Multi-day anchor ice cycles and bedload transport in a gravel-bed stream

Abstract

Summary River dynamics in cold regions and the physical processes involving ice formation and release remain relatively understudied topics. Current research suggests that anchor ice forms in diurnal cycles and has the potential to move sediments when released from the bed. Given the importance of river ice dynamics, studies are needed to describe the physical processes of anchor ice and its impact on sediment transport. The study presented in this paper investigated in situ anchor ice formation on the Stoke River in Quebec, Canada. In the fall of 2012, we observed multi-day anchor ice formation cycles and release, which usually ended with a small runoff event. During a cycle, there was little or no release of anchor ice, thus allowing its gradual growth as the air temperature remained cold. Surface and anchor ice layers also often merged, leading to the formation of thick ice masses. Sediment transport was monitored using bed particles individually tagged with passive integrated transponders (PIT-tags). Movement of the experimental particles, measured after each multi-day cycle event, ranged from 0.5 to 4 m. Possible transport mechanisms include: (1) anchor ice rafting, (2) ice jam breakup creating a jave with high erosive capacity, (3) flow corridors through anchor ice masses with high erosive capacity, (4) mechanical pushing of particles by drifting ice blocks during ice breakup, and (5) entrainment by flow or drifting ice blocks of anchored ice with strong ice-pebble bonds. Given the coincidental occurrence of anchor ice release and runoff events, it is uncertain which specific mechanism caused the particles to move. This study is a step forward in understanding the behavior of anchor ice processes and ice-related sediment transport.