ISO/TR 9212:2006
(Main)Hydrometry — Measurement of liquid flow in open channels — Methods of measurement of bedload discharge
Hydrometry — Measurement of liquid flow in open channels — Methods of measurement of bedload discharge
ISO/TR 9212:2006 reviews the current status of direct and indirect bedload-measurement techniques. The methods are mainly based on grain size distribution of the bedload, channel width, depth and velocity of flow. ISO/TR 9212:2006 outlines and explains several methods for direct and indirect measurement of bedload in streams, including various types of sampling devices.
Hydrométrie — Mesurage du débit des liquides dans les canaux découverts — Méthodes de mesurage du débit des matériaux charriés sur le fond
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Standards Content (Sample)
TECHNICAL ISO/TR
REPORT 9212
Second edition
2006-08-01
Hydrometry — Measurement of liquid
flow in open channels — Methods of
measurement of bedload discharge
Hydrométrie — Mesurage du débit des liquides dans les canaux
découverts — Méthodes de mesurage du débit des matériaux charriés
sur le fond
Reference number
ISO/TR 9212:2006(E)
©
ISO 2006
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ISO/TR 9212:2006(E)
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ISO/TR 9212:2006(E)
Contents Page
Foreword. iv
Introduction . v
1 Scope.1
2 Normative references.1
3 Terms and definitions .2
4 Measurement of bedload .2
4.1 General.2
4.2 Principle.2
4.2.1 Measurement using bedload samplers .2
4.2.2 Indirect measurement of bedload transport .8
4.3 Requirements of an ideal bedload sampler .9
5 Site selection.9
6 Procedures for measurement of bedload discharge using bedload samplers.10
6.1 General.10
6.2 Calculations.11
6.3 Characteristics of bedload samplers.12
6.4 Errors .14
6.5 Sample identification.14
7 Indirect measurement of bedload .15
7.1 General.15
7.2 Differential measurement method.15
7.3 Volumetric methods .15
7.4 Dune-tracking method.16
7.5 Tracers.16
Bibliography .17
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ISO/TR 9212:2006(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
In exceptional circumstances, when a technical committee has collected data of a different kind from that
which is normally published as an International Standard (“state of the art”, for example), it may decide by a
simple majority vote of its participating members to publish a Technical Report. A Technical Report is entirely
informative in nature and does not have to be reviewed until the data it provides are considered to be no
longer valid or useful.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO/TR 9212 was prepared by Technical Committee ISO/TC 113, Hydrometry, Subcommittee SC 6, Sediment
transport.
This second edition cancels and replaces the first edition (ISO/TR 9212:1992), of which it constitutes a
technical revision.
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ISO/TR 9212:2006(E)
Introduction
The bedload is the material transported on or near the bed by rolling or sliding (contact load) and the material
bouncing along the bed, or moving directly or indirectly by the impact of bouncing particles (saltation load).
The knowledge of the rate of sediment transport in a stream is essential in the solution of practically all
problems associated with the flow in alluvial channels. The problems include river management, such as
design and operation of flood control works, navigation channels and harbours, irrigation reservoirs and
canals, and hydroelectric installations. Knowledge of the bedload transport rate is necessary in designing
reservoir capacity because virtually 100 % of all bedload entering a reservoir accumulates there. Bedload
should not enter canals and distributaries, and diversion structures should be designed to minimize the
transfer of bedload from rivers to canals.
The bedload-transport rate can be measured either as mass per unit time or volume per unit time. Volume
measurements should be converted to a mass rate. Measurements of mass rate of movement are made
during short time periods (seconds, minutes), whereas measurements of volume rates of movement are
measured over longer periods of time (hours, days). Regardless of whether the mass or volume rate is
measured, the average particle size distribution of moving material should be determined. Knowledge of
particle size distribution is needed to estimate the volume that the bedload material will occupy after it has
been deposited. Knowledge of particle size distribution also assists in the estimation of bedload transport
rates in other rivers transporting sediment.
The movement of bedload material is seldom uniform across the bed of a river. Depending upon the river size
and gradation, the bedload may move in various forms, such as ripples, dunes, or narrow ribbons. Its
downstream rate of movement is also extremely variable. It is difficult to actually sample the rate of movement
in a river cross-section, or to determine and verify theoretical methods of estimation.
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TECHNICAL REPORT ISO/TR 9212:2006(E)
Hydrometry — Measurement of liquid flow in open channels —
Methods of measurement of bedload discharge
1 Scope
This Technical Report reviews the current status of direct and indirect bedload-measurement techniques. The
methods are mainly based on grain size distribution of the bedload, channel width, depth and velocity of flow.
