The existence of river ice has a significant role in flow characteristics during the winter and spring seasons. From the onset of freeze-up until the ice cover melts, river ice alters the flow structures, resulting in severe consequences such as ice jams, ice dams, and flash floods in spring. Nonetheless, the hydraulic and hydrologic mechanisms of river ice remain largely unknown due to difficulties of the field scale studies in severe winter seasons. In this work, the impacts of the ice cover on the vertical and cross-sectional velocity profile, secondary flow patterns, and shear velocity are investigated using analytical methods and fieldwork observations as well as the state-of-the-art computational fluid dynamics (large-eddy simulation) model. Results show the presence of river ice alters the secondary flow patterns and may induce double circulation in the thalweg area of natural cross-sections or near vertical channel walls of artificial channels/flumes. Results also indicate that the lateral distribution of the shear velocity is differentiated from the open surface condition as the high shear velocity can be observed near the inner and outer banks in ice-covered conditions. In this work, a numerical method is also developed to estimate the depth-averaged velocity profile based on the cross-section geometry. Model results demonstrate that the numerical method can accurately capture the velocity profile in irregular cross-sections based on fieldwork observations. This method helps to minimize the fieldwork efforts during the winter seasons. The future work will focus on the combined impact of the ice cover and the channel curvature (river bend) on the three-dimensional flow structures under different scenarios including the transitional stage. This work provides insights into the transient dynamics of flows during the freeze-up and breakup periods.