Suspended sediment measurements by hydro-acoustic multi-frequency echosounders

The suspended sediment concentration (SSC) in rivers is commonly indirectly estimated from optical turbidity measurements in one single point. Calibration based on regular sampling and laboratory analysis allows converting the optical turbidity into SSC. The regular sampling and laboratory analysis are time-consuming and expensive.

A hydro-acoustic multi-frequency approach has advantages as an alternative to optical turbidity measurements. Backscatter data collected with hydro-acoustic echosounders contains information on the suspended particles along an entire profile. The conversion of backscatter into SSCs from an acoustic single-frequency system, like most standard ADCPs are, requires knowledge on the characteristics of the suspended particles, in particular on their average size and the grain size distribution. These characteristics can be estimated by analysing water samples in the laboratory.

The present contribution reports measurements of the SSC along an entire profile with a multi-frequency system. The multi-frequency approach allows estimating the particle characteristics from the backscatter data. Hence, the conversion of backscatter into SSC does not require water samples and laboratory analysis anymore. The potential of the hydro-acoustic multi-frequency approach is illustrated with in-situ river measurements and laboratory experiments that cover a broad range of sediment concentrations and sediment characteristics.