In physical geography, a channel is a type of landform consisting of the outline of a path of relatively shallow and narrow body of water or of other fluids (e.g., lava), most commonly the confine of a river, river delta or strait. The word is generally used to refer to a natural formation of a narrow and is cognate to canal, which is more commonly used to denote an artificial formation.
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.
The term is also traditionally used to describe the waterless surface features on Venus.
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 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.
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]
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-dredgedship-navigable parts of an estuary or river leading to port facilities, but also to lesser channels accessing boatport-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.
^ abcdefghiBierman, R. B, David R. Montgomery (2014). Key Concepts in Geomorphology. W. H. Freeman and Company Publishers. United States.
^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.
^Edward Beighley, R.; Killgore, Mark W. (23 May 2011). World Environmental and Water Resources Congress 2011. ISBN9780784476628. from the original on 24 June 2016. Retrieved 26 November 2015.
^History of the Waterways of the Atlantic Coast of the United States January 3, 2007, at the Wayback Machine, USACE, January 1983
Sources
Thoresen, Carl A. (2003). Port Designer's Handbook: Recommendations and Guidelines. Thomas Telford. ISBN978-0-7277-3228-6.
Fahmy, Wael Ahmed; Hekal, Nasr Tawfik Hassan (January 2023). "Upgrading the Navigable Channels along the River Nile within Egypt for Satisfying New Transportation Requirements" (PDF). JAET. 42 (1): 33–47. doi:10.21608/jaet.2021.70109.1105. ISSN 2682-2091. S2CID 245210824.
August 24, 2023
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In physical geography a channel is a type of landform consisting of the outline of a path of relatively shallow and narrow body of water or of other fluids e g lava most commonly the confine of a river river delta or strait The word is generally used to refer to a natural formation of a narrow and is cognate to canal which is more commonly used to denote an artificial formation Vivari Channel in Albania links Lake Butrint with the Straits of Corfu 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 The term is also traditionally used to describe the waterless surface features on Venus Contents 1 Formation 2 Natural channels 3 Waterflow channels 4 Nautical channels 5 See also 6 References 7 SourcesFormation EditChannel 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 EditThis section does not cite any sources Please help improve this section by adding citations to reliable sources Unsourced material may be challenged and removed February 2019 Learn how and when to remove this template message 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 EditThe 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 EditSee also Navigability Navigation canal and Fairway navigation 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 EditChannel pattern Hydrology transport model Lava channel Ship canal Stream flow Stream gradient Stream restoration Surge channelReferences Edit a b c d e f g h i Bierman R B David R Montgomery 2014 Key Concepts in Geomorphology W H Freeman and Company Publishers United States 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 Edward Beighley R Killgore Mark W 23 May 2011 World Environmental and Water Resources Congress 2011 ISBN 9780784476628 Archived from the original on 24 June 2016 Retrieved 26 November 2015 a b Thoresen 2003 p 78 Fahmy amp Hekal 2023 p 33 Thoresen 2003 p 79 History of the Waterways of the Atlantic Coast of the United StatesArchived January 3 2007 at the Wayback Machine USACE January 1983Sources EditThoresen Carl A 2003 Port Designer s Handbook Recommendations and Guidelines Thomas Telford ISBN 978 0 7277 3228 6 Fahmy Wael Ahmed Hekal Nasr Tawfik Hassan January 2023 Upgrading the Navigable Channels along the River Nile within Egypt for Satisfying New Transportation Requirements PDF JAET 42 1 33 47 doi 10 21608 jaet 2021 70109 1105 ISSN 2682 2091 S2CID 245210824 Retrieved from https en wikipedia org w index php title Channel geography amp oldid 1159464767, wikipedia, wiki, book, books, library,
