NATIONALSTANDARD

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OFTHEPEOPLESREPUBLICOFCHINA

CODEFORDISCHARGEMEASUREMENTINRIVERS

GB50179-2015

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Beijing2024

ChineseeditionfirstpublishedinthePeoplesRepublicofChinain2016

EnlisheditionfirstublishedinthePeolesReublicofChinain2024

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PrintedinChinabyBeijinghouchengzemingPrintingTechnologyCo.Ltd

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thePeoplesRepublicofChina

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ISBN978-7-5182-1701-4NOTICE

IntroductiontoEnglishversion

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MeasurementinOpenChannels，

CodeforDischargeMeasurementinRivers，

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AnnouncementoftheMinistryofHousingandUrban-Rural

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DevelopmentofthePeoplesRepublicofChina

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CodeforDischargeMeasurementinRivers

CodeforDischargeMeasurementinRivers

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LiquidFlowMeasurementinOpenChannels

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Foreword

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ChiefDevelopmentOrganization：

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·2·Contents

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……………（）1Generalprovisions

1.0.1Thiscodeisformulatedtostandardizethetechniquesofdischargemeasurementmethods，and

analysisandcalculationofrivers，andensurethequalityofdischargemeasurement.

1.0.2Thiscodeisapplicabletothedischargemeasurementofnaturalrivers，lakes，reservoirs，artificial

openchannels，andreachesaffectedbytidesandhydraulicprojects.

1.0.3Accordingtotheaccuracygradeandrequirementsofdischargemeasurement，benchmark

hydrometricstationsmaybeclassifiedasClassⅠ，ClassⅡandClassⅢ.Theclassificationmethod

shallmeettherequirementsofAppendixAofthiscode.

1.0.4Ifnewdischargemeasurementtechnologyisapplied，dischargemeasurementmethods

recommendedinthiscodeshallbeusedforcomparativegauging，andtheaccuracyofresultsevaluated.

Thedischargemeasurementresultsofthemulti-verticalandmulti-pointcurrentmetermethodmaybe

usedasthecriteriaforthecalibrationorcheckofotherdischargemeasurementmethods.

1.0.5Theaccuracyofvariousitemsspecifiedinthiscodemaybeusedforthequalitycontroland

evaluationofdischargemeasurementscheme.Basinorprovincialinstitutionsofhydrologyshallselect

representativestationsforthecollectionandaccumulationofmeasurementdataforalongtermand

accuracycheck.

1.0.6Inadditiontotherequirementsofthiscode，dischargemeasurementinriversshallalsocomply

withthosespecifiedintherelevantcurrentnationalstandards.

·1·2Selectionofmeasuringreachandsetting-upofcross-section

2.1Selectionandsurveyofmeasuringreach

2.1.1Ameasuringreachshallfulfillthepurposeofsetting-upahydrometricstation，ensurethe

accuracyofmeasurementdata，meettherequirementsoffacilitatingobservationandthecomputation

andprocessingofthedata，andshallbeinaccordancewiththefollowingrequirements：

1Anupstreamreachofstonebeams，rapids，bends，constrictedsections，artificialweirs，etc.，

wherecross-sectioncontroliseasilyformed，shouldbeselectedasthemeasuringreach.Thedistanceof

theupstreamreachofstonebeams，rapids，bendsandconstrictedsectionstocross-sectioncontrolshould

be5timestheriverwidth，andthatofamountainstreamtocross-sectioncontroldistancemaybe

relaxedto3timesthestreamwidth.Orareach，wherethebottomslope，cross-sectionshape，roughness

andotherfactorsofchannelarerelativelystableandthechanneliseasilycontrolledbyresistancealong

thechannel，maybeselected.Thereshallbenohugestoneblockingwater，hugevortex，orturbulencein

ameasuringreach.

2Ifcross-sectioncontrolandchannelcontroloccuratdifferentlocationsofareach，areachwith

cross-sectioncontrolshallbeselectedasthemeasuringreach.Amongseveralreacheswiththesame

controllingcharacteristics，anarrowreachwithalargerdepthshallbeselectedasthemeasuringreach.

3Ifitisdifficultforthemeasuringreachofsmallormedium-sizedriverstomeetthe

requirementsstipulatedinItem1ofthisarticle，therequirementsmayberelaxedappropriately.Butthe

applicationconditionsofmeasuringmethodsshallbemet.

2.1.2Alocationpronetolandslide，collapseanddebrisflowmustbeavoidedasameasuringreach.

2.1.3Areachmeasuredbythecurrentmetermethodshouldbestraightandstable，withconcentrated

flowandwithoutdiversionflow，obliqueflow，backflow，stagnantwater，etc.Thelengthofastraight

measuringreachshouldbegreaterthan5timesthemainchannelwidthduringaflood.Theimpactsof

variablebackwater，largefloodplain，rapidscouringandsilting，etc.producedbytheinflowofmajor

tributariesorbylargewaterbodiesoflakesandreservoirsonthemeasuringreachshouldbeavoided，

andthemeasuringreachshallbeinaccordancewiththefollowingrequirements：

1Forriversinplainareas，ameasuringreachshouldbestraightandregular.Thewidth，depthand

channelslopeofthewholemeasuringreachshallhavenoobviousvariation.Theriverbedofsingle

channelshouldbefreeofwaterplants.Ifitisimpossibletoavoidwanderingreach，shiftingsandbar

shallbeavoided.

2Fortidalrivers，areachwithnarrowwatersurface，straightpathoffloodtideandebbtide，good

intervisibility，relativelysimplecross-section，andlessimpactofwindsandwavesshouldbeselectedas

themeasuringreach.

3Forreservoirandlakeoutletstationorweirstation，ameasuringreachshouldbeselected

downstreamofstructures，andtheimpactsoflargeflowfluctuationsandabnormalturbulenceavoided.If

itisdifficulttomeasureatdownstreamcross-sectionandthereisalongstraightreachupstreamof

structures，ameasuringreachmaybeselectedattheupstream.

4Forfrozenrivers，thereshouldnothaveiceaccumulation，icejamoricedaminameasuring

·2·reach.Fortheriverreachwithmulti-layericestructuresintercalatedwithicelayersandwaterlayers，a

measuringreachshallbeselectedwhereinvestigationshowsthefreezingconditionsarerelatively

simple.Forspecialtopographicalandgeographicalconditions，anunfrozenreachshouldbeselectedas

themeasuringreach.

5Forthemeasuringreachaffectedbyhydraulicprojectsorhumanactivitiesorameasuringreach

fortourgaugingcross-section，selectionrequirementsmaybeappropriatelyrelaxedaccordingtothe

purposeorneedsofsettingupahydrometricstationandbasedontheprincipleofmeetingmeasuring

accuracyrequirements.

2.1.4Ifotherdischargemeasurementmethodsareusedatahydrometricstation，ameasuringreach

shallbeselectedaccordingtothefollowingrequirements：

1Forthemeasuringreachwiththefloatmethod，thelengthofstraightreachshallbegreaterthan

2timesthedistancebetweenthecross-sectionsoftheupstreamanddownstreamfloats.Themedium

cross-sectionoffloatsshallbeofrepresentativeness，withoutlargeerosionditchesorbackflows.There

shallbegoodintervisibilityandcommunicationamongcross-sections.

2Forthemeasuringreachwiththeslope-areamethod，thelengthofstraightreachshallsatisfy

theonerequiredfortheaccuracyrequirementofslopeobservation，theslopecontourlinesofbothbanks

shallbenearlyparallel，thetransverseslopeofwatersurfaceshallbesmall，andlongitudinalslopeshall

beuniformwithoutanobviousturningpoint.Sandbars，shoals，branchingreachesandobviously

diffusedreachesshallbeavoided.

3ForthemeasuringreachwiththeacousticDopplercurrentprofilermethod，areachwithlarge

waterdepth，smallsideshoal，noinfluenceofwatertrafficondischargemeasurement，andnointensive

impactsofriverbedsedimentmovemen（tmovingbed）shouldbeselectedundertheconditionofmeeting

therequirementsstipulatedinArticle2.1.3ofthiscode.

4Forthemeasuringreachwiththemeasuringstructuremethod，thelengthofstraightreachshall

begreaterthan5timesthemaximumwatersurfacewidthofapproachchannel，andsteepandturbulent

reachesshallbeavoided.Thereshallbeasmoothflowinapproachchannelsectionwithregularchannel

cross-sectionandsymmetricalanduniformflowvelocitydistributioninthecross-section，andnowater

blockingobjectssuchasripraps，soilpiles，waterplants，etc.intheriverbedoralongthebanks.Ifa

naturalriverchannelfailstomeettheaboverequirements，itshallbeartificiallyregulatedtomeetthe

hydraulicconditionsfordischargemeasurementbythemeasuringstructuremethod.

5Forthemeasuringreachwiththedilutionmethod，areachwithbends，narrowsections，shoals，

submergedreefsandhydraulicdropsandwithoutwaterplantsorstagnantwatermaybeselected，and

theinflow，diversionflowandbankoverflowoftributariesshallbeavoided.Thelengthofmeasuring

reachshallbesuchthattracerinjectedintowaterflowcanbefullyanduniformlydiffused.

6Forthemeasuringreachwithotherdischargemeasurementmethods，itshallmeetthe

applicableconditionsofinstrumentperformanceandhydrologicdataprocessingrequirements.

2.1.5Atthetimeofthelocationdeterminationofmeasuringreachandthearrangementofcross-

sections，thegeologicalandgeomorphicfeatures，underlyingsurface，rivercharacteristics，upstreamand

downstreamprojectsandwaterresourcesdevelopmentplanning，etc.ofthemeasuringreachshallbe

surveyedandinvestigatedindetail，andtheriverregimeshallalsobeinvestigatedtounderstandthe

lengthsofbendsandstraightsectionsoftheriver，thefloodcontrolabilityofbanks，andwhetherthereis

anoverflowoutlet.Onthepremiseoffulfillingthepurposeofsettingupahydrometricstation，thesiteof

·3·thestationshouldbeclosetourbanresidentialarea，withconsiderationoftheconditionsof

transportation，electricity，communication，etc.

2.1.6Thesurveyofrivercharacteristicsshallmainlycoverthefollowing：

1Toinvestigatethepositionofcontrolcross-sectionandidentifythestabilityextentofcross-

sectioncontrolorchannelcontrol.

2Toinvestigatewhetherdiversionflows，erosionditches，backflows，stagnantwatersandthe

widthofsideshoalsareinfavorofmeasuringfacilitiesarrangement.Anumberofchannelcross-sections

aresetupinthepreliminarilyselectedmeasuringreach，andthevelocitydistributionofonecross-section

ismapped.

3Tounderstandriverbedcomposition，cross-sectionshape，scouringandsiltingchanges，the

historyofsandbarsandriverchannelchanges，aswellasmainflow，flowvelocity，flowdirectionand

theirchangesatallstages，andinvestigatethedistributionofrocks，gravels，pebbles，boulders，sand，

loam，clay，silt，etc.ontheriverbedofmeasuringreach.

4Tounderstandthegrowingseasonandrangeofwaterplants，thetimeoffreezing-upand

driftingice，thelocationoficedamsandicejams，andtheheightofbackwater.

2.1.7Themeasuringreachofanon-tidalcurrentstationshouldbeselectedoutsidetherangeof

variablebackwater，andthedistanceandprobabilityofdownstreamvariablebackwatershallbe

identifiedaccordingtothefollowingrequirements：

1Iftherearehydraulicstructuresatthedownstreamofmeasuringreach，thebackwater

calculationdataatthedesignhighestfloodstageofthehydraulicstructuresatthenearestdownstream

locationshallbeusedtoidentifywhetherthemeasuringreachisaffected，andtoestimatethedistanceof

backwater.

2Ifthereareinflowriversorlakeswithinacertaindistancedownstreamofmeasuringreach，the

probabilityofbackwateroccurrenceandlimitdistanceshallbeestimated.

2.1.8Atthetimeofmeasurementschemeandequipmentselection，thespeedoffloodriseandfall，the

highestandloweststageinhistoryandthemaximumfloodplainboundaryshallbeunderstood，the

maximumandminimumdischargeshallbeestimatedroughly，andthesourceoffloodandthecausesof

soilandwaterlossesanddebrisflowshallbesurveyed.

2.1.9Thesurveyofthephysicalandgeographicalofabasinshallincludethefollowing：

1Toinvestigategroundfeaturesandlandforms，understandtheclosureofawatershed，andcheck

whetherthereisexternalwaterinflowandinternalwateroutflow.

2Toinvestigatesoildistributionandvegetationconditions，andunderstandsoilandwaterlosses

andupstreamsedimentproduction.

3Tounderstandgeologicalandhydrogeologicalconditions，withfocusonthedevelopmentand

distributionofkarstsinlimestoneareas.

2.1.10Thesurveyofconstructionprojectsmeasures，planecoordinatesandcontrolconditionsina

basinshallincludethefollowing：

1Thecurrentsituationofthescaleandquantityofwaterstorageanddiversionprojectsandtheir

short-termandlong-termplanning.

