ASTM D5614-94(2003)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation:D5614–94(Reapproved2003)
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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope nels byWeirs and Flumes—Round-Nose Horizontal Crest
Weirs
1.1 This test method covers measurement of the volumetric
flow rate of water in open channels with two types of
3. Terminology
horizontal broad-crested weirs: those having a square (sharp)
3.1 Definitions—For definitions of terms used in this test
upstream corner and those having a well-rounded upstream
method, refer to Terminology D1129.
corner.
3.2 Definitions of Terms Specific to This Standard:
1.2 The values stated in inch-pound units are to be regarded
3.2.1 boundary layer displacement thickness—theboundary
as the standard. The values given in parentheses are for
layer is a layer of fluid flow adjacent to a solid surface (in this
information only.
case, the weir crest and sidewalls) in which, due to viscous
1.3 This standard does not purport to address all of the
friction, the velocity increases from zero at the stationary
safety concerns, if any, associated with its use. It is the
surface to an essentially frictionless-flow value at the edge of
responsibility of the user of this standard to establish appro-
the layer. The displacement thickness is a distance normal to
priate safety and health practices and determine the applica-
the solid surface that the flow streamlines can be considered to
bility of regulatory limitations prior to use.
have been displaced by virtue of the boundary-layer informa-
2. Referenced Documents tion.
3.2.2 crest—the horizontal plane surface of the weir.
2.1 ASTM Standards:
3.2.3 critical flow—open channel flow in which the energy,
D1129 Terminology Relating to Water
expressed in terms of depth plus velocity head, is a minimum
D2777 Practice for Determination of Precision and Bias of
for a given flow rate and channel. The Froude number is unity
Applicable Methods of Committee D19 on Water
at critical flow.
D3858 Practice for Open-Channel Flow Measurement of
2 3.2.4 Froude number—a dimensionless number expressing
Water by Velocity-Area Method
the ratio of inertial to gravity forces in free surface flow. It is
2.2 ISO Standards:
equal to the average velocity divided by the square root of the
ISO 555-1973 Liquid Flow Measurement in Open
product of the average depth and the acceleration due to
Channels—Dilution Methods for Measurement of Steady
3 gravity.
Flow—Constant Rate Injection Method
3.2.5 head—in this test method, the depth of water above a
ISO 3846-1989 Liquid Flow Measurement in Open Chan-
specified elevation. The measuring head is the depth of flow
nels by Weirs and Flumes—Rectangular Broad-Crested
above the weir crest measured at an appropriate location
Weirs
upstream of the weir; the downstream head is referenced
ISO 4373-1979 Measurement of Liquid Flow in Open
similarly to the crest elevation and measured downstream of
Channels—Water Level Measuring Devices
the weir. The head plus the corresponding velocity head is
ISO 4374-1990 Liquid Flow Measurement in Open Chan-
often termed the total head or total energy head.
3.2.6 hydraulic jump—an abrupt transition from supercriti-
cal flow to subcritical or tranquil flow, accompanied by
This test method is under the jurisdiction of ASTM Committee D19 on Water
considerable turbulence or gravity waves, or both.
and is the direct responsibility of Subcommittee D19.07 on Sediments, Geomor-
3.2.7 nappe—thecurvedsheetorjetofwateroverfallingthe
phology, and Open-Channel Flow.
Current edition approved June 10, 2003. Published August 2003. Originally
downstream end of the weir.
approved in 1994. Last previous edition approved in 1998 as D5614–94(1998).
3.2.8 primary device—thedevice(inthiscase,theweir)that
Annual Book of ASTM Standards, Vol 11.01.
creates a hydrodynamic condition that can be sensed by the
Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
4th Floor, New York, NY 10036. secondary instrument.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D5614–94 (2003)
3.2.9 Reynolds number—a dimensionless number express- 6. Interferences
ingtheratioofinertialtoviscousforcesinaflow.Thepertinent
6.1 Broad-crestedweirsarenotsuitableforuseinsediment-
Reynolds number on the weir crest is equal to the (critical)
laden streams that are carrying heavy bed loads. However,
velocity multiplied by the crest length and divided by the
floating debris is readily passed, particularly by the rounded
kinematic viscosity of the water.
weir (see 7.2.1).
3.2.10 secondary instrument—in this case, a device that
6.2 Broad-crested weirs cannot be used beyond submer-
measures the depth of flow (referenced to the crest elevation)
gence limits because insufficient data exist to document their
at an appropriate location upstream of the weir.The secondary
performance. It is therefore necessary to adhere to the
instrumentmayalsoconvertthismeasuredheadtoanindicated
tailwater-level limitations described in this test method.
flow rate or could totalize flow rate.
