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 without reaching another body of water. Small rivers can be referred to using names such as stream, creek, brook, rivulet, and rill. There are no official definitions for the generic term river as applied to geographic features, although in some countries or communities a stream is defined by its size. Many names for small rivers are specific to geographic location; examples are "run" in some parts of the United States, "burn" in Scotland and northeast England, and "beck" in northern England. Sometimes a river is defined as being larger than a creek, but not always: the language is vague. Rivers are part of the hydrological cycle. Water generally collects in a river from precipitation through a drainage basin from surface runoff and other sources such as groundwater recharge, springs, and the release of stored water in natural ice and snowpacks (e.g., from glaciers). Potamology is the scientific study of rivers, while limnology is the study of inland waters in general.
1.1 Subsurface streams 1.2 Permanence of flow
3 Uses 4 Ecosystem 5 Chemistry 6 Brackish water 7 Flooding 8 Flow
8.1 Direction 8.2 Rate
Melting toe of Athabasca Glacier, Jasper National Park, Alberta, Canada
A river begins at a source (or more often several sources), follows a
path called a course, and ends at a mouth or mouths. The water in a
river is usually confined to a channel, made up of a stream bed
between banks. In larger rivers there is often also a wider floodplain
shaped by flood-waters over-topping the channel. Floodplains may be
very wide in relation to the size of the river channel. This
distinction between river channel and floodplain can be blurred,
especially in urban areas where the floodplain of a river channel can
become greatly developed by housing and industry.
Rivers can flow down mountains, through valleys (depressions) or along
plains, and can create canyons or gorges.
The term upriver (or upstream) refers to the direction towards the
source of the river, i.e. against the direction of flow. Likewise, the
term downriver (or downstream) describes the direction towards the
mouth of the river, in which the current flows.
The term left bank refers to the left bank in the direction of flow,
right bank to the right.
The river channel typically contains a single stream of water, but
some rivers flow as several interconnecting streams of water,
producing a braided river. Extensive braided rivers are now found
in only a few regions worldwide, such as the South
Island of New Zealand. They also occur on peneplains and some of the
larger river deltas. Anastamosing rivers are similar to braided rivers
and are quite rare. They have multiple sinuous channels carrying large
volumes of sediment. There are rare cases of river bifurcation in
which a river divides and the resultant flows ending in different
seas. An example is the bifurcation of Nerodime
A river flowing in its channel is a source of energy which acts on the
river channel to change its shape and form. In 1757, the German
Albert Brahms empirically observed that the submerged
weight of objects that may be carried away by a river is proportional
to the sixth power of the river flow speed. This formulation is
also sometimes called Airy's law. Thus, if the speed of flow is
doubled, the flow would dislodge objects with 64 times as much
submerged weight. In mountainous torrential zones this can be seen as
erosion channels through hard rocks and the creation of sands and
gravels from the destruction of larger rocks. A river valley that was
created from a U-shaped glaciated valley, can often easily be
identified by the V-shaped channel that it has carved. In the middle
reaches where a river flows over flatter land, meanders may form
through erosion of the river banks and deposition on the inside of
bends. Sometimes the river will cut off a loop, shortening the channel
and forming an oxbow lake or billabong. Rivers that carry large
amounts of sediment may develop conspicuous deltas at their mouths.
Rivers whose mouths are in saline tidal waters may form estuaries.
Throughout the course of the river, the total volume of water
transported downstream will often be a combination of the free water
flow together with a substantial volume flowing through sub-surface
rocks and gravels that underlie the river and its floodplain (called
the hyporheic zone). For many rivers in large valleys, this unseen
component of flow may greatly exceed the visible flow.
Most but not all rivers flow on the surface. Subterranean rivers flow
underground in caves or caverns. Such rivers are frequently found in
regions with limestone geologic formations. Subglacial streams are the
braided rivers that flow at the beds of glaciers and ice sheets,
permitting meltwater to be discharged at the front of the glacier.
