ISO 772:1996/Amd 2:2004
(Amendment)Hydrometric determinations — Vocabulary and symbols — Amendment 2
Hydrometric determinations — Vocabulary and symbols — Amendment 2
Déterminations hydrométriques — Vocabulaire et symboles — Amendement 2
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INTERNATIONAL ISO
STANDARD 772
Fourth edition
1996-04-15
AMENDMENT 2
2004-05-01
Hydrometric determinations —
Vocabulary and symbols —
AMENDMENT 2
Déterminations hydrométriques — Vocabulaire et symboles —
AMENDEMENT 2
Reference number
ISO 772:1996/Amd.2:2004(E)
©
ISO 2004
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ISO 772:1996/Amd.2:2004(E)
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ISO 772:1996/Amd.2:2004(E)
Contents Page
Foreword. iv
1 General terms. 1
2 Velocity area-methods. 2
6 Sediment transport. 14
8 Groundwater. 15
Annex C (informative) Classification of flow measurement structures . 17
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ISO 772:1996/Amd.2:2004(E)
Foreword
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(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
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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.
Amendment 2 to ISO 772:1996 was prepared by Technical Committee ISO/TC 113, Hydrometric
determinations, Subcommittee SC 3, Terminology and symbols.
This amendment consists of the complete revision of Clause 3 “Notches, weirs and flumes” comprising the
modification of several definitions and the inclusion of some new terms and definitions. In addition, the terms
and definitions have been arranged in a more logical sequence. New terms are also added to Clauses 6 and 8
and some minor changes are made to the definitions of a few terms in Clauses 1, 2, 6 and 8.
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ISO 772:1996/Amd.2:2004(E)
Hydrometric determinations — Vocabulary and symbols —
AMENDMENT 2
Contents
Page ii, Contents
Replace the existing title of Clause 3 with “Flow measurement structures”.
1 General terms
Page 2, Term 1.6
After the definition for critical flow, add the following Note 1 and renumber the Note as Note 2:
“NOTE 1 This is the generic definition of critical flow. See critical flow (3.26) for the specific definition when used in
reference to the field of flow measurement structures.”
Pages 6, 7 and 9, Clause 1
Replace the definitions for Terms 1.35, 1.41, 1.42, 1.61 and 1.62 as follows:
1.35
transition
crossover
inflection reach between two meander loops in which the main flow crosses from one side of the channel to
the other
NOTE The depth of flow in a transition is usually reduced from normal depth and is more uniform than in the curved
reach.
1.41
stream gauging
all of the operations necessary for the measurement of discharge of a stream
1.42
discharge measurement
process of measuring the discharge of liquid in an open channel
1.61
converging reach
reach in which the cross-sectional area gradually decreases in the direction of flow
1.62
expanding reach
reach in which the cross-sectional area gradually increases in the direction of flow
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ISO 772:1996/Amd.2:2004(E)
2 Velocity area-methods
Page 26, Clause 2
Replace the definition for Term 2.21 as follows:
2.21
moving boat method
method of measuring discharge from a boat by traversing the stream along the measuring section while
continuously measuring velocity, depth, distance travelled and angle of current velocity
Page 32, Clause 3
Delete Clause 3, entitled Notches, weirs and flumes, and replace the entire Clause 3 by the following new text
and figures.
3 Flow measurement structures
NOTE A classification of flow measurement structures is given in Annex C.
3.1
flow measurement structure
hydraulic structure (e.g. weir, flume or gate) installed in an open channel where in most cases the discharge
can be derived from the measured upstream water level
NOTE The structure is an artificial reduction of the cross-sectional area in the channel, where part of the upstream
total head is converted into kinetic energy used to obtain critical flow.
3.2
weir
overflow structure that may be used for controlling upstream surface level or for measuring discharge or both.
See Figure 6.
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ISO 772:1996/Amd.2:2004(E)
Key
1 weir crest
2 weir block
3 hydraulic jump
4 total head line
5 direction of flow
6 control block
7 stilling basin
Figure 6 — Weir
3.3
height of weir
apex height
height from the upstream bed to the lowest point of the crest
3.4
head over the weir
elevation of the water surface above the lowest point of the crest, measured at a point sufficiently upstream to
be unaffected by the drawdown of the weir
NOTE The distance upstream of the point of measurement depends on the type of weir used.
3.5
upstream total head
elevation of the total head relative to the flume invert level or the weir crest level, measured upstream of the
structure
3.6
downstream total head
elevation of the total head relative to the flume invert level or weir crest level, measured downstream of the
structure
3.7
weir abutment
abutment
wing wall
wall at the side of a channel, generally parallel to the longitudinal axis of the weir, against which the weir
terminates
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ISO 772:1996/Amd.2:2004(E)
3.8
weir block
weir body
part of a weir lying between the abutments and over which the water flows
See Figure 6.
