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Abstract Impact of ice coverage is significant in controlling the depth-averaged velocity profile and influencing morphological processes in alluvial channels. However, this impact is largely unknown under field conditions. In this work, a numerical method is introduced to compute the depth-averaged velocity profile in irregular cross-sections of ice-covered flows, based on the Shiono-Knight approach. The momentum equation is modified to account for the presence of secondary flows and the ice coverage. The equations are discretized and solved with velocity boundary conditions at the bank and at one vertical. Our approach only requires the cross-section geometry and a single velocity measurement near the high-velocity region, offering a significant advantage in inaccessible locations by avoiding the need to measure the velocity profile in the entire cross-section. The proposed model is then validated using depth-averaged velocity profile and secondary flow patterns from laboratory observations, analytical solution, and Large-Eddy Simulation. Finally, the method is applied to infer depth-averaged velocity profiles in the Red River of the North, United States, to test its performance in meandering sections. The proposed method demonstrates its robustness in reconstructing flow profiles in ice-covered conditions with a minimal amount of available data, which is crucial for assessing erosion risks and managing spring floods in cold regions. 

Abstract Distribution of bed shear stress is the critical factor in regulating the meandering of single-thread rivers. However, the impact of ice cover on bed shear stress is largely unknown. In this study, we develop a theoretical model of cross-stream momentum balance to examine the distribution of bed shear stresses in ice-covered meandering rivers. To validate the theoretical model, field surveys were carried out in a river reach of the Red River in Fargo, North Dakota. Data monitoring was completed using an Acoustic Doppler Current Profiler to obtain time-averaged velocity profiles. Our theoretical model indicates that an ice covering develops high-shear zones near both the inner and outer banks, which might exacerbate sediment transport and enhance bank erosion. Velocity measurements confirm the results of the proposed model and demonstrate a clear impact of meandering river banks on velocity profiles and secondary flow patterns under ice cover. Based on our results, we hypothesize that ice cover increases turbulent stresses near banks, which in turn lead to the enhancement of the bed shear stress. Our work provides new insights into the impact of ice cover on bed shear stress distribution, which could play an important role in driving sediment-transport processes and the long-term morphodynamic evolution of meandering rivers seasonally covered by ice.