ISO 772:2022
(Main)Hydrometry — Vocabulary and symbols
Hydrometry — Vocabulary and symbols
This document defines terms and symbols used in standards in the field of hydrometry.
Hydrométrie — Vocabulaire et symboles
Le présent document définit les termes et symboles utilisés dans les normes couvrant le domaine de l'hydrométrie.
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INTERNATIONAL ISO
STANDARD 772
Sixth edition
2022-02
Hydrometry — Vocabulary and
symbols
Hydrométrie — Vocabulaire et symboles
Reference number
ISO 772:2022(E)
© ISO 2022
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ISO 772:2022(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2022
All rights reserved. Unless otherwise specified, or required in the context of its implementation, 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.
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Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
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ISO 772:2022(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Terms related to velocity-area methods .13
5 Terms related to flow measurement structures .17
6 Terms related to dilution method .30
7 Terms related to instruments and equipment .32
8 Terms related to sediment transport .38
9 Terms related to precipitation . 44
10 Terms related to snow .45
11 Terms related to groundwater .51
12 Terms related to uncertainties in hydrometric determinations .61
Annex A (informative) Symbols used in hydrometry .70
Bibliography .73
Index .74
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ISO 772:2022(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 of 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
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 113, Hydrometry, in collaboration with
the European Committee for Standardization (CEN) Technical Committee CEN/TC 318, Hydrometry, in
accordance with the Agreement on technical cooperation between ISO and CEN (Vienna Agreement).
This sixth edition cancels and replaces the fifth edition (ISO 772:2011) which has been technically
revised. The main changes compared with the previous edition are as follows:
— terms related to precipitation have been added in a new Clause 9;
— additional terms have been added in Clause 10;
— Figures 1, 3, 4, 5, 6, 9, 11 and 12 have been modified and updated.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
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ISO 772:2022(E)
Introduction
In the preparation of this document, the following principles were adopted wherever possible:
a) to standardize suitable terms and symbols without perpetuating unsuitable ones;
b) to discard any term or symbol with differing meanings in different countries, or for different
people, or for the same person at different times, and to replace that term or symbol by one which
has an unequivocal meaning;
c) to exclude terms which are self-evident.
Terms in existing International Standards have been included as much as possible; however, these
terms can be subject to future amendments.
NOTE Similar or identical terms can have separate definitions under the different categories.
It is recognized that it is not possible to produce a complete set of definitions which will be universally
acceptable, but it is hoped that the definitions provided and the symbols used will find widespread
acceptance and that their use will lead to a better understanding of hydrometric practices.
The terminology entries are presented in systematic order, grouped into sections according to
particular methods of determination or in relation to particular subjects. Annex A lists the symbols
used in this document.
The structure of each entry is in accordance with the ISO 10241 series. Country codes are in accordance
with ISO 3166-1.
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INTERNATIONAL STANDARD ISO 772:2022(E)
Hydrometry — Vocabulary and symbols
1 Scope
This document defines terms and symbols used in standards in the field of hydrometry.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
hydrometry
science and practice of measuring the components of the hydrological cycle (3.92), including rainfall
(9.10), water level (3.64), flow and sediment transport (8.2) of surface waters, and groundwater (11.1)
characteristics
3.2
hydrology
science that deals with the waters above and below the land surfaces of the Earth, their occurrence,
circulation and distribution, their properties and their reaction with the environment
3.3
flow
water flowing on or below the land surface under gravitational influence
3.4
runoff
volume of water flowing through a given channel cross-section related to a given drainage basin (3.103)
in a defined period of time
3.5
discharge
Q
volume of water flowing through a given channel cross-section in unit time
3.6
current
directed movement of water
3.7
steady flow
flow (3.3) in which parameters [such as velocity (3.113), pressure, density and temperature] are
constant with respect to time
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ISO 772:2022(E)
3.8
unsteady flow
flow (3.3) in which one or more parameters [such as velocity (3.113), pressure, density and temperature]
change with respect to time
3.9
uniform flow
flow (3.3) in which the magnitude and direction of flow at a given moment are constant with respect to
distance
Note 1 to entry: For uniform flow, the velocity vector is constant along every stream line. Uniform flow is possible
only in an open channel (3.19) of constant slope and cross-section.
3.10
non-uniform flow
flow (3.3) in which the magnitude and direction of flow at a given moment are changing with respect to
distance
3.11
critical flow
flow (3.3) in an open channel (3.19) in which the specific energy is a minimum for
a given discharge (3.5)
Note 1 to entry: Under this condition, the Froude number (3.89) is equal to unity and small surface disturbances
cannot travel upstream.
3.12
subcritical flow
flow (3.3) in an open channel (3.19) at less than critical velocity (3.17), which has a Froude number (3.89)
of less than unity and in which small surface disturbances can travel upstream
3.13
supercritical flow
flow (3.3) in an open channel (3.19) at more than critical velocity (3.17), which has a Froude number
(3.89) of greater than unity and in which small surface disturbances cannot travel upstream
3.14
transverse flow
lateral flow
flow (3.3) horizontally perpendicular to the main direction of flow
Note 1 to entry: Transverse (lateral) flow is frequently associated with secondary flow.
Note 2 to entry: Transverse (lateral) flow in open channels (3.19) with a curved plan form causes superelevation
of the water surface at the outside of the bend.
3.15
stratification
state of a water body that consists of two or more layers arranged according to their density, the lightest
layer being on top and the heaviest at the bottom
3.16
critical depth
depth (3.78) of flow (3.3) at which critical flow (3.11) occurs
3.17
critical velocity
velocity (3.113) of flow (3.3) that has minimum specific energy for a given discharge (3.5) or has unit
Froude number (3.89)
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ISO 772:2022(E)
3.18
channel
course of a river (3.27), stream (3.26) or other watercourse
3.19
open channel
longitudinal boundary surface consisting of the bed and banks or sides within which water flows with
a free surface
3.20
canal
man-made channel (3.18), usually of regular cross-sectional shape
3.21
stable channel
open channel (3.19) in which the bed and the sides remain essentially stable over a substantial period
of time in the reach (3.34) under consideration, and in which the scour and deposition (10.5) during the
rising and falling stages are negligible
3.22
unstable channel
open channel (3.19) that changes frequently and significantly in its plan form and/or cross-sectional
form for the reach (3.34) under consideration
3.23
tidal channel
open channel (3.19) in which the flow (3.3) is subject to tidal influence
3.24
tide
periodic rise and fall of water due principally to the gravitational attraction of the sun and the moon
3.25
estuary
lower tidal reaches (3.34) of a river (3.27) that is freely connected with the sea which receives fresh
water supplies from upland drainage areas
3.26
stream
water course, water flowing in an open channel (3.19)
3.27
river
large natural water course
3.28
large river
major river
large natural water course that generally flows into the sea
3.29
creek
brook
small natural water course
3.30
torrent
small natural water course that is characterized by steep slopes and significant rapid changes in
discharge (3.5) and that can transport considerable volumes of solid material
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ISO 772:2022(E)
3.31
alluvial river
river (3.27) which flows through alluvium formed from its own deposits
3.32
incised river
river (3.27) which has formed its channel (3.18) by a process of erosion
3.33
braided river
river (3.27) characterized by a wide and shallow open channel (3.19) in which flow (3.3) passes through
a number of small interlaced channels (3.18)
3.34
reach
length of open channel (3.19) between two defined cross-sections
3.35
meandering channel
water course formed by natural flow processes and movement of sediments following generally an
alternating regular sinuous path
3.36
thalweg
line joining the lowest points of successive cross-sections of a water course
3.37
unit discharge
discharge per unit width
q
u
discharge (3.5) through a unit width of a given vertical section
3.38
yield specific discharge
q
discharge (3.5) per unit area of catchment or aquifer (11.15)
3.39
stream gauging
discharge measurement
flow measurement
stream flow measurement
river gauging
all of the operations necessary for the measurement of discharge (3.5) of a stream (3.26)
3.40
gauge
device installed at a gauging station for measuring the level of the surface of water relative to a datum
3.41
left bank
bank to the left of an observer looking downstream
3.42
right bank
bank to the right of an observer looking downstream
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ISO 772:2022(E)
3.43
channel bed
invert
stream bed
stream bottom
channel bottom
lower part of the stream channel situated between the banks
3.44
bed slope
bottom slope
S
o
difference in elevation of the bed per unit horizontal distance, measured in the direction of flow (3.3)
Note 1 to entry: The slope is usually mathematically negative in the direction of flow.