2Thetypesofmeasuresofirrigation，drainage，ruralwatersupplyandsoilandwaterconservation

andtheirpossibleimpactsonsedimentinducedbyflood.

3Waterwaynavigationandtimberraftingseason，andmodeofraftingoperation.

·4·4Thecoordinateposition，elevationandgradeofelevationcontrolpointsandplanecontrolpoints

nearaproposedhydrometricstation.

2.1.11Thepreparationofsurveyreportshallincludethefollowing：

1Thepurpose，tasks，timeandscopeofthesurvey，andtheprofessionalcategoryandtechnical

levelofmainstaffs.

2Sortingoutvarioussurveydataandsummarizingthemintoconciseresultsbyclassification.

3Therecommendationofselectedmeasuringreachforsurvey，theelaborationofanalysisopinions，

andproposalsonthearrangementofhydrologicalmeasuringitemsandmethods，basicfacilities，etc.

2.2Layoutofmeasuringcross-section

2.2.1Basicstaffgaugecross-sectionandcorrespondingdischargegaugingcross-sectionmaybesetup

asappropriatelyaccordingtothedischargemeasurementmethodsofahydrometricstation.

2.2.2Thelayoutofabasicstaffgaugecross-sectionshallbeinaccordancewiththefollowing

requirements：

1Thereissmoothflowwithnotransverseslopeofwatersurfaceorsmalltransverseslopeof

watersurface，andnovortex，backfloworstagnantwater，etc.atthecross-section.Topographic

conditionsarefavorableformanualobservationandtheinstallationofstageauto-recordersandother

instruments.

2Thecross-sectionshouldbeperpendiculartothemeanflowdirectionatthecross-sectionand

maybelocatedinthemiddleofameasuringreachandcoincidewithorapproachthegaugingcross-

section.Ifthebasicstaffgaugecross-sectiondoesnotcoincidewiththegaugingcross-section，thestages

ofthetwocross-sectionsshallbeofastablecorrelation.

3Oncethepositionofthebasicstaffgaugecross-sectionisdetermined，itshouldnotbechanged.

Ifthepositionofthecross-sectionhastoberelocatedintheeventofunforeseenspecialsituations，the

stagesofthecurrentandpreviouscross-sectionsshallbecomparativelygauged，andthestagevariation

ofcomparativegaugingshallreachmorethan75%ofmeanannualrangeofstage.

4Ifthereisafixeddiversionflowinareach，andthediversiondischargeexceeds20%ofthetotal

dischargeofthecross-section，andthereisnostablecorrelationbetweenthediversiondischargeand

totaldischarge，staffgaugecross-sectionsshallbesetupadditionally.

2.2.3Thelayoutofcurrentmetergaugingcross-sectionshallbeinaccordancewiththefollowing

requirements：

1Thecross-sectionshouldbeselectedatthemiddleofariverreachwithstraightbanks，

approximatelyparallelcontourlinesandconcentratedflow.Ifdischargemeasurementbythefloat

methodorslope-areamethodisrequired，thefloatgaugingcross-section，cross-sectionforslope

observationandgaugingcross-sectionmaybeoverlappedandarrangedforconcertedoperation.Ifthe

physicalconditionsofameasuringreachallow，thegaugingcross-section，themediumcross-sectionof

floatsandthebasicstaffgaugecross-sectionshouldcoincidewitheachother.

2Flowvelocityanddirectionaremeasuredaccordingtohigh，mediumandlowstages，

respectively.Themeasurementmethodofflowdirectionshallcomplywiththerequirementsstipulated

inSectionB.10ofthiscode.Thegaugingcross-sectionshouldbeperpendiculartothemeanflow

directionofthecross-section，anddeflectionangleshallnotexceed10°.Ifthedeflectionangleexceeds

10°duetotheconstraintofphysicalconditions，gaugingcross-sectionsshallbearrangedaccordingtothe

·5·flowdirectionindifferentperiods，andthereshallbenoinfloworoutflowbetweengaugingcross-

sectionsindifferentperiods.

3Iftherearediversionflowsanderosionditchesinariverinthelow-flowperiodandthe

diversionflowdirectionsarequitedifferentfromthatofthemainstream，gaugingcross-sections

perpendiculartodifferentflowdirectionsshouldbearrangedrespectively.

4Thecurrentmetergaugingcross-sectionontheupstreamordownstreamofhydraulicprojects

suchasreservoirs，weirgates，etc.shallbelaidouttoavoidtheinfluenceofabnormalturbulenceofflow.

5Forthevarioustypesofhydrometricstationsaffectedbytides，gaugingcross-sectionsmaybe

arrangedinaccordancewiththerequirementsstipulatedinItems1to4ofthisarticle.

2.2.4InadditiontoArticle2.2.3ofthiscode，thelayoutoffloatgaugingcross-sectionshallbein

accordancewiththefollowingrequirements：

1Themiddlecross-sectionforthefloatmethodshouldcoincidewiththecurrentmetergauging

cross-sectionandbasicstaffgaugecross-section.Theymaybesetupseparatelyifitisconstrainedby

topographicconditions，butthereshallnothaveinfloworoutflowbetweenthemiddlecross-sectionof

thefloatmethodandcurrentmetergaugingcross-section.

2Theupstreamanddownstreamcross-sectionsofthefloatmethodshallbeparalleltothemiddle

cross-sectionofthefloatmethodwithequalspacing，andthechangeofrivertopographyinbetweenshall

besmall.Thedistancebetweentheupstreamanddownstreamcross-sectionsofthefloatmethodshall

begreaterthan50timesthemaximummeanflowvelocityatacross-section.Ifrestrictedbytopographic

conditions，itmaybeshortenedappropriately，butshallnotbelessthan20timesthemaximummean

flowvelocityatacross-section.

3Ifthemeanflowvelocitiesatacross-sectionatmediumandhighstagesdiffergreatly，the

upstreamanddownstreamcross-sectionsofthefloatmethodmaybesetupseparatelyaccordingto

differentstages.

2.2.5Thereshouldbenoobvioustransverseslopeatthegaugingcross-sectionoftheslope-area

method，andthefollowingshallbecompliedwith：

1Theup-section，mid-sectionanddown-sectionarearrangedinareachforwatersurfaceslope

observation.Thespacingbetweentheup-sectionandmid-sectionshallbeequaltothatbetweenthemid-

sectionanddown-section.Themid-sectionoftheslopeshouldcoincidewiththecurrentmetergauging

cross-sectionorthemid-sectionofthefloatmethod.

2Thespacingbetweenup-sectionanddown-sectionforslopeobservationshallmakewater

surfacefallmuchlargerthanfallobservationerror.

2.2.6Thelayoutofgaugingcross-sectionbyothermethodsshallmeettheapplicableconditionsfor

instrumentperformanceandtherequirementsforhydrologicdataprocessing.

2.2.7Baselinelayoutshallbeinaccordancewiththefollowingrequirements：

1Ifthedistancefrominitialpointismeasuredbytheodolite，electronictotalstation，distance

gaugeortheintersectionmethodofflatpanelmeter，baselineshouldbeperpendiculartogaugingcross-

section，andthestartingpointofthebaselineshallbesetonthecross-section.Ifrestrainedby

topographicconditions，thebaselinemaynotberequiredtobeperpendiculartothecross-section.The

baselinelengthshallbesuchthattheanglebetweenthefarthestpointoftheviewlineoftheinstrument

andacross-sectionverticalisgreaterthan30°，andnolessthan15°inspecialcases.Correspondingbase

linesathighandlowstagesmaybesetupontheshoreandthebeachrespectivelyforstationswiththe

·6·largewidevariationofwatersurfacewidthatdifferentstages.

2Ifthedistancefrominitialpointismeasuredbythemethodofsextantintersectionata

hydrometricstation，thebaselinelayoutshallmaketheanglebetweenthetwoviewlinesofsextant

greaterthanorequalto30°andlessthanorequalto120°.Thedistancefromthetwoendsofthebase

linetothenearshorewateredgeshouldbegreaterthan7timestheheightdifferencebetweenthe

intersectionsignanddrystage.Ifonebaselinecannotmeettheaboverequirements，theintersection

baselinesofhighandlowstagesmaybesetuprespectively.

3Thebaselinelengthshouldbeanintegralmultipleof10m.Thediscrepancyvalueofround-trip

measurementresultswithasteelrulerorothercalibratedgaugesshallnotexceed1/1000.

2.2.8Thelayoutofelevationbasepointshallbeinaccordancewiththefollowingrequirements：

1Thedistancefrominitialpointmaybemeasuredbythepolarcoordinateintersectionmethodif

thereisatallandsturdybuildingonthecross-section.Elevationbasepointshallbesetuponthecross-

section，anditsheightshallbesuchthatthedepressionangleofinstrumenttothefarthestpointofsight

isnolessthan4°，ornolessthan2°inspecialcases.Ifrestrictedbyphysicalconditionssuchas

topographyandothers，elevationbasepointmaybesetupneartheupstreamordownstreamofthecross-

section.

2Theelevationbasepointshallbesetuponasolidrockorstake，anditselevationshallbe

determinedbythefourth-grade-leveling.Ifthedifferencebetweentheelevationofthebasepointand

thehighestfloodstageislessthan5m，thethird-grade-levelingshallbeusedtomeasurethe

elevation.

2.2.9Afterthepositionsofbaselineandcross-sectionaredetermined，measuringsignssuchasbase

linestake，cross-sectionstakeandcross-sectionsignstakeneedtobelaidout，whichshallbeset

accordingtothefollowrequirements：

1Baselinestakesshouldbesetupatthestartandendofthebaseline，andthebaselinestakeat

thestartpointmaybeusedascross-sectionstake.Thebaselinestakesofhighstageshallbesetup

abovethehighestfloodstageovertheyears.

2Permanentcross-sectionstakesshallbesetuponthebanksofvariouswaterstaffgaugecross-

sectionandgaugingcross-section，respectively.Thecross-sectionstakesofhighstageshallbelocatedat

0.5mto1.0mabovethehighestfloodstageovertheyears.Forriversfarfromfloodplains，theymaybe

locatedoutsidethefloodboundary.Forriverswithlevees，theymaybelocatedonthegroundofthe

backsidesoftherivers.

3Solidandeye-catchingcross-sectionsignsshallbesetuponbanksofthegaugingcross-sections

laidoutforvariousdischargemeasurementmethods.Ifariversurfaceisnarrow，twocross-sectionsign

stakesmaybesetuponthesamebank，thespacingbetweenthetwostakesshallbe5%-10%ofthe

distancefromthenearshoresignstakestothefarthestmeasuringpoint，andshallnotbelessthan5m.If

cableways，bridgesandotherstructuresathydrometricstationsareused，gaugingcross-sectionsign

stakesmaynotbesetup.

4Ifariversurfaceisparticularlywideandpositionedwithasextant，aneye-catchingbaseline

signshouldbesetuponbanks.

2.2.10Temporarycross-sectionspositionedbysatellitepositioningsystemmaynotbemarkedwith

cross-sectionsigns.

2.2.11Hydrologicalprotectionsignsshallbesetupforahydrometricreach.Safetysignsshallbeset

·7·uponnavigableriverchannelsasrequiredandshallcomplywiththerelevantrequirementsof

waterwaysormaritimeadministrationdepartments.

2.2.12Forariverwithlargefloodplainarea，asignrodmaybesetupatthefixedverticalofthe

floodplain，anditstopshallbehigherthanthehighestfloodstageovertheyears.Forahydrometric

stationwherethepositionsofflowvelocity-measuringandsoundingverticalsarefixedbythe

radiationordirectionallinemethod，fixedsignssetupashoreshallmaketheanglebetweeneach

radiationlineordirectionallineandgaugingcross-sectionnolessthan30°，andthedistancebetween

thefrontandrearsignsinthesamelineofsightshallnotbelessthan5%to10%ofthedistance

fromthenearshoresigntothefixedflowvelocity-measuringandsoundingverticalsandshallnotbe

lessthan5m（Figure2.2.12）.

Figure2.2.12Radiationanddirectionallines

2.2.13Foreachtypeofhydrometricstations，stationidentificationshallbecarriedoutatthebeginning

ofitsconstruction，andarecordsheetofahydrometricstationidentificationformulated，whichshallbe

comprehensivelyrevisedintheyearendingwith0and5.Incaseofanychange，thechangedpartshallbe

supplementedandrevisedinthesameyear.Forastationwithmorechanges，thesheetshallberevised

inacomprehensiveway.Basinorprovincialinstitutionsofhydrologyshalladopttheuniformformatof

thesheet.Thesheetshallincludethefollowing：

1Stationlocation.

2Stationpurpose.

3Stationevolution.

4Generalsituationandphysicalgeographyofriverbasin.

5Layoutandvariationofbasicstaffgaugecross-section，slopemeasuringstaffgaugecross-

sectionandgaugingcross-section，etc.

6Elevationanditschangeofdatum，referencebenchmark，basicbenchmark，checkbenchmark

andstaffgaugezero，anddescriptionofbenchmarks.

7Measuringfacilitiesandequipmentandtheirchanges.

8Observationitemsandtheirchanges.

