1、Designation: D3858 95 (Reapproved 2014)Standard Test Method forOpen-Channel Flow Measurement of Water by Velocity-AreaMethod1This standard is issued under the fixed designation D3858; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision,
2、 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 determinin
3、g 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 ofReclamation, U.S. Army Corps of E
4、ngineers, U.S. Departmentof Agriculture, Water Survey Canada, and many state andprovincial 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 meters
5、 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 field da
6、ta 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 metho
7、d.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 any, as
8、sociated 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:4D1129 Terminology Relating to WaterD2777 Practice for D
9、etermination of Precision and Bias ofApplicable Test Methods of Committee D19 on WaterD4409 Test Method for Velocity Measurements of Water inOpen Channels with Rotating Element Current MetersD5089 Test Method for Velocity Measurements of Water inOpen Channels with Electromagnetic Current Meters2.2 I
10、SO Standard:5ISO 3455 (1976) Calibration of Rotating-Element CurrentMeters in Straight Open Tanks3. 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 current meteran instrument used to measu
11、re, at apoint, velocity of flowing water.3.2.2 dischargethe volume of flow of water through across section in a unit of time, including any sediment or othersolids that may be dissolved in or mixed with the water.3.2.3 floata buoyant article capable of staying suspendedin or resting on the surface o
12、f a fluid; often used to mark thethread or trace of a flow line in a stream and to measure themagnitude of the flow velocity along that line.3.2.4 stagethe height of a water surface above an estab-lished (or arbitrary) datum plane; also termed gage height.4. Summary of Test Method4.1 The principal o
13、f this test method consists in effectivelyand accurately measuring the flow velocity and cross-sectional1This 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
14、approved Jan. 1, 2014. Published January 2014. Originallyapproved in 1979. Last previous edition approved in 2008 as D3858 95 (2008).DOI: 10.1520/D3858-95R14.2The boldface numbers in parentheses refer to a list of references at the end ofthis standard.3Available from International Electrotechnical C
15、ommission (IEC), 3, rue deVaremb, P.O. Box 131, CH-1211 Geneva 20, Switzerland, http:/www.iec.ch.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 Docum
16、ent Summary page onthe ASTM website.5Available 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 States1area of an open channel
17、 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-ties. The equation representing the computation is:Q 5(av!where:Q = total discharge,a = individual partial cross-sectional area, andv = co
18、rresponding 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 cr
19、oss sections, 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
20、about 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 variat
21、ions 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
22、 section 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 m
23、ean velocity 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) (2),(2) two points (0.2 and0.8 depth below water surface), (3) one point (0.6 depth), (4)one point (0.
24、2 depth), (5) three points (0.2, 0.6, and 0.8 depth),and (6) subsurface (that is, just below the water surface) (see10.9 for 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
25、 orthrough large man-made structures. It can also be used tocalibrate such measuring structures as dams and flumes.FIG. 1 Typical Open-Channel Vertical-Velocity Curve (Modified from Buchanan and Somers) (2)D3858 95 (2014)2Measurements may be made from bridges, cableways, or boats;by wading; or throu
26、gh holes cut in an ice cover.5.2 This test method is used in conjunction with determina-tions of physical, chemical, and biological quality and 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 con
27、ventional discharge measurement.The magnitude of the velocity and discharge, location of thecross section, weather conditions, whether suspended, floating,or particulate matter are present in the water, and vegetativegrowth in the cross sections are all factors determiningequipment needs. Instrument
28、s and equipment used normallyinclude current-meters, width-measuring equipment, depth-sounding equipment, timers, angle-measuring devices, andcounting equipment. The apparatus is further described in thefollowing paragraphs.6.1.1 Current MeterCurrent meters used to measure open-channel flow are usua
29、lly of the rotating-element (see Note 2)orelectromagnetic types. Refer to Test Methods D4409 andD5089 for more specific information. However, the equipmentsections of this test method emphasize the rotating-elementmeters mainly because of their present widespread availabilityand use. The operation o
30、f these meters is based on proportion-ality between the velocity of the water and the resulting angularvelocity of the meter rotor. Hence, by placing this instrument ata point in a stream and counting the number of revolutions ofthe rotor during a measured interval of time, the velocity ofwater at t
