1、Designation: D 3858 95 (Reapproved 2008)Standard Test Method forOpen-Channel Flow Measurement of Water by Velocity-AreaMethod1This standard is issued under the fixed designation D 3858; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revisio
2、n, 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 the measurement of the volumerate of flow of water in open channels by determin
3、ing the flowvelocity and cross-sectional area and computing the dischargetherefrom (Refs (1-7).21.2 The procedures described in this test method are widelyused by those responsible for the collection of streamflow data,for example, the U.S. Geological Survey, Bureau of Reclama-tion, U.S. Army Corps
4、of Engineers, U.S. Department ofAgriculture, Water Survey Canada, and many state and pro-vincial agencies. The procedures are generally from internaldocuments of the above listed agencies, which have becomethe defacto standards as used in North America.1.3 This test method covers the use of current
5、meters tomeasure flow velocities. Discharge measurements may bemade to establish isolated single values, or may be made in setsor in a series at various stages or water-level elevations toestablish a stage-discharge relation at a site. In either case, thesame test method is followed for obtaining fi
6、eld data andcomputation of discharge.1.4 Measurements for the purpose of determining the dis-charge in efficiency tests of hydraulic turbines are specified inInternational Electrotechnical Commission Publication 413forthe field acceptance tests of hydraulic turbines, and are notincluded in this test
7、 method.1.5 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.1.6 This standard does not purport to address all of thesafety concerns, if a
8、ny, 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:4D 1129 Terminology Relating to WaterD 2777 Practi
9、ce for Determination of Precision and Bias ofApplicable Test Methods of Committee D19 on WaterD 4409 Test Method for Velocity Measurements of Water inOpen Channels with Rotating Element Current MetersD 5089 Test Method for Velocity Measurements of Water inOpen Channels with Electromagnetic Current M
10、eters2.2 ISO Standard:5ISO 3455 (1976) Calibration of Rotating-Element CurrentMeters in Straight Open Tanks3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 current meteran instrument used to measure, at apoint, velocity of flowing water.3.1.2 dischargethe volume of flow of wate
11、r through across section in a unit of time, including any sediment or othersolids that may be dissolved in or mixed with the water.3.1.3 floata buoyant article capable of staying suspendedin or resting on the surface of a fluid; often used to mark thethread or trace of a flow line in a stream and to
12、 measure themagnitude of the flow velocity along that line.3.1.4 stagethe height of a water surface above an estab-lished (or arbitrary) datum plane; also termed gage height.3.2 DefinitionsFor definitions of terms used in this testmethod, refer to Terminology D 1129.4. Summary of Test Method4.1 The
13、principal of this test method consists in effectivelyand accurately measuring the flow velocity and cross-sectionalarea of an open channel or stream. The total flow or dischargemeasurement is the summation of the products of partial areasof the flow cross section and their respective average veloci-
14、ties. The equation representing the computation is:1This test method is under the jurisdiction of ASTM Committee D19 on Waterand is the direct responsibility of Subcommittee D19.07 on Sediments, Geomor-phology, and Open-Channel Flow.Current edition approved Oct. 1, 2008. Published November 2008. Ori
15、ginallyapproved in 1979. Last previous edition approved in 2003 as D 3858 95 (2003).2The boldface numbers in parentheses refer to the references listed at the end ofthis test method.3For availability of this publication, contact the International ElectrotechnicalCommission, 3 rue de Varembe, CH 1211
16、, Geneva 20, Switzerland.4For 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.5Available from American National St
17、andards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.Q 5 ( av!where:Q = total discharge,a = individual partial cross-sectional area, andv = corresp
18、onding mean velocity of the flow normal (per-pendicular) to the partial area.4.2 Because computation of total flow is a summation orintegration process, the overall accuracy of the measurement isgenerally increased by increasing the number of partial crosssections. Generally 25 to 30 partial cross s
