Braided Stream Channel

Braided channel at Denali National Park (Alaksa)
Braided channel at Denali National Park (Alaska)

NPSphoto/Lisa Merkhofer

Braided channels are rivers where the trunk is divided into a series of small, shallow channels, with deposition of 'braid bars' separating them. Braided channels support large amount of sediment transport; it is the deposition of this overload of sediment that creates the bars.

The development of braided channels is favored by several factors. The most important factors leading to their development are large bed load and readily erodible bank material, which enable channel shifts to occur with relative ease. Once formed, bars in braided channels can become vegetated and thereby stabilized as islands. However, highly variable discharge is also typical of many braided rivers. These large fluctuations in discharge promote alternating channel degradation and aggradation which can suppress the establishment of vegetation on braided- channel bars (Summerfield, 1991).

As discharge declines after a flood, the coarse bed load is the first to be deposited in the channel. This material forms the nucleus of bars that grow downstream as the flow velocity is reduced and finer sediment accumulates. With further decreases in discharge the water level progressively falls and the bars are gradually exposed. During subsequent floods, some or all of the bars in a braided channel may be submerged depending on the discharge attained. During large floods braided channels can experience major diversions of flow (Summerfield, 1991).

NPS—River Systems and Fluvial Landforms