Impacts of ice coverage on velocity profiles in a bend

Hydrodynamics of river ice plays an important role in morphological dynamics not only in winter but also during spring flood. It is a challenging problem due to signal interference during field measurements because of low temperature and surface access issues. In this work, we investigate the impact of ice coverage on the variation of velocity profile and its associated shear velocity in a river bend of the Red River in Fargo, North Dakota, using both field measurement and numerical simulation. Acoustic Doppler Current Profiler (ADCP), Sontek M9, is employed in fixed-vessel deployment mode under ice-covered (Feb/2021) and open surface (Oct/2020 and Jun/2021) conditions. Large-Eddy Simulation is performed to determine the three-dimensional flow structures using the input data from the United States Geological Survey and North Dakota Water Commission. Under ice-covered and open-surface conditions, our results show a similar pattern of velocity magnitude distribution across the cross-sections with a maximum velocity (Umax) near the outer bank. However, our results show that the ice coverage alters drastically the secondary flows in the bend, especially in regions near both banks. Under open-surface condition, a single circulation is found in the measured cross-section whereas a more complex flow structure is observed under ice coverage (clockwise and counterclockwise directions). The shear velocity distribution (ub) in the bed layer is derived from both the traditional logarithmic law and the quartic solution. Under open-surface condition, the peak value of ub exists close to the center of circulations. However, the magnitude of ub is increased drastically in both banks under ice coverage. Our results suggest that ice coverage might induce complex flow structures near banks and increase local bed shear stress. Therefore, ice coverage could play an important role in regulating sediment transport during spring flood. This work is supported by ND EPSCoR Office, ND Water Resources Research Institute and a grant from ESIP Lab with support from NASA, NOAA and USGS.