3.45
bed profile
shape of the bed in a longitudinal vertical plane
3.46
side slope
difference in elevation between the bottom and top of a bank per unit horizontal distance
3.47
surface slope
S
w
inclination of the surface of the stream (3.26) in a reach (3.34) measured in the direction of flow (3.3)
3.48
fall
difference in elevation of the water surface between the extremities of a defined reach (3.34) at a given
instant of time
EXAMPLE As recorded at a slope station (3.71).
3.49
top width
width of the open channel (3.19) measured across the stream (3.26) at the water surface normal to the
direction of flow (3.3)
3.50
wetted perimeter
P
w
contact length between a stream (3.26) of flowing water and its containing open channel (3.19),
measured in a direction normal to the flow (3.3)
3.51
wetted cross-section
section normal to the mean direction of flow (3.3) bounded by the free surface and wetted
perimeter (3.50)
3.52
gauging section
measuring section
section at which discharge (3.5) measurements are taken
3.53
high water mark
flood mark
mark left on a structure or any other object indicating exceptional stages of flood
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ISO 772:2022(E)
3.54
debris line
trash line
traces of any kind left on the banks or obstacles or flood plain by a flood
Note 1 to entry: The debris line may be used to determine the highest level attained by the water surface during
a flood.
3.55
surface velocity
flow (3.3) velocity (3.113) at a given point on the surface
3.56
mean velocity
flow (3.3) velocity (3.113) at a given cross-section of a stream (3.26), obtained by
dividing the discharge (3.5) by the cross-sectional area
3.57
slush ice
mass of loosely packed anchor ice (3.105) that is released from the bottom, or frazil ice (3.104) that
floats or accumulates under surface ice (3.107)
3.58
velocity head
theoretical vertical height to which liquid particles can be elevated by kinetic energy
Note 1 to entry: It is expressed as the square of the velocity (3.113) divided by twice the acceleration due to
gravity.
3.59
gauged head
elevation of the free surface above the horizontal datum of a section
3.60
total head
energy head
H
sum of the elevation of the free surface above the horizontal datum of a section plus the velocity head
(3.58) based on the mean velocity (3.56) at that section
Note 1 to entry: The total head, H, is given by the following formula:
2
v
Hh=+α
2g
where
h is the gauged head of water level (3.64);
v
is the mean velocity of the water;
α is the Coriolis coefficient;
g is the acceleration due to gravity.
Note 2 to entry: The Coriolis coefficient (α ≥ 1), also known as “energy coefficient” or “energy correction factor”,
takes into account the non-uniform velocity distribution. In many cases, α is assumed to equal unity.
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ISO 772:2022(E)
3.61
total head line
energy head line
plot of the total head (3.60) in the direction of flow (3.3)
3.62
energy gradient
difference in total head (3.60) per unit horizontal distance, measured in the direction of flow (3.3)
3.63
energy loss
head loss
difference in total head (3.60) between two cross-sections in the direction of flow (3.3)
3.64
water level
stage
gauge height
elevation of the free surface of a stream (3.26), lake or reservoir relative to a specified datum
3.65
reference gauge
stage gauge that discharge (3.5) is normally linked to
3.66
stage-discharge relation
rating curve
rating table
equation, curve or table that expresses the relation between the stage and the discharge (3.5) in an open
channel (3.19) at a given cross-section
3.67
hydrograph
graphical representation of changes of hydrometric parameters with respect to
time
Note 1 to entry: Typically, stage and discharge hydrographs are used for open channel flows.
3.68
cumulative volume curve
curve in which the cumulative value of a hydrometric parameter is plotted against time
Note 1 to entry: Integral of the hydrograph (3.67), such as cumulative discharge curve.
3.69
storage curve
table
curve depicting the volume of stored water plotted against water level (3.64)
3.70
gauging station
site on a stream (3.26), river (3.27) or lake at which systematic measurements of water level (3.64),
velocity (3.113) or discharge (3.5) or any combination of the three are made
3.71
slope station
twin-gauge station
gauging station (3.70) at which two water-level gauges (3.40) define a reach (3.34) for measurement of
water-surface slope as an essential parameter for establishing a stage-discharge relation (3.66)
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ISO 772:2022(E)
3.72
control
physical properties of a cross-section or a reach (3.34) of an open channel (3.19), either natural or
artificial, that govern the relation between stage and discharge (3.5) at a location in the open channel
3.73
rating
relation between discharge (3.5) and other variables, or the taking of observations and making of
calculations needed to establish the relation
3.74
unit-fall rating
relation between stage and discharge (3.5) when the fall (3.48) is equal to one
3.75
afflux
rise in water level (3.64) immediately upstream of, and due to, an obstruction
3.76
backwater curve
profile of water surface, along an open channel (3.19), from the raised surface at an obstruction or
confluence to the point upstream at which the flow (3.3) is at normal depth (3.78)
Note 1 to entry: The term is also used to denote all liquid surface profiles that are non-uniform with respect to
distance upstream or downstream. However, this usage is deprecated.
3.77
drawdown curve
profile of the liquid surface when its surface slope (S ) (3.47) exceeds the bed slope (S ) (3.44)
w o
Note 1 to entry: From the point at which the bed slope increases, or bed level drops abruptly, to the point at which
normal depth (3.78) occurs, the profile along an open channel (3.19) is convex upwards in an upstream direction
and concave upwards in a downstream direction.
3.78
depth
D
linear dimension measured in the vertical direction from the water surface to the bed
3.79
peak stage
maximum instantaneous stage during a given period
3.80
friction
drag
boundary shear resistance that opposes the flow (3.3) of a liquid
3.81
conveyance
K
carrying capacity of a channel (3.18)
Note 1 to entry: The term “conveyance factor” is also used, e.g. in the formula:
−12/
KQ= S
where
K is the conveyance factor;
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ISO 772:2022(E)
Q is the total discharge (3.5);
S is the energy gradient (3.62).
3.82
hydraulic jump
sudden transition from supercritical flow (3.13) to subcritical flow (3.12)
Note 1 to entry: Immediately upstream of the hydraulic jump, the velocity (3.113) and the depth (3.78) are
respectively greater and less than their critical values. Beyond the jump, the velocity and the depth are
respectively less and greater than their critical values.
3.83
hydraulic mean depth
mean depth
D
m
area of the cross-section of water flowing in an open channel (3.19) divided by the width of the open
channel at the water surface
3.84
hydraulic radius
r
h
wetted cross-sectional area of water flowing in an open channel (3.19) divided by the length of the
wetted perimeter (3.50) at that cross-section
3.85
gauge datum
elevation of the zero of the gauge (3.40) to which the level of the liquid surface is referred
Note 1 to entry: The gauge datum is related to a benchmark (3.86).
3.86
benchmark
permanent mark, the elevation of which should be related, where practicable, to a national datum
3.87
gauge/float well
stilling well/tube
chamber open to the atmosphere and connected with the stream (3.26) in such a way as to permit the
measurement of the water level (3.64) in relatively still water
3.88
roughness coefficient
coefficient that characterizes the roughness of the channel cross-section and which is taken into
account when computing the resistance to flow (3.3) or the energy gradient (3.62)
Note 1 to entry: The common types are the Manning’s/Strickler n, Chezy C or an element roughness height, k.
3.89
Froude number
Fr
mean velocity (3.56) divided by the square root of the product of the hydraulic mean depth (3.83) and the
acceleration due to gravity
v
Fr =
12/
gD
()
m
where
v
is the mean velocity of the liquid;
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ISO 772:2022(E)
g is the acceleration due to gravity;
D is the hydraulic mean depth of the cross-section.
m
Note 1 to entry: The Froude number is dimensionless.
3.90
Reynolds number
Re
ratio of the forces of inertia to forces of viscosity (11.68)
Note 1 to entry: For open channels (3.19):
vr
h
Re=
η
where
v
is the mean velocity (3.56) of the liquid;
r is the hydraulic radius (3.84) of the cross-section;
h
η is the kinematic viscosity (11.69) of the liquid.
Note 2 to entry: The Reynolds number is dimensionless.
3.91
free surface flow
flow (3.3) within a closed or open conduit, under gravity and having a free surface
Note 1 to entry: Where the flow exceeds the free surface capacity of the conduit, the flow will become surcharged
with the consequent disappearance of the free surface. Instances of surcharging of short duration do not normally
affect the overall concept of free surface flow in closed conduits.
