ISO 26906:2015

Hydrometry — Fishpasses at flow measurement structures

ISO 29606:2015 specifies requirements for the integration of fishpasses with flow measurement structures. It identifies those fishpasses which have satisfactory hydrometric calibration data and gives methods for computing combined flows and uncertainties. NOTE Flow measurement structures and fishpasses have inherently different hydraulic performance criteria. Flow measurement structures perform better with uniform flow patterns; conversely, fish passage performance is improved by the variability of the flow conditions that allow fish and other aquatic inhabitants to select the passage conditions that best meet their mode of movement. This International Standard does not suggest that the fishpasses discussed are the preferred methods of fish passage or that they are good enough that passage performance can be sacrificed to obtain a single structure that meets both the fish passage and flow measurement requirements.

Hydrométrie — Échelles à poissons auprès des structures mesurant le débit

General Information

• Status: Published
• Publication Date: 19-Oct-2015
• ICS: 17.120.20 - Flow in open channels
• Technical Committee: ISO/TC 113/SC 2 - Flow measurement structures
• Drafting Committee: ISO/TC 113/SC 2 - Flow measurement structures
• Current Stage: 9093 - International Standard confirmed
• Completion Date: 08-Mar-2021

Relations

• Revises: ISO 26906:2009 - Hydrometry — Fishpasses at flow measurement structures
• Effective Date: 06-Jul-2012

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 26906
Second edition
2015-10-15
Hydrometry — Fishpasses at flow
measurement structures
Hydrométrie — Échelles à poissons auprès des structures mesurant le
débit
Reference number
ISO 26906:2015(E)
©
ISO 2015

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ISO 26906:2015(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2015, Published in Switzerland
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form
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ISO 26906:2015(E)

Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3  Terms and definitions . 1
4  Symbols . 2
5  Principle . 4
6  Installation . 4
6.1 Requirements for gauging structure and fishpass installations . 4
6.1.1 Selection of site . 4
6.1.2 Installation conditions . 5
6.1.3 Upstream channel . 6
6.1.4 Separate channel . 6
6.1.5 Downstream channel . 7
6.1.6 Flow measurement and fishpass structures . 7
6.1.7 Maintenance . 7
6.1.8 Measurement of head . 8
6.2 Requirements specific to the fishpass. 8
6.2.1 General. 8
6.2.2 Guidelines for basic parameters of fishpasses . 9
6.2.3 Location and attraction flows . 9
6.2.4 Downstream entry/exit to fishpass . 9
6.2.5 Upstream exit/entry from fishpass .10
7 Fishpass performance .10
7.1 General .10
7.1.1 Types .10
7.1.2 Fishpasses with interconnected pools .10
7.1.3 Fishpasses with continuous energy dissipation .10
7.1.4 Calibration and discharge coefficient .11
7.2 Larinier super-active baffle fishpass with baffle sizes between 75 mm and 150 mm .11
7.2.1 Description . . .11
7.2.2 The following features apply to the range of baffle sizes from 75 mm to
150 mm .12
7.2.3 Limitations .13
7.2.4 Modular flow calibration .14
7.2.5 Modular limit .15
7.3 Pool-type fishpass with V-shaped overfalls.15
7.3.1 Description . . .15
7.3.2 Determination of discharge under free flow conditions .18
7.3.3 Modular limit .21
7.3.4 Determination of discharge under submerged flow conditions .22
7.3.5 Limitations .23
7.3.6 Scaling up to standard design .23
7.4 Dutch pool and orifice fishpass .23
7.4.1 Description . . .23
7.4.2 Determination of discharge .25
7.4.3 Scaling up the standard design .27
8 Computation of discharge .27
8.1 Principles .27
8.2 Details .28
9  Uncertainties in flow determination .28
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ISO 26906:2015(E)