19、ections, even forextremely large channels, are adequate depending on thevariability and complexity of the flow and the cross section.With a smooth cross section and uniform velocity distribution,fewer sections may be used. The partial sections should bechosen so that each contains no more than about
20、 5 % of thetotal discharge. No partial section shall contain more than 10 %of the total discharge.NOTE 1There is no universal “rule of thumb” that can be applied tofix the number of partial sections relative to the magnitude of flow,channel width, and channel depth because of the extreme variations
21、inchannel shape, size, roughness, and velocity distribution. Where a ratingtable or other estimate of total flow is available, this flow divided by 25can serve as an estimate of the appropriate flow magnitude for each partialsection.4.3 Determination of the mean velocity in a given partialcross sect
22、ion is really a sampling process throughout thevertical extent of that section. The mean can be closely andsatisfactorily approximated by making a few selected velocityobservations and substituting these values in a known math-ematical expression. The various recognized methods fordetermining mean v
23、elocity entail velocity observations atselected distances below the water surface. The depth selec-tions may include choice of (1) enough points to define avertical-velocity curve (see Fig. 1),6(2) two points (0.2 and 0.8depth below water surface), (3) one point (0.6 depth), (4) onepoint (0.2 depth)
24、, (5) three points (0.2, 0.6, and 0.8 depth), and(6) subsurface (that is, just below the water surface) (see 10.9for further description of each method.)5. Significance and Use5.1 This test method is used to measure the volume rate offlow of water moving in rivers and streams and moving over orthrou
25、gh large man-made structures. It can also be used to6Buchanan, T. J., and Somers, W. P., “Discharge Measurements at GagingStations,” U.S. Geological Survey Techniques of Water-Resources Investigations,Book 3, Chapter A8.FIG. 1 Typical Open-Channel Vertical-Velocity Curve (Modified from Buchanan and
26、Somers)7D 3858 95 (2008)2calibrate such measuring structures as dams and flumes.Measurements may be made from bridges, cableways, or boats;by wading; or through holes cut in an ice cover.5.2 This test method is used in conjunction with determina-tions of physical, chemical, and biological quality an
27、d sedi-ment loadings where the flow rate is a required parameter.6. Apparatus6.1 Many and varied pieces of equipment and instrumentsare needed in making a conventional discharge measurement.The magnitude of the velocity and discharge, location of thecross section, weather conditions, whether suspend
28、ed, floating,or particulate matter are present in the water, and vegetativegrowth in the cross sections are all factors determiningequipment needs. Instruments and equipment used normallyinclude current-meters, width-measuring equipment, depth-sounding equipment, timers, angle-measuring devices, and
29、counting equipment. The apparatus is further described in thefollowing paragraphs.6.1.1 Current MeterCurrent meters used to measureopen-channel flow are usually of the rotating-element (seeNote 2) or electromagnetic types. Refer to Test MethodsD 4409 and D 5089 for more specific information. However
30、,the equipment sections of this test method emphasize therotating-element meters mainly because of their present wide-spread availability and use. The operation of these meters isbased on proportionality between the velocity of the water andthe resulting angular velocity of the meter rotor. Hence, b
31、yplacing this instrument at a point in a stream and counting thenumber of revolutions of the rotor during a measured intervalof time, the velocity of water at that point is determined.Rotating-element meters can generally be classified into twomain types: those having vertical-axis rotors, and those
32、 havinghorizontal-axis rotors. The principal comparative characteris-tics of the two types may be summarized as follows: (1) thevertical-axis rotor with cups and vanes operates in lowervelocities than does the horizontal-axis rotor, has bearings thatare well protected from silty water, is repairable
33、 in the fieldwithout adversely affecting the meter rating, and works effec-tively over a wide range of velocities; (2) the horizontal-axisrotor with vanes disturbs the flow less than does the vertical-axis rotor because of axial symmetry with flow direction, andis less likely to be fouled by debris.