3.92
hydrological cycle
constant movement of water in all states of its form, above, on and below the Earth’s surface
3.93
hydrogeology
study of subsurface water in its geological context
3.94
live storage
reservoir storage which can be drawn off for users downstream
3.95
total storage
reservoir storage between the lowest bed level and the top water level (3.64)
3.96
flood storage
volume of water temporarily held above the top water level (3.64) of a reservoir during a flood event
Note 1 to entry: Flood storage is not retained in the reservoir but is discharged through an overflow until the
normal top water level is reached.
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ISO 772:2022(E)
3.97
standing wave
stationary wave
curved symmetrically shaped wave on the water surface and on the channel bed (3.43) that is virtually
stationary
Note 1 to entry: When standing waves form, the water surface and the bed surfaces are roughly parallel and in
phase.
3.98
tributary
surface or underground stream (3.26) which contributes its water, continuously or intermittently, to
another stream
3.99
river delta
reach (3.34) of a river (3.27) when it approaches a body of quieter water with very gradual bed slope (S )
o
(3.44) and surface slope (S ) (3.47), and, at low velocity (3.113), deposits its sediment and divides out
w
into channels (3.18) on either side of the deposits, resulting in the formation of deltas
3.100
annual flood
highest momentary peak discharge (3.5), recorded at the respective point of observation, which is
equalled or exceeded once every year
3.101
annual storage within-the-year storage
difference between the maximum and minimum volumes in storage over a year of reservoir operation
3.102
base flow
sustained flow of a stream (3.26) resulting from outflow of groundwater (11.1) and from drainage of
large lakes and swamps
Note 1 to entry: Base flow includes water sustained in glaciers (10.9), snow and other sources, not a result of
direct runoff (3.4).
3.103
drainage basin
catchment area
part of the land area enclosed by a topographic divide from which direct surface runoff (3.4) from
precipitation (9.9) drains by gravity into a stream (3.26) or other water body
3.104
frazil ice
fine spicules, plates or discoids of ice suspended in water that are generally formed by the supercooling
of turbulent water
Note 1 to entry: Frazil ice may float or accumulate under surface ice (3.107) or adhere to the channel bed (3.43) as
anchor ice (3.105).
3.105
anchor ice
submerged ice found attached to the bed, irrespective of the nature of its formation
3.106
rime ice
white mass of tiny ice crystals or granular ice tufts formed on exposed objects due to atmospheric
moisture
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ISO 772:2022(E)
3.107
surface ice
ice cover
ice sheet
layer of ice formed on the surface of a lake or river (3.27)
3.108
flow regime
state of flow (3.3) in alluvial streams (3.26) characterized by a bed configuration of ripples (3.111),
dunes (3.109) (lower regime), plane bed (transition), standing waves (3.97) and antidunes (3.110) (upper
regime)
Note 1 to entry: The lower-regime flow is subcritical. The upper-regime flow is supercritical.
3.109
dune
large bed form having a triangular profile, a gentle upstream slope and a steep downstream slope
Note 1 to entry: Dunes are formed in quiet flow and thus are out of phase with any possible water surface
disturbance they produce. They travel slowly downstream as sand is moved across their comparatively gentle
upstream slopes and deposited on their steeper downstream slopes.
3.110
antidune
bed form of a curved symmetrically shaped sand or gravel wave that may move upstream, remain
stationary or move downstream
Note 1 to entry: Antidunes are curved in a wave train but they are in phase and interact strongly with gravity
water surface waves.
3.111
ripple
small triangular-shaped bed form similar to a dune (3.109)
Note 1 to entry: Ripples have much smaller and more uniform amplitudes and lengths than dunes. Ripple
wavelengths are less than 0,6 m and wave heights are less than 0,06 m.
3.112
transition
crossover
inflection reach (3.34) between two meander loops in which the main flow (3.3) crosses from one side
of the channel (3.18) to the other
Note 1 to entry: The depth (3.78) of flow in a transition is usually reduced from normal depth and is more uniform
than in the cu
...
NORME ISO
INTERNATIONALE 772
Sixième édition
2022-02
Hydrométrie — Vocabulaire et
symboles
Hydrometry — Vocabulary and symbols
Numéro de référence
ISO 772:2022(F)
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ISO 772:2022(F)
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Publié en Suisse
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ISO 772:2022(F)
Sommaire Page
Avant-propos .iv
Introduction .v
1 Domaine d'application .1
2 Références normatives .1
3 Termes et définitions . 1
4 Termes relatifs aux méthodes d'exploration du champ des vitesses .13
5 Termes liés aux ouvrages de mesurage de l'écoulement .18
6 Termes liés à la méthode de dilution .31
7 Termes relatifs aux instruments et aux équipements .33
8 Termes relatifs au transport des sédiments .39
9 Termes relatifs à la précipitation .45
10 Termes relatifs à la neige .46
11 Termes relatifs à l'eau souterraine .52
12 Termes liés aux incertitudes des calculs hydrométriques .64
Annexe A (informative) Symboles utilisés en hydrométrie .72
Bibliographie .75
Index .76
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ISO 772:2022(F)
Avant-propos
L'ISO (Organisation internationale de normalisation) est une fédération mondiale d'organismes
nationaux de normalisation (comités membres de l'ISO). L'élaboration des Normes internationales est
en général confiée aux comités techniques de l'ISO. Chaque comité membre intéressé par une étude
a le droit de faire partie du comité technique créé à cet effet. Les organisations internationales,
gouvernementales et non gouvernementales, en liaison avec l'ISO participent également aux travaux.
L'ISO collabore étroitement avec la Commission électrotechnique internationale (IEC) en ce qui
concerne la normalisation électrotechnique.
Les procédures utilisées pour élaborer le présent document et celles destinées à sa mise à jour sont
décrites dans les Directives ISO/IEC, Partie 1. Il convient, en particulier, de prendre note des différents
critères d'approbation requis pour les différents types de documents ISO. Le présent document a
été rédigé conformément aux règles de rédaction données dans les Directives ISO/IEC, Partie 2 (voir
www.iso.org/directives).
L'attention est attirée sur le fait que certains des éléments du présent document peuvent faire l'objet de
droits de propriété intellectuelle ou de droits analogues. L'ISO ne saurait être tenue pour responsable
de ne pas avoir identifié de tels droits de propriété et averti de leur existence. Les détails concernant
les références aux droits de propriété intellectuelle ou autres droits analogues identifiés lors de
l'élaboration du document sont indiqués dans l'Introduction et/ou dans la liste des déclarations de
brevets reçues par l'ISO (voir www.iso.org/brevets).
Les appellations commerciales éventuellement mentionnées dans le présent document sont données
pour information, par souci de commodité, à l’intention des utilisateurs et ne sauraient constituer un
engagement.
Pour une explication de la nature volontaire des normes, la signification des termes et expressions
spécifiques de l'ISO liés à l'évaluation de la conformité, ou pour toute information au sujet de l'adhésion
de l'ISO aux principes de l’Organisation mondiale du commerce (OMC) concernant les obstacles
techniques au commerce (OTC), voir www.iso.org/avant-propos.
Le présent document a été élaboré par le comité technique ISO/TC 113, Hydrométrie, en collaboration
avec le comité technique CEN/TC 318, Hydrométrie, du Comité européen de normalisation (CEN),
conformément à l'Accord de coopération technique entre l'ISO et le CEN (Accord de Vienne).
Cette sixième édition annule et remplace la cinquième édition (ISO 772:2011), qui a fait l'objet d'une
révision technique.
Les principales modifications sont les suivantes:
— des termes relatifs aux précipitations ont été ajoutés dans un nouvel Article 9;
— des termes supplémentaires ont été ajoutés à l'Article 10;
— les Figures 1, 3, 4, 5, 6, 9, 11 et 12 ont été modifiées et mises à jour.
Il convient que l’utilisateur adresse tout retour d’information ou toute question concernant le présent
document à l’organisme national de normalisation de son pays. Une liste exhaustive desdits organismes
se trouve à l’adresse www.iso.org/fr/members.html.
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ISO 772:2022(F)
Introduction
Lors de l'élaboration du présent document, les principes suivants ont été respectés dans la mesure du
possible:
a) normaliser les termes et symboles adaptés, en évitant de perpétuer l'utilisation de termes et
symboles inadaptés;
b) rejeter tout terme ou symbole pouvant avoir une signification différente selon les pays, les
personnes ou les contextes et le remplacer par un terme ou symbole non équivoque;
c) exclure les termes dont la signification est évidente.
