ASTM D5243-92(2019)

Standard Test Method for Open-Channel Flow Measurement of Water Indirectly at Culverts

SIGNIFICANCE AND USE
5.1 This test method is particularly useful to determine the discharge when it cannot be measured directly with some type of current meter to obtain velocities and sounding equipment to determine the cross section. See Test Method D3858.  
5.2 Even under the best of conditions, the personnel available cannot cover all points of interest during a major flood. The 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 measurements, or if the cross section of an alluvial channel is scouring or filling significantly.  
5.3 Under flood conditions, access roads may be blocked, cableways and bridges may be washed out, and knowledge of the flood frequently comes too late. Therefore, some type of indirect measurement is necessary. The use of culverts to determine discharges is a commonly used practice.
SCOPE
1.1 This test method covers the computation of discharge (the volume rate of flow) of water in open channels or streams using culverts as metering devices. In general, this test method does not apply to culverts with drop inlets, and applies only to a limited degree to culverts with tapered inlets. Information related to this test method can be found in ISO 748 and ISO 1070.  
1.2 This test method produces the discharge for a flood event if high-water marks are used. However, a complete stage-discharge relation may be obtained, either manually or by using a computer program, for a gauge located at the approach section to a culvert.  
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-2019
• ICS: 17.120.20 - Flow in open channels
• Technical Committee: D19 - Water
• Drafting Committee: D19.07 - Sediments, Geomorphology, and Open-Channel Flow

Relations

• Replaces: ASTM D5243-92(2013) - Standard Test Method for Open-Channel Flow Measurement of Water Indirectly at Culverts
• Effective Date: 01-Nov-2019
• Refers: ASTM D1129-13(2020)e2 - Standard Terminology Relating to Water
• Effective Date: 01-May-2020
• Refers: ASTM D2777-12 - Standard Practice for Determination of Precision and Bias of Applicable Test Methods of Committee D19 on Water
• Effective Date: 15-Jun-2012
• Refers: ASTM D1129-10 - Standard Terminology Relating to Water
• Effective Date: 01-Mar-2010
• Refers: ASTM D3858-95(2008) - Standard Test Method for Open-Channel Flow Measurement of Water by Velocity-Area Method
• Effective Date: 01-Oct-2008
• Refers: ASTM D2777-08 - Standard Practice for Determination of Precision and Bias of Applicable Test Methods of Committee D19 on Water
• Effective Date: 15-Jan-2008
• Refers: ASTM D1129-06ae1 - Standard Terminology Relating to Water
• Effective Date: 01-Sep-2006
• Refers: ASTM D1129-06a - Standard Terminology Relating to Water
• Effective Date: 01-Sep-2006
• Refers: ASTM D2777-06 - Standard Practice for Determination of Precision and Bias of Applicable Test Methods of Committee D19 on Water
• Effective Date: 15-Aug-2006
• Refers: ASTM D1129-06 - Standard Terminology Relating to Water
• Effective Date: 15-Feb-2006
• Refers: ASTM D1129-04e1 - Standard Terminology Relating to Water
• Effective Date: 01-Mar-2004
• Refers: ASTM D1129-04 - Standard Terminology Relating to Water
• Effective Date: 01-Mar-2004
• Refers: ASTM D1129-03a - Standard Terminology Relating to Water
• Effective Date: 10-Aug-2003
• Refers: ASTM D2777-03 - Standard Practice for Determination of Precision and Bias of Applicable Methods of Committee D-19 on Water
• Effective Date: 10-Aug-2003
• Refers: ASTM D3858-95(2003) - Standard Test Method for Open-Channel Flow Measurement of Water by Velocity-Area Method
• Effective Date: 10-Jun-2003

Overview

ASTM D5243-92(2019): Standard Test Method for Open-Channel Flow Measurement of Water Indirectly at Culverts provides a standardized approach for computing discharge in open channels and streams using culverts as metering devices. Developed by ASTM, this international standard is crucial for hydrologists, civil engineers, water resource managers, and technicians who need to determine water flow where direct measurement techniques are impractical-particularly during flood events, when safety risks and access issues prevent direct velocity or depth measurements.

This method is especially applicable when conditions such as rapidly changing water levels, ice or debris, or inaccessible sites disrupt the use of current meters or sounding equipment. By using culverts as indirect metering devices, accurate discharge measurement is possible even under adverse or emergency conditions.

Key Topics

• Scope and Applicability:

  • Calculation of water discharge in open channels using culverts.
  • Primarily for culverts without drop inlets; limited use for those with tapered inlets.
  • Can generate flood-event discharge based on high-water marks or develop continuous stage-discharge relations.

• Significance and Use:

  • Essential for determining discharge when direct measurement is not feasible.
  • Indirect measurement techniques are critical during floods, where access is often restricted and conventional equipment may be compromised.
  • Offers a reliable methodology for collecting vital hydrological data in challenging field conditions.

• Units and Compliance:

  • Standardized using inch-pound units, with SI conversions provided for reference.
  • Developed following World Trade Organization (WTO) guidelines for international standardization.

• Safety Considerations:

  • Users are responsible for ensuring all necessary safety, health, and environmental practices.
  • Awareness of regulatory requirements is crucial prior to implementation.

Applications

The ASTM D5243 test method is widely used in:

• Flood Hydrology and Disaster Response:

  • Estimating peak discharges at culvert crossings during and after flood events via surveys of high-water marks.
  • Determining flood magnitude where direct monitoring stations are absent or inoperative.

• Culvert Performance Assessment:

  • Evaluation of culvert capacity and behavior under variable flow conditions.
  • Informing design, maintenance, and retrofitting decisions for roadway and railway drainage infrastructure.

• Environmental Engineering:

  • Monitoring stream flows for ecological studies, sediment transport, and habitat assessment where natural cross-sections are unstable.

• Infrastructure Planning:

  • Supporting hydraulic modeling for urban and rural drainage projects.
  • Developing stage-discharge relationships for setting up gauging stations where culverts serve as feasible control sections.

