1、Designation: D5640 95 (Reapproved 2014)Standard Guide forSelection of Weirs and Flumes for Open-Channel FlowMeasurement of Water1This standard is issued under the fixed designation D5640; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revis
2、ion, 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 guide covers recommendations for the selection ofweirs and flumes for the measurement of the vol
3、umetric flowrate of water and wastewater in open channels under a varietyof field conditions.1.2 This guide emphasizes the weirs and flumes for whichASTM standards are available, namely, thin-plate weirs, broad-crested weirs, Parshall flumes, and Palmer-Bowlus (and otherlong-throated) flumes. Howeve
4、r, reference is also made toother measurement devices and methods that may be useful inspecific situations.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 no
5、t 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
6、to use.2. Referenced Documents2.1 ASTM Standards:2D1129 Terminology Relating to WaterD1941 Test Method for Open Channel Flow Measurementof Water with the Parshall FlumeD3858 Test Method for Open-Channel Flow Measurementof Water by Velocity-Area MethodD5242 Test Method for Open-Channel Flow Measureme
7、ntof Water with Thin-Plate WeirsD5389 Test Method for Open-Channel Flow Measurementby Acoustic Velocity Meter SystemsD5390 Test Method for Open-Channel Flow Measurementof Water with Palmer-Bowlus FlumesD5614 Test Method for Open Channel Flow Measurementof Water with Broad-Crested Weirs2.2 ISO Standa
8、rd:3ISO 555-1973: Liquid Flow Measurement in OpenChannelsDilution Methods for Measurement of SteadyFlowConstant-Rate Injection Method3. Terminology3.1 DefinitionsFor definitions of terms used in this guide,refer to Terminology D1129.3.2 Definitions of Terms Specific to This Standard:3.2.1 blackwater
9、an increase in the depth of flow upstreamof a channel obstruction, in this case a weir or flume.3.2.2 contracted weirscontractions of thin-plate weirs re-fer to the widths of weir plate between the notch and thesidewalls of the approach channel. In fully contracted weirs,the ratio of the notch area
10、to the cross-sectional area of theapproach channel is small enough for the shape of the channelto have little effect. In suppressed (full-width) rectangularweirs, the contractions are suppressed, and the weir crestextends the full width of the channel.3.2.3 crestin rectangular thin-plate weirs, the
11、horizontalbottom of the overflow section; in broad-crested weirs andflumes, the plane, level floor of the flow section.3.2.4 critical flowopen-channel flow in which the energy,expressed in terms of depth plus velocity head, is a minimumfor a given flow rate and channel.3.2.4.1 DiscussionThe Froude n
12、umber is unity at criticalflow.3.2.5 Froude numbera dimensionless number expressingthe ratio of inertial to gravity forces in free-surface flow. It isequal to the average velocity divided by the square root of theproduct of the average depth and the acceleration due togravity.3.2.6 headin this conte
13、xt, the depth of flow referenced tothe crest of the weir or flume and measured at a specified1This guide is under the jurisdiction of ASTM Committee D19 on Water and isthe direct responsibility of Subcommittee D19.07 on Sediments, Geomorphology,and Open-Channel Flow.Current edition approved Jan. 1,
14、2014. Published March 2014. Originallyapproved in 1995. Last previous edition approved in 2008 as D5640 95 (2008).DOI: 10.1520/D5640-95R14.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume
15、 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 19428-2
16、959. United States1location; this depth plus the velocity head are often termed thetotal head or total energy head.3.2.7 hydraulic jumpan abrupt transition from supercriti-cal to subcritical or tranquil flow, accompanied by considerableturbulence or gravity waves, or both.3.2.8 long-throated flumea
17、flume in which the prismaticthroat is long enough, relative to the head, for a region ofessentially critical flow to develop on the crest.3.2.9 nappethe curved sheet or jet of water overfalling aweir.3.2.10 notchthe overflow section of a triangular weir or ofa rectangular weir with side contractions
18、.3.2.11 primary instrumentthe device (in this case, a weiror flume) that creates a hydrodynamic condition that can besensed by the secondary instrument.3.2.12 rangeabilitythe spread between the maximum,Qmax, and minimum, Qmin, flow rates that a measuringinstrument can usefully and reliably accommoda
19、te; this may bedescribed as the ratio Qmax/Qmin.3.2.13 secondary instrumentin this case, a device thatmeasures the head on the weir or flume; it may also convert thismeasured head to an indicated flowrate or could totalize theflow.3.2.14 subcritical flowopen-channel flow that is deeperand at a lower
