ASTM D5640-95(2008)
(Guide)Standard Guide for Selection of Weirs and Flumes for Open-Channel Flow Measurement of Water
Standard Guide for Selection of Weirs and Flumes for Open-Channel Flow Measurement of Water
SIGNIFICANCE AND USE
Each type of weir and flume possesses advantages and disadvantages relative to the other types when it is considered for a specific application; consequently, the selection process often involves reaching a compromise among several features. This guide is intended to assist the user in making a selection that is hydraulically, structurally, and economically appropriate for the purpose.
It is recognized that not all open-channel situations are amenable to flow measurement by weirs and flumes and that in some cases, particularly in large streams, discharges may best be determined by other means. (See 6.2.2.)
SCOPE
1.1 This guide covers recommendations for the selection of weirs and flumes for the measurement of the volumetric flow rate of water and wastewater in open channels under a variety of field conditions.
1.2 This guide emphasizes the weirs and flumes for which ASTM standards are available, namely, thin-plate weirs, broad-crested weirs, Parshall flumes, and Palmer-Bowlus (and other long-throated) flumes. However, reference is also made to other measurement devices and methods that may be useful in specific situations.
1.3 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.
1.4 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: D5640 − 95 (Reapproved2008)
Standard Guide for
Selection of Weirs and Flumes for Open-Channel Flow
Measurement of Water
This standard is issued under the fixed designation D5640; 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 D5390 Test Method for Open-Channel Flow Measurement
of Water with Palmer-Bowlus Flumes
1.1 This guide covers recommendations for the selection of
D5614 Test Method for Open Channel Flow Measurement
weirs and flumes for the measurement of the volumetric flow
of Water with Broad-Crested Weirs
rate of water and wastewater in open channels under a variety
2.2 ISO Standard:
of field conditions.
ISO 555-1973: Liquid Flow Measurement in Open
1.2 This guide emphasizes the weirs and flumes for which
Channels—Dilution Methods for Measurement of Steady
ASTMstandardsareavailable,namely,thin-plateweirs,broad-
Flow—Constant-Rate Injection Method
crested weirs, Parshall flumes, and Palmer-Bowlus (and other
long-throated) flumes. However, reference is also made to 3. Terminology
other measurement devices and methods that may be useful in
3.1 Definitions—For definitions of terms used in this guide,
specific situations.
refer to Terminology D1129.
1.3 The values stated in inch-pound units are to be regarded
3.2 Definitions of Terms Specific to This Standard:
as standard. The values given in parentheses are mathematical
3.2.1 blackwater—an increase in the depth of flow upstream
conversions to SI units that are provided for information only
of a channel obstruction, in this case a weir or flume.
and are not considered standard.
3.2.2 contracted weirs—contractions of thin-plate weirs re-
1.4 This standard does not purport to address all of the
fer to the widths of weir plate between the notch and the
safety concerns, if any, associated with its use. It is the
sidewalls of the approach channel. In fully contracted weirs,
responsibility of the user of this standard to establish appro-
the ratio of the notch area to the cross-sectional area of the
priate safety and health practices and determine the applica-
approach channel is small enough for the shape of the channel
bility of regulatory limitations prior to use.
to have little effect. In suppressed (full-width) rectangular
weirs, the contractions are suppressed, and the weir crest
2. Referenced Documents
extends the full width of the channel.
2.1 ASTM Standards:
3.2.3 crest—in rectangular thin-plate weirs, the horizontal
D1129 Terminology Relating to Water
bottom of the overflow section; in broad-crested weirs and
D1941 Test Method for Open Channel Flow Measurement
flumes, the plane, level floor of the flow section.
of Water with the Parshall Flume
3.2.4 critical flow—open-channel flow in which the energy,
D3858 Test Method for Open-Channel Flow Measurement
expressed in terms of depth plus velocity head, is a minimum
of Water by Velocity-Area Method
for a given flow rate and channel.
D5242 Test Method for Open-Channel Flow Measurement
3.2.4.1 Discussion—The Froude number is unity at critical
of Water with Thin-Plate Weirs
flow.
D5389 Test Method for Open-Channel Flow Measurement
by Acoustic Velocity Meter Systems
3.2.5 Froude number—a dimensionless number expressing
the ratio of inertial to gravity forces in free-surface flow. It is
equal to the average velocity divided by the square root of the
This guide is under the jurisdiction ofASTM Committee D19 on Water and is
product of the average depth and the acceleration due to
the direct responsibility of Subcommittee D19.07 on Sediments, Geomorphology,
and Open-Channel Flow. gravity.
