ASTM D5614-94(2008)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: D5614 − 94(Reapproved 2008)
Standard Test Method for
Open Channel Flow Measurement of Water with Broad-
Crested Weirs
This standard is issued under the fixed designation D5614; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope ISO 4373-1979Measurement of Liquid Flow in Open
Channels—Water Level Measuring Devices
1.1 This test method covers measurement of the volumetric
ISO 4374-1990Liquid Flow Measurement in Open Chan-
flow rate of water in open channels with two types of
nels byWeirs and Flumes—Round-Nose Horizontal Crest
horizontal broad-crested weirs: those having a square (sharp)
Weirs
upstream corner and those having a well-rounded upstream
corner.
3. Terminology
1.2 Thevaluesstatedininch-poundunitsaretoberegarded
3.1 Definitions—For definitions of terms used in this test
as standard. The values given in parentheses are mathematical
method, refer to Terminology D1129.
conversions to SI units that are provided for information only
3.2 Definitions of Terms Specific to This Standard:
and are not considered standard.
3.2.1 boundary layer displacement thickness— the bound-
1.3 This standard does not purport to address all of the
ary layer is a layer of fluid flow adjacent to a solid surface (in
safety concerns, if any, associated with its use. It is the
thiscase,theweircrestandsidewalls)inwhich,duetoviscous
responsibility of the user of this standard to establish appro-
friction, the velocity increases from zero at the stationary
priate safety and health practices and determine the applica-
surface to an essentially frictionless-flow value at the edge of
bility of regulatory limitations prior to use.
the layer. The displacement thickness is a distance normal to
the solid surface that the flow streamlines can be considered to
2. Referenced Documents
have been displaced by virtue of the boundary-layer informa-
2.1 ASTM Standards:
tion.
D1129Terminology Relating to Water
3.2.2 crest—the horizontal plane surface of the weir.
D2777Practice for Determination of Precision and Bias of
3.2.3 critical flow—open channel flow in which the energy,
Applicable Test Methods of Committee D19 on Water
expressed in terms of depth plus velocity head, is a minimum
D3858Test Method for Open-Channel Flow Measurement
for a given flow rate and channel. The Froude number is unity
of Water by Velocity-Area Method
at critical flow.
2.2 ISO Standards:
3.2.4 Froude number—a dimensionless number expressing
ISO 555-1973 Liquid Flow Measurement in Open
the ratio of inertial to gravity forces in free surface flow. It is
Channels—Dilution Methods for Measurement of Steady
equal to the average velocity divided by the square root of the
Flow—Constant Rate Injection Method
product of the average depth and the acceleration due to
ISO 3846-1989Liquid Flow Measurement in Open Chan-
gravity.
nels by Weirs and Flumes—Rectangular Broad-Crested
Weirs 3.2.5 head—in this test method , the depth of water above a
specified elevation. The measuring head is the depth of flow
above the weir crest measured at an appropriate location
This test method is under the jurisdiction ofASTM Committee D19 on Water
upstream of the weir; the downstream head is referenced
and is the direct responsibility of Subcommittee D19.07 on Sediments,
similarly to the crest elevation and measured downstream of
Geomorphology, and Open-Channel Flow.
the weir. The head plus the corresponding velocity head is
Current edition approved Oct. 1, 2008. Published November 2008. Originally
approved in 1994. Last previous edition approved in 1998 as D5614–94(1998). often termed the total head or total energy head.
DOI: 10.1520/D5614-94R08.
3.2.6 hydraulic jump—an abrupt transition from supercriti-
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
cal flow to subcritical or tranquil flow, accompanied by
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
considerable turbulence or gravity waves, or both.
the ASTM website.
3.2.7 nappe—thecurvedsheetorjetofwateroverfallingthe
Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
4th Floor, New York, NY 10036, http://www.ansi.org. downstream end of the weir.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D5614 − 94 (2008)
3.2.8 primary device—thedevice(inthiscase,theweir)that 6. Interferences
creates a hydrodynamic condition that can be sensed by the
6.1 Broad-crestedweirsarenotsuitableforuseinsediment-
secondary instrument.
laden streams that are carrying heavy bed loads. However,
3.2.9 Reynolds number—a dimensionless number express-
floating debris is readily passed, particularly by the rounded
ingtheratioofinertialtoviscousforcesinaflow.Thepertinent
weir (see 7.2.1).
