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2、 95 (Reapproved 2003)An American National StandardStandard 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
3、of revision, 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 test method covers the measurement of the volume rate of flow of water in open channels
4、 by determining the flow velocity and cross-sectional area and computing the discharge therefrom (Refs (1-7) ).21.2 The procedures described in this test method are widely used by those responsible for the collection of streamflow data, for example, the U.S. Geological Survey, Bureau of Reclama- tio
5、n, U.S. Army Corps of Engineers, U.S. Department of Agriculture, Water Survey Canada, and many state and pro- vincial agencies. The procedures are generally from internal documents of the above listed agencies, which have become the defacto standards as used in North America.1.3 This test method cov
6、ers the use of current meters to measure flow velocities. Discharge measurements may be made to establish isolated single values, or may be made in sets or in a series at various stages or water-level elevations to establish a stage-discharge relation at a site. In either case, the same test method
7、is followed for obtaining field data and computation of discharge.1.4 Measurements for the purpose of determining the dis- charge in efficiency tests of hydraulic turbines are specified in International Electrotechnical Commission Publication 413 for the field acceptance tests of hydraulic turbines,
8、 and are not included in this test method.1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appro- priate safety and health practices and determine the applica- bility of regul
9、atory limitations prior to use.1 This test method is under the jurisdiction of ASTM Committee D19 on Water and is the direct responsibility of Subcommittee D19.07 on Sediments, Geomor- phology, and Open-Channel Flow.Current edition approved June 10, 2003. Published August 2003. Originally approved i
10、n 1979. Last previous edition approved in 1999 as D 3858 95(1999).2. Referenced Documents2.1 ASTM Standards:D 1129 Terminology Relating to Water4D 2777 Practice for Determination of Precision and Bias ofApplicable Methods of Committee D-19 on Water4D 4409 Test Method for Velocity Measurements of Wat
11、er inOpen Channels with Rotating Element Current Meters4D 5089 Test Method for Velocity Measurements of Water inOpen Channels with Electromagnetic Current Meters42.2 ISO Standard:ISO 3455 (1976) Calibration of Rotating-Element CurrentMeters in Straight Open Tanks53. Terminology3.1 Definitions of Ter
12、ms Specific to This Standard:3.1.1 current meteran instrument used to measure, at a point, velocity of flowing water.3.1.2 dischargethe volume of flow of water through a cross section in a unit of time, including any sediment or other solids that may be dissolved in or mixed with the water.3.1.3 flo
13、ata buoyant article capable of staying suspended in or resting on the surface of a fluid; often used to mark the thread or trace of a flow line in a stream and to measure the magnitude of the flow velocity along that line.3.1.4 stagethe height of a water surface above an estab- lished (or arbitrary)
14、 datum plane; also termed gage height.3.2 DefinitionsFor definitions of terms used in this test method, refer to Terminology D 1129.4. Summary of Test Method4.1 The principal of this test method consists in effectively and accurately measuring the flow velocity and cross-sectional area of an open ch
15、annel or stream. The total flow or discharge measurement is the summation of the products of partial areas of the flow cross section and their respective average veloci- ties. The equation representing the computation is:2 The boldface numbers in parentheses refer to the references listed at the end
16、 of this test method.3 For availability of this publication, contact the International ElectrotechnicalCommission, 3 rue de Varembe, CH 1211, Geneva 20, Switzerland.4 Annual Book of ASTM Standards, Vol 11.01.5 Available from American National Standards Institute, 25 W. 43rd St., 4thFloor, New York,
17、NY 10036.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.1D 3858 95 (2003)FIG. 1 Typical Open-Channel Vertical-Velocity Curve (Modified from Buchanan and Somers) 7where:Q = total discharge,Q 5 ( av!4.3 Determination of the mean veloci
18、ty in a given partialcross section is really a sampling process throughout the vertical extent of that section. The mean can be closely anda = individual partial cross-sectional area, andv = corresponding mean velocity of the flow normal (per-pendicular) to the partial area.4.2 Because computation o
19、f total flow is a summation or integration process, the overall accuracy of the measurement is generally increased by increasing the number of partial cross sections. Generally 25 to 30 partial cross sections, even for extremely large channels, are adequate depending on the variability and complexit
20、y 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 be chosen so that each contains no more than about 5 % of the total discharge. No partial section shall contain more than 10 % of the total disc
21、harge.NOTE 1There is no universal “rule of thumb” that can be applied to fix the number of partial sections relative to the magnitude of flow, channel width, and channel depth because of the extreme variations insatisfactorily approximated by making a few selected velocityobservations and substituti
22、ng these values in a known math- ematical expression. The various recognized methods for determining mean velocity entail velocity observations at selected distances below the water surface. The depth selec- tions may include choice of (1) enough points to define a vertical-velocity curve (see Fig.
