ISO 1100-1:1996

Measurement of liquid flow in open channels - Part 1: Establishment and operation of a gauging station

Deals with the establishment and operation of a gauging station for the measurement of stage oder discharge, or both, of a lake, reservoir, river or artificial open channel. Replaces the first edition.

Mesurage de débit des liquides dans les canaux découverts — Partie 1: Établissement et exploitation d'une station hydrométrique

General Information

• Status: Withdrawn
• Publication Date: 07-Feb-1996
• Withdrawal Date: 07-Feb-1996
• ICS: 17.120.20 - Flow in open channels
• Technical Committee: ISO/TC 113/SC 1 - Velocity area methods
• Drafting Committee: ISO/TC 113/SC 1 - Velocity area methods
• Current Stage: 9599 - Withdrawal of International Standard
• Start Date: 06-Dec-2013
• Completion Date: 13-Dec-2025

Relations

• Consolidated By: ISO 3457:2003 - Earth-moving machinery - Guards - Definitions and requirements
• Effective Date: 06-Jun-2022
• Revised: ISO 18365:2013 - Hydrometry - Selection, establishment and operation of a gauging station
• Effective Date: 16-Jun-2012
• Revises: ISO 1100-1:1981 - Liquid flow measurement in open channels - Part 1: Establishment and operation of a gauging station
• Effective Date: 15-Apr-2008

Standards Content (Sample)

INTERNATIONAL IS0
STANDARD 1100-1
Second edition
1996-02-I 5
Measurement of liquid flow in open
channels -
Part 1:
Establishment and operation of a gauging
station
Mesurage de d6bit des liquides dans /es canaux dkouverts -
Partie I: &ablissement et exploitation d’une station hydrom&ique
Reference number
IS0 1100-l :I 996(E)
IS0 1100=1:1996(E)
Foreword
IS0 (the International Organization for Standardization) is a worldwide
federation of national standards bodies (IS0 member bodies). The work
of preparing International Standards is normally carried out through IS0
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. IS0
collaborates closely with the International Electrotechnical Commission
(I EC) on all matters of electrotechnical standardization.
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.
International Standard IS0 1100-I was prepared by Technical Committee
lSO/TC 113, Hydrometric determinations, Subcommittee SC 1, Velocity
area methods.
This second edition cancels and replaces the first edition
which has been technically revised.
(IS0 1100-I :I 981)
IS0 1100 consists of the following parts, under the general title Meas-
urement of liquid flow in open channels:
- Part 7: Establishment and operation of a gauging station
- Part 2: Determination of the stage-discharge relation
Annex A of this part of IS0 1100 is for information only.
0 IS0 1996
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced
or utilized in any form or by any means, electronic or mechanical, including photocopying and
microfilm, without permission in writing from the publisher.
International Organization for Standardization
Case Postale 56 l CH-1211 Geneve 20 l Switzerland
Printed in Switzerland
ii
IS0 1100=1:1996(E)
INTERNATIONAL STANDARD Q ISO
Measurement of liquid flow in open channels -
Part 1: .
aauaina station
Establishment and operation of a
IS0 1000: 1992, SI units and recommendations for the
1 Scope
use of their multiples and of certain other units.
1.1 This part of IS0 1100 deals with the establish-
IS0 1070:1992, Liquid flow measurement in open
ment and operation of a gauging station for the
channels - Slope-area method.
measurement of stage or discharge, or both, of a lake,
reservoir, river or artificial open channel. IS0 1 IOO-2:1982, Liquid flow measurement in open
channels - Part 2: Determination of the stage-
discharge rela Con.
1.2 Requirements are specified for stage and for
stage-discharge stations in natural channels and
IS0 3454:1983, Liquid flow measurement in open
stations with artificial structures, for direct discharge
channels - Direct depth sounding and suspension
measurement and for measurement under ice condi-
equlpmen t.
tions.
IS0 3846:1989, Liquid flow measurement in open
channels by weirs and flumes - Rectangular broad-
2 Normative references
crested weirs.
The following standards contain provisions which,
IS0 3847:1977, Liquid flow measurement in open
through reference in this text, constitute provisions
channels by weirs and flumes - End-depth method
of this part of IS0 II 00. At the time of publication, the
for estimation of flow in rectangular channels with a
editions indicated were valid. All standards are subject
free 0 verfall.
to revision, and parties to agreements based on this
part of IS0 1100 are encouraged to investigate the
IS0 4359:1983, Liquid flow measurement in open
possibility of applying the most recent editions of the
channels - Rectangular, trapezoidal and U-shaped
standards indicated below. Members of IEC and IS0
flumes.
maintain registers of currently valid International
Standards.
IS0 4360:1984, Liquid flow measurement in open
channels by weirs and flumes - Triangular profile
IS0 31 :I992 Quantities and units, all parts.
weirs.
