Ice-Cover Influence on Near-Field Mixing in Dune-Bed Channel: Numerical Simulation

Abstract

This paper presents the results of a numerical-simulation investigation of ice-cover influence on the mixing and transport of a neutrally buoyant contaminant released in a straight reach of a dune-bed channel. The investigation used a three-dimensional computational fluid dynamics model, validated against flume data for flow distribution in the channel and against a simple analytical solution for mixing in the channel. The model was used to simulate contaminant release near the ice-cover underside and near the bed. The results show that, for constant water discharge, cover presence reduces near-field mixing because it redistributes the flow, increases flow depth, decreases bulk velocity, reduces maximum level of turbulence, and modifies dune geometry. For the ice-covered flow, a contaminant released near the bed or near the cover underside remains closer to those boundaries over a longer distance than for open-water flow. The simulation shows that cover presence reduces the depth-averaged diffusivity to ∼45% of the corresponding diffusivity for open-water flow. The distance to attain full mixing across the flow depth increases by a commensurate amount.