Velocity profiles and incipient motion of frazil particles under ice cover

A series of experiments for the incipient motion of frazil particles under ice cover have been carried out in laboratory under different flow and boundary conditions. Measurements on flow velocities across the measuring cross-section at different water depths have been conducted. Based on these experiments under both ice-covered and open flow conditions, the impacts of solid boundary (such as ice cover and flume sidewall) on the distribution of flow velocity profiles have been discussed. The criteria for the incipient motion of frazil particles under both smooth covered and rough covered conditions have been investigated. The influence of the roughness of ice cover has been assessed. The relation between shear Reynolds number and dimensionless shear stress for incipient motion of frazil particles under ice cover have been established compared with the incipient motion of sediment particles under ice covered condition. A diagram describing the relationship between critical shear Reynolds number and dimensionless shear stress for incipient motion of frazil particle under both smooth covered and rough covered conditions has been established. Additionally, it is found that the steeper the slope of ice cover is, the greater the critical shear stress for incipient motion of frazil particles becomes. However, the steeper the riverbed slope, the less the critical shear stress for incipient motion of river sediment.