The role of hydro-peaking in freeze-up consolidation events on regulated rivers

Periods of rapid frazil production followed by sudden warming can instigate the consolidation of a developing river ice cover. Although empirical evidence suggests that hydro-peaking operations can also precipitate or exacerbate such events, little is actually known about the specific implications of hydro-peaking during ice cover development because, until recently, numerical ice process models could not simulate such events reliably. Nevertheless, given that fluctuating water levels can destabilize a fragile developing ice cover, resulting in a severe freeze-up ice jam and associated flooding, winter is typically a time of severely constrained flow-peaking operations for hydro-power facilities. ace River in northern Alberta presents just such a case; the river has been regulated for hydro-power production since 1972 and numerous consolidation events have been documented along the river over the past few decades, including a particularly extreme event in January 1982. As a consequence of that event, voluntary flow controls have since been implemented each winter during the ice cover development period. In this study, recently developed hydrodynamic ice process modeling tools are used to diagnose such events in order to explore the relative importance of the causative factors and to facilitate a more comprehensive understanding of this phenomenon. Based on this analysis, it appears that meteorological factors may play an equally important role as hydro-peaking in precipitating ice cover consolidation events.