ISO 4363:2002

INTERNATIONAL ISO
STANDARD 4363
Third edition
2002-12-01


Measurement of liquid flow in open
channels — Methods for measurement of
characteristics of suspended sediment
Mesure de débit des liquides dans les canaux découverts — Méthodes de
mesurage des caractéristiques des sédiments en suspension




Reference number
ISO 4363:2002(E)
©
 ISO 2002

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ISO 4363:2002(E)
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ISO 4363:2002(E)
Contents Page
Foreword . iv
Introduction. v
1 Scope. 1
2 Normative references. 1
3 Terms and definitions. 1
4 Units of measurement. 2
5 Selection of site. 3
6 Selection of samplers . 3
7 Measurement methods and frequencies . 3
7.1 Principle for measurement of cross-sectional mean sediment mass concentration . 3
7.2 Principle for measurement and calculation of cross-sectional mean particle size distribution . 4
7.3 Conventional method. 4
7.4 Simplified method. 7
7.5 Distribution and requirements of measurements. 8
7.6 Additional information. 8
7.7 Source and control of errors. 9
8 Calculation. 10
8.1 Sediment discharge and mass concentration. 10
8.2 Calculation of particle size distribution. 11
9 Estimation of random uncertainty and systematic error for measurement of suspended
sediment. 12
9.1 General. 12
9.2 Sources of error . 13
9.3 Estimation of component errors. 13
9.4 Total random uncertainty for measurement of cross-sectional mean sediment mass
concentration. 13
9.5 Total systematic error for one measurement of cross-sectional mean sediment mass
concentration. 14
Annex A (informative) Data collection for determining the error in measurement of cross-sectional
mean sediment mass concentration and estimation of errors. 15
Annex B (informative) Procedures and examples of methods for combining samples collected in a
cross-section . 22


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ISO 4363:2002(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 3.
The main task of technical committees is to prepare International Standards. Draft International Standards adopted
by the technical committees are circulated to the member bodies for voting. Publication as an International
Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this International Standard may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 4363 was prepared by Technical Committee ISO/TC 113, Hydrometric determinations, Subcommittee SC 6,
Sediment transport.
This third edition cancels and replaces the second edition (ISO 4363:1993), which has been technically revised.
Annexes A and B of this International Standard are for information only.
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ISO 4363:2002(E)
Introduction
Sediment has been defined generally as solid particles that are moved or might be moved, by stream flow in a
channel. Sediment transportation creates numerous problems such as soil erosion, local scour, degradation and
aggradation of streams, siltation in irrigation canals and navigation channels, loss of capacity of reservoirs,
meandering of streams, damages to hydraulic machinery, etc. For solving varied sediment related issues arising
out of human endeavours for development and management of water resources, a comprehensive knowledge of
the mechanism of sediment transport and methods of determination of sediment load is highly essential.
Erosion is caused by water, wind, ice and human activities such as cultivation urbanization, mining, etc. Clods and
aggregates of soil in the catchment area are broken down into small particles which are thrown into suspension
and carried away as sediment. Not all the eroded material enters the stream channel. The total amount of eroded
material which travels from a source to a downstream measuring point is termed as sediment yield.
The purpose for making measurements on suspended sediment is to determine the variation of the cross-sectional
mean mass concentration and mean particle size distribution of suspended sediment in sediment transport
processes using appropriate methods at a suitable frequency; then to determine the characteristic values of
suspended sediment transport such as sediment load, mean particle size distribution, and sediment load of various
particle sizes in various periods by jointly using the data of water stage, discharge, and suspended sediment.


