1、A Referencenumbe r ISO4362:1999 (E) INTERNATIONAL STANDARD ISO 4362 Secondedition 19990901 HydrometricdeterminationsFlow measurementinopenchannelsusing structuresTrapezoidalbroadcrestedweirs DterminationshydromtriquesMesurededbitdanslescanaux dcouvertsaumoyendestructuresDversoirstrapzodauxseuil pais
2、ISO4362:1999(E) ISO1999 Allrightsreserved.Unlessotherwisespecified,nopartofthispublicationmaybereproducedorutilizedinanyformorbyan ymeans,electronic ormechanical,includingphotocopyingandmicrofilm,withoutpermissioninwritingfromthepublisher. InternationalOrganizationforStandardization Casepostale56 CH
3、1211Genve20 Switzerland Internet isoiso.ch PrintedinSwitzerland ii Contents 1Scope 1 2Normativereference 1 3Termsanddefinitions .1 4InstallationGeneralconsiderations 1 5Maintenance .3 6Measurementofwaterlevels 3 7Trapezoidalbroadcrestedweirsinrectangularchannels 4 8Trapezoidalbroadcrestedweirsintrap
4、ezoidalchannels .15 9Uncertaintiesinflowmeasurement .24 10Example . .27 Bibliography31ISO ISO4362:1999(E) iii Foreword ISO(theInternationalOrganizationforStandardization)isaworldwidefederationofnationalstandardsbodies(ISO memberbodies).TheworkofpreparingInternationalStandardsisnormallycarriedoutthro
5、ughISOtechnical committees.Eachmemberbodyinterestedinasubjectforwhichatechnicalcommitteehasbeenestablishedhas therighttoberepresentedonthatcommittee.Internationalorganizations,governmentalandnongovernmental,in liaisonwithISO,alsotakepartinthework.ISOcollaboratescloselywiththeInternationalElectrotech
6、nical Commission(IEC)onallmattersofelectrotechnicalstandardization. InternationalStandardsaredraftedinaccordancewiththerulesgivenintheISO/IECDirectives,Part3. DraftInternationalStandardsadoptedbythetechnicalcommitteesarecirculatedtothememberbodiesforvoting. PublicationasanInternationalStandardrequir
7、esapprovalbyatleast75%ofthememberbodiescastingavote. InternationalStandardISO4362waspreparedbyTechnicalCommitteeISO/TC113, Hydrometricdeterminations, SubcommitteeSC2, Notches,weirsandflumes. Thissecondeditioncancelsandreplacesthefirstedition(ISO4362:1992),whichhasbeenextendedtoincludethe useofthewei
8、rintrapezoidalchannelsinadditiontoitsuseinrectangularchannels.INTERNATIONALSTANDARD ISO ISO4362:1999(E) 1 HydrometricdeterminationsFlowmeasurementinopen channelsusingstructuresTrapezoidalbroadcrestedweirs 1Scope ThisInternationalStandardspecifiesamethodofsteadyflowmeasurementinopenchannelsusingatrap
9、ezoidal broadcrestedweirundermodularandnonmodularconditions.Considerationisgiventotheuseoftheweirinboth rectangularandtrapezoidalchannels. Limitationstotheuseoftheweiraregivenin7.6and8.6. 2Normative reference Thefollowingnormativedocumentcontainsprovisionswhich,throughreferenceinthistext,constitutep
10、rovisionsof thisInternationalStandard.Fordatedreferences,subsequentamendmentsto,orrevisionsof,thedocumentdonot apply.However,partiestoagreementsbasedonthisInternationalStandardareencouragedtoinvestigatethe possibilityofapplyingthemostrecenteditionofthenormativedocumentindicatedbelow.Forundatedrefere
