ation of point A to B )Surve(*
&o.ation of point B to C )Surve(*
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&o.ation of point C to D )Surve(*
&o.ation of point D to E )Surve(*
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&o.ation of point E to " )surve(*
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T(pes of sewer pipes availa/le
The table below shows the di6erent types of sewer types a"ailable on
mar,et.
• As/estos .ement
pipe These t(pse of pipes are
manufa.tured using mi8ed of as/estos
2/ers, sili.a and .ement=
Sies availa/le 9#9 .m internal
diameter and length up to m=
%t .an /e easil( assem/le with the
help of .ouplingsknown as ring tie .oupling=
• itri2ed .la( pipe Kitri7ed clay pipes are made of clay and
are sub4ected to high temperature toachie"e "itri7cation.
Kitri7cation is a process which gi"es the
results of hard and inert ceramic.
Mainly used for gra"ity sewer collection
due to it long life span and resistance
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against corrosion.
%d"antages
1. Resistant to corrosion! it can carry
polluted water &such as sewage'.*. #nterior surface is smooth and it is
hydraulically e5cient. Pipe is imper"ious and strong in
compression.
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• lasti. sewers#
C pipe Plastic sewer pipe are recent material used
for sewer pipe. They are a"ailable in si@es
-+ to 1+ mm e3ternal diameter and used
for drainage wor,s
They are resistant to corrosion! lightweight!
economical in laying &4ointing and
maintenance'! pipe is tough rigid and ease
for transportation.
• 3lass 2/er
reinfor.ed plasti.
pipes
These pipes ha"e a better strength! high
tensile strength! durability! high resistance
corrosion and it is lightweight. #t can bemanufactured up to *. m diameter and
1:m in length.
/lass reinforced plastic pipes represent the
ideal solution for transport of any ,ind of
water! chemicals! eNuent and sewage!
because they combine the ad"antages of
corrosion resistance with a mechanical
strength which can be compared with the
steel pipes.re.ast sanitar( sewer manholes sies availa/le on market This table below shows the di6erent si@es of rings a"ailable for precast
manhole. The minimum manhole diameter si@e is -+)mm and the
ma3imum manhole diameter a"ailable is *))mm. &referencing'
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$oncrete chamber manhole ring
(i@es a"ailable
9))mm 3 *+)mm
9))mm 3 +))mm
9))mm 3 1)))m
1)+)mm 3 *+)mm
1)+)mm 3 +))mm
1)+)mm 3 -+)mm
1)+)mm 3 1)))mm
1*))mm 3 *+)mm
1*))mm 3 -+)mm
1*))mm 3 1)))mm
1+)mm 3 +))mm
1+)mm 3 -+)mm
1+))mm 3 +))mm
1+))mm 3 -+)mm
1:))mm 3 +))mm
1:))mm 3 +))mm
1:))mm3 -+)mm
*))mm 3 +))mm
Con.rete ring .over sla/
Sies availa/le
Hmm 8 !mm
9>mm 8 !mm
9;mm 8 !mm
95>mm 8 !mm
9>mm 8 !mm
9:mm 8 !mm
;mm 8 !mm
Cast iron manhole .over
!& 8 !' 8 9<
!G>& 8 !w 8 9G><
0ase ring(i@es a"ailable
9))mm 3 =))mm
1)+)mm 3 ))mm
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1)+)mm 3 =))mm
1*))mm 3 1+)mm
1*))mm 3 ))mm
1*))mm 3 =))mm
1*))mm 3 9))mm
1+))mm 3 =))mm
1:))mm 3 =))mm
*))mm 3 =))mm
4C Sewer pipeSies availa/le
Sewer ipe Dou/le So.ket
Bran.h > Degree
Sies availa/le
;mm 8 99mm
;mm 8 9>mm
;>mm 8 ;>mm
59>mm 8 9>mm
Sewer ipe Coupler
99mm to mm
Sewer pipe Bend So.ket >
Degree
99mm to mm
Page *
Diam
eter)
mm*
'all
Thi.k
ness
)mm*
&engt
h)m*
99 5=; !9> =9 !
; =; !;> !=; !59> G=G !
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3ull( trap outlet
Sies availa/le
>mm 8 G>mm 89>mm
5G>mm 8 Hmm 8
5>mm
4C 3ull( Trap
Sies availa/le
@utlet 99mm
@utlet 9>mm
Design stage
Cal.ulation to determine velo.it( and dis.harge in sewer pipeConsider point A to B
/round slope O100.244−100.000
14.018 O1
57.5
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The actual ground slope is &1I+-.+'! but for the design # will choose a
slope of &1I=)'.