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INTERNATIONAL STANDARD ISO 4363:2002(E)

Measurement of liquid flow in open channels — Methods for
measurement of characteristics of suspended sediment
1 Scope
This International Standard specifies conventional and simplified methods for the measurement of cross-sectional
mean suspended sediment mass concentration and mean particle size distribution. The conventional method is
used for routine measurements in periods of stable or slowly varied flow. The simplified method is mainly used for
sediment measurements for the purpose of observing the variation process of sediment transport and can be
performed under difficult conditions. Empirical relationships are established between the cross-sectional mean
suspended sediment mass concentrations and mean particle size distributions measured by conventional and
simplified methods.
The methods specified in this International Standard are applicable to suspended sediment measurements at
hydrological stations.
2 Normative references
The following normative documents contain provisions which, through reference in this text, constitute provisions of
this International Standard. For dated references, subsequent amendments to, or revisions of, any of these
publications do not apply. However, parties to agreements based on this International Standard are encouraged to
investigate the possibility of applying the most recent editions of the normative documents indicated below. For
undated references, the latest edition of the normative document referred to applies. Members of ISO and IEC
maintain registers of currently valid International Standards.
ISO 31 (all parts), Quantities and units
ISO 748, Measurement of liquid flow in open channels — Velocity-area methods
ISO 772, Hydrometric determinations — Vocabulary and symbols
ISO 1000, SI units and recommendations for the use of their multiples and of certain other units
ISO 3716, Liquid flow measurement in open channels — Functional requirements and characteristics of suspended
sediment load samplers
ISO 4365, Liquid flow in open channels — Sediment in streams and canals — Determination of concentration,
particle size distribution and relative density
3 Terms and definitions
For the purposes of this International Standard, the terms and definitions given in ISO 772 and the following apply.
3.1
suspended sediment discharge
mass of suspended sediment passing through a specific cross-section of streams or canals per unit time
3.2
suspended sediment load
total mass of suspended sediment, generally expressed in mass or volume of dry sediment, passing through a
specific cross-section of streams or canals in a given period of time
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ISO 4363:2002(E)
3.3
vertical average sediment mass concentration
ratio of the suspended sediment discharge per unit width (q ) to the flow discharge per unit width (q) in a vertical
s
3.4
cross-sectional mean sediment mass concentration
ratio of the cross-sectional suspended sediment discharge (Q ) to the cross-sectional flow discharge (Q )
A,s A
3.5
method for combining samples collected in a cross-section
method for measurement of cross-sectional mean sediment mass concentration in accordance with the segmental
discharge-weighted principle
NOTE The method involves dividing a cross-section by verticals into several segments with equal water surface width, or
equal flow area or equal discharge. Samples are taken by a specific method in each vertical passing through each segment
centre. (The flow velocity at a sediment sampling point should be measured simultaneously with the taking of the sediment
sample or as soon as practicable after the collection of the sediment sample. In rivers subjected to rapidly changing stage, it is
strongly recommended that the sediment sample be taken at the same time as the measurement of flow velocity.) Then the
sediment mass concentration of the combined samples is determined as the cross-sectional mean sediment mass
concentration.
3.6
particle size analysis
entire technological operation for determining the ratio of sediment mass of each size group to the total sediment
mass of a sample as specified in ISO 4365
3.7
particle size distribution
distribution in ratios of sediment mass of each size group to the total sediment mass of a sample
NOTE It is generally expressed in ratios of mass of sediment coarser or finer than a given diameter to the total sediment
mass of the sample.
3.8
cross-sectional mean size distribution of suspended sediment
conceptual characteristic value representing the ratios of sediment mass of each size group to the total suspended
sediment mass in the cross-section
4 Units of measurement
4.1 The International System of Units (SI Units) is used in this International Standard in accordance with ISO 31
(all parts) and ISO 1000.
4.2 The suspended sediment concentration is expressed in one of the following three ways.
a) Mass concentration of the water-sediment mixture ρ , generally expressed in milligrams per litre (mg/l),
ws
3
grams per litre (g/l) or kilograms per cubic metre (kg/m ), is dry sediment per unit volume of the water-
sediment mixture. This is the expression used in this International Standard.
b) Volume fraction ϕ, expressed as a percentage (%), is the ratio of the volume of sediment to the volume of the
water-sediment mixture and is given by Equation (1):
V
s
ϕ = (1)
V
ws
where
V is the volume of sediment;
s
V is the volume of the water-sediment mixture.
ws
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ISO 4363:2002(E)
c) Mass fraction, w , expressed as a percentage (%), is the ratio of the mass of dry sediment to the mass of
w
water-sediment mixture and is given by Equation (2):
ρ
ws
w = (2)
w