11、nces, thelatesteditionofthenormativedocumentreferredtoapplies.MembersofIECandISOmaintainregistersof currentlyvalidInternationalStandards. ISO772:1996, HydrometricdeterminationsVocabularyandsymbols. 3 Termsanddefinitions ForthepurposesofthisInternationalStandard,thetermsanddefinitionsgiveninISO772app
12、ly. 4 InstallationGeneralconsiderations NOTEParticularrequirementsfortrapezoidalbroadcrestedweirsaregiveninclause7fortrapezoidalbroadcrestedweirsin rectangularchannels;inclause8fortrapezoidalbroadcrestedweirsintrapezoidalchannels. 4.1 Selectionofsite Apreliminarysurveyshallbemadeofthephysicalandhydr
13、aulicfeaturesoftheproposedsite,tocheckthatit conforms(ormaybemadetoconform)withtherequirementsnecessaryfordischargemeasurementbyaweir. Particularattentionshallbepaidtothefollowingfeaturesinselectingthesite: a) theavailabilityofanadequatelengthofchannelofregularcrosssection; b) theexistingvelocitydis
14、tribution; c) theavoidanceofasteepchannel,ifpossible; d) theeffectsofanexcessiveincreaseinupstreamwaterlevelowingtoinstallationofthemeasuringstructure; e) thesedimentcontentofthestreamandwhetherheavydepositionjustupstreamoftheweirislikelytooccur;ISO4362:1999(E) ISO 2 f) theimpermeabilityofthegroundo
15、nwhichthestructureistobefoundedandthenecessityforpiling,groutingor othermeansofcontrollingseepage; g) thenecessityforfloodbankstoconfinethemaximumdischargetothechannel; h) thestabilityofthebanksandthenecessityfortrimmingand/orrevetmentinnaturalchannels; i) theneedforclearanceofrocksorbouldersfromthe
16、bedoftheapproachchannel; j) theeffectofwindontheflowovertheweir,especiallywhentheweiriswideandtheheadissmallandwhen theprevailingwindisinadirectiontransversetothedirectionofflow. Ifthesitedoesnotpossessthecharacteristicsnecessaryforsatisfactorymeasurements,itshallnotbeusedunless suitableimprovements
17、arepracticable. Theexistingvelocitydistributionintheapproachchannelshallbecheckedbyinspectionandmeasurementusing, forexample,currentmeters,velocityrodsandfloats. NOTE1 Concentrationsofdyearealsousefultochecktheconditionsatthebottomofthechannel. NOTE2 Acompleteandquantitativeassessmentofthevelocitydi
18、stributionmaybemadebyusingacurrentmeter.More informationontheuseofcurrentmetersisgiveninISO748. Ifaninspectionofthestreamshowsthattheexistingvelocitydistributionisregular,thenitmaybeassumedthatthe velocitydistributionwillremainsatisfactoryaftertheweirhasbeenconstructed. Iftheexistingvelocitydistribu
19、tionisirregularandnoothersiteforaweirisfeasible,dueconsiderationshallbegiven tocheckingthedistributionaftertheinstallationoftheweirandtoimprovingitifnecessary. 4.2Installation conditions 4.2.1General Thecompletemeasuringinstallationconsistsofanapproachchannel,ameasuringstructureandadownstream channe
20、l.Theconditionofeachofthesecomponentsaffectstheoverallaccuracyofthemeasurements. Inaddition,featuressuchasthesurfacefinishoftheweir,thecrosssectionalshapeofthechannelandits roughness,andtheinfluencesofthecontrolsectionanddevicesupstreamordownstreamofthegaugingstructure shallbetakenintoconsideration.