Les termes figurant dans les normes internationales existantes ont été inclus dans la mesure du
possible; toutefois, ces termes peuvent faire l'objet de modifications ultérieures.
NOTE Des termes similaires ou identiques peuvent avoir des définitions séparées dans les différentes
catégories.
Il est admis qu'il est impossible de produire un ensemble complet de définitions universellement
acceptables; il est cependant souhaité que les définitions fournies et les symboles employés soient
largement adoptés et que leur utilisation permette une meilleure compréhension des pratiques de
l'hydrométrie.
Les entrées terminologiques sont présentées selon un ordre systématique et regroupées en sections
en fonction de méthodes de calculs ou de thèmes spécifiques. L'Annexe A établit la liste des symboles
utilisés dans le présent document.
La structure de chaque entrée est conforme à la série ISO 10241. Les codes de pays sont conformes à
l'ISO 3166-1.
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NORME INTERNATIONALE ISO 772:2022(F)
Hydrométrie — Vocabulaire et symboles
1 Domaine d'application
Le présent document définit les termes et symboles utilisés dans les normes couvrant le domaine de
l'hydrométrie.
2 Références normatives
Le présent document ne contient aucune référence normative.
3 Termes et définitions
L’ISO et l’IEC tiennent à jour des bases de données terminologiques destinées à être utilisées en
normalisation, consultables aux adresses suivantes:
— ISO Online browsing platform: disponible à l’adresse https:// www .iso .org/ obp
— IEC Electropedia: disponible à l’adresse https:// www .electropedia .org/
3.1
hydrométrie
science et pratique ayant pour objet de mesurer les composantes du cycle hydrologique (3.92) et qui
comprend les chutes de pluie (9.10), le niveau de l'eau (3.64), le débit et le transport des sédiments (8.2)
des eaux de surface, ainsi que les caractéristiques des eaux souterraines (11.1)
3.2
hydrologie
science traitant des eaux au-dessus et au-dessous de la surface de la Terre, de leur occurrence, de leur
circulation et de leur distribution, de leurs propriétés et de leur réaction avec l'environnement
3.3
écoulement
eau s'écoulant au-dessus et au-dessous de la surface terrestre, sous l'effet de la pesanteur
3.4
débit de ruissellement
volume d'eau qui traverse une section en travers de chenal pour un bassin hydrographique (3.103)
donné, pendant une période définie
3.5
débit
Q
volume d'eau qui traverse une section en travers de chenal dans une unité de temps
3.6
courant
écoulement d'eau suivant une direction perceptible
3.7
écoulement stationnaire
écoulement (3.3) dont les paramètres [tels que la vitesse (3.113), la pression, la masse volumique et la
température] sont constants dans le temps
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ISO 772:2022(F)
3.8
écoulement transitoire
écoulement (3.3) dont un ou plusieurs paramètres [tels que la vitesse (3.113), la pression, la masse
volumique et la température] varient dans le temps
3.9
écoulement uniforme
écoulement (3.3) dont la magnitude et la direction sont, à un moment donné, constantes sur une certaine
distance
Note 1 à l'article: Dans un écoulement uniforme, le vecteur vitesse est constant le long de toutes les lignes de
courant. Un écoulement uniforme n'est possible que dans un chenal à surface libre (3.19) présentant une pente et
une section en travers constantes.
3.10
écoulement non uniforme
écoulement (3.3) dont la magnitude et la direction, à un moment donné, varient sur une certaine distance
3.11
écoulement critique
<écoulement à surface libre> écoulement (3.3) dans un chenal à surface libre (3.19) dont l'énergie
spécifique est minimale pour un débit (3.5) donné
Note 1 à l'article: Dans cette situation, le nombre de Froude (3.89) est égal à l'unité et les petites perturbations en
surface ne peuvent pas remonter le courant.
3.12
écoulement fluvial
écoulement (3.3), dans un chenal à surface libre (3.19), présentant une vitesse inférieure à la vitesse
critique (3.17), avec un nombre de Froude (3.89) inférieur à l'unité et des petites perturbations en
surface pouvant remonter le courant
3.13
écoulement torrentiel
écoulement (3.3), dans un chenal à surface libre (3.19), présentant une vitesse supérieure à la vitesse
critique (3.17), avec un nombre de Froude (3.89) supérieur à l'unité et des petites perturbations en
surface ne pouvant pas remonter le courant
3.14
écoulement transversal
écoulement latéral
écoulement (3.3) perpendiculaire horizontalement à la direction principale d'écoulement
Note 1 à l'article: Un écoulement transversal (latéral) est souvent lié à un écoulement secondaire.
Note 2 à l'article: Dans les chenaux à surface libre (3.19) de forme plane et incurvée, un écoulement transversal
(latéral) entraîne une surélévation de la surface de l'eau à l'extérieur de la courbe.
3.15
stratification
état d'une masse d'eau constituée d'au moins deux couches disposées en fonction de leur masse
volumique, la couche la plus légère se trouvant en haut et la plus lourde en bas
3.16
profondeur critique
profondeur (3.78) d'écoulement (3.3) à laquelle l'écoulement critique (3.11) se produit
3.17
vitesse critique
vitesse (3.113) d'écoulement (3.3) qui a une énergie spécifique minimale pour un débit (3.5) donné ou un
nombre de Froude (3.89) unitaire
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ISO 772:2022(F)
3.18
chenal
parcours d'une rivière (3.27), d'un cours d'eau (3.26) ou d'une autre voie d'eau
3.19
chenal à surface libre
surface délimitée sur le plan longitudinal, comprenant le lit et les rives ou berges dans lesquels l'eau
s'écoule avec une surface libre
3.20
canal
chenal (3.18) artificiel, présentant généralement une section en travers régulière
3.21
chenal stable
chenal à surface libre (3.19) dont le lit et les berges restent stables sur une longue période dans le bief
(3.34) considéré et dans lequel, lors de la montée et de la descente du niveau de l'eau, l'affouillement et
l'alluvionnement sont négligeables
3.22
chenal instable
chenal à surface libre (3.19) dont le bief (3.34) considéré subit des modifications fréquentes et
importantes de forme et/ou de section en travers
3.23
chenal à marée
chenal à surface libre (3.19) dans lequel l'écoulement (3.3) est soumis à l'action de la marée
3.24
marée
phénomène périodique de montée et de baisse de l'eau, principalement dû à l'attraction gravitationnelle
du soleil et de la lune
3.25
estuaire
biefs (3.34) inférieurs, soumis à la marée, d'une rivière (3.27) naturellement reliée à la mer et qui reçoit
de l'eau douce de bassins hydrographiques situés en amont
3.26
ruisseau
cours d'eau
voie d'eau s'écoulant dans un chenal à surface libre (3.19)
3.27
rivière
grande voie d'eau naturelle
3.28
grande rivière
rivière principale
grande voie d'eau naturelle s'écoulant généralement dans la mer
3.29
ruisseau
petite voie d'eau naturelle
3.30
torrent
petite voie d'eau naturelle caractérisée par des pentes raides et des changements de débit (3.5) rapides
et significatifs, pouvant transporter des volumes considérables de matières solides
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ISO 772:2022(F)
3.31
rivière alluviale
rivière (3.27) qui s'écoule au travers d'alluvions formés par ses propres dépôts
3.32
rivière encaissée
rivière (3.27) qui a formé son chenal (3.18) par un processus d'érosion
3.33
rivière en tresses
rivière (3.27) caractérisée par un chenal à surface libre (3.19) large et peu profond, où l'écoulement (3.3)
a lieu dans plusieurs petits chenaux (3.18) entrelacés
3.34
bief
tronçon d'un chenal à surface libre (3.19) compris entre deux sections en travers définies
3.35
chenal à méandres
voie d'eau formée par des processus d'écoulement naturels et par le mouvement de sédiments suivant
généralement une trajectoire sinueuse régulière et changeant de direction
3.36
thalweg
ligne joignant les points les plus bas des sections en travers successives d'un cours d'eau
3.37
débit unitaire
débit par unité de largeur
q
u
débit (3.5) traversant une unité de largeur d'une section verticale donnée
3.38
débit spécifique
q
débit (3.5) par unité de surface d'un bassin versant ou d'un aquifère (11.15)
3.39
jaugeage
mesurage du débit
mesure de l'écoulement
jaugeage de rivière
ensemble des opérations nécessaires pour mesurer le débit (3.5) d'un cours d'eau (3.26)
3.40
sonde
dispositif installé dans une station de jaugeage hydrométrique afin de mesurer le niveau de la surface
de l'eau par rapport à un plan de référence
3.41
rive gauche
rive située à gauche pour une personne regardant vers l'aval
3.42
rive droite
rive située à droite pour une personne regardant vers l'aval
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ISO 772:2022(F)
3.43
lit du chenal
radier
lit du cours d'eau
fond du cours d'eau
fond du chenal
partie basse du chenal d'un cours d'eau, située entre les rives
3.44
pente du lit
pente du fond
S
o
différence de hauteur du lit par unité de longueur, mesurée horizontalement dans la direction
d'écoulement (3.3)
Note 1 à l'article: En règle générale, la pente est négative (du point de vue mathématique) dans la direction
d'écoulement.
