Braided river
From Wikipedia, the free encyclopedia
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 or, in British usage, aits or eyots. Braided streams are common wherever a drastic reduction in stream gradient causes the rapid deposition of the stream's sediment load. Braided channels are also typical of river deltas and peneplains.
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 has cut a channel 100 metres deep into the surrounding plains.
The dynamic nature and uneven terrain of braided rivers present particular challenges to bridge construction.
Conditions which promote braided channel formation are:
- an abundant supply of sediment
- rapid and frequent variations in water discharge
- erodible banks
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.
Extensive braided river systems are found in only a few regions world-wide:
- Alaska
- Canada
- New Zealand's South Island
- the Himalaya
- the Yellow River
All the above regions contain young, eroding mountains.