ρ
w
ρρ+−1

wws
ρ
s

where ρ is defined in a) and ρ and ρ are the mass concentrations of water and sediment, respectively,
ws w s
3 3
expressed in mg/l, g/l, or kg/m . If no measured data are available, ρ may be adopted as 2 650 kg/m .
s
5 Selection of site
The cross-section for measurement of suspended sediment shall preferably coincide with that for measurement of
velocity and shall meet the requirements specified in ISO 748.
6 Selection of samplers
Samplers shall conform to the requirements specified in ISO 3716.
In measurement of suspended sediment, a time-integration type sampler and an in-situ velocity measurement
device with good performance shall be used to eliminate or mitigate the influence of fluctuation of sediment
concentration.
7 Measurement methods and frequencies
7.1 Principle for measurement of cross-sectional mean sediment mass concentration
As the distributions of velocity and sediment mass concentration in a cross-section of a stream vary spatially, the
time-mean velocity v and sediment mass concentration ρ shall be measured at a number of points in the cross-
section, with each point representing a small area of dA = dhdb. From
BH BH
Qv= ddhb and Qv= ρ ddhb .
A A,s
∫∫ ∫∫
00 00
the cross-sectional flow discharge and sediment discharge can be calculated. From the definition given in 3.4, the
ρ
cross-sectional mean sediment mass concentration A is given by:
BH Q
ρρvhddb dq
A
∫∫ ∫
Q
A,s
00 0
ρ
== = (3)
A
BH Q
Q
A
vhddb
dq
A
∫∫ ∫
00
0
where
db and dh are the width and depth of the small area represented by the point, respectively;
B and H are the surface width and vertical depth of flow, respectively;
dq (= vdhdb) is the discharge passing through the small area.
A
The cross-sectional mean sediment mass concentration is determined by weighting the mass concentration for the
discharge of each section. This is the basic principle for measurement of cross-sectional mean sediment mass
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ISO 4363:2002(E)
concentration. In practice, it is normally simplified into the sediment discharge method and the method for
combining samples collected in a cross-section.
7.2 Principle for measurement and calculation of cross-sectional mean particle size distribution
The product of the cross-sectional mean particle size distribution and the cross-sectional sediment discharge shall
be equal to the sum of the products of segmental particle size distribution and the corresponding sediment
discharges. The cross-sectional mean particle size distribution conforms to the principle of weighting sediment
mass concentration based on water discharge. The particle size distribution determined by the method for
combining samples collected in a cross-section specified in this International Standard also conforms to the cross-
sectional mean particle size distribution.
The cross-sectional mean mass fraction of sediment finer than a given diameter in the total sediment mass of
w
sample can be expressed by Equation (4):
dA,
n
wq⋅
∑ di si
i=1
w
, = (4)
dA
n
q
si
∑
i=1
where
w is the average percentage of the mass of sediment finer than the given diameter in the total sediment
di
mass of sample for segment i;
q is the sediment discharge of segment i;
si
d is the given diameter;
n is the number of segments.
In practice, some simplified sampling methods may be designed based on the above principle. Normally, the same
sampling method for both measurements of cross-sectional mean sediment mass concentration and cross-
sectional particle size analysis may be used.
7.3 Conventional method
7.3.1 General
The conventional method is designed for measurement of cross-sectional mean sediment mass concentration in
accordance with the discharge-weighted principle. In this International Standard, the sediment discharge method
and the method for combining samples collected in a cross-section are specified with respect to their
characteristics.
7.3.2 Sediment discharge method (for measurement of sediment mass concentration)
7.3.2.1 Cross-sectional mean sediment mass concentration
In this method the cross-section is divided into several segments by verticals along the cross-section and the
velocity and sediment mass concentration are measured by the selected point method or depth integration method
in each vertical. The flow discharge and sediment discharge of each segment are calculated and totalled
respectively as the total cross-sectional flow discharge and sediment discharge. The ratio of the cross-sectional
sediment discharge to the cross-sectional flow discharge is taken as the cross-sectional mean sediment mass
concentration.
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ISO 4363:2002(E)
ρ
The cross-sectional mean sediment mass concentration determined by the sediment discharge method can be
A
expressed by Equation (5).
nn
ρ v
h
qbii
i
sii
∑∑
ii==11
ρ
== (5)
A
nn
v
h
qb
i
i
∑∑ii
ii==11
where
q and q are the sediment discharge and flow discharge passing through segment i, respectively;
si i
ρ and v are the mean sediment mass concentration and mean velocity of segment i, respectively;