3.45
profil du lit
forme du lit sur le plan vertical longitudinal
3.46
pente du talus
différence de hauteur entre le bas et le haut d'une berge par unité de distance horizontale
3.47
pente de la ligne d'eau
S
w
dénivellation de la surface du cours d'eau (3.26) dans un bief (3.34), mesurée dans le sens de l'écoulement
(3.3)
3.48
dénivelée
différence de hauteur en surface entre les deux extrémités d'un bief (3.34) défini à un instant donné
EXEMPLE Tel qu'enregistré à une station hydrométrique à dénivelée (3.71).
3.49
largeur au miroir
largeur du chenal à surface libre (3.19), mesurée en surface sur toute la largeur du cours d'eau (3.26)
perpendiculairement à la direction d'écoulement (3.3)
3.50
périmètre mouillé
P
w
longueur de contact entre un cours d'eau (3.26) en écoulement et le chenal à surface libre (3.19) qui le
contient, mesurée perpendiculairement à la direction principale d'écoulement (3.3)
3.51
section en travers mouillée
section normale par rapport à la direction moyenne d'écoulement (3.3) et délimitée
par la surface libre et le périmètre mouillé (3.50)
3.52
section de jaugeage
section de mesurage
section dans laquelle le débit (3.5) est mesuré
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ISO 772:2022(F)
3.53
laisses de crue
délaissés de crue
marque laissée sur un ouvrage ou tout autre objet indiquant des niveaux exceptionnels d'inondation
3.54
ligne de débris
ligne de résidus
traces de tous types laissées sur les rives, sur les obstacles ou sur les plaines d'inondation après une
inondation
Note 1 à l'article: Les lignes de débris peuvent être utilisées pour déterminer le niveau le plus haut atteint par la
surface de l'eau pendant une inondation.
3.55
vitesse à la surface libre de l'écoulement
vitesse (3.113) de l'écoulement (3.3) à la surface en un point donné
3.56
vitesse moyenne
vitesse (3.113) de l'écoulement (3.3) dans une section en travers donnée
d'un cours d'eau (3.26), obtenue en divisant le débit (3.5) par la surface de la section en travers
3.57
bouillie de glace
masse de glace de fond (3.105) peu liée qui se détache du fond ou frazil (3.104) qui flotte ou s'accumule
sous la glace de surface (3.107)
3.58
charge dynamique
hauteur verticale théorique à laquelle des particules liquides peuvent être élevées sous l'effet de
l'énergie cinétique
Note 1 à l'article: Elle est exprimée comme le carré de la vitesse (3.113) divisé par le double de l'accélération de la
pesanteur.
3.59
charge mesurée
élévation de la surface libre au-dessus du plan de référence horizontal d'une section
3.60
charge totale
H
somme de la hauteur de la surface libre au-dessus du plan de référence horizontal d'une section et de la
charge dynamique (3.58) calculée à partir de la vitesse moyenne (3.56) dans cette section
Note 1 à l'article: La charge totale, H, est donnée par l'équation suivante:
2
v
Hh=+α
2g
où
h est la charge mesurée du niveau de l'eau (3.64);
v
est la vitesse moyenne de l'eau;
α est le coefficient de Coriolis;
g est l'accélération de la pesanteur.
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ISO 772:2022(F)
Note 2 à l'article: Le coefficient de Coriolis (α ≥ 1), également appelé coefficient énergétique ou facteur de
correction énergétique, tient compte de la distribution non uniforme des vitesses. Dans de nombreux cas, α est
supposé égal à 1.
3.61
ligne de charge totale
tracé représentant la charge totale (3.60) dans la direction d'écoulement (3.3)
3.62
gradient de charge
différence de charge totale (3.60) par unité de longueur horizontale, mesurée dans la direction
d'écoulement (3.3)
3.63
perte d'énergie
perte de charge
différence de charge totale (3.60) entre deux sections en travers dans la direction d'écoulement (3.3)
3.64
niveau de l'eau
hauteur d'eau
hauteur à l'échelle
hauteur de la surface libre d'un cours d'eau (3.26), d'un lac ou d'un réservoir par rapport à un plan de
référence spécifié
3.65
limnimètre de référence
échelle limnimétrique à laquelle le débit (3.5) est normalement associé
3.66
relation hauteur-débit
courbe de tarage
barème de tarage
équation, courbe ou tableau exprimant la relation entre la hauteur et le débit (3.5) dans un chenal à
surface libre (3.19) à une section en travers donnée
3.67
hydrogramme
<écoulement à surface libre> représentation graphique des variations de débits dans le temps
Note 1 à l'article: En règle générale, on utilise des limnigrammes ou des hydrogrammes pour analyser l'écoulement
à surface libre.
3.68
courbe des débits cumulés
courbe représentant l'évolution dans le temps de la valeur cumulée d'un débit
Note 1 à l'article: Intégrale de l'hydrogramme (3.67), telle que la courbe des débits cumulés.
3.69
courbe de remplissage
barème
courbe représentant le volume d'eau stocké en fonction du niveau de l'eau (3.64)
3.70
station hydrométrique
site choisi dans un cours d'eau (3.26), une rivière (3.27) ou un lac pour réaliser des mesurages
systématiques de niveau de l'eau (3.64), de vitesse (3.113) ou de débit (3.5), ou toute combinaison de ces
trois paramètres
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ISO 772:2022(F)
3.71
station hydrométrique à dénivelée
station à double échelle
station hydrométrique (3.70) où deux sondes (3.40) définissent un bief (3.34) pour mesurer la pente de
la ligne d'eau, cette mesure constituant un paramètre essentiel pour établir une relation hauteur-débit
(3.66)
3.72
contrôle hydraulique
dans un chenal à surface libre (3.19) naturel ou artificiel, propriétés physiques d'une section en travers
ou d'un bief (3.34) qui déterminent la relation entre la hauteur et le débit (3.5) à un point du chenal à
surface libre
3.73
courbe de tarage
relation entre le débit (3.5) et d'autres variables, ou les relevés et calculs nécessaires pour l'établissement
de cette relation
3.74
tarage avec une unité de chute
relation entre hauteur et débit (3.5) lorsque la dénivelée (3.48) est égale à un
3.75
remous d'exhaussement
élévation du niveau de l'eau (3.64) immédiatement en amont d'un obstacle et causé par celui-ci
3.76
courbe de remous
dans un chenal à surface libre (3.19), profil de la surface de l'eau entre le point où la surface est surélevée
par un obstacle ou une confluence et le point en amont où l'écoulement (3.3) a une profondeur (3.78)
normale
Note 1 à l'article: Ce terme est également utilisé pour décrire tous les profils de surface de l'eau qui ne sont pas
uniformes sur une certaine distance en amont ou en aval. Cet usage est cependant déconseillé.
3.77
courbe de descente
profil de la surface de l'eau dans lequel la pente de la ligne d'eau (S ) (3.47) est plus importante que la
w
pente du lit (S ) (3.44)
o
Note 1 à l'article: Entre le point où la pente du fond monte ou le niveau du lit descend brutalement et le point où la
profondeur (3.78) est normale, le profil du chenal à surface libre (3.19) est convexe vers le haut en direction amont
et concave vers le haut en direction aval.
3.78
profondeur
D
dimension linéaire mesurée à la verticale depuis la surface de l'eau jusqu'au lit
3.79
hauteur maximale
hauteur instantanée maximale pendant une période donnée
3.80
frottement
traînée
résistance due au cisaillement aux parois s'opposant à l'écoulement (3.3) d'un liquide
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ISO 772:2022(F)
3.81
débitance
K
capacité de transport d'un chenal (3.18)
Note 1 à l'article: Le terme «facteur de transport» est également utilisé dans la formule:
−12/
KQ= S
où
K est le facteur de transport;
Q est le débit (3.5) total;
S est le gradient de charge (3.62).