Reynolds number on the weir crest is equal to the (critical)
6.2 Broad-crested weirs cannot be used beyond submer-
velocity multiplied by the crest length and divided by the
gence limits because insufficient data exist to document their
kinematic viscosity of the water.
performance. It is therefore necessary to adhere to the
3.2.10 secondary instrument— in this case, a device that
tailwater-level limitations described in this test method.
measures the depth of flow (referenced to the crest elevation)
at an appropriate location upstream of the weir.The secondary
7. Apparatus
instrumentmayalsoconvertthismeasuredheadtoanindicated
7.1 A broad-crested weir measuring system consists of the
flow rate or could totalize flow rate.
weir itself and its immediate channel (the primary) and a head
3.2.11 stilling well—a small free-surface reservoir con-
measuring device (the secondary). The secondary device can
nected through a restricted passage to the head-measurement
range from a simple staff gage for visual readings to an
location upstream of the weir so that a head measurement can
instrument that senses the depth continuously, converts it to a
be made under quiescent conditions.
flow rate, and displays or transmits a readout or record of the
3.2.12 subcritical flow—open channel flow that is deeper
instantaneous flow rate or totalized flow, or both.
and at lower velocity than critical flow for the same flow rate;
7.2 Square-Edge (Rectangular) Broad-Crested Weir:
sometimescalledtranquilflow.AFroudenumberlessthanone
exists. 7.2.1 Configuration— The square-edge broad-crested weir
as shown in Fig. 1 is rectangular in longitudinal profile and
3.2.13 submergence—a condition in which the water level
provides a plane horizontal crest that has finite length in the
onthedownstreamsideoftheweirishighenoughtoaffectthe
direction of flow and extends the full width of the channel
flow over the weir and hence alter the head-discharge relation.
between vertical sidewalls. A contracted section must be
It is usually expressed as a ratio or percentage of downstream
constructed as shown (see also 7.4.1.2) if the channel does not
to upstream head or downstream to upstream total head.
have vertical sidewalls or is wider than the desired crest. The
3.2.14 supercritical flow—open channel flow that is shal-
vertical sidewalls must extend downstream of the downstream
lowerandathighervelocitythancriticalflowforthesameflow
faceoftheweiradistanceofatleasttwicethemaximumhead.
rate. A Froude number greater than one exists.
Recommended limits on dimensions and geometric ratios are
3.2.15 tailwater—the water elevation immediately down-
given in 7.2.5. The upstream and downstream faces must be
stream of the weir.
vertical and perpendicular to the channel surfaces, and it is
important that the upstream corner be square and sharp.
3.2.16 tranquil flow—see subcritical flow.
3.2.17 velocity head—the square of the average velocity
NOTE 1—High flow rates combined with floating debris may damage
the sharp edge; rounded-edge weirs should be considered for such
divided by twice the acceleration due to gravity.
applications.
4. Summary of Test Method
7.2.2 Construction Requirements:
7.2.2.1 The structure must be sturdy enough to withstand
4.1 Inbroad-crestedweirs,thelengthofthehorizontalcrest
the maximum flow rate and must be watertight so that no
inthedirectionofflowislargeenoughrelativetotheupstream
measurable leakage can bypass it.
head for essentially rectilinear critical flow to occur at some
point along the crest. This ideally permits the flow rate to be 7.2.2.2 Finish—Large weirs constructed in the field should
obtained from a single measurement of the upstream head; a have a finish equivalent to that of smooth concrete. Smaller
corrective coefficient must be applied in practice. This coeffi- weirs, such as those in a laboratory environment, should have
cient has been evaluated experimentally for square-edge weirs a smoothness equivalent to that of rolled sheet metal.
and can be determined analytically for rounded weirs.
7.2.2.3 Level—Thecrestmustnotdeviatefromalevelplane
by more than 0.01 ft (2 mm) at any point or exceed a slope of
5. Significance and Use
0.01 anywhere.
7.2.3 Head Measurement Location—Make the head mea-
5.1 Broad-crested weirs can be used for accurate measure-
surement at a distance of 3 h to 4 h upstream of the
ments of a wide range of flow rates, but their structural
max
upstream face of the weir, where h is the anticipated
simplicity and sturdiness make them particularly useful for
max
maximum head.
measuring large flows under field conditions.
7.2.4 Head-Discharge Relations:
5.2 Because they require vertical sidewalls, broad-crested
7.2.4.1 Basic Equations— The basic relation for the flow
weirs are particularly adaptable to rectangular artificial chan-
rate, Q, over a broad-crested weir is, in compatible units,
nels or to natural and artificial channels that can readily be
3/2 1/2 3/2
lined with vertical sidewalls in the immediate vicinity of the
Q 5 2/3 g C C Bh (1)
~ !
v d
weir.
