Dynamics of Particle Clouds in Ambient Currents with Application to Open-Water Sediment Disposal

Abstract

Flow visualization experiments were performed in a glass-walled recirculating flume to observe the fate of sediments released instantaneously in a current. For releases at the surface, criteria were developed to characterize ambient currents as “weak,” “transitional,” or “strong” as a function of particle size. In weak ambient currents, particle clouds were advected downstream with a velocity equal to the ambient current, but otherwise their behavior and structure were similar to those in quiescent conditions. A substantial portion of the mass initially released, up to 30%, was not incorporated into the parent cloud and formed the trailing stem. This percentage was dependent on the initial release variables, with the greatest sensitivity on particle size. The “loss” of sediment during descent, defined as the fraction of mass missing a designated target with a radius equal to the water depth, was quantified and found to increase sharply with current speed. Laws of geometric, kinematic, and dynamic similitude provide a basis for scaling laboratory results to the real world and formulating guidelines to reduce the losses that could result from open-water sediment disposal.