ASTM D5129-95(2014)
(Test Method)Standard Test Method for Open Channel Flow Measurement of Water Indirectly by Using Width Contractions
Standard Test Method for Open Channel Flow Measurement of Water Indirectly by Using Width Contractions
SIGNIFICANCE AND USE
5.1 This test method is particularly useful to determine the discharge when it cannot be measured directly by some type of current meter to obtain velocities and with sounding weights to determine the cross section.
5.2 Even under the best conditions, the personnel available cannot cover all points of interest during a major flood. The engineer or technician cannot always obtain reliable results by direct methods if the stage is rising or falling very rapidly, if flowing ice or debris interferes with depth or velocity measurements, or if the cross section of an alluvial channel is scouring or filling significantly.
5.3 Under the worst conditions, access roads are blocked, cableways and bridges may be washed out, and knowledge of the flood frequently comes too late. Therefore, some type of indirect measurement is necessary. The contracted-opening method is commonly used on valley-floor streams.
SCOPE
1.1 This test method covers the computation of discharge (the volume rate of flow) of water in open channels or streams using bridges that cause width contractions as metering devices.2
1.2 This test method produces the maximum discharge for one flow event, usually a specific flood. The computed discharge may be used to help define the high-water portion of a stage-discharge relation.
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:D5129 −95(Reapproved 2014)
Standard Test Method for
Open Channel Flow Measurement of Water Indirectly by
Using Width Contractions
This standard is issued under the fixed designation D5129; 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 3. Terminology
1.1 This test method covers the computation of discharge
3.1 Definitions—For definitions of terms used in this test
(the volume rate of flow) of water in open channels or streams
method, refer to Terminology D1129.
using bridges that cause width contractions as metering de-
2 3.2 Definitions of Terms Specific to This Standard:
vices.
3.2.1 alpha (α)—a velocity-head coefficient that adjusts the
1.2 This test method produces the maximum discharge for
velocity head computed on basis of the mean velocity to the
one flow event, usually a specific flood. The computed dis-
true velocity head.
charge may be used to help define the high-water portion of a
stage-discharge relation. 3.2.2 area (A)—the area of a cross section, parts of a cross
section, or parts of bridges below the water surface. Subscripts
1.3 Thevaluesstatedininch-poundunitsaretoberegarded
indicate specific areas as follows:
as standard. The values given in parentheses are mathematical
conversions to SI units that are provided for information only
A = area of subsection i,
i
and are not considered standard.
A = area of piers or piles that is submerged,
j
1.4 This standard does not purport to address all of the A = area of total cross section 1 (see Fig. 1), and
A = gross area of section 3.
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
3.2.3 conveyance, (K)—a measure of the carrying capacity
priate safety and health practices and determine the applica-
of a channel cross section, or parts of a cross section, and has
bility of regulatory limitations prior to use.
units of cubic feet per second or cubic metres per second.
Conveyance is computed as follows:
2. Referenced Documents
*1.486
2.1 ASTM Standards:
2/3
K 5 AR
n
D1129Terminology Relating to Water
D2777Practice for Determination of Precision and Bias of
where:
Applicable Test Methods of Committee D19 on Water
n = the Manning roughness coefficient,
D3858Test Method for Open-Channel Flow Measurement
2 2
A = the cross-section area, ft (m ), and
of Water by Velocity-Area Method
R = the hydraulic radius, ft (m).
2.2 ISO Standard:
*in SI units = 1.0
ISO 748Liquid Flow Measurements in Open Channels—
The following subscripts refer to specific conveyances for
Velocity-Area Measurements
parts of a cross section:
This test method is under the jurisdiction ofASTM Committee D19 on Water K,K = conveyances of parts of the approach section to
a b
and is the direct responsibility of Subcommittee D19.07 on Sediments,
either side of the projected bottom width of the
Geomorphology, and Open-Channel Flow.
contracted section (see Fig. 2). K is always the
d
Current edition approved Jan. 1, 2014. Published March 2014. Originally
smaller of the two,
approved in 1990. Last previous edition approved in 2008 as D5129–95 (2008).
DOI: 10.1520/D5129-95R14. K = conveyance at the upstream end of the dikes,
d
This test method is similar to methods developed by the U.S. Geological
K = conveyance of subsection i,
i
Survey and described in documents referenced in Footnote 5.
K = conveyance of the part of the approach section
q
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
corresponding to the projected bottom-width, and
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
K = total conveyance of cross section.
Standards volume information, refer to the standard’s Document Summary page on
T
the ASTM website.
