Morphology and Dynamics of Braided RIvers
Treatise on Geomorphology
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Braided rivers are characterized by multiple, unstable channel and ephemeral bars formed by intense bed-load transport, and a set of very active channel processes. They occur in a range of environments associated with high-energy, coarse-bedded rivers with limited development of riparian vegetation. The occurrence of braiding can be predicted from empirical and rational analysis of regime conditions and in-channel process mechanisms, although exact prediction is made difficult by the gradual transitions between channel pattern types and the limited analysis of vegetation effects. Despite an apparent chaotic appearance, braiding rivers follow hydraulic geometry relations similar in form to those of single-thread channels and appear to have distinctive statistical topographic characteristics. Bar formation, migration, and accretion processes are a major component of river morphology, as are the dynamics of bifurcation, and confluences of individual anabranches. These processes, and the length scale of the associated morphology, account for apparent regularity in the structure of the network of channels. Intensity of braiding also seems to be adjusted to discharge and sediment mobility but only parts of the channel network are active at any one time, even at channel-forming flows. Consequently, the braided channel is formed progressively by channel migration and avulsion, not by simultaneous formation of the entire braided channel network. Large amplitude variations in bedload transport rate occur locally and over short time periods associated with the complex set of channel- and bar-forming processes. Observations, empirical results, rational theory, and numerical models have all contributed to an understanding of braided river processes and are the basis for a more complete theory of the development and morpho-dynamics of braiding.