Vertical Sorting of Graded Sediments by Waves and Currents

To verify the diffusion concept for the description of time-averaged sediment concentration profiles in a fractional approach, suspended sediment concentrations and grain size distributions were measured for the same hydraulic conditions, using a `uniform' (D90/D10 approx. 2) and a graded (D90/D10 approx. 5) type of sediment. From the measurements, it was found that suspended sediment concentrations are larger for the graded sediment. Further, a very strong vertical sorting was measured close to the bed, especially for the graded sediment. Finally, it was found that the time-averaged sediment concentrations and the grain size distributions (including the strong vertical sorting) of the suspended sediment are described well, using the diffusion concept.