ISO 1438:2017
(Main)Hydrometry — Open channel flow measurement using thin-plate weirs
Hydrometry — Open channel flow measurement using thin-plate weirs
ISO 1438:2017 defines the requirements for the use of rectangular and triangular (V-notch) thin-plate weirs for the measurement of flow of clear water in open channels under free flow conditions. It includes the requirements for the use of full-width rectangular thin-plate weirs in submerged (drowned) flow conditions.
Hydrométrie — Mesure de débit dans les canaux à écoulement à surface libre au moyen de déversoirs en mince paroi
Le présent document définit les exigences d'utilisation de déversoirs en mince paroi à échancrures rectangulaires et triangulaires pour le mesurage du débit d'eau claire dans des canaux à écoulement à surface libre pleinement aéré. Il comprend les exigences d'utilisation de déversoirs en mince paroi rectangulaires sans contraction latérale en conditions d'écoulement noyé.
Hidrometrija - Meritev pretoka odprtega kanala z uporabo jezov iz tanke plošče
Ta dokument določa zahteve za uporabo jezov iz pravokotne in trikotne (V-zareza) tanke plošče
za meritev pretoka čiste vode v odprtih kanalih v pogojih prostega pretoka. Vključuje zahteve za uporabo jezov iz široke pravokotne tanke plošče v pogojih potopljenega preliva.
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Standards Content (Sample)
SLOVENSKI STANDARD
SIST ISO 1438:2018
01-junij-2018
1DGRPHãþD
SIST ISO 1438:2015
SIST ISO 1438:2015/Cor 1:2015
+LGURPHWULMD0HULWHYSUHWRNDRGSUWHJDNDQDOD]XSRUDERMH]RYL]WDQNHSORãþH
Hydrometry - Open channel flow measurement using thin-plate weirs
Hydrométrie - Mesure de débit dans les canaux découverts au moyen de déversoirs à
paroi mince
Ta slovenski standard je istoveten z: ISO 1438:2017
ICS:
17.120.20 Pretok v odprtih kanalih Flow in open channels
SIST ISO 1438:2018 en,fr
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST ISO 1438:2018
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SIST ISO 1438:2018
INTERNATIONAL ISO
STANDARD 1438
Third edition
2017-04
Hydrometry — Open channel flow
measurement using thin-plate weirs
Hydrométrie — Mesure de débit dans les canaux découverts au moyen
de déversoirs à paroi mince
Reference number
ISO 1438:2017(E)
©
ISO 2017
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SIST ISO 1438:2018
ISO 1438:2017(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2017, Published in Switzerland
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form
or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior
written permission. Permission can be requested from either ISO at the address below or ISO’s member body in the country of
the requester.
ISO copyright office
Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel. +41 22 749 01 11
Fax +41 22 749 09 47
copyright@iso.org
www.iso.org
ii © ISO 2017 – All rights reserved
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SIST ISO 1438:2018
ISO 1438:2017(E)
Contents Page
Foreword .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms . 1
5 Principle . 2
6 Installation . 2
6.1 General . 2
6.2 Selection of site . 2
6.3 Installation conditions. 2
6.3.1 General. 2
6.3.2 Weir . 3
6.3.3 Approach channel . 3
6.3.4 Downstream channel . 4
7 Measurement of head . 4
7.1 Head-measuring devices . 4
7.2 Stilling or float well . 5
7.3 Head-measurement section . 5
7.3.1 Upstream head-measurement . 5
7.3.2 Downstream head measurement . 5
7.4 Head-gauge datum (gauge zero) . 5
8 Maintenance . 6
9 Rectangular thin-plate weir . 6
9.1 Types. 6
9.2 Specifications for the standard weir . 8
9.3 Specifications for installation . 8
9.4 Determination of gauge zero . 8
9.5 Discharge formulae — General . 11
9.6 Formulae for the basic weir form (all values of b/B) . 11
9.6.1 Kindsvater-Carter formula . 11
9.6.2 Evaluation of C , k and k .
d b h 11
9.6.3 Formulae for C .
d 13
9.6.4 Practical limitations on h/p, h, b and p . 14
9.7 Formulae for full-width weirs (b/B = 1,0) .14
9.7.1 Modular flow discharge formula .14
9.7.2 Non-modular flow discharge formula .15
10 Triangular-notch thin-plate weir .16
10.1 Specifications for the standard weir .16
10.2 Specifications for the installation .19
10.3 Specifications for head measurement .19
10.3.1 General.19
10.3.2 Determination of notch angle .19
10.3.3 Determination of gauge zero .19
10.4 Discharge formulae — General .20
10.5 Formula for all notch angles between π/9 and 5 π/9 radians (20° and 100°) .20
10.5.1 Kindsvater-Shen formula .20
10.5.2 Evaluation of C and k .
d h 20
10.5.3 Practical limitations on α, h/p, p/B, h and p . 22
10.6 Formula for specific notch angles (fully-contracted weir) .22
10.7 Accuracy of discharge coefficients — Triangular-notch weirs .23
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11 Uncertainties of flow measurement .23
11.1 General .23
11.2 Combining measurement uncertainties .24
*
11.3 Uncertainty of discharge coefficient, u (C ), for thin-plate weirs .25
d
11.4 Uncertainty budget.26
12 Example .26
12.1 General .26
12.2 Characteristics — Gauging structure .26
12.3 Characteristics — Gauged head instrumentation .27
12.4 Discharge coefficient .27
12.5 Discharge estimate .27
12.6 Uncertainty statement .27
Annex A (informative) Flow measurement with small weir tanks .30
Annex B (normative) Guide to the design and installation of a flow straightener .32
Annex C (informative) Introduction to measurement uncertainty.34
Annex D (informative) Sample measurement performance for use in
hydrometric worked examples .42
Annex E (informative) Specimen tables .45
Bibliography .60
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SIST ISO 1438:2018
ISO 1438:2017(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.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO’s adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following
URL: w w w . i s o .org/ iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 113, Hydrometry, Subcommittee SC 2,
Flow measurement structures.
