Review of alluvial-channel responses to river ice

The extent to which alluvial channels respond to ice-cover formation, presence. and break-up is not well understood. Some responses are well known and observed, such as increased flow stage or localized scour beneath the toe of an ice jam. Other responses are known in concept. such as altered bedform geometry, but are not well documented. Some potential responses are barely recognized, such as channel-thalweg adjustment. Many responses are temporal, such as the channel readjusting itself once ice is gone. A few responses may have a more enduring impact. such as a meander-loo cutoff. Most responses have not been investigated rigorously. The responses affect the full gamut of relationships between flow discharge and stage, macroturbulence structures, sediment-tran sport and mixing processes. and alluvial-channel stability. Of importance are the relative scales of length and time associated with ice-cover formation, presence and breakup, and a channel's facility to respond to ice. This paper reviews alluvial-channel responses to ice formation, and raises practical engineering issues stemming from them.