Also important to channel development is the proportion of suspended load sediment to bed load. Any slope over this threshold created a braided stream, while any slope under the threshold created a meandering stream or – for very low slopes – a straight channel. A threshold slope was experimentally determined to be 0.016 (ft/ft) for a 0.15 cu ft/s (0.0042 m 3/s) stream with poorly sorted coarse sand. On timescales long enough for the river to evolve, a sustained increase in sediment load will increase the bed slope of the river, so that a variation of slope is equivalent to a variation in sediment load, provided the amount of water carried by the river is unchanged. Įxperiments with flumes suggest that a river becomes braided when a threshold level of sediment load or slope is reached. However, there is wide agreement that a river becomes braided when it carries an abundant supply of sediments. The physical processes that determine whether a river will be braided or meandering are not fully understood. ![]() state of Washington transports a large sediment load from the Emmons Glacier of Mount Rainier, a young, rapidly eroding volcano. These channels may themselves be braided. However, anastomosing rivers consist of semi-permanent channels which are separated by floodplain rather than channel bars. Anastomosing rivers are similar to braided rivers in that they consist of multiple interweaving channels. It is also distinct from an anastomosing river. Ī braided river differs from a meandering river, which has a single sinuous channel. When the islets separating channels are stabilized by vegetation, so that they are more permanent features, they are sometimes called aits or eyots. ![]() The channels and braid bars are usually highly mobile, with the river layout often changing significantly during flood events. The braid bars, also known as channel bars, branch islands, or accreting islands, are usually unstable and may be completely covered at times of high water. This gives the river a fancied resemblance to the interwoven strands of a braid. Description Ī braided river consists of a network of multiple shallow channels that diverge and rejoin around ephemeral braid bars. They are also associated with rivers with rapid and frequent variation in the amount of water they carry, i.e., with "flashy" rivers, and with rivers with weak banks.īraided channels are found in a variety of environments all over the world, including gravelly mountain streams, sand bed rivers, on alluvial fans, on river deltas, and across depositional plains. The Rakaia River in the South Island of New Zealand is braided over most of its courseĪ braided river, or braided channel, consists of a network of river channels separated by small, often temporary, islands called braid bars or, in British English usage, aits or eyots.īraided streams tend to occur in rivers with high sediment loads or coarse grain sizes, and in rivers with steeper slopes than typical rivers with straight or meandering channel patterns.
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