%ssume a sewer pipe of 1+)mm diameter connect to the gully trap
o"er a distance of -m until the stand pipe.
Brom manning e2uation! # will determine the "elocity in the sewer pipe
%pply manning formula; K O1
n. R
2
3 . S1
2
RO Cydraulic radius O
π D
2
4
πD
2
= D
4 O0.15
4=0.0375
(O (lope O &1I=)'nO Manning roughness coe5cientO ).)1
Replacing all "alue appropriately! the "alue obtain for "elocity is 1.1
mIs.
Bor the discharge in the pipe! # will apply the continuity e2uation.
Dis.harge, 7A
%O π D
2
4
%O ).)1-= m2
KO 1.1mIs
QO ).)1-= 3 1.1 O ).)19=
m3
Is
Brom con"ersion1cubic metre O 1))) litresQO ).)19= 3 1))) O 19. ?Is"rom stand pipe to point B# will use the manning e2uation to determine the "elocity.
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R O Cydraulic radiusO
π D
2
4
πD
2
= D
4 O0.2
4=0.05
( O (lope O 160
n O Manning roughness coe5cientO ).)1When replacing all "alues appropriately in the manning e2uation! the
"elocity obtain is 1.mIs.Bor the discharge in the pipe! # will apply the continuity e2uation.
Dis.harge, 7A
%O π D
2
4
%O ).)1 m2
KO 1.mIs
QO ).)1 3 1. O ).)):* m3
Is
Brom con"ersion1cubic metre O 1))) litres
QO ).)):* 3 1))) O ).: ?Is
Consider point B to C The data obtained after # carried out sur"ey are as follows;
/round le"el at point A7 9=;m and at point C7 9=;9m
The distance between % and 0 is >=;m
9= Determine the a.tual ground slope /etween A and B
/round slope O100.244−100.214
50.200 O1
1633.3
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A propose sewer network design for KBTC
(ince the actual ground slope is not enough steep! # will choose an
appropriate slope of &1I:)' for the design.;= Assume a sewer pipe 4C of ;mm )=;m* for the design
and using the $anningIs E1uation to 2nd the velo.it( in the
pipe= )
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A propose sewer network design for KBTC
Consider points C to D# will apply the same method to determine the "elocity and capacity of
sewer pipe UPK$ *))mm.
/round slope O100139−100.214
59.400=
1
792
The actual slope of ground is not enough steep to be use for the
design. # will choose a slope of &1I:)' to proceed with the design.
Brom manning e2uation! # will determine the "alue of K mIs &"elocity'.
R O Cydraulic radiusO
π D
2
4
πD
2
= D
4 O0.2
4=0.05
( O (lope O
1
80 O ).)1*+
n O Manning roughness coe5cientO ).)1When replacing all "alues appropriately in the manning e2uation! the
"elocity obtained is 1.*mIs.
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A propose sewer network design for KBTC
%gain # will be using the continuity e2uation to determine discharge in
sewer pipe.Dis.harge, 7A
QO ).)1 3 1.* O ).)-* m3/s
Brom con"ersion1cubic metre O 1))) litresQO ).)-* 3 1))) O -.* ?IsCence! the pipe 0 to $ has a capacity of -.* ?Is.
Consider points C to D#
will apply the same method to determine the "elocity and capacity of sewer
pipe UPK$ *))mm.
/round slope O100139−100.214
59.400=
1
792
The actual slope of ground is not enough steep to be use for the
design. # will choose a slope of &1I:)' to proceed with the design.
Brom manning e2uation! # will determine the "alue of K mIs &"elocity'.
R O Cydraulic radiusOπ
D2
4
πD
2
= D
4 O0.2
4=0.05
( O (lope O 1
80 O ).)1*+
n O Manning roughness coe5cientO ).)1When replacing all "alues appropriately in the manning e2uation! the
"elocity obtained is 1.*mIs.
%gain # will be using the continuity e2uation to determine discharge in
sewer pipe.Dis.harge, 7A
QO ).)1 3 1.* O ).)-* m3/s
Brom con"ersion
Page :
oint ipe diameter
)mm*
elo.it( )ms* Capa.it( )&s*
B to C ; 9=; 5G=;
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A propose sewer network design for KBTC
1cubic metre O 1))) litresQO ).)-* 3 1))) O -.* ?Is
Cence! the pipe 0 to $ has a capacity of -.* ?Is.
Consider point D to E
/round slope O100.282−100.237
12.600=
1
280
The actual slope of ground is not enough steep to be use for the
design. # will choose a slope of &1I1))' to proceed with the design.
Brom manning e2uation! # will determine the "alue of K mIs &"elocity'.
