Experimental Exploration of Sediment Density Interactions

Sediment is typically modeled using a single density for the entire system, often silica. However, some systems contain a mixture of materials with densities that range from organic particles to heavy metals. If models do account for density, they treat the density-classes independently. This paper describes initial results from flume experiments with variable-density mixtures to explore interactions between density classes. We ran a series of tests in a 3’ wide by 75’ long flume with a light-colored silica (s.g. ~2.65) and a red garnet (s.g. ~3.6). The selected silica and garnet materials have similar angularity and gradation curves with a d50 of ~0.45mm (medium sand). We thoroughly mixed the materials in a bed and fed the same mixture into the upstream end of the flume during each run. We collected lidar scans to estimate final bed slope and bedform geometry. The stoss slope transported the denser particles while the lighter sand collected in the troughs. This paper presents the qualitative results of early experiments and the testable hypotheses about density-class interdependence that the rest of the study explored.