Ice-cover influence on flow structure over dunes

Laser-Doppler-velocimetry mappings of open-water and covered dune-bed flows show how cover presence and roughness influence overall channel resistance and flow structure, including turbulence quantities. The mappings show that skin friction along the upstream slope of dunes does not decrease, and may even increase initially, in response to cover presence and increasing cover roughness. Such an increase may be the immediate mechanism whereby an ice cover causes dunes to flatten. The mappings also show that dunes modify distributions of velocity and Reynolds stress from their flat-bed shapes to the extent that the two-layer hypothesis (which suggests ice-covered flows can be treated as a sandwich of two free surface flows) for analysis of ice covered flow is not accurate for dune-bed channels.