ISO 8368:1999
(Main)Hydrometric determinations — Flow measurements in open channels using structures — Guidelines for selection of structure
Hydrometric determinations — Flow measurements in open channels using structures — Guidelines for selection of structure
Déterminations hydrométriques — Mesure de débit dans les canaux découverts au moyen de structures — Lignes directrices pour le choix des structures
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Standards Content (Sample)
INTERNATIONAL ISO
STANDARD 8368
Second edition
1999-04-01
Hydrometric determinations — Flow
measurements in open channels using
structures — Guidelines for selection
of structure
Déterminations hydrométriques — Mesure de débit dans les canaux
découverts au moyen de structures — Lignes directrices pour le choix
des structures
A
Reference number
ISO 8368:1999(E)
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ISO 8368:1999(E)
Contents
1 Scope .1
2 Normative references .1
3 Terms, definitions and symbols.2
4 Types of structure.2
5 Factors affecting choice .3
5.1 General.3
5.2 Purpose.3
5.3 Range of flow .3
5.4 Afflux.3
5.5 Size and nature of channel .6
5.6 Channel slope and sediment load.6
5.7 Operation and maintenance .6
5.8 Passage of fish.6
5.9 Cost.7
6 Recommendations.7
6.1 Thin-plate weirs.7
6.2 Broad-crested weirs .7
6.3 Triangular-profile weirs.8
6.4 Streamlined triangular-profile weirs .8
6.5 Flat-V weirs.8
6.6 Compound gauging structures .8
6.7 Trapezoidal-profile weirs .8
6.8 Vertical underflow gates and radial gates.9
6.9 End-depth method .9
6.10 Flumes .9
7 Parameters governing choice of structures .9
© ISO 1999
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© ISO
ISO 8368:1999(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO
member bodies). The work of preparing International Standards is normally carried out through ISO technical
committees. Each member body interested in a subject for which a technical committee has been established has
the right to be represented on that committee. International organizations, governmental and non-governmental, in
liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical
Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 3.
Draft International Standards adopted by the technical committees are circulated to the member bodies for voting.
Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote.
International Standard ISO 8368 was prepared by Technical Committee ISO/TC 113, Hydrometric determinations,
Subcommittee SC 2, Notches, weirs and flumes.
This second edition cancels and replaces the first edition (ISO 8368:1985). This second edition of ISO 8368 was
prepared in order to bring the techniques described up to date. The format has been improved to make the information
easier to interpret.
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INTERNATIONAL STANDARD © ISO ISO 8368:1999(E)
Hydrometric determinations — Flow measurements in open
channels using structures — Guidelines for selection of structure
1 Scope
This International Standard gives guidelines for selection of a particular type of flow-gauging structure for measurement
of liquid flow in open channels. It sets out the factors, and summarizes the parameters which may influence such a
selection.
NOTE In general, a flow-gauging structure is used when high accuracy is required for continuous records of flow.
2 Normative references
The following normative documents contain provisions which, through reference in this text, constitute provisions of this
International Standard. For dated references, subsequent amendments to, or revisions of, any of these publications do
not apply. However, parties to agreements based on this International Standard are encouraged to investigate the
possibility of applying the most recent editions of the normative documents listed below. For undated references, the
latest edition of the normative document referred to applies. Members of IEC and ISO maintain registers of currently
valid International Standards.
ISO 772, Hydrometric determinations — Vocabulary and symbols.
ISO 1438-1, Water flow measurement in open channels using weirs and Venturi flumes — Part 1: Thin-plate weirs.
ISO 3846, Liquid flow measurement in open channels by weirs and flumes — Rectangular broad-crested weirs.
ISO 3847, Liquid flow measurement in open channels by weirs and flumes — End-depth method for estimation of flow
in rectangular channels with a free overfall.
ISO 4359, Liquid flow measurement in open channels — Rectangular, trapezoidal and U-shaped flumes.
ISO 4360, Liquid flow measurement in open channels by weirs and flumes — Triangular-profile weirs.
ISO 4362, Measurement of liquid flow in open channels — Trapezoidal profile weirs.
ISO 4371, Measurement of liquid flow in open channels by weirs and flumes — End depth method for estimation of
flow in non-rectangular channels with a free overfall (approximate method).
ISO 4374, Liquid flow measurement in open channels — Round-nose horizontal broad-crested weirs.
ISO 4377, Liquid flow measurement in open channels — Flat-V weirs.
ISO 8333, Liquid flow measurement in open channels by weirs and flumes — V-shaped broad-crested weirs.
ISO 9826:1992, Measurement of liquid flow in open channels — Parshall and SANIIRI flumes.
ISO 9827, Measurement of liquid flow in open channels by weirs and flumes — Streamlined triangular-profile weirs.
ISO 13550 , Hydrometric determinations — Flow measurements in open channels using structures — Use of vertical
underflow gates and radial gates.
ISO 14139, Hydrometric determinations — Flow measurements in open channels using structures — Compound
gauging structures.
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© ISO
ISO 8368:1999(E)
3 Terms, definitions and symbols
For the purposes of this International Standard, the terms, definitions and symbols together with the corresponding
units of measurement given in ISO 772 apply.