9.1 General .28
9.2 Combining uncertainties .29
9.3 Uncertainty in the discharge coefficient u*(C ) for the fish-pass .30
De 68
9.4 Uncertainty in the effective head .30
9.5 Uncertainty budget.30
9.5.1 General.30
9.5.2 Compound structures – sources of uncertainty .31
10  Example .31
10.1 Installation .31
10.2 Flow conditions .32
10.3 Computation of discharge .32
10.3.1 Modularity .32
10.3.2 Flow over the flat-V weir .32
10.3.3 Flow through the fish-pass.33
10.3.4 Total flow .33
10.3.5 Uncertainty in flow through the fish-pass .33
10.3.6 Uncertainty in flow over the flat-V weir .34
10.3.7 Uncertainty in total flow .34
10.3.8 Reduction in overall uncertainty if second head gauge were to be installed
upstream of the fish-pass .34
Annex A (informative) Introduction to measurement uncertainty .35
Annex B (informative) Performance guide for hydrometric equipment for use in
technical standards.44
Bibliography .48
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ISO 26906:2015(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 meaning of ISO specific terms and expressions related to conformity
assessment, as well as information about ISO’s adherence to the WTO principles in the Technical
Barriers to Trade (TBT) see the following URL: Foreword - Supplementary information
The committee responsible for this document is ISO/TC 113, Hydrometry, Subcommittee SC 2, Flow
measurement structures.
This second edition cancels and replaces the first edition (ISO 26906:2009), which has been
technically revised.
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ISO 26906:2015(E)

Introduction
Flow gauging structures are commonly used for the determination of open channel flows. To operate
satisfactorily, these structures require a head difference to be generated between the upstream and
downstream water levels. At structures designed to operate in the modular flow range, an upstream
head measurement is used to interpret flow rates. At structures designed to operate in both the
modular and drowned flow ranges, the upstream head measurement is augmented by a second
measurement which senses tailwater conditions. The former type tends to require higher head losses
over the structure.
In recent years, greater emphasis has been placed on environmental issues, including the free migration
of fish in watercourses. It is acknowledged that flow measurement structures, with their requirement
for a head loss between upstream and downstream conditions, that create high velocities may inhibit
the movement of fish. It has become important, therefore, to consider ways of aiding fish migration
without significantly affecting flow measurement accuracy.
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INTERNATIONAL STANDARD ISO 26906:2015(E)
Hydrometry — Fishpasses at flow measurement structures
1 Scope
This International Standard specifies requirements for the integration of fishpasses with flow
measurement structures. It identifies those fishpasses which have satisfactory hydrometric calibration
data and gives methods for computing combined flows and uncertainties.
NOTE Flow measurement structures and fishpasses have inherently different hydraulic performance
criteria. Flow measurement structures perform better with uniform flow patterns; conversely, fish passage
performance is improved by the variability of the flow conditions that allow fish and other aquatic inhabitants
to select the passage conditions that best meet their mode of movement. This International Standard does not
suggest that the fishpasses discussed are the preferred methods of fish passage or that they are good enough
that passage performance can be sacrificed to obtain a single structure that meets both the fish passage and flow
measurement requirements.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. 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
ISO 14139, Hydrometric determinations — Flow measurements in open channels using structures —
Compound gauging structures
3  Terms and definitions
For the purpose of this document, the terms and definitions given in ISO 772 and the following apply.
3.1
fish pass design range
range of flows within which fish require passage
Note 1 to entry: This may be defined on an annual or a seasonal basis, e.g. for spawning.
Note 2 to entry: In some countries the design range is determined in terms of flow statistics. For example, the
design range for coarse fish in the UK is usually between the estimated mean daily flow that is exceeded 95 % of
the time and the mean daily flow that is exceeded 20 % of the time. While for migratory salmonids including sea
trout and salmon, it is 95 % and 90 % to 10 % respectively.
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ISO 26906:2015(E)