Related Standards

For comprehensive and harmonized water flow measurement practices, users should consider the following related standards:

• ASTM D3858: Test Method for Open-Channel Flow Measurement of Water by Velocity-Area Method – provides procedures for direct discharge measurement using current meters.
• ISO 748: Liquid Flow Measurement in Open Channels – Velocity-Area Methods – global benchmark for open-channel flow velocity measurements.
• ISO 1070: Liquid Flow Measurement in Open Channels – Slope-Area Methods – recommended for indirect measurements similar to those in ASTM D5243.

Consulting these standards ensures consistency, accuracy, and international compatibility in open-channel flow measurement practices.

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Keywords: ASTM D5243, open-channel flow measurement, culvert discharge, indirect flow measurement, flood discharge, water measurement standard, hydrological standards, culvert metering, ISO 748, ISO 1070, indirect discharge computation.

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: D5243 −92 (Reapproved 2019)
Standard Test Method for
Open-Channel Flow Measurement of Water Indirectly at
Culverts
This standard is issued under the fixed designation D5243; 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 D2777Practice for Determination of Precision and Bias of
Applicable Test Methods of Committee D19 on Water
1.1 This test method covers the computation of discharge
D3858Test Method for Open-Channel Flow Measurement
(the volume rate of flow) of water in open channels or streams
of Water by Velocity-Area Method
using culverts as metering devices. In general, this test method
2.2 ISO Standards:
does not apply to culverts with drop inlets, and applies only to
ISO 748Liquid Flow Measurements in Open Channels-
a limited degree to culverts with tapered inlets. Information
Velocity-Area Methods
related to this test method can be found in ISO 748 and ISO
ISO 1070Liquid Flow Measurements in Open Channels-
1070.
Slope-Area Methods
1.2 This test method produces the discharge for a flood
event if high-water marks are used. However, a complete
3. Terminology
stage-discharge relation may be obtained, either manually or
3.1 Definitions:
by using a computer program, for a gauge located at the
3.1.1 For definitions of terms used in this standard, refer to
approach section to a culvert.
Terminology D1129.
1.3 The values stated in inch-pound units are to be regarded
3.2 Several of the following terms are illustrated in Fig. 1.
as standard. The values given in parentheses are mathematical
3.3 Definitions of Terms Specific to This Standard:
conversions to SI units that are provided for information only
3.3.1 alpha (α), n—a velocity-head coefficient that adjusts
and are not considered standard.
thevelocityheadcomputedonbasisofthemeanvelocitytothe
1.4 This standard does not purport to address all of the
truevelocityhead.Itisassumedequalto1.0ifthecrosssection
safety concerns, if any, associated with its use. It is the
is not subdivided.
responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter- 3.3.2 conveyance (K), n—ameasureofthecarryingcapacity
of a channel and having dimensions of cubic feet per second.
mine the applicability of regulatory limitations prior to use.
1.5 This international standard was developed in accor- 3.3.2.1 Discussion—Conveyance is computed as follows:
dance with internationally recognized principles on standard-
1.486
2/3
K 5 R A
ization established in the Decision on Principles for the
n
Development of International Standards, Guides and Recom-
where:
mendations issued by the World Trade Organization Technical
n = the Manning roughness coefficient,
Barriers to Trade (TBT) Committee.
2 2
A = the cross section area, in ft (m ), and
2. Referenced Documents R = the hydraulic radius, in ft (m).
2.1 ASTM Standards:
3.3.3 cross sections, n—(numbered consecutively in down-
D1129Terminology Relating to Water stream order):
3.3.3.1 The approach section, Section 1, is located one
culvert width upstream from the culvert entrance.
This test method is under the jurisdiction of ASTM Committee D19 on Water
3.3.3.2 Cross Sections 2 and 3 are located at the culvert
and is the direct responsibility of Subcommittee D19.07 on Sediments,
Geomorphology, and Open-Channel Flow. entrance and the culvert outlet, respectively.
Current edition approved Nov. 1, 2019. Published January 2020. Originally
3.3.3.3 Subscripts are used with symbols that represent
approved in 1992. Last previous edition approved in 2013 as D5243–92 (2013).
cross sectional properties to indicate the section to which the
DOI: 10.1520/D5243-92R19.
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 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
D5243 − 92 (2019)
NOTE1—Thelossofenergyneartheentranceisrelatedtothesuddencontractionandsubsequentexpansionofthelivestreamwithintheculvertbarrel.
FIG. 1 Definition Sketch of Culvert Flow
αV
property applies. For example, A is the area of Section 1.
h 5
v
Items that apply to a reach between two sections are identified 2g
by subscripts indicating both sections. For example, h is the
f
1–2
where:
friction loss between Sections 1 and 2.
α = the velocity-head coefficient,
3.3.4 cross sectional area (A), n—the area occupied by the
V = the mean velocity in the cross section, in ft/s (m/s), and
water.
3.3.5 energy loss (h), n—the loss due to boundary friction
f g = the acceleration due to gravity, in ft/s/s (m/s/s).
between two locations.
3.3.11 wetted perimeter (WP), n—the length along the
3.3.5.1 Discussion—Energy loss is computed as follows:
boundary of a cross section below the water surface.
Q
h 5 L
S D
f
K K 4. Summary of Test Method
1 2
4.1 The determination of discharge at a culvert, either after
where:
3 3
a flood or for selected approach stages, is usually a reliable
Q = the discharge in ft /s (m /s), and
practice. A field survey is made to determine locations and
L = the culvert length in ft (m).
elevationsofhigh-watermarksupstreamanddownstreamfrom
3.3.6 Froude number (F), n—anindextothestateofflowin
theculvert,andtodetermineanapproachcrosssection,andthe
the channel. In a rectangular channel, the flow is subcritical if
culvert geometry. These data are used to compute the eleva-
the Froude number is less than 1.0, and is supercritical if it is