R O Cydraulic radiusO
π D
2
4
πD
2
= D
4 O0.2
4=0.05
( O (lope O 1
100 O ).)1
n O Manning roughness coe5cientO ).)1When replacing all "alues appropriately in the manning e2uation! the
"elocity obtain is 1.)mIs.%gain # will be using the continuity e2uation to determine discharge in
sewer pipe.
Dis.harge, 7A
QO ).)1 3 1.) O ).)1 m3/s
Brom con"ersion1cubic metre O 1))) litres
QO ).)1 3 1))) O 1 ?Is
Cence! the pipe 0 to $ has a capacity of 1 ?Is.
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oint ipe diameter
)mm*
elo.it( )ms* Capa.it( )&s*
C to D ; 9=; 5G=;
oint ipe diameter
)mm*
elo.it( )ms* Capa.it( )&s*
D to E ; 9= 59
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A propose sewer network design for KBTC
oint E to "
/round slope O100.282−100.237
12.600 O1
280
The actual ground slope is &1I*:)'! but for the design # will choose a
slope of &1I1))'.
%ssume a sewer pipe of 1+)mm diameter connect to the gully trap
o"er a distance of =m until the stand pipe.
Brom manning e2uation! # will determine the "elocity in the sewer pipe
%pply manning formula; K O1
n. R
2
3 . S1
2
RO Cydraulic radius O
π D
2
4
πD
2
= D
4 O0.15
4=0.0375
(O (lope O &1I1))'
nO Manning roughness coe5cientO ).)1
Replacing all "alue appropriately! the "alue obtain for "elocity is
).:=mIs.
Bor the discharge in the pipe! # will apply the continuity e2uation.
Dis.harge, 7A
%O π D
2
4
%O ).)1-= m2
KO ).:=mIs
QO ).)1-= 3 ).:= O ).)1+1 m3
Is
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A propose sewer network design for KBTC
Brom con"ersion1cubic metre O 1))) litresQO ).)1+1 3 1))) O 1+.1 ?Is
"rom stand pipe to point E
# will use the manning e2uation to determine the "elocity.
R O Cydraulic radiusO
π D
2
4
πD
2
= D
4 O0.2
4=0.05
( O (lope O 1
100
n O Manning roughness coe5cientO ).)1When replacing all "alues appropriately in the manning e2uation! the
"elocity obtain is 1.)mIs.Bor the discharge in the pipe! # will apply the continuity e2uation.
Dis.harge, 7A
%O π D
2
4
%O ).)1 m2
KO 1.)mIs
QO ).)1 3 1.) O ).)*=+ m3
Is
Brom con"ersion1cubic metre O 1))) litres
QO ).)*=+ 3 1))) O *.- ?Is
Summaried ta/le for velo.it( and .apa.it(oint ipe diameter
)mm*
elo.it( )ms* Capa.it( )&s*
A to B 9> 9=9 9H=
A to B ; 9=5 =:
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A propose sewer network design for KBTC
B to C ; 9=; 5G=;
C to D ; 9=; 5G=;
D to E ; 9= 59=
E to " ; 9= 5;=G
E to " 9> =:> 9>=9
Cal.ulation to determine invert level
Consider point A to B%t point % /ully trapO =))mm and /round le"elO 1)).)))m
#n"ert le"elO 1)).)))).=O 99.))m
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A propose sewer network design for KBTC
1
60 Oertical
7.018 O ).11-)m
KerticalO ).11-)m
The fall from point 0 to foot of stand pipe is ).11-)m
#n"ert le"el at foot of stand pipeO 9:.)).11-)O 9-.9*-mConsider point B to C
/round le"elO 1)).*m! /radientO &1I:)'! Pipe diameterO *))mm
%ssume a co"er of *m
#n"ert le"el at point 0O /round le"el $o"er Pipe diameter
#n"ert le"el at point 0O 1)).* * ).* O 9:.)m
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A propose sewer network design for KBTC
Consider point C to D
#n"ert le"el at point $O 9-.1-m!
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A propose sewer network design for KBTC
Consider point E to "
%t point B /ully trapO =))mm and /round le"elO 1)).*-m
#n"ert le"elO 1)).*-).=O 99.=-m
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A propose sewer network design for KBTC
The ta/le /elow shows the invert level and .hainage of the
following points+
Point #n"ert le"el &m' $hainage &m'
% HH= =
0 H:= 9=9:
$ HG=9G !=;9:
< H!=!G 9;5=!9:
E H!=H! 99=5!:
B HH=!5G 9>5=H!:
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Dis.ussion
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A propose sewer network design for KBTC