Ultrasonic sediment flux profiling with ACVP Technology: application to sediment-laden Boundary Layer flows

Sediment transport in geophysical boundary layer flows has relevance to a broad spectrum of sciences ranging from the physical and chemical, to the biological, ecological and geological. Advances in sediment transport modelling and prediction strongly suffer from lack of space and time-resolved sediment flux measurements due to sediment induced flow opacity hindering the utilization of standard optical flow measurement tools known as LDV, LDA, PIV or PTV technologies. This lack of highresolution measurements in sediment transport flows strongly limits the identification and quantification of the key boundary layer interaction processes between the (generally highly turbulent) fluid phase, the entrained sediment phase and the underlying flow bed, commonly defined as the dynamic sediment transport process triad [1]. The first part of this study describes the basic measurements principles and methods of (a) ultrasound 1D-2C/3C Doppler velocity profiling, (b) ultrasound spectrometry for sediment concentration profiling. The combination of these two methods into the multi-frequency measurement system as the Acoustic Concentration & Velocity Profiler (ACVP) technology, provides time-resolved profiles of multi-component sediment fluxes across both the suspension and bedload layers at rates resolving small turbulent flow scales. Its application to mean and time-resolved flow quantity measurements is shown in sediment-laden open-channel flow experiments carried out in the LEGI tilting flume facility. Measurement uncertainty in net sediment transport rate is quantified over a wide range of open-channel flow conditions for two sediment sizes.