ISO 4359:2022

Overview - What ISO 4359:2022 covers

ISO 4359:2022, "Flow measurement structures - Rectangular, trapezoidal and U-shaped flumes", specifies standardized methods for measuring flow in rivers and artificial channels using selected types of critical‑depth (standing‑wave) flumes. The standard applies where flow is steady or slowly varying, with subcritical approach flow that accelerates through a contraction to reach critical depth in the flume throat. It covers three widely used geometries: rectangular‑throated, trapezoidal‑throated and U‑throated (round‑bottomed) flumes. The document excludes Venturi‑type flumes in which flow remains subcritical.

Key technical topics and requirements

• Flume types & hydraulic principles: definitions and operating principles for rectangular, trapezoidal and U‑shaped critical‑depth flumes.
• Installation and site selection: guidelines on approach channel, structure requirements and downstream conditions so downstream water level does not affect flume performance.
• Head measurement: recommended locations for gauging upstream head, gauge wells, and zero‑setting procedures.
• Discharge computation: general formulae, coefficient methods and stage–discharge relationship calculations, including treatment of approach velocity and velocity coefficients.
• Size and shape selection: criteria for choosing flume geometry and dimensions appropriate to the expected flow range.
• Maintenance and operation: practical advice to preserve measurement accuracy over time.
• Measurement uncertainty: methods to estimate and combine uncertainties of discharge, with example calculations and uncertainty budgets.
• Supporting material: informative annexes providing simplified head–discharge curves, an introduction to uncertainty, sample performance data, and spreadsheets for practical use.

Practical applications and who uses this standard

ISO 4359:2022 is essential for professionals involved in open‑channel flow measurement and hydrometry:

• Hydrologists and water resources engineers measuring river flows and canal discharges.
• Irrigation and drainage managers monitoring channel deliveries and return flows.
• Environmental agencies and regulators requiring standardized flow data for compliance and reporting.
• Design and civil engineering consultants specifying gauging structures for monitoring networks.
• Manufacturers and installers of flumes and gauging equipment ensuring conformity and interchangeability.

Using ISO 4359 helps achieve reliable, reproducible stage–discharge measurements without in‑situ calibration for accepted flume types, and supports traceable uncertainty estimation for water accounting, flood studies, and operational control.

Related standards

• ISO 772 (Hydrometry - Vocabulary and symbols) is cited for terms and definitions.
• Prepared by ISO/TC 113 (Hydrometry) - consult national standards bodies for implementation and national adoption details.