ASTM D3858-95(2008)
(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)).
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 Corps 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 41 for the field acceptance tests of hydraulic turbines, and are not included in this test method.
1.5 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.
1.6 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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Designation:D3858 −95(Reapproved 2008)
Standard Test Method for
Open-Channel Flow Measurement of Water by Velocity-Area
Method
This standard is issued under the fixed designation D3858; 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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica-
1.1 This test method covers the measurement of the volume
bility of regulatory limitations prior to use.
rate of flow of water in open channels by determining the flow
velocity and cross-sectional area and computing the discharge
2. Referenced Documents
therefrom (Refs (1-7)).
2.1 ASTM Standards:
1.2 The procedures described in this test method are widely
D1129 Terminology Relating to Water
used by those responsible for the collection of streamflow data,
D2777 Practice for Determination of Precision and Bias of
for example, the U.S. Geological Survey, Bureau of
Applicable Test Methods of Committee D19 on Water
Reclamation, U.S.Army Corps of Engineers, U.S. Department
D4409 Test Method for Velocity Measurements of Water in
of Agriculture, Water Survey Canada, and many state and
Open Channels with Rotating Element Current Meters
provincialagencies.Theproceduresaregenerallyfrominternal
D5089 Test Method for Velocity Measurements of Water in
documents of the above listed agencies, which have become
Open Channels with Electromagnetic Current Meters
the defacto standards as used in North America.
2.2 ISO Standard:
ISO 3455 (1976) Calibration of Rotating-Element Current
1.3 This test method covers the use of current meters to
Meters in Straight Open Tanks
measure flow velocities. Discharge measurements may be
madetoestablishisolatedsinglevalues,ormaybemadeinsets
3. Terminology
or in a series at various stages or water-level elevations to
3.1 Definitions of Terms Specific to This Standard:
establish a stage-discharge relation at a site. In either case, the
3.1.1 current meter—an instrument used to measure, at a
same test method is followed for obtaining field data and
point, velocity of flowing water.
computation of discharge.
3.1.2 discharge—the volume of flow of water through a
1.4 Measurements for the purpose of determining the dis-
cross section in a unit of time, including any sediment or other
charge in efficiency tests of hydraulic turbines are specified in
solids that may be dissolved in or mixed with the water.
International Electrotechnical Commission Publication 41 for
the field acceptance tests of hydraulic turbines, and are not 3.1.3 float—a buoyant article capable of staying suspended
included in this test method. 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
1.5 The values stated in inch-pound units are to be regarded
magnitude of the flow velocity along that line.
as standard. The values given in parentheses are mathematical
3.1.4 stage—the height of a water surface above an estab-
conversions to SI units that are provided for information only
lished (or arbitrary) datum plane; also termed gage height.
and are not considered standard.
1.6 This standard does not purport to address all of the 3.2 Definitions—For definitions of terms used in this test
safety concerns, if any, associated with its use. It is the method, refer to Terminology D1129.
4. Summary of Test Method
This test method is under the jurisdiction of ASTM Committee D19 on Water
4.1 The principal of this test method consists in effectively
and is the direct responsibility of Subcommittee D19.07 on Sediments,
and accurately measuring the flow velocity and cross-sectional
Geomorphology, and Open-Channel Flow.
Current edition approved Oct. 1, 2008. Published November 2008. Originally
approved in 1979. Last previous edition approved in 2003 as D3858 – 95 (2003). For referenced ASTM standards, visit the ASTM website, www.astm.org, or
DOI: 10.1520/D3858-95R08. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
The boldface numbers in parentheses refer to the references listed at the end of Standards volume information, refer to the standard’s Document Summary page on
this test method. the ASTM website.