4  Symbols
Where a symbol applies to a particular type of fishpass, it is indicated as follows.
[L] indicates applicable to the Larinier super-active baffle fishpass (see 7.2)
[PT] indicates applicable to the pool type fishpass with V-shaped overfalls (see 7.3)
[PO] indicates applicable to the Dutch pool and orifice fishpass (see 7.4)
[D] indicates distance between baffles in a Larinier Fish Pass
[S] indicates the Slope of the Larinier Fish Pass in degrees
Symbol Term Unit
a height of baffle [L] m
a proportion of total flow through fish-pass [L]
fp
b orifice width [PO] m
b crest breadth measured at transverse section of upstream baffle [L] m
b proportion of total flow through flow measuring structure [L]
fms
B total width of fishpass channel [L] m
B pool width [PT and PO] m
B width of the non-aerated nappe [PT] m
2
C characteristic discharge coefficient [PO]
C dimensionless coefficient of discharge [L]
de
C characteristic discharge coefficient [PT]
D
C coefficient for the approach velocity [PT]
V
D longitudinal spacing of transverse baffles [L] m
D pipe diameter [PO] m
2
g acceleration due to gravity [All] m/s
h maximum head m
max
h orifice height [PO] m
v
h upstream gauged head relative to transverse section of upstream baffle [L] m
1
h upstream head [PT] m
1
h downstream head [PT] m
2
H upstream total head relative to transverse section of upstream baffle [L] m
1
H upstream total head [PT] m
1
H effective upstream total head relative to transverse section of upstream baffle m
1e
[L]
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ISO 26906:2015(E)

Symbol Term Unit
k head correction factor taking into account fluid property effects [L] m
h
l pool length [PT] m
L crest length [PT] m
L pool length [PO] m
L width of one unit of Larinier fishpass [L] m
n number of partitions [PO]
n length scale factor [PO]
l
n flow velocity scale [PO]
V
n discharge scale [PO]
Q
n scale factor for length dimensions [PT]
ℓ
P height of the top baffle above the upstream bed [L] m
P pool depth [PT] m
3
Q discharge [All] m /s
3
Q design discharge [PT and PO] m /s
d
S bed slope of fishpass [PO and L]
U burst velocity of fish [PO] m/s
v flow velocity [PT and PO] m/s
v velocity of approach at tapping location [L] m/s
1
mean flow velocity [PO] m/s
V
W upstream water level [PO] m
L1
W downstream water level [PO] m
L2
X distance to h measurement section [PT] m
1
u*C standard uncertainty in discharge coefficient C [L, PT and PO] %
De68 D
u* uncertainty in the gauging structure breadth measurement [L, PT and PO] %
b
u(E) absolute uncertainty in gauge/head zero [L, PT and PO] m or mm
u* uncertainty in the total head measurement [L, PT and PO] %
H1e
u absolute uncertainty in the measured upstream head [L, PT and PO] m or mm
h1
U* overall uncertainty in fish pass flow [L, PT and PO] %
fp
U* overall uncertainty in flow measurement structure [L, PT and PO] %
fms
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ISO 26906:2015(E)

Symbol Term Unit
U* combined overall uncertainty in fish pass and flow measurement structure %
c
flows [L, PT and PO]
Y downstream water depth, related to upstream bed level [PO] m
d
Y upstream water depth, related to upstream bed level [PO] m
0
α angle of V-shape [PT] deg
δ error in measurement of h [PT] m
h 1
Δh drop over the fishpass for modular flow [PT] m
head drop per pool [PO] m
Δh
design head drop per pool [PO] m
Δh
d
Δt pool drop [PT] m
5  Principle
The discharge over a flow measurement structure is a function of the upstream head (plus a measure
of the downstream head in the case of those structures designed to operate in the non-modular flow
range). When a fishpass is placed alongside a flow gauging structure, an additional flow path is created.
In certain circumstances, where the fishpass has a well-defined hydrometric calibration, total flows and
uncertainties may be calculated. Thus the fishpass becomes an integral part of the flow measurement
system. This International Standard provides the necessary design and performance information for
this type of arrangement.
6  Installation
NOTE General requirements of combined flow measurement structure and fishpass installations are given
in the following clauses.
6.1  Requirements for gauging structure and fishpass installations
NOTE Requirements for the installation of measuring structures are given in the appropriate International
Standard (see Clause 2 and the Bibliography). There is much in common between the different structures and
the requirements, which can also be applied to flow measurement structure and fishpass installations, and are
summarized in the following clauses.
6.1.1  Selection of site
6.1.1.1 A preliminary survey shall be made of the physical and hydraulic features of the proposed
site, to check that it conforms (or may be made to conform) to the requirements necessary for flow
determination by a structure, or combination of structures.
6.1.1.2 Particular attention shall be paid to the following features when investigating a site:
— at existing measurement locations the type(s), state of repair and hydraulic performance of existing
structures shall be assessed;
— availability of an adequate length of channel of regular cross-section;
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ISO 26906:2015(E)

