ASTM D5130-95(2003)
(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
SIGNIFICANCE AND USE
This test method is particularly useful for determining 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 optimum conditions, the personnel available cannot cover all points of interest during a major flood. Field personnel 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.
Under the worst conditions, access roads are blocked, cableways and bridges may be washed out, and knowledge of the flood frequently comes too late to obtain direct measurements of flow. Therefore, some type of indirect measurement is necessary. The slope-area method is a commonly used 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.²
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.
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Standards Content (Sample)
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Designation: D 5130 – 95 (Reapproved 2003)
Standard Test Method for
Open-Channel Flow Measurement of Water Indirectly by
Slope-Area Method
This standard is issued under the fixed designation D5130; 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
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 Thevaluesstatedininch-poundunitsaretoberegarded
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 appro-
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use.
FIG. 1 Definition Sketch of a Slope-Area Reach
2. Referenced Documents
2.1 ASTM Standards:
3. Terminology
D1129 Terminology Relating to Water
3.1 Definitions: For definitions of terms used in this test
D2777 Practice for Determination of Precision and Bias of
method, refer to Terminology D1129.
Applicable Methods of Committee D-19 on Water
3.2 Definitions of Terms Specific to This Standard: Several
D3858 Practice for Open-Channel Flow Measurement of
of the following terms are illustrated in Fig. 1:
Water by Velocity-Area Method
3.2.1 alpha (a)—a velocity-head coefficient that represents
2.2 ISO Standards:
the ratio of the true velocity head to the velocity head
ISO 748 Liquid Flow Measurements in Open Channels—
computedonthebasisofthemeanvelocity.Itisassumedequal
Velocity-Area Method
to 1.0 if the cross section is not subdivided. For subdivided
ISO 1070 Liquid Flow Measurements in Open Channels—
sections, a is computed as follows:
Slope-Area Method
a5
k
i
(
S 2D
A
i
This test method is under the jurisdiction ofASTM Committee D19 on Water
and is the direct responsibility of Subcommittee D19.07 on Sediments, Geomor-
phology, and Open-Channel Flow.
Current edition approved June 10, 2003. Published August 2003. Originally
approved in 1990. Last previous edition approved in 1999 as D5130–95(1999).
K
This test method is similar to methods developed by the U.S. Geological
T
Survey and described in documents referenced in Footnotes 5, 6, and 7.
A
T
Annual Book of ASTM Standards, Vol 11.01.
Available from American National Standards Institute, 25 W. 43rd St., 4th
where:
Floor, New York, NY 10036.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D 5130 – 95 (2003)
when Dh is negative (for a contracting reach),
K and A = the conveyance and area of the subsection
v
or:
indicated by the subscript i, and
K and A = the conveyance and area of the entire cross
Dh
T T
v
Dh 1
section.
S 5
f
L
3.2.2 conveyance (K)—a measure of the carrying capacity
of a channel and has dimensions of cubic feet per second or
cubic metres per second. Conveyance is computed as follows:
when D h is positive (for an expanding reach).
v
1.486
2/3 3.2.8 Froude number (F)—an index to the state of flow in
K 5 AR
n
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
where:
computed as follows:
n = the Manning roughness coefficient,
2 2
A = the cross-section area, ft (m ), and
V
F 5
R = the hydraulic radius, ft (m).
=gd
m
NOTE 1—1.486 = 1.00 SI unit.
where:
V = the mean velocity in ft/s (m/s),
3.2.3 cross sections (numbered consecutively in downstream
d = the average depth in the cross section in feet, and
m
order)—representativeofareachofchannelandarepositioned
g = the acceleration of gravity in ft/s/s (m/s/s).
as nearly as possible at right angles to the direction of flow.
3.2.9 high-water marks—the evidence of the highest stage
Theymustbedefinedbycoordinatesofhorizontaldistanceand
reached by a flood. Debris, stains, foam lines, and scour marks
ground elevation. Sufficient ground points must be obtained so
are common types of high-water marks. Water-surface slopes
that straight-line connection of the coordinates will adequately
are determined by the elevations of these marks.
describe the cross-section geometry. If major breaks in the
high-waterprofileareevident,crosssectionsshouldbelocated
3.2.10 hydraulic radius (R)—defined as the area of a cross
at the breaks.
section or subsection divided by the corresponding wetted
3.2.4 cross-section area (A)—the area of the water below perimeter.