D5614 − 94 (2008)
FIG. 1 Square-Edge Broad-Crested Weir
longer truly broad crested in accordance with 4.1, since the
h = measured upstream head referenced to the crest el-
flow over the crest is curvilinear throughout.)
evation,
7.2.5 Limiting Conditions—Theflowconditionsanddimen-
B = width of the weir between the vertical side-walls,
g = acceleration due to gravity,
sions of the square-edge weir are subject to the following
C = discharge coefficient that accounts for departures
limits:
d
from ideal conditions, and
(1) h > 0.2 ft (0.06 m), or 0.1 L, whichever is larger;
C = velocity-of-approach coefficient that permits the flow
(2) B > 1 ft (0.3 m);
v
ratetoberelatedtothemeasuredheadratherthanthe
(3) P > 0.5 ft (0.15 m);
total head, H. Then,
(4) 0.1 < h/L < 1.6;
3/2 2 3/2
(5) h/P < 1.6; and
C 5 ~H/h! 5 @~h1αV /2g!/h# (2)
v u
(6) 0.1 < L/P<4.
The minimum h is recommended in order to minimize the
V = average velocity at the head-measurement location,
u
effects of surface tension, viscosity, and surface roughness and
and
to avoid small heads that may be difficult to measure accu-
α = coefficient that accounts for any increase in the
rately. The minimum h/L prevents frictional effects from
kinetic energy term caused by a nonuniform velocity
causing the point of critical flow to shift away from the
distribution. However, in this test method, the ap-
upstream end of the crest. The limitation on maximum h/P is
proach velocity is considered sufficiently close to
intendedtoreducethelikelihoodofupstreamdisturbances,and
uniform (see 7.4.1) for α to be essentially unity.
theremaininglimitationsarerecommendedmainlytoconform
7.2.4.2 In the case of square-edge weirs, both C and C are to the experiments from which the coefficients were obtained.
d v
affected by the head-to-weir height ratio, h/P, so it is conve-
Limiting values of tailwater depth to avoid submergence are
nient to combine them into a single coefficient, C; then, given in 7.4.2.2.
3/2 1/2 3/2
Q 5 ~2/3! g CBh (3)
7.3 Rounded Broad-Crested Weir :
7.3.1 Configuration:
7.2.4.3 Discharge Coeffıcient, C: 7.3.1.1 The rounded broad-crested weir is shown in Fig. 3.
(1) The discharge coefficient is given as a function of h/L As in the square-edge weir, a plane level crest of finite
and h/P in Fig. 2, which has been adapted from ISO 3846- streamwiselengthextendsoverthefullchannelwidthbetween
1989. vertical sidewalls. If the channel is not rectangular or of
(2) The discharge coefficient for h/L≤0.3 is constant at suitable width, construct a contracted section as shown. The
0.850, provided that h/P < 0.15. (For h/L > 0.4, the weir is no upstream face must be vertical and perpendicular to the
D5614 − 94 (2008)
FIG. 2 Discharge Coefficients for Square-Edge Weirs (Dashed Portions of Curves Are Outside of the Recommended Limits)
channel surfaces. However, the following geometric features 7.3.4.1 For rounded-edge weirs, the discharge coefficient,
depart from those of the square-edge weir. C,in Eq 1 is associated with frictional effects along the crest
d
and may be expressed in terms of boundary layer growth as
7.3.1.2 To prevent separation round the upstream corner to
a radius of at least 0.2 H , where H is the anticipated 3/2
max max
C 5 1 2 2δ /L L/B 1 2 δ /L L/h (4)
@ ~ !~ !#@ ~ !~ !#
d * *
maximum upstream total head.
NOTE 2—Sources customarily express rounded-weir dimensions in
δ = boundary-layer displacement thickness.
*
terms of total head, H. Users can place them in terms of measured head,
h, by using (Eq 2) and Table 1.If H/P is limited to a maximum of 1.5 as
The value of δ /L as a function of Reynolds number (see
*
recommended in 7.3.5, H/h will not exceed approximately 1.06.
3.2.9) and relative surface roughness can be determined by
methods given in ISO 4374-1990 and in fluid mechanics texts;
7.3.1.3 Thelengthofthehorizontalpartofthecrestmustbe
at least 1.75 H , and the total length (including radius) must however, unless the surfaces are excessively rough, it is
max
sufficiently accurate to use δ / L=0.003 for relatively small
be at least 2.25 H .
*
max
7.3.1.4 The downstream face of the rounded weir can be and smooth weirs, as in a laboratory, and δ / L=0.004 for
*
larger concrete weirs.
sloped rather than vertical; the only effect is on the tailwater
depth necessary to avoid submergence (see 7.4.2.3).
7.3.4.2 The velocity-of-approach coefficient, C,in Eq 1 is
v
7.3.2 Construction Requirements: given in Table 1 as a function of C Bh/A , where A is the
d u u
7.3.2.1 The watertightness and finish requirements for the cross-sectional
...