ASTM D5130-95(1999)
(Test Method)Standard Test Method for Open-Channel Flow Measurement of Water Indirectly by Slope-Area Method
Standard Test Method for Open-Channel Flow Measurement of Water Indirectly by Slope-Area Method
SCOPE
1.1 This test method covers the computation of discharge (the volume rate of flow) of water in open channels or streams using representative cross-sectional characteristics, the water-surface slope, and coefficient of channel roughness as input to gradually-varied flow computations.
1.2 This test method produces an indirect measurement of the maximum discharge for one flow event, usually a specific flood. The computed discharge may be used to help define the high-water segment 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.
General Information
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Standards Content (Sample)
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Designation: D 5130 – 95 (Reapproved 1999)
Standard Test Method for
Open-Channel Flow Measurement of Water Indirectly by
Slope-Area Method
This standard is issued under the fixed designation D 5130; 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 method, refer to Terminology D 1129.
3.2 Definitions of Terms Specific to This Standard: Several
1.1 This test method covers the computation of discharge
of the following terms are illustrated in Fig. 1:
(the volume rate of flow) of water in open channels or streams
3.2.1 alpha (a)—a velocity-head coefficient that represents
using representative cross-sectional characteristics, the water-
the ratio of the true velocity head to the velocity head
surface slope, and coefficient of channel roughness as input to
computed on the basis of the mean velocity. It is assumed equal
gradually-varied flow computations.
to 1.0 if the cross section is not subdivided. For subdivided
1.2 This test method produces an indirect measurement of
sections, a is computed as follows:
the maximum discharge for one flow event, usually a specific
flood. The computed discharge may be used to help define the a5
k
i
high-water segment of a stage-discharge relation. (
S D
A
i
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
K
safety concerns, if any, associated with its use. It is the T
A
responsibility of the user of this standard to establish appro- T
priate safety and health practices and determine the applica-
where:
bility of regulatory limitations prior to use.
K and A 5 the conveyance and area of the subsection
indicated by the subscript i, and
2. Referenced Documents
K and A 5 the conveyance and area of the entire cross
T T
2.1 ASTM Standards:
section.
D 1129 Terminology Relating to Water
3.2.2 conveyance (K)—a measure of the carrying capacity
D 2777 Practice for Determination of Precision and Bias of
of a channel and has dimensions of cubic feet per second or
Applicable Methods of Committee D-19 on Water
cubic metres per second. Conveyance is computed as follows:
D 3858 Practice for Open-Channel Flow Measurement of
1.486
Water by Velocity-Area Method 2/3
K 5 AR
n
2.2 ISO Standards:
ISO 748 Liquid Flow Measurements in Open Channels—
Velocity-Area Method
where:
ISO 1070 Liquid Flow Measurements in Open Channels—
n 5 the Manning roughness coefficient,
4 2 2
Slope-Area Method
A 5 the cross-section area, ft (m ), and
R 5 the hydraulic radius, ft (m).
3. Terminology
NOTE 1—1.486 5 1.00 SI unit.
3.1 Definitions: For definitions of terms used in this test
3.2.3 cross sections (numbered consecutively in downstream
order)—representative of a reach of channel and are positioned
This test method is under the jurisdiction of ASTM Committee D-19 on Water as nearly as possible at right angles to the direction of flow.
and is the direct responsibility of Subcommittee D19.07 on Sediments, Geomor-
They must be defined by coordinates of horizontal distance and
phology, and Open-Channel Flow.
ground elevation. Sufficient ground points must be obtained so
Current edition approved Sept. 10, 1995. Published November 1995. Original-
that straight-line connection of the coordinates will adequately
lypublished as D 5130 – 90. Last previous edition D 5130 – 90.
This test method is similar to methods developed by the U.S. Geological describe the cross-section geometry. If major breaks in the
Survey and described in documents referenced in Footnotes 5, 6, and 7.
high-water profile are evident, cross sections should be located
Annual Book of ASTM Standards, Vol 11.01.
at the breaks.
Available from American National Standards Institute, 1430 Broadway, NY,
3.2.4 cross-section area (A)—the area of the water below
NY 10018.
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 5130
3.2.8 Froude number (F)—an index to the state of flow in
the channel. In a prismatic channel, the flow is tranquil or
subcritical if the Froude number is less than 1.0 and is rapid or
supercritical if it is greater than 1.0. The Froude number is
computed as follows:
V
F 5
gd
=
m
where:
V 5 the mean velocity in ft/s (m/s),
d 5 the average depth in the cross section in feet, and
m
g 5 the acceleration of gravity in ft/s/s (m/s/s).
