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Source (river or stream)
Encyclopedia
River
A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...
or stream
Stream
A stream is a body of water with a current, confined within a bed and stream banks. Depending on its locale or certain characteristics, a stream may be referred to as a branch, brook, beck, burn, creek, "crick", gill , kill, lick, rill, river, syke, bayou, rivulet, streamage, wash, run or...
is the place from which the water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
in the river or stream originates.
Definition
United States Geological Survey
The United States Geological Survey is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, and the natural hazards that threaten it. The organization has four major science disciplines, concerning biology,...
(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 identified as the source stream". As an example of the second definition above, the USGS at times considers the Missouri River
Missouri River
The Missouri River flows through the central United States, and is a tributary of the Mississippi River. It is the longest river in North America and drains the third largest area, though only the thirteenth largest by discharge. The Missouri's watershed encompasses most of the American Great...
as a tributary of the Mississippi River
Mississippi River
The Mississippi River is the largest river system in North America. Flowing entirely in the United States, this river rises in western Minnesota and meanders slowly southwards for to the Mississippi River Delta at the Gulf of Mexico. With its many tributaries, the Mississippi's watershed drains...
. 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 river lengths around the world.
This most common definition of a river source specifically utilizes the most distant point (along watercourses from the river mouth) in the drainage basin
Drainage basin
A drainage basin is an extent or an area of land where surface water from rain and melting snow or ice converges to a single point, usually the exit of the basin, where the waters join another waterbody, such as a river, lake, reservoir, estuary, wetland, sea, or ocean...
from which water runs year-around (perennially
Perennial stream
A perennial stream or perennial river is a stream or river that has continuous flow in parts of its bed all year round during years of normal rainfall. "Perennial" streams are contrasted with "intermittent" streams which normally cease flowing for weeks or months each year, and with "ephemeral"...
), or, alternatively, as the furthest point from which water could possibly flow (ephemeral
Ephemeral
Ephemeral things are transitory, existing only briefly. Typically the term is used to describe objects found in nature, although it can describe a wide range of things....
ly). 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
Smithsonian Institution
The Smithsonian Institution is an educational and research institute and associated museum complex, administered and funded by the government of the United States and by funds from its endowment, contributions, and profits from its retail operations, concessions, licensing activities, and magazines...
, is also used by the National Geographic Society
National Geographic Society
The National Geographic Society , headquartered in Washington, D.C. in the United States, is one of the largest non-profit scientific and educational institutions in the world. Its interests include geography, archaeology and natural science, the promotion of environmental and historical...
when pinpointing the source of rivers such as the Amazon
Amazon River
The Amazon of South America is the second longest river in the world and by far the largest by waterflow with an average discharge greater than the next seven largest rivers combined...
or Nile. A definition given by the state of Montana
Montana
Montana is a state in the Western United States. The western third of Montana contains numerous mountain ranges. Smaller, "island ranges" are found in the central third of the state, for a total of 77 named ranges of the Rocky Mountains. This geographical fact is reflected in the state's name,...
agrees, stating that a river source is never a confluence
Confluence (geography)
In geography, a confluence is the meeting of two or more bodies of water. It usually refers to the point where two streams flow together, merging into a single stream...
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
Lake Victoria
Lake Victoria is one of the African Great Lakes. The lake was named for Queen Victoria of the United Kingdom, by John Hanning Speke, the first European to discover this lake....
's outlet where the name "Nile" first appears, which would reduce the Nile's length by over 900 km (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
Kagera River
The Kagera River, also Akagera River, is an East African river, forming part of the upper headwaters of the Nile and carrying water from its most distant source....
. Likewise, the source of the Amazon River has been determined this way, even though the river changes names numerous times along its course.
When not listing river lengths, however, alternate definitions may be used. The Missouri River's source is named by some USGS and other federal and state agency sources, following Lewis and Clark's naming convention, as the confluence of the Madison
Madison River
The Madison River is a headwater tributary of the Missouri River, approximately 183 miles long, in Wyoming and Montana. Its confluence with the Jefferson and Gallatin rivers near Three Forks, Montana form the Missouri River....
and Jefferson
Jefferson River
The Jefferson River is a tributary of the Missouri River, approximately long, in the U.S. state of Montana. The Jefferson River and the Madison River form the official beginning of the Missouri at Missouri Headwaters State Park near Three Forks...
rivers, rather than the source of its longest tributary (the Jefferson). This is contradicted by an US Army Corps of Engineers official on a USGS site who states the most common definition: "Geographers generally follow the longest tributary to identify the source of rivers and streams. In the case of the Missouri River, Lewis
and Clark would have had to travel to the east...to reach the source"...He states that the Missouri River source is well upstream from Lewis and Clark's confluence, "following the Jefferson River to the Beaverhead River to Red Rock River, then Red Rock Creek to Hell Roaring Creek."
