ASTM D5388-21

Standard Test Method for Indirect Measurements of Discharge by Step-Backwater Method

SIGNIFICANCE AND USE
5.1 This test method is particularly useful for determining the discharge when it cannot be measured directly (such as during high flow conditions) by some type of current meter to obtain velocities and with sounding weights to determine the cross section (refer to Test Method D3858). This test method requires only one high-water elevation, unlike the slope-area test method that requires numerous high-water marks to define the fall in the reach. It can be used to determine a stage-discharge relation without data from several high-water events.  
5.1.1 The user is encouraged to verify the theoretical stage-discharge relation with direct current-meter measurements when possible.  
5.1.2 To develop a rating curve, plot stage versus discharge for several discharges and their computed stages on a rating curve together with direct current-meter measurements.
SCOPE
1.1 This test method covers the computation of discharge of water in open channels or streams using representative cross-sectional characteristics, the water-surface elevation of the upstream-most cross section, and coefficients of channel roughness as input to gradually-varied flow computations.2  
1.2 This test method produces an indirect measurement of the discharge for one flow event, usually a specific flood. The computed discharge may be used to define a point on the 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 31-Oct-2021
• ICS: 17.220.20 - Measurement of electrical and magnetic quantities
• Technical Committee: D19 - Water
• Drafting Committee: D19.07 - Sediments, Geomorphology, and Open-Channel Flow

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation:D5388 −21
Standard Test Method for
Indirect Measurements of Discharge by Step-Backwater
1
Method
This standard is issued under the fixed designation D5388; 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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope Applicable Test Methods of Committee D19 on Water
D3858 Test Method for Open-Channel Flow Measurement
1.1 This test method covers the computation of discharge of
of Water by Velocity-Area Method
water in open channels or streams using representative cross-
sectional characteristics, the water-surface elevation of the
3. Terminology
upstream-most cross section, and coefficients of channel
2
roughness as input to gradually-varied flow computations.
3.1 Definitions:
1.2 This test method produces an indirect measurement of 3.1.1 For definitions of terms used in this standard, refer to
the discharge for one flow event, usually a specific flood. The
Terminology D1129.
computed discharge may be used to define a point on the 3.2 Definitions of Terms Specific to This Standard:
stage-discharge relation.
NOTE—Several of the following terms are illustrated in Fig.
1.
1.3 The values stated in inch-pound units are to be regarded
as standard. The values given in parentheses are mathematical 3.2.1 alpha (α), n—a dimensionless velocity-head coeffi-
cient that represents the ratio of the true velocity head to the
conversions to SI units that are provided for information only
and are not considered standard. velocity head computed on the basis of the mean velocity. It is
assumed equal to unity if the cross section is not subdivided.
1.4 This standard does not purport to address all of the
For subdivided sections, α is computed as follows:
safety concerns, if any, associated with its use. It is the
3
responsibility of the user of this standard to establish appro-
k
i
( 2
priate safety, health, and environmental practices and deter-
a
i
α 5 (1)
3
mine the applicability of regulatory limitations prior to use.
K
T
2
1.5 This international standard was developed in accor-
A
T
dance with internationally recognized principles on standard-
where:
ization established in the Decision on Principles for the
k and a = the conveyance and area of the subsection indi-
Development of International Standards, Guides and Recom-
cated by the subscript I, and
mendations issued by the World Trade Organization Technical
K and A = theconveyanceandareaofthetotalcrosssection
Barriers to Trade (TBT) Committee.
indicated by the subscript T.
2. Referenced Documents
3.2.2 conveyance (K), n—ameasureofthecarryingcapacity
3
2.1 ASTM Standards:
of a channel without regard to slope and has dimensions of
D1129 Terminology Relating to Water
cubic feet per second. Conveyance is computed as follows:
D2777 Practice for Determination of Precision and Bias of
1.49
2/3
K 5 AR (2)
n
1
This test method is under the jurisdiction of ASTM Committee D19 on Water
3.2.3 cross-section area (A), n—the area at the water below
and is the direct responsibility of Subcommittee D19.07 on Sediments,
the water-surface elevation that it computed. The area is
Geomorphology, and Open-Channel Flow.
computed as the summation of the products of mean depth
Current edition approved Nov. 1, 2021. Published January 2022. Originally
approved in 1993. Last previous edition approved in 2013 as D5388 – 93 (2013). multiplied by the width between stations of the cross section.
DOI: 10.1520/D5388-21.
2 3.2.4 cross sections (numbered consecutively in downstream
Barnes, H. H., Jr., “Roughness Characteristics of Natural Streams,” U.S.
Geological Survey Water Supply Paper 1849, 1967.
order), n—representative portions of a reach and channel and
3
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
are positioned as nearly as possible at right angles to the
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
direction of flow. They must be defined by coordinates of
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. horizontal distance and ground elevation. Sufficient ground
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
1