tions of the water surface and selected properties of the
greater than 1.0.
sections. This information is used along with Manning’s n in
3.3.6.1 Discussion—The Froude number is computed as
the Manning equation for uniform flow and discharge coeffi-
follows:
cients for the particular culvert to compute the discharge, Q,in
V
cubic feet (metres) per second.
F 5
=
gd
m
5. Significance and Use
where:
5.1 This test method is particularly useful to determine the
V = the mean velocity in the cross section, ft/s (m/s),
discharge when it cannot be measured directly with some type
d = the average depth in the cross section, in ft (m), and
m
ofcurrentmetertoobtainvelocitiesandsoundingequipmentto
2 2
g = the acceleration due to gravity (32 ft/s ) (9.8 m/s ).
determine the cross section. See Test Method D3858.
3.3.7 high-water marks, n—indications of the highest stage
5.2 Even under the best of conditions, the personnel avail-
reached by water including, but not limited to, debris, stains,
able cannot cover all points of interest during a major flood.
foam lines, and scour marks.
The engineer or technician cannot always obtain reliable
3.3.8 hydraulic radius (R), n—the area of a cross section or
results by direct methods if the stage is rising or falling very
subsection divided by the wetted perimeter of that section or
rapidly,ifflowingiceordebrisinterfereswithdepthorvelocity
subsection.
measurements, or if the cross section of an alluvial channel is
scouring or filling significantly.
3.3.9 roughness coeffıcient (n), n—Manning’s n is used in
the Manning equation.
5.3 Under flood conditions, access roads may be blocked,
3.3.10 velocity head (h ), n—is computed as follows: cableways and bridges may be washed out, and knowledge of
v
D5243 − 92 (2019)
the flood frequently comes too late. Therefore, some type of 9.2 The placement of a roadway fill and culvert in a stream
indirect measurement is necessary. The use of culverts to channel causes an abrupt change in the character of flow. This
determine discharges is a commonly used practice. channel transition results in rapidly varied flow in which
acceleration due to constriction, rather than losses due to
6. Apparatus boundary friction, plays the primary role. The flow in the
approach channel to the culvert is usually tranquil and fairly
6.1 The equipment generally used for a “transit-stadia”
uniform. Within the culvert, however, the flow may be
survey is recommended. An engineer’s transit, a self-leveling
subcritical,critical,orsupercriticaliftheculvertispartlyfilled,
level with azimuth circle, newer equipment using electronic
or the culvert may flow full under pressure.
circuitry, or other advanced surveying instruments may be
9.2.1 The physical features associated with culvert flow are
used.Necessaryequipmentincludesalevelrod,rodlevel,steel
illustrated in Fig. 1. They are the approach channel cross
and metallic tapes, survey stakes, and ample note paper.
section at a distance equivalent to one opening width upstream
6.2 Additional items of equipment that may expedite a
from the entrance; the culvert entrance; the culvert barrel; the
survey are tag lines (small wires with markers fixed at known
culvert outlet; and the tailwater representing the getaway
spacings), vividly colored flagging, axes, shovels, hip boots or
channel.
waders, nails, sounding equipment, ladder, and rope.
9.2.2 The change in the water-surface profile in the ap-
6.3 Acamerashouldbeavailabletotakephotographsofthe
proach channel reflects the effect of acceleration due to
culvert and channel. Photographs should be included with the
contraction of the cross-sectional area. Loss of energy near the
field data.
entrance is related to the sudden contraction and subsequent
expansion of the live stream within the barrel, and entrance
6.4 Safety equipment should include life jackets, first aid
geometry has an important influence on this loss. Loss of
kit, drinking water, and pocket knives.
energy due to barrel friction is usually minor, except in long
rough barrels on mild slopes. The important features that
7. Sampling
controlthestage-dischargerelationattheapproachsectioncan
D1129 is not
7.1 Sampling as defined in Terminology
be the occurrence of critical depth in the culvert, the elevation
applicable in this test method.
of the tailwater, the entrance or barrel geometry, or a combi-
nation of these.
8. Calibration
9.2.3 Determine the discharge through a culvert by applica-
8.1 Checkadjustmentofsurveyinginstruments,transit,etc.,
tion of the continuity equation and the energy equation
daily when in continuous use or after some occurrence that
between the approach section and a control section within the
may have affected the adjustment.
culvert barrel. The location of the control section depends on
the state of flow in the culvert barrel. For example: If critical
8.2 The standard check is the “two-peg” or “double-peg”
flow occurs at the culvert entrance, the entrance is the control
test. If the error is over 0.03 in 100 ft (0.091 m in 30.48 m),
section, and the headwater elevation is not affected by condi-
adjust the instrument. The two-peg test and how to adjust the
tions downstream from the culvert entrance.
instrumentaredescribedinmanysurveyingtextbooks.Referto
manufacturers’ manual for the electronic instruments.
10. General Classification of Flow
8.3 The “reciprocal leveling” technique (1) is considered
the equivalent of the two-peg test between each of two 10.1 Culvert Flow—Culvert flow is classified into six types
successive hubs.
on the basis of the location of the control section and the
relative heights of the headwater and tailwater elevations to
8.4 Visually check sectional and telescoping level rods at
heightofculvert.ThesixtypesofflowareillustratedinFig.2,
frequent intervals to be sure sections are not separated. A
and pertinent characteristics of each type are given in Table 1.
properfitateachjointcanbecheckedbymeasurementsacross
the joint with a steel tape.
10.2 Definition of Heads—The primary classification of
flowdependsontheheightofwaterabovetheupstreaminvert.
8.5 Check all field notes of the transit-stadia survey before
This static head is designated as h − z, where h is the height
proceeding with the computations. 1 1
abovethedownstreaminvertand zisthechangeinelevationof
theculvertinvert.Numericalsubscriptsareusedtoindicatethe
