ASTM D5640-95(1999)
(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
SCOPE
1.1 This guide covers recommendations for 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 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 5640 – 95 (Reapproved 1999)
Standard Guide for
Selection of Weirs and Flumes for Open-Channel Flow
Measurement of Water
This standard is issued under the fixed designation D 5640; 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 3. Terminology
1.1 This guide covers recommendations for selection of 3.1 Definitions—For definitions of terms used in this guide,
weirs and flumes for the measurement of the volumetric flow refer to Terminology D 1129.
rate of water and wastewater in open channels under a variety 3.2 Definitions of Terms Specific to This Standard:
of field conditions. 3.2.1 blackwater—an increase in the depth of flow upstream
1.2 This guide emphasizes the weirs and flumes for which of a channel obstruction, in this case a weir or flume.
ASTM standards are available, namely, thin-plate weirs, broad- 3.2.2 contracted weirs—contractions of thin-plate weirs
crested weirs, Parshall flumes, and Palmer-Bowlus (and other refer to the widths of weir plate between the notch and the
long-throated) flumes. However, reference is also made to sidewalls of the approach channel. In fully contracted weirs,
other measurement devices and methods that may be useful in the ratio of the notch area to the cross-sectional area of the
specific situations. approach channel is small enough for the shape of the channel
1.3 This standard does not purport to address all of the to have little effect. In suppressed (full-width) rectangular
safety concerns, if any, associated with its use. It is the weirs, the contractions are suppressed, and the weir crest
responsibility of the user of this standard to establish appro- extends the full width of the channel.
priate safety and health practices and determine the applica- 3.2.3 crest—in rectangular thin-plate weirs, the horizontal
bility of regulatory limitations prior to use. bottom of the overflow section; in broad-crested weirs and
flumes, the plane, level floor of the flow section.
2. Referenced Documents
3.2.4 critical flow—open-channel flow in which the energy,
2.1 ASTM Standards:
expressed in terms of depth plus velocity head, is a minimum
D 1129 Terminology Relating to Water for a given flow rate and channel.
D 1941 Test Method for Open Channel Flow Measurement
3.2.4.1 Discussion—The Froude number is unity at critical
of Water with the Parshall Flume flow.
D 3858 Test Method for Open-Channel Flow Measurement
3.2.5 Froude number—a dimensionless number expressing
of Water by Velocity-Area Method the ratio of inertial to gravity forces in free-surface flow. It is
D 5242 Test Method for Open-Channel Flow Measurement
equal to the average velocity divided by the square root of the
of Water with Thin-Plate Weirs product of the average depth and the acceleration due to
D 5389 Test Method for Open-Channel Flow Measurement gravity.
of Water by Acoustic Velocity Meter Systems
3.2.6 head—in this context, the depth of flow referenced to
D 5390 Test Method for Open-Channel Flow Measurement the crest of the weir or flume and measured at a specified
of Water with Palmer-Bowlus Flume
location; this depth plus the velocity head are often termed the
D 5614 Test Method for Open-Channel Flow Measurement total head or total energy head.
of Water with Broad-Crested Weirs
3.2.7 hydraulic jump—an abrupt transition from supercriti-
2.2 ISO Standard: cal to subcritical or tranquil flow, accompanied by considerable
ISO 555-1973: Liquid Flow Measurement in Open
turbulence or gravity waves, or both.
Channels—Dilution Methods for Measurement of Steady 3.2.8 long-throated flume—a flume in which the prismatic
Flow—Constant-Rate Injection Method
throat is long enough relative to the head for a region of
essentially critical flow to develop on the crest.
3.2.9 nappe—the curved sheet or jet of water overfalling a
This guide is under the jurisdiction of ASTM Committee D-19 on Water and is
weir.
the direct responsibility of Subcommittee D19.07 on Sediments, Geomorphology,
3.2.10 notch—the overflow section of a triangular weir or of
and Open-Channel Flow.
a rectangular weir with side contractions.
