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CE331EnvironmentalEngineeringI
Water DistributionWaterDistribution
Dr.Tanvir AhmedAssistant ProfessorAssistantProfessorDept.ofCivilEngineering,BUET
Coursematerials:teacher.buet.ac.bd/tanvirahmed/
PurposeoftheWaterDistributionSystem
o Tomakewateravailableincloseproximitytotheconsumerso Tosupplywaterinadequatequantitiesaccordingtothe
demandoftheconsumers
o Tosupplywaterwithadequatepressureo Toregulatewatersupplyasperrequirementg pp y p q
CE331:EnvironmentalEngineering Dr.Tanvir Ahmed
ClassificationofT&DSystem
1) Gravityflowsystem2) SystemwithDirectPumping3) System with pumping and storage3) Systemwithpumpingandstorage
Gravityflowsystem
CE331:EnvironmentalEngineering Dr.Tanvir Ahmed
ClassificationofT&DSystem
SystemwithDirectPumpingy p g
SystemwithPumping
CE331:EnvironmentalEngineering Dr.Tanvir Ahmed
y p gandStorage
GravityFlowSystem
1) Requiresnoenergytooperate2) N f i
Advantages
2) Nopumps,veryfewmovingparts3) Construction,operationandmaintenancesimple
1) NotsuitableforflatcountrieswhereanelevatedwaterDisadvantages)sourceisunavailable
2) Waterlossbyleakageandwastageiscomparativelyhigheras the system remains under constant pressureasthesystemremainsunderconstantpressure
CE331:EnvironmentalEngineering Dr.Tanvir Ahmed
DirectPumpingSystem
1) Watercanbepumpedonlywhenrequired2) L l d l k
Advantages
2) Lowwaterlossduetosystemleakage
1) PowerfailuremeansbreakdownofthesystemDisadvantages) y
2) Directpumpingatauniformrateisnotabletomeetvaryingwaterdemandandmaintainrequiredpressureunder varying rates of consumptionundervaryingratesofconsumption
3) Maintenanceandoperationcostsarehigh4) Inflowofwaterthroughleakscausecontaminationduring
i h
CE331:EnvironmentalEngineering Dr.Tanvir Ahmed
nonpumpinghours
PumpingwithStorageSystem
1) Systemmorereliableandcancopewithfluctuationofd d
Advantages
waterdemand2) Thepumpscanbeoperatedatratedcapacityresultingin
higherefficiencyandeconomyinoperationg y y p3) Reasonablepressurecanbemaintainedwithvaryingwater
demandandthereisnopossibilityofinflowofpollutedwater in the systemwaterinthesystem
Disadvantages
1) Relativelyhigherinitialcost2) Comparativelyhigherlossduetoleakageandwastage
CE331:EnvironmentalEngineering Dr.Tanvir Ahmed
DistributionNetwork
1) BranchedDistributionNetwork2) LoopedDistributionNetwork
CE331:EnvironmentalEngineering Dr.Tanvir Ahmed
BranchedNetwork
1) Relativelycheapaslengthofpiperequiredisless2) E f h d li d i d d i i di h d
Advantages
2) Easyforhydraulicdesignanddeterminingdischargeandpressureatanypoint
3) Canbeeasilyexpandedtoprovidecoveragetonewly) y p p g ydevelopedareas
Disadvantages
1) Stagnantwater(i.e.atdeadends)promotessedimentationand water contamination
Disadvantages
andwatercontamination2) Frequentblowofforflushingisneededtokeepthesystem
clean3) Repair work in mains and sub mains cuts off water supply
CE331:EnvironmentalEngineering Dr.Tanvir Ahmed
3) Repairworkinmainsandsubmainscutsoffwatersupplydownstream
LoopedNetwork
1) Nostagnationofwater,consumptionofwateratanypointi fl i h h l k
Advantages
activatesflowinthewholenetwork2) Repairworkdoesnotdisruptcontinuityofwaterflow3) Goodcontroloverflowofwater)
Disadvantages
1) Highinitialcost2) A large number of valves is needed if control of flow in the
Disadvantages
2) Alargenumberofvalvesisneededifcontrolofflowinthesystemisdesired
CE331:EnvironmentalEngineering Dr.Tanvir Ahmed
DistributionSystemDesign
54.063.055.0 LhCDV = (BritishUnits)RecallHazenWilliamsFormulaforcircularpipes:
L
54.063.26107.3 LhCDV= (Qinlitre/sec,Dinmm,hL inm/m)
874851610391 DQh (when C = 130)87.485.161039.1 = DQhL (whenC=130)87.485.161059.1 = DQhL (whenC=120)
CE331:EnvironmentalEngineering Dr.Tanvir Ahmed
DesignProcedureforBranchedNetwork
1) Preparelayoutofthepipesusingthemapofroadnetworks2) D i k fl diff i d h b2) Determinepeakflowatdifferentpointsandthereby
determinethequantityflowingthrougheachsectionofthepipe.Peakflow=averagedailyflow peakfactorp p g y p
3) Assumepipesizesofallpipesinthenetwork(tocalculatepipesizethevelocitymaybeassumedtobe1m/s)
4) Calculate h (use Hazen Williams Formula) and total head4) CalculatehL (useHazenWilliamsFormula)andtotalheadloss(usingtotallengthofthepipe)
5) Determinetheterminalpressureheadtakingintoaccounth h i l i f h ithechangeinelevationofthepipe
6) Incaseofdifferencebetweenthecomputedandpermissibleterminalpressure,revisethepipesize
CE331:EnvironmentalEngineering Dr.Tanvir Ahmed
p p p p
DesignProcedureforLoopedNetwork
Requirestrialanderrorsolution
Principle:Principle: Theflowenteringajunctionmustbeequaltotheflow
leavingit Thealgebraicsumofthepressuredrop(headloss)around
anyclosedloopmustbezero
H d C d l d th d f i i ti iHardyCrossdevelopedamethodofsuccessiveapproximationinwhichthecircuitsarebalanced,distributionofflowisdeterminedandtheabovetwoconditionsofflowaresatisfied.
