ASTM D5129-95(2008)
(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
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.
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.
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.
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 (Reapproved2008)
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
safety concerns, if any, associated with its use. It is the A = gross area of section 3.
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
2.1 ASTM Standards: *1.486
2/3
K 5 AR
D1129Terminology Relating to Water n
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—
Thefollowingsubscriptsrefertospecificconveyancesforparts
Velocity-Area Measurements
of a cross section:
K,K = conveyances of parts of the approach section to
This test method is under the jurisdiction of ASTM Committee D19 on
a b
Waterand 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 Oct. 1, 2008. Published November 2008. Originally
smaller of the two,
approved in 1990. Last previous edition approved in 2003 as D5129–95 (2003).
DOI: 10.1520/D5129-95R08. 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 (2008)
dischargecoefficients,determinedbyextensivehydrauliclabo-
y = depthofflowincrosssection1(approachsection),and
ratory investigations and verified at field sites, in a discharge
y = depth of flow in cross section 3(contracted section).
equation to compute the discharge, Q.
3.2.5 eccentricity (e)—a measure of the symmetry of the
contraction in relation to the approach channel.
5. Significance and Use
3.2.6 friction slope (S)—the energy loss, h, divided by the
f f
5.1 This test method is particularly useful to determine the
length of the reach, L.
dischargewhenitcannotbemeasureddirectlybysometypeof
3.2.7 Froude number (F)—an index to the state of flow in a currentmetertoobtainvelocitiesandwithsoundingweightsto
channel. In a rectangular channel, the flow is tranquil or
determine the cross section.
subcritical if the Froude number is less than 1.0 and is rapid or
5.2 Even under the best conditions, the personnel available
supercritical if it is greater than 1.0.
cannot cover all points of interest during a major flood. The
3.2.8 head (h)—static or piezometric head above an arbi-
engineer or technician cannot always obtain reliable results by
trary datum. Subscripts indicate specific heads as follows:
direct methods if the stage is rising or falling very rapidly, if
flowingiceordebrisinterfereswithdepthorvelocitymeasure-
h = head loss due to friction, and
f
ments, or if the cross section of an alluvial channel is scouring
h = stagnation-surface level at embankment face.
s
or filling significantly.
3.2.9 hydraulic radius (R)—is equal to the area of a cross
5.3 Under the worst conditions, access roads are blocked,
section or subsection divided by its wetted perimeter.
cableways and bridges may be washed out, and knowledge of
3.2.10 length (L)—length of bridge abutment in direction of
the flood frequently comes too late. Therefore, some type of
flow. Subscripts or symbols identify other lengths as follows:
indirect measurement is necessary. The contracted-opening
method is commonly used on valley-floor streams.
L = length of dikes,
d
L = distance from approach section to upstream side of
w 6. Apparatus
contraction,
6.1 The equipment generally used for a “transit-stadia”
u = length of projection of abutment beyond wingwall
survey is recommended. An engineer’s transit, a self-leveling
junction, and
level with azimuth circle, newer equipment using electronic
x = horizontal distance from the intersection of the abut-
circuitry, or other advanced surveying instruments may be
ment and embankment slopes to the location on
used. Standard level rods, a telescoping, 25-ft (7.62 m) level
upstream embankment having the same elevation as
rod, rod levels, hand levels, steel and metallic tapes, tag lines
the water surface at section 1.
(small wires with markers fixed at known spacings), vividly
3.2.11 wetted perimeter (P)—is the sum of the hypotenuse
colored flagging, survey stakes, a camera, and ample note
of a right triangle defined by the distance between adjacent
paper are necessary items.
stations of the cross section and the difference in bed eleva-
6.2 Additional equipment that may expedite a survey in-
tions.
cludes axes, shovels, a portable drafting machine, a boat with
3.2.12 width (b)—width of contracted flow section. Sub-
oars and motor, hip boots, waders, nails, sounding equipment,
scripts denote specific widths as follows:
two-way radios, ladder, and rope.
b = offset distance for straight dikes, and
d 6.3 Safety equipment should include life jackets, first aid
b = width of contracted flow section at water surface.
t
kit, drinking water, and pocket knives.
3.3 Symbols:
7. Sampling
3.3.1 flow contraction ratio= m.
7.1 Sampling as defined in Terminology D1129 is not
3.3.2 coeffıcients—
applicable in this test method.
C = coefficient of discharge,
8. Calibration
C` = coefficient of discharge for base condition,
n = Manning roughness coefficient, and
8.1 The surveying instruments, transit, etc., should have
k = discharge coefficient adjustment.
their adjustment checked, possibly daily when in continuous
use or after some occurrence that may have affected the
4. Summary of Test Method
adjustment.
4.1 The contraction of a stream channel by a bridge creates
8.2 The standard check is the “two-peg” or“ double-peg”
anabruptdropinwater-surfaceelevationbetweenanapproach
test. If the error is over 0.03 ft in 100 ft (0.091 m in 30.48 m),
section and the contracted section under the bridge that can be
theinstrumentshouldbeadjusted.Thetwo-pegtestandhowto
related to the discharge using the bridge as a metering device.
adjust the instrument are described in many surveying text-
A field survey is made to determine distances between and
books. Refer to manufacturers’ manual for the electronic
elevationsofhigh-watermarksupstreamanddownstreamfrom
instruments.
thecontractionandthegeometryofthebridgestructure.These
data are used to compute the fall in the water surface between 8.3 If the “reciprocal leveling” technique is used in the
an approach section and the contracted section and selected survey, it is the equivalent of the two-peg test between each of
properties of the sections. This information is used along with two successive hubs.