4 3.2.4 depth (y)—depth of flow at a cross section. Subscripts
Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
4th Floor, New York, NY 10036, http://www.ansi.org. denote specific cross section depths as follows:
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D5129−95 (2014)
FIG. 1 Definition Sketch of an Open-Channel Contraction
3.2.7 Froude number (F)—an index to the state of flow in a
y = depth of flow in cross section 1(approach section), and
y = depth of flow in cross section 3(contracted section). channel. In a rectangular channel, the flow is tranquil or
subcritical if the Froude number is less than 1.0 and is rapid or
3.2.5 eccentricity (e)—a measure of the symmetry of the
supercritical if it is greater than 1.0.
contraction in relation to the approach channel.
3.2.6 friction slope (S)—the energy loss, h, divided by the 3.2.8 head (h)—static or piezometric head above an arbi-
f f
length of the reach, L. trary datum. Subscripts indicate specific heads as follows:
D5129−95 (2014)
FIG. 2 Definition Sketch of an Eccentric Contraction
h = head loss due to friction, and C = coefficient of discharge,
f
h = stagnation-surface level at embankment face. C' = coefficient of discharge for base condition,
s
n = Manning roughness coefficient, and
3.2.9 hydraulic radius (R)—is equal to the area of a cross
k = discharge coefficient adjustment.
section or subsection divided by its wetted perimeter.
3.2.10 length (L)—length of bridge abutment in direction of
4. Summary of Test Method
flow. Subscripts or symbols identify other lengths as follows:
4.1 The contraction of a stream channel by a bridge creates
anabruptdropinwater-surfaceelevationbetweenanapproach
L = length of dikes,
d
section and the contracted section under the bridge that can be
L = distance from approach section to upstream side of
w
related to the discharge using the bridge as a metering device.
contraction,
u = length of projection of abutment beyond wingwall A field survey is made to determine distances between and
elevationsofhigh-watermarksupstreamanddownstreamfrom
junction, and
x = horizontal distance from the intersection of the abut- thecontractionandthegeometryofthebridgestructure.These
ment and embankment slopes to the location on up- data are used to compute the fall in the water surface between
stream embankment having the same elevation as the an approach section and the contracted section and selected
water surface at section 1. properties of the sections. This information is used along with
dischargecoefficients,determinedbyextensivehydrauliclabo-
3.2.11 wetted perimeter (P)—is the sum of the hypotenuse
ratory investigations and verified at field sites, in a discharge
of a right triangle defined by the distance between adjacent
equation to compute the discharge, Q.
stations of the cross section and the difference in bed eleva-
tions.
5. Significance and Use
3.2.12 width (b)—width of contracted flow section. Sub-
5.1 This test method is particularly useful to determine the
scripts denote specific widths as follows:
dischargewhenitcannotbemeasureddirectlybysometypeof
currentmetertoobtainvelocitiesandwithsoundingweightsto
b = offset distance for straight dikes, and
d
b = width of contracted flow section at water surface.
determine the cross section.
t
3.3 Symbols: 5.2 Even under the best conditions, the personnel available
3.3.1 flow contraction ratio= m. cannot cover all points of interest during a major flood. The
3.3.2 coeffıcients— engineer or technician cannot always obtain reliable results by
D5129−95 (2014)
direct methods if the stage is rising or falling very rapidly, if site cannot be found, other methods, such as the slope-area
flowing ice or debris interferes with depth or velocity method, may yield better results.
measurements, or if the cross section of an alluvial channel is
9.1.1 The channel under the bridge should be relatively
scouring or filling significantly.
stable. Because the amount of scour at the time of the peak
flow cannot be determined, do not use this test method at
5.3 Under the worst conditions, access roads are blocked,
contractions on sand channels.Avoid contractions where large
cableways and bridges may be washed out, and knowledge of
scour holes have formed because the coefficients presented
the flood frequently comes too late. Therefore, some type of
herein do not apply.
indirect measurement is necessary. The contracted-opening
method is commonly used on valley-floor streams. 9.1.2 The fall, ∆h, is the difference in the computed water
surface elevation, between sections 1 and 3, and is not to be
6. Apparatus
less than 0.5 ft (0.15 m). It is defined by high-water marks.
6.1 The equipment generally used for a “transit-stadia” 9.1.3 The fall should be at least four times the friction loss
survey is recommended. An engineer’s transit, a self-leveling between sections 1 and 3. Therefore, avoid long bridges
level with azimuth circle, newer equipment using electronic downstream from heavily wooded flood plains.
circuitry, or other advanced surveying instruments may be
9.2 Theapproachsection,section1,isacrosssectionofthe
used. Standard level rods, a telescoping, 25-ft (7.62 m) level
natural, unconstricted channel upstream from the beginning of
rod, rod levels, hand levels, steel and metallic tapes, tag lines
drawdown. Locate section 1 one bridge-opening width, b,
(small wires with markers fixed at known spacings), vividly
upstreamfromthecontractiontobesureitisupstreamfromthe
colored flagging, survey stakes, a camera, and ample note
drawdown zone. For a completely eccentric contraction, one
paper are necessary items.
with no contraction on one bank, locate section 1two bridge-
6.2 Additional equipment that may expedite a survey in-
openingwidthsupstreambecausesuchacontractionisconsid-
cludes axes, shovels, a portable drafting machine, a boat with
ered as half a normal contraction. Section 1 includes the entire
oars and motor, hip boots, waders, nails, sounding equipment,
width of the valley perpendicular to the direction of flow.
two-way radios, ladder, and rope.