3.82
ressaut hydraulique
passage soudain d'un écoulement torrentiel (3.13) à un écoulement fluvial (3.12)
Note 1 à l'article: Immédiatement en amont du ressaut hydraulique, la vitesse (3.113) et la profondeur (3.78) sont
respectivement supérieure et inférieure aux valeurs critiques. En aval du ressaut, la vitesse et la profondeur sont
respectivement inférieure et supérieure aux valeurs critiques.
3.83
profondeur hydraulique moyenne
profondeur moyenne
D
m
dans un chenal à surface libre (3.19), division de la surface d'une section en travers par la largeur au
miroir
3.84
rayon hydraulique
r
h
dans un chenal à surface libre (3.19), division de la surface d'une section en travers par la longueur du
périmètre mouillé (3.50) de cette section en travers
3.85
zéro de la sonde (niveau de référence)
hauteur du zéro de la sonde (3.40) utilisée pour déterminer le niveau de la surface de l'eau
Note 1 à l'article: Le zéro de l'échelle est associé à un repère de nivellement (3.86).
3.86
repère de nivellement
marque permanente dont il convient d'associer la hauteur, dans la mesure du possible, à un plan de
référence national
3.87
puits de tranquillisation
tube de tranquillisation
chambre ouverte reliée au cours d'eau (3.26) de manière à permettre le mesurage du niveau de l'eau
(3.64) relativement calme
9
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---------------------- Page: 14 ----------------------
ISO 772:2022(F)
3.88
coefficient de frottement
coefficient caractérisant la rugosité de la section en travers de chenal et qui est pris en compte pour le
calcul de la résistance à l'écoulement (3.3) ou le gradient de charge (3.62)
Note 1 à l'article: Les types communs sont le nombre de Manning/le coefficient de Strickler, n, le coefficient de
Chézy, C, ou une hauteur de rugosité d'élément, k.
3.89
nombre de Froude
Fr
vitesse moyenne (3.56) divisée par la racine carrée du produit de la profondeur hydraulique moyenne
(3.83) et de l'accélération de la pesanteur
v
Fr =
12/
()gD
m
où
v
est la vitesse moyenne du liquide;
g est l'accélération de la pesanteur;
D est la profondeur hydraulique moyenne de la section en travers.
m
Note 1 à l'article: Le nombre de Froude est un nombre sans dimension.
3.90
nombre de Reynolds
Re
rapport entre les forces d'inertie et les forces de viscosité (11.68)
Note 1 à l'article: Pour les chenaux à surface libre (3.19):
vr
h
Re=
η
où
v
est la vitesse moyenne (3.56) du liquide;
r est le rayon hydraulique (3.84) de la section en travers;
h
η est la viscosité cinématique (11.69) du liquide.
Note 2 à l'article: Le nombre de Reynolds est un nombre sans dimension.
3.91
écoulement à surface libre
écoulement (3.3) dans une conduite fermée ou ouverte soumise à la pesanteur et ayant une surface libre
Note 1 à l'article: Lorsque l'écoulement est supérieur à la capacité de la surface libre de la conduite, l'écoulement
se met en charge et la surface libre disparaît. Les mises en charge de courte durée n'affectent normalement pas le
caractère général d'écoulement à surface libre dans les conduites fermées.
3.92
cycle hydrologique
mouvement constant de l'eau dans tous les états de sa forme, au-dessus, sur et sous la surface terrestre
3.93
hydrogéologie
étude des eaux souterraines dans leur contexte géologique
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ISO 772:2022(F)
3.94
capacité utile
volume d'un réservoir qui peut être exploité pour satisfaire les différents usages à l'aval.
3.95
capacité totale
volume d'un réservoir entre le niveau le plus bas du lit et le niveau de l'eau (3.64) maximal
3.96
stockage des crues
volume d'eau temporairement situé au-dessus du niveau de l'eau (3.64) maximal d'un réservoir lors
d'une inondation
Note 1 à l'article: Le surremplissage n'est pas conservé dans le réservoir: il est déversé par un évacuateur jusqu'à
ce que le niveau d'eau revienne au niveau maximal normal.
3.97
onde
onde stationnaire
vague incurvée de forme symétrique, présente à la surface de l'eau et sur le lit du chenal (3.43),
pratiquement stationnaire
Note 1 à l'article: Lorsque des ondes stationnaires se forment, la surface de l'eau et les surfaces du lit sont
pratiquement parallèles et en phase.
3.98
affluent
cours d'eau (3.26) souterrain ou de surface qui alimente en eau, de manière continue ou discontinue, un
autre cours d'eau
3.99
delta fluvial
bief (3.34) d'une rivière (3.27) qui se rapproche d'une masse d'eau plus calme, avec une pente du lit (S )
o
(3.44) et une pente de la ligne d'eau (S ) (3.47) très progressives, et qui, à faible vitesse (3.113), dépose
w
ses sédiments et se divise en plusie
...
FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 772
PROJET
FINAL
NORME
INTERNATIONALE
ISO/TC 113
Hydrometry — Vocabulary and
Secretariat/
Secrétariat: BIS
symbols
Voting begins on/
Début de vote:
Hydrométrie — Vocabulaire et
2021-11-09
symboles
Voting terminates on/
Vote clos le:
Hydrometrie — Begriffe und Symbole
2022-01-04
RECIPIENTS OF THIS DRAFT ARE INVITED TO
SUBMIT, WITH THEIR COMMENTS, NOTIFICATION
OF ANY RELEVANT PATENT RIGHTS OF WHICH
THEY ARE AWARE AND TO PROVIDE SUPPOR TING
DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN
DARDS TO WHICH REFERENCE MAY BE MADE IN
NATIONAL REGULATIONS.
ISO/CEN PARALLEL PROCESSING
LES DESTINATAIRES DU PRÉSENT PROJET SONT
INVITÉS À PRÉSENTER, AVEC LEURS OBSER
VATIONS, NOTIFICATION DES DROITS DE PRO
PRIÉTÉ DONT ILS AURAIENT ÉVENTUELLEMENT
CONNAISSANCE ET À FOURNIR UNE DOCUMEN
TATION EXPLICATIVE.
OUTRE LE FAIT D’ÊTRE EXAMINÉS POUR
ÉTABLIR S’ILS SONT ACCEPTABLES À DES FINS
INDUSTRIELLES, TECHNOLOGIQUES ET COM
Reference number
MERCIALES, AINSI QUE DU POINT DE VUE
Numéro de référence
DES UTILISATEURS, LES PROJETS DE NORMES
INTERNATIONALES DOIVENT PARFOIS ÊTRE
ISO/FDIS 772:2021(E/F)
CONSIDÉRÉS DU POINT DE VUE DE LEUR POSSI
BILITÉ DE DEVENIR DES NORMES POUVANT
SERVIR DE RÉFÉRENCE DANS LA RÉGLEMENTA
TION NATIONALE. © ISO 2021
---------------------- Page: 1 ----------------------
ISO/FDIS 772:2021(E/F)
COPYRIGHT PROTECTED DOCUMENT
DOCUMENT PROTÉGÉ PAR COPYRIGHT
© ISO 2021
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
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ii
© ISO 2021 – All rights reserved/ Tous droits réservés
---------------------- Page: 2 ----------------------
FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 772
ISO/TC 113
Hydrometry — Vocabulary and
Secretariat: BIS
symbols
Voting begins on:
2021-11-09
Hydrometrie — Begriffe und Symbole
Voting terminates on:
Hydrométrie — Vocabulaire et symboles
2022-01-04
ISO/CEN PARALLEL PROCESSING
RECIPIENTS OF THIS DRAFT ARE INVITED TO
SUBMIT, WITH THEIR COMMENTS, NOTIFICATION
OF ANY RELEVANT PATENT RIGHTS OF WHICH
THEY ARE AWARE AND TO PROVIDE SUPPOR TING
DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
Reference number
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
ISO/FDIS 772:2021(E)
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN-
DARDS TO WHICH REFERENCE MAY BE MADE IN
NATIONAL REGULATIONS. © ISO 2021
---------------------- Page: 3 ----------------------
ISO/FDIS 772:2021(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2021
All rights reserved. Unless otherwise specified, or required in the context of its implementation, 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
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
© ISO 2021 – All rights reserved
---------------------- Page: 4 ----------------------
ISO/FDIS 772:2021(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Terms related to velocity-area methods .13
5 Terms related to flow measurement structures .17
6 Terms related to dilution method .30
7 Terms related to instruments and equipment .32
8 Terms related to sediment transport .38
9 Terms related to precipitation . 44
10 Terms related to snow .45
11 Terms related to groundwater .51
12 Terms related to uncertainties in hydrometric determinations .61
Annex A (informative) Symbols used in hydrometry .70
Bibliography .73
Index .74
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---------------------- Page: 5 ----------------------
ISO/FDIS 772:2021(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 of 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
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 113, Hydrometry, in collaboration with
the European Committee for Standardization (CEN) Technical Committee CEN/TC 318, Hydrometry, in
accordance with the Agreement on technical cooperation between ISO and CEN (Vienna Agreement).
