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In , a channel is a type of consisting of the outline of a path of relatively shallow and narrow body of fluid, most commonly the confine of a river, or . The word is cognate to , and sometimes takes this form, e.g. the .


Formation

Channel initiation refers to the site on a mountain slope where water begins to flow between identifiable banks.Bierman, R. B, David R. Montgomery (2014). Key Concepts in Geomorphology. W. H. Freeman and Company Publishers. United States. This site is referred to as the channel head and it marks an important boundary between hillslope processes and fluvial processes. The channel head is the most upslope part of a channel network and is defined by flowing water between defined identifiable banks. A channel head forms as overland flow and/or subsurface flow accumulate to a point where shear stress can overcome erosion resistance of the ground surface. Channel heads are often associated with , s and . is a primary factor in channel initiation where saturation overland flow deepens to increase shear stress and begin channel incision. Overland flows converge in topographical depressions where channel initiation begins. Soil composition, vegetation, precipitation, and topography dictate the amount and rate of overland flow. The composition of a soil determines how quickly saturation occurs and cohesive strength retards the entrainment of material from overland flows. Vegetation slows infiltration rates during precipitation events and plant roots anchor soil on hillslopes. Subsurface flow destabilizes soil and resurfaces on hillslopes where channel heads are often formed. This often results in abrupt channel heads and landslides. Hollows form due to concentrated subsurface flows where concentrations of colluvium are in a constant flux. Channel heads associated with hollows in steep terrain frequently migrate up and down hillslopes depending on sediment supply and precipitation.


Natural channels

Natural channels are formed by process and are found across the . These are mostly formed by flowing from the , though can also be formed by other fluids such as flowing can form s. Channels also describe the deeper course through a , , , or any shallow body of water. An example of a river running through a sand bar is the —the mouth of the . A stream channel is the physical confine of a () consisting of a and s. Stream channels exist in a variety of geometries. Stream channel development is controlled by both and movement. There is a difference between low streams (less than a couple of percent in gradient or slightly sloped) and high gradient streams (steeply sloped). A wide variety of stream can be distinguished (e.g. s, wandering rivers, single-thread rivers etc.). During s, water flow may exceed the capacity of the channel and flood waters will spill out of the channel and across the bottom, or . Examples of rivers that are trapped in their channels: and . In a larger nautical context, as a geographical place name, the term ''channel'' is another word for , which is defined as a relatively narrow body of water that connects two larger bodies of water. In this context, the terms ''strait'', ''channel'', ''sound'', and ''passage'' are synonymous and usually interchangeable. For example, in an , the water between s is typically called a ''channel'' or ''passage''. The is the strait between England and France.


Waterflow channels

The channel form is described in terms of geometry (plan, cross-sections, profile) enclosed by the materials of its bed and banks. This form is under influence of two major forces: water discharge and sediment supply. For erodible channels the mutual dependence of its parameters may be qualitatively described by Lane's Principle (also known as Lane's relationship): the product of the sediment load and bed Bukhara size is proportional to the product of discharge and channel slope.


Nautical channels

It is especially used as a to mean the dredged and marked lane of safe travel which a cognizant governmental entity ''guarantees'' to have a minimum depth across its specified minimum width to all transiting a body of water (''see'' ). The term not only includes the   parts of an or river leading to facilities, but also to lesser channels accessing such as s. When dredged channels traverse or sandy bottoms, repeated dredging is often necessary because of the unstable subsequent movement of benthic soils.''History of the Waterways of the Atlantic Coast of the United States''
, , January 1983
Responsibility for monitoring navigability conditions of ''navigation channels'' to various port facilities varies, and the actual maintenance work is frequently performed by a third party. Storms, sea-states, flooding, and seasonal sedimentation adversely affect . In the U.S., navigation channels are monitored and maintained by the (USACE), although dredging operations are often carried out by private contractors (under USACE supervision). USACE also monitors water quality and some remediation. This was first established under the and modified under acts of 1913, 1935, and 1938. For example, the USACE developed the , and has the responsible for the from the Gulf to , the for New York Harbor and , and the for and . Waterways policing as well as some emergency spill response falls under jurisdiction, including inland channels serving s like hundreds of miles from any coast. The various state or local governments maintain lesser channels, for example former .


Extraterrestrial channels

Extraterrestrial natural channels are found elsewhere in the than the and the longest and widest of which are the on and the channels of many of which are tens of kilometres wide (the network of channels flowing from on Mars for example is 8000 km in length and the Venus is 7000 km compared to the 6,650 km Nile, the largest active channel on Earth). The exact formation of these large ancient channels is unknown although it is theorised that those on Mars may have been formed due to catastrophic flooding and on Venus by lava flow. In the term "" is sometimes used for similar formations found on and that are of inconclusive origin. Channels have also been recently discovered on . The Saturnian moon has the only known liquid-filled channels in the Solar System other than Earth, the largest of which () is 400 km in length. These are believed to be formed from flowing hydrocarbons in the hypothesized .pg 71. Large Rivers: Geomorphology and Management. Avijit Gupta. John Wiley & Sons, 2007


See also

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References

{{coastal geography Water streams