
A river is a natural flowing
watercourse, usually
freshwater
Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the term specifically excludes seawater and brackish water, it does include ...
, flowing towards an
ocean,
sea
The sea, connected as the world ocean or simply the ocean, is the body of salty water that covers approximately 71% of the Earth's surface. The word sea is also used to denote second-order sections of the sea, such as the Mediterranean 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
creek
A creek in North America and elsewhere, such as Australia, is a stream that is usually smaller than a river. In the British Isles it is a small tidal inlet.
Creek may also refer to:
People
* Creek people, also known as Muscogee, Native Americans
...
,
brook
A brook is a small river or natural stream of fresh water. It may also refer to:
Computing
*Brook, a programming language for GPU programming based on C
*Brook+, an explicit data-parallel C compiler
*BrookGPU, a framework for GPGPU programming ...
, 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
A stream is a continuous body of water, body of surface water Current (stream), flowing within the stream bed, bed and bank (geography), banks of a channel (geography), channel. Depending on its location or certain characteristics, 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 water cycle. Water generally collects in a river from precipitation through a drainage basin from surface runoff
Surface runoff (also known as overland flow) is the flow of water occurring on the ground surface when excess rainwater, stormwater, meltwater, or other sources, can no longer sufficiently rapidly infiltrate in the soil. This can occur when th ...
and other sources such as groundwater recharge, springs
Spring(s) may refer to:
Common uses
* Spring (season), a season of the year
* Spring (device), a mechanical device that stores energy
* Spring (hydrology), a natural source of water
* Spring (mathematics), a geometric surface in the shape of a he ...
, and the release of stored water in natural ice and snowpacks.
Rivers are often considered major features within a landscape; however, they actually only cover around 0.1% of the land on Earth. They are made more obvious and significant to humans since many human cities and civilizations are built around the freshwater supplied by rivers and streams. Most of the major cities of the world are situated on the banks of rivers, as they are, or were, used as a source of water, for obtaining food, for transport, as borders, as a defensive measure, as a source of hydropower to drive machinery, for bathing, and as a means of disposing of waste. In the pre-industrial era, larger rivers were a major obstruction to the movement of people, goods, and armies across them. Towns often developed at the few locations they could be crossed. Many major cities such as London are located at the lowest point at which a river could be bridged.
Potamology is the scientific study of rivers, while limnology is the study of inland waters in general.
Topography
Source and drainage basin
A river begins at a source (or more often several sources) which is usually a watershed
Watershed is a hydrological term, which has been adopted in other fields in a more or less figurative sense. It may refer to:
Hydrology
* Drainage divide, the line that separates neighbouring drainage basins
* Drainage basin, called a "watershe ...
, drains all the streams in its drainage basin, follows a watercourse, and ends either at a mouth
In animal anatomy, the mouth, also known as the oral cavity, or in Latin cavum oris, is the opening through which many animals take in food and issue vocal sounds. It is also the cavity lying at the upper end of the alimentary canal, bounded on ...
or mouths which could be a confluence
In geography, a confluence (also: ''conflux'') occurs where two or more flowing bodies of water join to form a single channel. A confluence can occur in several configurations: at the point where a tributary joins a larger river (main stem); o ...
, river delta, etc. The water in a river is usually confined to a channel
Channel, channels, channeling, etc., may refer to:
Geography
* Channel (geography), in physical geography, a landform consisting of the outline (banks) of the path of a narrow body of water.
Australia
* Channel Country, region of outback Austral ...
, made up of a stream bed
A stream bed or streambed is the bottom of a stream or river (bathymetry) or the physical confine of the normal water flow (Channel (geography), channel). The lateral confines or channel margins are known as the stream Bank (geography), banks ...
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.
The term upriver (or upstream) refers to the direction towards the source of the river, i.e. against the direction of flow
Flow may refer to:
Science and technology
* Fluid flow, the motion of a gas or liquid
* Flow (geomorphology), a type of mass wasting or slope movement in geomorphology
* Flow (mathematics), a group action of the real numbers on a set
* Flow (psych ...
. 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 in the direction of flow.
Channels
Rivers can flow down mountains, through valleys or along plains, and can create canyon
A canyon (from ; archaic British English spelling: ''cañon''), or gorge, is a deep cleft between escarpments or cliffs resulting from weathering and the erosion, erosive activity of a river over geologic time scales. Rivers have a natural tenden ...
s or gorges. The river channel typically contains a single stream, but some rivers flow as several interconnecting streams, producing a braided river
A braided river, or braided channel, consists of a network of river channels separated by small, often temporary, islands called braid bars or, in English usage, ''aits'' or ''eyots''.
Braided streams tend to occur in rivers with high sediment l ...
. Braided rivers 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 channel - 1 carrying large volumes of sediment. There are rare cases of river bifurcation
River bifurcation (from la, furca, fork) occurs when a river flowing in a single stream separates into two or more separate streams (called distributaries) which then continue downstream. Some rivers form complex networks of distributaries, typi ...
in which a river divides, and the resultant flows end in different seas. An example is the Nerodime River
The Nerodime ( sq, Nerodimja or Nerodime; sr-cyr, Неродимка) is a river in the Nerodime region of Kosovo, a 41 km-long left tributary to the Lepenc river. It represents Europe's only instance of a river bifurcation flowing into tw ...
in Kosovo.
A river flowing in its channel is a source of energy that acts on the river channel to change its shape and form. In 1757, German hydrologist Albert Brahms
Albert Brahms (October 24, 1692 – August 3, 1758) was a Frisian dike judge, an elected community leader responsible for maintaining the dikes that protected the area against the Wadden Sea, and a pioneer of hydraulic engineering.
Biography
Brah ...
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
An oxbow lake is a U-shaped lake or pool that forms when a wide meander of a river is cut off, creating a free-standing body of water. In South Texas, oxbows left by the Rio Grande are called '' resacas''. In Australia, oxbow lakes are call ...
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.
Types and ratings
Rivers have been classified by many criteria including their topography, their biotic
Biotics describe living or once living components of a community; for example organisms, such as animals and plants.
Biotic may refer to:
*Life, the condition of living organisms
*Biology, the study of life
* Biotic material, which is derived from ...
status, and their relevance to white water rafting or canoeing activities.
Subsurface rivers: subterranean and subglacial
Most but not all rivers flow on the surface. Subterranean rivers flow underground in caves. Such rivers are frequently found in regions with limestone geologic formations. Subglacial stream Subglacial streams are conduits of glacial meltwater that flow at the base of glaciers and ice caps.
Hooke, Roger LeB. ...
s are the braided rivers that flow at the beds of glaciers and