Overview
ISO 1438:2017 - Hydrometry - Open channel flow measurement using thin-plate weirs specifies requirements and best practices for measuring flow of clear water in open channels using thin‑plate weirs. The standard covers both rectangular and triangular (V‑notch) thin‑plate weirs under free‑flow conditions and includes provisions for full‑width rectangular weirs in submerged (drowned) flow. It defines installation, head measurement, discharge formulae, uncertainty evaluation and maintenance needed to achieve reliable flow gauging.
Key Topics and Technical Requirements
- Scope and principle: Discharge depends on upstream head, geometry of the weir and approach channel, and an experimentally determined discharge coefficient (C).
- Installation requirements: Site selection, approach channel and downstream conditions, stilling or float well design, and flow straightener guidance to ensure valid hydraulic conditions.
- Head measurement: Specifications for head‑measuring devices, head‑measurement sections, determination of gauge zero, and placement distance upstream of the crest.
- Weir specifications:
- Rectangular thin‑plate weirs - standard and full‑width forms, installation details, and practical limits.
- Triangular (V‑notch) thin‑plate weirs - notch angle, installation and head‑measurement rules.
- Discharge formulae: Includes established empirical formulae such as Kindsvater–Carter (rectangular) and Kindsvater–Shen (triangular) approaches, with guidance for evaluating coefficients and applicable ranges.
- Submerged flow: Requirements and correction factors for drowning/submergence effects on full‑width rectangular weirs.
- Uncertainty and accuracy: Methods to quantify measurement uncertainty, combine component uncertainties (instrumentation, geometric, coefficient), and sample uncertainty budgets.
- Maintenance and verification: Regular inspection, cleaning, and calibration procedures to maintain measurement integrity.
- Annexes: Informative and normative annexes on small weir tanks, flow straightener design, and introductory guidance on measurement uncertainty.
Applications and Practical Value
ISO 1438:2017 is applicable to:
- River and stream gauging stations using thin‑plate weirs
- Irrigation channel flow measurement and water distribution networks
- Environmental monitoring and regulatory compliance where accurate open‑channel flow data are required
- Laboratory and field calibration of flow instrumentation
Practical benefits include standardized installation guidance, improved comparability of discharge data, and a clear framework for calculating discharge and reporting uncertainty.
Who Should Use This Standard
- Hydrologists and water resource engineers
- River basin and water quality agencies
- Hydrometric laboratories and field technicians
- Instrumentation manufacturers and calibration service providers
- Consultants and researchers involved in open‑channel flow measurement
Related Standards
- Normative reference: ISO 772 (Hydrometry - Vocabulary and symbols)
- Developed by ISO/TC 113 (Hydrometry), Subcommittee SC 2 (Flow measurement structures)
Keywords: ISO 1438:2017, hydrometry, thin‑plate weirs, open channel flow measurement, rectangular weir, V‑notch weir, discharge coefficient, head measurement, submerged flow, flow gauging, measurement uncertainty.