ASTM D3858-95(2003)
(Test Method)Standard Test Method for Open-Channel Flow Measurement of Water by Velocity-Area Method
Standard Test Method for Open-Channel Flow Measurement of Water by Velocity-Area Method
SIGNIFICANCE AND USE
This test 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 to calibrate 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.
This test method is used in conjunction with determinations of physical, chemical, and biological quality and sediment loadings where the flow rate is a required parameter.
SCOPE
1.1 This test method covers the measurement of the volume rate of flow of water in open channels by determining the flow velocity and cross-sectional area and computing the discharge therefrom (Refs (1-7) ).²
1.2 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 Reclamation, U.S. Army Coprs of Engineers, U.S. Department of Agriculture, Water Survey Canada, and many state and provincial 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 covers 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 is followed for obtaining field data and computation of discharge.
1.4 Measurements for the purpose of determining the discharge in efficiency tests of hydraulic turbines are specified in International Electrotechnical Commission Publication 41³ for the field acceptance tests of hydraulic turbines, 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 appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Standards Content (Sample)
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Designation: D 3858 – 95 (Reapproved 2003)
Standard Test Method for
Open-Channel Flow Measurement of Water by Velocity-Area
Method
This standard is issued under the fixed designation D 3858; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope 2. Referenced Documents
1.1 This test method covers the measurement of the volume 2.1 ASTM Standards:
rate of flow of water in open channels by determining the flow D 1129 Terminology Relating to Water
velocity and cross-sectional area and computing the discharge D 2777 Practice for Determination of Precision and Bias of
2 4
therefrom (Refs (1-7) ). Applicable Methods of Committee D-19 on Water
1.2 The procedures described in this test method are widely D 4409 Test Method forVelocity Measurements ofWater in
used by those responsible for the collection of streamflow data, Open Channels with Rotating Element Current Meters
for example, the U.S. Geological Survey, Bureau of Reclama- D 5089 Test Method forVelocity Measurements ofWater in
tion, U.S. Army Corps of Engineers, U.S. Department of Open Channels with Electromagnetic Current Meters
Agriculture, Water Survey Canada, and many state and pro- 2.2 ISO Standard:
vincial agencies. The procedures are generally from internal ISO 3455 (1976) Calibration of Rotating-Element Current
documents of the above listed agencies, which have become Meters in Straight Open Tanks
the defacto standards as used in North America.
3. Terminology
1.3 This test method covers the use of current meters to
3.1 Definitions of Terms Specific to This Standard:
measure flow velocities. Discharge measurements may be
madetoestablishisolatedsinglevalues,ormaybemadeinsets 3.1.1 current meter—an instrument used to measure, at a
point, velocity of flowing water.
or in a series at various stages or water-level elevations to
establish a stage-discharge relation at a site. In either case, the 3.1.2 discharge—the volume of flow of water through a
cross section in a unit of time, including any sediment or other
same test method is followed for obtaining field data and
solids that may be dissolved in or mixed with the water.
computation of discharge.
1.4 Measurements for the purpose of determining the dis- 3.1.3 float—a buoyant article capable of staying suspended
in or resting on the surface of a fluid; often used to mark the
charge in efficiency tests of hydraulic turbines are specified in
International Electrotechnical Commission Publication 41 for thread or trace of a flow line in a stream and to measure the
magnitude of the flow velocity along that line.
the field acceptance tests of hydraulic turbines, and are not
included in this test method. 3.1.4 stage—the height of a water surface above an estab-
lished (or arbitrary) datum plane; also termed gage height.
1.5 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the 3.2 Definitions—For definitions of terms used in this test
method, refer to Terminology D 1129.
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica-
4. Summary of Test Method
bility of regulatory limitations prior to use.
4.1 The principal of this test method consists in effectively
and accurately measuring the flow velocity and cross-sectional
area of an open channel or stream. The total flow or discharge
This test method is under the jurisdiction of ASTM Committee D19 on Water
measurement is the summation of the products of partial areas
and is the direct responsibility of Subcommittee D19.07 on Sediments, Geomor-
of the flow cross section and their respective average veloci-
phology, and Open-Channel Flow.
Current edition approved June 10, 2003. Published August 2003. Originally
ties. The equation representing the computation is:
approved in 1979. Last previous edition approved in 1999 as D 3858 – 95(1999).
The boldface numbers in parentheses refer to the references listed at the end of
this test method. Annual Book of ASTM Standards, Vol 11.01.
