Overview - ISO 9555-1:1994 (Measurement of liquid flow in open channels)
ISO 9555-1 defines the general principles for using tracer dilution methods to measure steady flow in open channels. It covers the two fundamental approaches - the constant rate injection method and the sudden (integration) injection method - and sets out the core principles of injection, sampling and analysis that apply regardless of tracer type. The standard stresses that tracer choice and concentrations must comply with national regulations and health guidance (e.g., WHO guidelines) for occasional short-duration discharges to natural waters.
Keywords: ISO 9555-1, tracer dilution methods, open channels, flow measurement, constant rate injection, sudden injection
Key topics and technical requirements
- Methods described
- Constant rate injection: continuous tracer injection until a steady concentration plateau is reached downstream; discharge derived from injection rate and plateau dilution.
- Sudden (integration) injection: single known volume of tracer injected quickly; discharge calculated from integrated tracer mass passing a downstream section.
- Injection and equipment
- Equipment types referenced (e.g., Mariotte vessel, floating siphon) for achieving constant injection rates.
- Preparation of injection solution and measurement of injection rate.
- Sampling and analysis
- Location and selection of sampling cross-section (sampling station), sample timing, number of samples and analytical considerations.
- Treatment of background concentration and calculation of concentration of added tracer.
- Mixing and site selection
- Concepts of mixing length, degree of mixing, and transverse mixing coefficients to ensure representative dilution before sampling.
- Selection of measuring reach and need for preliminary tests.
- Calculations and uncertainty
- General formulae for discharge estimation, direct determination of dilution factor, and procedures for estimating systematic and random uncertainties.
- Annexes
- Practical aids (standard dilution procedures, microburette ranges, variance tests) and bibliography.
Applications and users
ISO 9555-1 is used by:
- Hydrologists and field technicians conducting stream and river discharge measurements
- Environmental and water resources engineers measuring flows in irrigation channels, drainage ditches and small rivers
- Laboratories and consultants performing tracer-based gauging where conventional devices are impractical (e.g., during floods)
- Regulatory bodies and researchers needing standardized procedures for flow gauging, calibration of hydraulic models, and impact assessments
Practical benefits include safer gauging during high flows, methods adaptable to different tracer types, and standardized approaches for sampling and uncertainty estimation.
Related standards
- ISO 9555-2: Radioactive tracers (specific analytical procedures)
- ISO 9555-3: Chemical tracers
- ISO 9555-4: Fluorescent tracers
- ISO 772: Vocabulary and symbols for liquid flow measurement in open channels
ISO 9555-1 serves as the general framework; refer to the tracer-specific parts for analytical details and regulatory compliance.