I SO 748:---I), Measurement of liquid flow in open
IS0 4369:1979, Measurement of liquid flow in open
channels - Velocity-area methods.
channels - Moving-boat method.
Measurement of liquid flow in open
I SO 772:-J,
channels - Vocabulary and symbols.
1) To be published. (Revision of IS0 748:1979)
2) To be published. (Revision of IS0 772:1988)

0 IS0
IS0 1100=1:1996(E)
IS0 437311995, Measurement of liquid flow in open
5 Stage-discharge gauging stations
channels - Water--level measuring devices.
(natural channels)
IS0 4375:1979, Measurement of liquid flow in open
channels - Cableway system for stream gauging.
5.1 Principle
IS0 4377:1990, Liquid flow measurement in open
Water levels (stages) of rivers, lakes or reservoirs are
- Flat-V weirs.
channels
used in delineating flood hazard areas, and in the de-
sign of structures in or near rivers, lakes or reservoirs.
IS0 6416:1992, Measurement of liquid flow in open
channels - Measurement of discharge by the ultra-
The stage or water level of a stream or lake is the
sonic (acoustic) method.
height of the water surface above an established da-
tum plane.
IS0 8368: 1985, Liquid flow measurement in open
channels - Guidelines for the selection of flow
Water-level records are obtained by systematic ob-
gauging structures.
servations of a reference gauge, or from a water-level
sensor.
lSO/TR 9123:1986, Liquid flow measurements in
open channels - Stage-fall-discharge relations.
When records of water level in streams are to be
used as a basis for computation of discharge, the re-
IS0 9196: 1992, Liquid flow measurement in open
lation between stage and discharge should be deter-
channels - Flow measurements under ice
mined.
conditions.
In a stable channel with appropriate control of the
IS0 9213:1992, Measurement of total discharge in
downstream water level, a single relation may exist
Electromagnetic method using a
open channels -
between stage and discharge. In this case, the re-
full-channel-width coil.
lation shall be determined from discharge measure-
ments at selected stages throughout the range of
IS0 9555-l :I 994, Measurement of liquid flow in open
stage experienced at the station.
channels - Tracer dilution methods for the measure-
ment of steady flow - Part 1: General.
Discharges can be determined using either velocity-
area methods according to IS0 748, tracer dilution
IS0 9555-2: 1992, Measurement of liquid flow in open
methods according to IS0 9555-1, IS0 9555-2,
channels - Tracer dilution methods for the measure-
IS0 9555-3 or IS0 9555-4, or ultrasonic methods us-
ment of steady flow - Part 2: Radioactive tracers.
ing a temporary installation (see IS0 6416).
IS0 9555-3:1992, Measurement of liquid flow in open
In the case where no single relation exists between
Tracer dilution methods for the measure-
channels -
stage and discharge, a relation may exist between the
Part 3: Chemical tracers.
ment of steady flow -
surface slope or fall, stage and discharge which may
require the establishment of a second stage (slope)
IS0 9555-4: 1992, Measurement of liquid flow in open
gauge. Relations shall then be established on the ba-
channels - Tracer dilution methods for the measure-
sis of these three factors, and discharge shall be de-
ment of steady flow - Part 4: Fluorescent tracers.
termined from measurements of surface slope and
stage (see IS0 1070 or lSO/TR 9123 as appropriate).
3 Definitions
5.2 Main elements of a gauging station
For the purposes of this part of IS0 1100, the defi-
The main elements required for establishing the his-
nitions and symbols given in IS0 772 apply.
torical records of discharge in a stream from water-
level records are as follows:
- choice of control section or reach (see 5.2.1);
4 Units of measurement
- stage-measuring device (see 5.2.2);
The units of measurement used in this part of
- stage-sensing and -recording device (see 5.2.3 and
IS0 1100 are SI units in accordance with the appro-
5.2.5);
priate parts of IS0 31 and IS0 1000.
0 IS0 IS0 11004:1996(E)
section (or reach) (see 5.2.2.1 Vertical and inclined staff gauges
- discharge-measuring
5.2.6).
Vertical and inclined staff gauges shall meet the
For a stage-measuring station, the aim of which is to
functional requirements described in IS0 4373, which
establish stage records only, see 5.2.2 to 5.2.4.
may be briefly summarized as follows.
The graduations of a staff gauge shall be clearly,
a)
5.2.1 Control section (or reach)
accurately and permanently marked directly on a
smooth surface. The numerals shall be distinct
A control section or control reach of a channel is a
and placed so that an ambiguous reading is not
natural or artificial section or reach whose physical
likely.
characteristics are measured and used to determine
the relation between stage (or stage and slope) and
b) The gauges shall be durable and easy to maintain.
discharge.