20、 velocity than critical flow for the same flow rate;sometimes called tranquil flow.3.2.14.1 DiscussionThe Froude number is less than unityfor this flow.3.2.15 submergencethe ratio of downstream head to up-stream head on a weir or flume. Submergence greater than acritical value affects the discharge
21、for a given upstream head.3.2.16 supercritical flowopen-channel flow that is shal-lower and at higher velocity than critical flow for the same flowrate.3.2.16.1 DiscussionThe Froude number is greater thanunity for this flow.3.2.17 throatthe constricted portion of a flume.3.2.18 velocity headthe squa
22、re of the average velocitydivided by twice the acceleration due to gravity.4. Significance and Use4.1 Each type of weir and flume possesses advantages anddisadvantages relative to the other types when it is consideredfor a specific application; consequently, the selection processoften involves reach
23、ing a compromise among several features.This guide is intended to assist the user in making a selectionthat is hydraulically, structurally, and economically appropriatefor the purpose.4.2 It is recognized that not all open-channel situations areamenable to flow measurement by weirs and flumes and th
24、at insome cases, particularly in large streams, discharges may bestbe determined by other means. (See 6.2.2.)5. Weirs and Flumes5.1 Weirs:5.1.1 Weirs are overflow structures of specified geometriesfor which the volumetric flow rate is a unique function of asingle measured upstream head, the other el
25、ements in thehead-discharge relation having been experimentally or analyti-cally determined. Details of the individual weirs may be foundin the ASTM standards cited as follows:5.1.2 Standard WeirsThe following weirs, for whichASTM standards are available, are considered in this guide:5.1.2.1 Thin-pl
26、ate weirs (see Test Method D5242).(1) Rectangular weirs (see Fig. 1).(2) Triangular (V-notch) weirs (see Fig. 2).5.1.2.2 Broad-crested weirs (see Test Method D5614).(1) Square-edge (rectangular) weirs (see Fig. 3).(2) Rounded-edge weirs (see Fig. 4).5.1.3 The quantitative information on weirs presen
27、ted inFigs. 1-4 is intended to give the user only an overview andassist in the preliminary assessments for selection. To that end,some approximations and omissions were necessary for thesake of brevity and convenience, and the published standardsmust be consulted for exact and complete information o
28、nrequirements, conditions, and equations.5.2 Flumes:FIG. 1 Rectangular Thin-Plate WeirsD5640 95 (2014)25.2.1 Flumes use sidewall constrictions or bottom shapes orslopes of specified geometries, or both, to cause the flow topass through the critical condition; this permits determinationof the flow ra
29、te from a measured head and a head-dischargerelation that has been experimentally or analytically obtained.Details of the individual flumes may be found in the ASTMstandards cited as follows:5.2.2 Standard FlumesThe following flumes, for whichASTM standards are available, are emphasized in this guid
30、e.Other flumes, which may be useful in specific situations, arecited in 5.2.4.5.2.2.1 Parshall flumes (see Test Method D1941, Fig. 5, andTable 1).5.2.2.2 Palmer-Bowlus (and other long-throated) flumes(see Test Method D5390 and Fig. 6).5.2.3 The quantitative information on flumes presented inFig. 5 a
31、nd Fig. 6 is intended to give the user only an overviewand assist in the preliminary assessments for selection. To thatend, some approximations and omissions were necessary forthe sake of brevity and convenience, and the publishedstandards must be consulted for exact and complete informa-tion on req
32、uirements, conditions, and equations.5.2.4 Other FlumesThe following flumes are not coveredby ASTM standards but are listed here because they weredeveloped for specific situations that may be of interest to usersof this guide. Detailed information on them can be found in thereference section.5.2.4.1
33、 H-Series Flumes (1), (2)This flume, which wasdeveloped for use on agricultural watersheds, is actually acombination of flume and triangular weir and consequentlyexhibits very high rangeability along with good sedimenttransport capability.5.2.4.2 Portable Parshall Flume (1)This 3-in. (7.6-cm)flume c
34、losely resembles the 3-in. standard Parshall flume withthe downstream divergent section removed. Its small sizemakes it convenient to transport and install in some low-flowfield applications.5.2.4.3 Supercritical-Flow Flumes (1)These flumes weredeveloped for use in streams with heavy loads of coarse