This sixth edition cancels and replaces the fifth edition (ISO 772:2011) which has been technically
revised. The main changes compared with the previous edition are as follows:
— terms related to precipitation have been added in a new Clause 9;
— additional terms have been added in Clause 10;
— Figures 1, 3, 4, 5, 6, 9, 11 and 12 have been modified and updated.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
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ISO/FDIS 772:2021(E)
Introduction
In the preparation of this document, the following principles were adopted wherever possible:
a) to standardize suitable terms and symbols without perpetuating unsuitable ones;
b) to discard any term or symbol with differing meanings in different countries, or for different
people, or for the same person at different times, and to replace that term or symbol by one which
has an unequivocal meaning;
c) to exclude terms which are self-evident.
Terms in existing International Standards have been included as much as possible; however, these
terms can be subject to future amendments.
NOTE Similar or identical terms can have separate definitions under the different categories.
It is recognized that it is not possible to produce a complete set of definitions which will be universally
acceptable, but it is hoped that the definitions provided and the symbols used will find widespread
acceptance and that their use will lead to a better understanding of hydrometric practices.
The terminology entries are presented in systematic order, grouped into sections according to
particular methods of determination or in relation to particular subjects. Annex A lists the symbols
used in this document.
The structure of each entry is in accordance with the ISO 10241 series. Country codes are in accordance
with ISO 3166-1.
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FINAL DRAFT INTERNATIONAL STANDARD ISO/FDIS 772:2021(E)
Hydrometry — Vocabulary and symbols
1 Scope
This document defines terms and symbols used in standards in the field of hydrometry.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
hydrometry
science and practice of measuring the components of the hydrological cycle (3.92), including rainfall
(9.10), water level (3.64), flow and sediment transport (8.2) of surface waters, and groundwater (11.1)
characteristics
3.2
hydrology
science that deals with the waters above and below the land surfaces of the Earth, their occurrence,
circulation and distribution, their properties and their reaction with the environment
3.3
flow
water flowing on or below the land surface under gravitational influence
3.4
runoff
volume of water flowing through a given channel cross-section related to a given drainage basin (3.103)
in a defined period of time
3.5
discharge
Q
volume of water flowing through a given channel cross-section in unit time
3.6
current
directed movement of water
3.7
steady flow
flow (3.3) in which parameters [such as velocity (3.113), pressure, density and temperature] are
constant with respect to time
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ISO/FDIS 772:2021(E)
3.8
unsteady flow
flow (3.3) in which one or more parameters [such as velocity (3.113), pressure, density and temperature]
change with respect to time
3.9
uniform flow
flow (3.3) in which the magnitude and direction of flow at a given moment are constant with respect to
distance
Note 1 to entry: For uniform flow, the velocity vector is constant along every stream line. Uniform flow is possible
only in an open channel (3.19) of constant slope and cross-section.
3.10
non-uniform flow
flow (3.3) in which the magnitude and direction of flow at a given moment are changing with respect to
distance
3.11
critical flow
flow (3.3) in an open channel (3.19) in which the specific energy is a minimum for
a given discharge (3.5)
Note 1 to entry: Under this condition, the Froude number (3.89) is equal to unity and small surface disturbances
cannot travel upstream.
3.12
subcritical flow
flow (3.3) in an open channel (3.19) at less than critical velocity (3.17), which has a Froude number (3.89)
of less than unity and in which small surface disturbances can travel upstream
3.13
supercritical flow
flow (3.3) in an open channel (3.19) at more than critical velocity (3.17), which has a Froude number
(3.89) of greater than unity and in which small surface disturbances cannot travel upstream
3.14
transverse flow
lateral flow
flow (3.3) horizontally perpendicular to the main direction of flow
Note 1 to entry: Transverse (lateral) flow is frequently associated with secondary flow.
Note 2 to entry: Transverse (lateral) flow in open channels (3.19) with a curved plan form causes superelevation
of the water surface at the outside of the bend.
3.15
stratification
state of a water body that consists of two or more layers arranged according to their density, the lightest
layer being on top and the heaviest at the bottom
3.16
critical depth
depth (3.78) of flow (3.3) at which critical flow (3.11) occurs
3.17
critical velocity
velocity (3.113) of flow (3.3) that has minimum specific energy for a given discharge (3.5) or has unit
Froude number (3.89)
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ISO/FDIS 772:2021(E)
3.18
channel
course of a river (3.27), stream (3.26) or other watercourse
3.19
open channel
longitudinal boundary surface consisting of the bed and banks or sides within which water flows with
a free surface
3.20
canal
man-made channel (3.18), usually of regular cross-sectional shape
3.21
stable channel
open channel (3.19) in which the bed and the sides remain essentially stable over a substantial period
of time in the reach (3.34) under consideration, and in which the scour and deposition (10.5) during the
rising and falling stages are negligible
3.22
unstable channel
open channel (3.19) that changes frequently and significantly in its plan form and/or cross-sectional
form for the reach (3.34) under consideration
3.23
tidal channel
open channel (3.19) in which the flow (3.3) is subject to tidal influence
3.24
tide
periodic rise and fall of water due principally to the gravitational attraction of the sun and the moon
3.25
estuary
lower tidal reaches (3.34) of a river (3.27) that is freely connected with the sea which receives fresh
water supplies from upland drainage areas
3.26
stream
water course, water flowing in an open channel (3.19)
3.27
river
large natural water course
3.28
large river
major river
large natural water course that generally flows into the sea
3.29
creek
brook
small natural water course
3.30
torrent
small natural water course that is characterized by steep slopes and significant rapid changes in
discharge (3.5) and that can transport considerable volumes of solid material
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ISO/FDIS 772:2021(E)
3.31
alluvial river
river (3.27) which flows through alluvium formed from its own deposits
3.32
incised river
river (3.27) which has formed its channel (3.18) by a process of erosion
3.33
braided river
river (3.27) characterized by a wide and shallow open channel (3.19) in which flow (3.3) passes through
a number of small interlaced channels (3.18)
3.34
reach
length of open channel (3.19) between two defined cross-sections
3.35
meandering channel
water course formed by natural flow processes and movement of sediments following generally an
alternating regular sinuous path
3.36
thalweg
line joining the lowest points of successive cross-sections of a water course
3.37
unit discharge
discharge per unit width
q
u
discharge (3.5) through a unit width of a given vertical section
3.38
yield specific discharge
q
discharge (3.5) per unit area of catchment or aquifer (11.15)
3.39
stream gauging
discharge measurement
flow measurement
stream flow measurement
river gauging
all of the operations necessary for the measurement of discharge (3.5) of a stream (3.26)
3.40
gauge
device installed at a gauging station for measuring the level of the surface of water relative to a datum
3.41
left bank
bank to the left of an observer looking downstream
3.42
right bank
bank to the right of an observer looking downstream
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ISO/FDIS 772:2021(E)
3.43
channel bed
invert
stream bed
stream bottom
channel bottom
lower part of the stream channel situated between the banks
3.44
bed slope
bottom slope
S
o
difference in elevation of the bed per unit horizontal distance, measured in the direction of flow (3.3)
Note 1 to entry: The slope is usually mathematically negative in the direction of flow.
3.45
bed profile
shape of the bed in a longitudinal vertical plane
3.46
side slope
difference in elevation between the bottom and top of a bank per unit horizontal distance
3.47
surface slope
S
w
inclination of the surface of the stream (3.26) in a reach (3.34) measured in the direction of flow (3.3)
3.48
fall
difference in elevation of the water surface between the extremities of a defined reach (3.34) at a given
instant of time
EXAMPLE As recorded at a slope station (3.71).
