Ice-cover influence on near-field mixing in dune-bed channel: Numerical simulation

This paper presents the results of a numerical-simulation investigation of ice-cover influence on the mixing and transport of a neutrally buoyant cont aminant released in a straight reach of a dune-bed channel. The investigati on used a three-dimensional computational fluid dynamics model, validated a gainst flume data for flow distribution in the channel and against a simple analytical solution for mixing in the channel. The model was used to simul ate contaminant release near the ice-cover underside and near the bed. The results show that, for constant water discharge, cover presence reduces nea r-field mixing because it redistributes the Bow, increases flow depth, decr eases 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 Bow. The simulation shows that cover presence reduces the depth-averaged diffusivity to similar to 45% of the correspondi ng diffusivity for open-water Bow. The distance to attain full mixing acros s the flow depth increases by a commensurate amount.