ASTM D5130-95(2008)
(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.
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 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:D5130 −95(Reapproved 2008)
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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope 2.2 ISO Standards:
ISO 748 Liquid Flow Measurements in Open Channels—
1.1 This test method covers the computation of discharge
Velocity-Area Method
(the volume rate of flow) of water in open channels or streams
ISO 1070 Liquid Flow Measurements in Open Channels—
using representative cross-sectional characteristics, the water-
Slope-Area Method
surface slope, and coefficient of channel roughness as input to
gradually-varied flow computations.
3. Terminology
1.2 This test method produces an indirect measurement of
3.1 Definitions: For definitions of terms used in this test
the maximum discharge for one flow event, usually a specific
method, refer to Terminology D1129.
flood. The computed discharge may be used to help define the
3.2 Definitions of Terms Specific to This Standard:
high-water segment of a stage-discharge relation.
3.2.1 SeveralofthefollowingtermsareillustratedinFig.1:
1.3 Thevaluesstatedininch-poundunitsaretoberegarded
3.2.2 alpha (α)—a velocity-head coefficient that represents
as standard. The values given in parentheses are mathematical
the ratio of the true velocity head to the velocity head
conversions to SI units that are provided for information only
computedonthebasisofthemeanvelocity.Itisassumedequal
and are not considered standard.
to 1.0 if the cross section is not subdivided. For subdivided
sections, α is computed as follows:
1.4 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the 3
k
i
S D
responsibility of the user of this standard to establish appro- ( 2
A
i
priate safety and health practices and determine the applica-
α 5
bility of regulatory limitations prior to use. K
T
A
T
2. Referenced Documents
where:
2.1 ASTM Standards:
K and A = the conveyance and area of the subsection
D1129Terminology Relating to Water
indicated by the subscript i, and
D2777Practice for Determination of Precision and Bias of
K and A = the conveyance and area of the entire cross
T T
Applicable Test Methods of Committee D19 on Water
section.
D3858Test Method for Open-Channel Flow Measurement
3.2.3 conveyance(K)—ameasureofthecarryingcapacityof
of Water by Velocity-Area Method
achannelandhasdimensionsofcubicfeetpersecondorcubic
metres per second. Conveyance is computed as follows:
This test method is under the jurisdiction ofASTM Committee D19 on Water
1.486
and is the direct responsibility of Subcommittee D19.07 on Sediments,
2/3
K 5 AR
Geomorphology, and Open-Channel Flow.
n
Current edition approved Oct. 1, 2008. Published November 2008. Originally
approved in 1990. Last previous edition approved in 2003 as D5130–95 (2003).
where:
DOI: 10.1520/D5130-95R08.
n = the Manning roughness coefficient,
This test method is similar to methods developed by the U.S. Geological
2 2
A = the cross-section area, ft (m ), and
Survey and described in documents referenced in Footnotes 5, 6, and 7.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
the ASTM website. 4th Floor, New York, NY 10036, http://www.ansi.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D5130−95 (2008)
h
f
S 5
f
L
that becomes:
∆h1∆h
v
S 5
f
L
when ∆h is negative (for a contracting reach),
v
or:
∆h
v
∆h1
S 5
f
L
when ∆ h is positive (for an expanding reach).
v
3.2.9 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:
FIG. 1 Definition Sketch of a Slope-Area Reach
V
F 5
=gd
m
R = the hydraulic radius, ft (m).
where:
NOTE 1—1.486 = 1.00 SI unit.
V = the mean velocity in ft/s (m/s),
3.2.4 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.
3.2.10 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
3.2.11 hydraulic radius (R)—defined as the area of a cross
high-waterprofileareevident,crosssectionsshouldbelocated
section or subsection divided by the corresponding wetted
at the breaks.
perimeter.
