ASTM_D_5129_-_95_2014e1.pdf

Designation:D512995(Reapproved 2014)1Standard Test Method forOpen Channel Flow Measurement of Water Indirectly byUsing Width Contractions1This standard is issued under the fixed designation D5129;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.1NOTEEditorial corrections were made throughout in July 2015.1.Scope1.1 This test method covers the computation of discharge(the volume rate of flow)of water in open channels or streamsusing bridges that cause width contractions as metering de-vices.21.2 This test method produces the maximum discharge forone flow event,usually a specific flood.The computed dis-charge may be used to help define the high-water portion of astage-discharge relation.1.3 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.1.4 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:3D1129 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 Standard:4ISO 748 Liquid Flow Measurements in Open ChannelsVelocity-Area Measurements3.Terminology3.1 DefinitionsFor definitions of terms used in this testmethod,refer to Terminology D1129.3.2 Definitions of Terms Specific to This Standard:3.2.1 alpha()a velocity-head coefficient that adjusts thevelocity head computed on basis of the mean velocity to thetrue velocity head.3.2.2 area(A)the area of a cross section,parts of a crosssection,or parts of bridges below the water surface.Subscriptsindicate specific areas as follows:Ai=area of subsection i,Aj=area of piers or piles that is submerged,A1=area of total cross Section 1(see Fig.1),andA3=gross area of Section 3.3.2.3 conveyance,(K)a measure of the carrying capacityof a channel cross section,or parts of a cross section,and hasunits of cubic feet per second or cubic metres per second.Conveyance is computed as follows:K 5*1.486nAR2/3where:n=the Manning roughness coefficient,A=the cross-section area,ft2(m2),andR=the hydraulic radius,ft(m).*in SI units=1.01This 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.1,2014.Published March 2014.Originallyapproved in 1990.Last previous edition approved in 2008 as D5129 95(2008).DOI:10.1520/D5129-95R14E01.2This test method is similar to methods developed by the U.S.GeologicalSurvey and described in documents referenced in Footnote 5.53For 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.4Available 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 FIG.1 Definition Sketch of an Open-Channel ContractionD5129 95(2014)12 The following subscripts refer to specific conveyances forparts of a cross section:Ka,Kb=conveyances of parts of the approach section toeither side of the projected bottom width of thecontracted section(see Fig.2).Kdis always thesmaller of the two,Kd=conveyance at the upstream end of the dikes,Ki=conveyance of subsection i,Kq=conveyance of the part of the approach sectioncorresponding to the projected bottom-width,andKT=total conveyance of cross section.3.2.4 depth(y)depth of flow at a cross section.Subscriptsdenote specific cross section depths as follows:y1=depth of flow in Cross Section 1(approach section),andy3=depth of flow in Cross Section 3(contracted section).3.2.5eccentricity(e)a measure of the symmetry of thecontraction in relation to the approach channel.3.2.6 friction slope(Sf)the energy loss,hf,divided by thelength of the reach,L.3.2.7 Froude number(F)an index to the state of flow in achannel.In a rectangular channel,the flow is tranquil orsubcritical if the Froude number is less than 1.0 and is rapid orsupercritical if it is greater than 1.0.3.2.8 head(h)static or piezometric head above an arbi-trary datum.Subscripts indicate specific heads as follows:hf=head loss due to friction,andhs=stagnation-surface level at embankment fac