physical geography Physical geography (also known as physiography) is one of the three main branches of geography. Physical geography is the branch of natural science which deals with the processes and patterns in the natural environment such as the atmosphere, ...

, a channel is a type of landform consisting of the outline of a path of relatively shallow and narrow

body of water A body of water or waterbody (often spelled water body) is any significant accumulation of water on the surface of Earth or another planet. The term most often refers to oceans, seas, and lakes, but it includes smaller pools of water such a ...

or of other fluids (e.g.,

lava Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or un ...

), most commonly the confine of a river,

river delta A river delta is a landform shaped like a triangle, created by deposition of sediment that is carried by a river and enters slower-moving or stagnant water. This occurs where a river enters an ocean, sea, estuary, lake, reservoir, or (more ra ...

or strait. The word is cognate to

canal Canals or artificial waterways are waterways or engineered channels built for drainage management (e.g. flood control and irrigation) or for conveyancing water transport vehicles (e.g. water taxi). They carry free, calm surface flo ...

, and sometimes takes this form, e.g. the

Hood Canal Hood Canal is a fjord forming the western lobe, and one of the four main basins,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

colluvium Colluvium (also colluvial material or colluvial soil) is a general name for loose, unconsolidated sediments that have been deposited at the base of hillslopes by either rainwash, sheetwash, slow continuous downslope creep, or a variable combinati ...

, hollows and

landslides Landslides, also known as landslips, are several forms of mass wasting that may include a wide range of ground movements, such as rockfalls, deep-seated slope failures, mudflows, and debris flows. Landslides occur in a variety of environments, ...

Overland flow Surface runoff (also known as overland flow) is the flow of water occurring on the ground surface when excess rainwater, stormwater, meltwater, or other sources, can no longer sufficiently rapidly infiltrate in the soil. This can occur when the s ...

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 fluvial process and are found across the

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

. These are mostly formed by flowing

water Water (chemical formula ) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living ...

from the hydrological cycle, though can also be formed by other fluids such as flowing

can form

lava channel A lava channel is a stream of fluid lava contained within zones of static (i.e., solid and stationary) lava or lava levees. The initial channel may not contain levees per se, until the parental flow solidifies over what develops into the channel and ...

s. Channels also describe the deeper course through a

reef A reef is a ridge or shoal of rock, coral or similar relatively stable material, lying beneath the surface of a natural body of water. Many reefs result from natural, abiotic processes— deposition of sand, wave erosion planing down rock o ...

, sand bar, bay, or any shallow body of water. An example of a river running through a sand bar is the Columbia Bar—the mouth of the Columbia river. A stream channel is the physical confine of a stream (

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 ...

) consisting of a

bed A bed is an item of furniture that is used as a place to sleep, rest, and relax. Most modern beds consist of a soft, cushioned mattress on a bed frame. The mattress rests either on a solid base, often wood slats, or a sprung base. Many beds ...

and stream banks. Stream channels exist in a variety of geometries. Stream channel development is controlled by both

and

sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sa ...

movement. There is a difference between low

gradient In vector calculus, the gradient of a scalar-valued differentiable function of several variables is the vector field (or vector-valued function) \nabla f whose value at a point p is the "direction and rate of fastest increase". If the gr ...

streams (less than a couple of percent in gradient or slightly sloped) and high gradient streams (steeply sloped). A wide variety of stream channel types can be distinguished (e.g. braided rivers, wandering rivers, single-thread sinuous rivers etc.). During

flood A flood is an overflow of water ( or rarely other fluids) that submerges land that is usually dry. In the sense of "flowing water", the word may also be applied to the inflow of the tide. Floods are an area of study of the discipline hydrol ...

s, water flow may exceed the capacity of the channel and flood waters will spill out of the channel and across the

valley A valley is an elongated low area often running between hills or mountains, which will typically contain a river or stream running from one end to the other. Most valleys are formed by erosion of the land surface by rivers or streams ove ...

bottom,

floodplain A floodplain or flood plain or bottomlands is an area of land adjacent to a river which stretches from the banks of its channel to the base of the enclosing valley walls, and which experiences flooding during periods of high discharge.Goudi ...

or drainage area. Examples of rivers that are trapped in their channels: Grand Canyon and

Black Canyon of the Gunnison Black Canyon of the Gunnison National Park is an American national park located in western Colorado and managed by the National Park Service. There are two primary entrances to the park: the south rim entrance is located east of Montrose, while ...

. In a larger nautical context, as a geographical place name, the term ''channel'' is another word for strait, which is defined as a relatively narrow body of water that connects two larger bodies of water. In this

nautical Seamanship is the art, knowledge and competence of operating a ship, boat or other craft on water. The'' Oxford Dictionary'' states that seamanship is "The skill, techniques, or practice of handling a ship or boat at sea." It involves topics ...

context, the terms ''strait'', ''channel'', ''sound'', and ''passage'' are synonymous and usually interchangeable. For example, in an

archipelago An archipelago ( ), sometimes called an island group or island chain, is a chain, cluster, or collection of islands, or sometimes a sea containing a small number of scattered islands. Examples of archipelagos include: the Indonesian Arc ...

, the water between

island An island (or isle) is an isolated piece of habitat that is surrounded by a dramatically different habitat, such as water. Very small islands such as emergent land features on atolls can be called islets, skerries, cays or keys. An island ...

s is typically called a ''channel'' or ''passage''. The

English Channel The English Channel, "The Sleeve"; nrf, la Maunche, "The Sleeve" (Cotentinais) or ( Jèrriais), (Guernésiais), "The Channel"; br, Mor Breizh, "Sea of Brittany"; cy, Môr Udd, "Lord's Sea"; kw, Mor Bretannek, "British Sea"; nl, Het Kana ...