3.2.9 high-water marks—the evidence of the highest stage
reached by a flood. Debris, stains, foam lines, and scour marks
are common types of high-water marks. Water-surface slopes
are determined by the elevations of these marks.
3.2.10 hydraulic radius (R)—defined as the area of a cross
section or subsection divided by the corresponding wetted
FIG. 1 Definition Sketch of a Slope-Area Reach
perimeter.
3.2.11 roughness coeffıcient (n)— or Manning’s n is used in
the Manning equation. Roughness coefficient or Manning’s n is
the high-water surface elevations that are computed by assum-
a measure of the resistance to flow in a channel. The factors
ing a straight-line interpolation between elevations on each
that influence the magnitude of the resistance to flow include
bank. The area is computed as the summation of the products
the character of the bed material, cross section irregularities,
of mean depth multiplied by the width between stations of the
depth of flow, vegetation, and alignment of the channel. A
cross section.
reasonable evaluation of the resistance to flow in a channel
3.2.5 friction loss (h )—the loss due to boundary friction in
f
depends on the experience of the person selecting the coeffi-
the reach and is equivalent to the following:
cient and reference to texts and reports that contain values for
D h1Dh 2 k~Dh !
,
v v 5 6
similar stream and flow conditions. (See 9.3).
3.2.12 velocity head (h )—computed as follows:
where: v
Dh 5 the fall in the reach, 2
aV
Dh 5 the upstream velocity head minus the down- h 5
v v
2g
stream velocity head,
(kDh ) 5 the energy loss due to acceleration or deceleration
v
where:
and to eddies in a contracting or expanding reach,
a5 the velocity-head coefficient,
where k is a coefficient for energy losses.
V 5 the mean velocity in the cross section in ft/s (m/s), and
All of the equations presented in this standard are based on
g 5 the acceleration of gravity in ft/s/s (m/s/s).
the assumption that k is zero for contracting reaches and 0.5 for
3.2.13 wetted perimeter (WP)—the total length of the
expanding reaches.
boundary between the channel bed and the water for a cross
3.2.6 fall (Dh)—the drop in the water-surface computed as
section. It is computed as the sum of the hypotenuse of the
the difference in the average water-surface elevation at adja-
right triangle defined by the distance between adjacent stations
cent cross sections.
of the cross section and the difference in bed elevations.
3.2.7 friction slope (S )—the energy loss divided by the
f
length of the reach or:
4. Summary of Test Method
h
f
4.1 The slope-area method is used to indirectly determine
S 5
f
L
the discharge through a reach of channel, usually after a flood,
using evidence left by the event and the physical characteristics
that becomes:
of the channel reach. A field survey is made to determine
Dh1Dh distances between and elevations of high-water marks and to
v
S 5
f
L define cross sections of the stream. These data are used to
compute the fall in the water surface between sections and
selected properties of the sections. This information is used
when Dh is negative (for a contracting reach),
v
or:
Dh
Benson, M. A., and Dalrymple, T., “General Field and Office Procedures for
v
Dh 1
2 Indirect Discharge Measurements,” Techniques of Water Resources Investigations,
S 5
f Book 3, Chapter , U.S. Geological Survey, 1967.
L
Matthai, Howard F., “Measurement of Peak Discharge at Width Contractions
by Indirect Methods,” Techniques of Water Resources Investigations, Book 3,
when D h is positive (for an expanding reach). Chapter A4, U.S. Geological Survey, 1984.
v
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 5130
along with Manning’s n in the Manning equation to compute 8.3 If the “reciprocal leveling” technique is used in the
the discharge, Q. The Manning equation in terms of discharge, survey, it is the equivalent of the two-peg test between each of
Q, is as follows: the two successive hubs.
8.4 Sectional and telescoping level rods should be checked
1.486
2/3 ½
Q 5 AR S or Q
f visually at frequent intervals to be sure sections are not
n
½
separated. A proper fit at each joint can be quickly checked by
5 KS
f
measurements across the joint with a steel tape.
8.5 All field notes of the transit-stadia survey should be
The symbols on the right sides of the equations are defined
checked before proceeding with the computations.
in Section 3.
