Overview
ISO 13550:2002 - "Hydrometric determinations - Flow measurements in open channels using structures - Use of vertical underflow gates" specifies methods for determining discharge in open channels under steady-flow conditions using vertical underflow gates installed on a flat horizontal floor between vertical side walls. The standard covers both modular and non‑modular conditions and is intended to support the development of reliable stage–discharge relations for existing installations and to guide design features for new structures.
Key topics and requirements
- Scope and definitions: Clear definitions (e.g., vertical underflow gate) and use of SI units for hydrometric determinations.
- Site selection: Requirements for approach channel geometry, flow velocity distribution, sediment and debris control, bank stability, seepage control and fish passage considerations.
- Installation conditions: Tolerances for channel width, bottom flatness and gate edge alignment; requirements for rigid, watertight construction and smooth finishes (e.g., concrete sill and sidewalls).
- Approach and downstream channels: Minimum straight lengths, disturbance limits, and criteria distinguishing modular vs non‑modular operation.
- Measurement of head: Preferred methods (hook, point or staff gauges; float-operated or pressure-sensing gauges) and recommendation to measure heads in separate stilling wells.
- Operational guidance: Gate operation, maintenance, and measures to avoid changes that affect discharge characteristics.
- Discharge relationships and uncertainty: Treatment of two‑ and three‑dimensional flow regimes, limits of application, computation examples and guidance on uncertainty evaluation and presentation of results.
Practical applications
ISO 13550 is used to:
- Establish or improve stage–discharge rating curves at gauging stations with vertical underflow gates.
- Provide design and installation guidance when adding gates to irrigation canals, drainage channels, wastewater outfalls, or stream gauging sites.
- Support routine monitoring, quality assurance and uncertainty evaluation in hydrometric measurements.
- Inform calibration strategies where higher accuracy is required (actual discharge calibration recommended).
Who uses this standard
- Hydrologists and river gauging technicians
- Water resources and hydraulic engineers
- Infrastructure and irrigation authorities
- Environmental monitoring agencies and consultants
- Asset owners responsible for flow monitoring and compliance
Related standards
Normative references cited in ISO 13550 include:
- ISO 772 (vocabulary and symbols for hydrometric determinations)
- ISO 4373 (water-level measuring devices)
- ISO/TR 5168 (evaluation of uncertainties in fluid flow measurement)
Using ISO 13550 helps ensure consistent, defensible flow measurements where vertical underflow gates are the measuring structure of choice.