This third edition cancels and replaces the second edition (ISO 1438:2008), which has been technically
revised. It also incorporates the Technical Corrigendum ISO 1438:2008/Cor 1:2008.
The major changes from ISO 1438:2008 are as follows:
a) the modular flow discharge formula for weirs with weir plate height of 1 m ≤ p ≤ 2,5 m has been
supplemented in 9.7.1;
b) the C formula for rectangular weir with b/B = 1,0, Formula (5), has been corrected to the same
d
formula as the full-width weir, Formula (15);
c) subclause numbers of 9.6 have been re-numbered.
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SIST ISO 1438:2018
INTERNATIONAL STANDARD ISO 1438:2017(E)
Hydrometry — Open channel flow measurement using
thin-plate weirs
1 Scope
This document defines the requirements for the use of rectangular and triangular (V-notch) thin-plate
weirs for the measurement of flow of clear water in open channels under free flow conditions. It includes
the requirements for the use of full-width rectangular thin-plate weirs in submerged (drowned) flow
conditions.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 772, Hydrometry — Vocabulary and symbols
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 772 apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at http:// www .electropedia .org/
— ISO Online browsing platform: available at http:// www .iso .org/ obp
4 Symbols and abbreviated terms
Symbol Unit Description
2
A m Area of approach channel
B m Width of approach channel
b m Measured width of the notch
b m Width of notch at maximum head (V-notch)
max
C Discharge coefficient (gauged head)
C Coefficient of discharge
d
f Drowned flow reduction factor
C Coefficient of velocity
v
e m Random uncertainty in the width measurement
b
2
g m/s Acceleration due to gravity
H m Total head above crest level
h m Upstream gauged head above crest level (upstream head is inferred if no subscript is used)
J Numerical constant
l m Distance of the head measurement section upstream of the weir
n Number of measurements in a set
p m Height of the crest relative to the floor
3
Q m /s Volumetric rate of flow
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Symbol Unit Description
S Submergence ratio, h /h
2 1
S Modular limit
1
m/s Mean velocity
V
U % Expanded percentage uncertainty
u*(b) % Percentage uncertainty in b
u*(C) % Percentage uncertainty in C
u*(E) % Percentage uncertainty in datum measurement
u*(h ) % Percentage uncertainty in h
1 1
u*(Q) % Percentage uncertainty in Q
α ° Notch angle
Subscripts
1 upstream
2 downstream
e effective
r rectangular
t triangular
5 Principle
The discharge over thin-plate weirs is a function of the upstream head on the weir (for free-flow),
upstream and downstream head (for drowned flow), the size and shape of the discharge area, and an
experimentally determined coefficient which takes into account the head, the geometrical properties of
the weir and approach channel, and the dynamic properties of the water.
6 Installation
6.1 General
General requirements of weir installations are described in the following clauses. Special requirements
of different types of weirs are described in clauses which deal with specific weirs (see Clause 9 and
Clause 10).
6.2 Selection of site
The type of weir to be used for discharge measurement is determined in part by the nature of the
proposed measuring site. Under some conditions of design and use, weirs shall be located in rectangular
flumes or in weir boxes which simulate flow conditions in rectangular flumes. Under other conditions,
weirs may be located in natural channels, as well as flumes or weir boxes, with no significant difference
in measurement accuracy. Specific site-related requirements of the installation are described in 6.3.
6.3 Installation conditions
6.3.1 General
Weir discharge is critically influenced by the physical characteristics of the weir and the weir
channel. Thin-plate weirs are especially dependent on installation features which control the velocity
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distribution in the approach channel and on the construction and maintenance of the weir crest in
meticulous conformance with standard specifications.
6.3.2 Weir
Thin-plate weirs shall be vertical and perpendicular to the walls of the channel. The intersection of the
weir plate with the walls and floor of the channel shall be watertight and firm, while the weir shall be
capable of withstanding the maximum flow without distortion or damage.
Stated practical limits associated with different discharge formulae such as minimum width, minimum
weir height, minimum head, and maximum values of h/p and b/B (where h is the measured head, p is the
height of crest relative to floor, b is the measured width of the notch and B is the width of the approach
channel), are factors which influence both the selection of weir type and the installation.
6.3.3 Approach channel
For the purposes of this document, the approach channel is the portion of the weir channel which
extends upstream from the weir a distance not less than five times the width of the nappe at maximum
head. If the weir is located in a weir tank, ideally, the length of the tank should equal up to 10 times the
width of the nappe at maximum head. Information on the use of small weir tanks is given in Annex A.
The flow in the approach channel shall be uniform and steady, with the velocity distribution
approximating that in a channel of sufficient length to develop satisfactory flow in smooth, straight
channels. Figure 1 shows measured velocity distributions perpendicular to the direction of flow in
rectangular channels, upstream from the influence of a weir. Baffles and flow straighteners can be used
to simulate satisfactory velocity distribution, but their location with respect to the weir shall be not
less than the minimum length prescribed for the approach channel.
The influence of approach-channel velocity distribution on weir flow increases as h/p and b/B increase
in magnitude. If a weir installation unavoidably results in a velocity distribution that is appreciably non-
uniform, the possibility of error in calculated discharge should be checked by means of an alternative
discharge-measuring method for a representative range of discharges.
If the approach conditions are judged to be unsatisfactory, then flow straighteners shall be introduced
in accordance with Annex B.
