Hydrometry — Fishpasses at flow measurement structures

ISO 26906:2009 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 Measurement structures and fishpasses have inherently different hydraulic performance criteria. Water 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. ISO 26906:2009 does not suggest that the fishpasses discussed are the preferred methods of passage or that they are good enough that passage performance can be sacrificed to obtain a single structure that does both.

Hydrométrie — Échelles à poissons auprès des structures mesurant le débit

General Information

Status
Withdrawn
Publication Date
24-Mar-2009
Withdrawal Date
24-Mar-2009
Current Stage
9599 - Withdrawal of International Standard
Start Date
20-Oct-2015
Completion Date
20-Oct-2015
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INTERNATIONAL ISO
STANDARD 26906
First edition
2009-04-01
Hydrometry — Fishpasses at flow
measurement structures
Hydrométrie — Échelles à poissons auprès des structures mesurant
le débit
Reference number
ISO 26906:2009(E)
ISO 2009
---------------------- Page: 1 ----------------------
ISO 26906:2009(E)
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© ISO 2009

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ii © ISO 2009 – All rights reserved
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ISO 26906:2009(E)
Contents Page

Foreword............................................................................................................................................................ iv

Introduction ........................................................................................................................................................ v

1 Scope ..................................................................................................................................................... 1

2 Normative references ........................................................................................................................... 1

3 Terms and definitions........................................................................................................................... 1

4 Symbols ................................................................................................................................................. 1

5 Principle................................................................................................................................................. 3

6 Installation ............................................................................................................................................. 3

7 Fishpass performance.......................................................................................................................... 7

8 Computation of discharge ................................................................................................................. 25

9 Computation of uncertainty of measurement.................................................................................. 25

10 Example ............................................................................................................................................... 26

Bibliography ..................................................................................................................................................... 29

© ISO 2009 – All rights reserved iii
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ISO 26906:2009(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 2.

The main task of technical committees is to prepare International Standards. 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.

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.

ISO 26906 was prepared by Technical Committee ISO/TC 113, Hydrometry, Subcommittee SC 2, Flow

measurement structures.
iv © ISO 2009 – All rights reserved
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ISO 26906:2009(E)
Introduction

Flow gauging structures are commonly used for the measurement 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, may inhibit the movement of fish. It has become

important, therefore, to consider ways of aiding fish migration without seriously affecting flow measurement

accuracy.
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INTERNATIONAL STANDARD ISO 26906:2009(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 Measurement structures and fishpasses have inherently different hydraulic performance criteria. Water

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 passage or that they are good enough that passage performance can be sacrificed to obtain a single

structure that does both.
2 Normative references

The following references are indispensable for the application 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

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 apply.

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)
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ISO 26906:2009(E)
Symbol Term Unit
a height of baffle [L] m
b orifice width [PO] m
b crest breadth measured at transverse section of upstream baffle [L] m
B width of fishpass [L] m
B pool width [PT and PO] m
B width of the non-aerated nappe [PT] m
C characteristic discharge coefficient [PO]
C dimensionless coefficient of discharge [L]
C characteristic discharge coefficient [PT]
C coefficient for the approach velocity [PT]
D longitudinal spacing of transverse baffles [L] m
D pipe diameter [PO] m
g acceleration due to gravity [All] m/s
h maximum head m
max
h orifice height [PO] m
h upstream gauged head relative to transverse section of upstream baffle [L] m
h upstream head [PT] m
h downstream head [PT] m
H upstream total head relative to transverse section of upstream baffle [L] m
H upstream total head [PT] m

H effective upstream total head relative to transverse section of upstream baffle [L] m

k head correction factor taking into account fluid property effects [L] m
l pool length [PT] m
L crest length [PT] m
L pool length [PO] m
n number of partitions [PO]
n length scale factor [PO]
n flow velocity scale [PO]
n discharge scale [PO]
n scale factor for length dimensions [PT]
P height of the top baffle [L] m
P pool depth [PT] m
Q discharge [All] m /s
Q design discharge [PT and PO] m /s
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
V mean flow velocity [PO] m/s
W upstream water level [PO] m
W downstream water level [PO] m
X distance to h measurement section [PT] m
X uncertainty in C [PT] %
C D
X uncertainty in measured or calculated discharge [PT and PO] %
Y downstream water depth, related to upstream bed level [PO] m
Y upstream water depth, related to upstream bed level [PO] m
2 © ISO 2009 – All rights reserved
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ISO 26906:2009(E)
α angle of V-shape [PT] deg
δ error in measurement of h [PT] m
h 1
∆h drop over the fishpass for modular flow [PT] m
∆h head drop per pool [PO] m
∆h design head drop per pool [PO] m
∆t 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 drowned 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

document provides the necessary design and performance information for this type of arrangement.