9. Description of Flow at Culverts
section where the head was measured.Asecondary part of the
9.1 Relations between the head of water on and discharge
classification, described in more detail in Section 18, depends
through a culvert have been the subjects of laboratory inves-
onacomparisonoftailwaterelevation h totheheightofwater
tigations by the U.S. Geological Survey, the Bureau of Public
at the control relative to the downstream invert. The height of
Roads,theFederalHighwayAdministration,andmanyuniver-
water at the control section is designated h .
c
sities. The following description is based on these studies and
10.3 General Classifications—From the information in Fig.
field surveys at sites where the discharge was known.
2, the following general classification of types of flow can be
made:
10.3.1 If h /D is equal to or less than 1.0 and (h − z)/D is
The boldface numbers in parentheses refer to a list of references at the end of 4 1
this standard. less than 1.5, only Types 1, 2 and 3 flow are possible.
D5243 − 92 (2019)
FIG. 2 Classification of Culvert Flow
TABLE 1 Characteristics of Flow Types
NOTE 1—D=maximum vertical height of barrel and diameter of circular culverts.
h 2z h h
1 4 4
Location of
Flow Type Barrel Flow Kind of Control Culvert Slope
D h D
c
Terminal Section
1 Partly full Inlet Critical depth Steep <1.5 <1.0 91.0
2 do Outlet do Mild <1.5 <1.0 91.0
3 do do Backwater do <1.5 >1.0 91.0
4 Full do do Any >1.0 . . . >1.0
5 Partly full Inlet Entrance geometry do :1.5 . 91.0
6 Full Outlet Entrance and barrel geometry do :1.5 . 91.0
10.3.2 If h /D and (h − z)/D are both greater than 1.0, only illustratedinFig.3.Thespecificenergy, H ,istheheightofthe
4 1 o
Type 4 flow is possible. energy grade line above the lowest point in the cross section.
10.3.3 If h /D is equal to or less than 1.0 and (h − z)/D is
Thus:
4 1
equal to or greater than 1.5, only Types 5 and 6 flow are
V
possible. H 5 d1
o
2g
10.3.4 If h /D is equal to or greater than 1.0 on a steep
culvert and (h − z)/D is less than 1.0, Types 1 and 3 flows are where:
z
possible. Further identification of the type of flow requires a
H = specific energy,
o
trial-and-error procedure that takes time and is one of the
d = maximum depth in the section, in ft,
reasons use of the computer program is recommended.
V = mean velocity in the section, in ft/s, and
2 2
g = acceleration of gravity (32 ft/s ) (9.8 m/s ).
11. Critical Depth
11.2 Relation Between Discharge and Depth—It can be
11.1 Specific Energy—In Type 1 flow, critical depth occurs
shown that at the point of minimum specific energy, that is, at
attheculvertinlet,andinType2flowcriticalflowoccursatthe
critical depth, d , there is a unique relation between discharge
c
culvert outlet. Critical depth, d , is the depth of water at the
c
(or velocity) and depth as shown by the following equations:
point of minimum specific energy for a given discharge and
crosssection.Therelationbetweenspecificenergyanddepthis
D5243 − 92 (2019)
FIG. 3 Relation Between Specific Energy and Depth
2 3
Q A 11.3 Discharge at Critical Depth—For the condition of
g T minimum specific energy and critical depth, the discharge
equation for a section of any shape can be written as follows:
and:
g
V A
3/2
Q 5 A Π(1)
5 d 5
c
m
g T T
where:
or:
3 3
Q = discharge, in ft /s (m /s),
2 2
Q 5 A =gd (2)
c m
A = area of cross section below the water surface, ft (m ),
11.4 Discharge and Shape of Sections—Thedischargeequa-
T = width of the section at the water surface, in ft (m),
tion can be simplified according to the shape of the sections.
d = maximumdepthofwaterinthecritical-flowsection,in
c
Thus, for rectangular sections:
ft (m), and
3/2
Q 5 5.67bd (3)
d = mean depth in section= A/T, in ft (m).
c
m
Therefore,assumingeitherdepthofdischargefixestheother.
and for circular sections:
The computational procedures utilize trial iterations where
5/2
Q 5 C D (4)
q
critical depth is assumed and the resultant discharge is used as
a trial value for computing energy losses, which are in turn
where:
used to compute a discharge from variations of the continuity
b = width of section, in ft (m),
equation. Iterations continue until the trial and computed
C = function of d /D, and is obtained from tables,
q c
discharges agree.
D5243 − 92 (2019)
12.3 Backwater—When backwater is the controlling factor
d = maximumdepthofwaterinthecritical-flowsection,in
c
in culvert flow, critical depth cannot occur and the upstream
ft (m), and
water-surface elevation for a given discharge is a function of
D = inside diameter of a circular section, in ft (m).
the surface elevation of the tailwater. The two types of flow in
Eq4alsoappliestosectionshavingapipearchcrosssection
this classification are Types 3 and 4.
in which D becomes the maximum inside height (rise) of the
12.3.1 Type 3 Flow—Type 3 flow is tranquil throughout the
arch.
length of the culvert, as indicated in Fig. 2. The headwater-
diameter ratio is less than 1.5, and the culvert barrel flows
12. Discharge Equations
partly full. The tailwater elevation does not submerge the
12.1 Development—Discharge equations have been devel-
culvert outlet, but it does exceed the elevation of critical depth
oped for each type of flow by application of the continuity and
at the outlet. If the culvert slope is steep enough that under
energy equations between the approach section and the control
free-fall conditions critical depth at the inlet would result from
or terminal section. For most types of flow, the discharge may
a given elevation of headwater, the tailwater elevation must be
be computed directly from these equations after the type of
higher than the elevation of critical depth at the inlet for Type
flow and various energy losses have been identified.
3 flow to occur. The discharge equation for Type 3 flow is as
12.2 Flow at Critical Depth—Flow at critical depth may follows:
occur at either the upstream or the downstream end of a
α V
1 1
culvert, depending on the headwater elevation, the slope of the
Q 5 CA 2g h 1 2 h 2 h 2 h (7)
ΠS D
3 1 3 f f
122 223
2g
culvert, the roughness of the culvert barrel, and the tailwater
elevation.
wheretheterminologyisasexplainedin12.2.1.2exceptthat
12.2.1 Type 1 Flow:
A is the area at the outlet.
12.2.1.1 In Type 1 flow, as illustrated on Fig. 2, the water
12.3.2 Type 4 Flow—In Type 4 flow the culvert is sub-
