ASTM_D_1941_-_21.pdf

Designation:D194121Standard 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 The values stated in inch-pound units are to be regardedas standard.The values given in parentheses are mathematicalconversions to SI units that are provided for information onlyand are not considered standard.1.3 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,health,and environmental practices and deter-mine the applicability of regulatory limitations prior to use.1.4 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards,Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade(TBT)Committee.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 555-2:1987 Liquid Flow Measurements in OpenChannelsDilution Methods for Measurement of SteadyFlowConstant Rate Injection MethodISO 1438:2017 Liquid Flow Measurement in Open Chan-nels Using Thin-Plate WeirsISO 4359:2013 Liquid Flow Measurement in OpenChannelsRectangularTrapezoidalandU-shapedFlumes3.Terminology3.1 Definitions:3.1.1 For definitions of terms used in this standard,refer toTerminology D1129.3.2 Definitions of Terms Specific to This Standard:3.2.1 free flow,na condition where the flowrate is gov-erned by the state of flow at the crest overfall and hence can bedetermined from a single upstream depth measurement.3.2.2 head,nthe height of a liquid above a specified point.3.2.2.1 DiscussionThat is,the flume crest.3.2.3 hydraulic jump,nan abrupt transition from super-critical to subcritical flow,accompanied by considerable tur-bulence or gravity waves,or both.3.2.4 normal depth,nthe uniform depth of flow for agiven flowrate in a long open channel of specific shape,roughness,and slope.3.2.5 primary instrument,nthe device that creates a hy-drodynamic condition that can be sensed by the secondaryinstrument.3.2.5.1 DiscussionIn this example,the primary instrumentis the flume.3.2.6 scow float,nan in-stream flat for depth sensing thatis usually mounted on a hinged cantilever.3.2.7 secondary instrument,na device which measuresthe depth of flow at an appropriate location in the 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 Dec.15,2021.Published February 2022.Originallyapproved in 1962.Last previous edition approved in 2013 as D1941 91(2013).DOI:10.1520/D1941-21.2For 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 StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards,Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade(TBT)Committee.13.2.7.1 DiscussionThe secondary instrument may alsoconvert the measured depth to an indicated flow rate.3.2.8 stilling well,na 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 flow,nopen channel flow at a velocityless than the velocity of gravity waves in the same depth ofwater.3.2.9.1 DiscussionSubcritical flow is affected by down-stream conditions,since disturbances are able to travel up-stream.3.2.10 submerged flow,na condition where the waterstage downstream of the flume is sufficiently high to affect theflow over the flume crest and invalid