ASTM D5129-95(1999)
(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
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 the standard. The SI units given in parentheses are for information only.
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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Standards Content (Sample)
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.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.
Designation: D 5129 – 95 (Reapproved 1999)
Standard Test Method for
Open Channel Flow Measurement of Water Indirectly by
Using Width Contractions
This standard is issued under the fixed designation D 5129; 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 velocity head computed on basis of the mean velocity to the
true velocity head.
1.1 This test method covers the computation of discharge
3.2.2 area (A)— the area of a cross section, parts of a cross
(the volume rate of flow) of water in open channels or streams
section, or parts of bridges below the water surface. Subscripts
using bridges that cause width contractions as metering de-
indicate specific areas as follows:
vices.
1.2 This test method produces the maximum discharge for
one flow event, usually a specific flood. The computed dis-
A 5 area of subsection i,
i
charge may be used to help define the high-water portion of a
A 5 area of piers or piles that is submerged,
j
stage-discharge relation.
A 5 area of total cross section 1 (see Fig. 1), and
1.3 The values stated in inch-pound units are to be regarded
A 5 gross area of section 3.
as the standard. The SI units given in parentheses are for
3.2.3 conveyance, (K)—a measure of the carrying capacity
information only.
of a channel cross section, or parts of a cross section, and has
1.4 This standard does not purport to address all of the
units of cubic feet per second or cubic metres per second.
safety concerns, if any, associated with its use. It is the
Conveyance is computed as follows:
responsibility of the user of this standard to establish appro-
*1.486
2/3
priate safety and health practices and determine the applica-
K 5 AR
n
bility of regulatory limitations prior to use.
where:
2. Referenced Documents
n 5 the Manning roughness coefficient,
2 2
A 5 the cross-section area, ft (m ), and
2.1 ASTM Standards:
R 5 the hydraulic radius, ft (m).
D 1129 Terminology Relating to Water
*in SI units 5 1.0
D 2777 Practice for Determination of Precision and Bias of
The following subscripts refer to specific conveyances for
Applicable Methods of Committee D-19 on Water
parts of a cross section:
D 3858 Test Method for Open Channel Flow Measurements
of Water by Velocity-Area Method
2.2 ISO Standard:
K ,K 5 conveyances of parts of the approach section to
a b
ISO 748 Liquid Flow Measurements in Open Channels—
either side of the projected bottom width of the
Velocity-Area Measurements
contracted section (see Fig. 2). K is always the
d
smaller of the two,
3. Terminology
K 5 conveyance at the upstream end of the dikes,
d
3.1 Definitions—For definitions of terms used in this test
K 5 conveyance of subsection i,
i
method, refer to Terminology D 1129.
K 5 conveyance of the part of the approach section
q
3.2 Definitions of Terms Specific to This Standard:
corresponding to the projected bottom-width, and
3.2.1 alpha (a)—a velocity-head coefficient that adjusts the
K 5 total conveyance of cross section.
T
3.2.4 depth (y)—depth of flow at a cross section. Subscripts
denote specific cross section depths as follows:
This test method is under the jurisdiction of ASTM Committee D-19 on
Waterand is the direct responsibility of Subcommittee D19.07 on Sediments,
Geomorphology, and Open-Channel Flow.
Current edition approved Sept. 10, 1995. Published November 1995. Originally
y 5 depth of flow in cross section 1(approach section),
published as D 5129 – 90. Last previous edition D 5129 – 90.
and
This test method is similar to methods developed by the U.S. Geological
y 5 depth of flow in cross section 3(contracted section).
Survey and described in documents referenced in Footnote 5.
3.2.5 eccentricity (e)—a measure of the symmetry of the
Annual Book of ASTM Standards, Vol 11.01.
Available from American National Standards Institute, 11 W. 42nd St., 13th
contraction in relation to the approach channel.
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.
Contact ASTM International (www.astm.org) for the latest information.
D 5129
3.2.6 friction slope (S )— the energy loss, h , divided by the 5. Significance and Use
f f
length of the reach, L.
5.1 This test method is particularly useful to determine the
3.2.7 Froude number (F)—an index to the state of flow in a
discharge when it cannot be measured directly by some type of
channel. In a rectangular channel, the flow is tranquil or
current meter to obtain velocities and with sounding weights to
subcritical if the Froude number is less than 1.0 and is rapid or
determine the cross section.
supercritical if it is greater than 1.0.
5.2 Even under the best conditions, the personnel available
3.2.8 head (h)—static or piezometric head above an arbi-
cannot cover all points of interest during a major flood. The
trary datum. Subscripts indicate specific heads as follows:
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 measure-
h 5 head loss due to friction, and
f
ments, or if the cross section of an alluvial channel is scouring
h 5 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 5 length of dikes,
d
6. Apparatus
L 5 distance from approach section to upstream side of
w
contraction, 6.1 The equipment generally used for a “transit-stadia”
u 5 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 5 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.
6.3 Safety equipment should include life jackets, first aid
kit, drinking water, and pocket knives.
b 5 offset distance for straight dikes, and
d
b 5 width of contracted flow section at water surface.
7. Sampling
t
3.3 Symbols: Symbols:
7.1 Sampling as defined in Terminology D 1129 is not
3.3.1 flow contraction ratio 5 m.
applicable in this test method.
3.3.2 coeffıcients—
8. Calibration
8.1 The surveying instruments, transit, etc., should have
C 5 coefficient of discharge,
their adjustment checked, possibly daily when in continuous
C8 5 coefficient of discharge for base condition,
use or after some occurrence that may have affected the
n 5 Manning roughness coefficient, and
adjustment.
k 5 discharge coefficient adjustment.