passes through critical depth near the culvert entrance. The
merged by both headwater and tailwater, as is shown in Fig. 2.
headwater-diameter ratio, (h − z)/D, is limited to a maximum
Theheadwater-diameterratiocanbeanythinggreaterthan1.0.
of 1.5 and the culvert barrel flows partly full. The slope of the
No differentiation is made between low-head and high-head
culvertbarrel,S ,mustbegreaterthanthecriticalslope,S ,and
o c
flow on this basis for Type 4 flow. The culvert flows full and
the tailwater elevation, h , must be less than the elevation of
the energy equation between Sections 1 and 4 becomes as
thewatersurfaceatthecontrolsection, h .Inthiscase, h = h .
c c 2
follows:
12.2.1.2 The discharge equation for Type 1 flow is as
h 1h 5 h 1h 1h 1h 1h 1h 1 h 2 h (8)
~ !
1 v 4 v f e f f v v
follows: 1 4 122 223 324 3 4
2 where:
α V
1 1
Q 5 CA Œ2g h 2 z1 2 d 2 h (5)
S D
c 1 c f h = head loss due to entrance contraction, and all other
e
2g
terms are as previously defined.
where:
In the derivation of the discharge equation shown below, the
C = the discharge coefficient,
velocity head at Section 1 and the friction loss between
2 2
A = the flow area at the control section, in ft (m ),
c
Sections 1 and 2 and between Sections 3 and 4 have been
V = the mean velocity in the approach section, in ft/s
neglected. Between Sections 3 and 4 the energy loss due to
(m/s),
sudden expansion is assumed to be (h − h ).
v v
α = the velocity-head coefficient at the approach section
3 4
Thus:
computation explained in 18.5.4,
h = the head loss due to friction between the approach
h 5 h 1h 1h 1h (9)
f
1–2 1 4 e f v
223 3
section and the inlet= L (Q /K K ),
w 1 2
or in terms of Q the equation becomes:
and
2/3
K = conveyance5~1.486/n! R A, and subscripts indicate
2g~h 2 h !
1 4
Q 5 CA (10)
Sections 1 and 2.
2 2
o
29C n L
!
4/3
12.2.2 Type 2 Flow—Type2flow,asshowninFig.2,passes R
o
through critical depth at the culvert outlet. The headwater-
where the subscript o refers to the area and hydraulic radius
diameter ratio does not exceed 1.5, and the barrel flows partly
of the full culvert barrel.
full. The slope of the culvert is less than critical, and the
tailwater elevation does not exceed the elevation of the water
12.4 High-Head Flow—High-head flow will occur if the
surface at the control section h . The discharge equation for
tailwater is below the crown at the outlet and the headwater-
Type 2 flow is as follows:
diameter ratio is equal to or greater than 1.5. The two types of
flow under this category areTypes 5 and 6.The type of flow is
α V
1 1
determined from curves in 18.10.1. French (2) points out that
Q 5 CA 2g h 1 2 d 2 h 2 h (6)
ΠS D
c 1 c f f
122 223
2g
a particular inlet and barrel does not necessarily have a single
where terminology is as explained in 12.2.1.2 with the and unique performance curve relating the pool level to rate of
addition of h =the head loss due to friction in the culvert, discharge at a given culvert slope. In general, the performance
f
2–3
barrel= L(Q /K K ),andsubscriptsindicateSections2and3. will vary widely depending upon the characteristics of the
2 3
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approach channel and in particular the effects of these charac- flow do not apply to tapered-inlets and drop-inlets and should
teristicsonthedegreeofvortexactionovertheinlet.Itfollows not be applied to culverts with such inlets. Research by
that the subatmospheric pressure that must be present at the National Institute for Standards Technology (2) shows that
inlet throat in order for full conduit flow to exist cannot, under when tapered end-sections or inlets are used inlet control can
adverse conditions, be relied upon to produce a full culvert occur either at the face or throat of the end-section, depending
Type 6 flow in moderately steep culverts. Adverse approach on culvert slope and relative areas of the face and throat. The
conditions involving strong air-carrying vortices over the inlet research shows further that inlet control at the face can occur
may cause inlet control, Type 5, flow. Within a certain range at either the outside or inside corner of the end-section wall
either Type 5 or Type 6 flow may occur, depending upon depending on wall thickness.
factors that are very difficult to evaluate. For example, the
wave pattern superimposed on the water-surface profile
13. Procedure
through the culvert can be important in determining full or
13.1 Culvert Site—Make a transit-stadia survey of the cul-
part-full flow. Within the range of geometries tested, however,
vert site. Obtain elevations of hubs, reference marks, culvert
theflowtypegenerallycanbedeterminedfromaknowledgeof
features, and if a flood event is involved, high-water marks to
entrance geometry and length, culvert slope, and roughness of
hundredths of a foot and ground elevations to tenths of a foot.
the culvert barrel.
13.2 Approach Section—Locate the approach section one
12.4.1 Type 5 Flow—As shown in Fig. 2, part-full flow
culvert width upstream from the culvert entrance to keep it out
under a high head is classified as Type 5. Type 5 flow is rapid
of the drawdown region. Where wingwalls exist and contrac-
at the inlet. The headwater-diameter ratio exceeds 1.5, and the
tion occurs around the ends of one or both wingwalls, locate it
tailwater elevation is below the crown at the outlet. The top
a distance upstream from the end of the wingwalls equal to the
edge of the culvert entrance contracts the flow in a manner
width between the wingwalls at their upstream end. Position
similar to a sluice gate.The culvert barrel flows partly full and
the section as nearly as possible at right angles to the direction
at a depth less than critical. The discharge equation for Type 5
of flow.
flow is as follows:
13.2.1 An approach section is not needed if only high flows
Q 5 CA =2g~h 2 z! (11)
o 1
areofinterestandtheareaoftheapproachchannelisestimated
to be equal to or greater than five times the area of the culvert
The occurrence of Type 5 flow requires a relatively square
barrel. Then the approach velocity is assumed to be zero.
entrance that will cause contraction of the area of live flow to
However, if no approach section is surveyed one may need to
much less than the area of the culvert barrel. In addition, the
be synthesized for use in computer programs.
combinationofbarrellength,roughness,andbedslopemustbe
