Channel (geography)

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Vivari Channel in Albania links Lake Butrint with the Straits of Corfu. Vivari Channel.jpg
Vivari Channel in Albania links Lake Butrint with the Straits of Corfu.

In physical geography and hydrology, a channel is a landform on which a relatively narrow body of water is situated, such as a river, river delta or strait. While channel typically refers to a natural formation, the cognate term canal denotes a similar artificial structure.

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Channels are important for the functionality of ports and other bodies of water used for navigability for shipping. Naturally, channels will change their depth and capacity due to erosion and deposition processes. Humans maintain navigable channels by dredging and other engineering processes.

By extension, the term also applies to fluids other than water, e.g., lava channels. The term is also traditionally used to describe the waterless surface features on Venus.

Formation

Channel initiation refers to the site on a mountain slope where water begins to flow between identifiable banks. [1] This site is referred to as the channel head and it marks an important boundary between hillslope processes and fluvial processes. [1] The channel head is the most upslope part of a channel network and is defined by flowing water between defined identifiable banks. [1] 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. [1] Channel heads are often associated with colluvium, hollows and landslides. [1]

Overland flow is a primary factor in channel initiation where saturation overland flow deepens to increase shear stress and begin channel incision. [1] 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. [1] Vegetation slows infiltration rates during precipitation events and plant roots anchor soil on hillslopes. [1]

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. [1] 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. These are mostly formed by flowing water from the hydrological cycle, though can also be formed by other fluids such as flowing lava can form lava channels. Channels also describe the deeper course through a reef, 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) consisting of a bed and stream banks. Stream channels exist in a variety of geometries. Stream channel development is controlled by both water and sediment movement. There is a difference between low gradient 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 floods, water flow may exceed the capacity of the channel and flood waters will spill out of the channel and across the valley bottom, floodplain or drainage area.

Examples of rivers that are trapped in their channels: Grand Canyon and Black Canyon of the Gunnison.

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 context, the terms strait, channel, sound, and passage are synonymous and usually interchangeable. For example, in an archipelago, the water between islands is typically called a channel or passage. The English Channel 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): [2] the product of the sediment load and bed Bukhara size is proportional to the product of discharge and channel slope. [3]

Nautical channels

Wooden pilings mark the navigable channel for vessels entering Lake George from the St. Johns River in Florida. Lake George Channel.jpg
Wooden pilings mark the navigable channel for vessels entering Lake George from the St. Johns River in Florida.

A term "navigable channel" is used as a nautical term to mean a lane for ship travel, frequently marked (cf. Buoy) and sometimes dredged. Thoresen distinguishes few categories of channels, from A (suitable for day and night navigation with guaranteed fairway depth) all the way to D with no navigational aids and only estimated depths provided to the shipmaster. [4] With regard to the dredging, channels can be unrestricted (wide enough to accommodate 10-15 widths of a largest ship used in this channel, semi-restricted with limited dredging in shallow waters, and fully restricted, where the entire channel is dredged. [4] The latter, entirely human-made, channel is frequently called a canal , [5] with the Panama Canal providing an example. [6]

The term not only includes the deep-dredged   ship-navigable parts of an estuary or river leading to port facilities, but also to lesser channels accessing boat 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. [7]

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. In the U.S., navigation channels are monitored and maintained by the United States Army Corps of Engineers (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 and modified under acts of 1913, 1935, and 1938. For example, the USACE developed the Intracoastal Waterway, and has the Mississippi Valley Division responsible for the Mississippi River from the Gulf to Cairo, Illinois, the North Atlantic Division for New York Harbor and Port of Boston, and the South Pacific Division for Port of Los Angeles and Port of Long Beach. Waterways policing as well as some emergency spill response falls under United States Coast Guard jurisdiction, including inland channels serving ports like Saint Louis hundreds of miles from any coast. The various state or local governments maintain lesser channels, for example former Erie Canal.

See also

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<span class="mw-page-title-main">Geomorphology</span> Scientific study of landforms

Geomorphology is the scientific study of the origin and evolution of topographic and bathymetric features generated by physical, chemical or biological processes operating at or near Earth's surface. Geomorphologists seek to understand why landscapes look the way they do, to understand landform and terrain history and dynamics and to predict changes through a combination of field observations, physical experiments and numerical modeling. Geomorphologists work within disciplines such as physical geography, geology, geodesy, engineering geology, archaeology, climatology, and geotechnical engineering. This broad base of interests contributes to many research styles and interests within the field.

