ce 331_water distribution.pdf

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


ClassificationofT&DSystem

SystemwithDirectPumpingy p g

SystemwithPumping


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


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


nonpumpinghours

PumpingwithStorageSystem

1) Systemmorereliableandcancopewithfluctuationofd d

Advantages

waterdemand2) Thepumpscanbeoperatedatratedcapacityresultingin

higherefficiencyandeconomyinoperationg y y p3) Reasonablepressurecanbemaintainedwithvaryingwater

demandandthereisnopossibilityofinflowofpollutedwater in the systemwaterinthesystem

Disadvantages

1) Relativelyhigherinitialcost2) Comparativelyhigherlossduetoleakageandwastage


DistributionNetwork

1) BranchedDistributionNetwork2) LoopedDistributionNetwork


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


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


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)


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


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


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)


(x=1.85accordingtoHazenWilliamsformula)


( ) 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/


aQ aQ


( ) ( )( ) ( )( ) ( )[ ]adcdcadabcbcab

dcadbcab

QHHQHHxHHHH

// +++++=


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


ExampleProblem

Calculatetheflowineachofthepipesinthefollowingloopedpipenetwork


WaterDistributionNetwork:Saidabad phIII


StorageReservoirC d h d b dConstructedinthedistributionsystemtoprovidestoragetomeetthefluctuationofwaterdemand,stabilizepressureandprovidestorageforemergencyrequirementsp g g y q

IntheabsenceofstoragereservoirPumpinghastocontinueforallhoursofsupplysupplyPumpinghastoberegulatedtomeetthefluctuationofdemand

Thisisnottechnicallyandeconomically


feasible

HowtoDesignaStorageReservoirSteps:Steps:CumulativewaterdemandandsupplyatdifferenthoursofapeakdayareplottedTh l b i f th hi h t diff i d d d l iThealgebraicsumofthehighestdifferencesindemandandsupplyisthecapacityofthestoragereservoir


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 /


ExampleProblem


StorageReservoirsinDhakaCity

OverheadTanksatMohakhali DOHSandGulshanI

DWASA has 43 Overhead tanks 17 of which are currently operational


DWASAhas43Overheadtanks,17ofwhicharecurrentlyoperational

FireHydrantAn outlet from a water main provided chiefly for the purpose of formingAnoutletfromawatermainprovidedchieflyforthepurposeofformingaconnectionwithafirehose

Usuallymadeofcastironwithbronzesurfaces

Agatevalveisdesirableinadditiontothemainvalve


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


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


NRWIndicators

%NRWasashareofwaterproduced:MostcommonandeasytounderstandnotanappropriateindicatortobenchmarkNRWlevelsbetweenpp putilitiesoreventomonitorchangesovertime

Lossesperconnectionperday: recommended by IWALossesperconnectionperday: recommendedbyIWA

Percentage,lossesperconnectionorlossesperkmoft kt thnetworktogether:

RecommendedbyTheInternationalBenchmarkingNetworkforWaterandSanitation Lossesperkilometerofnetworkaremoreappropriatetobenchmarkreallosses,whilelossesperconnectionaremoreappropriatetobenchmarkapparentlosses.


BenefitsofNRWReduction

financialgainsfromincreasedwatersalesorreducedwaterproduction,includingpossiblythedelayofcostlycapacity

iexpansion;increasedknowledgeaboutthedistributionsystem;increasedfirefightingcapabilityduetoincreasedpressure;g g p y preducedpropertydamage;reducedriskofcontaminationMore stabilized water pressure throughout the systemMorestabilizedwaterpressurethroughoutthesystem


ReadingMaterialsforthisLecture

Chapter20:WaterSupplyandSanitation(byF.AhmedandM.Rahman)

http://en.wikipedia.org/wiki/Nonrevenue_water


ce 331_water distribution.pdf

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