13.2.2 Record the stationing where the shape of the channel
such that the contracted jet will not expand to the full area of
changes,suchaswherealowwaterchanneljoinsabroadflood
the barrel. If the water surface of the expanding flow comes in
terrace and where water leaves the banks and goes into a flood
contact with the top of the culvert, Type 6 flow will occur,
plain or overflow area. Also record the stationing of points
because the passage of air to the culvert will be sealed off
where bed material or vegetation cover change.
causing the culvert to flow full throughout its length. The
headwater elevation for a given discharge is generally lower
13.3 High Water Marks:
forType 6 flow than forType 5, indicating a more efficient use
13.3.1 For a computation of a flood discharge, obtain
of the culvert barrel.
high-water mark elevations at both ends of the approach
12.4.2 Type 6 Flow—InType6flowtheculvertisfullunder
section, preferably from short high-water profiles defined by a
pressure with free outfall as shown in Fig. 2. The headwater-
minimum of four marks on each bank or by marks along the
diameterratioexceeds1.5andthetailwaterdoesnotsubmerge
embankment located at least one culvert width away from the
the culvert outlet. The discharge equation between Sections 1
culvert entrance. The elevation at the top of the mark is the
and 3, neglecting V /2g and h , is as follows:
1 f
1–2 elevation needed to be consistent with field methods used to
verifytheroughnesscoefficient.High-waterelevationsonboth
Q 5 CA =2g h 2 h 2 h (12)
~ !
o 1 3 f
banks at the approach section are essential. Compute the
A straightforward application of Eq 12 is hampered by the discharge on basis of the average elevation. Also, a gauge
necessity of determining h , which varies from a point below located at one end of the approach section may register higher
thecenteroftheoutlettoitstop,eventhoughthewatersurface or lower than the average; therefore, establish a relation
is at the top of the culvert. This variation in piezometric head
betweenseveralaverageelevationsandtherecordedelevations
is a function of the Froude number at the outlet.This difficulty sothatastage-dischargerelationwillbecorrect.Markswillbe
has been circumvented by basing the data analysis upon high on the outside of banks, against the embankment over the
dimensionless ratios of physical dimensions related to the culvert, and on upstream side protruding points. Marks will be
Froude number. These functional relationships have been low on the inside of bends, within the area of drawdown, and
defined by laboratory experiment, and they have been incor- below protruding points.
porated into both manual computation methods and computer
13.3.2 Obtainthetailwaterelevationsalongthedownstream
programs. The relationships are given in 18.10.2.
banksorembankmentifthereisanypossibilityofbackwaterat
12.4.3 Tapered Inlets and Drop Inlets—Methods given in theculvertoutlet.Locatedownstreammarksasneartheculvert
this test method for distinguishing between Type 5 and Type 6 as possible but not within the area affected by the issuing jet.
D5243 − 92 (2019)
13.4 Culvert Geometry and Material: headwall join. Measure the invert elevations on a line normal
to the axis of the culvert and at the point where a full barrel
13.4.1 Record the type of material used for the culvert and
section begins or ends. Measure the length of the approach
the shape of the culvert, that is concrete pipe, concrete box,
corrugated pipe, corrugated pipe arch, multi-plate pipe or pipe reach to the invert line described above and the culvert length
is the distance between those lines. If multiple barrels are
arch, etc., and the condition of the culvert. Measure culvert
geometry, width (b) and height; or diameter (D); length (L); present, measure invert elevations separately in each barrel.
wingwall angle (θ); and chamfers or entrance rounding. The
13.9 Mitered Pipe and Pipes Arches—Miter pipes and pipe
wingwallangle,theta,istheacuteanglebetweenthewingwall
arches to match the slope of the highway embankment, as
andanextensionoftheheadwall.Obtainelevationsofinvertat
showninFig.4.Determinetheinvertelevationsattheextreme
inlet and at any place where there is a break in invert slope.
ends of the pipe and vertically below the points where the full
Obtain the elevation on the top of corrugations for corrugated
diameter of the pipe becomes effective. Measure crown eleva-
pipe and within the minimum diameter for concrete pipe.
tions at both ends of the full pipe section. Record the total
Measure the elevations of inverts of a box culvert at the end of
length between the extreme ends, the length of the miter, and
the culvert along lines perpendicular to the side walls. As a
the length of the full section of the culvert. Each of these
minimum,obtaininvertelevationsofboxculvertsatthecenter
dimensions enters into the computation of discharge as ex-
and at the walls. Obtain for wide culverts elevations at several
plained in 18.5.
placesacrosstheculvert.Determineelevationsofthecrownor
13.10 Flared and Tapered Inlets—Culverts may have end
top of the barrel at both ends. Locate relative positions of
sections designed to protect the culvert from deposition of
culvert barrel, wingwalls, aprons, and other features. Deter-
material eroded from embankment and to improve flow con-
mine the elevation at the upstream end of the apron if one is
ditions (see Figs. 5-7). These are most commonly used on
present.
corrugated metal pipes and pipe arches and on concrete pipes,
13.4.1.1 Paved Inverts—Some culverts are completely or
but they may also be used on box culverts. The face of an end
partially covered with cement, tar, or asphalt to protect the
section generally is wider than the culvert and at times it may
metal. Frequently corrugations near the bottom of the culvert
also have a greater depth than the culvert. Improved end
are filled with the material. If culvert is paved, record that fact
sectionsareoftwobasictypes.Onetypeisopenatthetop(see
anddeterminetheportionoftheculvertwherecorrugationsare
Figs. 5 and 6), the other tapers into the culvert from the sides,
filled.
top, and possibly the bottom (see Fig. 7). By convention and
13.4.1.2 Projection—Measure the amount of projection of
for convenience in distinguishing the two types, designate the
corrugated metal pipes.An acceptable method for determining
