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 A landform is a natural or anthropogenic land feature on the solid surface of the Earth or other planetary body. Landforms together make up a given terrain, and their arrangement in the landscape is known as topography. Landforms include hills, ...

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 ...

), 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 rare ...

strait A strait is an oceanic landform connecting two seas or two other large areas of water. The surface water generally flows at the same elevation on both sides and through the strait in either direction. Most commonly, it is a narrow ocean chan ...

. 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 f ...

, 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 environme ...

. Overland flow 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 In geography and geology, fluvial processes are associated with rivers and streams and the deposits and landforms created by them. When the stream or rivers are associated with glaciers, ice sheets, or ice caps, the term glaciofluvial or fluviog ...

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 sur ...

. These are mostly formed by flowing

water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as ...

from the

hydrological cycle The water cycle, also known as the hydrologic cycle or the hydrological cycle, is a biogeochemical cycle that describes the continuous movement of water on, above and below the surface of the Earth. The mass of water on Earth remains fairly const ...

, though can also be formed by other fluids such as flowing

can form lava channels. 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 ...

sand bar In oceanography, geomorphology, and geoscience, a shoal is a natural submerged ridge, bank, or bar that consists of, or is covered by, sand or other unconsolidated material and rises from the bed of a body of water to near the surface. It ...

bay A bay is a recessed, coastal body of water that directly connects to a larger main body of water, such as an ocean, a lake, or another bay. A large bay is usually called a gulf, sea, sound, or bight. A cove is a small, circular bay with a na ...

, or any shallow body of water. An example of a river running through a sand bar is the

Columbia Bar The Columbia Bar, also frequently called the Graveyard of the Pacific, is a system of bars and shoals at the mouth of the Columbia River spanning the U.S. states of Oregon and Washington. It is known as one of the most dangerous bar crossings in ...

—the mouth of the

Columbia river The Columbia River ( Upper Chinook: ' or '; Sahaptin: ''Nch’i-Wàna'' or ''Nchi wana''; Sinixt dialect'' '') is the largest river in the Pacific Northwest region of North America. The river rises in the Rocky Mountains of British Columbia ...

. A stream channel is the physical confine of a

stream A stream is a continuous body of surface water flowing within the bed and banks of a channel. Depending on its location or certain characteristics, a stream may be referred to by a variety of local or regional names. Long large streams ...

(

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 ...

) 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 bank In geography, a bank is the land alongside a body of water. Different structures are referred to as ''banks'' in different fields of geography, as follows. In limnology (the study of inland waters), a stream bank or river bank is the terra ...

s. 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, sand ...

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 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 t ...

can be distinguished (e.g.

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 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 ...

drainage area A drainage basin is an area of land where all flowing surface water converges to a single point, such as a river mouth, or flows into another body of water, such as a lake or ocean. A basin is separated from adjacent basins by a perimeter, ...

. Examples of rivers that are trapped in their channels:

Grand Canyon The Grand Canyon (, yuf-x-yav, Wi:kaʼi:la, , Southern Paiute language: Paxa’uipi, ) is a steep-sided canyon carved by the Colorado River in Arizona, United States. The Grand Canyon is long, up to wide and attains a depth of over a m ...

and Black Canyon of the Gunnison. 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

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 Arch ...

, 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 isla ...

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 Ka ...

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 A buoy () is a floating device that can have many purposes. It can be anchored (stationary) or allowed to drift with ocean currents. Types Navigational buoys * Race course marker buoys are used for buoy racing, the most prevalent form of y ...

). 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 i ...

port-facilities such as

marina A marina (from Spanish , Portuguese and Italian : ''marina'', "coast" or "shore") is a dock or basin with moorings and supplies for yachts and small boats. A marina differs from a port in that a marina does not handle large passenger ships or ...

s. When dredged channels traverse

bay mud Bay mud consists of thick deposits of soft, unconsolidated silty clay, which is saturated with water; these soil layers are situated at the bottom of certain estuaries, which are normally in temperate regions that have experienced cyclical glac ...

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 responsible for the

Mississippi River The Mississippi River is the List of longest rivers of the United States (by main stem), second-longest river and chief river of the second-largest Drainage system (geomorphology), drainage system in North America, second only to the Hudson B ...

from the Gulf to

Cairo, Illinois Cairo ( ) is the southernmost city in Illinois and the county seat of Alexander County. The city is located at the confluence of the Ohio and Mississippi rivers. Fort Defiance, a Civil War camp, was built here in 1862 by Union General Ulysse ...

, the

North Atlantic Division The North Atlantic Division of the U.S. Army Corps of Engineers is one of the eight permanent divisions within the Corps. Made up of roughly 3,500 employees in six districts and a Division headquarters, the North Atlantic Division is a major ...

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 The Port of Los Angeles is a seaport managed by the Los Angeles Harbor Department, a unit of the City of Los Angeles. It occupies of land and water with of waterfront and adjoins the separate Port of Long Beach. Promoted as "America's Port", ...

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, m ...

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 ...

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 on

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 Baltis Vallis is a sinuous channel on Venus ranging from wide and ~ long, slightly longer than the Nile and the longest known channel of any kind in the Solar System. It is thought the channel once held a river of lava. It is a single channel ...

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 Planetary science (or more rarely, planetology) is the scientific study of planets (including Earth), celestial bodies (such as moons, asteroids, comets) and planetary systems (in particular those of the Solar System) and the processes of their ...

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 The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...

and Mercury that are of inconclusive origin. Channels have also been recently discovered on

Titan Titan most often refers to: * Titan (moon), the largest moon of Saturn * Titans, a race of deities in Greek mythology Titan or Titans may also refer to: Arts and entertainment Fictional entities Fictional locations * Titan in fiction, fictiona ...

. 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.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