Modelling shear stress distribution in ice-covered streams

Abstract

Distribution of bed shear stress is the critical factor in regulating the meandering of single-thread rivers. However, the impact of the 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 are carried out in a river reach of the Red River in Fargo, North Dakota. Data monitoring is completed using Acoustic Doppler Current Profiler (ADCP), to obtain time-averaged velocity profiles. Our theoretical model indicates that 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 the 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 long-term morphodynamic evolution of meandering rivers seasonally covered by ice.