Current edition approved Oct. 1, 2008. Published November 2008. Originally
3.2.6 head—in this context, the depth of flow referenced to
approved in 1995. Last previous edition approved in 2003 as D5640 – 95 (2003).
the crest of the weir or flume and measured at a specified
DOI: 10.1520/D5640-95R08.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
the ASTM website. 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
D5640 − 95 (2008)
location; this depth plus the velocity head are often termed the 5.1.1 Weirs are overflow structures of specified geometries
total head or total energy head. for which the volumetric flow rate is a unique function of a
single measured upstream head, the other elements in the
3.2.7 hydraulic jump—an abrupt transition from supercriti-
head-discharge relation having been experimentally or analyti-
caltosubcriticalortranquilflow,accompaniedbyconsiderable
cally determined. Details of the individual weirs may be found
turbulence or gravity waves, or both.
in the ASTM standards cited as follows:
3.2.8 long-throated flume—a flume in which the prismatic
5.1.2 Standard Weirs—The following weirs, for which
throat is long enough, relative to the head, for a region of
ASTM standards are available, are considered in this guide:
essentially critical flow to develop on the crest.
5.1.2.1 Thin-plate weirs (see Test Method D5242).
3.2.9 nappe—the curved sheet or jet of water overfalling a
(1) Rectangular weirs (see Fig. 1).
weir.
(2) Triangular (V-notch) weirs (see Fig. 2).
3.2.10 notch—the overflow section of a triangular weir or of 5.1.2.2 Broad-crested weirs (see Test Method D5614).
(1) Square-edge (rectangular) weirs (see Fig. 3).
a rectangular weir with side contractions.
(2) Rounded-edge weirs (see Fig. 4).
3.2.11 primary instrument—the device (in this case, a weir
5.1.3 The quantitative information on weirs presented in
or flume) that creates a hydrodynamic condition that can be
Figs. 1-4 is intended to give the user only an overview and
sensed by the secondary instrument.
assist in the preliminary assessments for selection. To that end,
3.2.12 rangeability—the spread between the maximum,
some approximations and omissions were necessary for the
Qmax, and minimum, Qmin, flow rates that a measuring
sake of brevity and convenience, and the published standards
instrumentcanusefullyandreliablyaccommodate;thismaybe
must be consulted for exact and complete information on
described as the ratio Qmax/Qmin.
requirements, conditions, and equations.
3.2.13 secondary instrument—in this case, a device that
5.2 Flumes:
measurestheheadontheweirorflume;itmayalsoconvertthis
measured head to an indicated flowrate or could totalize the
flow.
3.2.14 subcritical flow—open-channel flow that is deeper
andatalowervelocitythancriticalflowforthesameflowrate;
sometimes called tranquil flow.
3.2.14.1 Discussion—The Froude number is less than unity
for this flow.
3.2.15 submergence—the ratio of downstream head to up-
stream head on a weir or flume. Submergence greater than a
critical value affects the discharge for a given upstream head.
3.2.16 supercritical flow—open-channel flow that is shal-
lowerandathighervelocitythancriticalflowforthesameflow
rate.
3.2.16.1 Discussion—The Froude number is greater than
unity for this flow.
3.2.17 throat—the constricted portion of a flume.
3.2.18 velocity head—the square of the average velocity
divided by twice the acceleration due to gravity.
4. Significance and Use
4.1 Each type of weir and flume possesses advantages and
disadvantages relative to the other types when it is considered
for a specific application; consequently, the selection process
often involves reaching a compromise among several features.
This guide is intended to assist the user in making a selection
that is hydraulically, structurally, and economically appropriate
for the purpose.
4.2 It is recognized that not all open-channel situations are
amenable to flow measurement by weirs and flumes and that in
some cases, particularly in large streams, discharges may best
be determined by other means. (See 6.2.2.)
5. Weirs and Flumes
5.1 Weirs: FIG. 1 Rectangular Thin-Plate Weirs
D5640 − 95 (2008)
A
FIG. 2 Triangular Thin-Plate Weir
5.2.1 Flumes use sidewall constrictions or bottom shapes or
slopes of specified geometries, or both, to cause the flow to
FIG. 3 Rectangular (Square-Edge) Broad-Crested Weirs
pass through the critical condition; this permits determination
of the flow rate from a measured head and a head-discharge
combination of flume and triangular weir and consequently
relation that has been experimentally or analytically obtained.
exhibits very high rangeability along with good sediment
Details of the individual flumes may be found in the ASTM
transport capability.
standards cited as follows:
5.2.4.2 Portable Parshall Flume (1)—This 3-in. (7.6-cm)
5.2.2 Standard Flumes—The following flumes, for which
flume closely resembles the 3-in. standard Parshall flume with
ASTM standards are available, are emphasized in this guide.
the downstream divergent section removed. Its small size
Other flumes, which may be useful in specific situations, are
makes it convenient to transport and install in some low-flow
cited in 5.2.4.
field applications.
5.2.2.1 Parshall flumes (seeTest Method D1941, Fig. 5, and
5.2.4.3 Supercritical-Flow Flumes (1)—These flumes were
Table 1).
developed for use in streams with heavy loads of coarse
5.2.2.2 Palmer-Bowlus (and other long-throated) flumes
sediment. The depth measurement is made in the supercritical-
(see Test Method D5390 and Fig. 6).
flow portion of the flume rather than upstream.
