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32-660: Assateague Channel is a channel on the Eastern Shore of Virginia between Chincoteague Island and Assateague Island . The Assateague Channel connects to Assateague Bay to the northeast and Chincoteague Inlet to the southwest. On the last Wednesday in July, the Chincoteague Volunteer Fire Department conducts the annual Wild Pony Swim as part of Pony Penning . Salt Water Cowboys round up wild Chincoteague Ponies from Assateague Island and drive them across

64-483: 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 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

96-428: A habitat for mobile benthic organisms. These biotic reef types take on additional names depending upon how the reef lies in relation to the land, if any. Reef types include fringing reefs , barrier reefs , and atolls . A fringing reef is a reef that is attached to an island. Whereas, a barrier reef forms a calcareous barrier around an island, resulting in a lagoon between the shore and the reef. Conversely, an atoll

128-652: A skeletal framework. A microbial mound might be built exclusively or primarily by cyanobacteria . Examples of biostromes formed by cyanobacteria occur in the Great Salt Lake in Utah , United States, and in Shark Bay on the coast of Western Australia . Cyanobacteria do not have skeletons, and individual organisms are microscopic. However, they can encourage the precipitation or accumulation of calcium carbonate to produce distinct sediment bodies in composition that have relief on

160-420: 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

192-530: 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 (non-living) processes such as deposition of sand or wave erosion planning down rock outcrops. However, reefs such as the coral reefs of tropical waters are formed by biotic (living) processes, dominated by corals and coralline algae . Artificial reefs , such as shipwrecks and other man-made underwater structures, may occur intentionally or as

224-470: Is a ring reef with no land present. The reef front, facing the ocean, is a high energy locale. Whereas, the internal lagoon will be at a lower energy with fine grained sediments. Both mounds and reefs are considered to be varieties of organosedimentary buildups, which are sedimentary features, built by the interaction of organisms and their environment. These interactions have a synoptic relief and whose biotic composition differs from that found on and beneath

256-456: Is frequently called a canal , with the Panama Canal providing an example. 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

288-661: 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 , hollows and landslides . 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

320-610: The Old Norse word rif, meaning "rib" or "reef". Rif comes from the Proto-Germanic term ribją meaning "rib". Reefs may be classified in terms of their origin, geographical location, depth, and topography . For example a tropical coral fringing reef, or a temperate rocky intertidal reef. A variety of biotic reef types exists, including oyster reefs and sponge reefs , but the most massive and widely distributed are tropical coral reefs . Although corals are major contributors to

352-469: The Rigs-to-Reefs program), scuttling ships , or by deploying rubble or construction debris . Other artificial reefs are purpose built (e.g. the reef balls ) from PVC or concrete. Shipwrecks become artificial reefs on the seafloor. Regardless of construction method, artificial reefs generally provide stable hard surfaces where algae and invertebrates such as barnacles , corals, and oysters attach;

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384-581: 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 ,

416-597: The 17th century. 37°55′35″N 75°20′30″W  /  37.92639°N 75.34167°W  / 37.92639; -75.34167 This Accomack County, Virginia state location article is a stub . You can help Misplaced Pages by expanding it . Channel (geography) 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,

448-681: The Assateague Channel to Veteran's Memorial Park on Chincoteague Island . Once on Chincoteague Island, the Salt Water Cowboys herd the ponies to pens on the Chincoteague Carnival Grounds where some of the foals are auctioned off the next day. This traditional event in its current form has taken place since 1925 to raise money for the Chincoteague Volunteer Fire Department, but its roots date back to

480-481: The adjacent unconsolidated surface with varying relief. They can be found in depth ranges from intertidal to deep water and provide a substrate for a large range of sessile benthic organisms, and shelter for a large range of mobile organisms. They are often located in sub-tropical, temperate, and sub-polar latitudes. Ancient reefs buried within stratigraphic sections are of considerable interest to geologists because they provide paleo-environmental information about