If the maximum head to be measured is restricted to (2/3)p for all types of weirs, flow straighteners
can be used to reduce the effective length of the approach channel to B + 3h for triangular and
max
rectangular weirs and to B + 5h for full-width weirs.
max
NOTE This restriction on the maximum head to be measured is necessary due to distortion of the velocity
near the water surface in the approach channel that results from flow coming through the openings in the baffle
of the flow straightener.
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a)
b)
c)
NOTE The contours refer to values of local flow velocity relative to the mean cross-sectional velocity.
Figure 1 — Examples of normal velocity distribution in rectangular channels
6.3.4 Downstream channel
For most applications, the level of the water in the downstream channel shall be a sufficient vertical
distance below the crest to ensure free, fully ventilated discharges. Free (non-submerged) discharge
occurs when the discharge is independent of the downstream water level. Fully ventilated discharge
is ensured when the air pressure on the lower surface of the nappe is fully ventilated. Drowned
flow operation is permitted for full-width weirs under certain conditions (see 9.7.2). Under these
circumstances, downstream water levels may rise above crest level.
7 Measurement of head
7.1 Head-measuring devices
In order to obtain the discharge measurement accuracies specified for the standard weirs, the head
on the weir shall be measured with a laboratory-grade hook gauge, point gauge, manometer, or other
gauge of equivalent accuracy. For a continuous record of head variants, precise float gauges and servo-
operated point gauges can be used. Staff and tape gauges can be used when less accurate measurements
are acceptable.
Additional specifications for head-measuring devices are given in ISO 4373.
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7.2 Stilling or float well
For the exceptional case where surface velocities and disturbances in the approach channel are
negligible, the headwater level can be measured directly (for example, by means of a point gauge
mounted over the water surface). Generally, however, to avoid water-level variations caused by waves,
turbulence or vibration, the headwater level should be measured in a separate stilling well.
Separate stilling wells are connected to the approach channel by means of a suitable conduit, equipped
if necessary with a throttle valve to damp oscillations. At the channel end of the conduit, the connection
is made to floor or wall piezometers or a static tube at the head-measurement section.
Additional specifications for stilling wells are given in ISO 18365.
7.3 Head-measurement section
7.3.1 Upstream head-measurement
The head-measurement section shall be located a sufficient distance upstream from the weir to avoid
the region of surface drawdown caused by the formation of the nappe. On the other hand, it shall be
sufficiently close to the weir that the energy loss between the head-measurement section and the weir
is negligible. For the weirs included in this document, the location of the head-measurement section
will be satisfactory if it is at a distance equal to two to four times the maximum head (2h to 4h )
max max
upstream from the weir.
If high velocities occur in the approach channel or if water-surface disturbances or irregularities occur
at the head-measurement section because of high values of h/p or b/B, it may be necessary to install
several pressure intakes to ensure that the head measured in the gauge well is representative of the
average head across the measurement section.
In the case of a full-width thin-plate weir, the effect of frictional effects upon the upstream channel
requires an adjustment to the standard coefficient of discharge. The correction is in terms of both l/h
and h/p and given in Table 1.
Table 1 — Factors to be applied to the standard discharge coefficient values
h/p l/h
2 4 6 8
3,5 to 4,0 1,00 1,00 0,96 0,92
3,0 to 3,5 1,00 1,00 0,97 0,94
2,5 to 3,0 1,00 1,00 0,98 0,96
2,0 to 2,5 1,00 1,00 0,99 0,98
Less than 2,0 1,00 1,00 1,00 1,00
7.3.2 Downstream head measurement
If the weir is to be operated in the submerged (drowned) flow range, a measurement of downstream
head is required in addition to the upstream. The downstream head measurement position shall be
10 h downstream from the upstream face of the weir. If a stilling well is included in the design, it is
max
recommended that the downstream head measurement be located no closer to the weir than 4 h .
max
7.4 Head-gauge datum (gauge zero)
Accuracy of head measurements is critically dependent upon the determination of the head-gauge
datum or gauge zero, which is defined as the gauge reading corresponding to the level of the weir crest
(rectangular weirs) or the level of the vertex of the notch (triangular-notch weirs). When necessary,
the gauge zero shall be checked. Numerous acceptable methods of determining the gauge zero are in
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use. Typical methods are described in subsequent clauses dealing specifically with rectangular and
triangular weirs. See Clause 9 and Clause 10.
Because of surface tension, the gauge zero cannot be determined with sufficient accuracy by reading the
head gauge with the water in the approach channel drawn down to the apparent crest (or notch) level.
8 Maintenance
Maintenance of the weir and the weir channel is necessary to ensure accurate measurements.
The approach channel shall be kept free of silt, vegetation and obstructions which might have deleterious
effects on the flow conditions specified for the standard installation. The downstream channel shall be
kept free of obstructions which might cause submergence or inhibit full ventilation of the nappe under
all conditions of flow.
The we
...
INTERNATIONAL ISO
STANDARD 1438
Third edition
2017-04
Hydrometry — Open channel flow
measurement using thin-plate weirs
Hydrométrie — Mesure de débit dans les canaux découverts au moyen
de déversoirs à paroi mince
Reference number
ISO 1438:2017(E)
©
ISO 2017
---------------------- Page: 1 ----------------------
ISO 1438:2017(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2017, Published in Switzerland
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form
or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior
written permission. Permission can be requested from either ISO at the address below or ISO’s member body in the country of
the requester.