9. Procedure
5. Significance and Use
9.1 Selection of a reach of channel is the first and probably
5.1 This test method is particularly useful for determining
the most important step to obtain reliable results. Ideal reaches
the discharge when it cannot be measured directly by some
rarely exist; so the various elements in a reach must be
type of current meter to obtain velocities and with sounding
evaluated and compromises made so that the best reach
weights to determine the cross section.
available is selected. Selection soon after the flood event is
5.2 Even under optimum conditions, the personnel available
recommended because livestock, humans, heavy rain, and bank
cannot cover all points of interest during a major flood. Field
sloughing can destroy high-water marks.
personnel cannot always obtain reliable results by direct
9.1.1 Good high-water marks are essential for good results.
methods if the stage is rising or falling very rapidly, if flowing
At times a reach with poor quality marks must be used because
ice or debris interferes with depth or velocity measurements.
of other complicating factors such as inflow, proximity to a
5.3 Under the worst conditions, access roads are blocked,
gaging station, etc. List high-water marks in a format such as
cableways and bridges may be washed out, and knowledge of
shown in Fig. 2.
the flood frequently comes too late to obtain direct measure-
9.1.2 The nearer the reach to a uniform channel the better.
ments of flow. Therefore, some type of indirect measurement is
Marked changes in channel shape should be avoided because
necessary. The slope-area method is a commonly used method.
of uncertainties regarding the value of the expansion/
contraction loss coefficient ( k) and the friction losses in the
6. Apparatus
reach. Changes in channel conveyance should be fairly uni-
6.1 The equipment generally used for a “transit-stadia”
form from section to section to be consistent with the assump-
survey is recommended. An engineer’s transit, a self-leveling
tion that the mean conveyance is equal to the geometric mean
level with azimuth circle, newer equipment using electronic
of the conveyances at the end sections.
circuitry, or other advanced surveying instruments may be
9.1.3 A reach with flow confined to a roughly trapezoidal
used. Standard level rods, a telescoping, 25-ft (7.6 m) level rod,
channel is desirable because roughness coefficients have been
rod levels, hand levels, steel and metallic tapes, tag lines (small
determined for such shapes. However, compound channels,
wires with markers fixed at known spacings), vividly colored
those with overbank flow, for example, can be used if they are
flagging, survey stakes, a camera (preferably stereo) with color
properly subdivided into subareas that are approximately
film, light meter, and ample note paper are necessary items.
trapezoidal.
6.2 Additional equipment that may expedite a survey in-
9.1.4 A straight reach that contracts is preferred, but both
clude axes, shovels, a portable drafting machine, a boat with
conditions seldom exist in the same reach. Whether or not a
oars and motor, hip boots, waders, rain gear, nails, sounding
reach is contracting or expanding depends solely upon the
equipment, two-way radios, ladder, and rope.
difference in velocity head (Dh ) between sections. The reach
v
6.3 Safety equipment should include life jackets, first aid
is contracting if the difference in the velocity head is negative.
kit, drinking water, and pocket knives.
The reach is expanding if the velocity-head difference is
positive.
7. Sampling
9.1.5 Cross sections are assumed to be carrying water in
7.1 Sampling as defined in Terminology D 1129 is not
accordance with the conveyance for each part of the section.
applicable in this test method.
Therefore, the channel for some distance upstream should be
similar to that of the reach. Then the discharge will be
8. Calibration
distributed in relation to depths, roughness, and shape. If the
8.1 The surveying instruments, levels and transits, etc.,
upstream section is located too close to a sharp bend, a bridge
should have their adjustment checked before each use and
that constricts the width, or a natural constriction, slack water,
possibly daily when in continuous use or after some occurrence
or even an eddy may occupy part of the section; and the section
that may have affected the adjustment.
will not be effective in carrying water downstream in propor-
8.2 The standard check is the “two-peg” or“ double-peg”
tion to the computed conveyance.
test. If the error is over 0.03 ft in 100 ft (0.9 cm in 30.5 m), the
instrument should be adjusted. The two-peg test and how to
adjust the instrument are described in many surveying text-
Benson, M. A., and Dalrymple, Tate, “Measurement of Peak Discharge by the
books and in instructions provided by the manufacturer. Refer
Slope-Area Method,” Techniques of Water Resources Investigations, Book 3,
to manufacturer’s manual for the electronic instruments. Chapter . U.S. Geological Survey, 1967.
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 5130
FIG. 2 Sample Slope-Area Computation, Listing of High-Water Marks
9.1.6 Channels in mountainous areas may be very rough
...
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