the high-water surface elevations that are computed by assum-
3.2.11 roughness coeffıcient (n)—orManning’snisusedin
ing a straight-line interpolation between elevations on each
theManningequation.RoughnesscoefficientorManning’snis
bank. The area is computed as the summation of the products
a measure of the resistance to flow in a channel. The factors
of mean depth multiplied by the width between stations of the
that influence the magnitude of the resistance to flow include
cross section.
the character of the bed material, cross section irregularities,
3.2.5 friction loss (h)—the loss due to boundary friction in depth of flow, vegetation, and alignment of the channel. A
f
the reach and is equivalent to the following:
reasonable evaluation of the resistance to flow in a channel
depends on the experience of the person selecting the coeffi-
D h1Dh 2 k~Dh !
v v
cient and reference to texts and reports that contain values for
5,6
where:
similar stream and flow conditions. (See 9.3).
Dh = the fall in the reach,
3.2.12 velocity head (h )—computed as follows:
v
Dh = the upstream velocity head minus the down-
v
aV
stream velocity head,
h 5
v
2g
(kDh ) = theenergylossduetoaccelerationordeceleration
v
andtoeddiesinacontractingorexpandingreach,
where k is a coefficient for energy losses.
where:
All of the equations presented in this standard are based on
a = the velocity-head coefficient,
theassumptionthat kiszeroforcontractingreachesand0.5for
V = the mean velocity in the cross section in ft/s (m/s), and
expanding reaches. g = the acceleration of gravity in ft/s/s (m/s/s).
3.2.6 fall (Dh)—the drop in the water-surface computed as 3.2.13 wetted perimeter (WP)—the total length of the
the difference in the average water-surface elevation at adja-
boundary between the channel bed and the water for a cross
cent cross sections. section. It is computed as the sum of the hypotenuse of the
right triangle defined by the distance between adjacent stations
3.2.7 friction slope (S )—the energy loss divided by the
f
of the cross section and the difference in bed elevations.
length of the reach or:
h
f
S 5
f
L
Benson, M. A., and Dalrymple, T., “General Field and Office Procedures for
Indirect Discharge Measurements,” Techniques of Water Resources Investigations,
that becomes:
Book 3, Chapter , U.S. Geological Survey, 1967.
Dh1Dh 6
v
Matthai, Howard F., “Measurement of Peak Discharge at Width Contractions
S 5
f
L
by Indirect Methods,” Techniques of Water Resources Investigations, Book 3,
Chapter A4, U.S. Geological Survey, 1984.
D 5130 – 95 (2003)
4. Summary of Test Method possiblydailywhenincontinuoususeoraftersomeoccurrence
that may have affected the adjustment.
4.1 The slope-area method is used to indirectly determine
8.2 The standard check is the “two-peg” or“ double-peg”
the discharge through a reach of channel, usually after a flood,
test.Iftheerrorisover0.03ftin100ft(0.9cmin30.5m),the
usingevidenceleftbytheeventandthephysicalcharacteristics
instrument should be adjusted. The two-peg test and how to
of the channel reach. A field survey is made to determine
adjust the instrument are described in many surveying text-
distances between and elevations of high-water marks and to
books and in instructions provided by the manufacturer. Refer
define cross sections of the stream. These data are used to
to manufacturer’s manual for the electronic instruments.
compute the fall in the water surface between sections and
8.3 If the “reciprocal leveling” technique is used in the
selected properties of the sections. This information is used
survey, it is the equivalent of the two-peg test between each of
along with Manning’s n in the Manning equation to compute
the two successive hubs.
the discharge, Q.The Manning equation in terms of discharge,
8.4 Sectional and telescoping level rods should be checked
Q, is as follows:
visually at frequent intervals to be sure sections are not
1.486
2/3 ½
separated.Aproper fit at each joint can be quickly checked by
Q 5 AR S or Q
f
n
measurements across the joint with a steel tape.
½
5 KS
f
8.5 All field notes of the transit-stadia survey should be
checked before proceeding with the computations.
The symbols on the right sides of the equations are defined
in Section 3.