ISO copyright office
Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel. +41 22 749 01 11
Fax +41 22 749 09 47
copyright@iso.org
www.iso.org
ii © ISO 2017 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 1438:2017(E)
Contents Page
Foreword .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms . 1
5 Principle . 2
6 Installation . 2
6.1 General . 2
6.2 Selection of site . 2
6.3 Installation conditions. 2
6.3.1 General. 2
6.3.2 Weir . 3
6.3.3 Approach channel . 3
6.3.4 Downstream channel . 4
7 Measurement of head . 4
7.1 Head-measuring devices . 4
7.2 Stilling or float well . 5
7.3 Head-measurement section . 5
7.3.1 Upstream head-measurement . 5
7.3.2 Downstream head measurement . 5
7.4 Head-gauge datum (gauge zero) . 5
8 Maintenance . 6
9 Rectangular thin-plate weir . 6
9.1 Types. 6
9.2 Specifications for the standard weir . 8
9.3 Specifications for installation . 8
9.4 Determination of gauge zero . 8
9.5 Discharge formulae — General . 11
9.6 Formulae for the basic weir form (all values of b/B) . 11
9.6.1 Kindsvater-Carter formula . 11
9.6.2 Evaluation of C , k and k .
d b h 11
9.6.3 Formulae for C .
d 13
9.6.4 Practical limitations on h/p, h, b and p . 14
9.7 Formulae for full-width weirs (b/B = 1,0) .14
9.7.1 Modular flow discharge formula .14
9.7.2 Non-modular flow discharge formula .15
10 Triangular-notch thin-plate weir .16
10.1 Specifications for the standard weir .16
10.2 Specifications for the installation .19
10.3 Specifications for head measurement .19
10.3.1 General.19
10.3.2 Determination of notch angle .19
10.3.3 Determination of gauge zero .19
10.4 Discharge formulae — General .20
10.5 Formula for all notch angles between π/9 and 5 π/9 radians (20° and 100°) .20
10.5.1 Kindsvater-Shen formula .20
10.5.2 Evaluation of C and k .
d h 20
10.5.3 Practical limitations on α, h/p, p/B, h and p . 22
10.6 Formula for specific notch angles (fully-contracted weir) .22
10.7 Accuracy of discharge coefficients — Triangular-notch weirs .23
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ISO 1438:2017(E)
11 Uncertainties of flow measurement .23
11.1 General .23
11.2 Combining measurement uncertainties .24
*
11.3 Uncertainty of discharge coefficient, u (C ), for thin-plate weirs .25
d
11.4 Uncertainty budget.26
12 Example .26
12.1 General .26
12.2 Characteristics — Gauging structure .26
12.3 Characteristics — Gauged head instrumentation .27
12.4 Discharge coefficient .27
12.5 Discharge estimate .27
12.6 Uncertainty statement .27
Annex A (informative) Flow measurement with small weir tanks .30
Annex B (normative) Guide to the design and installation of a flow straightener .32
Annex C (informative) Introduction to measurement uncertainty.34
Annex D (informative) Sample measurement performance for use in
hydrometric worked examples .42
Annex E (informative) Specimen tables .45
Bibliography .60
iv © ISO 2017 – All rights reserved
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ISO 1438:2017(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.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO’s adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following
URL: w w w . i s o .org/ iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 113, Hydrometry, Subcommittee SC 2,
Flow measurement structures.
This third edition cancels and replaces the second edition (ISO 1438:2008), which has been technically
revised. It also incorporates the Technical Corrigendum ISO 1438:2008/Cor 1:2008.
The major changes from ISO 1438:2008 are as follows:
a) the modular flow discharge formula for weirs with weir plate height of 1 m ≤ p ≤ 2,5 m has been
supplemented in 9.7.1;
b) the C formula for rectangular weir with b/B = 1,0, Formula (5), has been corrected to the same
d
formula as the full-width weir, Formula (15);
c) subclause numbers of 9.6 have been re-numbered.
© ISO 2017 – All rights reserved v
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INTERNATIONAL STANDARD ISO 1438:2017(E)
Hydrometry — Open channel flow measurement using
thin-plate weirs
1 Scope
This document defines the requirements for the use of rectangular and triangular (V-notch) thin-plate
weirs for the measurement of flow of clear water in open channels under free flow conditions. It includes
the requirements for the use of full-width rectangular thin-plate weirs in submerged (drowned) flow
conditions.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 772, Hydrometry — Vocabulary and symbols
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 772 apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at http:// www .electropedia .org/
— ISO Online browsing platform: available at http:// www .iso .org/ obp
4 Symbols and abbreviated terms
Symbol Unit Description
2
A m Area of approach channel
B m Width of approach channel
b m Measured width of the notch
b m Width of notch at maximum head (V-notch)
max
C Discharge coefficient (gauged head)
C Coefficient of discharge
d
f Drowned flow reduction factor
C Coefficient of velocity
v
e m Random uncertainty in the width measurement
b
2
g m/s Acceleration due to gravity
H m Total head above crest level
h m Upstream gauged head above crest level (upstream head is inferred if no subscript is used)
J Numerical constant
l m Distance of the head measurement section upstream of the weir
n Number of measurements in a set
p m Height of the crest relative to the floor
3
Q m /s Volumetric rate of flow
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ISO 1438:2017(E)
Symbol Unit Description
S Submergence ratio, h /h
2 1
S Modular limit
1
m/s Mean velocity
V
U % Expanded percentage uncertainty
u*(b) % Percentage uncertainty in b
u*(C) % Percentage uncertainty in C
u*(E) % Percentage uncertainty in datum measurement
u*(h ) % Percentage uncertainty in h
1 1
u*(Q) % Percentage uncertainty in Q
α ° Notch angle
Subscripts
1 upstream
2 downstream
e effective
r rectangular
t triangular
5 Principle
The discharge over thin-plate weirs is a function of the upstream head on the weir (for free-flow),
upstream and downstream head (for drowned flow), the size and shape of the discharge area, and an
experimentally determined coefficient which takes into account the head, the geometrical properties of
the weir and approach channel, and the dynamic properties of the water.