The material shall have a low coefficient of ex-
A control section is one in which any change in the
pansion, and shall be resistant to alternating wet
downstream stage does not affect the upstream
and dry conditions and to wear or fading of the
in the control section,
stage. Whatever the discharge markings.
recorded. In a control
a critical stage can always be
reach no critical stage can be recorded. A control c) The gauges shall be placed near the bank, in an
section may be natural (e.g. a rock outcrop or sandbar) easily accessible position, so that water level can
or artificial (e.g. a weir, flume or culvert). be read from the shortest possible distance.
The sensitivity of a control section or reach shall be
d) The gauges shall be simple to install and use.
such that any significant change in discharge shall re-
sult in either
e) The gauges shall be placed in a calm area, as
close as possible to, and preferably in the same
- a measurable change in stage (for control
cross-section as, the stage sensor, without how-
sections), or
ever affecting stage at this level. When the am-
plitude of variation of stage can exceed the
- a measurable change in stage at one extremity of
capacity of a staff gauge, other additional ele-
the control reach, and a measurable change in
ments may be installed in the same cross-
surface slope between the two extremities.
sectional area, normal to the direction of flow.
In order to establish a stable stage-discharge relation,
the control section or reach shall be stable, i.e. no
5.2.2.2 Other devices
change shall occur over time in its physical character-
istics.
In some cases, a reference-point gauge with a device
for locating the water level with respect to the refer-
Several control sections may be considered for dis-
ence may be substituted for a vertical or inclined
charge measurement for one gauging station.
gauge.
Under given discharge conditions, the presence of a
Needle gauges may be used when level variation is
downstream weir may create a water level which
small (I m max.) and when the water surface is sta-
submerges an upstream weir used as a control sec-
ble .
tion. This downstream weir may then be considered
as the new control section.
When it is not possible to install vertical or inclined
gauges, wire-weight gauges may be used if a struc-
ture exists permitting their installation over the water.
5.2.2 Stage-measuring devices
The functional requirements and conditions of instal-
Stage-sensing and -measuring devices are the basic
lation of these gauges are specified in IS0 4373.
elements of the equipment for measuring and re-
cording stage. They shall be stable.
5.2.2.3 Gauge-zero elevation (see IS0 4373)
near
A vertical or inclined staff g auge shall be located
the stage sensor, to act as the refere nce gauge.
The establishment of the gauge zero shall be chosen
The water level indicated by the stage sensor should so as to avoid negative readings. To ensure that the
gauge zero remains the same over the duration of the
follow the water level indicated by the reference
station operation, care shall be taken to ensure that it
gauge.
0 IS0
IS0 1100=1:1996(E)
expensive or impractical. The principle of the sensor
is fixed low enough, especially for sites where scour
consists of discharging a small flow of compressed
is severe.
gas into a tube, the free end (orifice) of which has
The zero of the gauge shall be correlated with a na-
been placed in the water and fixed at an elevation
tional datum through a station benchmark. The gauge
below the level to be measured. The sensor at the
zero and the other gauge divisions should be checked
opposite end of the tube detects the pressure of the
annually with respect to this benchmark.
gas, which is proportional to the head of water above
the orifice. Servomanometer and servo beam balance
This procedure allows replacement of the gauge in
devices are some of the mechanisms employed in
case of destruction and maintenance of the same
which pressure is detected, and a strip chart recording
stage-discharge relation provided the control section
or electrical signal is obtained through a servometer.
is not modified. At least two independent station
Pressure transducers of appropriate range and accu-
benchmarks should be established so that the gauge
racy based on a piezoresistive principle, quartz crystal
zero can be conveniently recovered if one of the
or other type may also be used to produce an elec-
benchmarks is lost or destroyed.
trical signal proportional to the water head. The func-
tional requirements and conditions of installation of
5.2.3 Stage-sensing devices
these devices are described in IS0 4373.
When variations in stage are small, stage records may
5.2.3.3 Diaphragm pressure sensor
be established by direct readings of the reference
gauge by an observer. However, when stage varies
This is a differential pressure transducer which senses
rapidly, the station should preferably be equipped with
the difference between hydrostatic and atmospheric
a sensor and recorder (see also 5.4.5).
pressures. The body of the sensor is fixed in the
channel at an elevation below the lowest stage to be
The stage sensor converts a change in stage into a
measured. It is fitted with a diaphragm, one face of
proportional quantity of shaft rotation or electrical sig-
which is in contact with the water and the other face
nal, which is then recorded. The stage sensor may be
is subjected to atmospheric pressure through a
a mechanical, pressure, electronic or acoustic device.
capillary tube which is vented to the atmosphere
The recorder associated with a stage sensor may be
above water level.
a graphic (analog), digital, magnetic tape or electronic
device.
