Overview
ISO 11657:2014 - Hydrometry - Suspended sediment in streams and canals - Determination of concentration by surrogate techniques specifies standardized methods for determining suspended-sediment concentration (SSC) and particle-size distributions using non‑sample surrogate techniques. The standard describes the operating principles, instrument types, measurement principles and limitations for optical and acoustic surrogates used in continuous monitoring of sediment in streams and canals.
Key topics and requirements
- Scope: Methods for estimating SSC and particle-size distribution by surrogate techniques (optical and acoustic) rather than direct grab or bottle sampling.
- Measuring principles:
- Transmission (attenuation of light through a sample; Beer’s Law)
- Scattering / Nephelometry (measuring scattered light, often at right angles - turbidity)
- Transmission–Scattering (combined approaches)
- Acoustic Backscatter (ABS) and acoustic attenuation techniques
- Laser Diffraction (LD) for particle-size analysis
- Properties of sediment: Guidance on how particle characteristics (size, shape, density, refractive index, colour) and bulk properties affect optical/acoustic responses and calibration.
- Instrumentation: Brief descriptions of available instruments and the operating principles for OBS (optical backscatter), nephelometers, laser diffraction sensors, and acoustic sensors.
- Calibration and validation: Emphasis on the need for site‑specific calibration, validation against physical samples and awareness of nonlinearity and sensitivity to particle size and colour. The standard notes laser-based sensors can reduce some errors.
- Annexes: Detailed methods and limitations are provided in Annex A, B and C (nephelometry/OBS, LD, ABS).
Applications and who uses it
ISO 11657:2014 is intended for professionals involved in river, canal and reservoir sediment monitoring, including:
- Hydrologists and sedimentologists monitoring sediment transport and fluxes
- Water‑resource and reservoir managers concerned with turbine safety and sediment-related maintenance
- Environmental and water‑quality engineers tracking suspended solids, stormwater runoff and long‑term sediment trends
- Operators of hydropower and drinking‑water systems requiring high‑temporal‑resolution SSC data
- Researchers developing automated monitoring networks and instrument vendors
Practical benefits include higher temporal resolution SSC records, reduced field labour and improved automation compared with conventional sampling - provided careful calibration and validation are performed.
Related standards and references
- ISO 772 - Hydrometry: Vocabulary and symbols
- ISO 4363 - Measurement of liquid flow in open channels; methods for suspended sediment
- ISO 13320:2009 - Particle size analysis - Laser diffraction methods
Keywords: ISO 11657:2014, suspended sediment, surrogate techniques, hydrometry, optical backscatter, nephelometry, laser diffraction, acoustic backscatter, suspended-sediment concentration, particle-size distribution.