Experiments and modeling of density instabilities driven by interface shear and their influence on removal of sediment from buoyant plumes

This paper focuses on the development of the experimental and numerical methods needed to study sedimentation from buoyant river plumes under the elTects of shear instabilities. For the experiments, a layer of freshwater and flocculated kaolinite was run over clear saltwater in an acrylic flume. The setup was designed such that measurements could be made from the plume body under steadystate conditions and not just in the propagating plume head. Three-dimensional numerical modeling with Large Eddy Simulations (LES) was also carried out to reveal more detail of the plume dynamics. The primary objective of this paper is to present the methods associated with such experiments. In addition, we present the preliminary' findings from the experiment and numerical simulation that suggests that density instabilities and convective sedimentation may not exert strong enhancement on sedimentation rates in the plume body. In fact, the effective shear driven settling velocity extracted from the sediment concentration data was lower than the floc settling velocity observed in saltwater. This information implies that sedimentation from the plume was reduced from what would be expected by the product of local concentration with the particle or aggregate settling velocity. Further investigations are needed to better understand this process.