D5129 − 95 (2008)
8.4 Sectional and telescoping level rods should be checked 9.4 Water-surface levels for sections 1 and 3 must be
visually at frequent intervals to be sure sections are not determined as described below; otherwise, the discharge coef-
separated. A proper fit at each joint can be checked by
ficients will not be applicable.
measurements across the joint with a steel tape.
9.4.1 At section 1, develop a profile on each bank near the
ends of the section from high-water marks in the vicinity. If
8.5 All field notes of the transit-stadia survey should be
there are not marks in these areas and a large degree of
checked before proceeding with the computations.
contraction exists, draw a profile of marks along the upstream
face of the embankment. If this profile is level for much of the
9. Procedure
distance along the embankment, assume this elevation is the
9.1 Toobtainreliableresults,thesiteselectedshouldbeone
same as that of section 1.
wherethegeometryofthebridgeisclosetooneofthestandard
9.4.2 For section 3, obtain water-surface elevations along
types or modified types described in Section 11. If a desirable
the downstream side of the embankment adjacent to the
site cannot be found, other methods, such as the slope-area
abutments regardless of the location of section 3.
method, may yield better results.
9.1.1 The channel under the bridge should be relatively 9.4.3 Compute water-surface elevations at sections 1 and 3
stable. Because the amount of scour at the time of the peak as the average of the elevations on each bank.
flow cannot be determined, do not use this test method at
9.4.4 Theoneexceptionisanopeningwithahighdegreeof
contractions on sand channels.Avoid contractions where large
eccentricity. In this area, determine the elevation of section 3
scour holes have formed because the coefficients presented
from marks on the contracted side only and use this elevation
herein do not apply.
tocomputeboththeareaofsection3andfallbetweensections
9.1.2 The fall, ∆h, is the difference in the computed water
1 and 3.
surface elevation, between sections 1 and 3, and is not to be
9.5 Complete details of the bridge geometry should be
less than 0.5 ft (0.15 m). It is defined by high-water marks.
obtainedsothatbothplanandelevationdrawingscanbemade.
9.1.3 The fall should be at least four times the friction loss
Determine wingwall angles and lengths, lengths of abutments,
between sections 1 and 3. Therefore, avoid long bridges
position and slopes of the embankments and abutments,
downstream from heavily wooded flood plains.
elevation of roadway, top width of embankment, details of
9.2 Theapproachsection,section1,isacrosssectionofthe
piers or piles, and elevations of the bottom of girders or beams
natural, unconstricted channel upstream from the beginning of
spanning the contraction. Use a steel tape for most lineal
drawdown. Locate section 1 one bridge-opening width, b,
measurements rather than scaling distances from a plan.
upstreamfromthecontractiontobesureitisupstreamfromthe
Pictures of the upstream corners of both abutments should be
drawdown zone. For a completely eccentric contraction, one
taken. Note which of the four types of contractions the
with no contraction on one bank, locate section 1two bridge-
constriction is.
openingwidthsupstreambecausesuchacontractionisconsid-
ered as half a normal contraction. Section 1 includes the entire
10. Basic Computations
width of the valley perpendicular to the direction of flow.
9.2.1 When water-surface profiles are level for some dis-
10.1 The drop in water-surface level between an upstream
tancealongtheembankmentorupstreamfromthecontraction,
section and a contracted section is related to the corresponding
ponded approach conditions may exist. Even so, survey an
changeinvelocity.Thedischargeequationresultsfromwriting
approach section because under some conditions, the approach
theenergyandcontinuityequationsforthereachbetweenthese
velocity head just balances the friction loss.
two sections, designated as sections 1 and 3 in Fig. 1.
9.3 The contracted section, section 3, is the minimum area
V
on a line parallel to the contraction. Generally, the section is Q 5 CA Œ2g ∆h1α 2 h (1)
S D
3 1 f
2g
between the abutments. When abutments of a skewed bridge
areparalleltotheflow,section3isstillsurveyedparalleltothe
where:
contraction even though the minimum section is actually
Q = discharge,
perpendicular to the abutments. An angularity factor (see
C = coefficient of discharge,
13.3.1) adjusts the surveyed section to the minimum section.
A = gross area of section 3, this is the minimum
9.3.1 The area, A , is always the gross area of the section 3
section between the abutments and is not
below the level of the free water surface. No deductions are
necessarily at the downstream side of the
made for areas occupied by piles, piers, or submerged parts of
bridge,
the bridge if they lie in the plane of the contracted section.
∆h = difference in elevation of the water surface
9.3.2 The mean velocity, V , is computed using the gross
between sections 1 and 3,
area, A .
V1 2
α ⁄2g = weighted average velocity head at 1,
9.3.3 The conveyance, K , is comp
...
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