ASTM_D_1941_-_91_2013.pdf

Designation:D194191(Reapproved 2013)Standard Test Method forOpen Channel Flow Measurement of Water with the ParshallFlume1This standard is issued under the fixed designation D1941;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope1.1 This test method covers measurement of the volumetricflowrate of water and wastewater in open channels with theParshall flume.1.1.1 Information related to this test method can be found inISO 1438 and ISO 4359.1.2 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:2D1129 Terminology Relating to WaterD2777 Practice for Determination of Precision and Bias ofApplicable Test Methods of Committee D19 on WaterD3858 Test Method for Open-Channel Flow Measurementof Water by Velocity-Area Method2.2 ISO Standards:3ISO 555 Liquid Flow Measurements in Open ChannelsDilution Methods for Measurement of Steady FlowConstant Rate Injection MethodISO 1438 Liquid Flow Measurement in Open ChannelsUsing Thin-Plate Weirs and Venturi FlumesISO 4359 Liquid Flow Measurement in Open ChannelsRectangular Trapezoidal and U-shaped Flumes3.Terminology3.1 Definitions:For definitions of terms used in this testmethod,refer to Terminology D1129.3.2 Definitions of Terms Specific to This Standard:3.2.1 free flowa condition where the flowrate is governedby the state of flow at the crest overfall and hence can bedetermined from a single upstream depth measurement.3.2.2 headthe height of a liquid above a specified point;that is,the flume crest.3.2.3 hydraulic jumpan abrupt transition from supercriti-cal to subcritical flow,accompanied by considerable turbulenceor gravity waves,or both.3.2.4 normal depththe uniform depth of flow for a givenflowrate in a long open channel of specific shape,roughness,and slope.3.2.5 primary instrumentthe device(in this case,theflume)that creates a hydrodynamic condition that can besensed by the secondary instrument.3.2.6 scow floatan in-stream flat for depth sensing usuallymounted on a hinged cantilever.3.2.7 secondary instrumentin this case,a device whichmeasures the depth of flow at an appropriate location in theflume.The secondary instrument may also convert the mea-sured depth to an indicated flow rate.3.2.8 stilling wella small reservoir connected through aconstricted passage to the main channel,that is,the flume,sothat a depth measurement can be made under quiescentconditions.3.2.9 subcritical flowopen channel flow at a velocity lessthan the velocity of gravity waves in the same depth of water.Subcritical flow is affected by downstream conditions,sincedisturbances are able to travel upstream.3.2.10 submerged flowa condition where the water stagedownstream of the flume is sufficiently high to affect the flowover the flume crest and hence the free-flow depth-dischargerelation no longer applies and discharge depends on two headmeasurements.3.2.11 supercritical flowopen channel flow at a velocitygreater than that of gravity waves in the same depth,sodisturbances cannot travel upstream,and downstream condi-tions do not affect the flow.3.2.12 throatthe constriction in a flume.1This test method is under the jurisdiction of ASTM Committee D19 on Waterand is the direct responsibility of Subcommittee D19.07 on Sediments,Geomorphology,and Open-Channel Flow.Current edition approved Jan.1,2013.Published January 2013.Originallyapproved in 1962.Last previous edition approved in 2007 as D1941 91(2007).DOI:10.1520/D1941-91R13.2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.3Available from American National Standards Institute(ANSI),25 W.43rd St.,4th Floor,New York,NY 10036,http:/www.ansi.org.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 4.Summary of Test Method4.1 Parshall flumes are measuring flumes of specified ge-ometries for which empirical relations of the formQ 5 C Han(1)have been established so that the flowrate,Q,can bedetermined from a single depth measurement,Ha,in free flow.If the flow is submerged,an addition downstream depth,Hb,must be measured and suitable adjustments made.5.Significance and Use5.1 Flume designs are available for throat sizes of 1 in.(2.54cm)to 50 ft(15.2 m)which cover maximum flows of 0.2 to3000 ft3/s(0.0057 to 85 m3/s)(1)and(2)4.They can thereforebe applied to a wide range of flows,with head losses that aremoderate