The deformation of the diaphragm under hydrostatic
pressure is converted into an electrical signal which
5.2.3.1 Float system
is proportional to the head of water above the sensor.
The typical float system consists of a float operating
The use of such sensors is generally limited to re-
in a stilling well, a graduated steel tape or wire, a
stricted measuring ranges because of the difficulty in
counterweight, a pulley and a pointer. The stage fluc-
meeting the accuracy requirements defined in 5.2.4
tuations are sensed by the float and converted into
over extended measuring ranges. The installation re-
an angular moment of the pulley-bearing shaft.
quirements for these sensors are similar to those for
pneumatic sensors.
The dimensions of the float and counterweight deter-
mine the sensor sensitivity and the driving torque on
the output shaft. The functional requirements of still- 5.2.3.4 Downward-looking ultrasonic device
ing wells are given in IS0 4373 and are summarized
This device is located above the water surface, away
as follows:
from the influence of the banks. The time is measured
- to provide, within the well, an accurate represen-
for pulses of ultrasound to travel from the device to
tation of the water level in the channel;
the water surface and back. The speed of sound in
air is assessed either from a measurement of air
- to damp out oscillations of the water surface;
temperature, or by direct measurement using a target
placed at a fixed distance between the device and the
- to accommodate the recording instrument and
water surface.
protect the float system.
The manufacturer’s recommendations for minimum
distances between the device and the banks and wa-
Pneumatic pressure sensor
5.2.3.2
ter surface should be followed. In the presence of
waves on the water surface, the device tends to de-
This type of stage-sensing device is frequently used
termine the elevation of the wave crests. The range
where the installation of a stilling well would be too
@a IS0 IS0 1100=1:1996(E)
of these devices (meeting the accuracy requirements surface of the flood water, and is deposited on the
of 5.2.4) is limited to about 2 m. centre rod as the water recedes, thus indicating the
maximum stage. Alternatively, the centre rod may be
coated with a paint whose colour is permanently af-
5.2.3.5 Upward-looking ultrasonic device
fected by water.
A transducer is located below the water surface away
from the banks, and connected to an electronic unit. 5.2.4 Accuracy of stage measurements
The time is measured for pulses of ultrasound to
For the measurement of stage, in certain installations
travel from the transducer to the water surface and
an uncertainty of + 10 mm may be satisfactory; in
back. The speed of sound in water is assessed either
others, an uncertainty of + 3 mm or better may be
by direct measurement, using a target placed at a
required; however, in no case should the uncertainty
fixed distance above the transducer, or from data de-
be greater than + 10 mm, or + 0,l % of the range of
rived from an ultrasonic flowmeter (see IS0 6416) of - -
the measuring device, whichever is greater (see
which the level sensor is an integral part.
IS0 4373).
The manufacturer’s recommendations for the mini-
mum distances between the transducer and the
5.2.5 Water-level recorders
banks and water surface should be followed. In the
presence of waves on the water surface, the device
5.2.5.1 Analog recorders
tends to determine the elevation of the wave troughs.
Analog recorders produce a continuous graphic record
A common configuration consists of a vertical tube
on a paper chart of the rise and fall of the stream with
extending above the water surface, with the
respect to time, as measured by the stage sensor.
transducer and target at the lower end.
Graphic recorders may be mechanical, with a shaft
rotation as input signal delivered directly by the level
5.2.3.6 Other stage sensors
sensor, or electronic (e.g. potentiometric recorders).
Other types of sensors exist which operate according
Regardless of their type, graphic recorders shall meet
to mechanical principles (buoyancy), electrical prin-
the requirements of IS0 4373.
ciples (capacitance or resistance sensors), or optical
principles.
5.2.5.2 Digital paper tape recorders
However, they are not covered in this part of
IS0 1100. Digital paper tape recorders punch or inscribe coded
instantaneous or discrete values on paper tape at
preselected time intervals.
5.2.3.7 Maximum-stage gauge
A maximum-stage gauge may be used to obtain a re- 5.2.5.3 Magnetic tape recorders
cord of the peak level reached during a flood when
Magnetic type recorders record coded values of a
other methods of recording levels cannot be used.
variable on a magnetic tape at preselected time inter-
Peak discharges may be calculated from the water
vals. Coding may be incremental, i.e. only level vari-
levels at two gauges installed some distance apart in
ations between two measurements are recorded over
a stretch of channel, provided that the time lag be-
the time interval, or discrete values may be recorded.
tween measurements is negligible (see IS0 1070).
