Lateral Momentum Transfer in Ice‐Covered Rivers

Abstract Ice cover alters river hydrodynamics by introducing surface roughness. This roughness modifies momentum redistribution and bed shear stress. Using theoretical arguments, we present an approach for the lateral momentum load in ice‐covered streams. This approach is derived from the depth‐integrated Reynolds‐Averaged Navier–Stokes equations. Field measurements were conducted during the winters of 2022–2025 in a meandering reach of the Red River of the North (Fargo, ND, USA). We used an Acoustic Doppler Current Profiler (ADCP) to obtain time‐ and depth‐averaged velocities across three cross‐sections. Results show that secondary flows and Reynolds stresses both contribute to the lateral momentum load. Also, the ice cover suppresses the development of coherent secondary cells. A term‐by‐term analysis of streamwise momentum budget demonstrates that lateral gradients of momentum load are closely tied to variations in bed shear stress, highlighting the coupling between momentum load and near‐bed dynamics. The resulting momentum balance yields three depth‐averaged velocity and shear stress models for ice‐covered rivers. All models require minimal parameterization and provide practical tools for monitoring and predicting flow profiles under ice conditions.