3 5
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Commission, 3 rue de Varembe, CH 1211, Geneva 20, Switzerland. Floor, New York, NY 10036.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D 3858 – 95 (2003)
FIG. 1 Typical Open-Channel Vertical-Velocity Curve (Modified from Buchanan and Somers)
Q 5 ( ~av! 4.3 Determination of the mean velocity in a given partial
cross section is really a sampling process throughout the
where:
vertical extent of that section. The mean can be closely and
Q = total discharge,
satisfactorily approximated by making a few selected velocity
a = individual partial cross-sectional area, and
observations and substituting these values in a known math-
v = corresponding mean velocity of the flow normal (per-
ematical expression. The various recognized methods for
pendicular) to the partial area.
determining mean velocity entail velocity observations at
4.2 Because computation of total flow is a summation or
selected distances below the water surface. The depth selec-
integration process, the overall accuracy of the measurement is
tions may include choice of (1) enough points to define a
generally increased by increasing the number of partial cross
vertical-velocity curve (see Fig. 1), (2) two points (0.2 and
sections. Generally 25 to 30 partial cross sections, even for
0.8 depth below water surface), (3) one point (0.6 depth), (4)
extremely large channels, are adequate depending on the
one point (0.2 depth), (5) three points (0.2, 0.6, and 0.8 depth),
variability and complexity of the flow and the cross section.
and (6) subsurface (that is, just below the water surface) (see
With a smooth cross section and uniform velocity distribution,
10.9 for further description of each method.)
fewer sections may be used. The partial sections should be
chosen so that each contains no more than about 5 % of the
5. Significance and Use
totaldischarge.Nopartialsectionshallcontainmorethan10 %
5.1 This test method is used to measure the volume rate of
of the total discharge.
flow of water moving in rivers and streams and moving over or
NOTE 1—There is no universal “rule of thumb” that can be applied to
through large man-made structures. It can also be used to
fix the number of partial sections relative to the magnitude of flow,
channel width, and channel depth because of the extreme variations in
channel shape, size, roughness, and velocity distribution. Where a rating
table or other estimate of total flow is available, this flow divided by 25
Buchanan, T. J., and Somers, W. P., “Discharge Measurements at Gaging
can serve as an estimate of the appropriate flow magnitude for each partial
Stations,” U.S. Geological Survey Techniques of Water-Resources Investigations,
section. Book 3, Chapter A8.
D 3858 – 95 (2003)
accordingly. Meters must be checked frequently during a discharge
calibrate such measuring structures as dams and flumes.
measurement to ensure that they have not been damaged or fouled.
Measurementsmaybemadefrombridges,cableways,orboats;
by wading; or through holes cut in an ice cover.
6.1.2 Counting Equipment—The number of revolutions of a
5.2 This test method is used in conjunction with determina-
rotor in a rotating-element type current meter is obtained by an
tions of physical, chemical, and biological quality and sedi-
electrical circuit through a contact chamber in the meter.
ment loadings where the flow rate is a required parameter.
Contact points in the chamber are designed to complete an
electrical circuit at selected frequencies of revolution. Contacts
6. Apparatus
can be selected that will complete the circuit once every five
6.1 Many and varied pieces of equipment and instruments
revolutions, once per revolution, or twice per revolution of the
are needed in making a conventional discharge measurement.
rotor. The electrical impulse produces an audible click in a
The magnitude of the velocity and discharge, location of the
headphone or registers a unit on a counting device. The count
cross section, weather conditions, whether suspended, floating,
rate is usually measured manually with a stopwatch, or
or particulate matter are present in the water, and vegetative
automatically with a timing device built into the counter.
growth in the cross sections are all factors determining
6.1.3 Width-Measuring Equipment—The horizontal dis-
equipment needs. Instruments and equipment used normally
tance to any point in a cross section is measured from an initial
include current-meters, width-measuring equipment, depth-
point on the stream bank. Cableways, highway bridges, or foot
sounding equipment, timers, angle-measuring devices, and
bridges used regularly in making discharge measurements are
counting equipment. The apparatus is further described in the
commonly marked with paint marks at the desired distance
following paragraphs.