---------------------- Page: 1 ----------------------
D5388−21
subcritical if the Froude number is less than unity and a rapid
or supercritical if it is greater than unity.The Froude number is
computed as follows:
V
F 5 (7)
=gdm
where:
V = the mean velocity,
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D5388 − 93 (Reapproved 2013) D5388 − 21
Standard Test Method for
Indirect Measurements of Discharge by Step-Backwater
1
Method
This standard is issued under the fixed designation D5388; 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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This test method covers the computation of discharge of water in open channels or streams using representative cross-sectional
characteristics, the water-surface elevation of the upstream-most cross section, and coefficients of channel roughness as input to
2
gradually-varied flow computations.
1.2 This test method produces an indirect measurement of the discharge for one flow event, usually a specific flood. The computed
discharge may be used to define a point on the stage-discharge relation.
1.3 The values stated in inch-pound units are to be regarded as the standard. The SI units values given in parentheses are for
information only.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, health, and environmental practices and determine the applicability of
regulatory limitations prior to use.
1.5 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
3
2.1 ASTM Standards:
D1129 Terminology Relating to Water
D2777 Practice for Determination of Precision and Bias of Applicable Test Methods of Committee D19 on Water
D3858 Test Method for Open-Channel Flow Measurement of Water by Velocity-Area Method
3. Terminology
3.1 Definitions:
3.1.1 For definitions of terms used in this test method, standard, refer to Terminology D1129.
3.2 Definitions of Terms Specific to This Standard:
1
This test method is under the jurisdiction of ASTM Committee D19 on Water and is the direct responsibility of Subcommittee D19.07 on Sediments, Geomorphology,
and Open-Channel Flow.
Current edition approved Jan. 1, 2013Nov. 1, 2021. Published January 2013January 2022. Originally approved in 1993. Last previous edition approved in 20072013 as
D5388 – 93 (2007).(2013). DOI: 10.1520/D5388-93R13.10.1520/D5388-21.
2
Barnes, H. H., Jr., “Roughness Characteristics of Natural Streams,” U.S. Geological Survey Water Supply Paper 1849, 1967.
3
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
1

---------------------- Page: 1 ----------------------
D5388 − 21
NOTE—Several of the following terms are illustrated in Fig. 1.
3.2.1 alpha (α)—(α), n—a dimensionless velocity-head coefficient that represents the ratio of the true velocity head to the velocity
head computed on the basis of the mean velocity. It is assumed equal to unity if the cross section is not subdivided. For subdivided
sections, α is computed as follows:
3
k
i
2
(
a
i
α5 (1)
3
K
T
2
A
T
where:
k and a = the conveyance and area of the subsection indicated by the subscript I, and
K and A = the conveyance and area of the total cross section indicated by the subscript T.
3.2.2 conveyance (K)—(K), n—a measure of the carrying capacity of a channel without regard to slope and has dimensions of
cubic feet per second. Conveyance is computed as follows:
1.49
2/3
K 5 AR (2)
n
3.2.3 cross-section area (A)—(A), n—the area at the water below the water-surface elevation that it computed. The area is
computed as the summation of the products of mean depth multiplied by the width between stations of the cross section.
3.2.4 cross sections (numbered consecutively in downstream order)—order), n—representative portions of a reach and channel and
are positioned as nearly as possible at right angles to the direction of flow. They must be defined
...