first type as a flared entrance and the second as a tapered
the amount of projection is to measure L at various points
p
entrance. If a flared or tapered entrance is present it must be
around the pipe entrance between the invert and the top of the
fully measured in the field and dimensioned in the field notes.
culvert. A good way to designate where each measurement is
Record width and shape of the face, elevation of top and
taken is to represent the culvert barrel as a circular clock face
bottom of the face, and elevation of breaks in slope of side
withhands.Thelocationofeachmeasurementisrepresentedas
walls of the end section.
a time on the clock.
13.5 Roughness Coeffıcient—Select a value of Manning’s n
14. Special Conditions
for the approach reach unless the approach section must be
14.1 Hydraulic characteristics of culverts in the field can be
subdivided when more than one n is necessary.Assign a value
greatly different from closely controlled laboratory conditions.
of n for each sub-area. If a computer program is to be used to
Before coefficients and methods derived in the laboratory can
compute discharge, assign the n-values according to specifics
be applied to field installations, consider any features that tend
of the program. A reasonable evaluation of the resistance to
to destroy model-prototype similarity.
flow in a channel depends on the experience of the person
selecting the coefficient and reference to texts and reports that
14.2 Drift—Examine drift found lodged at the inlet of a
contain values for similar stream and flow conditions. See Ref
culvert after a rise and evaluate its effect. It is not uncommon
(1)and9.3inthistestmethod.Selectan n-valuefortheculvert
formaterialtofloataboveaculvertatthepeakwithoutcausing
barrel. See Section 15 in this test method.
obstruction and then lodge at the bottom when the water
subsides. However, if examination shows it to be well com-
13.6 Obstructions—Describe and evaluate the effect, if
pacted in the culvert entrance and probably in the same
possible,ofanymaterialorconditionsthatmightobstructflow
position as during the peak, measure the obstructed area and
through the culvert.
deduct it from the total area.
13.7 Road Overflow—Note whether or not there was flow
14.2.1 Deposits in Culvert—Sand and gravel found within a
over the road nearby that should be included in the total flood
culvertbarrelareoftendepositedaftertheextremevelocitiesof
discharge. If overflow is possible, survey a profile along the
peak flow have passed; where this occurs, use the full area of
highest part of the road.
the culvert. Careful judgment must be exercised because, in
13.8 Skews—Someculverts,bothboxandpipe,areskewed; many places, levels before and after a peak show virtually the
thatis,theendorheadwallisnotnormaltothecenterlineofthe same invert elevations even though high velocities occurred.
culvert. At these sites measure the wingwall angle as for a Deposits composed of unconsolidated sand and small gravel
normal culvert as the acute angle at which the wingwall and generally will not remain in place if the velocity of flow in the
D5243 − 92 (2019)
FIG. 4 Approach and Culvert Lengths for Mitered Pipe
culvert exceeds about 4 ft/s (1.2 m/s) and may wash out at entrance. At times the approach roughness coefficient may be
lower velocities. Consolidated deposits and large cobbles may
lower than 0.030 in sand channels or when the culvert apron
withstand somewhat higher velocities.
and wingwalls extend upstream to, or through, the approach
14.2.2 Ice and Snow—In certain areas ice and snow may
section.
present problems. Ice very often causes backwater partly
15.2.1 Selectpointsofsubdivisionofthecrosssectioninthe
blocking the culvert entrance. Snow frequently causes the
field and assign values of n to the various sub-areas. For the
deposition of misleading high-water marks as it melts.
computationofaratingwherevariousheadwaterelevationsare
14.3 Breaks in Slope—Sometimesculvertsareinstalledwith
used, n and the points of subdivision may change. For these
a break in bottom slope. At other times a break in slope will
sections, note the elevations at which the changes take place.
occur as a result of uneven settling in soft fill material.
15.3 Culvert Sections—Fieldinspectionisalwaysnecessary
Determinetheelevationandlocationoftheinvertateachbreak
before n values are assigned to any culvert. The condition of
inslope.Abreakinslopefrequentlyoccurswhereaculverthas
the material, the type of joint, and the kind of bottom, whether
been lengthened during road reconstruction. In rare cases the
natural or constructed, all influence the selection of roughness
size,shape,ormaterial,orallthree,oftheculvertsectionsmay
coefficients.
differ. Measure the length of each section and determine the
invert elevation at each change. 15.3.1 Corrugated Metal—A number of laboratory tests
have been run to determine the roughness coefficient for
14.4 Streambed Bottoms—Many culverts, especially small
corrugated-metal pipes of all sizes.
bridge-type structures and multiplate arches, have natural
stream-bed bottoms. The irregularity of the bottom may 15.3.2 Riveted Construction—The corrugated metal most
present difficulties in applying these data to the equations for commonly used in the manufacture of pipes and pipe arches
2 1
certain types of flow. Take special care in the field to properly has a 2 ⁄3-in. (67.7-mm) pitch with a rise of ⁄2 in. (12.7 mm).
define the bottom elevation at each end of the culvert. This is frequently referred to as standard corrugated metal.
Sections of pipe arc riveted together. According to laboratory
15. Roughness Coefficients
tests (3), n values for full pipe flow vary from 0.0266 for a 1-ft
15.1 Select roughness coefficients in the field for use in the
(0.3-m) diameter pipe to 0.0224 for an 8-ft (2.4-m) diameter
Manning equation for both the approach reach and the culvert
pipe for the velocities normally encountered in culverts. The
at the time of the field survey.
AmericanIronandSteelInstitute (4)recommendsthatasingle
valueof0.024beusedindeignofbothpartly-fullandfull-pipe
15.2 Approach Section—Assign roughness coefficients se-
flow for any size of pipe. This value is also considered
lected for the approach reach to the approach section as being
satisfactory for most computations of discharge. For more
