CGRG Bibliography of Canadian Geomorphology
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Author : Burge, L.M.; and Lapointe, M.F.
Date : 2001.
Title : The anabranch cycle in wandering cobble-bed rivers: creation, stability, and abandonment.
Publication : AGU 2001 Fall Meeting, Moscone Centre, San Franciso, California, December 10-14, 2001.
Issue :
Page(s) :
Abstract
Wandering rivers are composed of single and multiple channel reaches. Within multiple channel reaches, channels split into individual anabranches. Even though anabranches of various sizes are known to provide habitat complexity for salmonids, anabranch dynamics are not fully understood. The Renous River, New Brunswick, Canada, is a wandering river with multiple and single channel reaches and semi-permanent stable islands. The concept of the anabranch cycle and models of anabranch characteristics are based on the dynamics and sedimentology of this system. Anabranches display a cycle of creation, stability and abandonment. Anabranches may be created by avulsions or deposition of bars that stabilize to become islands. The anabranch cycle begins with a floodplain scarred with abandoned channels that are possible avulsion paths. A trigger, such as large floods, logjams, or ice jams, force water over the floodplain into an abandoned channel initiating an avulsion. However, not all avulsions become anabranches. Failed avulsions occur where the avulsion course is longer than the main channel. Ice jams may block the main channel forcing water into abandoned channels longer than the main channel. These avulsion channels are abandoned after the ice jam passes, maintaining a single channel. Where an avulsion course is much shorter than the main channel, the main channel quickly switches into the avulsion channel, abandoning the former main channel, leading to a single channel. Stable anabranches only occur where avulsion and main channel lengths are similar. These anabranches may be stable over long periods but eventually one anabranch will be abandoned. Abandonment may occur if the balance of sediment and water entering each anabranch is disturbed. If one anabranch receives more sediment than it can transport it may be abandoned. This occurs where the diffluence geometry is changed due to meandering of the channel upstream of the diffluence or if an avulsion occurs upstream increasing sediment transport into one anabranch. Channel abandonment leaves low semi-filled channels scarring floodplains. These may become future avulsion sites restarting the anabranch cycle and allowing the multiple channel system to be maintained indefinitely.
Bibliography of Canadian Geomorphology