Designation:D5388−93(Reapproved2013)StandardTestMethodforIndirectMeasurementsofDischargebyStep-BackwaterMethod1ThisstandardisissuedunderthefixeddesignationD5388;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginaladoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscriptepsilon(´)indicatesaneditorialchangesincethelastrevisionorreapproval.1.Scope1.1Thistestmethodcoversthecomputationofdischargeofwaterinopenchannelsorstreamsusingrepresentativecross-sectionalcharacteristics,thewater-surfaceelevationoftheupstream-mostcrosssection,andcoefficientsofchannelroughnessasinputtogradually-variedflowcomputations.21.2Thistestmethodproducesanindirectmeasurementofthedischargeforoneflowevent,usuallyaspecificflood.Thecomputeddischargemaybeusedtodefineapointonthestage-dischargerelation.1.3Thevaluesstatedininch-poundunitsaretoberegardedasthestandard.TheSIunitsgiveninparenthesesareforinformationonly.1.4Thisstandarddoesnotpurporttoaddressallofthesafetyconcerns,ifany,associatedwithitsuse.Itistheresponsibilityoftheuserofthisstandardtoestablishappro-priatesafetyandhealthpracticesanddeterminetheapplica-bilityofregulatorylimitationspriortouse.2.ReferencedDocuments2.1ASTMStandards:3D1129TerminologyRelatingtoWaterD2777PracticeforDeterminationofPrecisionandBiasofApplicableTestMethodsofCommitteeD19onWaterD3858TestMethodforOpen-ChannelFlowMeasurementofWaterbyVelocity-AreaMethod3.Terminology3.1Definitions:3.1.1Fordefinitionsoftermsusedinthistestmethod,refertoTerminologyD1129.3.2DefinitionsofTermsSpecifictoThisStandard:NOTE—SeveralofthefollowingtermsareillustratedinFig.1.3.2.1alpha(α)—adimensionlessvelocity-headcoefficientthatrepresentstheratioofthetruevelocityheadtothevelocityheadcomputedonthebasisofthemeanvelocity.Itisassumedequaltounityifthecrosssectionisnotsubdivided.Forsubdividedsections,αiscomputedasfollows:α5(ki3ai2KT3AT2(1)where:kanda=theconveyanceandareaofthesubsectionindi-catedbythesubscripti,andKandA=the...