intervals. Steel tapes, metallic tapes, or premarked taglines are
6.1.1 Current Meter— Current meters used to measure
used for discharge measurements made from boats or un-
open-channel flow are usually of the rotating-element (see
marked bridges, or by wading. Where the stream channel or
Note 2) or electromagnetic types. Refer to Test Methods
cross section is extremely wide, where no cableways or
D 4409 and D 5089 for more specific information. However,
suitable bridges are available, or where it is impractical to
the equipment sections of this test method emphasize the
stringatapeortagline,thedistancefromtheinitialpointonthe
rotating-element meters mainly because of their present wide-
bankcanbedeterminedbyopticalorelectricaldistancemeters,
spread availability and use. The operation of these meters is
by stadia, or by triangulation to a boat or man located on the
based on proportionality between the velocity of the water and
cross-section line.
the resulting angular velocity of the meter rotor. Hence, by
6.1.4 Depth-Sounding Equipment—The depth of the stream
placing this instrument at a point in a stream and counting the
below any water surface point in a cross section, and the
number of revolutions of the rotor during a measured interval
relative depth position of the current meter in the vertical at
of time, the velocity of water at that point is determined.
thatpoint,areusuallymeasuredbyarigidrodorbyasounding
Rotating-element meters can generally be classified into two
weight suspended on a cable. The selection of the proper
main types: those having vertical-axis rotors, and those having
weight is essential for the determination of the correct depth.A
horizontal-axis rotors. The principal comparative characteris-
light weight will be carried downstream and incorrectly yield
tics of the two types may be summarized as follows: (1) the
depth observations that are too large.A“rule of thumb” for the
vertical-axis rotor with cups and vanes operates in lower
selection of proper sized weights is to use a weight slightly
velocities than does the horizontal-axis rotor, has bearings that
heavier in pounds than the product of depth (feet) times
are well protected from silty water, is repairable in the field
velocity (feet per second) (no direct metric conversion is
without adversely affecting the meter rating, and works effec-
available). The sounding cable is controlled from above the
tively over a wide range of velocities; (2) the horizontal-axis
water surface either by a reel or by a handline. The depth-
rotor with vanes disturbs the flow less than does the vertical-
sounding equipment also serves as the position fixing and
axis rotor because of axial symmetry with flow direction, and
supporting mechanism for the current meter during velocity
is less likely to be fouled by debris. Also, the rotor can be
measurements. Sonic depth sounders are available but are
changed for different velocity ranges and meters of this type
usually not used in conjunction with a reel and sounding
are more difficult to service and adjust in the field.
weight.
NOTE 2—Vertical-axis current meters commonly used are of the Price
6.1.5 Angle-Measuring Devices—When the direction of
type and are available in two sizes, the large Price AA and the smaller
flow is not at right angles to the cross section, the velocity
Pygmymeter.TherotorassemblyofthetypeAAis5in.(127mm)andthe
vector normal to the cross section is needed for the correct
Pygmy is 2 in. (51 mm) in diameter. The rotor assemblies of both meters
determination of discharge. The velocity as measured by the
are formed with 6 hollow metal or solid plastic cone-shaped cups.
current meter, multiplied by the cosine of the horizontal angle
The small Price pygmy meter is generally used when the average depth
in a stream cross section is less than 1.5 ft (0.5 m) and velocity is below between the flow direction and a line perpendicular to the cross
2.5 ft/s (0.8 m/s).The large Price type meter should be used when average
section, will give the velocity component normal to the
depths are greater than 1.5 ft (0.5 m). For high velocities, the large meter
measuring cross section. A series of horizontal angles and
maybeusedforshallowerdepths.Donotchangethemeterifafewpartial
corresponding cosine values are usually indicated as a series of
sections are outside these limits. In any case, meters should not be used
marked points on the measurement note form (standard form)
closer to the streambed than 1.5 rotor or probe diameters.
or on a clipboard. The appropriate cosine value is then read
Current meters used in the measurement of open-channel flow are
directly by orienting the note form or clipboard with the
exposed to damage and fouling by debris, ice, particulate matter, sedi-
ment, moss, and extreme temperature variations, and should be selected direction of the cross section and the direction of flow. When
D 3858 – 95 (2003)
measuring in deep swift streams, it is possible to sound the 6.1.6 Miscellaneous Equipment—The type and size of the
depth but the force of the current moves the weight and meter equipment necessary to make a velocity-area discharge mea-
into positions downstream from the cross section; hence, the
surement are extremely variable, depending on the magnitude
depths measured are too large (see Fig. 2). Measurement of
of the discharge to be measured. Items such as sound
...
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