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Based on a series of experiments under both ice-covered and free surface conditions, the present article discusses the role of flow velocity and critical shear Reynolds number for incipient motion of bed material. The influence of the resistance coefficients of both the underside of the ice cover and the channel bed on the location of the maximum velocity has been discussed. In addition, the impacts of ice and composite resistance coefficients on flow velocity for incipient motion of bed material have been assessed. The diagram describing the critical shear Reynolds number and the dimensionless shear stress for the incipient motion of sediment under ice covered conditions with different under cover resistance coefficient has been established. The effects of grain size on densimetric Froude number for incipient motion of bed material have been investigated. A relationship between the densimetric Froude number for incipient motion of bed material and the median grain size of bed material as well as the roughness coefficient of channel bed and roughness coefficient of ice cover has been established.