512-545: 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

544-554: 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

576-482: The framework and bulk material comprising a coral reef, the organisms most responsible for reef growth against the constant assault from ocean waves are calcareous algae, especially, although not entirely, coralline algae . Oyster larvae prefer to settle on adult oysters and thereby develop layers building upwards. These eventually form a fairly massive hard stony calcium carbonate structure on which other reef organisms like sponges and seaweeds can grow, and provide

608-596: The framework builders. The corals which build reefs today, the Scleractinia , arose after the Permian–Triassic extinction event that wiped out the earlier rugose corals (as well as many other groups). They became increasingly important reef builders throughout the Mesozoic Era. They may have arisen from a rugose coral ancestor. Rugose corals built their skeletons of calcite and have a different symmetry from that of

640-609: The location in Earth's history . In addition, reef structures within a sequence of sedimentary rocks provide a discontinuity which may serve as a trap or conduit for fossil fuels or mineralizing fluids to form petroleum or ore deposits . Corals, including some major extinct groups Rugosa and Tabulata , have been important reef builders through much of the Phanerozoic since the Ordovician Period. However, other organism groups, such as calcifying algae, especially members of

672-400: The product of the sediment load and bed Bukhara size is proportional to the product of discharge and channel slope. 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

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704-578: The red algae ( Rhodophyta ), and molluscs (especially the rudist bivalves during the Cretaceous Period) have created massive structures at various times. During the Cambrian Period, the conical or tubular skeletons of Archaeocyatha , an extinct group of uncertain affinities (possibly sponges), built reefs. Other groups, such as the Bryozoa, have been important interstitial organisms, living between

736-536: The result of an accident. These are sometimes designed to increase the physical complexity of featureless sand bottoms to attract a more diverse range of organisms . Reefs are often quite near to the surface, but not all definitions require this. Earth's largest coral reef system is the Great Barrier Reef in Australia, at a length of over 2,300 kilometres (1,400 miles). The word "reef" traces its origins back to

768-421: The rugosan corals (which disappeared in the late Permian). An artificial reef is a human-created underwater structure, typically built to promote marine life in areas with a generally featureless bottom, to control erosion, block ship passage, block the use of trawling nets, or improve surfing . Many reefs are built using objects that were built for other purposes, for example by sinking oil rigs (through

800-465: The scleractinian corals, whose skeletons are aragonite . However, there are some unusual examples of well-preserved aragonitic rugose corals in the Late Permian . In addition, calcite has been reported in the initial post-larval calcification in a few scleractinian corals. Nevertheless, scleractinian corals (which arose in the middle Triassic) may have arisen from a non-calcifying ancestor independent of

832-850: The seafloor. Cyanobacterial mounds were most abundant before the evolution of shelly macroscopic organisms, but they still exist today. Stromatolites , for instance, are microbial mounds with a laminated internal structure. Whereas, bryozoans and crinoids , common contributors to marine sediments during the Mississippian period , produce a different kind of mound. Although bryozoans are small and crinoid skeletons disintegrate, bryozoan and crinoid meadows can persist over time and produce compositionally distinct bodies of sediment with depositional relief. The Proterozoic Belt Supergroup contains evidence of possible microbial mat and dome structures similar to stromatolite and chicken reef complexes. Rocky reefs are underwater outcrops of rock projecting above

864-431: The surrounding sea floor . However, reefs are held up by a macroscopic skeletal framework, as what is seen on coral reefs. Corals and calcareous algae grow on top of one another, forming a three-dimensional framework that is modified in various ways by other organisms and inorganic processes. Conversely, mounds lack a macroscopic skeletal framework. Instead, they are built by microorganisms or by organisms that also lack

896-430: 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 . Channel initiation refers to the site on a mountain slope where water begins to flow between identifiable banks. This site is referred to as the channel head and it marks an important boundary between hillslope processes and fluvial processes. The channel head

928-678: The unstable subsequent movement of benthic soils. 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

960-512: The water between islands is typically called a channel or passage . The English Channel is the strait between England and France. 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 ):

992-400: The way to D with no navigational aids and only estimated depths provided to the shipmaster . 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. The latter, entirely human-made, channel

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1024-1244: 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 . Reef A reef

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