31、hat point is determined. Rotating-element meters cangenerally be classified into two main types: those havingvertical-axis rotors, and those having horizontal-axis rotors.The principal comparative characteristics of the two types maybe summarized as follows: (1) the vertical-axis rotor with cupsand
32、vanes operates in lower velocities than does the horizontal-axis rotor, has bearings that are well protected from silty water,is repairable in the field without adversely affecting the meterrating, and works effectively over a wide range of velocities;(2) the horizontal-axis rotor with vanes disturb
33、s the flow lessthan does the vertical-axis rotor because of axial symmetrywith flow direction, and is less likely to be fouled by debris.Also, the rotor can be changed for different velocity ranges andmeters of this type are more difficult to service and adjust in thefield.NOTE 2Vertical-axis curren
34、t meters commonly used are of the Pricetype and are available in two sizes, the large Price AA and the smallerPygmy meter. The rotor assembly of the typeAAis 5 in. (127 mm) and thePygmy is 2 in. (51 mm) in diameter. The rotor assemblies of both metersare formed with six hollow metal or solid plastic
35、 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) 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
36、large metermay be used for shallower depths. Do not change the meter if a few partialsections are outside these limits. In any case, meters 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
37、 fouling by debris, ice, particulate matter,sediment, moss, and extreme temperature variations, and should beselected accordingly. Meters must be checked frequently during a dis-charge measurement to ensure that they have not been damaged or fouled.6.1.2 Counting EquipmentThe number of revolutions o
38、f arotor in a rotating-element type current meter is obtained by anelectrical circuit through a contact chamber in the meter.Contact points in the chamber are designed to complete anelectrical circuit at selected frequencies of revolution. Contactscan be selected that will complete the circuit once
39、every fiverevolutions, once per revolution, or twice per revolution of therotor. The electrical impulse produces an audible click in aheadphone 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 c
40、ounter.6.1.3 Width-Measuring EquipmentThe horizontal dis-tance to any point in a cross section is measured from an initialpoint on the stream bank. Cableways, highway bridges, or footbridges used regularly in making discharge measurements arecommonly marked with paint marks at the desired distancein
41、tervals. Steel tapes, metallic tapes, or premarked taglines areused for discharge measurements made from boats or un-marked bridges, or by wading. Where the stream channel orcross section is extremely wide, where no cableways orsuitable bridges are available, or where it is impractical tostring a ta
42、pe or tagline, the distance from the initial point on thebank can be determined by optical or electrical distance meters,by stadia, or by 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 sect
43、ion, and therelative depth position of the current meter in the vertical atthat point, are usually measured by a rigid rod or by a soundingweight suspended on a cable. The selection of the properweight is essential for the determination of the correct depth. Alight weight will be carried downstream
44、and incorrectly yielddepth observations that are too large. A “rule of thumb” for theselection of proper sized weights is to use a weight slightlyheavier in pounds than the product of depth (feet) timesvelocity (feet per second) (no direct metric conversion isavailable). The sounding cable is contro
45、lled from above thewater surface either by a reel or by a handline. The depth-sounding equipment also serves as the position fixing andsupporting mechanism for the current meter during velocitymeasurements. Sonic depth sounders are available but areusually not used in conjunction with a reel and sou
46、ndingweight.6.1.5 Angle-Measuring DevicesWhen the direction offlow is not at right angles to the cross section, the velocityvector normal to the cross section is needed for the correctdetermination of discharge. The velocity as measured by thecurrent meter, multiplied by the cosine of the horizontal
47、 anglebetween the flow direction and a line perpendicular to the crosssection, will give the velocity component normal to themeasuring cross section. A series of horizontal angles andcorresponding cosine values are usually indicated as a series ofmarked points on the measurement note form (standard
48、form)or on a clipboard. The appropriate cosine value is then readdirectly by orienting the note form or clipboard with thedirection of the cross section and the direction of flow. Whenmeasuring in deep swift streams, it is possible to sound theD3858 95 (2014)3depth but the force of the current moves
49、 the weight and meterinto positions downstream from the cross section; hence, thedepths measured are too large (see Fig. 2) (2). Measurement 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 special equipment which is avail-able. Tables of air-line and wet-line corrections are alsoavailable. Tags or colored streamers placed on the soundingline at
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