5.2.3 The quantitative information on flumes presented in
6. Selection Criteria
Fig. 5 and Fig. 6 is intended to give the user only an overview
and assist in the preliminary assessments for selection. To that
6.1 Accuracy:
end, some approximations and omissions were necessary for
6.1.1 The error of a flow-rate measurement results from a
the sake of brevity and convenience, and the published
combination of individual errors, including errors in the
standards must be consulted for exact and complete informa-
coefficients of the head-discharge relations; errors in the
tion on requirements, conditions, and equations.
measurement of the head; and errors due to nonstandard shape
5.2.4 Other Flumes—The following flumes are not covered or installation or other departures from the practices recom-
by ASTM standards but are listed here because they were mended in the various weir or flume standards, or both. This
developedforspecificsituationsthatmaybeofinteresttousers guide considers the accuracy of the primary devices only,
of this guide. Detailed information on them can be found in the based on their accuracy potential under optimum or standard
reference section. conditions; from information included in the individual stan-
5.2.4.1 H-Series Flumes (1), (2)—This flume, which was dards, users can estimate secondary-system errors and other
developed for use on agricultural watersheds, is actually a errors to obtain an estimate of the total measurement error.
D5640 − 95 (2008)
have a significant effect on the measured flow rate. Therefore,
it is important to select sizes or combinations of devices that
avoid prolonged operation near minimum head.
6.2 Flow rate:
6.2.1 This criterion includes the maximum anticipated flow
rate and the range of flow rate from minimum to maximum.
The latter consideration includes not only daily or seasonal
variationsbutalsoaflowchronologyinwhich,forexample,an
area under development generates an initially low waste-water
discharge followed in subsequent years by increasing flow
rates.
6.2.2 Flow capacities:
6.2.2.1 Small and Moderate Flows—Apart from consider-
ations of head loss (6.3) and sediment or debris transport (6.4),
thin-plate weirs are most suitable for lower flow rates, with the
triangular notches most appropriate for the smallest flows.
Small Parshall and Palmer-Bowlus flumes are also available
for low flows; these improve on the thin-plate weirs in
sediment passage and head loss, but at some sacrifice of
potential accuracy (6.1).
6.2.2.2 Large Flows—Large discharges are best measured
with flumes and broad-crested weirs, which can accommodate
large heads and flows and, given proper construction, are
inherently sturdy enough to withstand them. For example, the
50-ft (15.24-m) Parshall flume can be used for flow rates up to
3 3
about 3200 ft /s (90 m /s). However, flumes and broad-crested
FIG. 4 Rounded Broad-Crested Weirs
weirs that are adequate for very large flows require major
construction, and users may wish to consider establishing a
measuring station (3), (4) with other methods of discharge
6.1.2 The errors inherent in the basic head-discharge rela-
measurement, for example, velocity-area method (Test Method
tions of the primary devices are as follows:
D3858), acoustic velocity meters (Test Method D5389), or
6.1.2.1 Thin-Plate weirs:
tracer dilution (ISO 555).
(1) Triangular, fully contracted, 61to2%.
6.2.3 Range of Flow Rate:
(2) 90° notch, partially contracted, 62to3%.
(3) Rectangular, fully contracted, 61to2%.
6.2.3.1 Triangular thin-plate weirs have the largest range-
(4) Rectangular, partially contracted, 62to3%.
ability of the standard devices because of their 2.5-power
6.1.2.2 Broad-crested weirs:
dependence on head. This rangeability can vary from slightly
(1) Square-edge, 63 to 5 % (depending on head-to-weir
under 200 for fully contracted weirs to about 600 for partially
height ratio).
contracted 90° notches that can utilize the allowable range of
(2) Rounded, 63 % (in the optimum range of head-to-
head.
length ratio).
6.2.3.2 For rectangular thin-plate weirs, the rangeability
6.1.2.3 Flumes:
varies somewhat with the crest length-to-channel width ratio
(1) Parshall flumes, 65%.
andistypicallyabout90,increasingtoabout110forfull-width
(2) Palmer Bowlus and long-throated flumes, 63to5%
weirs. These results are based on a minimum head of 0.1 ft
(depending on head-to-length ratio).
(0.03 m) and a suggested (although not absolute) maximum
6.1.2.4 This listing indicates that, with no consideration of
head of 2 ft (0.6 m). However, the rangeability of smaller
otherselectioncriteria,thin-plateweirsarepotentiallythemost
rectangular weirs can be significantly less.
accurate of the devices.
6.2.3.3 The rangeability of the rounded broad-crested weir
6.1.3 Sensitivity—The discharge of weirs and flumes de-
is close to 40. However, large square-edge weirs, if used to the
pends upon the measured head to the three-halve
...
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