Quantified turbulent diffusion of suspended sediment using acoustic Doppler current profilers

Collocated profiles of the Reynolds stress tensor and eddy covariance fluxes are obtained to derive vertical profiles of turbulent momentum and sediment diffusivity in a tidal river, using coupled acoustic Doppler current profilers (ADCPs). Shear and normal stresses are obtained by combining the variances in radial velocities measured by the ADCP beams. The covariances between radial velocities and calibrated acoustic backscatter allow the determination of the three Cartesian components of the turbulent flux of suspended sediment. The main advantage of this new approach is that flow velocity and sediment concentration measurements are exactly collocated, and allowing for profiling over longer ranges, in comparison to existing techniques. Results show that vertical profiles of the inverse turbulent Prandtl-Schmidt number are coherent with corresponding profiles of the sediment diffusivity, rather than with profiles of the eddy viscosity.