Long‐Term and Large‐Scale River‐Ice Processes in Cold‐Region Watersheds

Understanding the various spatial and temporal scales to which river ice shapes and alters natural channels is a crucial step towards a better assessment of the full range of physical processes that occur in cold-region watersheds. InEttema andKempema’s paper on ice effects, the primary focus is on processes that typically occur at the intra-annual time scale and at length scales that are generally equal (and often inferior) to that of the channel reach. Of course, such scales are appropriate to investigate, on one hand, river-ice cover formation and break-up processes, and on the other hand, allow for the study of local sediment transport and ablation, the description of ice-covered hydraulics and the analysis ofmorphological and geotechnical changes that relate to ice dynamics. However, to establish whether or not river ice, per se, can be considered a geomorphologically significant agent in the long term remains to be evaluated on much larger time and spatial scales. Investigating ice effects at larger spatial and temporal scales in gravel-bed rivers, by definition, implies that the characteristics of the ice regime (frequency, magnitude, duration, moment of occurrence of events) and their variations through time and space need to be taken into account. For example, all of the following questions regarding ice jam dynamics need to be addressed with at least a partial understanding of ice regime characteristics