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Slide 1

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Aits and Braided
Rivers…read more

Slide 2

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- An ait (or eyot) is the equivalent of a small island. They are
typically formed by the deposition of sediment and silt in the
- Over time, this sediment accumulates, forming an ait.
- Characteristically, these are long and narrow, ranging from 1-
15m in width, and 1-60m in length.…read more

Slide 3

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· Logically, aits may become permanent small islands if we
think of the rates of deposition
· However, these aits may also be eroded: the resulting eroded
sediment is deposited once again further downstream, which
may even result in another ait
· A river channel with "myriads of aits" (Miranda Vickers) ­ or
numerous in any case ­ is what is called a braided channel
Even after the
river has run
dry, deposition
is visible more
than ever!…read more

Slide 4

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· - A braided channel is one of several channel types
· - It consists of a network of small channels separated small islands ­
aits (formally known as bars)
· - Braided channels are easily confused as a "large series of
meandering rivers" (Phil Ashworth)
Owen's River, California - Meandering River in the Cairngorms -Braided…read more

Slide 5

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· Braided channels 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 ­ there is a correlation, one could say that these two factors are synonymous
· The main controlling factor on the development of a braided river is the amount of sediment
that the river carries
· Another important factor to channel development is the proportion of suspended sediment
load to bed load.
· Channels in a braided-style river are usually highly mobile, with the river frequently
changing layout (particularly during floods, where the capacity of the river increases
drastically)…read more

Slide 6

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Braiding also occurs in environments in which there are rapidly
fluctuating discharges:
- Semi-arid areas of low relief that receive rivers from mountainous
- Glacial streams with variable annual discharge. In spring,
meltwater causes river discharge and competence to increase,
meaning the river can therefore transport more sediment particles.
As the temperature drops and river level falls, the load is deposited
as islands of deposition in the channel: aits.
- In tropical climates, where rivers such as the Amazon receive an
excessive amount of precipitation over a prolonged period of time, or
receive an intensive amount precipitation over a short period of time ­
the river levels and velocities fluctuate on a daily basis so deposition
in the form of aits occurs too.…read more

Slide 7

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