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.
- requiring documented uncertainty for compliance and reporting.
