In physical geography, a channel is the physical confine of a river, slough or ocean strait consisting of a bed and banks.
A channel is also the natural or man-made deeper course through a reef, sand bar, bay, or any shallow body of water. It is especially used as a Nautical term to mean the dredged and marked (See: Buoy) 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. 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. 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. In the United States, 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, which are contained in chapter 33 of the US Code, "Navigation and Navigable Waters." 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.
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.
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