In the latter case, the integer value is generally re-
These gauges do not meet the accuracy requirements
corded in binary form. These recorders are coupled to
of 5.2.4.
stage sensors via encoders, such as a rotational shaft
Maximum-stage gauges are locally made to different
movement or an electronic encoder delivering elec-
designs. Basically they may consist of a vertically in- trical signals.
stalled tube of approximately 50 mm internal diam-
eter, down the centre of which runs a rod. The tube
5.2.5.4 Electronic memory (solid state) recorders
is perforated to permit rising water to enter, the per-
forations being located to prevent drawdown or vel- These recorders store coded values in an electronic
ocity head from affecting the static water level. The memory. Like magnetic tape recorders, they are cou-
top of the tube shall be closed to prevent the entry pled to stage sensors via digital coders suited to the
of rain, but it should have an air vent to permit water signal delivered. Stored values may be retrieved on-
to rise up the tube without significant delay. Pow- site or remotely consulted, using an appropriate de-
dered cork in the bottom of the tube floats on the vice.

0 IS0
IS0 1100=1:1996(E)
5.2.6 Discharge-measuring section or reach removed. The field of view of a measuring section
(gauging section) shall extend sufficiently upstream to enable float-
ing debris, which might damage a measuring in-
The establishment of the stage-discharge relation at
strument, to be seen in sufficient time to permit
a gauging station is carried out by direct measurement the removal of the instrument from the stream.
of discharge using the methods described in the ap-
propriate International Standard. c) Suitable access to the site shall be constructed
where possible, to provide safe passage at all
In a permanent gauging station, the measurement
stages of flow and in all weather for personnel
section should be clearly identified and suitably
and for any vehicles used for the conveyance of
equipped to provide satisfactory performance.
instruments and equipment.
Regardless of the measuring method, the discharge
5.2.8 Discharge measurement by the dil ution
through the discharge-measuring section or reach
method
shall be the same as the discharge normal to the
reference-stage gauge, over the entire range of dis-
This method consists of injecting a tracer solution of
charge rates.
known concentration into the stream and sampling
the tracer concentration at a point further down-
At a gauging station, different measuring sections or
stream, where turbulence has mixed the tracer uni-
different methods may be used to cover the discharge
formly throughout the cross-section.
range.
The stream discharge is computed from a comparison
The various methods which can be used for calibrat-
between the concentrations of the injected solution
ing a gauging station are:
and of the samples taken downstream.
- the velocity-area method using a current-meter
The physical and hydraulic characteristics of the dis-
(see IS0 748), the moving boat method (see
charge measuring reach shall meet the requirements
IS0 4369) or floats (see IS0 748);
of the appropriate part of IS0 9555. The method relies
on there being good mixing of the water and tracer
- the dilution method using a tracer (see
throughout the entire cross-section. Adequate length
IS0 9555-1, IS0 9555-2, IS0 9555-3 and
of channel shall be used between the injection and
I so 9555-4);
sampling points.
- the ultrasonic method using a temporary instal-
lation in a self-calibrating mode (IS0 6416).
5.3 Preliminary survey and selection criteria
5.2.7 Discharge measurement by the
The site selected for observation of stage should be
velocity-area method
determined by the purpose for which the records are
collected, the accessibility of the site, and the avail-
The principle of the method is to measure the mean
ability of an observer if the gauge is nonrecording.
velocity and the area of cross-section of flow, the
Gauges on lakes and reservoirs are normally located
product of which is the discharge.
near the outlet, but upstream from the zone where
an increase in velocity causes a drawdown in water
The physical and hydraulic characteristics of the dis-
level. Gauges on large bodies of water should also be
charge measuring section shall meet the require-
located so as to reduce the fetch of strong winds,
ments of IS0 748 for the method to be implemented.
which may cause damage or misleading data. Hy-
draulic conditions are an important factor in site se-
Where the site does not offer the main requirements
lection on channels, particularly where water levels
for a gauging according to the specifications, condi-
are used to compute discharge records.
tions shall be improved as described below.
5.3.1 Preliminary survey
a) Minor irregularities in the bank or bed causing lo-
cal eddies shall be eliminated by trimming the
Detailed examination of a large-scale map is required
bank to a regular line and a stable slope, and by
in the first instance. A low-altitude aerial survey (using
removing from the bed any large stones or boul-
a plane or helicopter) may be made if the basin is
ders.
large and not readily accessible by road vehicles. This
Trees obst rutting the clear view of the measuring procedure gives a better view than ground surveys.
b)
section or measuring reac h shall be trimmed or Aerial views can be used as a basis for selecting po-
0 IS0 IS0 1100=1:1996(E)
nonsensitive station can result in large errors in the
tential sites, which can then be evaluated and studied
more precisely by ground reconnaissance. Ground re- discharges indicated by the stage-discharge relation.
connaissance will include a detailed visual examin-
A comparison shall be made between the change in
ation of the site and enquiry among competent
discharge and the corresponding minimum change in
services to determine whether hydraulic work pro-
stage to ensure that the sensitivity of the station is
jects exist which could modify the stream bed regime.
sufficient for the purpose for which the measure-
This enquiry should include an investigation of past
ments are required.
flow history, low water, high water, overflow areas,
floods and bed instability.