6 Installation
6.1 General
General requirements of weir installations are described in the following clauses. Special requirements
of different types of weirs are described in clauses which deal with specific weirs (see Clause 9 and
Clause 10).
6.2 Selection of site
The type of weir to be used for discharge measurement is determined in part by the nature of the
proposed measuring site. Under some conditions of design and use, weirs shall be located in rectangular
flumes or in weir boxes which simulate flow conditions in rectangular flumes. Under other conditions,
weirs may be located in natural channels, as well as flumes or weir boxes, with no significant difference
in measurement accuracy. Specific site-related requirements of the installation are described in 6.3.
6.3 Installation conditions
6.3.1 General
Weir discharge is critically influenced by the physical characteristics of the weir and the weir
channel. Thin-plate weirs are especially dependent on installation features which control the velocity
2 © ISO 2017 – All rights reserved
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ISO 1438:2017(E)
distribution in the approach channel and on the construction and maintenance of the weir crest in
meticulous conformance with standard specifications.
6.3.2 Weir
Thin-plate weirs shall be vertical and perpendicular to the walls of the channel. The intersection of the
weir plate with the walls and floor of the channel shall be watertight and firm, while the weir shall be
capable of withstanding the maximum flow without distortion or damage.
Stated practical limits associated with different discharge formulae such as minimum width, minimum
weir height, minimum head, and maximum values of h/p and b/B (where h is the measured head, p is the
height of crest relative to floor, b is the measured width of the notch and B is the width of the approach
channel), are factors which influence both the selection of weir type and the installation.
6.3.3 Approach channel
For the purposes of this document, the approach channel is the portion of the weir channel which
extends upstream from the weir a distance not less than five times the width of the nappe at maximum
head. If the weir is located in a weir tank, ideally, the length of the tank should equal up to 10 times the
width of the nappe at maximum head. Information on the use of small weir tanks is given in Annex A.
The flow in the approach channel shall be uniform and steady, with the velocity distribution
approximating that in a channel of sufficient length to develop satisfactory flow in smooth, straight
channels. Figure 1 shows measured velocity distributions perpendicular to the direction of flow in
rectangular channels, upstream from the influence of a weir. Baffles and flow straighteners can be used
to simulate satisfactory velocity distribution, but their location with respect to the weir shall be not
less than the minimum length prescribed for the approach channel.
The influence of approach-channel velocity distribution on weir flow increases as h/p and b/B increase
in magnitude. If a weir installation unavoidably results in a velocity distribution that is appreciably non-
uniform, the possibility of error in calculated discharge should be checked by means of an alternative
discharge-measuring method for a representative range of discharges.
If the approach conditions are judged to be unsatisfactory, then flow straighteners shall be introduced
in accordance with Annex B.
If the maximum head to be measured is restricted to (2/3)p for all types of weirs, flow straighteners
can be used to reduce the effective length of the approach channel to B + 3h for triangular and
max
rectangular weirs and to B + 5h for full-width weirs.
max
NOTE This restriction on the maximum head to be measured is necessary due to distortion of the velocity
near the water surface in the approach channel that results from flow coming through the openings in the baffle
of the flow straightener.
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ISO 1438:2017(E)
a)
b)
c)
NOTE The contours refer to values of local flow velocity relative to the mean cross-sectional velocity.
Figure 1 — Examples of normal velocity distribution in rectangular channels
6.3.4 Downstream channel
For most applications, the level of the water in the downstream channel shall be a sufficient vertical
distance below the crest to ensure free, fully ventilated discharges. Free (non-submerged) discharge
occurs when the discharge is independent of the downstream water level. Fully ventilated discharge
is ensured when the air pressure on the lower surface of the nappe is fully ventilated. Drowned
flow operation is permitted for full-width weirs under certain conditions (see 9.7.2). Under these
circumstances, downstream water levels may rise above crest level.
7 Measurement of head
7.1 Head-measuring devices
In order to obtain the discharge measurement accuracies specified for the standard weirs, the head
on the weir shall be measured with a laboratory-grade hook gauge, point gauge, manometer, or other
gauge of equivalent accuracy. For a continuous record of head variants, precise float gauges and servo-
operated point gauges can be used. Staff and tape gauges can be used when less accurate measurements
are acceptable.
Additional specifications for head-measuring devices are given in ISO 4373.
4 © ISO 2017 – All rights reserved
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ISO 1438:2017(E)
7.2 Stilling or float well
For the exceptional case where surface velocities and disturbances in the approach channel are
negligible, the headwater level can be measured directly (for example, by means of a point gauge
mounted over the water surface). Generally, however, to avoid water-level variations caused by waves,
turbulence or vibration, the headwater level should be measured in a separate stilling well.
Separate stilling wells are connected to the approach channel by means of a suitable conduit, equipped
if necessary with a throttle valve to damp oscillations. At the channel end of the conduit, the connection
is made to floor or wall piezometers or a static tube at the head-measurement section.
Additional specifications for stilling wells are given in ISO 18365.
7.3 Head-measurement section
7.3.1 Upstream head-measurement
The head-measurement section shall be located a sufficient distance upstream from the weir to avoid
the region of surface drawdown caused by the formation of the nappe. On the other hand, it shall be
sufficiently close to the weir that the energy loss between the head-measurement section and the weir
is negligible. For the weirs included in this document, the location of the head-measurement section
will be satisfactory if it is at a distance equal to two to four times the maximum head (2h to 4h )
max max
upstream from the weir.
If high velocities occur in the approach channel or if water-surface disturbances or irregularities occur
at the head-measurement section because of high values of h/p or b/B, it may be necessary to install
several pressure intakes to ensure that the head measured in the gauge well is representative of the
average head across the measurement section.
In the case of a full-width thin-plate weir, the effect of frictional effects upon the upstream channel
requires an adjustment to the standard coefficient of discharge. The correction is in terms of both l/h
and h/p and given in Table 1.