3.2.5 cross-section area (A)—the area of the water below
3.2.12 roughness coeffıcient (n)—or Manning’s n is used in
the high-water surface elevations that are computed by assum-
theManningequation.RoughnesscoefficientorManning’snis
ing a straight-line interpolation between elevations on each
a measure of the resistance to flow in a channel. The factors
bank. The area is computed as the summation of the products
that influence the magnitude of the resistance to flow include
of mean depth multiplied by the width between stations of the
the character of the bed material, cross section irregularities,
cross section.
depth of flow, vegetation, and alignment of the channel. A
3.2.6 friction loss (h)—the loss due to boundary friction in
f
reasonable evaluation of the resistance to flow in a channel
the reach and is equivalent to the following:
depends on the experience of the person selecting the coeffi-
∆ h1∆h 2 k ∆h cient and reference to texts and reports that contain values for
~ !
v v
5,6
similar stream and flow conditions. (See 9.3).
where:
3.2.13 velocity head (h )—computed as follows:
v
∆h = the fall in the reach,
αV
∆h = the upstream velocity head minus the down-
v
h 5
v
2g
stream velocity head,
(k∆h ) = theenergylossduetoaccelerationordeceleration
v
where:
andtoeddiesinacontractingorexpandingreach,
α = the velocity-head coefficient,
where k is a coefficient for energy losses.
V = themeanvelocityinthecrosssectioninft/s(m/s),and
All of the equations presented in this standard are based on
theassumptionthat kiszeroforcontractingreachesand0.5for
expanding reaches.
3.2.7 fall (∆h)—the drop in the water-surface computed as
Benson, M. A., and Dalrymple, T., “General Field and Office Procedures for
the difference in the average water-surface elevation at adja-
Indirect Discharge Measurements,” Techniques of Water Resources Investigations,
Book 3, U.S. Geological Survey, 1967.
cent cross sections.
Matthai,HowardF.,“MeasurementofPeakDischargeatWidthContractionsby
3.2.8 friction slope (S )—the energy loss divided by the
f Indirect Methods,” Techniques of Water Resources Investigations, Book 3, Chapter
length of the reach or: A4, U.S. Geological Survey, 1984.
D5130−95 (2008)
7. Sampling
g = the acceleration of gravity in ft/s/s (m/s/s).
7.1 Sampling as defined in Terminology D1129 is not
3.2.14 wetted perimeter (WP)—the total length of the
applicable in this test method.
boundary between the channel bed and the water for a cross
section. It is computed as the sum of the hypotenuse of the
8. Calibration
righttriangledefinedbythedistancebetweenadjacentstations
of the cross section and the difference in bed elevations.
8.1 The surveying instruments, levels and transits, etc.,
should have their adjustment checked before each use and
4. Summary of Test Method
possiblydailywhenincontinuoususeoraftersomeoccurrence
4.1 The slope-area method is used to indirectly determine
that may have affected the adjustment.
the discharge through a reach of channel, usually after a flood,
8.2 The standard check is the “two-peg” or“ double-peg”
usingevidenceleftbytheeventandthephysicalcharacteristics
test.Iftheerrorisover0.03ftin100ft(0.9cmin30.5m),the
of the channel reach. A field survey is made to determine
instrument should be adjusted. The two-peg test and how to
distances between and elevations of high-water marks and to
adjust the instrument are described in many surveying text-
define cross sections of the stream. These data are used to
books and in instructions provided by the manufacturer. Refer
compute the fall in the water surface between sections and
to manufacturer’s manual for the electronic instruments.
selected properties of the sections. This information is used
8.3 If the “reciprocal leveling” technique is used in the
along with Manning’s n in the Manning equation to compute
survey, it is the equivalent of the two-peg test between each of
the discharge, Q.The Manning equation in terms of discharge,
the two successive hubs.
Q, is as follows:
8.4 Sectional and telescoping level rods should be checked
1.486
2/3 ½ ½
Q 5 AR S or Q 5 KS
f f visually at frequent intervals to be sure sections are not
n
separated.Aproper fit at each joint can be quickly checked by
The symbols on the right sides of the equations are defined
measurements across the joint with a steel tape.
in Section 3.
8.5 All field notes of the transit-stadia survey should be
checked before proceeding with the computations.