6 Installation

NOTE General requirements of combined flow measurement structure/fishpass installations are given in the following

clauses.
6.1 Requirements for gauging structure/fishpass installations

NOTE Requirements for the installation of gauging 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/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 measurement by a weir.

6.1.1.2 Particular attention shall be paid to the following features in selecting the site:

⎯ availability of an adequate length of channel of regular cross-section;
⎯ 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.

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ISO 26906:2009(E)

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 regular, then it may be

assumed that the velocity distribution will remain satisfactory after the construction of a weir.

6.1.1.5 If the existing velocity distribution is irregular and no other site for a gauge 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 irregular 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 metre or acoustic Doppler profiler.

6.1.2 Installation conditions

6.1.2.1 The complete installation consists of an approach channel, the flow measurement/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.
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 normal 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. Unless

otherwise specified in the appropriate clauses, the following general requirements 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 upstream of the structure, which in time might affect the flow conditions. The likely

consequential changes in the water level shall be taken into account in the design of the structures.

6.1.3.3 In an artificial channel the cross-section shall be uniform and the channel shall be straight for a

length equal to at least five times its breadth.

6.1.3.4 In a natural stream or river the cross-section shall be reasonably uniform and the channel shall be

straight for such a length as to ensure regular velocity distribution.

6.1.3.5 If the entry to the upstream channel is through a bend or if the flow is discharged into the channel

through a conduit of a smaller cross-section, or at an angle, then a longer length of straight approach channel

may be required to achieve a regular velocity distribution.

6.1.3.6 There shall be no baffles in the upstream channel, which are nearer than five times the maximum

head to the point of head measurement.

6.1.3.7 Under certain conditions, a standing wave may occur upstream of the installation, for example if

the approach channel is steep. Provided this wave is at a distance of not less than 30 times the maximum

head upstream, flow measurement will be feasible, subject to confirmation that a regular velocity distribution

exists at the structure.
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ISO 26906:2009(E)
6.1.4 Downstream channel

6.1.4.1 The channel downstream of the structure is of no importance to flow measurement if the gauging

structure or gauging structure/fishpass installation has been so designed that the flow is modular under all

operating conditions. A downstream gauge shall be provided to measure tailwater levels to determine if and

when submerged flow occurs.

6.1.4.2 In the event of the possibility of scouring downstream, which may lead to the instability of the

structure, particular measures to prevent this happening may be necessary.

6.1.4.3 A separate head gauge to indicate downstream conditions and a second stilling well shall be fitted

if the flow measurement structure is designed to operate in the drowned condition or if there is a possibility

that the structure may drown in the future.

6.1.4.4 The circumstances described in 6.1.4.3 may arise if the altered flow conditions, due to the

construction of the structure, have the effect of building up shoals of debris immediately downstream of the

structure or if river works are carried out downstream at a later date.

6.1.4.5 For optimum fishpass performance the jet of water issuing into the downstream channel shall be

discernable to the fish amongst all the other competing flows and from as far away as possible. Care shall be

taken to avoid the jet being masked by cross-flows or turbulence in the receiving water. Further details, which

specifically relate to the fishpass, are given in 6.2.3.
6.1.5 Flow measurement and fishpass structures

6.1.5.1 The flow measurement structure should comply with the requirements given in the appropriate

International Standard (see Bibliography).

6.1.5.2 The fishpass shall comply with the requirements of Clause 7. The quality of construction,

particularly at the upstream entry, should match that of the flow measurement structure (see Bibliography).

6.1.6 Maintenance

6.1.6.1 Maintenance of the flow measurement structure, the fishpass and the approach channel is

important to secure accurate continuous measurements of discharge.

6.1.6.2 It is essential that the approach channel to flow measurement structure/fishpass installations be

kept clean and free from silt and vegetation. The float well and the entry from the upstream channel shall also

be kept clean and free from deposits.