typical of the reach. These coefficients will usually be in the
precisecomputations,take nvaluesfromTable2.The nvalues
range between 0.030 and 0.060 at culverts, because stream
channels are usually kept cleared in the vicinity of the culvert in Table 2 were derived from tables and graphs published by
D5243 − 92 (2019)
Selected dimensions for various diameters of pipe
Diam AB C D E
(in.)
(ft in.) (ft in.) (ft in.) (ft in.) (ft in.)
7 7
12 0 4 2 0 4 0 ⁄8 60 ⁄8 20
15 0 6 2 3 3 10 6 1 2 6
18 0 9 2 3 3 10 6 1 3 0
1 1
21 0 9 3 0 3 1 ⁄2 61 ⁄2 36
1 1 1
24* 0 9 ⁄2 37 ⁄2 26 6 1 ⁄2 40
1 1 1
27 0 10 ⁄2 41 ⁄2 20 6 1 ⁄2 46
3 3
30* 1 0 4 6 1 7 ⁄4 61 ⁄4 50
3 3
36 1 3 5 3 2 10 ⁄4 81 ⁄4 60
42 1 9 5 3 2 11 8 2 6 6
48 2 0 6 0 2 2 8 2 7 0
1 1
54 2 3 5 5 2 9 ⁄4 82 ⁄4 76
1 3
* Overall length (D) of Iowa design is 8 ft 1 ⁄2 in. for 24 in. and 8 ft 1 ⁄4 in. for 30 in.
NOTE 1—Slope 3:1 for all sizes except 54 in. which is 2.4:1.
FIG. 5 Dimensions of Flared End Sections for Reinforced Concrete Pipe
FHWA for culvert design (5), and apply to both annular and construction is used with both steel and aluminum. The steel
helical corrugations as noted in the table. has a 6-in. (152.4-mm) pitch and a 2-in. (50.8-mm) rise,
15.3.2.1 Riveted pipes are also made from corrugated metal aluminum has a 9-in. (228.6-mm) pitch and a 2.5-in. (63.1-
with a 1-in. (25.4-mm) rise and 3, 5, and 6-in. (76.2, 127, and mm) rise. Tests show n values for this construction to be
152.4-mm)pitch.Experimentaldatashowsaslightloweringof somewhat higher than for riveted-pipe construction.Average n
the n values as the pitch increases.The n values for these three values range from 0.035 (steel) and 0.036 (aluminum) for 5-ft
types of corrugation are also shown in Table 2. (1.52-m) diameter pipes to 0.033 for pipes of 18 ft (5.48 m) or
15.3.3 Structural-Plate (Multiplate)—The metal most com- greaterdiameter.The nvaluesforvariousdiametersofpipeare
monly used in structural-plate (also called multiplate construc- tabulated in Table 2.
tion) has much larger corrugations than does standard corru- 15.3.4 Paved Inverts—In many instances the bottom parts
gated metal, and plates are bolted together. Structural-plate of corrugated pipe and pipe-arch culverts are paved, usually
D5243 − 92 (2019)
Details of steel end sections for circular steel pipe.
Details of steel end sections for steel pipe-arches.
FIG. 6 Details of End Sections for Steel Pipes and Pipe Arches
0.012P 10.024 P 2 P
with a bituminous material. This reduces the roughness coef- ~ !
p p
n 5 , (13)
c
ficient to a value between that normally used and 0.012. The P
reduction is directly proportional to the percentage of wetted
where:
perimeter that is paved. The composite value of n for standard
P = length of wetted perimeter that is paved, and
p
pipes and pipe-arches may be computed by the following
P = total length of wetted perimeter.
equation:
D5243 − 92 (2019)
to 60 ft (12 to 20 m). King (7) stated that the losses in a 45°
bendmaybeabout ⁄4asgreatasthoseina90°bend,andlosses
fora22 ⁄2 ° bend may be about half as great as those of a 90°
bend.
15.3.6 Other Materials—Occasionally culverts will be con-
structed of some material other than concrete or corrugated
metal. Manning’s coefficients (7) for some of these materials
are given in Table 3.
15.3.6.1 Culverts made from cement rubble or rock may
have roughness coefficients ranging from 0.020 to 0.030,
depending on the type of material and the care with which it is
laid.
15.3.7 Natural Bottoms—Many culverts, especially the
large arch type, are constructed with the natural channel as the
bottom. The bottom roughness usually weights the composite
roughnesscoefficientquiteheavily,especiallywhenthebottom
is composed of cobbles and large angular rock. The formula
used for paved inverts can be used here if the correct n values
are substituted therein.
16. Coefficients of Discharge—General
16.1 Coefficients of discharge, C, for all six types of flow
have been defined by laboratory studies.They range from 0.39
FIG. 7 Details of Typical Tapered Entrances
to 0.98 for average entrances and are functions of the type of
flow, degree of channel contraction, and the geometry of the
culvert entrance.
15.3.4.1 Eq 13 is for corrugations having a 2 ⁄3-in. (67.7-
16.2 Entrance geometries may require an adjustment to a
mm) rise and a ⁄2-in. (12.7-mm) rise. For other corrugations,
base coefficient for entrance rounding (k ) or for beveling or
r
the value of 0.024 must be replaced with the correct value
wingwalls (k ). An adjusted coefficient of 0.98 is the limiting
w
corresponding to the corrugation and size of the pipe.
value.
15.3.4.2 Occasionally the paving material may extend sev-
eral inches (millimetres) above the corrugations. Where this 16.3 The coefficients are applicable to skewed culverts and
condition exists, the area and wetted perimeter should be to both single barrel and multi-barrel installations. If the width
adjusted accordingly. ofthewebbetweenbarrelsatamulti-barrelsiteislessthan0.1
15.3.5 Concrete—The roughness coefficient of concrete is the width of a single barrel, it should be disregarded when
dependent upon the condition of the concrete and the irregu- evaluating the entrance geometry. Bevels are considered as
larities of the surface resulting from construction. Suggested
suchonlyiftheyare0.1orlessofthediameter,depth,orwidth
values of n for general use are as follows: ofaculvertbarrel.Ifgreaterthan0.1,theyareconsideredtobe
wingwalls.
Condition of Concrete n
16.4 Thegeometryofthesidesdetermines CforTypes1,2,
Very smooth (spun pipe) 0.010
and 3 flow, and that for the top and sides determines C for
Smooth (cast or tamped pipe) 0.011–0.015
Ordinary field construction 0.012–0.015
Types 4, 5, and 6 flow.
Badly spalled 0.015–0.020
16.5 Coefficients for the six flow types have been divided
15.3.5.1 Displacement—At times, sections of concrete pipe
into three groups, each group having a discharge equation of
became displaced either vertically or laterally, resulting in a
the same general form. Thus, Types 1, 2, and 3 are in the first
much rougher interior surface than normal. When this occurs,
group, Types 4 and 6 in the second, and Type 5 in the third.
increase n commensurate with the degree of displacement of
16.6 The entrance geometries have been classified in four
the culvert sections. Laboratory tests
...