9Measurementtimeintervalofhydrologicalelementssuchasstageanddischargeandmaximum

·8·andminimumcharacteristicvaluesofstageanddischargeovertheyears.

10Investigationofrainstormandfloodinaregion.

11Riversituationandstationlocationmapofameasuringreachanditsadjacentarea，topographic

mapofhydrometricstation，possiblemaximumcross-sectionmap，layoutmapofmeasuringfacilities，

basicsituationtableanddistributionmapofmainhydraulicprojectsinacertainrangeoftheupstream

anddownstreamofhydrometricstation.

·9·3Cross-sectionmeasurement

3.1Possiblemaximumcross-sectionmeasurement

3.1.1Thebasicstaffgaugecross-sectionandgaugingcross-sectionofanewhydrometricstationshall

bemeasuredwithpossiblemaximumcross-section.

3.1.2Possiblemaximumcross-sectionmeasurementshallincludeunderwaterandlandcross-section

measurements.

3.1.3Forthemeasuringrangeofpossiblemaximumcross-section，thelandpartshallbemeasuredto

0.5mto1.0mabovethehighestfloodstageovertheyears.Forariverfarfromfloodplain，itmaybe

measuredtothemaximumfloodboundary.Forariverwithlevee，itshallbemeasuredtothegroundof

thebacksideoftheriver.

3.1.4Forthehydrometricstationwithastableriverbedatgaugingcross-section，thepossible

maximumcross-sectionshallbemeasuredonceayearbeforeorafterthefloodseasonifthestage-area

relationpointsdeviatefromthestage-arearelationcurvewithintherangefrom-3%to+3%.Forthe

stationwithanunstableriverbedatgaugingcross-section，thepossiblemaximumcross-sectionshallbe

measuredeachyearbeforeandafterthefloodseason，andthewettedcross-sectionmeasuredintime

aftertheflood.

3.1.5Thecross-sectionstakeatahighstageshallbetakenasthezerostartingpointforthedistance

frominitialpointofthebothpossiblemaximumcross-sectionandchannelcross-section.Distancefrom

initialpointandwaterdepthshallbemeasuredinaccordancewithSectionB.8ofthiscode.Theround-

tripmeasurementdiscrepancyofthetotaldistancebetweenthestakesatthestartandendofthecross-

sectiononbanksshallnotexceed1/500.

3.1.6Theelevationmeasurementofthepossiblemaximumcross-sectiononshoreshallbecarriedout

accordingtotheaccuracyrequirementofthefourth-grade-leveling.Iftopographyiscomplex，the

measurementrequirementmaybelowerthanthatofthefourth-grade-leveling.Butthediscrepancyof

heightdifferencebetweenround-tripmeasurementsshallbecontrolledintherangefrom-30kmm

to+30kmm，thedifferencebetweenfrontandrearvisualdistancesshallnotbegreaterthan5m，and

theaccumulateddifferenceshallnotbegreaterthan10m.Whenthepossiblemaximumcross-sectionis

repeatedlymeasured，one-waymeasurementmaybeclosedatafixedpointofknownelevation.

Note：kisthemeankilometerofthemeasuredroutelengthcalculatedbytheround-tripmeasurementortheleftandright

routes.

3.1.7Thearrangementofthesoundingverticalsatpossiblemaximumcross-sectionshallbein

accordancewiththefollowingrequirements：

1Ifanewhydrometricstationissetuporapossiblemaximumcross-sectionisadded，continuous

depthdetectionalongtheriverwidthshallbecarriedoutintheperiodofstablestage.Ifthewidthof

watersurfaceisgreaterthan25m，thenumberofsoundingverticalsshallnotbelessthan50.Ifthewidth

ofwatersurfaceisnogreaterthan25m，soundingverticalsmaybelaidoutwithaminimumspacingof

0.5m.Thenumberofsoundingverticalsshallsatisfytherequirementofunderstandingtheshapeof

channelcross-sections.

·10·2Soundingverticalsshouldbeevenlyarrangedandshallreflecttheturningpointsofriverbed

changesoastoavoidthemajorcompensationormajorcuttingofeachsegmentareaofchannelcross-

section.Thesoundingverticalsofthemainchannelshallbemoreintensifiedthanthatofthebeachif

thereisanobviousbeachofariver.

3Thenumberofsoundingverticalsofatidalrivermaybereducedasappropriate.

3.1.8Atthebeginningandendingofunderwatercross-sectionmeasurement，stageshallbeobserved

orextractedrespectively.

3.2Channelcross-sectionmeasurement

3.2.1Themeasurementofchannelcross-sectionshallbeinaccordancewiththefollowing

requirements：

1Thesoundingverticalsofchannelcross-sectionshallbearrangedinaccordancewiththe

requirementsgiveninArticle3.1.7ofthiscodeandinconformitywithflowvelocity-measuring

verticals.Forahydrometricstationwithunstableriverbed，soundingverticalsmaybeaddedproperlyin

additiontoflowvelocity-measuringverticals.

2Fornewhydrometricstationandstationwithunstableriverbed，depthshallbemeasured

simultaneouslywitheachdischargemeasurement.Iftherearenosignificantscouringandsilting

variationinthecross-sectionofthehydrometricstationwithanobviouschangeregularity，depthmay

notbemeasuredsimultaneouslywitheachdischargemeasurement.Whenspecialwaterregimesoccur

anditisdifficulttomeasuredepthduringdischargemeasurement，channelcross-sectionmaybe

measuredatafavorabletimebeforeorafterdischargemeasurement.

3Ahydrometricstationwithstableriverbedshallbeoverallsoundedonceayearbeforeandafter

thefloodseason，anddepthshallbeadditionallymeasuredaftereachmajorfloodinthefloodseason.

Thenumberofchannelcross-sectionmeasurementsmaybereducedforastationwithrockyriverbed.

4Intheicyperiod，thedepth，icesurfaceboundary，icethickness，immersedicethicknessand

frazilslushthicknessshallbemeasuredatthesametimeofdischargemeasurement.Ificebottomisnot

flat，thedistancefrominitialpointoficebottomedgeshallbemeasuredbythedetectionmethod.Ifice

bottomisflat，thelocationoftheicebottommaybefoundbyusingthebottomelevationprofileofice

holesalongbank.

3.2.2Themethodsofwidthmeasurementsoundingofchannelcross-sectionshallbedetermined

accordingtoriverwidth，depth，equipmentconditionsandmeasuringaccuracyrequirements，andcomply

withtherequirementsstipulatedinSectionB.8ofthiscode.Uncertaintyshallcomplywiththerelevant

requirementsstipulatedinSectionB.12ofthiscode.

3.3Errorsourcesandcontrol

3.3.1Theerrorsourcesofcross-sectionmeasurementshallincludethefollowing：

1Thefollowingcasesshallbeconsideredasthesourcesofsoundingerror：

1）Largewavesorthelargewaterresistanceofgaugesaffectsthemeasurement.

2）Soundingpositiondeviatesfromcross-sectionvertical.

3）Thedeflectionangleofsuspensioncablewaysislarge.

4）Themarkingofsoundingrodorropeisnotaccurate.

5）Asoundingrodorhammeristrappedinriverbed.

·11·6）Theacousticspeedsettingoftheultrasonicsounderisdifferentfromtheactualacousticspeed.

7）Theinstrumentsandequipmentforsoundingarenotcheckedandcalibratedasrequiredbefore

measurement.

2Thefollowingcasesshallbeconsideredasthesourcesofmeasurementerrorofdistancefrom

initialpoint：

1）Theaccuracyofbaselinemeasurementorthelengthofbaselinedoesnotmeetthe

requirements.

2）Theexpansionandsagvariationofcablewaysmakemeasurementinaccurate.

3）Whenthetheodoliteintersectionmethodisused，rear-viewobservationisinaccurateor

instrumentisdisplaced.

4）Whenthemethodofintersectionbysextantisused，theswayingofmeasuringshipmakes

positioninginaccurate.

5）Poorsatellitesignalscauseinaccuratepositioning.

6）Measuringpointdeviatesfromcross-sectionvertical.

7）Thecalibrationandobservationofinstrumentdonotmeetcoderequirements.

3.3.2Duringcross-sectionmeasurement，measuringerrorshallbecontrolledaccordingtothe

followingrequirements：

1Themeasurementshallbecarriedoutstrictlyinaccordancewiththerelevantoperation

regulations.

2Ifwavesarelarge，asoundingverticalshallnotbeobservedlessthan3timesandthemeanof

thetwoclosestvaluesshallbetaken.

3Themeasuringpositionofdepthanddistancefrominitialpointshallbecontrolledongauging

cross-sectionvertical.

4Ifanellipticaltypeweightisappliedforsounding，deflectionangleshallbereduced.Aheavy

ellipticaltypeweightshallbeusedwithinthetolerancerangeofsuspensioncableways.Ifthedeflection

angleexceeds10°，itshallbecorrected.

5Suitableultrasonicsoundershallbeselected.

6Widthmeasurementandsoundinginstrumentsandtoolsshallbecalibratedasrequired.

·12·4Stagegradationandmeansandmethodsofdischargemeasurement

4.1Generalrequirements

4.1.1Dischargemeasurementmethodsselectedforhydrometricstationsshallbesomatureatpresent

astobeappliedinpractices，satisfycertainaccuracyrequirements，andcomplywiththefollowing

requirements：

1Theselectedmeasurementmethodsshallbesuitablefortheflowcharacteristicsand

measurementconditionsofahydrometricstation（cross-sectionincluded）.

2Measurementaccuracyshallmeettherequirementsofdatapurpose.

4.1.2Theinstrumentationusedinvariousmethodsshallbecomparedwithcurrentmeterbeforebeing

putintohydrometricstationservice，andcomplywiththefollowingrequirements：

1Comparativegaugingshouldbecarriedoutwhenflowisrelativelystable，andmeasurement

timesshallbeuniformlydistributedatdifferentstages（ordischarge）ofhigh，mediumandlowstages.

2Theeffectivetimesofcomparativegaugingshallnotbelessthan30.

3Therandomuncertaintyofcomparativegaugingshallnotexceed6%，or7%underpoor

comparativegaugingconditions.Systematicerrorshallnotexceed±1%，or±2%underpoor

comparativegaugingconditions.

4.1.3Hydrometricstationsshallselecttwoormoremethodsfordischargemeasurementaccordingto

themeasurementconditionsofthestations，oneofwhichisfordailyusewiththerestasbackup.

4.1.4Thetimesofdischargemeasurementshallbearrangedinaccordancewiththefollowing

requirements：

1Thetimesofdischargemeasurementatahydrometricstationinayearshallbedetermined

comprehensivelyaccordingtotheflowcharacteristicsofhigh，mediumandlowstages，theflowcontrol

conditions，theaccuracyofmeasurement，therequirementsofthedeterminationofrelationcurveandthe

dischargecomputation，demands，etc.soastoaccuratelyunderstandwaterregimechangesinvarious

periodsandreasonablycontroltheturningpointofdifferentstagesandwaterregimechangeprocess.

Whenafloodoradryflowexceedstheequivalentstageofmeasureddischargeovertheyears，additional

dischargemeasurementsshallbeconductedfortheexcessivestages.

2Thetimesoftidaldischargemeasurementshallbearrangedreasonablyinrepresentativetidal

currentperiodaccordingtomeasurementdata.Tidaldischargevelocitymeasurementineachtidal

currentperiodshallbeproperlydistributedaccordingtothemagnitudeandurgencyofflowvelocity

changes，sothattheturningpointofflowvelocitychangesduringthewholetidalprocesscanbe

accuratelyunderstood.

3Thetimesanddistributionofdischargemeasurementsforice-frozenriversshallbeableto

controlthedischargechangeprocessorthechangeprocessofthecorrectioncoefficientoftheicyperiod.

Ifthedrifticeperiodislessthan5days，dischargeshallbemeasuredonceevery1dayor2days.Ifthe

drifticeperiodismorethan5days，dischargeshallbemeasuredonceevery2daysor3days.Thetimes

ofdischargemeasurementsinthestablefreeze-upperiodmaybeappropriatelyreducedcomparedwith

thatinthedrifticyperiod.Additionaldischargemeasurementsmaybeconductedasappropriatebefore

·13·freezingandafterthawing.Forhydrometricstationswithlargedailyvariationofdischarge，

measurementtimingwithrepresentativenessinonedayshallbedeterminedbyincreasingmeasurement

timesandconductingexperimentalanalysis.

4Thetimesofdischargemeasurementattheinitialstageofanewhydrometricstationshallbe

increasedappropriatelycomparedwiththatspecifiedinItem1ofthisarticle.

4.2Selectionofmeasurementmeans

4.2.1Dischargemaybemeasuredbymeansofstationarygauging（permanentstationarygaugingor

stationarygauginginthefloodseason），tourgaugingandintermittentgaugingaccordingtothechangeof

flowandsedimentcharacteristics，measurementaccuracy，requirementsfordataprocessing，

accessibility，etc.

