Overview
ISO 19234:2024 - Hydrometry - Low cost baffles to aid fish passage on triangular profile gauging weirs specifies how to integrate low‑cost baffles (LCBs) on the downstream face of triangular‑profile gauging weirs. It applies to weirs operated in modular flow (critical depth) and covers both Crump weirs (ISO 4360) and flat‑V weirs (ISO 4377). The first edition (2024) replaces the 2016 technical report and adds guidance for flat‑V weirs and spreadsheet design tools available from ISO.
Key topics and technical requirements
- Scope and applicability: Integration of baffles on triangular profile weirs used for open‑channel flow gauging under modular flow conditions.
- Principles of operation: Baffles are arranged in horizontal rows with staggered gaps forming oblique low‑velocity flow paths that:
- reduce flow acceleration on the downstream slope,
- maintain greater local depth,
- spread energy dissipation and reduce intense hydraulic jumps,
- provide routes exploitable by a range of fish species.
- Design and placement: Guidance on baffle geometry, spacing, gap alignment (including reflections), and the location of the first baffle for both Crump and flat‑V weirs. Spreadsheet tools are provided for layout calculations.
- Materials and construction: Requirements and recommendations for baffle materials and low‑cost construction methods appropriate for gauging weirs.
- Limitations and suitability: Criteria for site selection, species suitability (e.g., anguillid, salmonid, coarse fish), and operational limits (plunging vs streaming flow conditions).
- Maintenance: Considerations for inspection, debris management and long‑term performance.
- Normative references and terminology: Uses ISO 772 (vocabulary), ISO 4360 and ISO 4377 as normative references.
Note: The document indicates the coefficient of discharge normally remains unchanged, though recalibration is optional when baffles are fitted.
Practical applications and users
ISO 19234 is practical for:
- hydrologists and flow‑measurement engineers designing or retrofitting gauging structures;
- environmental and fisheries engineers seeking low‑cost fish passage mitigation at existing weirs;
- water resources managers and regulators balancing accurate flow measurement with aquatic habitat connectivity;
- contractors and maintenance teams implementing baffle installations.
Typical uses include retrofitting Crump or flat‑V gauging weirs to reduce fish migration barriers without compromising flow gauging accuracy.
Related standards
For design tools and the full standard text, consult ISO 19234:2024 and the spreadsheet resources at: https://standards.iso.org/iso/19234//ed-1/en/