1、Designation: D 5640 95 (Reapproved 2003)Standard Guide forSelection of Weirs and Flumes for Open-Channel FlowMeasurement of Water1This standard is issued under the fixed designation D 5640; the number immediately following the designation indicates the year oforiginal adoption or, in the case of rev
2、ision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) 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
3、volumetric 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. How
4、ever, reference is also made toother measurement devices and methods that may be useful inspecific situations.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 safet
5、y and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:D 1129 Terminology Relating to Water2D 1941 Test Method for Open Channel Flow Measurementof Water with the Parshall Flume2D 3858 Test Method for Open-Channel Flow
6、Measurementof Water by Velocity-Area Method2D 5242 Test Method for Open-Channel Flow Measurementof Water with Thin-Plate Weirs2D 5389 Test Method for Open-Channel Flow Measurementof Water by Acoustic Velocity Meter Systems2D 5390 Test Method for Open-Channel Flow Measurementof Water with Palmer-Bowl
7、us Flume2D 5614 Test Method for Open-Channel Flow Measurementof Water with Broad-Crested Weirs22.2 ISO Standard:ISO 555-1973: Liquid Flow Measurement in OpenChannelsDilution Methods for Measurement of SteadyFlowConstant-Rate Injection Method33. Terminology3.1 DefinitionsFor definitions of terms used
8、 in this guide,refer to Terminology D 1129.3.2 Definitions of Terms Specific to This Standard:3.2.1 blackwateran 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 weirsrefer to the widths of weir plate betwee
9、n the notch and thesidewalls of the approach channel. In fully contracted weirs,the ratio of the notch area 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 suppress
10、ed, and the weir crestextends the full width of the channel.3.2.3 crestin rectangular thin-plate weirs, the 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 ter
11、ms of depth plus velocity head, is a minimumfor a given flow rate and channel.3.2.4.1 DiscussionThe Froude number 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 t
12、he square root of theproduct of the average depth and the acceleration due togravity.3.2.6 headin this context, the depth of flow referenced tothe crest of the weir or flume and measured at a specifiedlocation; this depth plus the velocity head are often termed thetotal head or total energy head.3.2
13、.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 flume in which the prismaticthroat is long enough, relative to the head, for a region ofessentially critical flow to d
14、evelop on the crest.1This 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 June 10, 2003. Published August 2003. Originallyapproved in 1995. Last previous e
15、dition approved in 1999 as D 5640 95 (1999).2Annual Book of ASTM Standards, Vol 11.01.3Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 100361Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United
16、States.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.3.2.11 primary instrumentthe device (in this case, a weiror flume) that creates a hydrodynamic condition that can besensed by the
17、secondary instrument.3.2.12 rangeabilitythe spread between the maximum,Qmax, and minimum, Qmin, flow rates that a measuringinstrument can usefully and reliably accommodate; this may bedescribed as the ratio Qmax/Qmin.3.2.13 secondary instrumentin this case, a device thatmeasures the head on the weir
18、 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 velocity than critical flow for the same flow rate;sometimes called tranquil flow.3.2.14.1 DiscussionThe Froude number is less tha
19、n 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 for a given upstream head.3.2.16 supercritical flowopen-channel flow that is shal-lower and at higher velocity than critical flow f
20、or 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 square of the average velocitydivided by twice the acceleration due to gravity.4. Significance and Use4.1 Each type of weir and flume p
21、ossesses advantages anddisadvantages relative to the other types when it is consideredfor a specific application; consequently, the selection processoften involves reaching a compromise among several features.This guide is intended to assist the user in making a selectionthat is hydraulically, struc
22、turally, 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 that insome cases, particularly in large streams, discharges may bestbe determined by other means. (See 6.2.2.)5. Weirs and Flumes5.1
23、 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 elements in thehead-discharge relation having been experimentally or analyti-cally determined. Details of the individual weirs may be
24、 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-plate weirs (see Test Method D 5242).(1) Rectangular weirs (see Fig. 1).(2) Triangular (V-notch) weirs (see Fig. 2).5.1.2.2 Broad-cre
25、sted weirs (see Test Method D 5614).(1) Square-edge (rectangular) weirs (see Fig. 3).(2) Rounded-edge weirs (see Fig. 4).5.1.3 The quantitative information on weirs presented inFigs. 1-4 is intended to give the user only an overview andassist in the preliminary assessments for selection. To that end
