Laboratory validation of ADCP techniques for suspended sediments investigation

The aim of this paper is to validate a method of investigating the grain size distribution of suspended sediments using acoustic Doppler current profilers (ADCPs) and to compare different calibration strategies of the ADCP backscattering power, which can be correlated with the concentration of corresponding sediments. Over the last two decades, the methods for suspended sediment investigation using the backscattering power of ADCPs have been gaining increasing acceptance within the river engineering community. This acceptance is due to acoustic backscattering providing the opportunity to indirectly quantify suspended sediment by non-intrusive measurements with high temporal and spatial resolution. We have already presented the method using two ADCPs working at different frequencies (600 and 1200 kHz) on the same water column to profile the concentration and grain size in the Paraná River (Argentina). The present work, as a complement to the Paraná application, demonstrates the reliability of the method by a laboratory validation of monitored concentrations and known grain size distributions. The context of our research is introduced in a discussion of the topic of river sediment transport measurement using ADCPs. Then, the underwater acoustic physics is briefly presented with a focus on acoustic backscattering (ABS) methods for the estimation of suspended sediment grain size. The laboratory tests, which were conducted at the sediment tower-mixing facility using four different known distributions of sand in the range 50-700μm, are described in detail to demonstrate the reliability of the ABS methods and to justify the adopted experimental strategies to overcome undesired air bubble interference with the ABS due to injected sand.