2

4.2.2ClassⅠaccuracystationswithacatchmentareaofmorethan10000kmandallaccuracy

2

stationswithacatchmentareaoflessthan10000kmwheretheconditionsoftourgaugingand

intermittentgaugingarenotsatisfiedshallbesubjecttopermanentstationarygaugingorstationary

gauginginthefloodseason.

4.2.3Tourgaugingmaybeadoptedatvariousaccuracyhydrometricstationswithacatchmentareaof

2

lessthan10000kmifoneofthefollowingconditionsissatisfied：

1Ifstage-dischargerelationisinasinglecurve，thedeterminationofstage-dischargerelation

curvecanreachspecifiedaccuracy，andthereisnoneedtomeasurepeakdischargeorflooddischarge

process.

2Forhydrometricstationswithintermittentgauging，testgaugingshallbecarriedoutinthe

suspensionperiod.

3Ifthestage-dischargerelationinthedryperiodandicyperiodisrelativelystableordischarge

changeisgentle，thedischargemaybecalculatedbytourgaugingdata，andtheerrorofannualrunoff

shallbewithinapermissiblerange.

4Regulardischargemeasurementsshallbeadoptedinthedryperiod.

5Althoughstage-dischargerelationisnotinasinglecurve，thedischargecanbemeasuredin

timeaccordingtothechangeofwaterregimeiftheaccessibilityandcommunicationareconvenient.

6Therearespecialhydrometricstationsonsmallandmedium-sizedrivers.

2

4.2.4Forallaccuracyhydrometricstationswithacatchmentareaoflessthan10000km，wheremore

than10yearsofdataprovethatmeasureddischargeandequivalentstagehavecontrolledmorethan80%

ofstagevariationovertheyears（includingfloodanddryyears），andthestage-dischargerelationoverthe

yearsisinasinglecurve，intermittentgaugingmaybeadoptedifoneofthefollowingissatisfied：

1Themaximumrelativeerrorofthedeviationbetweentheannualstage-dischargerelationcurve

andthecomprehensiverelationcurveovertheyearsshallnotexceedthefollowingrequirements：

1）ClassⅠaccuracystation：3%forhighstage，5%formediumstageand10%forlowstage.

2）ClassⅡaccuracystation：5%forhighstage，8%formediumstageand12%forlowstage.

3）ClassⅢaccuracystation：8%forhighstage，10%formediumstageand15%forlowstage.

2Dischargemeasurementmaybesuspendedforoneyearwhenthemaximumrelativeerrorof

thecombinationofthestage-dischargerelationcurvesofeachadjacentyeardoesnotexceedthe

followingrequirements：

1）ClassⅠaccuracystation：4%forhighstageand5%formediumstage.

·14·2）ClassⅡaccuracystation：6%forhighstageand8%formediumstage.

3）ClassⅢaccuracystation：8%forhighstageand10%formediumstage.

3Withinapartialrangeofstagevariation，thestage-dischargerelationisinasinglecurveand

complieswithItem1ofthisarticle.

4Thestage-dischargerelationisinamultipleloopcurve，butconformstoItem1orItem2ofthis

articlethroughuniformizationtreatment.

5Inthedryperiod，theamplitudeofdischargevariationislittle，andthetotalrunoffofthedry

periodaccountsforlessthan5%ofthetotalannualrunoff，soitisnotnecessarytomeasuredischarge

process.Andaccordingtotheanalysisofrunoffdataofmanyyears，itisprovedthatthereisagood

relationshipbetweenmonthlyrunoffandfactorssuchaspreviousrunoff，precipitation，etc.

6Therelationshipbetweentidalelementsandtidaldischargeatatidalcurrentstationisproved

stablebymanyyearsofdata.

4.2.5Forhydrometricstationssubjecttointermittentgauging，testgaugingshallbecarriedoutinthe

suspensionperiod.Ifoneofthefollowingoccursintheperiodofintermittentgauging，thetimesoftest

gaugingshallbeincreasedornormaldischargemeasurementrestored：

1Floodordryflowoccursbeyondthescopeofintermittentgaugingplanforthestation.

2Itisfoundthathydraulicprojectsorotherhumanactivitieshavesignificantlychangedthecontrol

conditionsofthestation.

3PermissibleerrorexceedsthevaluespecifiedinItem1orItem2inArticle4.2.4ofthiscode.

4.3Selectionofmeasurementmethods

4.3.1Measurementmethodssuitableforthecharacteristicsofahydrometricstationmaybeselected

accordingtothemeasurementconditionsofameasuringreachandtechnicallevel.

4.3.2Thecurrentmetermethodmaybeadoptedifthefollowingaremet：

1Theflowvelocityofmostmeasuringpointsonthecross-sectiondoesnotexceedthemeasuring

rangeofacurrentmeter.

2Thedepthatverticalsshallnotbelessthanthenecessarydepthmeasuredbytheone-point

method.

3Inthebeginningandendingtimeofadischargemeasurement，thefluctuationdifferenceof

stageshallnotbegreaterthan10%ofthemeandepth，andthatforariverwithsmalldepthandthesharp

fluctuationofstageshallnotbegreaterthan20%ofthemeandepth.

4Floatingobjectsflowingthroughagaugingcross-sectionshallnotaffectthenormaloperation

ofacurrentmeter.

4.3.3Thefloatmethodmaybeadoptedifthefollowingaremet：

1Dischargeismeasuredundertheconditionsofhighflowvelocity，lowflowvelocityorsmall

depth，etc.，whichisdifficulttomeasurebyacurrentmeterorexceedstheapplicationrangeand

conditionsofthecurrentmeter.

2Thedepthatverticalsislessthanthenecessarydepthoftheone-pointmethodinthecurrent

metermethod.

3Stagerisesandfallssharply，andthefluctuationofthestageduringthemeasurementbythe

currentmeterexceedstherangespecifiedinItem3inArticle4.3.2ofthiscode.

4Toomanyfloatingobjectsonwatersurfaceaffectthenormalrotationofcurrentmeter.

·15·5Diversionfloodorbreachfloodoccurs.

4.3.4Theslope-areamethodmaybeadoptedinthefollowingcases：

1Themeasuringreachwithrelativelystablecross-sectionandlargesurfaceslopeinhighflood

period.

2Inthecaseofsharpstagefluctuation，smalldepthandmanyfloatingobjects，itisnotsuitableto

usethecurrentmetermethodorthefloatmethodtomeasurethedischarge.

3Floodexceedsthedischargemeasurementcapacityofahydrometricstation.

4Duetothemissingmeasurementoffloodpeak，itisnecessarytocarryoutfloodsurveyto

calculatethefloodpeakdischarge.

5Tourandintermittentgaugingstationswherefloodexceedsallowablestagevariation.

4.3.5TheacousticDopplercurrentprofilermethodmaybeadoptedwhenameasuringreachisinnon-

highsedimentconcentrationornon-clearwaterarea.

4.3.6Iftherearevarioushydraulicstructuressuchasdams，sluicegatesandpumpingstationsina

measuringreach，andthereisastablefunctionalrelationbetweendischargeandrelevanthydraulic

factors，thehydraulicstructurestreamgaugingmethodmaybeadopted.

4.3.7Themeasuringstructuremethodincludesvariousflowmeasurementweirsandflumes.Itis

applicabletoameasuringreachwithsmallwatersurfacewidth，smallwaterquantity，largeslope，and

lowsedimentconcentration.

4.3.8Forastraightandevenmeasuringreachwithlowsedimentconcentrationandlittlesuspended

solidsandwithoutwaterplantsorbubbles，theultrasonictransittimemethodmaybeadopted.

4.3.9Forameasuringreachwithmanywaterplantsandfloatingobjects，theelectromagneticmethod

maybeadopted.

4.3.10Forameasuringreachwithsmallwaterquantity，unstablecross-sectionandstrongturbulence，

thedilutionmethod（alsoknownastracermethod）maybeadopted.

4.3.11Forameasuringreachwithstageandstoragecapacitychangeinducedbyflowandcontrollable

intakeandoutlet，thevolumemethodmaybeadopted.

4.3.12Inthecaseofahighflooddischargemeasurementbeyondconventionalmeansandwater

quantitysurveywithoutfixeddischargemeasurementfacilities，theelectricwavecurrentmetermethod

maybeadopted.

4.3.13OtherdischargemeasurementmethodsrecommendedbytheInternationalOrganizationfor

Standardization（ISO）maybeadoptedaccordingtothemeasurementconditionsofastation.

4.4Gradationofstage（discharge）

4.4.1Rivercharacteristics，thefloodmeasuringcapacityofahydrometricstationandvariousfactors

affectingstagechangeshallbeconsideredforstage（discharge）grading，andgradationmethodssuitable

forthecharacteristicsofthehydrometricstationshallbeselected.

4.4.2Whenthewaterquantityofariverisabundantorstageisbasicallyinitsnaturalstate，the

occurrencefrequencyofstageinfreeflowperiodmaybeusedforstagegradation，andthefollowing

requirementsshallbecompliedwith：

1Thefrequencymaybecalculatedaccordingtothefollowingformula：

m

p=（4.4.2）

n+1

·16·wherep—frequency；

m—ordinalnumberofrandomvariablesindecreasingorderofvalue；

n—sequencenumberofrandomvariables，whichshouldnotbelessthan20.

2ForClassⅠaccuracyhydrometricstations，theannualeigenvaluemethodmaybeadoptedfor

stagegradation，andthefollowingrequirementsshallbecompliedwith：

1）AccordingtothehighestinstantaneousstageZineachyearofastation，thefrequencyis

M

calculatedandthefrequencydistributioncurvedrawn.Thestagecorrespondingtofrequencyp

of90%istakenasahighstage.

2）Accordingtotheaveragestagezofeachyearofastation，thefrequencyiscalculatedandthe

frequencydistributioncurvedrawn.Thestagecorrespondingtofrequencypof50%istaken

asamediumstage.

3）AccordingtotheminimuminstantaneousstageZineachyearofastation，thefrequencyis

m

calculatedandthefrequencydistributioncurvedrawn.Thestagecorrespondingtofrequencyp

of10%istakenasalowstage.

3ForClassⅡandClassⅢaccuracyhydrometricstations，thetypicalyearmethodmaybe

adoptedforstagegradation，andthefollowingrequirementsshallbecompliedwith：

1）AccordingtothetotalwaterquantityWofeachfloodseasonofastation，thefrequencyis

f

calculatedandthefrequencydistributioncurvedrawn.Theyearswithsimilarrunoff

correspondingtotherunofffrequencypof10%，50%and90%inthefloodseasonaretaken

asthetypicalyearsofwetflow，normalflowanddryflow.

2）Accordingtothedailyhigheststagez'ofthreetypicalyearsinthefloodseason，thefrequency

m

iscalculatedandthefrequencydistributioncurvedrawn.Thestagescorrespondingtothe

runofffrequencypof10%，50%and90%aretakenashigh，mediumandlowstages.

4.4.3Theoccurrencefrequencyofdischargemaybeusedfordischargegradationifahydrometric

stationwithsmallwaterquantityorwhosestageisseriouslyaffectedbywater-relatedprojects，andthe

followingrequirementsshallbecompliedwith：

1AccordingtothemeasuredmaximumdischargeQofastationeachyear，thefrequencyis

M

calculatedandthefrequencydistributioncurvedrawn.Thedischargecorrespondingtothefrequencyp

of90%istakenasahighdischarge.

-

2AccordingtothemeanannualdischargeQofastationeachyear，thefrequencyiscalculated

andthefrequencycurvedrawn.Thedischargescorrespondingtothefrequencypof50%and90%are

takenasamediumdischargeandlowdischarge，respectively.

4.4.4Accordingtothegradationresultsofstage（discharge），thehydrologicalcharacteristicsperiodof

ahydrometricstationmaybegradedasfourperiods，i.e.high-flowperiod，medium-flowperiod，low-flow

periodanddryperiod.

1Gradedbystage：

Whenthestageisnolowerthanthehighone，itishigh-flowperiod.

Whenthestageislowerthanthehighonebutnolowerthanthemediumone，itismedium-flow

period.

Whenthestageislowerthanthemediumonebutnolowerthanthelowone，itislow-flowperiod.

Whenthestageislowerthanthelowone，itisdryperiod.

·17·2Gradedbydischarge：

Whenthedischargeisnolessthanthehighone，itishigh-flowperiod.

Whenthedischargeislessthanthehighonebutnolessthanthemediumone，itismedium-flow

period.

Whenthedischargeislessthanthemediumonebutnolessthanthelowone，itislow-flowperiod.

Whenthedischargeislessthanthelowone，itisdryperiod.

4.4.5Iftheresultsofstage（discharge）gradationgradedbytheoccurrencefrequencyofstageor

dischargearegreatlydifferentfromtheactualsituationofahydrometricstation，gradedstage（discharge）

maybedeterminedbyanalysisbasedonhistoricaldataandpracticalcharacteristics.

4.4.6Stage（discharge）gradationmaybedeterminedbythefollowingmethodsfornewhydrometric

stations，andanalyzedafteracertainamountofdataiscollected：

1Thegradationmaybedeterminedbyinterpolationwithreferencetothegradedstagesof

upstreamanddownstreamhydrometricstations.