For availability of this publication, contact the International Electrotechnical Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
Commission, 3 rue de Varembe, CH 1211, Geneva 20, Switzerland. 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 States
D3858−95 (2008)
NOTE 1—There is no universal “rule of thumb” that can be applied to
area of an open channel or stream. The total flow or discharge
fix the number of partial sections relative to the magnitude of flow,
measurement is the summation of the products of partial areas
channel width, and channel depth because of the extreme variations in
of the flow cross section and their respective average veloci-
channel shape, size, roughness, and velocity distribution. Where a rating
ties. The equation representing the computation is:
table or other estimate of total flow is available, this flow divided by 25
can serve as an estimate of the appropriate flow magnitude for each partial
Q 5 ~av!
(
section.
where:
4.3 Determination of the mean velocity in a given partial
Q = total discharge, cross section is really a sampling process throughout the
a = individual partial cross-sectional area, and
vertical extent of that section. The mean can be closely and
v = corresponding mean velocity of the flow normal (per-
satisfactorily approximated by making a few selected velocity
pendicular) to the partial area.
observations and substituting these values in a known math-
ematical expression. The various recognized methods for
4.2 Because computation of total flow is a summation or
determining mean velocity entail velocity observations at
integration process, the overall accuracy of the measurement is
selected distances below the water surface. The depth selec-
generally increased by increasing the number of partial cross
tions may include choice of (1) enough points to define a
sections. Generally 25 to 30 partial cross sections, even for
vertical-velocitycurve(seeFig.1), (2)twopoints(0.2and0.8
extremely large channels, are adequate depending on the
depth below water surface), (3) one point (0.6 depth), (4) one
variability and complexity of the flow and the cross section.
point (0.2 depth), (5) three points (0.2, 0.6, and 0.8 depth), and
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
Buchanan, T. J., and Somers, W. P., “Discharge Measurements at Gaging
totaldischarge.Nopartialsectionshallcontainmorethan10 %
Stations,” U.S. Geological Survey Techniques of Water-Resources Investigations,
of the total discharge. Book 3, Chapter A8.
FIG. 1 Typical Open-Channel Vertical-Velocity Curve (Modified from Buchanan and Somers)
D3858−95 (2008)
2.5 ft/s (0.8 m/s).The large Price type meter should be used when average
(6) subsurface (that is, just below the water surface) (see 10.9
depths are greater than 1.5 ft (0.5 m). For high velocities, the large meter
for further description of each method.)
maybeusedforshallowerdepths.Donotchangethemeterifafewpartial
sections are outside these limits. In any case, meters should not be used
5. Significance and Use
closer to the streambed than 1.5 rotor or probe diameters.
5.1 This test method is used to measure the volume rate of Current meters used in the measurement of open-channel flow are
exposed to damage and fouling by debris, ice, particulate matter, sedi-
flow of water moving in rivers and streams and moving over or
ment, moss, and extreme temperature variations, and should be selected
through large man-made structures. It can also be used to
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;
6.1.2 Counting Equipment—The number of revolutions of a
by wading; or through holes cut in an ice cover.
rotor in a rotating-element type current meter is obtained by an
5.2 This test method is used in conjunction with determina-
electrical circuit through a contact chamber in the meter.
tions of physical, chemical, and biological quality and sedi-
Contact points in the chamber are designed to complete an
ment loadings where the flow rate is a required parameter.
electrical circuit at selected frequencies of revolution. Contacts
can be selected that will complete the circuit once every five
6. Apparatus
revolutions, once per revolution, or twice per revolution of the
6.1 Many and varied pieces of equipment and instruments
rotor. The electrical impulse produces an audible click in a
are needed in making a conventional discharge measurement.
headphone or registers a unit on a counting device. The count
The magnitude of the velocity and discharge, location of the
rate is usually measured manually with a stopwatch, or
cross section, weather conditions, whether suspended, floating,
automatically with a timing device built into the counter.
or particulate matter are present in the water, and vegetative
6.1.3 Width-Measuring Equipment—The horizontal dis-
growth in the cross sections are all factors determining
tance to any point in a cross section is measured from an initial
equipment needs. Instruments and equipment used normally
point on the stream bank. Cableways, highway bridges, or foot
include current-meters, width-measuring equipment, depth-
bridges used regularly in making discharge measurements are
sounding equipment, timers, angle-measuring devices, and
commonly marked with paint marks at the desired distance
counting equipment. The apparatus is further described in the
intervals. Steel tapes, metallic tapes, or premarked taglines are
following paragraphs.
