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270px, Farringdon_.html" ;"title="Farringdon,_Hampshire.html" ;"title="River Wey near its source at Farringdon, Hampshire">Farringdon ">Farringdon,_Hampshire.html" ;"title="River Wey near its source at Farringdon, Hampshire">Farringdon The headwaters of a river or stream is the farthest place in that river or stream from its estuary or downstream confluence with another river, as measured along the course of the river. It is also known as a river's source.


Definition

The
United States Geological Survey The United States Geological Survey (USGS, formerly simply Geological Survey) is a scientific government agency, agency of the Federal government of the United States, United States government. The scientists of the USGS study the landscape of ...
(USGS) states that a river's "length may be considered to be the distance from the mouth to the most distant headwater source (irrespective of stream name), or from the mouth to the headwaters of the stream commonly known as the source stream". As an example of the second definition above, the USGS at times considers the
Missouri River The Missouri River is the longest river in North America. Rising in the Rocky Mountains of western Montana, the Missouri flows east and south for before entering the Mississippi River north of St. Louis, Missouri, St. Louis, Missouri. The river ...
as a tributary of 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 on the North American continent, second only to ...
. But it also follows the first definition above (along with virtually all other geographic authorities and publications) in using the combined Missouri—lower Mississippi length figure in lists of lengths of rivers around the world. Most rivers have numerous tributaries and change names often; it is customary to regard the longest tributary or stem as the source, regardless of what name that watercourse may carry on local maps and in local usage. This most commonly identified definition of a river source specifically uses the most distant point (along watercourses from the
river mouth A river mouth is the part of a 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 wi ...
) in the
drainage basin
drainage basin
from which water runs year-around ( perennially), or, alternatively, as the furthest point from which water could possibly flow ephemerally. The latter definition includes sometimes-dry channels and removes any possible definitions that would have the river source "move around" from month to month depending on precipitation or ground water levels. This definition, from geographer Andrew Johnston of the
Smithsonian Institution The Smithsonian Institution ( ), also known simply as The Smithsonian, is a trust instrumentality of the United States composed as a group of museums and research centers. It was founded on August 10, 1846, "for the increase and diffusion of kno ...
, is also used by the
National Geographic Society The National Geographic Society (NGS), headquartered in Washington, D.C., United States The United States of America (USA), commonly known as the United States (U.S. or US), or America, is a country Contiguous United States, primarily ...
when pinpointing the source of rivers such as the
Amazon Amazon usually refers to: * Amazons In Greek mythology, the Amazons (Ancient Greek: Ἀμαζόνες ''Amazónes'', singular Ἀμαζών ''Amazōn'') are portrayed in a number of ancient Greek, ancient epic poems and legends, such as the L ...
or
Nile The Nile ( ar, النيل, an-Nīl, , Bohairic , lg, Kiira , Nobiin: Áman Dawū) is a major north-flowing river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In som ...
. A definition given by the state of
Montana Montana () is a U.S. state, state in the Mountain states, Mountain West region of the United States. It is bordered by Idaho to the west; North Dakota and South Dakota to the east; Wyoming to the south; and by the Provinces and territories ...
agrees, stating that a river source is never a
confluence In geography, a confluence (also: ''conflux'') occurs where two or more flowing bodies of water join together to form a single channel. A confluence can occur in several configurations: at the point where a tributary joins a larger river (main ...
but is "in a location that is the farthest, along water miles, from where that river ends." Under this definition, neither a lake (excepting lakes with no inflows) nor a confluence of tributaries can be a true river source, though both often provide the starting point for the portion of a river carrying a single name. For example, National Geographic and virtually every other geographic authority and atlas define the source of the Nile River not as Lake Victoria's outlet where the name "Nile" first appears, which would reduce the Nile's length by over (dropping it to fourth or fifth on the list of world's rivers), but instead use the source of the largest river flowing ''into'' the lake, the Kagera River. Likewise, the source of the Amazon River has been determined this way, even though the river changes names numerous times along its course. However, the source of the River Thames, Thames in England is traditionally reckoned according to the named river Thames rather than its longer tributary, the River Churn, Churn — although not without contention. When not listing river lengths, however, alternative definitions may be used. The Missouri River's source is named by some USGS and other federal and state agency sources, following Meriwether Lewis, Lewis and William Clark, Clark's naming convention, as the confluence of the Madison River, Madison and Jefferson Rivers, rather than the source of its longest tributary (the Jefferson). This contradicts the most common definition, which is, according to a United States Army Corps of Engineers, US Army Corps of Engineers official on a USGS site, that "[geographers] generally follow the longest tributary to identify the source of rivers and streams." In the case of the Missouri River, this would have the source be well upstream from Lewis and Clark's confluence, "following the Jefferson River to the Beaverhead River to Red Rock River (Montana), Red Rock River, then Red Rock Creek to Hell Roaring Creek."


Characteristics

Sometimes the source of the most remote tributary may be in an area that is more marsh-like, in which the "uppermost" or most remote section of the marsh would be the true source. For example, the source of the River Tees is marshland. The furthest stream is also often called the head stream. Headwaters are often small streams with cool waters because of shade and recently melted ice or snow. They may also be glacial headwaters, waters formed by the melting of Glacier, glacial ice. Headwater areas are the upstream areas of a drainage basin, watershed, as opposed to the outflow or discharge of a watershed. The river source is often but not always on or quite near the edge of the watershed, or watershed divide. For example, the source of the Colorado River is at the Continental Divide separating the Atlantic Ocean and Pacific Ocean watersheds of North America.


Example

A ''river'' is considered a ''linear'' geographic feature, with only one mouth and one source. For an example, note how 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 on the North American continent, second only to ...
and
Missouri River The Missouri River is the longest river in North America. Rising in the Rocky Mountains of western Montana, the Missouri flows east and south for before entering the Mississippi River north of St. Louis, Missouri, St. Louis, Missouri. The river ...
sources are officially defined: * *, Length: , Source: *, Length: , Source:


Related usages

The verb "rise" can be used to express the general region of a river's source, and is often qualified with an adverbial expression of place. For example: *''The River Thames rises in Gloucestershire.'' *''The White Nile rises in the Great Lakes region of central Africa.'' The word "source", when applied to lakes rather than rivers or streams, refers to the lake's inflow (hydrology), inflow.


See also

* Source of the Amazon River * Source of the Nile * Spring (hydrology) * Strahler number * Water well


References

DeBarry, Paul A. (2004). Watersheds: Processes, Assessment and Management. John Wiley & Sons. Water streams Fluvial landforms Freshwater ecology River morphology {{Hydrology-stub