This Technical Report outlines and explains several methods for direct and indirect measurement of bedload
in streams, including various types of sampling devices.
The purposes of measuring bedload transport rates are to:
a) increase the accuracy of estimating total sediment load in rivers,
b) gain knowledge of bedload-transport that cannot be completely measured by conventional
suspended-sediment collection methods,
c) provide data to calibrate or verify theoretical transport models, and
d) provide information needed in the design of river diversion and entrainment structures.
NOTE The units of measurement used in this Technical Report are SI units.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 772, Hydrometric determinations — Vocabulary and symbols
ISO 4363, Measurement of liquid flow in open channels — Methods for measurement of characteristics of
suspended sediment
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ISO/TR 9212:2006(E)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 772 and ISO 4363 and the following
apply.
3.1
bedload
material transported on or near the bed by rolling, sliding and bouncing
3.2
bedload transport rate
quantity of bedload passing through a section of the stream per unit width in unit time
NOTE The bedload transport rate is expressed in kilograms per metre (of width) per second.
3.3
bedload transport model
mathematical relation of hydraulic and sediment variables which can be used to estimate the bedload
transport rates of sediment
3.4
bedload sampler efficiency
ratio of the amount of bedload collected by the sampler to the amount of bedload that would have passed
through the sampler width in the same time in the absence of the sampler
4 Measurement of bedload
4.1 General
Bedload can be measured by direct measuring bedload samplers or by indirect methods.
a) Direct measuring bedload samplers:
In this method, a mechanical device or sampler is required for measuring the bedload transport rate. The
bedload sampler is designed so that it can be placed directly on the channel bed in the flow, or beneath
the channel bed to collect a sample of the bedload over a specific time interval. A sample thus obtained
represents a time-averaged mass per unit width per unit time.
b) Indirect measurement of bedload:
All other methods of bedload measurement in which no mechanical device, or bedload-sampler is used,
are indirect methods.
4.2 Principle
4.2.1 Measurement using bedload samplers
4.2.1.1 Basket or box type sampler
This type of sampler consists of a basket or box, usually made of mesh material on all sides except the front
and bottom. The bottom may be solid or of loosely woven iron rings, to enable it to conform to the irregular
shape of the stream bed. The sampler is placed on the channel bed with the help of a supporting frame and
cables. A steering fin or vane(s) attached to the basket assures positioning of the instrument in the direction of
the flow. The sediment is collected in the basket by causing a reduction of the flow velocity and/or screening
the sediment from flow for a measured time period.
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ISO/TR 9212:2006(E)
Since a part of the bedload is dropped in front of the sampler, the efficiency of basket type samplers is only of
the order of 45 %, for average sediment sizes varying from 10 mm to 50 mm. However, due to their large
capacity, basket type samplers are well suited for measuring of transport rate of large-sized sediment.
4.2.1.2 Pressure-difference sampler
This type of sampler (see Figures 1 to 6) is designed so that the velocity of water entering the sampler and the
stream velocity is approximately equal. Equalization of velocity is accomplished through creation of a pressure
drop at the exit due to a diverging configuration between the entrance and the exit. These are flow-through
samplers that trap coarse material behind baffles or in a mesh bag attached to the exit side or in a specially
designed chamber.
Key
1 transverse partitions
2 entrance
NOTE This is a pressure-difference bedload sampler. The SRIH sampler was the first of this type to be developed.
Such samplers can sample particles as small as fine sand to as large as 200 mm. Efficiencies are extremely variable.
Figure 1 — Scientific Research Institute of Hydrotechnics (SRIH) sampler
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ISO/TR 9212:2006(E)
Dimensions in metres
Key
1 steering fin
2 entrance
3 rubber connection
4 mesh bag
NOTE This is a pressure-difference bedload sampler. The Arnhem, or Dutch, sampler is comprised of a rigid
rectangular entrance connected by a diverging rubber-neck to a basket of 0,2 mm to 0,3 mm mesh. Efficiencies are
variable, but generally about 70 %. It is suitable for collection of fine bedload material. The fine net of the sampler can get
clogged leading to a drop in efficiency of the sampler.
