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A wide variety of river and stream channel types exist in limnology, the study of inland waters. All these can be divided into two groups by using the water-flow gradient as either ''low gradient channels'' for streams or rivers with less than two percent (2%) flow gradient, or ''high gradient channels'' for those with greater than a 2% gradient.


Low gradient channels

Low gradient channels of rivers and streams can be divided into
braided river A braided river, or braided channel, consists of a network of river channels separated by small, often temporary, islands called braid bars or, in English usage, '' aits'' or ''eyots''. Braided streams tend to occur in rivers with high sediment ...
s, wandering rivers, single thread sinuous rivers (meandering), and
anastomosing An anastomosis (, plural anastomoses) is a connection or opening between two things (especially cavities or passages) that are normally diverging or branching, such as between blood vessels, leaf veins, or streams. Such a connection may be norma ...
rivers. The channel type developed depends on stream gradient, riparian vegetation and sediment supply.
Braided river A braided river, or braided channel, consists of a network of river channels separated by small, often temporary, islands called braid bars or, in English usage, '' aits'' or ''eyots''. Braided streams tend to occur in rivers with high sediment ...
s tend to occur on steeper gradients where there is a large supply of sediment for
braid bar Braid bars, or mid-channel bars, are river landforms typically present in braided river channels.  These formations have many names, including medial, longitudinal, crescentic, and transverse bars, as well as the more colloquial sandflat.  Braid ...
s, while single thread sinuous channels occur where there is a lower sediment supply for
point bar A point bar is a depositional feature made of alluvium that accumulates on the inside bend of streams and rivers below the slip-off slope. Point bars are found in abundance in mature or meandering streams. They are crescent-shaped and located on ...
s. Anastomosing channels are multithreaded, but are much more stable than braided channels and commonly have thick clay and silt
bank A bank is a financial institution that accepts deposits from the public and creates a demand deposit while simultaneously making loans. Lending activities can be directly performed by the bank or indirectly through capital markets. Because ...
s and occur at lower gradients of stream bed. Wandering rivers fall between sinuous single thread and braided streams and are relatively stable multi-channel gravel bed rivers.


High gradient channels

High gradient channels of rivers and streams have been divided into riffle-pool (which can cover all of the low gradient channel morphologies discussed above), rapid/plane bed, step-pool and cascade unit morphologies. *
Riffle-pool sequence In a flowing stream, a riffle-pool sequence (also known as a pool-riffle sequence) develops as a stream's hydrological flow structure alternates from areas of relatively shallow to deeper water. This sequence is present only in streams carrying g ...
channels are composed of migrating pools and transverse bars called
riffle A riffle is a shallow landform in a flowing channel. Colloquially, it is a shallow place in a river where water flows quickly past rocks. However, in geology a riffle has specific characteristics. Topographic, sedimentary and hydraulic indica ...
s and occur on gradients less than 1-2 percent. *
Rapid Rapids are sections of a river where the river bed has a relatively steep gradient, causing an increase in water velocity and turbulence. Rapids are hydrological features between a ''run'' (a smoothly flowing part of a stream) and a '' cascade' ...
s (also called plane bed, but not to be confused with the plane beds described in sand bed rivers) lack distinct pools and bars but commonly have stone cells or clusters and occur on gradients in the range of 1-5 percent, and have " whitewater". *Step-pools are composed of channel-spanning pools and
boulder In geology, a boulder (or rarely bowlder) is a rock fragment with size greater than in diameter. Smaller pieces are called cobbles and pebbles. While a boulder may be small enough to move or roll manually, others are extremely massive. In c ...
/cobble steps that cause
subcritical flow A supercritical flow is a flow whose velocity is larger than the wave velocity. The analogous condition in gas dynamics is supersonic speed. According to the website Civil Engineering Terms, supercritical flow is defined as follows: The flow ...
in the pool and supercritical flow over the steps. They occur in gradients in the range of 5 and 20%. *
Cascade Cascade, Cascades or Cascading may refer to: Science and technology Science *Cascade waterfalls, or series of waterfalls * Cascade, the CRISPR-associated complex for antiviral defense (a protein complex) * Cascade (grape), a type of fruit * Bioc ...
units exist at steeper gradients (approx > 10–15 percent) where the channel is dominated by boulders and cobbles and channel spanning pools do not exist. Pocket pools are common. In all four channel types
large woody debris Large woody debris (LWD) are the logs, sticks, branches, and other wood that falls into streams and rivers. This debris can influence the flow and the shape of the stream channel. Large woody debris, grains, and the shape of the bed of the strea ...
may strongly influence the channel type.


See also

*
Relief ratio The relief ratio is a number calculated to describe the grade of a river or stream. The calculation is the difference in elevation between the river's source and the river's confluence or mouth divided by the total length of the river or stream ...
* Stream gradient *
Stream restoration Stream restoration or river restoration, also sometimes referred to as river reclamation, is work conducted to improve the environmental health of a river or stream, in support of biodiversity, recreation, flood management and/or landscape developm ...
**
Riparian zone restoration Riparian-zone restoration is the ecological restoration of riparian-zone habitats of streams, rivers, springs, lakes, floodplains, and other hydrologic ecologies. A riparian zone or riparian area is the interface between land and a river or str ...
*
Vladimir Lokhtin Vladimir Mikhailovich Lokhtin (russian: Владимир Михайлович Лохтин 1849 – 1919) was a Russian hydrologist who examined the mechanism of riverbed and channel maintenance and stability based on the slope and the size of the ...


References and further reading

* See Church (1992) for more details on low gradient streams and Grant et al. (1990) and Buffington and Montgomery (1997) for more details regarding high gradient streams. * Buffington, J. M., and D. R. Montgomery (1997), A systematic analysis of eight decades of incipient motion studies, with special reference to gravel-bedded rivers, Water Resources Research, 33, 1993-2029. * Church, M. (1992), Channel morphology and topology, in The River Handbook, edited by P. Calow and G. E. Petts, pp. 126–143, Blackwell. * Grant, G. E., F. J. Swanson, and M. G. Wolman (1990), Pattern and origin of stepped-bed morphology in high gradient streams, western Cascades, Oregon, Geological Society of America, Bulletin, 102, 340-352. Rivers Water streams Limnology Geomorphology {{geomorph-stub