Abstract: Ice cover is a natural phenomenon commonly observed in winter rivers of northern regions. Its presence alters the river’s motion from turbulent to laminar flow, affecting the vertical velocity distribution due to the roughness of the ice cover and further influencing the sediment transport on riverbed. To investigate the evolution of sediment transport in glacial rivers, a formula for incipient velocity of coarse and fine sediment particles is deduced theoretically suitable for ice-covered flow based on the Einstein assumption by using a rolling starting model. The effects of roughness change under the ice cover, the dry density of viscous sediment, and the relative exposure degree on sediment incipient motion are considered. Comparison with existing experimental data manifests that the relative error of the proposed formula ranges from 1% to 10%. Additionally, the applicability of the incipient motion formula to open channel flow is discussed. The formula can be considered suitable for calculating sediment starting velocity in open channel flow when the roughness of the ice cover is 0. The relative error validated by measured data is between 0% and 0.86%, meeting the precision requirement.

Key words: ice-cover flow, roughness, relative exposure degree, sediment, incipient velocity