The suspension of sediment particles by turbulent eddy diffusion in a non- uniform flow region was studied, using the convective-diffusion equation as a mathematical model. A simplified form of the equation for which mixing characteristics and flow velocities 'vere assumed uniform was found to accurately describe the sediment concentration profiles which had been measured in a 24-foot long flume. The experiments also showed that turbulent mixing was more uniform than predicted by existing theories, and that it depended on the geometric characteristics of the mobile, wavy bed. Although diffusivities in the non- uniform region tended towards uniformity with downstream distance the vertical diffusive transport rate was related to depth as a power law function. An expression with analytic support was derived for the diffusion coefficients as functions of sediment and hydraulic variables.