35、sediment. The depth measurement is made in the supercritical-flow portion of the flume rather than upstream.6. Selection Criteria6.1 Accuracy:6.1.1 The error of a flow-rate measurement results from acombination of individual errors, including errors in thecoefficients of the head-discharge relations
36、; errors in themeasurement of the head; and errors due to nonstandard shapeor installation or other departures from the practices recom-mended in the various weir or flume standards, or both. Thisguide considers the accuracy of the primary devices only,based on their accuracy potential under optimum
37、 or standardconditions; from information included in the individualFIG. 2 Triangular Thin-Plate WeirAFIG. 3 Rectangular (Square-Edge) Broad-Crested WeirsD5640 95 (2014)3standards, users can estimate secondary-system errors andother errors to obtain an estimate of the total measurementerror.6.1.2 The
38、 errors inherent in the basic head-discharge rela-tions of the primary devices are as follows:6.1.2.1 Thin-Plate Weirs:(1) Triangular, fully contracted, 61to2%.(2) 90 notch, partially contracted, 62to3%.(3) Rectangular, fully contracted, 61to2%.(4) Rectangular, partially contracted, 62to3%.6.1.2.2 B
39、road-Crested Weirs:(1) Square-edge, 63 to 5 % (depending on head-to-weirheight ratio).(2) Rounded, 63 % (in the optimum range of head-to-length ratio).6.1.2.3 Flumes:(1) Parshall flumes, 65%.(2) Palmer Bowlus and long-throated flumes, 63to5%(depending on head-to-length ratio).6.1.2.4 This listing in
40、dicates that, with no consideration ofother selection criteria, thin-plate weirs are potentially the mostaccurate of the devices.6.1.3 SensitivityThe discharge of weirs and flumes de-pends upon the measured head to the three-halves power forrectangular control sections (this is an approximation in t
41、hecase of Parshall flumes), to the five-halves power for triangularsections, and to intermediate powers for intermediate trapezoi-dal sections. Consequently, the accuracy of a flow-rate mea-surement is sensitive to errors in head measurement andparticularly so in the case of triangular control secti
42、ons. Itfollows that in all weirs and flumes operating at or nearminimum head, even a modest error or change in head canhave a significant effect on the measured flow rate. Therefore,it is important to select sizes or combinations of devices thatavoid prolonged operation near minimum head.6.2 Flow Ra
43、te:6.2.1 This criterion includes the maximum anticipated flowrate and the range of flow rate from minimum to maximum.The latter consideration includes not only daily or seasonalvariations but also a flow chronology in which, for example, anarea under development generates an initially low waste-wate
44、rdischarge followed in subsequent years by increasing flowrates.6.2.2 Flow Capacities:6.2.2.1 Small and Moderate FlowsApart from consider-ations of head loss (6.3) and sediment or debris transport (6.4),thin-plate weirs are most suitable for lower flow rates, with thetriangular notches most appropri
45、ate for the smallest flows.Small Parshall and Palmer-Bowlus flumes are also availablefor low flows; these improve on the thin-plate weirs insediment passage and head loss, but at some sacrifice ofpotential accuracy (6.1).6.2.2.2 Large FlowsLarge discharges are best measuredwith flumes and broad-cres
46、ted weirs, which can accommodatelarge heads and flows and, given proper construction, areinherently sturdy enough to withstand them. For example, the50-ft (15.24-m) Parshall flume can be used for flow rates up toabout 3200 ft3/s (90 m3/s). However, flumes and broad-crestedweirs that are adequate for
47、 very large flows require majorconstruction, and users may wish to consider establishing ameasuring station (3), (4) with other methods of dischargemeasurement, for example, velocity-area method (Test MethodD3858), acoustic velocity meters (Test Method D5389), ortracer dilution (ISO 555).6.2.3 Range
48、 of Flow Rate:6.2.3.1 Triangular thin-plate weirs have the largest range-ability of the standard devices because of their 2.5-powerdependence on head. This rangeability can vary from slightlyunder 200 for fully contracted weirs to about 600 for partiallycontracted 90 notches that can utilize the all
49、owable range ofhead.6.2.3.2 For rectangular thin-plate weirs, the rangeabilityvaries somewhat with the crest length-to-channel width ratioand is typically about 90, increasing to about 110 for full-widthweirs. These results are based on a minimum head of 0.1 ft(0.03 m) and a suggested (although not absolute) maximumhead of 2 ft (0.6 m). However, the rangeability of smallerrectangular weirs can be significantly less.6.2.3.3 The rangeability of the rounded broad-crested weiris close to 40. However, large square-edge weirs, if used to thegeometric
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