4 Types of structure
The following types of structure can be used for the purpose of liquid flow measurement:
a) thin-plate weirs:
1) rectangular;
2) V-notch.
b) broad-crested weirs:
1) round-nose horizontal;
2) rectangular horizontal;
3) V-shaped.
c) triangular-profile weirs.
d) streamlined triangular-profile weirs.
e) flat-V weirs.
f) flumes:
1) rectangular;
2) trapezoidal;
3) U-throated;
4) Parshall and SANIIRI.
g) end-depth method:
1) rectangular channel;
2) non-rectangular channel (approximate method).
h) trapezoidal-profile weirs.
i) compound gauging structures.
j) vertical underflow gates and radial gates.
Diagrams showing the construction of a particular type of flow-gauging structure are given in the appropriate
International Standard listed in clause 2.
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© ISO
ISO 8368:1999(E)
5 Factors affecting choice
5.1 General
The factors which affect choice can be considered under the following headings:
a) purpose;
b) range of flow;
c) afflux;
d) size and nature of channel;
e) channel slope and sediment load;
f) operation and maintenance;
g) environmental impact;
h) passage of fish;
i) cost.
5.2 Purpose
Table 1 tabulates the various structures and indicates some of the purposes for which they may be applicable, together
with guidelines to their limitations.
The purpose for which the structure is required will determine the range of flows and accuracies which is necessary.
The accuracy in a single determination of discharge depends upon the estimation of the component uncertainties
involved.
In broad terms, thin-plate weirs will have a range of uncertainties from 1 % to 4 %, flumes and certain types of weirs will
have a range from 2 % to 5 % and end methods and other weirs will have a range from 4 % to 10 %. Deviations from
the construction, installation or use as laid down in the appropriate International Standard will result in measurement
errors.
5.3 Range of flow
It is necessary to consider the relation between maximum flow and minimum flow when deciding which type of
structure to use, and an indication of the range of some typical structures is given in Table 2. For the best overall
accuracy over a wide range of small discharges, a thin-plate V-notch weir should be used in preference to a thin-plate
rectangular notch or rectangular full-width weir. For a wide range of larger discharges, a trapezoidal flume, a flat-V weir
or a triangular-profile weir should be used in preference to a broad-crested weir, free overfall or rectangular-throat
flume.
5.4 Afflux
The rise in level immediately upstream of, and due to, a structure may interfere with the flow system and cause
drainage problems, or limit the effectiveness of irrigation systems, or cause extra pumping costs. In addition, the
aquatic habitat upstream of the structure may be adversely affected. A number of structures have been developed with
high coefficients of discharge and whose accuracy is relatively unimpaired by high submergence ratios. The triangular-
profile and flat-V weirs, and flumes are examples of this type of structure.
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© ISO
ISO 8368:1999(E)
Table 1 — Applications and limitations of structures
Typical
uncer-
Inter-
1)
Modular
tainties in
Type national
Limitations Typical application
computed limit
Standard
discharge,
%
Thin-plate weirs ISO 1438-1 1 to 4 2) 3)
Laboratory, pump tests, sediment free water,
2
small streams, and for use in hydraulics
laboratories.
Broad-crested weirs
Broad-crested weirs are best used in rec-
3)
tangular channels, but they can be used with
a) rectangular profile ISO 3846 66 % 1,5
3) good accuracy in non-rectangular channels if a
b) round-nose horizontal ISO 4374 3 to 5 80 % 1,5
smooth, rectangular approach channel extends
crest
upstream of the weir for a distance not less
c) V-shaped
ISO 8333 80 % 1,5
than twice the maximum head. Irrigation
3)
3,0
channels with little fall available and wide
range of flow.
3)
Triangular-profile weirs ISO 4360 2 to 5 75 % 3,5 Hydrometric networks and principal irrigation
channels
Streamlined triangular- ISO 9827 2 to 5 ? ? Irrigation works and minor channels
profile weirs
3)
Flat-V weirs ISO 4377 2 to 5 70 % 2,5 Hydrometric works with wide range of flow
Compound gauging ISO 14139 2 to 5 Varies Vary Hydrometric works with wide range of flow
structures
3)
Trapezoidal-profile weirs ISO 4362 4 to 8 65 % to Where ease of construction is an important
1,3
4)
85 % factor. Irrigation works and minor channels.
2)
Vertical underflow gates ISO 13550 4 to 8 See Situations where a near constant upstream
and radial gates ISO 13550 water level is required.
2) 6)
End-depth method Where accuracy may be relaxed for simplicity
and economy.
a) rectangular ISO 3847 5 to 10
b) non-rectangular ISO 4371
5)
Long-throated flumes ISO 4359 2 to 5 74 % Flumes can be used in channels of any shape
0,7
if flow conditions in the approach channel are
reasonably uniform and steady. Sediment-
laden channels, flow with debris, flow with
migratory fish, conduits and partially filled
pipes, flow in sewers.
Parshall and SANIIRI ISO 9826 4 to 8 60 % to See Flumes can be used in channels of any shape
flumes 80 % if flow conditions in the approach channel are
ISO 9826
reasonably uniform and steady. Hydrometric
networks and water distribution channels.
1)
The modular limit of each device requires careful consideration. The submergence ratio should be checked for the whole range of flows to
be measured and compared with values for the modular limit given in Table 1.
2)
Nappe to be fully aerated.
3)
Maximum H/p, where H is the total upstream head and p is the height of the weir.
4)
Depends on geometry.
5)
Maximum A /A , where A and A are the cross-sectional areas of the throat and approach channel, respectivel
...
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