Figure 2 — Arnhem sampler
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ISO/TR 9212:2006(E)
Dimensions in millimetres
Figure 3 — Helley-Smith bedload sampler
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ISO/TR 9212:2006(E)
Key
1 bag to tail attachment spring
2 mesh polyester monofilament, 0,2 mm
3 dot fastener
4 aluminium alloy weld tail pieces except where side rails join tail
5 sliding collar
6 rail attachment bolt
7 hole for bag attachment spring
8 slot top rail to fit tail
9 aluminium tubing filled with lead after farming
10 tubing spacers where necessary
NOTE This is a pressure-difference bedload sampler. Field experiments indicate a nearly 100 % sampling efficiency
for sizes from about 0,5 mm to 16 mm. Laboratory studies indicate that sampling efficiencies vary widely with particle size
and transport rate.
Figure 3 (continued)
Dimensions in metres
NOTE This is a direct measurement sampler developed by Vinckers, Bijker and Schijft. The hydraulic efficiency
varies from about 1,09 for clear flow, to about 1,0 for extreme conditions. Sampling efficiency varies from about 93 % for
particle sizes finer than 0,2 mm to about 85 % for sizes finer than about 0,09 mm.
Figure 4 — Sphinx sampler
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ISO/TR 9212:2006(E)
NOTE The US BLH-84 is a hand-held 4,5 kg, wading type sampler used to collect bedload samples from a stream of
wading depth. The sampler consists of an expanding nozzle, a sampler bag, and a wading rod assembly. Particle sizes
less than 38 mm at mean velocities up to 3 m/s can be measured with this sampler. It was developed by the Federal
Interagency Sedimentation Project, USA. Size of sampler: Length: 711 mm, Width: 140 mm, Mass: 4,5 kg.
Figure 5 — US BLH-84 Wading type bedload sampler
NOTE The US BL-84 is a cable suspended 14,4 kg, sampler to collect bedload samples from a stream of any depth.
The sampler consists of an expanding nozzle mated to a frame, and a sampler bag. Particle sizes less than 38 mm at
mean velocities up to 3 m/s can be measured with this sampler. It is developed by the Federal Interagency Sedimentation
[3]
Project, USA . Size of sampler: Length: 921 mm, Width: 381 mm, Mass: 14,4 kg.
Figure 6 — US BL-84 Cable suspended bedload sampler
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ISO/TR 9212:2006(E)
4.2.2 Indirect measurement of bedload transport
4.2.2.1 Differential measurements
Such measurements may be used if three conditions exist simultaneously in a stream: namely,
a) the bedload particles are sand-size or smaller,
b) an artificial or natural turbulence section exists in which all moving sediment is in suspension, and
c) there is a normal section nearby where bedload material is moving along the bed.
Suspended-sediment samples may be collected from both the turbulent and normal sections by standard
suspended-sediment sampling techniques. The difference between the total sediment discharge measured in
the turbulent section and the suspended-sediment discharge measured in the normal section, should be
considered a good estimate of the bedload discharge in the normal section.
4.2.2.2 Volumetric method
Periodic volumetric measurements of changes in shape of deltoid deposits at river mouths may be used to
estimate bedload discharge. Periodic volumetric measurements of the accumulation of deposited sediment
behind dams or diversion structures may be used to estimate bedload discharge over longer periods of time.
4.2.2.3 Dune-tracking
Dune-tracking is a hydrographic survey method used when the bed forms are dune shaped. This method
involves the mapping of a relatively short, straight reach of a channel under steady-flow conditions. The
average parameters of the dune shapes are measured, and the average velocity of dune movement is
determined.
4.2.2.4 Tracers
Easily identifiable tracer particles of known mass and size can be injected in the channel bed and the rate of
their movement monitored for a specified time period.
4.2.2.5 Remote sensing
Where the channel bed is clearly visible through the water, time-lapse photography techniques can be used to
track the movement of bedload particles. Acoustical sensing and recording devices can also be used to track
the movement of very large bedload material, based on the theory that the noise created by particles hitting
each other can be correlated with bedload discharge.
4.2.2.6 Acoustic instruments
For streams with relatively coarse bed material, a base plate or fork-shaped rod with a microphone attachment
is lowered onto the stream bed. The sound of particle impact on the plate and inter particle collisions, picked
up by the microphone, is transmitted to a recording device or an oscilloscope or a headphone. The instrument
is useful in determining only the relative bedload transport in the cross-section and the relative variation with
time. Such information about the relative variation in the cross-section is useful in the choice of the number
and location of sampling points.
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ISO/TR 9212:2006(E)
4.3 Requirements of an ideal bedload sampler
In order that the s
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