9.2.1 When water-surface profiles are level for some dis-
tancealongtheembankmentorupstreamfromthecontraction,
6.3 Safety equipment should include life jackets, first aid
kit, drinking water, and pocket knives. ponded approach conditions may exist. Even so, survey an
approach section because under some conditions, the approach
7. Sampling
velocity head just balances the friction loss.
7.1 Sampling as defined in Terminology D1129 is not
9.3 The contracted section, section 3, is the minimum area
applicable in this test method.
on a line parallel to the contraction. Generally, the section is
between the abutments. When abutments of a skewed bridge
8. Calibration
areparalleltotheflow,section3isstillsurveyedparalleltothe
8.1 The surveying instruments, transit, etc., should have
contraction even though the minimum section is actually
their adjustment checked, possibly daily when in continuous
perpendicular to the abutments. An angularity factor (see
use or after some occurrence that may have affected the
13.3.1) adjusts the surveyed section to the minimum section.
adjustment.
9.3.1 The area, A , is always the gross area of the section
8.2 The standard check is the “two-peg” or“ double-peg” below the level of the free water surface. No deductions are
test. If the error is over 0.03 ft in 100 ft (0.091 m in 30.48 m),
made for areas occupied by piles, piers, or submerged parts of
theinstrumentshouldbeadjusted.Thetwo-pegtestandhowto the bridge if they lie in the plane of the contracted section.
adjust the instrument are described in many surveying text-
9.3.2 The mean velocity, V , is computed using the gross
books. Refer to manufacturers’ manual for the electronic
area, A .
instruments.
9.3.3 The conveyance, K , is computed with the area of
8.3 If the “reciprocal leveling” technique is used in the piles, piers, or submerged parts deducted from the gross area.
survey, it is the equivalent of the two-peg test between each of
9.3.4 The wetted perimeter used to compute the hydraulic
two successive hubs.
radius, R, will include the lengths of the sides of the piles,
piers, or bridge surfaces in contact with the water.
8.4 Sectional and telescoping level rods should be checked
visually at frequent intervals to be sure sections are not
9.4 Water-surface levels for sections 1 and 3 must be
separated. A proper fit at each joint can be checked by
determined as described below; otherwise, the discharge coef-
measurements across the joint with a steel tape.
ficients will not be applicable.
8.5 All field notes of the transit-stadia survey should be
9.4.1 At section 1, develop a profile on each bank near the
checked before proceeding with the computations.
ends of the section from high-water marks in the vicinity. If
there are not marks in these areas and a large degree of
9. Procedure
contraction exists, draw a profile of marks along the upstream
9.1 Toobtainreliableresults,thesiteselectedshouldbeone face of the embankment. If this profile is level for much of the
wherethegeometryofthebridgeisclosetooneofthestandard distance along the embankment, assume this elevation is the
types or modified types described in Section 11. If a desirable same as that of section 1.
D5129−95 (2014)
9.4.2 For section 3, obtain water-surface elevations along where:
the downstream side of the embankment adjacent to the
i = the subsections, and
abutments regardless of the location of section 3.
T = the total cross section.
9.4.3 Compute water-surface elevations at sections 1 and 3
10.3 The friction loss in the discharge equation is the loss
as the average of the elevations on each bank.
between sections 1 and 3 . The distance between the two
9.4.4 Theoneexceptionisanopeningwithahighdegreeof
sectionsisdividedintothereachfromsection1totheupstream
eccentricity. In this area, determine the elevation of section 3
side of the bridge opening and into the bridge-opening reach.
from marks on the contracted side only and use this elevation
The conveyance at the upstream side of the bridge opening is
tocomputeboththeareaofsection3andfallbetweensections
assumed to be the same as at section 3.The total head loss due
1 and 3.
to friction is computed as:
Q Q
9.5 Complete details of the bridge geometry should be
h 5 L 1L (3)
S D
f w
K K K
obtainedsothatbothplanandelevationdrawingscanbemade. 1 3 3
Determine wingwall angles and lengths, lengths of abutments,
where:
position and slopes of the embankments and abutments,
L = the length of t
...
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