Presentation: 2025 ND EPSCoR Annual conference 

October 21, 2025, NDSU Memorial Union, Fargo, North Dakota

Influences of Ice Coverage on Secondary Flow Development in Natural Meandering Rivers

River ice is a common phenomenon in the northern hemisphere and significantly modifies channel hydrodynamics by imposing an additional boundary layer at the water surface. This study investigates the influence of ice coverage on the development of helical motion (secondary flow) in river bends. Field measurements were conducted on a bend of the Red River of the North in Fargo, ND, during winter conditions using an Acoustic Doppler Current Profiler (ADCP). Results indicate that from the bend apex through the downstream portion, secondary flow does not exhibit the expected well-developed outward near-surface motion. Instead, the presence of ice cover leads to undeveloped helical structures and frequent double-stacked circulations at the bend apex, features typically observed only in the transition zone between consecutive bends under open-water conditions. These findings suggest that the roughness associated with ice coverage inhibits the development of classical secondary flow patterns. Consequently, existing models of secondary flow are not directly applicable under ice-covered conditions, highlighting the need for new modeling approaches that explicitly incorporate ice effects. This work is supported by the grant NSF CAREER No. 2239799.