2Thegradationmaybedeterminedbythepercentageofthehighestfloodstageinvestigated.

3Thegradationmayrefertothatofhydrometricstationswithsimilarhydrometricconditions.

4.5Measurementofhighflooddischarge

4.5.1Accordingtotheprincipleof＂safety，efficiencyandspeed＂，andthetechnicalandwaterregime

characteristicsofahydrometricstation，variousmeasurementschemesshallbeformulatedforhighflood

dischargemeasurement.

4.5.2Beforetheapplicationofallkindsofhighflooddischargemeasurementschemes，drills

mustbecarriedouttoensuremeasurementsafety.

4.5.3Thehighflooddischargemeasurementshallreachthehighestaccuracyofinstrumentsor

measuringmethods.Ifmeasurementconditionspermit，themeasurementschemewithahigheraccuracy

shouldbeselected.

4.5.4Thefollowingmethodsmaybeadoptedforhighflooddischargemeasurement：

1Thecurrentmetermethod.

2Thefloatmethod.

3Theslope-areamethod.

4TheacousticDopplercurrentprofilermethod.

5Theelectricwavecurrentmetermethod.

6Thehydraulicstructurestreamgaugingmethod.

4.5.5Accordingtotheflowcharacteristicsinthehighfloodperiodandthetechnicalequipmentofa

hydrometricstation，dischargemeasurementdurationshallbeshortened，andappropriatedischarge

measurementmethodselected，whichshallbeinaccordancewiththefollowingrequirements：

1Whenadischargemeasurementschemeinthehighfloodperiodisdeployed，thecommonly

useddischargemeasurementmethodsinthestationshallbepreferred.

2Whenthecurrentmetermethodisadoptedtomeasuredischarge，representativeverticalsmay

beusedtosimplifydischargemeasurementforspecialwaterregimessuchasthesharprisesandfallsof

stage，frequentstagechangesduetofluctuatingbackwater，severeiceflowanddramaticchangesin

waterregimeintheicyperiod.Therepresentativeverticalsshallbedeterminedthroughasimplified

analysisofhistoricaldata.Theuncertaintyofthevelocityofrepresentativeverticalsshallnotexceed

·18·8%and10%forstationswheredischargeismeasuredbythemulti-verticalandmulti-pointmethodand

bytheless-verticalandless-pointmethod，respectively.Cross-sectionareamaybereferencedfrom

recentmeasurementdata.

3Whenitisdifficulttoadoptthecurrentmetermethod，othercommonlyuseddischarge

measurementmethodsmaybeselectedaccordingtotherequirementsofthedischargemeasurement

necessitydurationandaccuracyinthiscode.

4Forsmallandmedium-sizedriverswithsharpstagerisesandfallsandthelargewatersurface

slopeofameasuringreach，theslope-areamethodmaybeusedifthecurrentmetermethodorthe

uniformfloatmethodcannotbeusedifthedischargemeasurementdurationisnotallowed.

5Floodswithsharpstagerisesandfallsandalargeamountoffloatingobjectsmaybemeasured

bythefloatingobjectsfloatmethodorthemidstreamfloatingobjectsfloatmethod.Forsmallslope

riversinplainwaternetworkarea，themidstreamfloatmethodmaybeadopted.

4.5.6Whenspecialflowconditionscausedbydambreach，flooddiversion，debrisflow，barrierlake，etc.

occur，dischargemeasurementmethodssuitableforthemeasurementconditionsandflowconditionsat

thattime，suchaselectricwavecurrentmeter，maybeadoptedforemergencydischargemeasurement.

4.6Dischargemeasurementindryperiod

4.6.1Thecurrentmetermethodshallbeprioritizedfordischargemeasurementinthedryperiod.The

smallfloatmethodmaybeadoptedwhendepthcannotmeetthemeasuringrequirementsofthecurrent

meter.Whensomeverticalsmeetthemeasuringrequirementsofthecurrentmetermethod，thecurrent

metermethodandthesmallfloatmethodmaybemixedtocompletethedischargemeasurement.

4.6.2Whenovergrownwaterplantsinariveroraccumulatedrocksatthebottomoftheriveraffect

normaldischargemeasurementinthedryperiod，thewaterplantsshallberemovedandtheriverbottom

flattenedwhenevernecessary.

4.6.3Whenthedepthinacross-sectionislessthanthatrequiredforvelocitymeasurementbytheone-

pointcurrentmetermethodorflowvelocityislowerthanthenormaloperatingrangeofmeasuring

instrument，thefollowingmeasuresmaybetaken：

1Ameasuringreachshallberegulatedwitharegulatedlengthofmorethan5timesthewidthof

watersurfaceinthedryperiod.

2Iftheaccuracyofdischargemeasurementcannotbeguaranteedafterregulation，thereachmay

benarrowedorbackwatermeasuresadopted.

3Ameasuringreachwithlargedepthandlowflowvelocitymaybenarrowed.Thelengthofthe

narrowedreachshallbegreaterthan1.0timestheriverwidth.Thegaugingcross-sectionshallbe

arrangedinthedownstreamofthenarrowedmeasuringreach.

4Ifwaterisshallowbutflowvelocityishighenough，anarrowedreachmaybecanalized，and

depthatmostverticalsshallbeabove0.2m.Theslopeofthenarrowedreachmaybebetween1∶2and1∶4，

andthecanalizedlengthshallbemorethan4timestheriverwidth.Thegaugingcross-sectionshallbe

locateddownstreamofthecanalizedreach，andthelengthfromtheintakeshouldbe60%ofthetotal

lengthofthecanalizedreach.

5Adistanceshouldbekeptfromtheregulatedreachtothebasicstaffgaugecross-section.A

temporarygaugemaynotbesetupifthestageofthebasicstaffgaugeandthedischargeoftheregulated

cross-sectionareingoodrelationinthedryperiod.Otherwise，atemporarygaugeshallbesetupinthe

·19·regulatedcross-section.

4.6.4Whendepthinthecross-sectionistoosmall，flowvelocitytoolow，orbackwaterhasobvious

influenceinthedryperiod，anditisdifficulttoregulateameasuringreachorcompletelyeliminate

backwaterinfluencebyregulation，ameasuringcross-sectionmaybesetup.Atemporarygaugeshallbe

setupinameasuringcross-sectioninthedryperiodifoneofthefollowingsituationsoccurs：

1Flowinbasicstaffgaugecross-sectionisscatteredortherearemultiplestreamsofflow，

backflows，etc.

2Thestageanddischargearepoorlycorrelated.

3Thedischargeofameasuringcross-sectionisfrequentlymeasuredinthedryperiod.

4Thereisinfloworoutflowbetweenmeasuringcross-sectionandbasicstaffgaugecross-section

inthedryperiod.

4.6.5Ifthecross-sectiondepthistoosmalland/orflowvelocityistoolowinashorttimewithinayear

tousecurrentmeterorartificialregulationmeasures，atemporarymeasuringcross-sectionmaybe

shiftedtoareachwithoutwaterinfloworoutflow.

4.6.6Forhydrometricstationsservingthepurposeofwaterresourcesmanagement，discharge

measurementaccuracyshouldbetestedinthedryperiodtodeterminedischargemeasurementscheme

inthedryperiod.Thepermissibleerrorofasingledischargemeasurementinthedryperiodshallbein

accordancewithTable6.1.2ofthiscodeandmeettherequirementsofwaterresourcesmanagement.

Flowvelocity-measuringverticalsinthedryperiodshallbeselectedaccordingtotheschemegivenin

TableB.12.12-1toTableB.12.12-3ofthiscodeifdischargemeasurementaccuracyisnottestedata

stationinthedryperiod.

4.6.7Ifwadingmeasurementisused，thepersonnelshallstandbesidethecurrentmeter，facingthe

directionnormaltotheflow，andthedistancebetweencurrentmeteranddischargemeasurershallbe

keptmorethan0.5mduringflowvelocitymeasurement.

4.7Dischargemeasurementinicyperiod

4.7.1ThecurrentmetermethodoracousticDopplercurrentprofilermethodmaybeadoptedfor

dischargemeasurementintheicyperiod.

4.7.2Ifthecurrentmetermethodisused，thefollowingrequirementsshallbecompliedwith：

1Ificeholesaredrilledfordischargemeasurement，brashiceorslushicerunshallberemoved

beforemeasurement.

2Ifthereisseverelyupwellingwateronagaugingcross-sectionortheareaoffrazilslushunder

theiceinthecross-sectionexceeds25%ofwettedcross-sectionarea，thegaugingcross-sectionmaybe

shiftedtoacross-sectionwithoutupwellingwaterovertheiceorwithlessfrazilslush.

3Whenicelayeristhickinthefreeze-upperiod，specialicedrillshouldbeusedtodrillholesfor

dischargemeasurement.

4Whentheboundaryofstagnantwaterundericeismeasured，ameasuringrodtiedwithredand

whitelightfiberclothoralongtubeisinjectedwithcoloredsolutionwithsimilarspecificgravityto

watermaybeextendedintoaneffectivedepthtoobservewhetherwaterflows.

5Underseverecoldweather，instrumentsurfacemaybecoatedwithkeroseneorcoveredbya

thermalinsulationandanti-freezingcovertopreventthesurfacefromfreezingaftertheinstrumentis

withdrawnfromwater.Iftheinstrumentfreezes，itshallbemeltedwithhotwater，shallnotbetwisted

·20·orknockedtheinstrumentforciblytoremovetheicelayerofitssurface.

6Ificelayerisnotstrongenough，dischargeshouldbemeasuredwhenthetemperatureislowin

themorning.

7Thefollowingmeasuresmaybetakenwhenicecoverwithintercalatedwaterlayersoccursata

gaugingcross-section：

1）Atemporarycross-sectionfordischargemeasurementmaybesetup.

2）Whenagaugingcross-sectionisnarrow，alltheiceonthecross-sectionandasmallsectionof

thereachnearbymayberemoved，anddischargemeasurementiscarriedoutaccordingtothe

measurementmethodinthefreeflowperiod.

3）Forlargerivers，layeredmeasurementmaybecarriedout.Ifitisdifficulttocarryoutlayered

measurement，longsloticeholesparalleltoflowdirectionmaybedrilledonthegaugingcross-

section.Thelengthoftheiceslotisdeterminedaccordingtoflowvelocityandthethicknessof

immersedice.

4）Whenthechannelcross-sectionbetweenvariousicelayersisnotfilledupwithwater，several

iceholespenetratingthrougheachicelayermaybedrilledatacertaindistanceupstreamofa

gaugingcross-sectiontoconcentrateflowthroughtheicelayerstothelowestlayer.After

stageturnsstable，dischargemeasurementmaybecarriedoutonthegaugingcross-section

accordingtonormalmethods.

4.8Tidaldischargemeasurement

4.8.1Accordingtotheflowcharacteristicsofahydrometricstationandexistingtechnicalequipment，

tidaldischargeshallbemeasuredbycurrentmeterwithmulti-verticalsimultaneousdischarge

measurementmethod，shipboard-typeacousticDopplercurrentprofilermethod，theultrasonictransit

timemethod，indexandcross-sectionaveragevelocitymethod，etc.Whenatidaldischarge

measurementschemeisdeployed，thecommondischargemeasurementmethodsofthestationshallbe

preferred.

4.8.2Forahydrometricstationadoptingoneverticalfortheindexvelocitymethod，cross-sectionarea

maybereferencedfromrecentmeasureddata，andthefollowingrequirementsshallbecompliedwith：

1Duringtidaldischargemeasurement，thecorrelationbetweenoriginalrepresentativevertical

andmeanflowvelocityatacross-sectionshallbecalibratedatleast15times，andthettestshallbe

carriedout.

2Whenthecorrelationbetweenrepresentativeverticalandmeanflowvelocityatacross-section

isreestablished，thetimesofcalibrationshallnotbelessthan30，andthetotalrandomuncertaintyofthe

errorofthedeterminationofrelationcurveshallnotexceed15%.

3Fortemporarytidaldischargemeasuringcross-section，theaccuracyofdeterminationof

relationcurvemayberelaxedasappropriate.

4.8.3ForhydrometricstationswiththehorizontalacousticDopplercurrentprofilermethod，the

accuracyrequirementsofdeterminationofrelationcurveshallbethesameasthoseinArticle4.8.2of

thiscode.Originalcorrelationcurveshallbecalibratedeveryyear，andthecalibrationtimesshallnotbe

lessthan15inandagainstflowdirection，respectively.

4.8.4Slacktidetimeshallbedeterminedaccordingtothefollowingmethods：

1Theverticalandthelocationofthemeasuringpointsoftheoccurrencetimeoftheslacktideof

·21·floodandebbtidesshouldbedeterminedbytestanalysis.Beforetest，acurrentmetermaybeplaced

nearthe0.4timesdepthtomeasurethemeanoccurrencetimeoftheslacktideatverticals.Acurrent

metermaybeplacedataverticalbetweenshoreandmidstreamtomeasurethemeanoccurrencetimeof

theslacktideoffullcross-sectionifthemultipleverticalsbyverticalmeasurementisadopted.If

multipleverticalsareusedforsimultaneousmeasurement，themeanoccurrencetimeofslacktideshall

bedeterminedaccordingtothearithmeticmeanvalueoftheslacktidetimesofeachvertical.Ifthereis

nosignalonacurrentmeterfor180s，itmayberegardedasslacktide.Ifmeasuredslacktidelastsfora

period，themeanvalueshallbetaken.