26、,some approximations and omissions were necessary for thesake of brevity and convenience, and the published standardsmust be consulted for exact and complete information onrequirements, conditions, and equations.5.2 Flumes:5.2.1 Flumes use sidewall constrictions or bottom shapes orslopes of specifie
27、d geometries, or both, to cause the flow topass through the critical condition; this permits determinationof the flow rate 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
28、as follows:5.2.2 Standard FlumesThe following flumes, for whichASTM standards are available, are emphasized in this guide.Other flumes, which may be useful in specific situations, arecited in 5.2.4.5.2.2.1 Parshall flumes (see Test Method D 1941, Fig. 5, andTable 1).FIG. 1 Rectangular Thin-Plate Wei
29、rsD 5640 95 (2003)25.2.2.2 Palmer-Bowlus (and other long-throated) flumes(see Test Method D 5390 and Fig. 6).5.2.3 The quantitative information on flumes presented inFig. 5 and Fig. 6 is intended to give the user only an overviewand assist in the preliminary assessments for selection. To thatend, so
30、me approximations and omissions were necessary forthe sake of brevity and convenience, and the publishedstandards must be consulted for exact and complete informa-tion on requirements, conditions, and equations.5.2.4 Other FlumesThe following flumes are not coveredby ASTM standards but are listed he
31、re 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 H-Series Flumes (1), (2)This flume, which wasdeveloped for use on agricultural watersheds, is actually acombination of flume
32、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 closely resembles the 3-in. standard Parshall flume withthe downstream divergent section removed. Its small sizemakes it conven
33、ient 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 coarsesediment. The depth measurement is made in the supercritical-flow portion of the flume rather than upstream.6. Selection Crite
34、ria6.1 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; errors in themeasurement of the head; and errors due to nonstandard shapeor installation or other departures from the practi
35、ces 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 or standardconditions; from information included in the individual stan-dards, users can estimate secondary-system errors and
36、 othererrors to obtain an estimate of the total measurement error.6.1.2 The 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
37、 contracted, 61to2%.(4) Rectangular, partially contracted, 62to3%.6.1.2.2 Broad-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%.FIG. 2 Triangular Thin-Plate WeirA
38、FIG. 3 Rectangular (Square-Edge) Broad-Crested WeirsD 5640 95 (2003)3(2) Palmer Bowlus and long-throated flumes, 63to5%(depending on head-to-length ratio).6.1.2.4 This listing indicates that, with no consideration ofother selection criteria, thin-plate weirs are potentially the mostaccurate of the d
39、evices.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 thecase of Parshall flumes), to the five-halves power for triangularsections, and to intermediate powers for intermediate t
40、rapezoi-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 sections. Itfollows that in all weirs and flumes operating at or nearminimum head, even a modest error or change in head canhav
41、e 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 rate:6.2.1 This criterion includes the maximum anticipated flowrate and the range of flow rate from minimum to maximum.The l
42、atter consideration includes not only daily or seasonalvariations but also a flow chronology in which, for example, anarea under development generates an initially low waste-waterdischarge followed in subsequent years by increasing flowrates.6.2.2 Flow capacities:6.2.2.1 Small and Moderate FlowsApar
43、t 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 appropriate for the smallest flows.Small Parshall and Palmer-Bowlus flumes are also availablefor low flows; these improve on the t
44、hin-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-crested weirs, which can accommodatelarge heads and flows and, given proper construction, areinherently sturdy enough to withs
45、tand 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 very large flows require majorconstruction, and users may wish to consider establishing ameasuring station (3), (4) with
46、other methods of dischargemeasurement, for example, velocity-area method (Test MethodD 3858), acoustic velocity meters (Test Method D 5389), ortracer dilution (ISO 555).6.2.3 Range of Flow Rate:6.2.3.1 Triangular thin-plate weirs have the largest range-ability of the standard devices because of thei
47、r 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 allowable range ofhead.6.2.3.2 For rectangular thin-plate weirs, the rangeabilityvaries somewhat with the crest length-to-c
48、hannel 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
49、.2.3.3 The rangeability of the rounded broad-crested weiris close to 40. However, large square-edge weirs, if used to thegeometric limits of the standard, exhibit a rangeability of about90.6.2.3.4 The rangeability of Parshall flumes varies widelywith size. (See Fig. 5 and Table 1.)6.2.3.5 For Palmer-Bowlus and other long-throated flumes,the rangeability depends on the shape of the throat crosssection, increasing as that shape varies from rectangular towardtriangular. For the typical commercial Palmer-Bowlus flume oftrapezoidal section, at least one
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