21、 Thesefeaturestogetherdeterminethedistributionanddirectionofvelocity,whichhaveanimportantinfluenceon theperformanceofaweir. Onceaninstallationhasbeendesignedandconstructed,theusershallpreventorrectifyanyphysicalchangesin theinstallationwhichcouldaffectthedischargecharacteristics. 4.2.2Approach chann
22、el Theflowintheapproachchannelshallbesmooth,freefromdisturbancesandshallhaveavelocitydistributionas symmetricalaspossibleoverthecrosssectionalarea. NOTE Thiscanusuallybeverifiedbyinspectionormeasurement. Inthecaseofnaturalstreamsorrivers,theseflowconditionscanonlybeattainedbyhavingalongstraight appr
23、oachchannelofuniformcrosssection,freefromprojectionsatthesideoronthebottom. Unlessotherwisespecified,thefollowinggeneralrequirementsshallbemet. a) Afterconstructionoftheweir,theflowconditionsintheapproachchannelcanalterowingtothebuildupof shoalsofdebrisupstreamofthestructure.Thelikelyconsequentialch
24、angesinthewaterlevelshallbetaken intoaccountinthedesignofthestructure.ISO ISO4362:1999(E) 3 b) Inanartificialchannel,thecrosssectionshallbeuniformandthechannelshallbestraightforalengthequalto atleast10timesitswidth. c) Iftheentryoftheapproachchannelisthroughabendoriftheflowisdischargedintothechannel
25、either throughaconduitofsmallercrosssectionoratanangle,thenagreaterlengthofstraightapproachchannelis requiredtoachievearegularvelocitydistribution.Thereshallbenobafflenearertothepointsofmeasurement than10timesthemaximumheadtobemeasured. d) Undercertainconditions,astandingwavemayoccurupstreamofthegau
26、gingdevice,forexampleifthe approachchannelissteep.Providedthatthiswaveisatadistanceupstreamofnotlessthan30timesthe maximumhead,flowmeasurementisfeasible,subjecttoconfirmationthataregularvelocitydistributionexists atthegaugingstation.Ifastandingwaveoccurswithinthisdistance,theapproachconditionsand/or
27、the gaugingdeviceshallbemodified. 4.2.3Weir structure Thestructureshallberigidandwatertight,andcapableofwithstandingfloodflowconditionswithoutdisplacement, distortionorfracture.Itshallbeatrightanglestothedirectionofflowandthegeometryoftheweirshallconform withthedimensionsgiveninthisInternationalStan
28、dard. 4.2.4Downstream channel Thechanneldownstreamofthestructureisusuallyofnoimportanceiftheweirhasbeendesignedtooperateunder freeflowconditions.Iftheweirisdesignedtooperateunderdrownedconditionsalso,thedownstreamchannelshall bestraightforalengthofatleasteighttimesthemaximumheadtobemeasured. Adownst
29、reamgaugeshallbeprovidedtodeterminethesubmergenceratio. 5Maintenance Maintenanceofthemeasuringstructureandtheapproachchannelisimportanttosecureaccuratecontinuous measurements. Itisessentialthat,asfaraspracticable,theapproachchanneltotheweirbekeptcleanandfreefromsiltand vegetationfortheminimumdistanc
30、especifiedin4.2.2.Thefloatwellandtheentryfromtheapproachchannelshall alsobekeptcleanandfreefromdeposits.Theweirstructureshallbekeptcleanandfreefromclingingdebrisand careshallbetakenintheprocessofcleaningtoavoiddamagetotheweircrest. 6 Measurementofwaterlevels 6.1General Wherespotmeasurementsarerequir
31、ed,waterlevels(heads)upstreamanddownstreamofthemeasuringstructure maybemeasuredbyusingahookgauge,apointgaugeorastaffgauge.Wherecontinuousrecordsarerequired,a floatoperatedrecordinggaugemaybeused;however,toreducetheeffectsofwatersurfaceirregularities,itis preferabletomeasurewaterlevelsinaseparatestil