5.3.2.4 Scale readability
5.3.2 Selection criteria
It is essential that the reference gauge is easily read-
able and accurate at all values of discharge, because
with their
A list of surveyed sites shall be establi shed
stage readings are the basis of discharge measure-
blishment
advantages and drawbacks as to the esta
ments.
of a gauging station. Selection shall then be made
according to the following criteria.
The water surface shall be calm to ensure that
readings shall correspond to the indication of the
stage sensor. The gauge and the sensor shall there-
5.3.2.1 Measurement range
fore be installed close to each other in a low-velocity
area.
The site selected shall be such that it is possible to
measure the entire range and all types of flow which
5.3.2.5 Accessibility
may be encountered or which are required to be
measured.
Ideally the station should be accessible, or made ac-
The entire range of measurement may be referred to
cessible, at all seasons regardless of the discharge
one reference gauge, or certain ranges of discharge
conditions.
may be referred to different gauges. Different meth-
ods of calibration may be employed for separate parts
5.3.2.6 Silting
of the range, the particular conditions relative to each
of the methods of calibration being specified in the When the stream carries a high sediment load, silting
relevant International Standard (see clause 2 and an- of the gauge may occur, especially in low-velocity
nex A). protected areas. Access to any stilling well should
therefore be provided to permit quick and easy
cleaning.
5.3.2.2 Stability
5.3.2.7 Flood protection
The operation of a gauging station is based on the
assumption of a relation between stage and dis-
Site inspection shall be carried out under low-water
charge.
and high-water conditions to study currents and
It is therefore desirable that this relation is stable at eddies. The sensor shall be placed out of reach of any
the selected site. This’ condition is met if the control
floating debris to avoid accidental damage, and the
section or reach is stable and not subject to variable recorder should be set at an elevation to avoid being
backwater. flooded under high-water conditions.
shall be
Sites where weed growth prevalent Public records shall be consulted, the vegetation shall
avoided, if possible. be observed and the population questioned to this
end.
There shall be no vortices, dead water or other
abnormalities in flow. Sites where difficult ice condi-
5.3.2.8 Discharge measurements
tions are prevalent shall be avoided, if possible.
During preliminary surveys, the possibility of using
one method of discharge measurement for the whole
5.3.2.3 Sensitivity
discharge range shall be considered. It is preferable,
The site shall be sensitive, such that a significant but not essential, that the discharge measuring sec-
change in discharge, even for the lowest discharges, tion, or reach, is situated at the gauging station, but
it is satisfactory to use a measuring section at a dif-
shall be accompanied by a significant change in stage.
ferent location from the gauge if the same discharge
Small errors in stage readings during calibration at a
0 IS0
IS0 1100-1:1996(E)
is reco r .ded at both places. Iloratory measuremen ts However, a stage-discharge relation cannot always be
EXP
should be carried o ut to ch eck this requirement. established for alluvial rivers. In this case, the stage-
discharge relation is only applicable for the interval of
time for which it has been verified by discharge
5.3.2.9 Possible site improvements
measurements.
When the main requirements for a measuring site
according to the specifications cannot all be satisfied,
improvements such as those described below can be
5.4.2 Preparatory work
contemplated at the surveying stage.
After the preliminary survey, a topographical survey
a) The loss of water from the main channel by
shall be made when selecting a permanent site for a
spillage can often be avoided by constructing
suitable measuring section. This shall include a plan
flood banks to confine the flow in a defined flood
of the site indicating the width of the water surface
channel.
at a specified stage, the edges of the natural banks
of the channel(s), the line of any definite discontinuity
b) Minor irregularities in the bank or bed causing lo-
of the slope of these banks and the toe and crest of
cal eddies may be eliminated by trimming the
any artificial flood bank.
bank to a regular line and a stable slope, and by
removing from the bed any large stones or boul-
At sites where a permanent measuring section is
ders.
warranted, the following preparatory work shall be
carried out.
c) Unstable banks should be protected wherever
possible. Such protections shall extend upstream
a) All obstructions in the channel or floodway shall
and downstream of a measuring section for a
be indicated.
distance equal to at least one quarter of the
bankfull width of the channel in each direction. In
b) A longitudinal section of the channel shall be
the case of float gauging; the whole of the meas-
drawn from a point downstream of a control,
uring reach shall be protected.
where this exists, to the upstream limit of the
reach showing the level of the deepest part of the
d) Instability of the bed may sometimes be corrected
bed and water surface gradients at low and high
by introducing an artificial control which may also
stages.
serve to improve the stage-discharge relation
(sensitivity) or to create conditions in the measur-
c) The reach containing the measuring section shall
ing section for instruments to be effectively used.
be checked to ensure that it contains no disconti-
Occasionally, it may be possible to eliminate vari-
nuities that may affect the measurement results.
able backwater effects by introducing an artificial
At least five cross-sections shall be surveyed in
control. Artificial controls are
however, not prac-
I
the measuring reach: two cross-sections up-
ticable in large alluvial rivers.
stream from the measuring section and two
downstream, at distances upstream and down-
e) Installation of cableways, wa kways or footbridges
stream of not less than one bankfull width of the
as necessary.
channel.