3.9
full-width weir
suppressed weir
weir whose crest fills the width of the channel in which it is placed, thus eliminating side contraction of the
stream
3.10
divide wall
wall running in the direction of flow and separating the individual sections of a compound structure
3.11
glacis
sloping downstream face of a weir block and continuation of the crest
3.12
weir slope
ratio of the horizontal to the vertical components of the upstream face, the downstream face or the cross-slope
of a weir
3.13
approach channel
reach of the channel upstream of the gauging structure in which suitable flow conditions have to be
established to ensure correct gauging
3.14
straightening vane
guide vane
baffle
device placed in the approach channel to improve flow conditions
cf. baffle (3.15)
3.15
baffle
wall or block placed downstream of a structure to dissipate energy or to cause improved velocity distribution
cf. straightening vane (3.14)
3.16
control block
baffle pier
energy-breaking block
block constructed in a channel or stilling basin to increase turbulence and thereby dissipate the energy of
water flowing at high velocity
NOTE See Figure 6 for the application of a control block to a weir construction.
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ISO 772:1996/Amd.2:2004(E)
3.17
stilling basin
basin constructed downstream of a structure to dissipate the energy of fast-flowing water and to protect the
bed and banks from erosion
See Figure 6.
3.18
separation pocket
〈at a corner or at a point of large curvature〉 region of recirculating flow at a structure caused by separation of
the main flow from the structure
cf. separation pocket (3.19)
NOTE This phenomenon can occur at broad-crested weirs which do not have rounded upstream or downstream
corners or which do not have a crest of sufficient length in the direction of flow.
3.19
separation pocket
〈triangular-profile weir〉 near-cylindrical volume of slowly moving water immediately downstream of the crest of
the structure
cf. separation pocket (3.18)
3.20
throat
that part of a flume at which critical flow occurs; usually where the wetted cross-sectional area is at a minimum
NOTE The throat may be rectangular, trapezoidal, U-shaped or of another specially designed shape.
3.21
modular flow
free flow
flow over or through a structure when the upstream level is independent of the downstream level for a given
discharge
3.22
discharge coefficient
coefficient in the discharge equation depending on the type and shape of the measuring structure, and the
head over the weir
3.23
modular limit
submergence ratio for flow over a weir at which the upstream level just begins to be affected by the
downstream level for a given discharge
3.24
drowned flow
nonmodular flow
submerged flow
flow, over or through a structure, when it is affected by changes in the level downstream
3.25
submergence ratio
ratio of the downstream total head to the upstream total head at a structure
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ISO 772:1996/Amd.2:2004(E)
3.26
critical flow
flow conditions for which the total energy head above the invert reaches a minimum at a given discharge and
for given channel dimensions
NOTE 1 This is the specific definition of critical flow when used in reference to the field of flow measurement structures.
See critical flow (1.6) for the generic definition.
NOTE 2 The water depth for these flow conditions is called critical depth and occurs during the transition from
subcritical to supercritical flow.
NOTE 3 Critical flow in overflow structures and undershot gates occurs at the critical section, also called the control
section. Critical flow in a measuring structure is a condition for modular flow.
3.27
double gauging
measurement of two simultaneous but independent heads to facilitate measurement in the drowned flow
range
NOTE The usual head measurement locations lie between 3H upstream of the weir and 3H downstream of the
max max
weir, where H is the maximum total head over the weir crest.
max
3.28
broad-crested weir
weir with a horizontal longitudinal crest which has a length equal to or greater than half the maximum
operating head
See Figure 7.
NOTE The streamlines above the crest are approximately straight and parallel at least over a short distance.
3.28.1
rectangular broad-crested weir
broad-crested weir (3.28) of which the crest is a horizontal rectangular plane surface and of which the
upstream face forms a sharp right-angled corner at its intersection with the plane of the crest
See Figure 7.
3.28.2
round-nosed broad-crested weir
broad-crested weir (3.28) of which the crest is a horizontal rectangular plane surface and of which the
upstream corner is rounded to avoid flow separation
See Figure 7.
3.28.3
trapezoidal broad-crested weir
broad-crested weir (3.28) of which the crest is an horizontal plane surface and of which the upstream face
and the downstream face are sloping
See Figure 7.
3.28.4
V-shaped broad-crested weir
broad-crested weir (3.28) with a triangular cross-sectional profile, rounded off at the upstream corner
See Figure 7.
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ISO 772:1996/Amd.2:2004(E)
Longitudinal profile C
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