Geography & Environment Publications
Document Type
Book Chapter
Publication Date
2022
Journal
Treatise on Geomorphology 2nd Edition
URL with Digital Object Identifier
https://dx.doi.org/10.1016/B978-0-12-409548-9.12086-X
Abstract
Braided rivers have multiple, unstable channels and ephemeral bars formed by intense bed-load transport, and active channel processes. They occur in a range of environments associated with high-energy, coarse bedded rivers with limited riparian vegetation, and relatively high sediment supply. The occurrence in some regions is strongly modified by human activity. Empirical and rational analysis of regime conditions and in-channel process mechanisms can predict occurrence of braiding, considering by the problem of gradual transitions between channel pattern types, transient flood influence and vegetation effects. Braided rivers have hydraulic geometry relations similar to those of single-thread channels as well as systematic relationships for braiding intensity, active width, bar and network length scales, morphological active layer dimensions and bedload transport rates. Bar-scale processes are the major component of morphology, along with the dynamics of bifurcation and confluences of individual anabranches. These processes account for apparent regularity in the structure of the network of channels. Intensity of braiding is to 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, braiding forms progressively by channel migration and avulsion, not by simultaneous formation of the entire braided channel. Large amplitude variations in bedload transport rate occur locally and over short time periods related to channel- and bar-forming processes. Morphological change rate is controlled by discharge and stream power relative to grain size. Morphological change and bedload transport rates are closely inter-dependent so that channel-scale and short-term morphological dynamics of braiding are also the bedload dynamics in gravel braided rivers.