Aflowisassumedforeachpipe,acorrectiontotheflowisappliedsuccessively for each pipe loop until the correction is reduced to
CE331:EnvironmentalEngineering Dr.Tanvir Ahmed
successivelyforeachpipeloopuntilthecorrectionisreducedtoanacceptablevalue
Thecorrection,inHardyCrossMethod
IfassumedflowisQa andactualflowisQ,thenthecorrectionisQ Qa
+= aQQ( ) 0=+ xaQk
87.485.161039.1/ == DQLHhL (whenC=130)
(kisaconstantdependingonthelength diameter and roughness ofxkQH = length,diameterandroughnessofthepipeaswellasfluidproperty)
(x = 1 85 according to Hazen Williams formula)
CE331:EnvironmentalEngineering Dr.Tanvir Ahmed
(x=1.85accordingtoHazenWilliamsformula)
Thecorrection,inHardyCrossMethod
( ) xExpandingtheequation ( ) 0=+ xaQk1 21 x 0
21 221 =+
++ KKxaxaxa QkxQkxkQ is small compared to Q the third and all successive termsissmallcomparedtoQ,thethirdandallsuccessivetermsoftheequationmaybeneglected
01+ xx QkkQ 0=+ aa QkxkQSolvingfor:
1
= xa
xa
Qkx
kQ
=
aQHxH/
CE331:EnvironmentalEngineering Dr.Tanvir Ahmed
aQ aQ
Thecorrection,inHardyCrossMethod
( ) ( )( ) ( )( ) ( )[ ]adcdcadabcbcab
dcadbcab
QHHQHHxHHHH
// +++++=
CE331:EnvironmentalEngineering Dr.Tanvir Ahmed
StepsinHardyCrossMethod
1) Assumereasonableratesofflowineachpipesuchthattheinflowequalsoutflowineachjunction
2) I h l d i h h d l H d H/Q f ll i2) Ineachloop,determinetheheadloss,HandH/Qforallpipes3) Computethetotalheadlossaroundeachcircuitwithgiving
dueconsiderationtosigng4) ComputeH/Qforthesamecircuitwithoutgivingany
considerationtosign5) Calculate the correction for each loop and apply to each loop5) Calculatethecorrection,foreachloopandapplytoeachloop.
