AS 3778.5.2-1991

Measurement of water flow in open channels Dilution methods - Integration method for the measurement of steady flow

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1 - AS 3778.5.2-1991 MEASUREMENT OF WATER FLOW IN OPEN CHANNELS - DILUTION METHODS - INTEGRATION METHOD FOR THE MEASUREMENT OF ST
4 - PREFACE
6 - 0 Introduction
6 - 1 Scope
6 - 2 Field of application
7 - 3 References
7 - 4 Definitions
7 - 4.1 tracer
7 - 4.2 background concentration:
7 - 4.3 adsorption:
7 - 5 Symbols
8 - 6 Principle of the method
8 - 6.1 General formula
8 - 6.2 Monitoring the passage of the tracer
8 - 6.2.1 Continuous recording
8 - 6.2.2 Multiple samples
8 - 6.2.3 Constant-rate sampling
8 - 7 Tracer requirements
8 - 7.1 General characteristics
9 - 7.2 Tracers for aqueous flows
9 - 7.2.1 Chemical tracers
9 - 7.2.2 Radioactive tracers
9 - 7.2.3 Fluorescent tracers
9 - 7.3 Tracers for non-aqueous flows
9 - 7.4 Quantity of tracer
9 - 8 Selection of measuring reach
9 - 8.1 General considerations
10 - 8.2 Estimation of the length of the measuring reach
10 - 8.2.1 Experimental techniques
10 - 8.2.2 Use of empirical formulae
10 - 9 Procedure
10 - 9.1 Laboratory and office preparations
10 - 9.2 General field procedure
11 - 9.3 Injection procedure
11 - 9.4 Sampling
11 - 9.4.1 Duration of sampling
11 - 9.4.2 Collection of background liquid
12 - 9.4.3 Measurement of the concentration of tracer in the downstream section
12 - 9.4.4 Incomplete tracer curves
12 - 10 Sample analysis
12 - 10.1 Chemical tracers
12 - 10.1.1 Sodium chloride by the electrical conductivity method
13 - 10.1.2 Sodium iodide by the catalytic spectro-photometric method
13 - 10.1.3 Lithium chloride by flame photometry
13 - 10.2 Fluorescent tracers
13 - 10.3 Radioactive tracers
13 - 10.4 Obtaining the calibration curve
13 - 11 Determination of uncertainty
13 - 11.1 Causes of errors
13 - 11.1.1 Error associated with the tracer
13 - 11.1.2 Error associated with the duration of gauging
13 - 11.1.3 Error associated with poor mixing in the gauging reach
13 - 11.1.4 Error associated with change in storage volume in the gauging reach
14 - 11.1.5 Error associated with sampling and sample analysis
14 - 11.1.6 Error associated with the operators
14 - 11.2 Estimation of uncertainties
14 - 11.3 Example of calculation of flow-rate and estimation of errors
14 - 11.3.1 Planning the injection
15 - 11.3.2 Sampling
15 - 11.3.3 Chemical analysis and calculation of results
18 - Annex - International standards for drinking water published by the World Health Organization

Abstract

This Standard specifies methods for the measurement of water flow in channels under steady flow conditions by the dilution method using a known amount of tracer. It is technically identical with and reproduced from ISO 555-2:1987.

Scope

This part of ISO 555 gives the principles of the integration method and describes several sampling procedures that may be used to establish that the tracer mixing is satisfactory at the cross-section where the measurement of flow is required. It deals with the choice of tracer and gives a brief outline of the channel characteristics necessary for the application of the method. The procedures that maybe required to inject the tracer, to determine the quantity injected and to measure the concentrations of tracer in the injection solution and in the samples are given. The complexity of these procedures can vary considerably, depending on the objectives. When only a rough estimate of discharge is required in a remote area or during spate flow conditions, the experimental and analytical techniques can be far less rigorous than those required when calibration of a gauging structure is required. Sample analysis is not dealt with in detail but a numerical example is given to illustrate the calculation of flow and the estimation of uncertainties.
Field of application
For a given discharge, the integration method requires less tracer than the constant-rate injection method. It is, therefore, particularly applicable for high discharges or where tracer economy is important because of considerations of cost. Discharges of several thousand cubic metres per second have been determined using the integration method. In the case of smaller flows, the method may be preferred on sites where access is difficult or when facilities are sparse, because the field operations can be very simple. Should any doubt exist as to the steadiness of the flow, the constant-rate injection method should be used, since the integration method may provide no information on the variation of flow with time and, consequently, errors in the computed flow would occur. In narrow channels such as sewers where the tracer concentrations may rise and fall too rapidly for samples to be taken in such a way as to represent accurately the passage of tracer, the constant-rate injection method shall be used (see ISO 555-1).
The method can only be applied when the mixing processes within the channel, whether caused by natural turbulence or otherwise, are sufficient for the tracer to be thoroughly mixed across the entire section of the channel at the sampling station and when all the tracer injected passes through the sampling cross-section. Dilution gauging is particularly suitable for turbulent rivers where other methods are difficult to apply, e.g. rock-strewn shallow rivers with steep slopes. The method may be used to calibrate other methods because dilution gauging involves absolute determinations of volumes and times and determinations of relative values of concentrations only. When calibrating other methods, the accuracy and cost of dilution gauging should be compatible with the device or structure under examination and for guidance on the correlation to be expected between results reference should be made to the relevant International Standards dealing with the other methods.