6.1.6.3 The flow measurement structure and the fishpass shall be kept clean and free from clinging

debris and care shall be taken in the process of cleaning to avoid damage to the weir or fishpass.

6.1.7 Measurement of head

6.1.7.1 When a fishpass is set alongside a flow measurement structure, an additional flow path is created

and the fishpass flow needs to be evaluated with a similar precision to that of the gauging structure itself. The

following are the two ways of doing this.

⎯ Head gauges are placed at both the fishpass and the gauging structure, and the two flows are determined

separately and then combined to give the total river flow. This method requires more computing and

telemetry but is reliable, particularly where the upstream entry to the fishpass is remote from the gauging

structure.

⎯ Head gauges are placed only at the gauging structure and the flow at the fishpass is determined by

transferring the single measured head to the fishpass using the established principles which apply to

compound weirs. This method is more economical and is particularly useful where the upstream entry to

the fishpass is close to the gauging structure.
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ISO 26906:2009(E)

6.1.7.2 Head gauges shall be designed and installed in accordance with the relevant International

Standard (see Bibliography for gauging structures and this International Standard for fishpasses).

6.1.7.3 Head gauges shall be zeroed to the crest of flow measurement weirs or to the invert level of

flumes. Accuracy in zeroing gauges is very important at low flows.
6.2 Requirements specific to the fishpass
6.2.1 General
The swimming performance of fish depends on many factors, including:
⎯ species;
⎯ individual size and ability;
⎯ water temperature;
⎯ water depth;
⎯ water velocity;
⎯ water quality;
⎯ turbulence;
⎯ motivation;
⎯ migration period.

It is thus a complex subject with many variations. The data available are variable in both quantity and quality,

and are complex to interpret. Furthermore, the effectiveness of a fishpass in terms of ease of passage

depends on a suitable match between the type of fishpass, the specific hydraulic conditions within the

fishpass and the particular species of fish wishing to migrate. It is not within the scope of this International

Standard to cover this complex subject in detail. Instead, basic requirements which apply to a range of

species of fish and a range of types of fishpass are identified to help those designing flow measurement

structure/fishpass installations.
6.2.2 Guidelines for basic parameters of fishpasses

Guidelines for maximum water velocities within, head drops across and lengths of fishpasses are given in

Table 1.
Table 1 — Guidelines for maximum water velocities within, head drops across
and lengths of fishpasses
Species
Pass parameters
Coarse fish Brown trout Sea trout Salmon
Max. velocity (m/s) 1,4 to 2,0 1,7 to 2,4 2,4 to 3,0 3,0 to 3,4
Pool pass
Max. head drop (m) 0,1 to 0,2 0,15 to 0,3 0,3 to 0,45 0,45 to 0,6
Max. velocity (m/s) 1,1 to 1,3 1,2 to 1,6 1,3 to 2,0 1,3 to 2,0
Baffled pass
Length of pass (m) 8 to 10 8 to 10 10 to 12 10 to 12
6 © ISO 2009 – All rights reserved
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ISO 26906:2009(E)
6.2.3 Location and attraction flows
6.2.3.1 General

In many respects, the most significant problem in passing fish, either upstream or downstream, is that of

attracting the fish into the fishpass facility.
6.2.3.2 Location

For those fish travelling upstream, the exit from the fishpass to the downstream reach shall be located as far

upstream as possible and shall be near one of the banks wherever practicable since this is the preferred

migration route for many species. This location facilitates monitoring and maintenance. Security risks may

need to be addressed. See also 6.2.4 and 6.2.5.
6.2.3.3 Attraction flows

The jet of water issuing from the fishpass shall be discernible to the fish. Exit velocities shall be in excess of

0,75 m/s and preferably in excess of 1,5 m/s for salmonids.

The discharge through the fishpass shall be large enough to attract fish towards the downstream entrance.

There are various criteria for this including:

⎯ 1 % to 5 % of the river flow during the migration period (larger watercourses);

⎯ 5 % to 10 % of the annual daily flow of the river (smaller watercourses);
⎯ a flow equal to the river flow which is exceeded 97 % of the time.

The discharge through the fishpass and the velocity of the outflow shall be determined in relation to the

specific circumstances, and the specific species and size of fish which need to be conveyed.