23、1), 6 (2) two points (0.2 and0.8 depth below water surface), (3) one point (0.6 depth), (4) one point (0.2 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 t
24、est method is used to measure the volume rate of flow of water moving in rivers and streams and moving over or through large man-made structures. It can also be used tochannel shape, size, roughness, and velocity distribution. Where a rating table or other estimate of total flow is available, this f
25、low divided by 25can serve as an estimate of the appropriate flow magnitude for each partial section.6 Buchanan, T. J., and Somers, W. P., “Discharge Measurements at GagingStations,” U.S. Geological Survey Techniques of Water-Resources Investigations, Book 3, Chapter A8.2D 3858 95 (2003)calibrate su
26、ch 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 and sedi- ment loadings where the flow
27、 rate is a required parameter.6. Apparatus6.1 Many and varied pieces of equipment and instruments are needed in making a conventional discharge measurement. The magnitude of the velocity and discharge, location of the cross section, weather conditions, whether suspended, floating, or particulate mat
28、ter are present in the water, and vegetative growth in the cross sections are all factors determining equipment needs. Instruments and equipment used normally include current-meters, width-measuring equipment, depth- sounding equipment, timers, angle-measuring devices, and counting equipment. The ap
29、paratus is further described in the following paragraphs.6.1.1 Current Meter Current meters used to measure open-channel flow are usually of the rotating-element (see Note 2) or electromagnetic types. Refer to Test Methods D 4409 and D 5089 for more specific information. However, the equipment secti
30、ons of this test method emphasize the rotating-element meters mainly because of their present wide- spread availability and use. The operation of these meters is based on proportionality between the velocity of the water and the resulting angular velocity of the meter rotor. Hence, by placing this i
31、nstrument at a point in a stream and counting the number of revolutions of the rotor during a measured interval of time, the velocity of water at that point is determined. Rotating-element meters can generally be classified into two main types: those having vertical-axis rotors, and those having hor
32、izontal-axis rotors. The principal comparative characteris- tics of the two types may be summarized as follows: (1) the vertical-axis rotor with cups and vanes operates in lower velocities than does the horizontal-axis rotor, has bearings that are well protected from silty water, is repairable in th
33、e field without adversely affecting the meter rating, and works effec- tively over a wide range of velocities; (2) the horizontal-axis rotor with vanes disturbs the flow less than does the vertical- axis rotor because of axial symmetry with flow direction, and is less likely to be fouled by debris.
34、Also, the rotor can be changed 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 Price type and are available in two sizes, the large Price AA and the smaller Pygmy meter. The rotor a
35、ssembly of the type AA is 5 in. (127 mm) and the Pygmy is 2 in. (51 mm) in diameter. The rotor assemblies of both meters are formed with 6 hollow metal or solid plastic cone-shaped cups.The small Price pygmy meter is generally used when the average depth in a stream cross section is less than 1.5 ft
36、 (0.5 m) and velocity is below2.5 ft/s (0.8 m/s). The large Price type meter should be used when average depths are greater than 1.5 ft (0.5 m). For high velocities, the large meter may be used for shallower depths. Do not change the meter if a few partial sections are outside these limits. In any c
37、ase, meters should not be used closer to the streambed than 1.5 rotor or probe diameters.Current meters used in the measurement of open-channel flow are exposed to damage and fouling by debris, ice, particulate matter, sedi- ment, moss, and extreme temperature variations, and should be selectedaccor
38、dingly. Meters 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 a rotor in a rotating-element type current meter is obtained by an electrical circuit through a contact chamber in the mete
39、r. Contact points in the chamber are designed to complete an electrical circuit at selected frequencies of revolution. Contacts can be selected that will complete the circuit once every five revolutions, once per revolution, or twice per revolution of the rotor. The electrical impulse produces an au
40、dible click in a headphone or registers a unit on a counting device. The count rate is usually measured manually with a stopwatch, or automatically 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
41、 initial point on the stream bank. Cableways, highway bridges, or foot bridges used regularly in making discharge measurements are commonly marked with paint marks at the desired distance intervals. Steel tapes, metallic tapes, or premarked taglines are used for discharge measurements made from boat
42、s or un- marked bridges, or by wading. Where the stream channel or cross section is extremely wide, where no cableways or suitable bridges are available, or where it is impractical to string a tape or tagline, the distance from the initial point on the bank can be determined by optical or electrical
43、 distance meters, by stadia, or by triangulation to a boat or man located on the cross-section line.6.1.4 Depth-Sounding EquipmentThe depth of the stream below any water surface point in a cross section, and the relative depth position of the current meter in the vertical at that point, are usually
44、measured by a rigid rod or by a sounding weight suspended on a cable. The selection of the proper weight is essential for the determination of the correct depth. A light weight will be carried downstream and incorrectly yield depth observations that are too large. A “rule of thumb” for the selection
45、 of proper sized weights is to use a weight slightly heavier in pounds than the product of depth (feet) times velocity (feet per second) (no direct metric conversion is available). The sounding cable is controlled from above the water surface either by a reel or by a handline. The depth- sounding eq
46、uipment also serves as the position fixing and supporting mechanism for the current meter during velocity measurements. Sonic depth sounders are available but are usually not used in conjunction with a reel and sounding weight.6.1.5 Angle-Measuring DevicesWhen the direction of flow is not at right angles to the cross section, the velocity vector normal to the cross section is needed for the correct determi