Dynamics of a transitional river pattern : a multi-scale investigation of controls on the wandering pattern of Miramichi rivers, New Brunswick, Canada

The wandering river pattern represents one of the last remaining river patterns that are not well understood. Many aspects of these rivers are not well known, particularly the processes of their creation and maintenance. The term wandering describes gravel or cobble bedded rivers, transitional between braided and meandering, with multiple channel sections around semi-permanent islands connected by single channel sections. This dissertation investigates the controls on the characteristics of wandering rivers within the Miramichi region of New Brunswick through time and at three nested spatial scales.At the scale of rivers, three factors appear to be needed for wandering to occur: (1) wide valleys, (2) channel energy between braiding and meandering, and (3) avulsion triggers, frequent overbank flows caused by icejams in the Miramichi. Principal component analysis showed that larger wandering rivers displayed greater anabranching intensity than smaller rivers, perhaps related to higher stage ice jams within larger rivers.At the scale of channels, the wandering pattern of the Renous River was found to be in a state of dynamic equilibrium, with channel creation balanced by channel abandonment. The anabranch cycle model was developed to illustrate the temporal dynamics of anabranch creation, maintenance and abandonment within wandering rivers.Also at the channel scale, principal component analysis of channel reaches within the Renous River displayed differences in grain size and hydraulic efficiency between side-channels and main-channels. Energy and sediment mobility within side-channels was related to their formation, maintenance and abandonment. Energy and sediment mobility within main-channels was related to mega bedforms called bedwaves. The apex of some bedwaves occurred at diffluences.At the scale of channel elements, diffluences are stable where a large bar is formed and accretes upstream, creating a large reservoir of sediment upstream of anabranch channels to buffer their degradation. Where diffluences are unstable, a large bar forms within one anabranch channel to partially block flow and may cause its abandonment. The dissertation illustrates that within wandering rivers, processes occurring at multiple spatial and temporal scales interact to create and maintain the pattern