Table 1 — Factors to be applied to the standard discharge coefficient values
h/p l/h
2 4 6 8
3,5 to 4,0 1,00 1,00 0,96 0,92
3,0 to 3,5 1,00 1,00 0,97 0,94
2,5 to 3,0 1,00 1,00 0,98 0,96
2,0 to 2,5 1,00 1,00 0,99 0,98
Less than 2,0 1,00 1,00 1,00 1,00
7.3.2 Downstream head measurement
If the weir is to be operated in the submerged (drowned) flow range, a measurement of downstream
head is required in addition to the upstream. The downstream head measurement position shall be
10 h downstream from the upstream face of the weir. If a stilling well is included in the design, it is
max
recommended that the downstream head measurement be located no closer to the weir than 4 h .
max
7.4 Head-gauge datum (gauge zero)
Accuracy of head measurements is critically dependent upon the determination of the head-gauge
datum or gauge zero, which is defined as the gauge reading corresponding to the level of the weir crest
(rectangular weirs) or the level of the vertex of the notch (triangular-notch weirs). When necessary,
the gauge zero shall be checked. Numerous acceptable methods of determining the gauge zero are in
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ISO 1438:2017(E)
use. Typical methods are described in subsequent clauses dealing specifically with rectangular and
triangular weirs. See Clause 9 and Clause 10.
Because of surface tension, the gauge zero cannot be determined with sufficient accuracy by reading the
head gauge with the water in the approach channel drawn down to the apparent crest (or notch) level.
8 Maintenance
Maintenance of the weir and the weir channel is necessary to ensure accurate measurements.
The approach channel shall be kept free of silt, vegetation and obstructions which might have deleterious
effects on the flow conditions specified for the standard installation. The downstream channel shall be
kept free of obstructions which might cause submergence or inhibit full ventilation of the nappe under
all conditions of flow.
The weir plate shall be kept clean and firmly secured. In the process of cleaning, care shall be taken
to avoid damage to the crest or notch, particularly the upstream edges and surfaces. Construction
specifications for these most sensitive features should be reviewed before maintenance is undertaken.
Head-measurement piezometers, connecting conduits and the stilling well shall be cleaned and checked
for leakage. The hook or point gauge, manometer, float or other instrument used to measure the head
shall be checked periodically to ensure accuracy.
If a flow straightener is used in the approach channel, perforated plates shall be kept clean so that the
percentage open area remains greater than 40 %.
9 Rectangular thin-plate weir
9.1 Types
The rectangular thin-plate weir is a general classification in which the rectangular-notch weir is the
basic form and the full-width weir is a limiting case. A diagrammatic illustration of the basic weir form
is shown in Figure 2 with intermediate values of b/B and h/p. When b/B = 1,0, that is, whe
...
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ISO 1438:2017(F)
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ISO 1438:2017(F)
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Avant-propos . vi
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1 Domaine d'application . 1
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2 Références normatives . 1
3 Termes et définitions . 1
4 Symboles et abréviations . 1
5 Principe . 2
6 Installation . 2
6.1 Généralités . 2
6.2 Choix du site . 2
6.3 Conditions d'installation . 2
6.3.1 Généralités . 2
6.3.2 Déversoir . 2
6.3.3 Chenal d'approche . 4
6.3.4 Chenal à l’aval du déversoir . 5
7 Mesurage de la charge . 6
7.1 Appareils de mesurage de la charge . 6
7.2 Puits de tranquillisation ou puits à flotteur . 6
7.3 Section de mesurage de la charge . 6
7.3.1 Mesurage de la charge à l'amont. 6
7.3.2 Mesurage de la charge à l'aval . 8
7.4 Zéro de l’échelle . 8
8 Entretien . 8
9 Déversoir en mince paroi rectangulaire . 9
9.1 Types . 9
9.2 Spécifications relatives au déversoir normalisé . 11
9.3 Spécifications d'installation . 11
9.4 Détermination du zéro de l'échelle . 12
9.5 Formules de débit — Généralités . 15
9.6 Formules pour la forme de déversoir de base (toutes valeurs de b/B) . 15
9.6.1 Formule de Kindsvater-Carter . 15
9.6.2 Évaluation de C , k et k . 15
d b h
9.6.3 Formule pour C . 18
d
9.6.4 Limites pratiques de h/p, h, b et p. 19
9.7 Formules pour déversoirs sans contraction latérale (b/B = 1,0) . 20
9.7.1 Formule de débit en écoulement dénoyé . 20
9.7.2 Formule de débit en écoulement noyé. 21
10 Déversoir triangulaire en mince paroi . 23
10.1 Spécifications relatives au déversoir normalisé . 23
10.2 Spécifications relatives à l'installation . 26
10.3 Spécifications relatives au mesurage de la hauteur de charge . 26
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ISO 1438:2017(F)
10.3.1 Généralités . 26
10.3.2 Détermination de l'angle de l'échancrure . 26
10.3.3 Détermination du zéro de l'échelle . 27
10.4 Formules de débit — Généralités . 27
10.5 Formule pour tous les angles d'échancrure entre π/9 et 5π/9 radians (20° et 100°) . 28
10.5.1 Formule de Kindsvater-Shen . 28
10.5.2 Évaluation de C et de k . 28
d h
10.5.3 Limites pratiques pour α, h/p, p/B, h et p . 31
10.6 Formule pour les angles d'échancrure spécifiques (déversoir totalement contracté) . 31
10.7 Précision des coefficients de débit — Déversoirs triangulaires . 33
11 Incertitudes relatives à la mesure de débit . 33
11.1 Généralités . 33
11.2 Combinaison d'incertitudes de mesure . 34
*
11.3 Incertitude du coefficient de débit, u (Cd), pour les déversoirs en mince paroi . 36
11.4 Bilan d'incertitude . 36
12 Exemple . 37
12.1 Généralités . 37
12.2 Caractéristiques — Structure de jaugeage . 37
12.3 Caractéristiques — Instrumentation de charge mesurée . 37
12.4 Coefficient de débit . 38
12.5 Estimation de débit . 38
12.6 Calcul de l’incertitude . 39
Annexe A (informative) Mesure de débit avec petits bassins de déversoir . 43
Annexe B (normative) Guide de conception et d'installation d'un stabilisateur d'écoulement . 45
Annexe C (informative) Introduction à l'incertitude de mesure . 48
Annexe D (informative) Performance des essais de mesure à utiliser à titre d’exemple en
hydrométrie . 59
Annexe E (informative) Tableaux de la relation hauteur/débit . 62
Bibliographie . 78
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Avant-propos
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L'ISO (Organisation internationale de normalisation) est une fédération mondiale d'organismes nationaux
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Structures mesurant le débit.
