ISO 4362-1999 Hydrometric determinations - Flow measurement in open channels using structures - Trapezoidal broad-crested weirs《水文测验 应用建筑物做明渠水流测量 梯形宽顶堰》.pdf

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