) The control shall be defined by one or more
54 Establishme lnt of stage -discharge
cross-sections or by a close grid of levels over the
tion gauging
Aa station
area.
) The detailed survey of the reach shall be extended
5.4.1 General
to an elevation well above the highest anticipated
flood level.
The history of stage data shall be traced either by
periodic observations of a reference gauge for
f) The spacing of levels or soundings should be
streams having small variations in stage, or by con-
close enough to reveal any abrupt change in the
tinuous stage recording at intervals as necessary to
contour of the channel.
define the hydrograph adequately.
The availability of a control section or reach establish- g) The bed of the reach shall be examined for the
ing a stable relation between stage and discharge can presence of rocks or boulders, particularly in the
vicinity of the measuring section.
convert stage records into discharge records.
0 IS0
IS0 1100=1:1996(E)
h) All key points at the site shall be permanently ible, the method of velocity distribution described in
marked on the ground by markers sunk to such a IS0 748 shall be used for these measurements to
depth below the surface as will secure them determine the feasibility of using reduced-point
against movement. Cross-section markers should methods (see 5.3.2.8 and 5.2.6).
be on the line of the cross-section to facilitate the
For stations calibrated with current-meters, a standard
repetition of levels or soundings when the section
profile on the measuring cross-section shall be drawn,
is checked.
indicating the position of the cross-section markers.
On this drawing, the positions selected for the meas-
i) Where the main requirements necessary for a
uring verticals may be recorded (see IS0 748). The
suitable gauging site, as specified, are not pres-
bed levels of the cross-section shall be frequently
ent, conditions may be improved as described in
checked and the profile revised, if necessary.
5.3.2.9.
The velocity measurements described above shall be
5.4.3 Stage measurement and recording
repeated at more than one stage to ensure that any
abnormality of flow is detected.
A recorder shall be installed so as to produce a con-
tinuous record of stage at intervals as necessary to If the site allows it, the discharge-measuring section
may be equipped with a device for improving the
define the hydrograph adequately (but see 5.4.5.1). It
may be desirable to establish gauges at both banks measuring equipment to be used. Bridges and
particularly when there is any risk of differential level. current-meter wading rods, cableways and current-
meter suspension equipment shall conform to
A station benchmark shall be established to conform
IS0 4375 and IS0 3454.
to 5.2.2.3.
5.4.4.2 When floats are to be used for velocity
If a section control regulates the stage at low and/or
measurements, trial runs of floats shall be closely
medium discharges at the gauging station, the gauge
spaced across the width of the channel.
shall be situated upstream from the control and suf-
ficiently remote from it to avoid any distortion of flow
For stations calibrated with floats, a standard plan
which might occur in that vicinity. It shall be close
shall be prepared on which the lines of the selected
enough to ensure that a variable stage-discharge re-
floats, runs and the release points for floats shall be
lation will not be introduced through the effect of
indicated. A copy of this plan shall be kept in the in-
wind or weed growth in the channel. Higher dis-
strument house at all times (see IS0 748).
charges are most often controlled by the general
characteristics of the channel for a considerable dis-
5.4.4.3 When dilution techniques are to be used to
tance downstream.
calibrate the station, trial measurements should be
made to check the efficiency of mixing (see
The reference gauge and water-level recorder shall be
IS0 9555-l ).
located as close as possible to the measuring reach
unless floats are used to measure the velocities, in
which case the reference gauge and water-level re-
5.4.5 Operation of a stage-discharge relation
corder shall be located near the midpoint of the
i ng station
ww
measuring reach.
5.4.5.1 The production of a satisfactory record de-
The reference gauge shall comply with 5.2.2 and
pends on the station being maintained in full operating
IS0 4373.
order at all times. This requires efficient attention to
the recorder and proper maintenance of the station,
5.4.4 Discharge measurement
its equipment and its calibration. Where a station is
fitted only with a reference gauge or reference
The stage-disc harge relation shall be establis hed by
gauges (vertical, inclined, wire-weight or hook) and no
mea suring the discha rges corresponding to res pective
water-level recorder, the local observers shall be re-
stage values.
quired to furnish readings at specified intervals of all
the gauges in their care. Preferably the readings shall
5.4.4.1 When the station is to be calibrated using be made at fixed hours. The intervals between the
readings shall be determined by the rate at which the
current meters to measure velocities, exploratory
water level at the site changes, but arrangements
measurements of velocities shall be made in the pro-
posed measuring section and in the cross-sections shall be made to have additional readings when the
immediately upstream and downstream. When poss- water level is changing more rapidly than usual.