— availability of an adequate width of cross sectional area outside the channel to install a bypass
channel if required. The banks of the river need to be low enough to install a bypass channel that is
not overdeep;
— the existing velocity distribution;
— the avoidance of a steep channel, if possible;
— the effects of any increased upstream water level due to the measuring structure;
— conditions downstream, including such influences as tides, confluences with other streams, sluice
gates, mill dams and other controlling features which might cause submerged flow;
— the impermeability of the ground on which the structure is to be founded, and the necessity for
piling, grouting or other sealing, in river installations;
— the necessity for the use of flood banks to confine the maximum discharge to the channel;
— the stability of the banks and the necessity for trimming and/or revetment in natural channels;
— the clearance of rocks or boulders from the bed of the approach channel;
— the effect of wind; wind can have a considerable effect on the flow in a river or over a weir, especially
when these are wide and the head is small and when the prevailing wind is in a transverse direction.
6.1.1.3 If the site does not possess the characteristics necessary for satisfactory measurement, the site
shall be rejected unless suitable improvements are practicable.
6.1.1.4 If an inspection of the stream shows that the existing velocity distribution is uniform, then it may
be assumed that the velocity distribution will remain satisfactory after the construction of a structure.
6.1.1.5 If the existing velocity distribution is irregular and no other site for a measurement is feasible,
due consideration shall be given to checking the distribution after the installation of the weir and to
improving it if necessary.
6.1.1.6 Several methods are available for obtaining a more precise indication of non-uniform velocity
distribution. Velocity rods, floats or concentrations of dye can be used in small channels, the latter being
useful in checking conditions at the bottom of the channel. A complete and quantitative assessment of
velocity distribution may be made by means of a current meter or acoustic doppler current profiler.
6.1.2  Installation conditions
6.1.2.1 The complete installation consists of an approach channel, the flow measurement and fishpass
structures and a downstream channel. The conditions of each of these three components affect the
overall accuracy of the measurements.
6.1.2.2 Installation requirements include such features as the quality of the structures, the cross-
sectional shape of channel, channel roughness and the influence of control devices upstream or
downstream of the structures.
6.1.2.3 The distribution and direction of velocity, determined by the features outlined in 6.1.1, have an
important influence on the performance of the flow measurement structure and the fishpass.
6.1.2.4 Once an installation has been constructed, the user shall prevent any change which could affect
the flow characteristics, particularly the accumulation of sediment or debris within the fishpass.
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ISO 26906:2015(E)

6.1.3  Upstream channel
6.1.3.1 At all installations the flow in the upstream channel shall be smooth, free from disturbance and
shall have a velocity distribution as uniform as possible over the cross-sectional area. This can usually be
verified by inspection or measurement. In the case of natural streams or rivers, this can only be attained
by having a long, straight upstream channel free from projections either at the side or on the bottom. It
is recommended that wherever possible the approach shall be straight for a distance of five times the
channel width upstream of the head measuring section. Unless otherwise specified in the appropriate
clauses, the following general 6.1.3.2 to 6.1.3.8 shall be complied with.
6.1.3.2 The altered flow-conditions due to the construction of the structure(s) might have the effect
of building up shoals of debris and sediment upstream of the structure, which in time might affect the
flow conditions. Changes in upstream bed level at
...