Overview
ISO 9826:1992 specifies methods for measuring liquid flow in open channels using Parshall and SANIIRI flumes. The standard covers installation, selection, construction tolerances, measurement of head(s) and maintenance for steady or slowly varying flows - particularly in irrigation canals. Both flume types are designed to operate under free‑flow and submerged conditions and provide calibrated geometries for reliable discharge measurement.
Key topics and requirements
- Scope of use
- Designed for open‑channel flow measurement under steady or slowly varying conditions; commonly used in irrigation and hydraulic monitoring.
- Both free‑flow and submergence operation modes are considered.
- Flume types and operating ranges
- Parshall flumes: rectangular throat, level entrance floor, inclined throat floor and diverging exit. Throat widths range from very small to large; medium sizes (≈0.15–2.5 m throat) are recommended for discharges ~0.0015–4.0 m3/s; large Parshall flumes (~3–15 m) suit much higher discharges.
- SANIIRI flumes: level‑floored with a small downstream drop, rectangular cross‑section; exit widths typically 0.3–1.0 m and suited for ~0.03–2.0 m3/s.
- Selection criteria
- Choose flume type based on discharge range, available head, modular limit, maximum submergence ratio, channel geometry, allowable head loss, sediment load, portability needs and cost.
- Site and installation
- Approach channel must be straight and uniform; recommended approach length equal to 5–10 times water surface width at maximum flow.
- Maintain subcritical approach flow (Froude number criteria noted in the standard).
- Flume axis must align with flow; smooth internal surfaces (concrete, metal or other) and proper wing‑wall connections required.
- Construction tolerances and calibration
- The standard specifies tight dimensional tolerances for throat width, planarity and slopes to minimize measurement uncertainty. Flumes must be measured after construction and average dimensions used for calibration.
- Maintenance and head measurement
- Regular cleaning of approach, throat, float well and stilling devices is essential. Head measurement procedures refer to ISO 4373.
Applications and users
- Practical applications: irrigation canal monitoring, wastewater and drainage flow gauging, laboratory flume studies, and field flow metering where simple, robust devices are needed.
- Typical users: irrigation engineers, water resources managers, hydraulic laboratories, environmental monitoring agencies, and contractors who install or maintain open‑channel flow measurement structures.
Related standards
- ISO 4373 - water‑level measuring devices and stilling wells (referenced for head measurement).
- ISO 772 - vocabulary and symbols for liquid flow measurement in open channels.
Keywords: ISO 9826:1992, Parshall flume, SANIIRI flume, open channel flow measurement, irrigation canals, discharge measurement, flume installation, head measurement, flume calibration.
