A wide variety of

river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of w ...

and stream channel types exist in

limnology Limnology ( ; from Greek λίμνη, ''limne'', "lake" and λόγος, ''logos'', "knowledge") is the study of inland aquatic ecosystems. The study of limnology includes aspects of the biological, chemical, physical, and geological characteris ...

, 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 rivers, wandering rivers, single thread

sinuous Sinuosity, sinuosity index, or sinuosity coefficient of a continuously differentiable curve having at least one inflection point is the ratio of the curvilinear length (along the curve) and the Euclidean distance (straight line) between the ...

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 normal ...

rivers. The channel type developed depends on stream gradient,

riparian A riparian zone or riparian area is the interface between land and a river or stream. Riparian is also the proper nomenclature for one of the terrestrial biomes of the Earth. Plant habitats and communities along the river margins and banks a ...

vegetation and sediment supply. Braided rivers 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. * Rapids (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 Whitewater forms in a rapid context, in particular, when a river's gradient changes enough to generate so much turbulence that air is trapped within the water. This forms an unstable current that froths, making the water appear opaque and ...

". *Step-pools are composed of channel-spanning pools and boulder/cobble steps that cause subcritical flow in the pool and

supercritical 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 a ...

over the steps. They occur in gradients in the range of 5 and 20%. * Cascade 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 stream ...

may strongly influence the channel type.

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

Low gradient channels

High gradient channels

See also

References and further reading