34、 Also, the rotor can bechanged for different velocity ranges and meters of this typeare more difficult to service and adjust in the field.NOTE 2Vertical-axis current meters commonly used are of the Pricetype and are available in two sizes, the large Price AA and the smallerPygmy meter. The rotor ass
35、embly of the typeAAis 5 in. (127 mm) and thePygmy is 2 in. (51 mm) in diameter. The rotor assemblies of both metersare formed with 6 hollow metal or solid plastic cone-shaped cups.The small Price pygmy meter is generally used when the average depthin a stream cross section is less than 1.5 ft (0.5 m
36、) and velocity is below2.5 ft/s (0.8 m/s). The large Price type meter should be used when averagedepths are greater than 1.5 ft (0.5 m). For high velocities, the large metermay be used for shallower depths. Do not change the meter if a few partialsections are outside these limits. In any case, meter
37、s should not be usedcloser to the streambed than 1.5 rotor or probe diameters.Current meters used in the measurement of open-channel flow areexposed to damage and fouling by debris, ice, particulate matter, sedi-ment, moss, and extreme temperature variations, and should be selectedaccordingly. Meter
38、s must be checked frequently during a dischargemeasurement to ensure that they have not been damaged or fouled.6.1.2 Counting EquipmentThe number of revolutions of arotor in a rotating-element type current meter is obtained by anelectrical circuit through a contact chamber in the meter.Contact point
39、s in the chamber are designed to complete anelectrical circuit at selected frequencies of revolution. Contactscan be selected that will complete the circuit once every fiverevolutions, once per revolution, or twice per revolution of therotor. The electrical impulse produces an audible click in ahead
40、phone or registers a unit on a counting device. The countrate is usually measured manually with a stopwatch, orautomatically with a timing device built into the counter.6.1.3 Width-Measuring EquipmentThe horizontal dis-tance to any point in a cross section is measured from an initialpoint on the str
41、eam bank. Cableways, highway bridges, or footbridges used regularly in making discharge measurements arecommonly marked with paint marks at the desired distanceintervals. Steel tapes, metallic tapes, or premarked taglines areused for discharge measurements made from boats or un-marked bridges, or by
42、 wading. Where the stream channel orcross section is extremely wide, where no cableways orsuitable bridges are available, or where it is impractical tostring a tape or tagline, the distance from the initial point on thebank can be determined by optical or electrical distance meters,by stadia, or by
43、triangulation to a boat or man located on thecross-section line.6.1.4 Depth-Sounding EquipmentThe depth of the streambelow any water surface point in a cross section, and therelative depth position of the current meter in the vertical atthat point, are usually measured by a rigid rod or by a soundin
44、gweight suspended on a cable. The selection of the properweight is essential for the determination of the correct depth.Alight weight will be carried downstream and incorrectly yielddepth observations that are too large. A “rule of thumb” for theselection of proper sized weights is to use a weight s
45、lightlyheavier in pounds than the product of depth (feet) timesvelocity (feet per second) (no direct metric conversion isavailable). The sounding cable is controlled from above thewater surface either by a reel or by a handline. The depth-sounding equipment also serves as the position fixing andsupp
46、orting mechanism for the current meter during velocitymeasurements. Sonic depth sounders are available but areusually not used in conjunction with a reel and soundingweight.6.1.5 Angle-Measuring DevicesWhen the direction offlow is not at right angles to the cross section, the velocityvector normal t
47、o the cross section is needed for the correctdetermination of discharge. The velocity as measured by thecurrent meter, multiplied by the cosine of the horizontal anglebetween the flow direction and a line perpendicular to the crosssection, will give the velocity component normal to themeasuring cros
48、s section. A series of horizontal angles andcorresponding cosine values are usually indicated as a series ofmarked points on the measurement note form (standard form)or on a clipboard. The appropriate cosine value is then readdirectly by orienting the note form or clipboard with thedirection of the
49、cross section and the direction of flow. WhenD 3858 95 (2008)3measuring in deep swift streams, it is possible to sound thedepth but the force of the current moves the weight and meterinto positions downstream from the cross section; hence, thedepths measured are too large (see Fig. 2).6Measurement ofthe vertical angle (between the displaced direction of thesounding line and the true vertical to the water surface) isnecessary for computation of both air-line and wet-line correc-tions to the measured depth.Aprotractor for measuring verticalangles is considered to be s
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