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 nautical term 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 vessels transiting a body of water (''see'' Buoy). The term not only includes the deep-dredged ship-navigable parts of an

estuary An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environm ...

or river leading to

port A port is a maritime facility comprising one or more wharves or loading areas, where ships load and discharge cargo and passengers. Although usually situated on a sea coast or estuary, ports can also be found far inland, such as H ...

facilities, but also to lesser channels accessing

boat A boat is a watercraft of a large range of types and sizes, but generally smaller than a ship, which is distinguished by its larger size, shape, cargo or passenger capacity, or its ability to carry boats. Small boats are typically found on inl ...

port-facilities such as marinas. When dredged channels traverse bay mud 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''
, USACE, 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

navigability A body of water, such as a river, canal or lake, is navigable if it is deep, wide and calm enough for a water vessel (e.g. boats) to pass safely. Such a navigable water is called a ''waterway'', and is preferably with few obstructions against di ...

. In the U.S., navigation channels are monitored and maintained by the

United States Army Corps of Engineers , colors = , anniversaries = 16 June (Organization Day) , battles = , battles_label = Wars , website = , commander1 = ...

(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

Rivers and Harbors Act of 1899 The Rivers and Harbors Appropriation Act of 1899 is the oldest federal environmental law in the United States. The Act makes it a misdemeanor to discharge refuse matter of any kind into the navigable waters, or tributaries thereof, of the United ...

and modified under acts of 1913, 1935, and 1938. For example, the USACE developed the

Intracoastal Waterway The Intracoastal Waterway (ICW) is a inland waterway along the Atlantic and Gulf of Mexico coasts of the United States, running from Massachusetts southward along the Atlantic Seaboard and around the southern tip of Florida, then following t ...

, and has the

Mississippi Valley Division The United States Army Corps of Engineers Mississippi Valley Division (MVD) is responsible for the Corps water resources programs within 370,000-square-miles of the Mississippi River Valley, as well as the watershed portions of the Red River ...

responsible for the

Mississippi River The Mississippi River is the second-longest river and chief river of the second-largest drainage system in North America, second only to the Hudson Bay drainage system. From its traditional source of Lake Itasca in northern Minnesota, it fl ...

from the Gulf to Cairo, Illinois, the North Atlantic Division for New York Harbor and

Port of Boston The Port of Boston ( AMS Seaport Code: 0401, UN/LOCODE: US BOS) is a major seaport located in Boston Harbor and adjacent to the City of Boston. It is the largest port in Massachusetts and one of the principal ports on the East Coast of the Unite ...

, and the South Pacific Division for Port of Los Angeles and

Port of Long Beach The Port of Long Beach, also known as the Harbor Department of the City of Long Beach, is a container port in the United States, which adjoins Port of Los Angeles. Acting as a major gateway for US–Asian trade, the port occupies of land with ...

. Waterways policing as well as some emergency spill response falls under

United States Coast Guard The United States Coast Guard (USCG) is the maritime security, search and rescue, and law enforcement service branch of the United States Armed Forces and one of the country's eight uniformed services. The service is a maritime, military, mu ...

jurisdiction, including inland channels serving

s like Saint Louis hundreds of miles from any coast. The various state or local governments maintain lesser channels, for example former

Erie Canal The Erie Canal is a historic canal in upstate New York that runs east-west between the Hudson River and Lake Erie. Completed in 1825, the canal was the first navigable waterway connecting the Atlantic Ocean to the Great Lakes, vastly reducing t ...

Extraterrestrial channels

Extraterrestrial natural channels are found elsewhere in the

Solar System The Solar System Capitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar ...

than the

and the longest and widest of which are the

outflow channels Outflow channels are extremely long, wide swathes of scoured ground on Mars. They extend many hundreds of kilometers in length and are typically greater than one kilometer in width. They are thought to have been carved by huge outburst floods. ...

Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury. In the English language, Mars is named for the Roman god of war. Mars is a terrestrial planet with a thin at ...

and the channels of

Venus Venus is the second planet from the Sun. It is sometimes called Earth's "sister" or "twin" planet as it is almost as large and has a similar composition. As an interior planet to Earth, Venus (like Mercury) appears in Earth's sky never f ...

many of which are tens of kilometres wide (the network of channels flowing from Argyre Planitia on Mars for example is 8000 km in length and the Baltis Vallis 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 planetary science the term "

rille Rille (German for 'groove') is typically used to describe any of the long, narrow depressions in the surface of the Moon that resemble channels. The Latin term is ''rima'', plural ''rimae''. Typically, a rille can be several kilometers wi ...

" is sometimes used for similar formations found on The Moon and Mercury that are of inconclusive origin. Channels have also been recently discovered on Titan. The Saturnian moon has the only known liquid-filled channels in the Solar System other than Earth, the largest of which ( Vid Flumina) is 400 km in length. These are believed to be formed from flowing hydrocarbons in the hypothesized

methanological cycle The climate of Titan (moon), Titan, the largest moon of Saturn, is similar in many respects to that of Earth, despite having a far lower surface temperature. Its thick atmosphere, methane rain, and possible cryovolcanism create an analogue, thoug ...

.pg 71. Large Rivers: Geomorphology and Management. Avijit Gupta. John Wiley & Sons, 2007

References

{{coastal geography Bodies of water Coastal and oceanic landforms Fluvial landforms Nautical terminology Water streams

Natural channels

Waterflow channels

Nautical channels

Extraterrestrial channels

See also

References