0 IS0
IS0 1100=1:1996(E)
- the application of the relevant International Stan-
It is essential that the local observer records the exact
time and correct date of each gauge observation. dard (see clause Z), or
- by a previous calibration using other methods.
5.4.5.2 When a recorder is provided, visits by the
observer should be made throughout the period to
verify that the recorder is operating satisfactorily. The
5.4.6.2 Survey and selection of site
observer shall be required to record readings of stage
from the reference gauge with the exact time of re-
A preliminary survey shall be made of the physical and
cording for comparison with the recorder reading. To
hydraulic features of the proposed site to check that
relate the readings to a chart trace, the observer may
it conforms (or may be constructed or modified so as
mark the chart. At all stations, the observer shall re-
to conform) to the requirements necessary for meas-
cord any obstruction of the channel, for example by
urement of discharge by the structure as specified in
weeds or ice, and shall note any casual obstruction
the relevant International Standard given in clause 2.
of the channel, inlet pipe(s), measuring structure or
transducer mountings caused by flood debris or any
Particular attention shall be paid to the following fea-
other cause. The site and equipment shall be kept
tures in selecting the site.
generally clean and tidy, particular attention being paid
to legibility of the reference gauge. The observer may
a) adequacy of the length of channel relative to the
be required to despatch all records, tapes or charts to
regular cross-section;
the record office for processing immediately after
they have been completed, together with any relevant b) uniformity of the existing velocity distribution;
notes or observations.
c) avoidance of a steep channel (Froude number
shall not exceed approximately 0,5);
5.4.5.3 Every gauging station shall be inspected
whenever any incident which might affect its accuracy
) effects of any increased upstream water levels
is reported by the observer.
due to the measuring structure;
5.4.5.4 All mechanical recorders and recorder clocks
) conditions downstream of the control structure
shall be cleaned and lubricated in accordance with the
(including tides, confluences with other controlling
manufacturer’s instructions or as indicated by experi-
features, seasonal weed growth);
ence under prevailing operating conditions.
f) impermeability of the ground on which the struc-
The elevation of all key points (including par-
5.4.5.5
ture is to be founded and the necessity for piling,
ticularly the zero of the reference gauge) shall be
grouting or other means of controlling seepage;
surveyed when the station is established and shall be
checked by reference to the station benchmark at
g) necessity for flood banks, to confine the maxi-
least annually or following any flood when equipment mum discharge to the channel;
might have been damaged by debris or by ice. At the
h) stability of the banks, and the necessity for trim-
same time, any vertical staff gauge shall be tested for
ming and/or revetment;
verticality. Where feasible, correlation of the station
benchmark with a National Survey datum shall be
uniformity of section of the approach channel.
checked at intervals of not greater than five years.
If the site does not possess the characteristics
Bed profiles shall be checked after a flood.
5.4.5.6
necessary for satisfactory measurements, or if an in-
spection of the stream shows that the velocity dis-
5 .4.6 Stage-discharge gauging stations with
tribution in the approach channel deviates appreciably
rtificial controls (notches, weirs and flu mes)
a
from uniformity, the site may have to be rejected un-
less suitable improvements are practicable. Alterna-
5.4.6.1 Principle tively, the performance of the installation shall be
checked by independent flow measurement.
When physical and hydraulic conditions permit, an ar-
The flow conditions downstream of the structure are
tificial control consisting of a fixed, undeformable
structure may be installed. The stage-discharge re- important in that they control the tail-water level
lation shall then depend on the geometrical charac- which may influence its operation. The structure shall
teristics of the artificial control and shall be defined be so designed that it cannot become drowned under
the operating conditions specified in the relevant
either by
0 IS0
IS0 1100=1:1996(E)
5.4.6.3.2 Nonstandardized measuring structures
International Standard. Construction of a measuring
structure in a river or stream may alter conditions and
A combination of different standardized measuring
cause scouring downstream of the structure, hence
structures is also permissible using standard cali-
appropriate bank and bed protection should be in-
bration equations for each structure (compound
cluded in the design.
gauging structures). Nonstandardized measuring
If the flow in the approach channel is disturbed by ir- structures require a field or laboratory calibration over
regularities in the boundary, for example large boul-
the entire range of discharge to be measured.
ders or rock outcrops, or by a bend, sluice gate or
other feature which causes asymmetry of discharge
5.4.6.4 Choice of measuring structure
across the channel, the accuracy of gauging may be
affected. The flow in the approach channel should
A guide for the selection of weirs and flumes is given
have a symmetrical velocity distribution; this can most
in IS0 8368, to which r
...