2Ifacurrentmeterisnotusedformeasurement，themeanflowvelocityhydrographatacross-

sectionintheperiodbeforeandaftertheturningoffloodandebbtidesmaybeplottedandinterpolated.

·22·5Checkandanalysisofdischargemeasurementresults

5.1Checkitemsandmethods

5.1.1Theresultsofasingledischargemeasurementshallbecheckedandanalyzedaccordingtothe

principleof＂computing，processingandanalyzingthedataoncedischargemeasurementisdone＂.If

errorsarefoundinmeasurementonsite，causesshallbetraced，andcorrespondingcorrectiveand

remedialmeasuresshallbetaken.

5.1.2Thecheckofasingledischargemeasurementresultsshallincludethefollowingitems：

1Standardizationandcompletenessofon-sitemeasurementprocessandrecords.

2Rationalityofdischargemeasurementresults.

3Rationalityofdischargemeasurementtimesarrangement.

5.1.3Thecheckofthemeasurementrecordsofflowvelocity，depthatameasuringpointanddistance

frominitialpointshallbemeasuredon-siteoneachmeasurementandcalculationresult，incombination

withstationcharacteristics，riverregimeandspecificconditionsatmeasuringsites，andshallbein

accordancewiththefollowingrequirements：

1Theflowvelocitydistributioncurveatverticalsshallbeplottedtocheckandanalyzeits

rationality.Ifabnormalitiesarefound，causesshallbeinvestigated.Ifthereareobviousmeasurement

errors，re-measurementshallbedone.

2Thetransversedistributionofthemeanflowvelocityatverticalsorfloatflowvelocityanda

channelcross-sectionshallbeplotted，andtherationalityofthetransversedistributioncheckedand

analyzed.Ifabnormalitiesarefound，causesshallbeinvestigated.Iftherearemeasurementerrors，re-

measurementshallbedone.

3Whenarepresentativeverticalisusedformeasurementatatidalcurrentstation，the

hydrographofindexvelocityshallbeplotted，andthecontinuity，uniformityandrationalityofflow

velocitychangeprocessshallbecheckedandanalyzed.

4Forastationwithflowvelocitymeasurementbyfixedverticals，whenitisdifficulttoplotan

analyzingdiagramonsiteduetotheconstraintofthemeasurementconditions，orwhenthetimefor

dischargemeasurementneedstobeshortenedduetothesharpfluctuationofstage，themeasuredresults

ofverticaldepth，flowvelocityatmeasuringpointsandthemeanflowvelocityatverticalsmaybefilled

intothecomparisonchecklistofvelocityandsoundingresultsmadebeforehand，whicharechecked

againstthemeasuredresultsofadjacentverticalsandpreviousmeasurement.

5.1.4Theresultsofdischargemeasurementshallbecomputedandcheckedonthedaywheneach

dischargemeasurementends，andtherationalityshallbecheckedandanalyzedaccordingtothe

followingrequirements：

1Thecurvesofcorrelationbetweenstageorotherhydraulicfactorsanddischarge，stageand

area，stageandvelocityshallbeplotted，andtheirchangetrendandtherationalityofcorresponding

relationsamongthethreecurvesshallbecheckedandanalyzed.

2Forstationsadoptingcontinuousmeasureddischargeprocesslineindataprocessing，stage，

flowvelocity，areaanddischargehydrographsmaybeplotted，andtherationalityofthechangeprocess

·23·ofvariouselementscheckedbycomparison.

3Fordischargemeasurementintheicyperiod，aflowcorrectioncoefficienthydrographor

immersedicethicknessandtemperaturehydrographintheicyperiodmaybeplottedtocheckthe

rationalityofdischargeintheicyperiod.

4Whenabnormaldischargemeasuringpointisfound，thecausesshallbeinvestigatedand

analyzed.Foracontrollablemeasurementwhichcannotbecorrected，on-siteinvestigationonthe

measuringreachshouldbeconducted，andadditionalmeasurementshallbetakenforverification.

5.1.5Intherationalitycheckandanalysisofdischargemeasurementarrangement，thedischarge

measuringpointsshallbeplottedonthecorrespondingpositionofanhourlystagehydrographaftereach

dischargemeasurement.Forstationsadoptingthefallmethodinhydrologicdataprocessingand

dischargecomputation，dischargemeasuringpointsshallbeplottedonadrophydrographatthesame

time，andacomparativecheckshallbemadeaccordingtothedistributionofthedischargemeasuring

pointsonthecurveofthecorrelationbetweenstageorhydraulicfactorsanddischarge.Ifthe

arrangementofmeasurementtimescannotsatisfytherequirementsofthedeterminationofrelation

curvefordataprocessing，measurementtimesshallbeincreasedaccordingtowaterregime，orthe

timingofthenextmeasurementshallbeadjusted.

5.2Checkandanalysis

5.2.1Thecharacteristicsofahydrometricstationshallberegularlyanalyzed，mainlyincludingthe

controlcharacteristicsofthestation，stage-dischargerelation，thechangingtendencyofthescouringand

siltingofacross-section，velocitydistributionpatternatverticalsandthetransversedistributiontrendof

flowverticalvelocityatacross-section.

5.2.2Theanalysisofthecontrolcharacteristicsofahydrometricstationshallbeinaccordancewiththe

followingrequirements：

1Toplotthecurveoftherelationbetweenstageorhydraulicfactorsanddischarge.The

correlationcurvesofthecurrentyearandpreviousyearshallbedrawnonthesamechartforcomparison

soastounderstandthechangeandtransferofthestationcontrolfromthedeviationtrendoftherelation

curve，andanalyzethecauses.

2Toplotthecurveoftherelationbetweenstageandpercentagedeviationcurveofdischarge

measuringpointssoastounderstandthetransferandchangeofthestationcontrolfromthedeviation

andtrendofthedischargemeasuringpoints，andanalyzethecauses.

3Toplotthecurveoftherelationbetweenthepositiveandnegativedeviationpercentageof

dischargemeasuringpointsandtimesoastounderstandthechangeofthestationcontrolwithtime，and

analyzethecauses.

4Todrawthecurveofthespecifieddischargevaluesaccordingtothemeasuredequivalentstage

formanyyearssoastounderstandthechangeofthestationcontrolfromthefallorrisetrendofastage

curvecorrespondingtothespecifieddischarge，andanalyzethecauses.

5.2.3Forastationwithunstableriverbed，therelationbetweenscouringandsiltingofthegauging

cross-sectionofthestationandhydraulicfactorsandthatbetweenscouringandsiltingandriverregime

shallbeanalyzedonceevery3to5years，andthescouringandsiltingtrendandthechangeoftheriver

bedshallbeanalyzed.

5.2.4Themeasureddataofthemulti-pointmethodshallbeusedtoanalyzetheflowvelocity

·24·distributionpatternatavertical.Whenvariousverticalsatacross-sectionaresimilarinvelocity

distributionpattern，astandardflowvelocitydistributioncurveataverticalmaybeplotted.Whenthe

flowvelocitydistributionpatternsofverticalsateachpartofacross-sectionarenotfullyidentical，two

orthreedistributioncurvesmaybeplotted，respectively.Forhydrometricstationswithlargestage

variationanddifferentverticalvelocitydistributionpatternsatdifferentstages，thedistributioncurveof

differentstagepointsshallbedrawn，andaflowvelocitydistributionformulaobtainedbycurvefitting

maybeusedtoanalyzetherelationbetweentheflowvelocityatvariousrelativedepthmeasuringpoints

andthemeanflowvelocityatavertical.

5.2.5Ahydrometricstationshalladoptthedatameasuredbythemulti-verticalmethodatdifferent

stagestoanalyzethetransversedistributionpatternandchangeofthemeanflowvelocityatavertical.

·25·6Assessmentofdischargemeasurementaccuracy

6.1Generalrequirements

6.1.1Thetestofdischargemeasurementerrororcomparativegaugingshallbemadeatahydrometric

stationwithcertainrepresentativenessandsuitablemeasurementorcomparisonconditions，andthe

accuracyoftheresultsmaybeassessedbyanalyzingtheerrortestorcomparativegaugingdata.For

hydrometricstationswiththesamecharacteristicsandmeasurementmethodsinthesameregion，the

comprehensiveresultsaccuracyoftheregionmaybeusedasassessmentbasis.

6.1.2Theaccuracyindexofasingledischargemeasurementshallbedeterminedaccordingtodata

purposeortheneedsofclient.Thepermissibleerrorofthecurrentmetermethodshallcomplywiththe

requirementsinTable6.1.2，whichmayalsobeusedasreferenceforotherdischargemeasurement

methods.Forhydrometricstationswithcomprehensivefunctions，thehighestaccuracyindexshallbe

adopted.

Table6.1.2Permissibleerrorofsingledischargemeasurementbythecurrentmetermethod

Permissibleerro（r%）

X

Q'

StationclassStagegradation

?

μ

Q

BasicdataHydrologicWaterresources

Flooddefense

collectioncomputationmanagement

High5655-1.5-1

ClassⅠMedium6766-2.0-1

Low9987-2.5-1

High6766-2.0-1

ClassⅡMedium7877-2.5-1

Low101098-3.0-1

High8987-2.5-1

ClassⅢMedium91098-3.0-1

Low12121110-3.5-1

Notes：1X—totalrandomuncertaintyat95%ofconfidencelevel.

Q'

?

2μ—systematicerror，acontrolindexfordifferentdatapurposes.Thepermissibleerrorofasingledischargemeasurementdata

Q

forotherpurposesmaybedeterminedbyanalysisasrequired.

6.1.3Appropriatemeasurementinstrumentsandmethodsforhydrometricstationsshallbeselected

accordingtotheaccuracyindexdeterminedinTable6.1.2ofthiscode.Ifconventionalinstrumentsand

methodsfailtomeetthespecifiedaccuracyrequirements，themeasurementmethodsshallbechangedor

ameasuringreachorameasuringcross-sectionartificiallyregulated.

6.1.4Themeasurementaccuracyofahydrometricstationforspecificpurposemaybedeterminedby

thepurposeofsetting-upthestationaccordingtoTable6.1.2ofthiscode.

6.1.5Forhydrometricstationswhosemeasurementconditionsareseriouslyaffectedbyhuman

activities，iftheaccuracyofasingledischargemeasurementfailstomeettherequirementsinTable

·26·6.1.2ofthiscode，theaccuracyclassmaybelowereddownorotherdischargemeasurementmethods

withequivalentaccuracyadopted.

6.1.6Inthecasesofspecialwaterregimescausedbydambreach，flooddiversion，debrisflow，barrier

lake，etc.，theaccuracyofemergencydischargemeasurementmaybedeterminedaccordingtothelocal

measurementconditionsandmethodsatthattime.

6.1.7Forriverswithasmallwaterquantity，whenthepermissibleerrorofdischargemeasurement

inthelow-flowperioddoesnotmeettherequirementsinTable6.1.2ofthiscode，itmaybe

expressedasabsoluteerror，anditsindexshallbedeterminedthroughtheanalysisofhistoricaldata

ofthestation.

6.1.8Inareaswithouterrortestdata，representativestationswithfavorableconditionsshallbe

selectedtochecktheaccuracyindexspecifiedinthiscode.Ifthemeasuredresultsofthestationandthe

accuracyindexspecifiedareinconsistent，datashallbeanalyzedandmeasurementschemeimproved.

6.2Errorsourcesandcontrol

6.2.1Dischargemeasurementerrorsmaybedividedintorandomerror，undeterminedsystematic

error，determinedsystematicerrorandspuriouserror.Randomerrorshallbedescribedwithrandom

uncertaintyataconfidencelevelof95%accordingtothenormaldistribution.Undetermined

systematicerrorshallbedescribedwithsystemuncertaintyataconfidencelevelofnolessthan

95%.Determinedsystematicerrorshallbecorrected，andmeasurementresultscontainingspurious

errorseliminated.

6.2.2Theerrorsourcesandcontrolofthecurrentmetermethodshallbeinaccordancewiththe

followingrequirements：

1Errorsourceanalysisshallincludethefollowing：

1）Positioningerrorofdistancefrominitialpoint.

2）Soundingerror.

3）Positioningerrorofflowvelocitymeasuringpoint.

4）Errorcausedbyflowdirectiondeflectionangle.

5）Errorcausedbythenon-parallelaxisofcurrentmeterandstreamline.

6）Errorcausedbytheinterferenceofanobjectenteringthewatermeasured.

7）Timingerror.

8）Errorofcurrentmetercalibration.