i i
h and b are the mean flow depth and surface width of segment i;
i i
n is the number of segments.
Two methods, namely the mid-section method and mean-section method, are used to calculate the segmental
ρ v
sediment discharge and segmental flow discharge (see ISO 748). In using the mid-section method, i and i are
ρ v
the vertical mean values, h is the vertical depth. In using the mean-section method, i , i , and h are the
i i
average values of two neighbouring verticals.
7.3.2.2 Methods for selecting verticals
Factors such as the shape and stability of the cross-section, characteristics of lateral distribution of sediment,
sampling devices and methods, and requirement for accuracy shall be considered comprehensively for the method
for selecting verticals. The following two methods are available.
a) Method for selecting verticals at turning points of sediment discharge per unit width:
This method is applicable to the cross-sections with stable shape and lateral distributions of velocity and
sediment, and clear turning points of sediment discharge per unit width. Its main advantage is that of obtaining
relatively high accuracy using fewer verticals.
b) Method for selecting verticals at centrelines of segments with equal discharge:
This method is applicable to stable cross-sections. If it meets the requirements of equal discharge increment
(EDI) method (see 7.3.2.4), the EDI method can be used directly.
7.3.2.3 Number of verticals
The number of verticals shall be determined by analysing experimental data so as to meet the requirements for
accuracy. Generally, it shall not be less than seven verticals for a water surface width larger than 300 m or it shall
not be less than five verticals for a water surface width smaller than 300 m.
In measuring both sediment and velocity simultaneously, the number of verticals should be determined by the
requirements for discharge measurement, as this is generally more than is required for the measurement of
suspended sediment load.
7.3.2.4 Methods for sediment sampling in a vertical
In using the sediment discharge method to measure sediment, the point velocity or mean velocity in a vertical shall
be measured simultaneously. The following three methods are available.
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ISO 4363:2002(E)
a) Depth-integration method:
In the depth-integration method, the time-integration type sampler is moved at a uniform transit rate along the
vertical. In sampling, the moving rate of the sampler, volume of the sample should match the water depth and
flow velocity. The method is highly accurate when the water is deep, the sampler is moved slowly and the
effect of unmeasured layer near the bed is negligible.
b) Selected-point method:
It includes the two-point method (0,2h and 0,8h from water surface, where h is total vertical depth of the water),
the three-point method (0,2h, 0,6h, and 0,8h from water surface), the five-point method [near water surface,
0,2h, 0,6h, and 0,8h from water surface, and near bottom (0,95h to 0,98h)]. The one-point method (0,6h from
water surface) can be used for either low water depth or lower accuracy requirements.
NOTE The accuracy of the method for sediment sampling in a vertical can be improved by increasing the number of
sampling points in a vertical. In this case, the seven-point method (see annex A) is usually used.
c) Method for combining samples collected in a vertical:
All the samples collected in a vertical are put together as one sample and its mass concentration is taken as
the vertical mean sediment mass concentration.
The sampling points and duration for the method for combining samples collected in a vertical often used are
listed in Table 1.
Table 1 — Sampling points and duration for the method of combining samples
a b
Method
Relative depth of points (from water surface) Sampling durations
Two-point 0,2h; 0,8h 0,5t; 0,5t
Three-point 0,2h; 0,6h; 0,8h t/3, t/3; t/3
Near surface, 0,2h; 0,6h; 0,8h
Five-point 0,1t; 0,3t; 0,3t; 0,2t; 0,1t
near riverbed
NOTE Generally, the accuracy of the vertical mean sediment increases as the number of sampling points in
the vertical increases. An accurate measurement of the vertical mean sediment concentration also can be
obtained using the depth-integration method when the water depth does not exceed 4,5 m.
In using the selected-point method, a relatively long duration of sampling can eliminate the effect of fluctuation
between measured points. The depth-integration method takes samples over the whole vertical, so that a good
spatial representative sampling can be obtained. However the sampling is instantaneous and fluctuation effects
are eliminated by random compensation of all sampling points. Both the selected-point method and depth-
integration method have their own advantages and disadvantages.
In accuracy tests, the seven-point method is commonly used as a standard method to evaluate the accuracy of
other vertical sampling methods (see A.4).
a
h is total vertical depth of the water.
b
t is the total sampling duration in a vertical.