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Les principaux changements par rapport à l'ISO 1438:2008 sont les suivants :
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a) la formule de débit en écoulement dénoyé pour les déversoirs dont la hauteur de paroi est de
1 m ≤ p ≤ 2,5 m a été complétée en 9.7.1 ; Formatted: std_suppl
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b) la formule Cd pour un déversoir rectangulaire avec b/B = 1,0, Formule (5), a été corrigée d'après la
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même formule que pour le déversoir sans contraction latérale, Formule (15) ;);
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c) les paragraphes du 9.6 ont été re-numérotés.
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NORME INTERNATIONALE ISO 1438:2017(F)
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Hydrométrie — Mesure de débit dans les canaux à écoulement à
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surface libre au moyen de déversoirs en mince paroi
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Formatted: French (France)
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1 Domaine d'application Formatted: Tab stops: 21.6 pt, Left
Le présent document définit les exigences d'utilisation de déversoirs en mince paroi à échancrures
rectangulaires et triangulaires pour le mesurage du débit d'eau claire dans des canaux à écoulement à
surface libre pleinement aéré. Il comprend les exigences d'utilisation de déversoirs en mince paroi
rectangulaires sans contraction latérale en conditions d'écoulement noyé.
Formatted: Tab stops: 21.6 pt, Left
2 Références normatives
Les documents suivants sont cités dans le texte de sorte qu’ils constituent, pour tout ou partie de leur Formatted: French (Switzerland)
contenu, des exigences du présent document. Pour les références datées, seule l'éditionl’édition citée
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ISO 772, Hydrométrie — Vocabulaire et symboles
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Formatted: French (Switzerland)
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3 Termes et définitions
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Pour les besoins du présent document, les termes et définitions donnés dans l'ISO 772 s'appliquent.
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normalisation, consultables aux adresses suivantes :
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— ISO Online browsing platform : disponible à l'adresse http://www.iso.org/obp
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1
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ISO 1438:2017(F)
NORME INTERNATIONALE ISO 1438:2017(F)
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12 pt, Tab stops: 207.65 pt, Centered + 415.3 pt, Right
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54 Symboles et abréviations
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Symbole Unité Description Formatted: Left
2 Formatted Table
A m Surface du chenal d'approche
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B m Largeur du chenal d'approche
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b m Largeur mesurée de l'échancrure Formatted: Left
Formatted: Left
b m Largeur de l'échancrure à la hauteur maximale de charge (échancrure en V)
max
Formatted: Left
C Coefficient de débit (charge mesurée)
Formatted: Left
C Coefficient de débit
d
Formatted: Font: Italic
f Facteur de réduction
Formatted: Left
Formatted: Left
C Coefficient de vitesse
v
Formatted: Left
e m Incertitude aléatoire de la mesure de la largeur
b
Formatted: Left
2
g m/s Accélération due à la pesanteur
Formatted: Left
H m Hauteur de charge totale au-dessus du niveau de crête
Formatted: Left
h m Hauteur de charge mesurée en amont au-dessus du niveau de crête (en l'absence d'indice, Formatted: Left
la charge à l'amont est déduite)
J Constante numérique
Formatted: Left
l m Distance de la section de mesurage de la charge à l'amont du déversoir Formatted: Left
n Nombre de mesures dans un ensemble
Formatted: Left
p m Hauteur de pelle Formatted: Left
3
Q m /s Débit
Formatted: Left
S Rapport de submersion, h /h
2 1 Formatted: Left
S1 Limite modulaire Formatted: Left
m/s Vitesse moyenne
Field Code Changed
V V
Formatted: Left
U % Incertitude de pourcentage élargie
Formatted: Left
u*(b) % Incertitude de pourcentage en b
Formatted: Left
u*(C) % Incertitude de pourcentage en C
Formatted: Left
u*(E) % Incertitude de pourcentage du mesurage du plan de référence
Formatted: Left
u*(h1) % Incertitude de pourcentage en h1 Formatted: Left
u*(Q) % Incertitude de pourcentage en Q
Formatted: Left
α ° Angle de l'échancrure Formatted: Left
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Indices
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1 en amont
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© ISO 2017 – Tous droits réservés1 1© ISO 2017 – Tous droits réservés
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ISO 1438:2017(F)
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65 Principe Formatted: Tab stops: 21.6 pt, Left
Le débit à travers des déversoirs en mince paroi dépend de la hauteur de charge (assimilée à la hauteur
d’eau) à l’amont du déversoir (pour l'écoulement libre), de la charge à l’amont et à l’aval (pour
l'écoulement noyé), de la taille et de la forme de la zone de déversement, et d'un coefficient déterminé
expérimentalement qui tient compte de la charge, des propriétés géométriques du déversoir et du
chenal d'approche, et des propriétés dynamiques de l'eau.