9. Procedure
9.1 Selection of a reach of channel is the first and probably
5. Significance and Use
the most important step to obtain reliable results. Ideal reaches
5.1 This test method is particularly useful for determining
rarely exist; so the various elements in a reach must be
the discharge when it cannot be measured directly by some
evaluated and compromises made so that the best reach
type of current meter to obtain velocities and with sounding
available is selected. Selection soon after the flood event is
weights to determine the cross section.
recommendedbecauselivestock,humans,heavyrain,andbank
5.2 Evenunderoptimumconditions,thepersonnelavailable
sloughing can destroy high-water marks.
cannot cover all points of interest during a major flood. Field
9.1.1 Good high-water marks are essential for good results.
personnel cannot always obtain reliable results by direct
Attimesareachwithpoorqualitymarksmustbeusedbecause
methods if the stage is rising or falling very rapidly, if flowing
of other complicating factors such as inflow, proximity to a
ice or debris interferes with depth or velocity measurements.
gaging station, etc. List high-water marks in a format such as
5.3 Under the worst conditions, access roads are blocked,
shown in Fig. 2.
cableways and bridges may be washed out, and knowledge of
9.1.2 The nearer the reach to a uniform channel the better.
the flood frequently comes too late to obtain direct measure-
Marked changes in channel shape should be avoided because
mentsofflow.Therefore,sometypeofindirectmeasurementis
of uncertainties regarding the value of the expansion/
necessary.Theslope-areamethodisacommonlyusedmethod.
contraction loss coefficient ( k) and the friction losses in the
6. Apparatus
reach. Changes in channel conveyance should be fairly uni-
form from section to section to be consistent with the assump-
6.1 The equipment generally used for a “transit-stadia”
tion that the mean conveyance is equal to the geometric mean
survey is recommended. An engineer’s transit, a self-leveling
of the conveyances at the end sections.
level with azimuth circle, newer equipment using electronic
9.1.3 A reach with flow confined to a roughly trapezoidal
circuitry, or other advanced surveying instruments may be
channel is desirable because roughness coefficients have been
used.Standardlevelrods,atelescoping,25-ft(7.6m)levelrod,
determined for such shapes. However, compound channels,
rodlevels,handlevels,steelandmetallictapes,taglines(small
those with overbank flow, for example, can be used if they are
wires with markers fixed at known spacings), vividly colored
properly subdivided into subareas that are approximately
flagging,surveystakes,acamera(preferablystereo)withcolor
trapezoidal.
film, light meter, and ample note paper are necessary items.
9.1.4 A straight reach that contracts is preferred, but both
6.2 Additional equipment that may expedite a survey in-
conditions seldom exist in the same reach. Whether or not a
clude axes, shovels, a portable drafting machine, a boat with
reach is contracting or expanding depends solely upon the
oars and motor, hip boots, waders, rain gear, nails, sounding
difference in velocity head (Dh ) between sections. The reach
equipment, two-way radios, ladder, and rope.
v
is contracting if the difference in the velocity head is negative.
6.3 Safety equipment should include life jackets, first aid
The reach is expanding if the velocity-head difference is
kit, drinking water, and pocket knives.
positive.
7. Sampling
9.1.5 Cross sections are assumed to be carrying water in
7.1 Sampling as defined in Terminology D1129 is not
accordance with the conveyance for each part of the section.
applicable in this test method.
8. Calibration
Benson, M.A., and Dalrymple, Tate, “Measurement of Peak Discharge by the
8.1 The surveying instruments, levels and transits, etc.,
Slope-Area Method,” Techniques of Water Resources Investigations, Book 3,
should have their adjustment checked before each use and Chapter . U.S. Geological Survey, 1967.
D 5130 – 95 (2003)
FIG. 2 Sample Slope-Area Computation, Listing of High-Water Marks
Therefore, the channel for some distance upstream should be 9.2 Cross sections represent the geometry of a reach of
similar to that of the reach. Then the discharge will be
channel. For example: section 2 should be typical of the reach
distributed in relation to depths, roughness, and shape. If the
from halfway upstream to section 1 to halfway downstream to
upstream section is located too close to a sharp bend, a bridge
section 3. A minimum of three cross sections is highly
that constricts the width, or a natural constriction, slack water,
recommended.
orevenaneddymayoccupypartofthesection;andthesection
9.2.1 Locatecrosssectionsatmajorbreaksinthehigh-water
will not be effective in carrying water downstream in propor-
profiles. To do so, the high-water marks should be plotted in
tion to the computed conveyance.
the field, and a profile for each bank drawn before sections are
9.1.6 Channelsinmountainousareasmaybeveryroughand
located and surveyed. Several high-water marks near the ends
steep and may have free fall over riffles and boulders. The
ofthesectionsaredesirabletodefinethehigh-waterelevations
Manning equation is not applicable wh
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