Whenthesignofisnegative,decreasetheclockwiseflow,increasethecounterclockwiseflowandviceversa
6) With dj t d fl t th d til d i d6) Withadjustedflows,repeattheprocedureuntildesiredaccuracyisobtained
CE331:EnvironmentalEngineering Dr.Tanvir Ahmed
ExampleProblem
Calculatetheflowineachofthepipesinthefollowingloopedpipenetwork
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WaterDistributionNetwork:Saidabad phIII
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StorageReservoirC d h d b dConstructedinthedistributionsystemtoprovidestoragetomeetthefluctuationofwaterdemand,stabilizepressureandprovidestorageforemergencyrequirementsp g g y q
IntheabsenceofstoragereservoirPumpinghastocontinueforallhoursofsupplysupplyPumpinghastoberegulatedtomeetthefluctuationofdemand
Thisisnottechnicallyandeconomically
CE331:EnvironmentalEngineering Dr.Tanvir Ahmed
feasible
HowtoDesignaStorageReservoirSteps:Steps:CumulativewaterdemandandsupplyatdifferenthoursofapeakdayareplottedTh l b i f th hi h t diff i d d d l iThealgebraicsumofthehighestdifferencesindemandandsupplyisthecapacityofthestoragereservoir
CE331:EnvironmentalEngineering Dr.Tanvir Ahmed
ExampleProblemDetermine the storage volume of an overhead tank to balance theDeterminethestoragevolumeofanoverheadtanktobalancethetreatmentplantoutputof113500m3/daywiththehighservicepumpingwiththefollowingschedule:
12Midnight 6A.M.=2.83m3/hr6A.M. 10P.M.=5.68m3/hr10P.M. 12Midnight=m3/hrg /
CE331:EnvironmentalEngineering Dr.Tanvir Ahmed
ExampleProblem
CE331:EnvironmentalEngineering Dr.Tanvir Ahmed
StorageReservoirsinDhakaCity
OverheadTanksatMohakhali DOHSandGulshanI
DWASA has 43 Overhead tanks 17 of which are currently operational
CE331:EnvironmentalEngineering Dr.Tanvir Ahmed
DWASAhas43Overheadtanks,17ofwhicharecurrentlyoperational
FireHydrantAn outlet from a water main provided chiefly for the purpose of formingAnoutletfromawatermainprovidedchieflyforthepurposeofformingaconnectionwithafirehose
Usuallymadeofcastironwithbronzesurfaces
Agatevalveisdesirableinadditiontothemainvalve
CE331:EnvironmentalEngineering Dr.Tanvir Ahmed
FireHydrantPlacement: footpath or street corner near the curb (streetPlacement:footpathorstreetcornernearthecurb(streetintersectionsaswellasintermediatepoints).AccordingtotheNationalBoardofFireUnderwriters,aspacingof200ftisrequiredforacommunity of 25000 to 30000 population requiring a fire flow of 5000communityof25000to30000populationrequiringafireflowof5000gpm.Forsmallcommunitiesrequiringonly1000gpm offireflow,therequirementis300ft.
Otherrequirements:oShouldbeabletodeliver600gpm withalossofnotmorethan2.5psiin the hydrant and a total loss of not more than 5 psi between the streetinthehydrantandatotallossofnotmorethan5psibetweenthestreetmainandtheoutlet.oNotlessthan2.5inchoutletsLarge s ction connection here engine ser ice is necessaroLargesuctionconnectionwhereengineserviceisnecessary
oHydrantshouldremainclosedwhenbarrelisbrokenoffoStreetconnectionsnotlessthan6inchdiameterandshallbegatedSi t l t 4 f t 2 5 l t l t 5 f th 2 5 l
CE331:EnvironmentalEngineering Dr.Tanvir Ahmed
oSize:atleast4fortwo2.5nozzles,atleast5forthree2.5nozzles,atleast6forfour2.5nozzles
NonRevenueWater(NRW)
Nonrevenuewater (NRW)iswaterthathasbeenproducedandislostbeforeitreachesthecustomer.
NRWhasthefollowingcomponents:oUnbilledauthorizedconsumption(firefighting,publicareap ( g g plandscapingetc.)oApparentlosses(watertheftandmeteringinaccuracies)oReal losses (from transmission mains storage facilitiesoReallosses(fromtransmissionmains,storagefacilities,distributionmainsorserviceconnections)
UnaccountedforWater
CE331:EnvironmentalEngineering Dr.Tanvir Ahmed
NRWIndicators
%NRWasashareofwaterproduced:MostcommonandeasytounderstandnotanappropriateindicatortobenchmarkNRWlevelsbetweenpp putilitiesoreventomonitorchangesovertime
Lossesperconnectionperday: recommended by IWALossesperconnectionperday: recommendedbyIWA
Percentage,lossesperconnectionorlossesperkmoft kt thnetworktogether:
RecommendedbyTheInternationalBenchmarkingNetworkforWaterandSanitation Lossesperkilometerofnetworkaremoreappropriatetobenchmarkreallosses,whilelossesperconnectionaremoreappropriatetobenchmarkapparentlosses.
CE331:EnvironmentalEngineering Dr.Tanvir Ahmed
BenefitsofNRWReduction
financialgainsfromincreasedwatersalesorreducedwaterproduction,includingpossiblythedelayofcostlycapacity
iexpansion;increasedknowledgeaboutthedistributionsystem;increasedfirefightingcapabilityduetoincreasedpressure;g g p y preducedpropertydamage;reducedriskofcontaminationMore stabilized water pressure throughout the systemMorestabilizedwaterpressurethroughoutthesystem
CE331:EnvironmentalEngineering Dr.Tanvir Ahmed
ReadingMaterialsforthisLecture
Chapter20:WaterSupplyandSanitation(byF.AhmedandM.Rahman)
http://en.wikipedia.org/wiki/Nonrevenue_water
CE331:EnvironmentalEngineering Dr.Tanvir Ahmed