6.2.4 Downstream entry/exit to fishpass

Fish normally find their way to the most upstream point. The downstream entrance to the fishpass shall

therefore be located at the most upstream position which is easily accessible to the fish, for example close to

the downstream truncation of a gauging structure. The downstream entry to the fishpass shall not be in areas

of either re-circulating flows or highly turbulent flows. A vertical slot entry shall be installed such that a

significant jet of water flows from the fishpass over a range of river flows.
6.2.5 Upstream exit/entry from fishpass

The upstream exit from the fishpass shall not be located where there is a danger of fish being immediately

swept back downstream. A submerged orifice exit will help to minimize the ingress of floating and demersal

trash. The size of the orifice shall be large enough to avoid significant head losses which would complicate

flow measurement. The edges of the orifice shall be rounded to minimize head losses.

7 Fishpass performance
7.1 General
7.1.1 Types

There are many different types of fishpass. Generally, they form variations on the themes of steps, slopes or

lifts.
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ISO 26906:2009(E)

The step approach involves splitting the height to be passed into a series of small drops with various forms of

traverse separating resting pools. The slope approach involves spilling water down relatively steep slopes

where various forms of baffles are used to dissipate energy and slow down the water velocity. To these can

be added fish lifts, diversion or by-pass channels that may vary from the totally artificial to the “natural stream-

mimicking” type and many adaptations to ease the passage of fish, including adaptations to the flow

measurement structure itself.
7.1.2 Fishpasses with interconnected pools

Fishpasses with interconnected pools are perhaps the oldest type of pass in use. They are generally

applicable for most fish species, are extensively used throughout the world and in most cases require low

maintenance. They can frequently change direction, even very sharply, and therefore may be integrated into

some locations much more easily than some other types of pass. The connection between the pools may take

one of several forms including simple over-falls, a variety of notches, vertical slots, or orifices. There may also

be a combination of these.

Constraints on the use of these fishpasses include the height between each pool and the need for little

turbulence within the pools to provide the fish with resting areas during transit.

This International Standard includes two types of fishpass which fit into the interconnected pools category:

⎯ the pool-type fishpass with V-shaped overfalls;
⎯ the Dutch pool and orifice fishpass.
7.1.3 Fishpasses with continuous energy dissipation
7.1.3.1 General

The two best known fishpasses with continuous energy dissipation along their length are:

a) the Denil fishpass, developed by a Belgian engineer;
b) the Larinier fishpass, first developed in France.

In both cases, fish should pass the length of any one flight in a single attempt. Therefore the length of flight

should be limited.

Accurate information on the hydraulic performance of Denil fishpasses is not yet available.

7.1.3.2 Larinier super-active baffle fishpasses

This type of pass, developed in France by Larinier and Miralles, is being widely used in Europe. It is suitable

not only for large migratory salmonids such as salmon and sea trout, but also for an extensive range of other

species including coarse fish. Fish exploit the heterogeneity of microvelocities in this type of fishpass.

It is a relatively wide and shallow type of fishpass (in comparison with a Denil fishpass), and only has baffles

on the bed of the pass. Channel width is only limited by site conditions and not by hydraulic operating

characteristics as is the case for other types of baffled fishpass. A significant advantage of this type of

fishpass is that major attraction flows can be created, by juxtaposing multiple ‘units’ of pass in to a very wide

channel.

One specific fishpass of the continuous energy dissipation type is included in this International Standard, i.e.

the Larinier super-active baffle fishpass with 100 mm high baffles.

7.1.4 The three types of fishpass included in this International Standard have all been subjected to rigorous

hydrometric testing in large-scale laboratory facilities to determine coefficients of discharge. The Larinier

super-active baffle fishpass with 100 mm high baffles has been calibrated using volumetric measurement

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ISO 26906:2009(E)

facilities for every individual flow rate. The pool-type fishpass with V-shaped overfalls and the Dutch pool and

orifice fishpass have been calibrated against a secondary flow measurement device with volumetric checks at

intervals.

Pending further rigorous studies the coefficient of discharge for the three types of fishpasses, at the 95 %

confidence level, shall be taken as follows:
⎯ the Larinier super-active baffle fishpass with 100 mm baffles is1 %
...

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