Current edition approved April 15, 1995. Published June 1995.
Annual Book of ASTM Standards, Vol 11.01.
3.2.11 primary instrument—the device (in this case, a weir
Available from American National Standards Institute, 11 W. 42nd St., 13th
or flume) that creates a hydrodynamic condition that can be
Floor, New York, NY 10036.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
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D 5640
sensed by the secondary instrument.
3.2.12 rangeability—the spread between the maximum,
Qmax, and minimum, Qmin, flow rates that a measuring
instrument can usefully and reliably accommodate; this may be
described as the ratio Qmax/Qmin.
3.2.13 secondary instrument—in this case, a device that
measures the head on the weir or flume; it may also convert this
measured head to an indicated flowrate or could totalize the
flow.
3.2.14 subcritical flow—open-channel flow that is deeper
and at lower velocity than critical flow for the same flow rate;
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-
lower and at higher velocity than critical flow for the same flow
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
FIG. 1 Rectangular Thin-Plate Weirs
for the purpose.
4.2 It is recognized that not all open-channel situations are
sake of brevity and convenience, and the published standards
amenable to flow measurement by weirs and flumes and that in
must be consulted for exact and complete information on
some cases, particularly in large streams, discharges may best
requirements, conditions, and equations.
be determined by other means. (See 6.2.2.)
5.2 Flumes:
5. Weirs and Flumes
5.2.1 Flumes use sidewall constrictions or bottom shapes or
5.1 Weirs: slopes of specified geometries, or both, to cause the flow to
5.1.1 Weirs are overflow structures of specified geometries pass through the critical condition; this permits determination
for which the volumetric flow rate is a unique function of a of the flow rate from a measured head and a head-discharge
single measured upstream head, the other elements in the relation that has been experimentally or analytically obtained.
head-discharge relation having been experimentally or analyti- Details of the individual flumes may be found in the ASTM
cally determined. Details of the individual weirs may be found standards cited as follows:
in the ASTM standards cited as follows: 5.2.2 Standard Flumes— The following flumes, for which
5.1.2 Standard Weirs— The following weirs, for which ASTM standards are available, are emphasized in this guide.
Other flumes, which may be useful in specific situations, are
ASTM standards are available, are considered in this guide:
5.1.2.1 Thin-plate weirs (see Test Method D 5242). cited in 5.2.4.
5.2.2.1 Parshall flumes (see Test Method D 1941, Fig. 5, and
(1) Rectangular weirs (see Fig. 1).
(2) Triangular (V-notch) weirs (see Fig. 2). Table 1).
5.1.2.2 Broad-crested weirs (see Test Method D 5614). 5.2.2.2 Palmer-Bowlus (and other long-throated) flumes
(1) Square-edge (rectangular) weirs (see Fig. 3). (see Test Method D 5390 and Fig. 6).
(2) Rounded-edge weirs (see Fig. 4). 5.2.3 The quantitative information on flumes presented in
5.1.3 The quantitative information on weirs presented in Fig. 5 and Fig. 6 is intended to give the user only an overview
Figs. 1-4 is intended to give the user only an overview and and assist in the preliminary assessments for selection. To that
assist in the preliminary assessments for selection. To that end, end, some approximations and omissions were necessary for
some approximations and omissions were necessary for the the sake of brevity and convenience, and the published
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
D 5640
A
FIG. 2 Triangular Thin-Plate Weir
standards must be consulted for exact and complete informa-
tion on requirements, conditions, and equations.
5.2.4 Other Flumes— The following flumes are not covered
by ASTM standards but are listed here because they were FIG. 3 Rectangular (Square-Edge) Broad-Crested Weirs
developed for specific situations that may be of interest to users
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.
combination of flume and triangular weir and consequently
6.1.2 The errors inherent in the basic head-discharge rela-
exhibits very high rangeability along with good sediment
tions of the primary devices are as follows:
transport capability.