32、lingwell.Otherheadmeasuringmethodsmaybeusedprovided thatsufficientaccuracyisobtainable. ThedischargescalculatedusingtheworkingequationsgiveninthisInternationalStandardarevolumetricfigures. Theliquiddensitydoesnotaffectthevolumetricdischargeforagivenwaterlevelprovidedthattheoperativelevelis gaugedinl
33、iquidofidenticaldensity.Ifthegaugingiscarriedoutinaseparatewell,acorrectionforthedifferencein densitymaybenecessaryifthetemperatureoftheliquidinthewellissignificantlydifferentfromthatoftheflowing liquid.However,itisassumedhereinthatthedensitiesareequal. 6.2 Stillingorfloatwell Whereprovided,thestill
34、ingwellshallbeverticalandshallbe0,6mhigherthanthemaximumwaterleveltobe recordedinthewell.Thebottomofthewellshallbelowerthantheelevationoftheweircrest.ISO4362:1999(E) ISO 4 Thewellshallbeconnectedtothechannelbyaninletpipeorslot,whichislargeenoughtopermitthewaterinthe welltofollowtheriseandfallofheadw
35、ithoutsignificantdelay. Theconnectingpipeorslotshall,however,beassmallaspossibleconsistentwitheaseofmaintenance,orshall alternativelybefittedwithaconstrictiontodampoutoscillationsduetoshortperiodwaves. Thewellandtheconnectingpipeorslotshallbewatertight.Whereprovidedfortheaccommodationofthefloatofa l
36、evelrecorder,thewellshallbeofadequatediameteranddepthtogiveclearancearoundandbeneaththefloatat allstages.Adequateadditionaldepthshallbeprovidedinwellstoavoidthedangeroffloatsgroundingonany accumulationofsiltordebris.Thefloatwellarrangementmayincludeanintermediatechamberofsimilarsizeand proportionsbe
37、tweenthestillingwellandtheapproachchanneltoenablesiltandotherdebristosettleoutwhere theymaybereadilyremoved. 6.3Zero setting Anaccuratemeansofcheckingthezerosettingofthewaterlevelmeasuringdeviceshallbeprovided.Forthis purpose,apointer,setexactlylevelwiththecrestoftheweirandfixedpermanentlyintheappro
38、achchannel,or alternativelyinthestillingwellorfloatwellwhereprovided,maybeused. Azerocheckbasedonthelevelofthewaterwhenthefloweitherceasesorjustbeginsisliabletoseriouserrors duetosurfacetensioneffects,andshallnotbeused. Withdecreasingsizeoftheweirandthewaterlevel,smallerrorsinconstructionandinthezer
39、osettingandreading ofthewaterlevelmeasuringdevicebecomeofgreaterimportance. 7 Trapezoidalbroadcrestedweirsinrectangularchannels 7.1 Specificationforthestandardweir Theweircomprisesanupstreamslopeof1: Z 1 ,ahorizontalcrest,andadownstreamslopeof1: Z 2 (seeFigure1), constructedinarectangularchannelsect
40、ion. Thevaluesof Z 1 and Z 2 forstandardtrapezoidalbroadcrestedweirsinrectangularchannelsinaccordancewith thisInternationalStandardarespecifiedinTable1. Table1Upstreamanddownstreamslopecombinations Upstreamslope Downstreamslope 1:Z 1 1:Z 2 1:1 1:5 1:2 1:2 1:2 1:3 1:2 1:5 1:3 1:3 1:3 1:5 Theintersect
41、ionofthesurfacesoftheupstreamanddownstreamslopeswiththehorizontalcrestshallformawell definedstraightsharpcornerwhichshallbehorizontalandatrightanglestothedirectionofflowintheapproach channel.Thecrestshallbehorizontalandshallhavearectangularplanesurface.Thesurfacesofthecrestandthe slopesshallbesmooth
42、Thewidth bofthecrestperpendiculartothedirectionofflowshallbeequaltothewidthof thechannelinwhichtheweirislocated.ISO ISO4362:1999(E) 5 AsketchofatypicaltrapezoidalbroadcrestedweirinarectangularchannelisgiveninFigure1. a)Longitudinalsection b)Planview c)Crosssection Key 1Directionofflow 5Horizontalcrest 2Stillingwell 65 h max to6 h max 3Headmeasurementsection 7Tailwaterlevelmeasurementsection 43 h max to4 h max Figure1TrapezoidalbroadcrestedweirinarectangularchannelISO4362