7.3.3 Methods for combining samples collected in a cross-section
7.3.3.1 General
There are three principal methods for combining samples collected in a cross-section. These methods are given in
7.3.3.2 to 7.3.3.4. Details for technical requirements and examples of methods for combining samples collected in
a cross-section are given in annex B.
7.3.3.2 Equal-width-increment (EWI) method
In this method, the cross-section is divided into several segments of equal width. Select the verticals at the
centrelines of segments. In each vertical, determine the mean sediment mass concentration using the depth-
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ISO 4363:2002(E)
integration method and/or the point sampling technique. Measure the velocity. Keep the nozzle diameter of the
sampler constant. Combine samples collected in all verticals in the cross-section into one sample and take the
sediment mass concentration as the cross-sectional mean sediment mass concentration.
7.3.3.3 Equal-area-increment (EAI) method
In this method, the cross-section is divided into several segments of equal area. Select the verticals at the centre of
segments. In each vertical, determine the mean sediment mass concentration using the depth-integration method
and/or point sampling technique. Keep the same sampling duration for all verticals. Keep the nozzle diameter of the
sampler constant. Measure the velocity. Combine samples collected in all verticals into one sample and take the
sediment mass concentration as the cross-sectional mean sediment mass concentration.
7.3.3.4 Equal-discharge-increment (EDI) method
In this method, a curve is obtained by plotting the percentage of cumulative discharge against the distance from the
left side or right side of the water surface using the discharge data. Using the curve, divide the cross-section into
several segments with equal discharge. Select the verticals at the segment centrelines. In each vertical, determine
the mean sediment mass concentration using the depth-integration method and/or the point sampling technique.
Collect the same volume from each vertical. Measure the velocity. Then combine all samples collected in the cross-
section into one sample and take the sediment mass concentration as the cross-sectional mean sediment mass
concentration.
If the volumes collected in verticals are not equal, treat each sample separately. Take the average value of
sediment mass concentrations from all verticals as the cross-sectional sediment mass concentration.
7.3.4 Sampling methods for particle size analysis
Another set of samples may be collected in all or a part of verticals for measurement of sediment mass
concentration using the same or different methods specifically for particle size analysis.
7.4 Simplified method
7.4.1 General
This method is a method for measurement of sediment mass concentration and particle size distribution in one or a
few verticals which are representative of the cross-sectional mean sediment mass concentration and the mean
particle size distribution.
7.4.2 Measurement of sediment mass concentration
7.4.2.1 Selection of sampling verticals
In the simplified method, it is necessary to statistically analyse the measured data and then to select verticals in a
cross-section. The ratio of the sediment mass concentration, obtained by the simplified method, to the cross-
sectional mean sediment
...