7. Apparatus
3.2.11 stilling well—a small free-surface reservoir con-
nected through a restricted passage to the head-measurement 7.1 A broad-crested weir measuring system consists of the
location upstream of the weir so that a head measurement can
weir itself and its immediate channel (the primary) and a head
be made under quiescent conditions. measuring device (the secondary). The secondary device can
range from a simple staff gage for visual readings to an
3.2.12 subcritical flow—open channel flow that is deeper
instrument that senses the depth continuously, converts it to a
and at lower velocity than critical flow for the same flow rate;
flow rate, and displays or transmits a readout or record of the
sometimescalledtranquilflow.AFroudenumberlessthanone
instantaneous flow rate or totalized flow, or both.
exists.
7.2 Square-Edge (Rectangular) Broad-Crested Weir:
3.2.13 submergence—a condition in which the water level
7.2.1 Configuration—The square-edge broad-crested weir
onthedownstreamsideoftheweirishighenoughtoaffectthe
as shown in Fig. 1 is rectangular in longitudinal profile and
flow over the weir and hence alter the head-discharge relation.
provides a plane horizontal crest that has finite length in the
It is usually expressed as a ratio or percentage of downstream
direction of flow and extends the full width of the channel
to upstream head or downstream to upstream total head.
between vertical sidewalls. A contracted section must be
3.2.14 supercritical flow—open channel flow that is shal-
constructed as shown (see also 7.4.1.2) if the channel does not
lowerandathighervelocitythancriticalflowforthesameflow
have vertical sidewalls or is wider than the desired crest. The
rate. A Froude number greater than one exists.
vertical sidewalls must extend downstream of the downstream
3.2.15 tailwater—the water elevation immediately down-
faceoftheweiradistanceofatleasttwicethemaximumhead.
stream of the weir.
Recommended limits on dimensions and geometric ratios are
3.2.16 tranquil flow—see subcritical flow.
given in 7.2.5. The upstream and downstream faces must be
3.2.17 velocity head—the square of the average velocity
vertical and perpendicular to the channel surfaces, and it is
divided by twice the acceleration due to gravity.
important that the upstream corner be square and sharp.
NOTE 1—High flow rates combined with floating debris may damage
4. Summary of Test Method
the sharp edge; rounded-edge weirs should be considered for such
4.1 In broad-crested weirs, the length of the horizontal crest
applications.
inthedirectionofflowislargeenoughrelativetotheupstream
7.2.2 Construction Requirements:
head for essentially rectilinear critical flow to occur at some
7.2.2.1 The structure must be sturdy enough to withstand
point along the crest. This ideally permits the flow rate to be
the maximum flow rate and must be watertight so that no
obtained from a single measurement of the upstream head; a
measurable leakage can bypass it.
corrective coefficient must be applied in practice. This coeffi-
7.2.2.2 Finish—Large weirs constructed in the field should
cient has been evaluated experimentally for square-edge weirs
have a finish equivalent to that of smooth concrete. Smaller
and can be determined analytically for rounded weirs.
weirs, such as those in a laboratory environment, should have
a smoothness equivalent to that of rolled sheet metal.
5. Significance and Use
7.2.2.3 Level—Thecrestmustnotdeviatefromalevelplane
5.1 Broad-crested weirs can be used for accurate measure-
by more than 0.01 ft (2 mm) at any point or exceed a slope of
ments of a wide range of flow rates, but their structural
0.01 anywhere.
simplicity and sturdiness make them particularly useful for
7.2.3 Head Measurement Location—Make the head mea-
measuring large flows under field conditions.
surement at a distance of 3 h to 4 h upstream of the
max
5.2 Because they require vertical sidewalls, broad-crested upstream face of the weir, where h is the anticipated
max
weirs are particularly adaptable to rectangular artificial chan- maximum head.
nels or to natural and artificial channels that can readily be 7.2.4 Head-Discharge Relations:
lined with vertical sidewalls in the immediate vicinity of the 7.2.4.1 Basic Equations—The basic relation for the flow
weir. rate, Q, over a broad-crested weir is, in compatible units,
D5614–94 (2003)
FIG. 1 Square-Edge Broad-Crested Weir
3 2 1 2 3 2
/ / /
(1) The discharge coefficient is given as a function of h/L
Q 5 2 3 g C C Bh (1)
~ !
v d
/
and h/P in Fig. 2, which has been adapted from ISO 3846-
1989.
where:
(2) The discharge coefficient for h/L#0.3 is constant at
h = measured upstream head referenced to the crest el-
0.850, provided that h/P < 0.15. (For h/L > 0.4, the weir is no
evation,
longer truly broad crested in accordance with 4.1, since the
B = width of the weir between the vertical side-walls,
flow over the crest is curvilinear throughout.)