used for discharge measurements made from boats or un-
6.1.1 Current Meter—Currentmetersusedtomeasureopen-
marked bridges, or by wading. Where the stream channel or
channelflowareusuallyoftherotating-element(seeNote2)or
cross section is extremely wide, where no cableways or
electromagnetic types. Refer to Test Methods D4409 and
suitable bridges are available, or where it is impractical to
D5089 for more specific information. However, the equipment
stringatapeortagline,thedistancefromtheinitialpointonthe
sections of this test method emphasize the rotating-element
bankcanbedeterminedbyopticalorelectricaldistancemeters,
meters mainly because of their present widespread availability
by stadia, or by triangulation to a boat or man located on the
and use. The operation of these meters is based on proportion-
cross-section line.
alitybetweenthevelocityofthewaterandtheresultingangular
6.1.4 Depth-Sounding Equipment—The depth of the stream
velocityofthemeterrotor.Hence,byplacingthisinstrumentat
below any water surface point in a cross section, and the
a point in a stream and counting the number of revolutions of
relative depth position of the current meter in the vertical at
the rotor during a measured interval of time, the velocity of
thatpoint,areusuallymeasuredbyarigidrodorbyasounding
water at that point is determined. Rotating-element meters can
weight suspended on a cable. The selection of the proper
generally be classified into two main types: those having
weight is essential for the determination of the correct depth.A
vertical-axis rotors, and those having horizontal-axis rotors.
light weight will be carried downstream and incorrectly yield
The principal comparative characteristics of the two types may
depth observations that are too large.A“rule of thumb” for the
be summarized as follows: (1) the vertical-axis rotor with cups
selection of proper sized weights is to use a weight slightly
andvanesoperatesinlowervelocitiesthandoesthehorizontal-
heavier in pounds than the product of depth (feet) times
axis rotor, has bearings that are well protected from silty water,
velocity (feet per second) (no direct metric conversion is
is repairable in the field without adversely affecting the meter
available). The sounding cable is controlled from above the
rating, and works effectively over a wide range of velocities;
water surface either by a reel or by a handline. The depth-
(2) the horizontal-axis rotor with vanes disturbs the flow less
sounding equipment also serves as the position fixing and
than does the vertical-axis rotor because of axial symmetry
supporting mechanism for the current meter during velocity
with flow direction, and is less likely to be fouled by debris.
measurements. Sonic depth sounders are available but are
Also, the rotor can be changed for different velocity ranges and
usually not used in conjunction with a reel and sounding
metersofthistypearemoredifficulttoserviceandadjustinthe
weight.
field.
6.1.5 Angle-Measuring Devices—When the direction of
NOTE 2—Vertical-axis current meters commonly used are of the Price flow is not at right angles to the cross section, the velocity
type and are available in two sizes, the large Price AA and the smaller
vector normal to the cross section is needed for the correct
Pygmymeter.TherotorassemblyofthetypeAAis5in.(127mm)andthe
determination of discharge. The velocity as measured by the
Pygmy is 2 in. (51 mm) in diameter. The rotor assemblies of both meters
current meter, multiplied by the cosine of the horizontal angle
are formed with 6 hollow metal or solid plastic cone-shaped cups.
betweentheflowdirectionandalineperpendiculartothecross
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 section, will give the velocity component normal to the
D3858−95 (2008)
measuring cross section. A series of horizontal angles and angles is considered to be special equipment which is avail-
corresponding cosine values are usually indicated as a series of able. Tables of air-line and wet-line corrections are also
marked points on the measurement note form (standard form)
available. Tags or colored streamers placed on the sounding
or on a clipboard. The appropriate cosine value is then read
line at known distances above the center of the me
...
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