Characteristics of Resuspension, Settling and Diffusion of Particulate Matter in a Water Column

Experiments were conducted in order to characterize the distributions of concentrations of suspended particulate matter (SPM) in water columns of lakes and reservoirs. The experiments, in a reduced model of the water column, used a set of oscillating grids. Runs were done with particles denser than water as well as with light particles. The results were in good agreement with analytical solutions for steady-state, and non-steady-state conditions. An approximate analytical solution was derived and found to be in agreement with the full solution. The threshold for resuspension was measured, and characterized in terms of a modified Shields parameter, which is appropriate to a zero-shear environment. All experiments showed that the distribution of SPM exhibited a layer near the bottom that is thought to be analogous to the benthic nepheloid layer (BNL) observed in larger lakes. The thickness of the nepheloid layer increases with the turbulence intensity.