5. Significance and Use
5.1 This test method is particularly useful for determining
9. Procedure
the discharge when it cannot be measured directly by some
9.1 Selection of a reach of channel is the first and probably
type of current meter to obtain velocities and with sounding
the most important step to obtain reliable results. Ideal reaches
weights to determine the cross section.
rarely exist; so the various elements in a reach must be
5.2 Evenunderoptimumconditions,thepersonnelavailable
evaluated and compromises made so that the best reach
cannot cover all points of interest during a major flood. Field
available is selected. Selection soon after the flood event is
personnel cannot always obtain reliable results by direct
recommendedbecauselivestock,humans,heavyrain,andbank
methods if the stage is rising or falling very rapidly, if flowing
sloughing can destroy high-water marks.
ice or debris interferes with depth or velocity measurements.
9.1.1 Good high-water marks are essential for good results.
5.3 Under the worst conditions, access roads are blocked,
Attimesareachwithpoorqualitymarksmustbeusedbecause
cableways and bridges may be washed out, and knowledge of
of other complicating factors such as inflow, proximity to a
the flood frequently comes too late to obtain direct measure-
gaging station, etc. List high-water marks in a format such as
mentsofflow.Therefore,sometypeofindirectmeasurementis
shown in Fig. 2.
necessary.Theslope-areamethodisacommonlyusedmethod.
9.1.2 The nearer the reach to a uniform channel the better.
Marked changes in channel shape should be avoided because
6. Apparatus
of uncertainties regarding the value of the expansion/
6.1 The equipment generally used for a “transit-stadia”
contraction loss coefficient (k) and the friction losses in the
survey is recommended. An engineer’s transit, a self-leveling
reach. Changes in channel conveyance should be fairly uni-
level with azimuth circle, newer equipment using electronic
form from section to section to be consistent with the assump-
circuitry, or other advanced surveying instruments may be
tion that the mean conveyance is equal to the geometric mean
used.Standardlevelrods,atelescoping,25-ft(7.6m)levelrod,
of the conveyances at the end sections.
rodlevels,handlevels,steelandmetallictapes,taglines(small
9.1.3 A reach with flow confined to a roughly trapezoidal
wires with markers fixed at known spacings), vividly colored
channel is desirable because roughness coefficients have been
flagging,surveystakes,acamera(preferablystereo)withcolor
determined for such shapes. However, compound channels,
film, light meter, and ample note paper are necessary items.
those with overbank flow, for example, can be used if they are
properly subdivided into subareas that are approximately
6.2 Additional equipment that may expedite a survey in-
trapezoidal.
clude axes, shovels, a portable drafting machine, a boat with
oars and motor, hip boots, waders, rain gear, nails, sounding
equipment, two-way radios, ladder, and rope.
Benson, M.A., and Dalrymple, Tate, “Measurement of Peak Discharge by the
6.3 Safety equipment should include life jackets, first aid
Slope-Area Method,” Techniques of Water Resources Investigations, Book 3, U.S.
kit, drinking water, and pocket knives. Geological Survey, 1967.
D5130−95 (2008)
FIG. 2 Sample Slope-Area Computation, Listing of High-Water Marks
9.1.4 A straight reach that contracts is preferred, but both 9.1.7 Thereachshouldbelongenoughtodevelopafallthat
conditions seldom exist in the same reach. Whether or not a is well beyond the range of error in the surveying method, in
reach is contracting or expanding depends solely upon the alternative interpretations of the high-water profile, or in
difference in velocity head (∆h ) between sections. The reach uncertainties related to the computation of the velocity head.
v
is contracting if the difference in the velocity head is negative. Onesuggestedcriteriaisthatthefallinthereachshouldbe0.5
The reach is expanding if the velocity-head difference is ft (0.15 m) or greater than the velocity head in the reach, or
positive. both.
9.1.5 Cross sections are assumed to be carrying water in
9.2 Cross sections represent the geometry of a reach of
accordance with the conveyance for each part of the section.
channel. For example: section 2 should be typical of the reach
Therefore, the channel for some distance upstream should be
from halfway upstream to section 1 to halfway downstream to
similar to that of the reach. Then the discharge will be
section 3. A minimum of three cross sections is highly
distributed in relation to depths, roughness, and shape. If the
recommended.
upstream section is located too close to a sharp bend, a bridge
9.2.1 Locatecrosssectionsatmajorbreak
...
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