Under ice cover roughness and flow structure.
Under ice cover roughness and flow structure.
Previously Published Material: Data were presented at the ACFAS meeting in Montréal in 2012. The presentation was in french.
Abstract ID#: 36782
English Abstract:
Quantifications of under ice roughness and flow structure under an ice cover are scarce but relevant to analyse the effects of ice cover on flow dynamics and to validate flow modelling. This paper documents the turbulent flow structure and the under ice cover roughness on two gravel-bed rivers. An ADV was used to measure twelve velocity profiles under various types of ice covers. A clear double turbulent boundary layer appears in most velocity profiles with an increase in turbulent intensity near the ice cover. Upstream from each velocity profile, the ice cover was subsequently exposed and scanned using a terrestrial laser to quantify the ice cover roughness. The under ice covers reveal great variability of forms that promote various scales of roughness. Forms are described and roughness is quantified by semivariance analysis. The under ice cover roughness affects the flow properties. The location where the highest velocity is found is further away from the ice cover when roughness is high, but the ice cover shear stress is not related with the under ice cover roughness. Scenarios describing the turbulence dynamics and structure of the boundary layer are proposed and discussed in the light of roughness conditions encountered in this study.