76 Installation Formatted: Tab stops: 21.6 pt, Left
7.16.1 Généralités
Les conditions générales relatives à l’installation des déversoirs sont décrites dans les articles suivants.
Les conditions particulières applicables aux différents types de déversoir sont décrites dans les articles
qui traitent de déversoirs spécifiques (voir les Articles 9 et 10). Formatted: cite_sec
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7.26.2 Choix du site
Le type de déversoir à utiliser pour la mesure de débit est en partie déterminé par la nature du site de
mesurage proposé. Dans certaines conditions de conception et d'utilisation, les déversoirs mince paroi
doivent être situés dans des canaux jaugeurs rectangulaires ou dans des chambres de déversoir qui
simulent les conditions d'écoulement dans des canaux jaugeurs rectangulaires. Dans d'autres
conditions, les déversoirs minces paroi peuvent être situés dans des chenaux naturels, dans des canaux
jaugeurs ou des chambres de déversoir, sans aucune différence significative dans la précision des
mesures. Les conditions particulières liées au site sont décrites en 6.3. Formatted: cite_sec
7.36.3 Conditions d'installation Formatted: Tab stops: 21.6 pt, Left
7.3.16.3.1 Généralités
Le débit mesuré à l’aide du déversoir mince paroi est influencé de manière critique par les
caractéristiques physiques de celui-ci et du chenal d’approche. Les déversoirs en mince paroi sont
particulièrement dépendants des conditions d’implantation, qui ont une influence sur la répartition des
vitesses dans le chenal d'approche, et de la fabrication et de l'entretien de la crête du déversoir
conformément aux spécifications normalisées.
7.3.26.3.2 Déversoir Formatted: Tab stops: 21.6 pt, Left
Les déversoirs en mince paroi doivent être verticaux et perpendiculaires aux parois du chenal.
L'intersection de la plaque du déversoir avec les parois et le fond du chenal doit être étanche et
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ISO 1438:2017(F)
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indéformable, et le déversoir doit être capable de résister à l'écoulement maximal sans déformation ni
dommage.
Les limites pratiques indiquées, liées aux diverses formules de débit telles que la largeur minimale, la
hauteur minimale du déversoir, la charge minimale et les valeurs maximales de h/p et b/B (où h est la
hauteur d’eau mesurée à l’amont du déversoir, p est la hauteur de pelle, b est la largeur mesurée de
l'échancrure et B est la largeur du chenal d'approche), sont des facteurs qui ont une influence à la fois
sur le choix du type de déversoir et sur l'installation.
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ISO 1438:2017(F)
7.3.36.3.3 Chenal d'approche
Dans le cadre du présent document, le chenal d'approche est la partie du chenal du déversoir qui
s'étend vers l'amont à partir du déversoir sur une distance d'au moins cinq fois la largeur de la lame
déversante à la hauteur maximale de charge. Si le déversoir est situé dans un bassin de déversoir, il
convient dans l'idéal que la longueur du bassin soit égale à jusqu'à 10 fois la largeur de la lame
déversante à la hauteur maximale de charge. Des informations sur l'utilisation de petits bassins de
déversoir sont données à l'Annexe A. Formatted: cite_app
L'écoulement dans le chenal d'approche doit être au régime permanent et uniforme, avec une
répartition des vitesses proche de celle que l'on trouve dans un chenal d'une longueur suffisante pour
générer un écoulement satisfaisant dans des chenaux lisses et rectilignes. La Figure 1 indique la Formatted: cite_fig
répartition normale des vitesses mesurées perpendiculairement à la direction d'écoulement dans des
chenaux rectangulaires, en amont de l'influence d'un déversoir. Des chicanes et des stabilisateurs
d'écoulement peuvent être utilisés pour obtenir une répartition normale des vitesses, mais leur
emplacement par rapport au déversoir ne doit pas être inférieur à la longueur minimale
prescritespécifiée pour le chenal d'approche.
L'influence de la répartition des vitesses dans le chenal d'approche sur l'écoulement ou sur le déversoir
augmente avec les rapports h/p et b/B. Si l’installation d’un déversoir conduit inévitablement à une
répartition des vitesses sensiblement non uniforme, il convient que la possibilité d’erreur dans le débit
calculé soit vérifiée au moyen d'une autre méthode de mesure de débit pour une plage représentative
de débits.
Si les conditions d'approche sont considérées comme non satisfaisantes, des stabilisateurs
d'écoulement devront être mis en place conformément à l'Annexe B. Formatted: cite_app
Si la hauteur maximale de charge à mesurer est limitée à (2/3)p pour tous les types de déversoir, des
stabilisateurs d'écoulement peuvent être utilisés pour réduire la longueur effective du chenal
d'approche à B + 3h pour les déversoirs triangulaires et rectangulaires, et à B + 5h pour les
max max
déversoirs sans contraction latérale.
NOTE Cette limite sur la hauteur maximale de charge à mesurer est nécessaire en raison de la déformation de
la vitesse à proximité de la surface de l'eau dans le chenal d'approche due à l'écoulement provenant des
ouvertures dans la chicane du stabilisateur d'écoulement.
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ISO 1438:2017(F)
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Formatted Table
a)
b)
c)
NOTE Les contours font référence aux valeurs de vitesse d'écoulement locale par rapport à la vitesse de
section transversale moyenne.
Figure 1 — Exemples de distribution normale des vitesses dans les chenaux rectangulaires
7.3.46.3.4 Chenal à l’aval du déversoir Formatted: Tab stops: 21.6 pt, Left
Pour la plupart des applications, le niveau de l'eau dans le chenal à l'aval du déversoir doit être à une
distance verticale suffisante en dessous de la crête, afin de gar
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