9）Errorcausedbytheimperfectionofameasurementscheme，mainlymanifestintheerrorof

flowvelocitypulsationcausedbytheinsufficientdurationoftheflowvelocitymeasurement

atmeasuringpoints，theerrorofthecomputationofthemeanflowvelocityatavertical

causedbytheinsufficientnumberofmeasuringpointsatthevertical，anderrorcausedby

theinsufficientnumberoftheflowvelocity-measuringverticalsonacross-section.

10）Errorcausedbyimproperoperationduringmeasurement.

11）Errorcausedbymeasurementconditionsbeyondtheproperuseofmeasurementinstrument.

2Thefollowingmeasuresmaybetakenforerrorcontrol：

1）Toestablisharegularinspectionandregistrationsystemformainmeasurementinstruments

andtoolsandrelevantmeasurementequipmentanddevices.

2）Totimelyverify，calibrateandmaintaininstrumentsaccordingtorelevantregulations.

·27·3）Tocarryoutwidthmeasurementandsoundingaccordingtotherequirementsstipulatedin

SectionB.8ofthiscode.

4）Toadopteffectivemeasuresforaccuratepositioningandthereductionofflowdirection

deflectionangleandthehydraulicresistanceofdischargemeasuringequipment.

5）Duringflowvelocitymeasurement，thelongitudinalaxisofahydrometricboatshouldbe

paralleltostreamline，andthestabilityofthehydrometricboatmaintained.

6）Toregulateoperationprocedures.

7）Toimprovethemeasurementschemes.

8）Measurementconditionsshallconformtotheproperuseofmeasurementinstrument.

6.2.3Theerrorsourcesandcontrolofthefloatmethodshallbeinaccordancewiththefollowing

requirements：

1Errorsourceanalysisshallincludethefollowing：

1）Floatcoefficientadoptionerror.

2）Cross-sectionborrowingormeasuringerror.

3）Whenthecross-sectionfloatmethodisused，floatdistributionisunevenortherearetoofew

effectivefloats，resultinginerrorcausedbytheinaccuratevelocitytransversedistributionof

floats.

4）Inareachwheredeep-waterfloatorfloatisusedtomeasuredischarge，errormaybecausedby

aconsiderablechangeofdepthalongtheway.

5）Floatobservationerror.

6）Timingerror.

7）Floatfabricationerror.

8）Errorcausedbytheinfluenceofwinddirectionandwindspeedonfloatoperation.

2Thefollowingmeasuresmaybetakenforerrorcontrol：

1）Tostrengthenfloatcoefficienttestanalysis.

2）Ifconditionspermit，ameasuringcross-sectionshallbeadoptedasmuchaspossible，andcross-

sectionmeasurementerrorshallbecontrolledaccordingtorelevantwidthmeasurementand

soundingregulations.

3）Whenthecross-sectionfloatmethodisused，thenumberandtransversedistributionposition

ofthefloatsshouldbecontrolledtomakethetransversedistributioncurveoffloatflow

velocitymorerepresentative.

4）Whenthedeep-waterfloatorfloatrodmethodisusedfordischargemeasurement，a

measuringreachshallbeselectedaccordingtoItem5inArticleC.1.1ofthiscode.

5）Measurementshallbecarriedoutinaccordancewiththerequirementsforfloatflowvelocity

measurementinthiscodeandtherelevantrequirementsfortheuniformdesignoffloatsshall

beusedfordischargemeasurement.

6）Totimewithastopwatchwithhighaccuracyandcheckfrequentlytoeliminatetiming

systematicerror.

6.2.4TheerrorsourceandcontroloftheacousticDopplercurrentprofilermethodshallbein

accordancewiththefollowingrequirements：

1Errorsourceanalysisshallincludethefollowing：

1）RandomerrorandsystematicerrorcausedbythenoiseofacousticDopplercurrentprofiler.

·28·2）Soundingerror.

3）Theflowvelocitymeasurementerrorofahydrometricboat，includingbottomtrackingerroror

GlobalPositioningSystem（GPS）positioningerror.

4）Measurementerrorofthedistancesfromthestartandendofthemeasurementtobank.

5）Errorcausedbyahighratioofhydrometricboatspeedtoflowvelocity.

6）Errorcausedbyahighratiooftheareaofnon-measuredzone（surfacelayer，bottomlayer，left

andrightbankarea）totheareaofmeasuredzone.

7）Themeasurementerrorofacross-sectionarea.

8）Errorscausedbyfactorsaroundflowincludingpulsationorturbulence，surfacewaves，shear

discharge，bedloadatthebottomofariver，extremelyslowvelocity，etc.

9）Errorscausedbyhumanfactors.

2Thefollowingmeasuresshallbetakenforerrorcontrol：

1）DifferentialGPSmaybeusedinsteadofbottomtrackingtomeasurehydrometricboatspeed

inameasuringreachaffectedby＂movingbed＂.

2）Forthegaugingcross-sectionwherewaterplantscannotbeavoided，thefixed-pointmultiple

verticalsmethodshouldbeadopted.

3）Atransducershallbeinstalledfirmlyanditsdepthmeasuredaccuratelytoavoidinputerror.

4）Shoredistanceshouldbeaccuratelymeasuredbyalaserrangefinderortape，andthevisual

estimationmethodnotbeused.

5）Shoreshapecoefficientorbankdischargecoefficientshallbecorrectlyselected.

6）Theflowvelocityextensionmodelsofsurfaceandbottomblankingdistanceshallbecorrectly

selected.The1/6powerfunctionlawmaybeused，andthepowerexponentorotherflow

velocityextensionmodelsshouldnotbechanged.Attentionshouldbepaidtotheinfluenceof

bidirectionalflow.

7）Blankingdistanceshallbesetaccordingtothefrequencyofatransducer，andtheblanking

distancevalueshallnotbesettoosmall.

8）Thecorrectdeflectionanglecorrectionvalueshallbeinputindischargemeasuringsoftware.

9）Appropriateworkingmodeshallbeselected.

10）Aunitlengthvalue（MS）shallbesetaccordingtothefrequencyofatransducer，the

maximumdepthorthemaximumnumberofunits（MN）.

11）Thetotaldurationofmeasurementshallnotbelessthan12minutes，andatleasttwoone-

waymeasurements（onemeasurementcycle）shallbeconducted.

6.2.5Theerrorsourcesandcontrolofotherdischargemeasurementmethodsshallbeinaccordance

withrelevantcodesandinstrumentinstructions，orinaccordancewiththefollowingrequirements：

1Errorsourceanalysisshallincludethefollowing：

1）Measurementconditionsdonotmeettheuseconditionsoftheinstrumentormethod.

2）Instrumenterror.

3）Instrumentverificationandcalibrationerror.

4）Positioningerror.

5）Improperparametersetting.

2Thefollowingmeasuresmaybetakenforerrorcontrol：

1）Toselectappropriatemeasurementinstrumentsandmethodsaccordingtothemeasurement

·29·conditions.

2）Totimelyverify，calibrateandmaintaininstrumentsaccordingtotherelevantregulations.

3）Ifconditionspermit，appropriateparametersareselectedthroughcomparativetest.

4）Tostrictlyabidebyinstrumentoperationprocedures.

6.3Assessmentofdischargemeasurementaccuracy

6.3.1Theaccuracyofdischargemeasurementresultsmaybeindicatedbysyntheticuncertainty.For

hydrometricstationsofallclasses，thesyntheticuncertaintyofeachstationshallbecomputedoncea

yearaccordingtohigh，mediumandlowstages，andfilledinadischargerecordtableasthebasisforthe

accuracyassessmentofmeasurementresults.

6.3.2Therelativestandarddeviationofeachcomponentofdischargeshallbeestimatedinaccordance

withthefollowingrequirements：

1Forthenindependentmeasurementsofacertaincomponent，therelativestandarddeviationof

thecomponentshallbeestimatedaccordingtothefollowingformulae：

n

1

Y=Y（6.3.2-1）

∑i

n

i=1

n

2

11

S=Y-Y（6.3.2-2）

Yi

∑

n-1

Y

i=1

whereS—relativestandarddeviationofdischargecomponents（%）；

Y

Y—arithmeticmeanvalueofnmeasuredvaluesofdischargecomponent；

Y—theithmeasurementvalueofdischargecomponent.

i

2Whenthenindependentmeasurementsmentionedaboveareconductedseveraltimesandtheir

relativevaluesmaybeusedassampleobservationsofthesameparent，therelativestandarddeviationof

thecomponentshallbeestimatedaccordingtothefollowingformulae：

n

YY

1

=（6.3.2-3）

∑

yny

i=1

i

2

n

1YY

S=-（6.3.2-4）

Y

∑

n-1yy

i=1

i

wherey—approximatetruevalueofdischargecomponent；

Y

—relativevalueobtainedfromtheithdischargemeasurementofacertaindischarge

y

i

component；

Y

—arithmeticmeanvalueofnrelativevaluesofacertaindischargecomponent.

y

6.3.3Therandomuncertaintyofeachindependentcomponentofdischargeistakenat95%of

confidencelevelandshallbeestimatedaccordingtothefollowingrequirements：

1Whenthesamplesizeofmeasurementseriesisnolessthan30，therandomuncertaintyshallbe

2timestherelativestandarddeviation.

2Whenthesamplesizeofmeasurementseriesislessthan30，therandomuncertaintyshallbe

calculatedbymultiplyingtheconfidencefactor［Student's（t）value］inTable6.3.3bytherelative

standarddeviation.

·30·Table6.3.3Student's（t）valueat95%ofconfidencelevel

Student's（t）Student's（t）Student's（t）Student's（t）

SamplesizeSamplesizeSamplesize

Samplesize

valuevaluevaluevalue

212.70692.306162.131232.074

34.303102.262172.120242.069

43.182112.228182.110252.064

52.776122.201192.101262.060

62.571132.179202.093272.056

72.447142.160212.086282.052

82.365152.145222.080292.048

6.3.4Theuncertaintyofadischargemeasuringinstrumentmaybedeterminedaccordingtothe

accuracyindexgivenbymanufacturer.

6.3.5Ifdischargecanbeexpressedasafunctionofseveralcomponentsandeachcomponentis

assumedtobeindependent，thetotalrandomuncertaintyshallbecalculatedaccordingtothefollowing

formula：

22

k

?QY

i

22

X=X（6.3.5）

Q'i'

∑

?YQ

i

i=1

whereX—totalrandomuncertaintyofdischarge（%）；

'

Q

k—numberofcomponents；

X—randomuncertaintyofdischargecomponentsY（%）.

'

ii

·31·AppendixAMethodsforaccuracyclassificationof

basichydrometricstations

A.0.1Theaccuracyclassificationofbasichydrometricstationsshallbedividedintothreeclasses

accordingtoTableA.0.1.

TableA.0.1Classificationcriteriaforaccuracyofhydrometricstations

Item

2

Drainagearea（km）

Accuracy

classification

AccuracyrequirementsMaintasksofhydrometricstation

Aridand

Wetarea

semiaridarea

Tocollectthelongseriesofsamplesrequired

Highestaccuracyofexistingtoexplorethevariationpatternof

ClassⅠoperationsandmethodsshallhydrologicalcharacteristicvaluesintimeand≥3000≥5000

beachievedalongriverandthedataneededbyeconomy

andsociety

Tocollecttherepresentativeseriesof

Accuracymaybeformulatedsamplesrequiredtoexplorethevariation

＜10000＜10000

ClassⅡaccordingtomeasurementpatternsofhydrologicalcharacteristicvalues

≥200≥500

conditionsalongriverandinregionandthedataneeded

byeconomyandsociety

Tocollectdatatoexploretherunoffyield，

flowconcentrationlawandrunoffchange

Requirementsontheaccuracyrulesofasmallstreamundervarious

ClassⅢofdatapurposeforstationunderlyingsurfaceconditions，aswellasthe＜200＜300

tasksshallbemethydrologicalanalysisandcalculation

requirementsforseriesrepresentativeness，

andthedataneededbyeconomyandsociety

A.0.2Basinorprovincialhydrologicalinstitutionsmayadjusttheaccuracyclassificationofstations

accordingtothefactors，suchasimportanceofbasichydrometricstations，datapurpose，service

requirementsandmeasuringdifficulty，etc.

A.0.3Ifitisdifficultforahydrometricstationtomeettheoriginalaccuracyrequirementsduetothe

constraintofstationcontrolandmeasurementconditions，itsaccuracymaybereducedbyoneclass，but

shallnotbelowerthanClassⅢ.

·32·AppendixBCurrentmetermethod

B.1Generalrequirements

B.1.1Thefollowingworkshallbedonesimultaneouslywheneverdischargeismeasured：

1Toobservethestageofbasicstaffgauge.Whenthereisagaugeinagaugingcross-section，

stageshallbeobservedatthesametime.Forahydrometricstationwithslopeobservationrequirement，

stageofslopestaffgaugeshallbeobservedatthesametime.

2Tomeasurechannelcross-section.Themeasurementofchannelcross-sectionshallcomply

withtherelevantrequirementsstipulatedinSection3.2andSectionB.8ofthiscode.

3Tomeasureflowvelocityatameasuringpointormeanflowvelocityatavertical.Whenflow

directionmeasurementisrequired，thedeflectionangleofflowdirectionshallbemeasured.