<span class="mw-page-title-main">Fluvial sediment processes</span> Sediment processes associated with rivers and streams

In geography and geology, fluvial sediment processes or fluvial sediment transport are associated with rivers and streams and the deposits and landforms created by sediments. It can result in the formation of ripples and dunes, in fractal-shaped patterns of erosion, in complex patterns of natural river systems, and in the development of floodplains and the occurrence of flash floods. Sediment moved by water can be larger than sediment moved by air because water has both a higher density and viscosity. In typical rivers the largest carried sediment is of sand and gravel size, but larger floods can carry cobbles and even boulders. When the stream or rivers are associated with glaciers, ice sheets, or ice caps, the term glaciofluvial or fluvioglacial is used, as in periglacial flows and glacial lake outburst floods. Fluvial sediment processes include the motion of sediment and erosion or deposition on the river bed.

Landforms are categorized by characteristic physical attributes such as their creating process, shape, elevation, slope, orientation, rock exposure, and soil type.

<span class="mw-page-title-main">Pearl River (Mississippi–Louisiana)</span> River in Mississippi and Louisiana, United States

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<span class="mw-page-title-main">Thalweg</span> Line of lowest elevation in a watercourse or valley

In geography, hydrography, and fluvial geomorphology, a thalweg or talweg is the line or curve of lowest elevation within a valley or watercourse. Its vertical position in maps is the nadir in the stream profile.

<span class="mw-page-title-main">Alluvial plain</span> Region on which rivers have deposited sediment

An alluvial plain is a plain created by the deposition of sediment over a long period of time by one or more rivers coming from highland regions, from which alluvial soil forms. A floodplain is part of the process, being the smaller area over which the rivers flood at a particular period of time, whereas the alluvial plain is the larger area representing the region over which the floodplains have shifted over geological time.

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<span class="mw-page-title-main">River engineering</span> Study of human intervention in the course, characteristics, or flow of rivers

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Streamflow, or channel runoff, is the flow of water in streams and other channels, and is a major element of the water cycle. It is one runoff component, the movement of water from the land to waterbodies, the other component being surface runoff. Water flowing in channels comes from surface runoff from adjacent hillslopes, from groundwater flow out of the ground, and from water discharged from pipes. The discharge of water flowing in a channel is measured using stream gauges or can be estimated by the Manning equation. The record of flow over time is called a hydrograph. Flooding occurs when the volume of water exceeds the capacity of the channel.

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<span class="mw-page-title-main">Perennial stream</span> Type of river

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<span class="mw-page-title-main">Stream</span> Body of surface water flowing down a channel

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 are usually called rivers, while smaller, less voluminous and more intermittent streams are known as streamlets, brooks or creeks.

<span class="mw-page-title-main">River</span> Natural flowing watercourse

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<span class="mw-page-title-main">Alluvial river</span> Type of river

An alluvial river is one in which the bed and banks are made up of mobile sediment and/or soil. Alluvial rivers are self-formed, meaning that their channels are shaped by the magnitude and frequency of the floods that they experience, and the ability of these floods to erode, deposit, and transport sediment. For this reason, alluvial rivers can assume a number of forms based on the properties of their banks; the flows they experience; the local riparian ecology; and the amount, size, and type of sediment that they carry.

<span class="mw-page-title-main">Bank erosion</span> Marginal wear of a watercourse

Bank erosion is the wearing away of the banks of a stream or river. This is distinguished from erosion of the bed of the watercourse, which is referred to as scour.

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<span class="mw-page-title-main">Meander cutoff</span>

A meander cutoff is a natural form of a cutting or cut in a river occurs when a pronounced meander (hook) in a river is breached by a flow that connects the two closest parts of the hook to form a new channel, a full loop. The steeper drop in gradient (slope) causes the river flow gradually to abandon the meander which will silt up with sediment from deposition. Cutoffs are a natural part of the evolution of a meandering river. Rivers form meanders as they flow laterally downstream, see sinuosity.

Gronda lagunare is a term used to indicate the area of the Lagoon of Venice by its mainland shore. The term is derived from the fact that it receives the waters from the rivers and streams which flow into the lagoon from the drainage basin of the plain of the mainland by the lagoon. It is also reached by the tidal flows form he sea., it is meant to be a belt that forms a transition area between the open lagoon and the mainland.

References

  1. 1 2 3 4 5 6 7 8 9 Bierman, R. B, David R. Montgomery (2014). Key Concepts in Geomorphology. W. H. Freeman and Company Publishers. United States.
  2. Lane, E.W. "The importance of fluvial morphology in hydraulic engineering", Proc. American Society of Civil Engineers, 1955, vol. 81, paper 745, pp. 533–551.
  3. Edward Beighley, R.; Killgore, Mark W. (23 May 2011). World Environmental and Water Resources Congress 2011. American Society of Civil Engineers. ISBN   9780784476628. Archived from the original on 24 June 2016. Retrieved 26 November 2015.
  4. 1 2 Thoresen 2003, p. 78.
  5. Fahmy & Hekal 2023, p. 33.
  6. Thoresen 2003, p. 79.
  7. History of the Waterways of the Atlantic Coast of the United States Archived January 3, 2007, at the Wayback Machine , USACE, January 1983

Sources