ISO 26906:2015

Overview

ISO 26906:2015 - Hydrometry - Fishpasses at flow measurement structures - provides guidance and requirements for integrating fishpasses with flow measurement structures (weirs, flumes and gauging installations). The standard identifies fishpass types with satisfactory hydrometric calibration data and sets out methods for computing combined discharges and associated measurement uncertainties. It also highlights the inherent trade‑off between the hydraulic uniformity needed for accurate flow gauging and the variable flow conditions that aid fish migration.

Key Topics and Technical Requirements

• Scope and principle
  • Specifies requirements for integration of fishpasses with flow gauging installations and the computational principles for combined flow.
• Installation requirements
  • Site selection, installation conditions, upstream/downstream channel considerations, separate channel options, maintenance and head measurement requirements.
• Fishpass-specific requirements
  • General guidelines for basic parameters, location and attraction flows, upstream and downstream entries/exits.
• Fishpass performance and types
  • Performance characteristics, calibration and discharge coefficient considerations for different fishpass designs including:
    • Larinier super‑active baffle fishpass (baffle sizes 75–150 mm)
    • Pool‑type fishpass with V‑shaped overfalls
    • Dutch pool and orifice fishpass
• Computation of discharge
  • Methods to compute flows through compound structures (flow through the fishpass plus the gauging structure) and procedures for modular and submerged conditions.
• Uncertainty analysis
  • Guidance on uncertainty sources, combining uncertainties, uncertainty in discharge coefficient and effective head, and preparing an uncertainty budget.
• Supporting material
  • Worked example, informative annex on measurement uncertainty, and performance guidance for hydrometric equipment.

Practical Applications and Users

ISO 26906:2015 is intended for professionals involved in the design, installation, operation and control of open‑channel flow measurement structures where fish passage must be preserved. Typical users include:

• Hydrometric and civil engineers designing gauging structures and fishpasses
• Water resource and river managers balancing measurement accuracy with ecological requirements
• Environmental and fisheries engineers assessing attraction flows and passage performance
• Regulatory authorities and consultants preparing compliant gauging installations

Practical outcomes include validated methods to compute total flow, documented calibration practices for select fishpass types, and clear procedures to quantify and reduce measurement uncertainty when fishpasses are present.

Related Standards

• ISO 772 - Hydrometry: vocabulary and symbols (terms used)
• ISO 14139 - Flow measurements in open channels using compound gauging structures

Keywords: ISO 26906, ISO 26906:2015, hydrometry, fishpass, flow measurement structures, flow gauging, discharge computation, measurement uncertainty, Larinier fishpass, pool‑type fishpass, Dutch pool and orifice.