4Toobserveweatherphenomenaandflowconditionnearameasuringcross-section.

5Tocalculate，checkandanalyzedischargemeasurementdataandcalculationresults.

B.1.2AdischargemeasurementschememaybeselectedaccordingtothatgiveninTableB.12.12-1to

TableB.12.12-3ofthiscode.Whenhighmeasurementaccuracyisrequired，theschemeofmultiple

verticals，multiplepointsandlongdurationmaybeselected.

B.1.3Thetotalrandomuncertaintyoftidaldischargemeasurementshallbelessthan15%，and

systematicuncertaintylessthan3%.

B.1.4Forahydrometricstationwithlittlechangesinriverbedscouringandsilting，thefluctuation

differenceofstageduringonedischargemeasurementshallnotexceedtherequirementsstipulatedin

Item3inArticle4.3.2ofthiscode.However，thecontinuousdischargemeasurementmethodmaybe

adoptedwhensharpstagefluctuationmakesthedistributionofmeasurementtimesunabletomeetthe

requirements.

B.1.5Forahydrometricstationwhereitsriverbedisrelativelystableandtherelationbetweenstageand

meanflowvelocityataverticalisstable，thesegmentalverticaldischargemeasurementmethodshouldbe

adoptedwhensharpstagefluctuationmakesthestagefluctuationdifferenceinonedischarge

measurementprocesslikelyexceedtherequirementsstipulatedinArticleB.11.4ofthiscode.

B.2Layoutofflowvelocity-measuringverticals

B.2.1Flowvelocity-measuringverticalsshallbeevenlydistributedingeneral，capableofbasically

controllingthemainturningpointsofcross-sectionterrainandvelocitydistributionalongriverwidth.

Theverticalsinmainchannelshallbedenserthanthoseinrivershore.

B.2.2Flowvelocity-measuringverticalsshallbearrangedforsingle-streamdiversionsanderosion

ditchesinacross-sectionwithadischargegreaterthan1%ofthecross-sectiondischarge.

B.2.3Forahydrometricstationwithobviouschangesincross-sectionshapeortransversedistribution

offlowvelocityasstagegradechanges，verticalsshallbearrangedaccordingtohigh，mediumandlow

stages.

B.2.4Thepositionofflowvelocity-measuringverticalsshouldbefixed.Whenoneofthefollowing

situationsoccurs，theverticalsshallbeadjustedorsupplementedanytime：

·33·1Stagefluctuationorriverbankscouringmakesverticalsnearriverbanktoofarawayfromor

tooclosetothebank.

2Thereisstagnantwaterorbackflowonacross-section，anditisnecessarytodetermine

stagnantwaterorbackflowboundaryorbackflowdischarge.

3Riverbottomtopographyortheflowvelocitydistributionofmeasuringpointsalongriverwidth

changessignificantly.

4Thedistributionoffrazilslushisunevenoraflowvelocity-measuringverticalisfrozeninthe

icyperiod.

5Intheicyperiod，bordericeappearsneartheboundarybetweenbordericeandexposedriver

surface.

B.2.5Forahydrometricstationwithcableway，soundingandwidthmeasurementinstruments，toolsand

cablesizesignsshallbecalibratedandcheckedaccordingtoSectionB.8ofthiscodebeforeusingthe

cableway.

B.2.6Thenumberofflowvelocity-measuringverticalsshallbedeterminedaccordingtoadischarge

measurementschemeselectedinSectionB.12ofthiscode.Forahydrometricstationwithaviolent

mainflowswingorunstableriverbed，andseverefloodplain，aschemewithmoreflowvelocity-

measuringverticalsshouldbeselected.

B.2.7Thenumberofflowvelocity-measuringverticalsintidalriversmaybeappropriatelylessthan

thatinnon-tidalrivers.5to7verticalsshouldbeusedforthemeasurementbyboat，and7to9verticalsused

forthemeasurementbyhydrometriccableway.Thenumberofverticalsinespeciallywideornarrow

riversmaybeincreasedordecreasedappropriately，butshallnotbelessthan3.Whenthewatersurface

widthanddepthathighandlowtidestagesvarysignificantly，thenumberofflowvelocity-measuring

verticalsandthepositionofflowvelocity-measuringverticalonbankshallbeadjustedaccordingtothe

fluctuationoftidestageineachtidalperiod.

B.3Flowvelocitymeasurement

B.3.1Iftheselectedpointmethodisusedtomeasuremeanflowvelocityatavertical，thedistribution

offlowvelocitymeasuringpointsshallbeinaccordancewiththefollowingrequirements：

1Theminimumdistancebetweentwoadjacentmeasuringpointsataverticalshouldnotbeless

thanthediameterofthepropellerorrotarycupofacurrentmeter.

2Whenflowvelocityonwatersurfaceismeasured，therotatingpartofinstrumentshallnotbe

exposedtowatersurface.

3Whenflowvelocityatriverbottomismeasured，acurrentmetershallbepositionedbelow0.9

timesdepth，andtheedgeoftherotatingpartoftheinstrumentbe2cmto5cmawayfromtheriver

bottom.Whenicebottomorfrazilslushbottomismeasured，theedgeoftherotatingpartofthe

instrumentshallbe5cmawayfromtheicebottomorfrazilslushbottom.

B.3.2Acurrentmetermaybesuspendedbysuspensionrodorsuspensioncable.Asuspendedcurrent

metershallbeinahorizontalstateunderwater.Ifthedepthorflowvelocityofmostverticalsissmall，a

suspensionrodshouldbeused.

B.3.3Thepositioningofcurrentmetermeasuringpointsshallbeinaccordancewiththefollowing

requirements：

1Thedistancefromcurrentmetertothesideofaboatshallnotbelessthan1.0m，andthattothe

·34·sideofasmallboatnotbelessthan0.5m.

2Ifasuspensionrodisadopted，thecurrentmetershallbeparalleltotheflowdirectionof

measuringpointatthattime，andtheinstrumentinstalledonthesuspensionrodshallbeabletorotate

freelywithinacertainrangeofhorizontalplane.Whenasuspensionrodisfixed，oneendoftherodshall

beequippedwithachassis，underwhichthereshallbeatip.

3Ifasuspensioncableisadopted，themethodofhangingellipticaltypeweightshallmakea

currentmeterparalleltotheflowdirectionofmeasuringpointatthattime，andasinglepointsuspension

ora＂splay＂suspensionwithanadjustablecenterofgravitymaybeadopted.Themethodofdeflection

anglecorrectionofsuspensioncableandmeasuringpointpositioningdeterminationshallbeselected

accordingtoSectionB.9ofthiscode.Iftheactualdepthcannotbemeasuredbyellipticaltypeweight，

depthislookedupbyborrowingtheresultsoflastcross-sectionmeasurement，anddeflectionangleof

suspensioncableisgreaterthan10°，thepositionofeachmeasuringpointbelowwatersurfaceshallbe

determinedbythe＂trialanderrormethod＂.

B.3.4Thenumberofmeasuringpointvelocityvaluesonflowvelocity-measuringverticalsshallbe

determinedaccordingtothedischargemeasurementschemeselectedinSectionB.12ofthiscode，and

thelocationdistributionofmeasuringpointvelocityshallcomplywiththerequirementsinTableB.3.4.

TableB.3.4Flowvelocitypositiondistributionofmeasuringpointsonvertical

Relativedepthposition

Measuringpointnumber

FreeflowperiodIcyperiod

One0.6or0.5，0.0，0.20.5

Two0.2，0.80.2，0.8

Three0.2，0.6，0.80.15，0.5，0.85

Five0.0，0.2，0.6，0.8，1.0-

Six0.0，0.2，0.4，0.6，0.8，1.0-

Eleven0.0，0.1，0.2，0.3，0.4，0.5，0.6，0.7，0.8，0.9，1.0-

B.3.5Thedurationofflowvelocitymeasurementatameasuringpointshallbedeterminedaccording

tothedischargemeasurementschemeselectedinSectionB.12ofthiscode.

B.3.6Whenastagnantwaterzoneoccursinagaugingcross-section，thestagnantwaterboundaryshall

bedeterminedbytheanalysisofprevioustestdataorvisualinspection.Whentheareaofthestagnant

waterzonedoesnotexceed3%ofthecross-sectionarea，itmaybetreatedasaflowingwaterzone.

Whentheareaofthestagnantwaterzoneexceeds3%，alow-speedcurrentmeter，deep-waterfloator

othermethodsshallbeusedtomeasurethestagnantwaterboundary，andtheareashallbetreatedasa

stagnantwaterzone.

B.3.7Whenabackflowzoneoccursinagaugingcross-section，thebackflowofthecross-sectiondoes

notexceed1%ofdownstreamflowofthecross-section，andtheupstreamanddownstreamflowsare

irregularatdifferenttimes，flowvelocity-measuringverticalsmayonlybearrangedonbothsidesof

upstreamanddownstreamflowjunctiontodeterminetheboundaryofbackflow，andthebackflowmay

betreatedasstagnantwater.Whenthebackflowofthecross-sectionexceeds1%ofdownstreamflow

ofthecross-section，inadditiontomeasuringitsboundary，appropriatenumberofflowvelocity-

measuringverticalsshallbearrangedinthebackflowareatomeasurethebackflowquantity.

B.3.8Round-tripmeasurementshouldbeadoptedforflowvelocitymeasurementataverticaloftidal

·35·currentstation，andthenumberofmeasuringpointsmaybedeterminedbyverticaldepthaccordingto

followingrequirements：

1Ifthedepthislessthan1.5m，theone-pointmethodwith0.6or0.5timesdepthmaybeadopted.

2Ifthedepthisnolessthan1.5mandlessthan3.0m，thetwo-pointmethodwith0.2and0.8

timesdepthmaybeadopted.

3Ifthedepthisnolessthan3.0mandlessthan5.0m，thethree-pointmethodmaybeadopted.

4Ifthedepthisnolessthan5.0m，thesix-pointmethodshouldbeadopted.

B.3.9Thedurationofflowvelocitymeasurementatasinglemeasuringpointoftidalcurrentstation

shouldbe60sto100s.Whenvelocityvariabilityislargeortherearemanymeasuringpointsona

vertical，themeasurementdurationmaybe30sto60s.

B.3.10Flowvelocityataverticaloftidalcurrentstationmaybemeasuredsimultaneouslyatvarious

measuringpointsontheverticalwithmultiplecurrentmeters，ortheflowvelocityofvariousmeasuring

pointsonaverticalmaybemeasuredsuccessivelywithonecurrentmeter，andthencorrectedto

simultaneousflowvelocity.

B.3.11Ifacurrentmeterisusedtomeasurethetidalflowvelocityofeachmeasuringpointinturn，the

measurementandcorrectionmethodsshallbeinaccordancewiththefollowingrequirements：

1Therevisedgraphicmethod.Itisadvisabletomeasure5to6points，andothermeasuring

pointsexceptthoseonwatersurfaceshallbedistributedatanequaldistance，tokeepthedistancefrom

riverbottomfixed.Whentidestagefluctuationcausesthedistancebetweenwatersurfacemeasuring

pointsandadjacentmeasuringpointstobetoolargeortoosmall，measuringpointsshallbeincreased，

decreasedoradjustedaccordingtotheprincipleofuniformityandequaldistance.Avelocity

hydrographisdrawnwithmeasuredvelocitiesateachmeasuringpointintimesequence（FigureB.3.11）.

Accordingtothissetofcurves，thesimultaneousvelocityofeachmeasuringpointonaverticalatany

timeinthemeasuringtidalcurrentperiodmaybefound.Measuringsequenceshallbefromriver

bottomtowatersurface.Thetimeintervalofeachmeasurementshouldbeshort，withmoretimesof

measurement.

Time（h）

FigureB.3.11Velocityhydrographofeachmeasuringpointontheverticaloffluctuatingtide

1-watersurfacemeasuringpoint；2-d3measuringpointfromriverbottom；3-d2measuringpointfromriverbottom；

4-d1measuringpointfromriverbottom；5-riverbottommeasuringpoint

2Therevisedvelocity-hydrographmethod.Thesix-pointmethodshouldbeadopted，and

measuringpointpositioncalculatedaccordingtorelativedepth.Measurementsequenceshallbefrom

riverbottomtowatersurface，andthemeasurementtimeateachpointshallberecorded.Thetime

intervalofeachmeasurementshouldbeshortandthetimesofmeasurementmore.Themeasurement

andcorrectionmethodsarethesameasthoseinItem1ofthisarticle.

3Therevisedisobath-velocitymethod.Thetwo-pointtosix-pointmethodmaybeadopted.

·36·Measurementsequenceshallbefromwatersurfacedowntothemeasuringpointwithamaximum

depth，andthenuptowatersurfacepointbypoint.Exceptforthemeasuringpointwithamaximum

depth，theothermeasuringpointsshallbemeasuredtwice.Thetimeintervalofflowvelocity

measurementateachmeasuringpointshouldbeshortandroughlyequal.Exceptforriverbottomflow

velocity，theflowvelocityoftheothermeasuringpointsisthemeanoftwomeasurements.The

measur