Channel patterns are found in rivers, streams, and other bodies of water that transport water from one place to another. Systems of branching river channels dissect most of the sub-aerial landscape, each in a valley proportioned to its size. Whether formed by chance or necessity, by headward erosion or downslope convergence, whether inherited or newly formed. Depending on different geological factors such as weathering, erosion, depositional environment, and sediment type, different types of channel patterns can form.

Bedrock vs. alluvial channels

There are two main types of channels,

bedrock In geology, bedrock is solid rock that lies under loose material (regolith) within the crust of Earth or another terrestrial planet. Definition Bedrock is the solid rock that underlies looser surface material. An exposed portion of bedro ...

and alluvial, which are present no matter the sub-classification. Bedrock channels are composed entirely of compacted rock, with only patches of

alluvium Alluvium (from Latin ''alluvius'', from ''alluere'' 'to wash against') is loose clay, silt, sand, or gravel that has been deposited by running water in a stream bed, on a floodplain, in an alluvial fan or beach, or in similar settings. Alluv ...

scattered throughout. Because the bedrock is constantly exposed it takes much less stream power to carve the channel. The

hydraulic Hydraulics (from Greek: Υδραυλική) is a technology and applied science using engineering, chemistry, and other sciences involving the mechanical properties and use of liquids. At a very basic level, hydraulics is the liquid counter ...

force of flowing water can push and pull detached joint blocks out of their initial position and roll or drag them downstream. Plucking is common in jointed rocks, where this occurs. Alluvial channels are much more common and can be large or small. All large rivers, and most small ones, have channels that are usually lined with alluvium, sediment that was carried to that channel reach by the river and that eventually will be carried farther downstream. This lining of alluvium creates a protective shield over the bedrock, which means it takes a much greater stream power to carve the channel.

Braided channels

There are a few distinctly different channel types based on their geological structure and depositional environment.

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 carry fairly coarse-grained sediment down a fairly steep gradient. They typically exhibit numerous channels that split off and rejoin each other to give a braided appearance. Additionally, the water

discharge Discharge may refer to Expel or let go * Discharge, the act of firing a gun * Discharge, or termination of employment, the end of an employee's duration with an employer * Military discharge, the release of a member of the armed forces from ser ...

tends to be highly variable. Consequently, braided rivers usually exist near mountainous regions, especially those with glaciers. These braided channels usually occur in tectonically active environments and have a larger sediment load due to varying water flow and discharge.

Anastomosed channels

Often confused with braided channels,

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 ...

is reserved for a type of river with multiple, interconnected, coexisting channel belts on alluvial plains. Based on its geomorphology, saucer-shaped islands called flood-basins characterize anastomosing rivers. These channels are classified as a composite form of which the individual channel belts may have braided, meandering or straight channels. Although similar to, and even encompass other channel types, anastomosed rivers are their own entity and have just begun to be studied by

geologist A geologist is a scientist who studies the solid, liquid, and gaseous matter that constitutes Earth and other terrestrial planets, as well as the processes that shape them. Geologists usually study geology, earth science, or geophysics, alth ...

s, revealing that much is still unknown. Fluvial processes form several channel patterns, including: *Straight, which are found in the most tectonically incised/active areas. This is more of a hypothetical end-member, and are not often found in nature. Straight-type channels can be found at

alluvial fans An alluvial fan is an accumulation of sediments that fans outwards from a concentrated source of sediments, such as a narrow canyon emerging from an escarpment. They are characteristic of mountainous terrain in arid to semiarid climates, but a ...

. *

s, which form in (tectonically active) areas that have a larger sedimentary load than the discharge of the river and a high gradient. *

Meandering river A meander is one of a series of regular sinuous curves in the channel of a river or other watercourse. It is produced as a watercourse erodes the sediments of an outer, concave bank (cut bank) and deposits sediments on an inner, convex bank ...

s, which form a sinuous path in a usually low-gradient plain toward the end of a fluvial system. * Anastomosed river is a rare case of a relatively straight, complicated vertical sequence of river deposits with banks held together by dense vegetation.

References

*Prothero, D. R. and Schwab, F., 1996, Sedimentary Geology, pg. 137-167, {{Rivers, streams and springs Geomorphology Fluvial landforms

Bedrock vs. alluvial channels

Braided channels

Anastomosed channels

See also

References