ISO 18365:2013

Overview

ISO 18365:2013 - "Hydrometry - Selection, establishment and operation of a gauging station" provides international requirements and guidance for siting, installing, operating and maintaining gauging stations used to measure stage (water level) and discharge (flow) in lakes, reservoirs, rivers, canals and other open channels. The standard covers stage-only gauges, stage–discharge installations (including those with hydraulic structures), direct/discrete discharge measurement in natural channels, velocity-discharge methods, and special procedures for difficult conditions such as ice.

ISO 18365 replaces ISO 1100‑1:1996 and ISO/TR 8363:1997, and references related documents such as ISO 772 (vocabulary) and ISO 4373 (level-measuring methods).

Key topics and technical requirements

• Preliminary requirements and constraints: Define measurement ranges, allowable uncertainty, data timeliness, budget, life expectancy, access and permits, and stakeholder needs prior to station establishment.
• Site selection: Use maps, aerial imagery and ground reconnaissance to evaluate hydraulic uniformity, bed stability, accessibility, power and telemetry availability, and future modifications (bridges, dams).
• Stage (water level) measurement: Guidance on staff gauges, ramp/inclined gauges and wire/tape weight gauges. Materials should have low thermal expansion; staff gauges typically use 5 or 10 mm graduations.
• Stage recording: Options from manual readings to continuous digital logging and telemetry; recommendation to use redundant measurement systems to reduce data loss.
• Stage–discharge gauging: Requirements for establishing reliable stage–discharge relationships, including selection of control reaches and use of hydraulic structures when appropriate.
• Velocity–discharge methods: Site selection, instrument types (ADCP, Doppler, acoustic transit-time, electromagnetic), calibration considerations and full-channel velocity measurement techniques.
• Difficult measurement conditions: Procedures and special considerations for ice, aquatic weed growth, extreme sedimentation and other challenging environments.
• Operation & maintenance: Inspection, calibration, benchmark checks, and maintenance routines to ensure long-term data quality.

Practical applications and users

ISO 18365 is essential for professionals and organizations involved in:

• Hydrology and water resources management
• River and reservoir monitoring
• Flood forecasting and early warning systems
• Dam and hydraulic infrastructure operation
• Environmental monitoring and research
• Consulting engineers and instrumentation suppliers

Adoption of ISO 18365 helps ensure consistent, comparable, and quality-assured hydrometric data for decision-making and regulatory compliance.

Related standards

• ISO 772 - Hydrometry: Vocabulary and symbols (normative reference)
• ISO 4373 - Level-measuring methods (referenced for stage recording)
• Previous publications replaced: ISO 1100‑1:1996 and ISO/TR 8363:1997

Keywords: ISO 18365, hydrometry, gauging station, stage-discharge, flow measurement, water level monitoring, velocity-discharge, gauging station operation, hydrometric standards.