6.1.2.1 Thin-Plate weirs:
5.2.4.2 Portable Parshall Flume (1)—This 3-in. (7.6-cm)
(1) Triangular, fully contracted, 61to2%.
flume closely resembles the 3-in. standard Parshall flume with
(2) 90° notch, partially contracted, 62to3%.
the downstream divergent section removed. Its small size
(3) Rectangular, fully contracted, 61to2%.
makes it convenient to transport and install in some low-flow
(4) Rectangular, partially contracted, 62to3%.
field applications.
6.1.2.2 Broad-crested weirs:
5.2.4.3 Supercritical-Flow Flumes (1)—These flumes were
(1) Square-edge, 63 to 5 % (depending on head-to-weir
developed for use in streams with heavy loads of coarse
height ratio).
sediment. The depth measurement is made in the supercritical-
(2) Rounded, 63 % (in the optimum range of head-to-
flow portion of the flume rather than upstream.
length ratio).
6.1.2.3 Flumes:
6. Selection Criteria
(1) Parshall flumes, 65%.
6.1 Accuracy: (2) Palmer Bowlus and long-throated flumes, 63to5%
6.1.1 The error of a flow-rate measurement results from a (depending on head-to-length ratio).
combination of individual errors, including errors in the 6.1.2.4 This listing indicates that, with no consideration of
coefficients of the head-discharge relations; errors in the other selection criteria, thin-plate weirs are potentially the most
measurement of the head; and errors due to nonstandard shape accurate of the devices.
or installation or other departures from the practices recom- 6.1.3 Sensitivity— The discharge of weirs and flumes de-
mended in the various weir or flume standards, or both. This pends upon the measured head to the three-halves power for
guide considers the accuracy of the primary devices only, rectangular control sections (this is an approximation in the
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
D 5640
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
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
measurement, for example, velocity-area method (Test Method
D 3858), acoustic velocity meters (Test Method D 5389), or
tracer dilution (ISO 555).
6.2.3 Range of Flow Rate:
6.2.3.1 Triangular thin-plate weirs have the largest range-
ability of the standard devices because of their 2.5-power
dependence on head. This rangeability can vary from slightly
under 200 for fully contracted weirs to about 600 for partially
contracted 90° notches that can utilize the allowable range of
head.
6.2.3.2 For rectangular thin-plate weirs, the rangeability
varies somewhat with the crest length-to-channel width ratio
and is typically about 90, increasing to about 110 for full-width
weirs. These results are based on a minimum head of 0.1 ft
(0.03 m) and a suggested (although not absolute) maximum
head of 2 ft (0.6 m). However, the rangeability of smaller
rectangular weirs can be significantly less.
6.2.3.3 The rangeability of the rounded broad-crested weir
is close to 40. However, large square-edge weirs, if used to the
geometric limits of the standard, exhibit a rangeability of about
90.
FIG. 4 Rounded Broad-Crested Weirs
6.2.3.4 The rangeability of Parshall flumes varies widely
with size. (See Fig. 5 and Table 1.)
case of Parshall flumes), to the five-halves power for triangular
6.2.3.5 For Palmer-Bowlus and other long-throated flumes,
sections, and to intermediate powers for intermediate trapezoi-
the rangeability depends on the shape of the throat cross
dal sections. Consequently, the accuracy of a flow-rate mea-
section, increasing as that shape varies from rectangular toward
surement is sensitive to errors in head measurement and
triangular. For the typical commercial Palmer-Bowlus flume of
particularly so in the case of triangular control sections. It
trapezoidal section, at least one manufacturer cites maximum-
follows that in all weirs and flumes operating at or near
to-minimum flow-rate ratios up to, and in some cases exceed-
minimum head, even a modest error or change in head can
ing, 100; (5) however, the head range is often beyond the
have a significant effect on the measured flow rate. Therefore,
recommendations of Test M
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