Effects of freeze-up consolidation event surges on river hydraulics and ice dynamics on the Lower Dauphin River

Abstract

Abstract Ice cover formation in fast-moving rivers during freeze-up involves progression of the leading edge with intermittent collapses that cause rapid consolidation (mechanical thickening) of the ice cover and withdrawal of the leading edge downstream. The release of water from storage during these consolidation events causes a surge wave to travel downstream, resulting in an unsteady flow condition that briefly increases water levels and other concomitant hydraulic parameters that are difficult to measure directly such as discharge, velocity, and shear stress. In this study, the previously published Rising Limb Analysis Method (RLAM) was used to deduce the transient hydraulic properties at several monitoring sites on the Lower Dauphin River during the release of surge waves caused by freeze-up consolidation events in 2016–2017. It was found that parameters were most greatly amplified near the toe of the consolidated reach, and decayed in the downstream direction. On one occasion, computed discharge was found to be nearly three times the steady state discharge during the passage of a surge wave that caused water levels to rise by 0.93\u202fm in less than 10\u202fmin at one gauge location. The calculated consolidation stress applied to the ice cover during this event increased by 99\u202fPa; the peak stress was approximately 2.5 times the unperturbed value. Results of the RLAM application highlight the interdependent relationship between ice dynamics and unsteady flow hydraulics during freeze-up, and the importance of considering the effects of consolidation events when predicting the final ice thickness in fast-moving rivers.