Spreading and Mixing in Near-Field River Plumes

Abstract

Near-field plumes are supercritical, jet-like regions of rapid flow expansion and strong mixing. The characteristics of near-field river plumes are described based on our understanding from numerical ocean models and observations. A simple mathematical model is presented that demonstrates two competing processes within the plume: spreading, which tends to accelerate the flow in the plume, and mixing, which acts to retard the flow. The simple model is used to make statements about the energetics of the flow, and net dilution of water properties flowing through a near-field plume. Shortcomings of the model---including the effects of rotation, and the difficulties in specifying a turbulence closure---are outlined and discussed.