Overview
EN ISO 25377:2022 - Hydrometric uncertainty guidance (HUG) provides practical guidance for understanding, estimating and reporting measurement uncertainty in hydrometry. Endorsed by CEN and identical to ISO 25377:2020, this standard focuses on flow measurements in natural and man-made channels (open-channel flow and structures). It clarifies the nature of random and systematic effects and explains how to quantify the “quality” of a hydrometric measurement. Rainfall measurements are excluded.
Key topics
- Foundations and GUM linkage: aligns with ISO/IEC Guide 98-3 (the GUM) for basic definitions, probability distributions and rules for uncertainty evaluation.
- Uncertainty modelling: treatment of random and systematic effects, combining uncertainties, and expressing results (including propagation of uncertainty).
- Open-channel flow methods: detailed guidance for velocity–area methods (mean velocity, velocity measurement, integration and perimeter flow uncertainties) and critical-depth methods (head, geometry and iterative calculations).
- Dilution and tracer methods: continuous feed and transient mass approaches for discharge estimation.
- Instrumentation and performance: performance specifications, evaluation of manufacturer claims, and a performance guide for hydrometric equipment.
- Practical tools and annexes: worked examples, Monte Carlo Simulation (MCS), Interpolated Variance Estimation (IVE), stage–discharge uncertainty analysis and velocity measurement guidance.
- Standards drafting: guidance for writing uncertainty clauses in hydrometric technical standards.
Applications
EN ISO 25377 is designed for professionals who need rigorous, transparent uncertainty estimates for flow and discharge measurements:
- Hydrologists and water-resource managers assessing monitoring network data quality.
- Gauging-station operators calculating uncertainty for routine discharge measurements.
- Environmental and regulatory bodies requiring documented uncertainty for compliance and reporting.
- Consultants and engineering firms performing flow measurements for design, licensing or flood-risk studies.
- Instrument manufacturers and testing laboratories validating performance claims.
- Standards developers and researchers implementing uncertainty methods (including Monte Carlo approaches).
Practical uses include calibrating rating curves (stage–discharge relations), verifying measurement systems, informing flood forecasting models, water allocation decisions, and compiling defensible monitoring reports.
Related standards
- ISO/IEC Guide 98-3 (GUM) - Evaluation of measurement uncertainty
- ISO 25377:2020 (original international text) - adopted as EN ISO 25377:2022 by CEN
Keywords: hydrometric uncertainty, HUG, ISO 25377, EN ISO 25377:2022, flow measurement, open channel flow, velocity–area method, Monte Carlo simulation, stage–discharge uncertainty.
