Misfit stream

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Misfit stream Gleann nan Eun meanders through the valley of the same name in the Scottish Highlands.

A misfit stream (or underfit stream) is a stream that is far too small to have eroded the valley which the stream occupies. The shape of the valley may also be inconsistent with a typical valley that has been eroded by water. Generally it is reasonable to expect a valley to be in proportion with the stream that occupies it. When a period of glaciation modifies the landscape by creating glacial troughs the rivers that occupy such valleys after the ice has retreated are not in proportion with the size of the valley. Given the scale of most glacial troughs almost all of them contain misfit streams.

[edit] Alternative causes

Misfit streams can be caused by reductions in the discharge of the stream. Channel size responds rapidly to variations in discharge, but valley size responds over much longer timescales. Many causes of reduced discharges are possible. If misfit streams are widespread in an area climate change, particularly a reduction in precipitation is likely to be the cause. If a single river appears to be a misfit stream it may be as a result of anthropogenic interference through groundwater extraction or dam construction upstream. Natural causes include stream capture or other changes in drainage patterns. For instance, New Zealand's largest river (the Waikato) used to flow through the Hauraki Plains to the North Island's east coast, but changed its course to exit on the west coast due to a large volcanic eruption, leaving its former course through the 1-km wide Hinuera Gap occupied by only a small stream.