g = acceleration due to gravity,
7.2.5 Limiting Conditions—Theflowconditionsanddimen-
C = discharge coefficient that accounts for departures
d
sions of the square-edge weir are subject to the following
from ideal conditions, and
limits:
C = velocity-of-approach coefficient that permits the flow
v
rate to be related to the measured head rather than the (1) h > 0.2 ft (0.06 m), or 0.1 L, whichever is larger;
total head, H. Then,
(2) B > 1 ft (0.3 m);
3 2 2 3 2
/ / (3) P > 0.5 ft (0.15 m);
C 5 H/h! 5[ h1aV /2g!/h] (2)
~ ~
v u
(4) 0.1 < h/L < 1.6;
(5) h/P < 1.6; and
where:
(6) 0.1 < L/P<4.
V = average velocity at the head-measurement location,
u
The minimum h is recommended in order to minimize the
and
effects of surface tension, viscosity, and surface roughness and
a = coefficientthataccountsforanyincreaseinthekinetic
to avoid small heads that may be difficult to measure accu-
energy term caused by a nonuniform velocity distri-
rately. The minimum h/L prevents frictional effects from
bution. However, in this test method, the approach
causing the point of critical flow to shift away from the
velocity is considered sufficiently close to uniform
upstream end of the crest. The limitation on maximum h/P is
(see 7.4.1) for a to be essentially unity.
intendedtoreducethelikelihoodofupstreamdisturbances,and
7.2.4.2 In the case of square-edge weirs, both C and C are
d v
the remaining limitations are recommended mainly to conform
affected by the head-to-weir height ratio, h/P, so it is conve-
to the experiments from which the coefficients were obtained.
nient to combine them into a single coefficient, C; then,
Limiting values of tailwater depth to avoid submergence are
3 2 1 2 3 2
/ / /
Q 5 2 3 g CBh (3)
~ !
given in 7.4.2.2.
/
7.3 Rounded Broad-Crested Weir:
7.2.4.3 Discharge Coeffıcient, C: 7.3.1 Configuration:
D5614–94 (2003)
FIG. 2 Discharge Coefficients for Square-Edge Weirs (Dashed Portions of Curves Are Outside of the Recommended Limits)
7.3.1.1 The rounded broad-crested weir is shown in Fig. 3. 7.3.3 Head Measurement Location—Measure the head at a
As in the square-edge weir, a plane level crest of finite distance of 3 H to 4 H upstream of the upstream face of the
max
streamwiselengthextendsoverthefullchannelwidthbetween weir.
vertical sidewalls. If the channel is not rectangular or of
7.3.4 Head-Discharge Relations:
suitable width, construct a contracted section as shown. The
7.3.4.1 For rounded-edge weirs, the discharge coefficient,
upstream face must be vertical and perpendicular to the
C , in Eq 1 is associated with frictional effects along the crest
d
channel surfaces. However, the following geometric features
and may be expressed in terms of boundary layer growth as
depart from those of the square-edge weir.
3 2
/
C 5[1 2 ~2d /L! ~L/B!#[1 2 ~d /L! ~L/h!# (4)
d * *
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
max max
maximum upstream total head.
where:
d = boundary-layer displacement thickness.
*
NOTE 2—Sources customarily express rounded-weir dimensions in
Thevalueof d /LasafunctionofReynoldsnumber(see3.2.9)
terms of total head, H. Users can place them in terms of measured head, *
and relative surface roughness can be determined by methods
h, by using (Eq 2) and Table 1.If H/P is limited to a maximum of 1.5 as
recommended in 7.3.5, H/h will not exceed approximately 1.06. giveninISO4374-1990andinfluidmechanicstexts;however,
unless the surfaces are excessively rough, it is sufficiently
7.3.1.3 Thelengthofthehorizontalpartofthecrestmustbe
accurate to use d / L=0.003 for relatively small and smooth
*
at least 1.75 H , and the total length (including radius) must
max
weirs, as in a laboratory, and d /L=0.004 for larger concrete
*
be at least 2.25 H .
max
weirs.
7.3.1.4 The downstream face of the rounded weir can be
7.3.4.2 The velocity-of-approach coefficient, C,inEq1is
sloped rather than vertical; the only effect is on the tailwater v
given in Table 1 as a function of C Bh/A , where A is the
depth necessary to avoid submergence (see 7.4.2.3). d u u
cross-sectional area of the approach flow and is equal to B
7.3.2 Construction Requirements:
(P+ h).
7.3.2.1 The watertightness and finish requirements for the
7.3.5 Limiting Conditions—Theflowconditionsanddimen-
rounded weir are the same
...