Because of the gradient in pressure due to the overlying weight of the
glacier, such streams can even flow uphill.
Permanence of flow
Main article: Intermittent river
An intermittent river (or ephemeral river) only flows occasionally and
can be dry for several years at a time. These rivers are found in
regions with limited or highly variable rainfall, or can occur because
of geologic conditions such as a highly permeable river bed. Some
ephemeral rivers flow during the summer months but not in the winter.
Such rivers are typically fed from chalk aquifers which recharge from
winter rainfall. In England these rivers are called bournes and give
their name to places such as
A radar image of a 400-kilometre (250 mi) river of methane and ethane near the north pole of Saturn's moon Titan
Rivers have been classified by many criteria including their
topography, their biotic status, and their relevance to white water
rafting or canoeing activities.
Rivers can generally be classified as either alluvial, bedrock, or
some mix of the two. Alluvial rivers have channels and floodplains
that are self-formed in unconsolidated or weakly consolidated
sediments. They erode their banks and deposit material on bars and
their floodplains. Bedrock rivers form when the river downcuts through
the modern sediments and into the underlying bedrock. This occurs in
regions that have experienced some kind of uplift (thereby steepening
river gradients) or in which a particular hard lithology causes a
river to have a steepened reach that has not been covered in modern
alluvium. Bedrock rivers very often contain alluvium on their beds;
this material is important in eroding and sculpting the channel.
Rivers that go through patches of bedrock and patches of deep alluvial
cover are classified as mixed bedrock-alluvial.
Alluvial rivers can be further classified by their channel pattern as
meandering, braided, wandering, anastomose, or straight. The
morphology of an alluvial river reach is controlled by a combination
of sediment supply, substrate composition, discharge, vegetation, and
At the start of the 20th century
William Morris Davis
Youthful river: A river with a steep gradient that has very few
tributaries and flows quickly. Its channels erode deeper rather than
wider. Examples are the Brazos, Trinity and Ebro rivers.
Mature river: A river with a gradient that is less steep than those of
youthful rivers and flows more slowly. A mature river is fed by many
tributaries and has more discharge than a youthful river. Its channels
erode wider rather than deeper. Examples are the Mississippi, Saint
Lawrence, Danube, Ohio, Thames and Paraná rivers.
Old river: A river with a low gradient and low erosive energy. Old
rivers are characterized by flood plains. Examples are the Yellow,
lower Ganges, Tigris, Euphrates, Indus and lower
The ways in which a river's characteristics vary between its upper and lower course are summarized by the Bradshaw model. Power-law relationships between channel slope, depth, and width are given as a function of discharge by "river regime". Biotic classification There are several systems of classification based on biotic conditions typically assigning classes from the most oligotrophic or unpolluted through to the most eutrophic or polluted. Other systems are based on a whole eco-system approach such as developed by the New Zealand Ministry for the Environment. In Europe, the requirements of the Water Framework Directive has led to the development of a wide range of classification methods including classifications based on fishery status A system of river zonation used in francophone communities divides rivers into three primary zones:
The crenon is the uppermost zone at the source of the river. It is further divided into the eucrenon (spring or boil zone) and the hypocrenon (brook or headstream zone). These areas have low temperatures, reduced oxygen content and slow moving water. The rhithron is the upstream portion of the river that follows the crenon. It has relatively cool temperatures, high oxygen levels, and fast, turbulent, swift flow. The potamon is the remaining downstream stretch of river. It has warmer temperatures, lower oxygen levels, slow flow and sandier bottoms.
Rivers have been used as a source of water, for obtaining food, for
transport, as a defensive measure, as a source of hydropower to drive
machinery, for bathing, and as a means of disposing of waste.
Rivers have been used for navigation for thousands of years. The
earliest evidence of navigation is found in the Indus Valley
Civilization, which existed in northwestern India around 3300 BC.
Riverine navigation provides a cheap means of transport, and is still
used extensively on most major rivers of the world like the Amazon,
the Ganges, the Nile, the Mississippi, and the Indus. Since river
boats are often not regulated, they contribute a large amount to
global greenhouse gas emissions, and to local cancer due to inhaling
of particulates emitted by the transports.
