On the Impacts of Ice Cover on Flow Profiles in a Bend

We investigate the impact of ice coverage on flow and bed shear stress profiles in a river bend. We perform field measurements using Acoustic Doppler Current Profiler in a bend of the Red River, North Dakota, the United States. Field campaigns were carried out under both open‐surface and ice‐covered conditions in 2020 and 2021. Our results show that the time‐averaged velocity profile follows closely the quartic solution (Guo et al., 2017, under full ice coverage. While the flow profile under open‐surface condition follows closely the logarithmic law near the bed, it is challenging to identify the logarithmic layers in our measured data under ice‐covered condition. Our results also show that the impact of ice coverage is most significant near both banks where the vertical velocity profile is modified significantly due to the interaction of turbulent flows with the ice cover. Our results suggest that the bend curvature and ice coverage both have significant impacts on the velocity profile as well as the distribution of the bed shear stresses. Our findings provide new insights on sediment transport processes of ice‐covered rivers, especially during the break‐up period when the surface coverage changes rapidly. Plain Language Summary As climate change continues, shorter winter is expected to result in a less number of ice‐covered days for natural streams. While ice cover has been linked to a variety of eco‐hydraulic issues, it is unclear on the relationship between ice coverage and changes in river hydrodynamics. Thus the understanding of ice‐covered flows has become a critical issue to predict morphological and ecological conditions of river flows in cold regions. This study aims to identify the impact of ice by conducting field‐scale observations and comparing with analytical models. Our results show that the ice layer alters flow patterns beneath it, which leads to active areas near banks. This new finding suggests that ice cover might play a significant role in sediment transport near banks in Spring when its extension can change sharply in a short amount of time. Key Points Under open‐surface condition, our data supports for the existence of the logarithmic layer near the river bed. Under ice‐covered condition, it is challenging to identify the existence of the logarithmic layers The ice cover alters the secondary flow pattern, and relocates the position of the main circulation Under ice‐covered condition, shear stresses are elevated near banks even at re