3.49
top width
width of the open channel (3.19) measured across the stream (3.26) at the water surface normal to the
direction of flow (3.3)
3.50
wetted perimeter
P
w
contact length between a stream (3.26) of flowing water and its containing open channel (3.19),
measured in a direction normal to the flow (3.3)
3.51
wetted cross-section
section normal to the mean direction of flow (3.3) bounded by the free surface and wetted
perimeter (3.50)
3.52
gauging section
measuring section
section at which discharge (3.5) measurements are taken
3.53
high water mark
flood mark
mark left on a structure or any other object indicating exceptional stages of flood
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---------------------- Page: 12 ----------------------
ISO/FDIS 772:2021(E)
3.54
debris line
trash line
traces of any kind left on the banks or obstacles or flood plain by a flood
Note 1 to entry: The debris line may be used to determine the highest level attained by the water surface during
a flood.
3.55
surface velocity
flow (3.3) velocity (3.113) at a given point on the surface
3.56
mean velocity
flow (3.3) velocity (3.113) at a given cross-section of a stream (3.26), obtained by
dividing the discharge (3.5) by the cross-sectional area
3.57
slush ice
mass of loosely packed anchor ice (3.105) that is released from the bottom, or frazil ice (3.104) that
floats or accumulates under surface ice (3.107)
3.58
velocity head
theoretical vertical height to which liquid particles can be elevated by kinetic energy
Note 1 to entry: It is expressed as the square of the velocity (3.113) divided by twice the acceleration due to
gravity.
3.59
gauged head
elevation of the free surface above the horizontal datum of a section
3.60
total head
energy head
H
sum of the elevation of the free surface above the horizontal datum of a section plus the velocity head
(3.58) based on the mean velocity (3.56) at that section
Note 1 to entry: The total head, H, is given by the following formula:
2
v
Hh=+α
2g
where
h is the gauged head of water level (3.64);
v
is the mean velocity of the water;
α is the Coriolis coefficient;
g is the acceleration due to gravity.
Note 2 to entry: The Coriolis coefficient (α ≥ 1), also known as “energy coefficient” or “energy correction factor”,
takes into account the non-uniform velocity distribution. In many cases, α is assumed to equal unity.
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ISO/FDIS 772:2021(E)
3.61
total head line
energy head line
plot of the total head (3.60) in the direction of flow (3.3)
3.62
energy gradient
difference in total head (3.60) per unit horizontal distance, measured in the direction of flow (3.3)
3.63
energy loss
head loss
difference in total head (3.60) between two cross-sections in the direction of flow (3.3)
3.64
water level
stage
gauge height
elevation of the free surface of a stream (3.26), lake or reservoir relative to a specified datum
3.65
reference gauge
stage gauge that discharge (3.5) is normally linked to
3.66
stage-discharge relation
rating curve
rating table
equation, curve or table that expresses the relation between the stage and the discharge (3.5) in an open
channel (3.19) at a given cross-section
3.67
hydrograph
graphical representation of changes of hydrometric parameters with respect to
time
Note 1 to entry: Typically, stage and discharge hydrographs are used for open channel flows.
3.68
cumulative volume curve
curve in which the cumulative value of a hydrometric parameter is plotted against time
Note 1 to entry: Integral of the hydrograph (3.67), such as cumulative discharge curve.
3.69
storage curve
table
curve depicting the volume of stored water plotted against water level (3.64)
3.70
gauging station
site on a stream (3.26), river (3.27) or lake at which systematic measurements of water level (3.64),
velocity (3.113) or discharge (3.5) or any combination of the three are made
3.71
slope station
twin-gauge station
gauging station (3.70) at which two water-level gauges (3.40) define a reach (3.34) for measurement of
water-surface slope as an essential parameter for establishing a stage-discharge relation (3.66)
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ISO/FDIS 772:2021(E)
3.72
control
physical properties of a cross-section or a reach (3.34) of an open channel (3.19), either natural or
artificial, that govern the relation between stage and discharge (3.5) at a location in the open channel
3.73
rating
relation between discharge (3.5) and other variables, or the taking of observations and making of
calculations needed to establish the relation
3.74
unit-fall rating
relation between stage and discharge (3.5) when the fall (3.48) is equal to one
3.75
afflux
rise in water level (3.64) immediately upstream of, and due to, an obstruction
3.76
backwater curve
profile of water surface, along an open channel (3.19), from the raised surface at an obstruction or
confluence to the point upstream at which the flow (3.3) is at normal depth (3.78)
Note 1 to entry: The term is also used to denote all liquid surface profiles that are non-uniform with respect to
distance upstream or downstream. However, this usage is deprecated.
3.77
drawdown curve
profile of the liquid surface when its surface slope (S ) (3.47) exceeds the bed slope (S ) (3.44)
w o
Note 1 to entry: From the point at which the bed slope increases, or bed level drops abruptly, to the point at which
normal depth (3.78) occurs, the profile along an open channel (3.19) is convex upwards in an upstream direction
and concave upwards in a downstream direction.
3.78
depth
D
linear dimension measured in the vertical direction from the water surface to the bed
3.79
peak stage
maximum instantaneous stage during a given period
3.80
friction
drag
boundary shear resistance that opposes the flow (3.3) of a liquid
3.81
conveyance
K
carrying capacity of a channel (3.18)
Note 1 to entry: The term “conveyance factor” is also used, e.g. in the formula:
−12/
KQ= S
where
K is the conveyance factor;
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ISO/FDIS 772:2021(E)
Q is the total discharge (3.5);
S is the energy gradient (3.62).
3.82
hydraulic jump
sudden transition from supercritical flow (3.13) to subcritical flow (3.12)
Note 1 to entry: Immediately upstream of the hydraulic jump, the velocity (3.113) and the depth (3.78) are
respectively greater and less than their critical values. Beyond the jump, the velocity and the depth are
respectively less and greater than their critical values.
3.83
hydraulic mean depth
mean depth
D
m
area of the cross-section of water flowing in an open channel (3.19) divided by the width of the open
channel at the water surface
3.84
hydraulic radius
r
h
wetted cross-sectional area of water flowing in an open channel (3.19) divided by the length of the
wetted perimeter (3.50) at that cross-section
3.85
gauge datum
elevation of the zero of the gauge (3.40) to which the level of the liquid surface is referred
Note 1 to entry: The gauge datum is related to a benchmark (3.86).
3.86
benchmark
permanent mark, the elevation of which should be related, where practicable, to a national datum
3.87
gauge/float well
stilling well/tube
chamber open to the atmosphere and connected with the stream (3.26) in such a way as to permit the
measurement of the water level (3.64) in relatively still water
3.88
roughness coefficient
coefficient that characterizes the roughness of the channel cross-section and which is taken into
account when computing the resistance to flow (3.3) or the energy gradient (3.62)
Note 1 to entry: The common types are the Manning’s/Strickler n, Chezy C or an element roughness height, k.
3.89
Froude number
Fr
mean velocity (3.56) divided by the square root of the product of the hydraulic mean depth (3.83) and the
acceleration due to gravity
v
Fr =
12/
gD
()
m
where
v
is the mean velocity of the liquid;
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ISO/FDIS 772:2021(E)
g is the acceleration due to gravity;
D is the hydraulic mean depth of the cross-section.
m
Note 1 to entry: The Froude number is dimensionless.
3.90
Reynolds number
Re
ratio of the forces of inertia to forces of viscosity (11.68)
Note 1 to entry: For open channels (3.19):
vr
h
Re=
η
where
v
is the mean velocity (3.56) of the liquid;
r is the hydraulic radius (3.84) of the cross-section;
h
η is the kinematic viscosity (11.69) of the liquid.
Note 2 to entry: The Reynolds number is dimensionless.
3.91
free surface flow
flow (3.3) within a closed or open conduit, under gravity and having a free surface
Note 1 to entry: Where the flow exceeds the free surface capacity of the conduit, the flow will become surcharged
with the consequent disappearance of the free surface. Instances of surcharging of short duration do not normally
affect the overall concept of free surface flow in closed conduits.
3.92
hydrological cycle
constant movement of water in all states of its form, above, on and below the Earth’s surface
3.93
hydrogeology
study of subsurface water in its geological context
3.94
live storage
reservoir storage which can be drawn off for users downstream
3.95
total storage
reservoir storage between the lowest bed level and the top water level (3.64)
3.96
flood storage
volume of water temporarily held above the top water level (3.64) of a reservoir during a flood event
Note 1 to entry: Flood storage is not retained in the reservoir but is discharged through an overflow until the
normal top water level is reached.
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ISO/FDIS 772:2021(E)
3.97
standing wave
stationary wave
curved symmetrically shaped wave on the water surface and on the channel bed (3.43) that is virtually
stat
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