Effect of Mixing on Suspended Particle-Size Distribution

Experiments were performed to evaluate changes in suspended particle-size distribution as a function of variations in mixing conditions. Suspensions were taken from Lake Erie near Buffalo, N.Y., and mixed in a standard jar apparatus using six different mixing intensities. These suspensions were monitored for changes in particle size and shape using a noninvasive image analysis technique. A relationship was derived between suspended particle size and mixing intensity, based on estimates of energy dissipation rates. The regression was also compared with mixing of suspensions taken from two other systems in the Buffalo, N.Y. area, a small lake on the University at Buffalo campus, and the Buffalo River (Buffalo, N.Y.). Samples from all three sites behaved similarly in terms of particle size as a function of mixing conditions. Estimates for dissipation rates in natural systems were then used to relate the laboratory data to field conditions. Dissipation rates produced at slow mixing speeds in the jar were similar to those calculated for more energetic riverine and estuarine environments. Results of this study should be useful for understanding suspended particle-size distributions under a variety of mixing conditions, and is of direct interest in a wide range of sediment and contaminant transport problems.