Experiments on Entrainment of Tailings into Suspension in an Annular Flume

Sediment entrainment formulations developed for noncohesive materials have been widely applied to determine suspended loads in fluvial environments. Most relations were developed based on laboratory experiments and field measurements taken in sand-rich environments. Due to the accidental discharge of mine tailings in riverine systems, it is imperative to develop new approaches to predict sediment entrainment and resulting near-bed concentrations, as field observations show that the primary mode of transport for tailings once they are eroded is in suspension. Based on laboratory experiments conducted with poorly sorted iron tailings samples in an annular flume, we found that existing sand-based relations predict relatively well equilibrium near-bed concentrations when treated as well-sorted material. However, to predict entrainment rates into suspension for the tested poorly sorted iron tailings samples, sand-based entrainment relations require adding two functions accounting for the relative roughness of the bed material and the Reynolds particle number for the effect of viscous sublayer thickness on entraining fine grains. This innovative approach, combining dimensional analysis, similarity parameters, and experimental observations in an annular flume, provides a general framework for developing formulations to estimate the flow conditions necessary to entrain into suspension and then transport tailings either accidentally released into riverine environments or resuspended during dredging operations in watercourses.