Braided Stream

A braided river is one of a number of channel types and has a channel that consists of a network of small channels separated by small and often temporary islands called braid bars. Braided streams occur in rivers with high slope and/or large sediment load. Braided channels are also typical of environments that dramatically decrease channel depth, and consequently channel velocity, such as river deltas, alluvial fans and peneplains.


Conditions which promote braided channel formation are:
an abundant supply of sediment
high stream gradient
rapid and frequent variations in water discharge
erodible banks

Braided rivers, as distinct from meandering rivers, occur when a threshold level of sediment load or slope is reached. Geologically speaking an increase in sediment load will over time increase the slope of the river, so these two conditions can be considered synonymous and consequently a variation of slope can model a variation in sediment load. Any slope over this threshold created a braided stream, and under the threshold created a meandering stream or for very low slopes a straight channel. So the main controlling factor on river development is the amount of sediment that the river carries, once a given system crosses a threshold value for sediment load it will convert from a meandering system to a braided system. Also important to channel development is the proportion of suspended load sediment to bed load. An increase in suspended sediment allowed for the deposition of fine erosion resistant material on the inside of a curve which accentuated the curve and in some instances caused a river to shift from a braided to a meandering profile.


The channels and braid bars are usually highly mobile, with the river layout often changing significantly during flood events. Channels move sideways via differential velocity: On the outside of a curve, deeper, swift water picks up sediment (usually gravel or larger stones), which is re-deposited in slow-moving water on the inside of a bend.

The braided channels may flow within an area defined by relatively stable banks or may occupy an entire valley floor. The Rakaia River in Canterbury, New Zealand, for example, has cut a channel 100 metres deep into the surrounding plains.

The most famous example of a large braided stream in the United States is the Platte River in central and western Nebraska. The sediment of the arid Great Plains is augmented by the presence of the nearby Sandhills region north of the river.