Characteristics of sources
Sometimes the source of the most remote tributary, may be in an area that is more marshMarsh
In geography, a marsh, or morass, is a type of wetland that is subject to frequent or continuous flood. Typically the water is shallow and features grasses, rushes, reeds, typhas, sedges, other herbaceous plants, and moss....
-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
River Tees
The River Tees is in Northern England. It rises on the eastern slope of Cross Fell in the North Pennines, and flows eastwards for 85 miles to reach the North Sea between Hartlepool and Redcar.-Geography:...
is marsh
Marsh
In geography, a marsh, or morass, is a type of wetland that is subject to frequent or continuous flood. Typically the water is shallow and features grasses, rushes, reeds, typhas, sedges, other herbaceous plants, and moss....
land.
The furthest stream is also often called the headstream. Headwaters are usually small streams that are often cool waters, because of shade and recently melted ice or snow. They may also be glacial headwaters, waters formed by the melting of glacial ice
Ice
Ice is water frozen into the solid state. Usually ice is the phase known as ice Ih, which is the most abundant of the varying solid phases on the Earth's surface. It can appear transparent or opaque bluish-white color, depending on the presence of impurities or air inclusions...
.
The source is the farthest point of the river stream from its estuary
Estuary
An estuary is a partly enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the open sea....
, mouth, or its confluence
Confluence (geography)
In geography, a confluence is the meeting of two or more bodies of water. It usually refers to the point where two streams flow together, merging into a single stream...
with another river or stream, regardless of what name that watercourse may carry on local maps and in local usage. Most rivers have numerous tributaries and change names often; it is customary to regard the longest tributary
Tributary
A tributary or affluent is a stream or river that flows into a main stem river or a lake. A tributary does not flow directly into a sea or ocean...
as its source.
Headwaters are the most extreme upstream areas of a watershed
Drainage basin
A drainage basin is an extent or an area of land where surface water from rain and melting snow or ice converges to a single point, usually the exit of the basin, where the waters join another waterbody, such as a river, lake, reservoir, estuary, wetland, sea, or ocean...
, 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
Colorado River
The Colorado River , is a river in the Southwestern United States and northwestern Mexico, approximately long, draining a part of the arid regions on the western slope of the Rocky Mountains. The watershed of the Colorado River covers in parts of seven U.S. states and two Mexican states...
is at the Continental Divide
Continental Divide
The Continental Divide of the Americas, or merely the Continental Gulf of Division or Great Divide, is the name given to the principal, and largely mountainous, hydrological divide of the Americas that separates the watersheds that drain into the Pacific Ocean from those river systems that drain...
separating the Atlantic Ocean
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
and Pacific Ocean
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
watersheds of North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
.
Example
A river is considered a linear geographic feature, with only one mouth and one source.For an example, note how the Mississippi River
Mississippi River
The Mississippi River is the largest river system in North America. Flowing entirely in the United States, this river rises in western Minnesota and meanders slowly southwards for to the Mississippi River Delta at the Gulf of Mexico. With its many tributaries, the Mississippi's watershed drains...
and Missouri River
Missouri River
The Missouri River flows through the central United States, and is a tributary of the Mississippi River. It is the longest river in North America and drains the third largest area, though only the thirteenth largest by discharge. The Missouri's watershed encompasses most of the American Great...
sources are officially defined:, Length: 2340 miles (3,765.9 km), Source: 47°14′22"N 95°12′29"W, Length: 2540 miles (4,087.7 km), Source: 45°55′39"N 111°30′29"W
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 lake
Lake
A lake is a body of relatively still fresh or salt water of considerable size, localized in a basin, that is surrounded by land. Lakes are inland and not part of the ocean and therefore are distinct from lagoons, and are larger and deeper than ponds. Lakes can be contrasted with rivers or streams,...
s rather than rivers or streams, refers to the lake's inflow
Inflow (hydrology)
In hydrology, the inflow of a body of water is the source of the water in the body of water. It can also refer to the average volume of incoming water in unit time. It is contrasted with outflow....
.