Influence of Dynamic Ice Cover on Sediment Transport in an Alluvial Channel

English Abstract:

Dynamic ice cover alters flow in ice covered rivers by adding a new boundary to the top of the stream. River hydraulics vary as a function of ice cover presence and condition. Amongst the important hydraulic characteristics influenced by ice cover, velocity magnitude and distribution, water stage and boundary shear stress are particularly consequential. Variation of these parameters has potential to affect the channel morphodynamics and morphology due to changes in sediment initiation and transport. On the other hand, dynamic ice cover conditions throughout the winter restrict field studies and thereby limit most research to laboratories. Hence, despite the importance of ice cover processes on river morphodynamics, it is poorly studied in rivers. This research studies ice cover effects on river hydraulics and morphodynamics by in-situ field investigations using acoustic techniques. Utilization of acoustic instruments provides the possibility of continuous measurement of water velocity and stage throughout the winter period. A 1200 kHz Teledyne RD Instruments Acoustic Doppler Current Profiler (ADCP) and 546 kHz ASL Shallow Water Ice Profiling Sonar (SWIPS) were deployed simultaneously on a bottom mount at Lower Nelson River, Northern Manitoba for four months (March-June, 2012). Different stages of the ice cover, its thickness and associated variation in water velocity and stage are demonstrated based on acoustic data. Variation in sediment transport is also estimated based on backscatter intensity of the emitted sound which can be interpreted as the concentration of suspended sediment particles. Considerable effect of ice cover on river hydraulics and sediment transport, especially during the break-up period, is concluded from the results. Data illustrate that average velocity and sediment flux respectively vary by factors of 2 and 10 compared to the open water condition.