Overview - ISO 9825:2005 (Hydrometry - Field measurement of discharge in large rivers and rivers in flood)
ISO 9825:2005 provides guidance for the field measurement of river discharge specifically in large rivers and rivers in flood. The standard addresses direct and indirect measurement methods, practical difficulties encountered at large scale (width, depth, high velocity, debris and turbulence), and the logistical and safety issues unique to flood conditions. Measurements and reporting use SI units and reference a suite of complementary ISO hydrometry standards.
Key topics and technical requirements
- Scope and purpose: Focus on discharge measurement techniques that are appropriate or require modification for large rivers and flood flows.
- Measurement challenges: Problems of scale (great width, great depth, high velocity), position fixing, and sampling accuracy under turbulent conditions.
- Primary methods covered:
- Velocity–area methods (current-meter from bridge, cableway or boat; moving-boat technique)
- Acoustic Doppler methods (ADCP/ADP profilers deployed from powerboats; internal compass and bottom-tracking; multi-beam velocity sampling)
- Tracer dilution techniques (for special circumstances; see ISO 9555 series)
- Weirs and flumes and other engineered structures where applicable
- Indirect methods when direct measurement is impractical (see ISO 1070)
- Operational guidance: Use of cableways for rivers up to ~500 m (trolley deployments), combined cable/boat approaches for 500 m–1 km, and position-fixing/advanced survey equipment for very wide sections. Emphasis on planning, crew safety, and use of multiple teams to reduce measurement time.
- Normative references and units: Cross-referenced to ISO 748, ISO 6416, ISO 6420, ISO 9555, ISO 1438‑1 and others; SI units mandated.
Applications - who uses ISO 9825:2005 and why
- Hydrologists and hydrometric technicians conducting field discharge surveys on large rivers and during flood events.
- Water resource and flood-risk engineers needing reliable discharge data for modelling, design and emergency response.
- Environmental agencies, utilities and researchers requiring standardized measurement practice for monitoring, compliance and data interoperability.
Benefits include improved measurement consistency, enhanced safety and clearer selection criteria for methods (current-meter, moving-boat, acoustic Doppler, tracer techniques, weirs/flumes) under extreme or large-scale river conditions.
Related standards
Relevant ISO standards referenced by ISO 9825:2005 include:
Keywords: ISO 9825:2005, hydrometry, field measurement of discharge, large rivers, flood flow measurement, acoustic Doppler, current-meter, moving-boat, tracer dilution, weirs and flumes.