8.2 The standard check is the “two-peg” or“ double-peg”
4. Summary of Test Method
test. If the error is over 0.03 ft in 100 ft (0.091 m in 30.48 m),
4.1 The contraction of a stream channel by a bridge creates the instrument should be adjusted. The two-peg test and how to
an abrupt drop in water-surface elevation between an approach adjust the instrument are described in many surveying text-
section and the contracted section under the bridge that can be books. Refer to manufacturers’ manual for the electronic
related to the discharge using the bridge as a metering device. instruments.
A field survey is made to determine distances between and 8.3 If the “reciprocal leveling” technique is used in the
elevations of high-water marks upstream and downstream from survey, it is the equivalent of the two-peg test between each of
the contraction and the geometry of the bridge structure. These two successive hubs.
data are used to compute the fall in the water surface between 8.4 Sectional and telescoping level rods should be checked
an approach section and the contracted section and selected visually at frequent intervals to be sure sections are not
properties of the sections. This information is used along with separated. A proper fit at each joint can be checked by
discharge coefficients, determined by extensive hydraulic labo- measurements across the joint with a steel tape.
ratory investigations and verified at field sites, in a discharge 8.5 All field notes of the transit-stadia survey should be
equation to compute the discharge, Q. checked before proceeding with the computations.
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 5129
9. Procedure contraction exists, draw a profile of marks along the upstream
face of the embankment. If this profile is level for much of the
9.1 To obtain reliable results, the site selected should be one
distance along the embankment, assume this elevation is the
where the geometry of the bridge is close to one of the standard
same as that of section 1.
types or modified types described in Section 11. If a desirable
site cannot be found, other methods, such as the slope-area 9.4.2 For section 3, obtain water-surface elevations along
the downstream side of the embankment adjacent to the
method, may yield better results.
9.1.1 The channel under the bridge should be relatively abutments regardless of the location of section 3.
stable. Because the amount of scour at the time of the peak
9.4.3 Compute water-surface elevations at sections 1 and 3
flow cannot be determined, do not use this test method at
as the average of the elevations on each bank.
contractions on sand channels. Avoid contractions where large
9.4.4 The one exception is an opening with a high degree of
scour holes have formed because the coefficients presented
eccentricity. In this area, determine the elevation of section 3
herein do not apply.
from marks on the contracted side only and use this elevation
9.1.2 The fall, Dh, is the difference in the computed water
to compute both the area of section 3 and fall between sections
surface elevation, between sections 1 and 3, and is not to be
1 and 3.
less than 0.5 ft (0.15 m). It is defined by high-water marks.
9.5 Complete details of the bridge geometry should be
9.1.3 The fall should be at least four times the friction loss
obtained so that both plan and elevation drawings can be made.
between sections 1 and 3. Therefore, avoid long bridges
Determine wingwall angles and lengths, lengths of abutments,
downstream from heavily wooded flood plains.
position and slopes of the embankments and abutments,
9.2 The approach section, section 1, is a cross section of the
elevation of roadway, top width of embankment, details of
natural, unconstricted channel upstream from the beginning of
piers or piles, and elevations of the bottom of girders or beams
drawdown. Locate section 1 one bridge-opening width, b,
spanning the contraction. Use a steel tape for most lineal
upstream from the contraction to be sure it is upstream from the
measurements rather than scaling distances from a plan.
drawdown zone. For a completely eccentric contraction, one
Pictures of the upstream corners of both abutments should be
with no contraction on one bank, locate section 1two bridge-
taken. Note which of the four types of contractions the
opening widths upstream because such a contraction is consid-
constriction is.
ered as half a normal contraction. Section 1 includes the entire
width of the valley perpendicular to the direction of flow.
10. Basic Computations
9.2.1 When water-surface profiles are level for some dis-
10.1 The drop in water-surface level between an upstream
tance along the embankment or upstream from the contraction,
ponded approach conditions may exist. Even so, survey an section and a contracted section is related to the corresponding
change in velocity. The discharge equation results from writing
approach section because under some conditions, the approach
velocity head just balances the friction loss. the energy and continuity equations for the reach between these
two sections, designated as sections 1 and 3 in Fig. 1.
9.3 The contracted section, section 3, is the minimum area
on a line parallel to the contraction. Generally, the section is
V
between the abutments. When abutments of a skewed bridge
Q 5 CA ˛2gSDh1a 2 hD (1)
3 1 f
2g
are parallel to the flow, section 3 is still surveyed parallel to the
contraction even though the minimum section is actually
where:
perpendicular to the abutments. An angularity factor (see
Q 5 discharge,
C 5 coefficient of discharge,
13.3.1) adjusts the surveyed section to the minimum section.
A 5 gross area of section 3, this is the minimum
9.3.1 The area, A , is always the gross area of the section
section between the abutments and is not nec-
below the level of the free water surface. No deductions are
essarily at the downstream side of the bridge,
made for areas occupied by piles, piers, or submerged parts of
Dh 5 difference in elevation of the water surface
the bridge if they lie in the plane of the contracted section.
between sections 1 and 3,
9.3.2 The mean velocity, V , is computed using the gross
V
a ⁄ ;2g 5 weighted average velocity head at 1,
area, A . 1 1
Q
V 5 average velocity, ⁄A1, and
9.3.3 The conveyance, K , is computed with the area of
h 5 head loss due to friction between sections 1 and
f
piles, piers, or subme
...
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