In some heavily forested regions such as
Fast flowing rivers and waterfalls are widely used as sources of
energy, via watermills and hydroelectric plants. Evidence of
watermills shows them in use for many hundreds of years, for instance
Flash flooding caused by a large amount of rain falling in a short amount of time
Flooding is a natural part of a river's cycle. The majority of the erosion of river channels and the erosion and deposition on the associated floodplains occur during the flood stage. In many developed areas, human activity has changed the form of river channels, altering magnitudes and frequencies of flooding. Some examples of this are the building of levees, the straightening of channels, and the draining of natural wetlands. In many cases human activities in rivers and floodplains have dramatically increased the risk of flooding. Straightening rivers allows water to flow more rapidly downstream, increasing the risk of flooding places further downstream. Building on flood plains removes flood storage, which again exacerbates downstream flooding. The building of levees only protects the area behind the levees and not those further downstream. Levees and flood-banks can also increase flooding upstream because of the back-water pressure as the river flow is impeded by the narrow channel banks. Flow Studying the flows of rivers is one aspect of hydrology. Direction
Rivers flow downhill with their power derived from gravity. The
direction can involve all directions of the compass and can be a
complex meandering path.
Rivers flowing downhill, from river source to river mouth, do not
necessarily take the shortest path. For alluvial streams, straight and
braided rivers have very low sinuosity and flow directly down hill,
while meandering rivers flow from side to side across a valley.
Bedrock rivers typically flow in either a fractal pattern, or a
pattern that is determined by weaknesses in the bedrock, such as
faults, fractures, or more erodible layers.
Main article: Streamflow
Volumetric flow rate, also known as discharge, volume flow rate, and
rate of water flow, is the volume of water which passes through a
given cross-section of the river channel per unit time. It is
typically measured in cubic metres per second (cumec) or cubic feet
per second (cfs), where 1 m3/s = 35.51 ft3/s; it is
sometimes also measured in litres or gallons per second.
Volumetric flow rate
Frozen river in Alaska
Dams or weirs may be built to control the flow, store water, or
Levees, known as dikes in Europe, may be built to prevent river water
from flowing on floodplains or floodways.
Canals connect rivers to one another for water transfer or navigation.
Environment portal Ecology portal
See also: geography, water cycle, and drainage basin
Arts, entertainment, and media
"Old Man River" The Riverkeepers (book)
Drought Fluvial Salt tide Water conflict
Bridge Ferry Ford (crossing) Tunnel
Exposed riverine sediments Riparian zone
Lists of rivers
List of international border rivers List of rivers by continent List of rivers by discharge List of rivers by length
List of waterways
^ "GNIS FAQ". United States Geological Survey. Retrieved 26 January
^ "WordNet Search: River". The Trustees of Princeton University.
Retrieved 2 October 2009.
^ "Domestic Names: Frequently Asked Question (FAQs), #17". United
States Geological Survey. Retrieved 2 October 2009.
^ Walther, John V. (15 February 2013). Earth's Natural Resources.
Jones & Bartlett Publishers. ISBN 978-1-4496-3234-2.
^ Garde, R. J. (1995). History of fluvial hydraulics. New Age
Publishers. p. 14. ISBN 81-224-0815-X.
^ Garde, R. J. (1995). History of fluvial hydraulics. New Age
Publishers. p. 19. ISBN 81-224-0815-X.
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Jeffrey W. Jacobs. "Rivers, Major World". Water Encyclopaedia. Luna B. Leopold (1994). A View of the River. Harvard University Press. ISBN 0-674-93732-5. OCLC 28889034. — a non-technical primer on the geomorphology and hydraulics of water. Middleton, Nick (2012). Rivers: a very short introduction. New York: Oxford University Press. ISBN 9780199588671.
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Rivers, streams and springs
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Floods and stormwater
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Bar (river morphology)
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