Suspended Sediment characterization by Multifrequency Acoustics

Sediment transport, either in natural environment or in sewer systems is of main interest to understand river geomorphology or handle the wastewater regulation and treatment. Knowledge on Suspended Sediment Concentration (SSC) and size distribution leads to a better understanding of sediment transport dynamics. In a wide range of rivers and sewer networks, suspended solids often have a bimodal distribution composed of mineral particles with high diameters and organic matter with smaller sizes. Acoustics methods for the measurement of small-scale sediment processes in water have gained increasing interest over the past decades. Ultrasonic multi-frequency profilers allowing acoustic turbidity profiles measurements at high spatial and temporal resolution which can be linked to the particle presence. The present work will focus on the use of acoustic signals over a wide frequency range to evaluate suspensions with monodispersed sediment distribution and with bimodal distribution of known particle sizes and fractions. Investigations on simple models linking the acoustic signal interpretation and the SSC will be shown, as well as the interpretation of the concentration profile when the granulometric distribution of suspended sediment shows several modes (sand and clay). Results obtained on laboratory test bench will be shown, as well as progress on field measurements.