
A river is a natural flowing
watercourse
A watercourse is the 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 Cou ...

, usually
freshwater
Fresh water or freshwater is any naturally occurring liquid or frozen water
Water (chemical formula H2O) is an , transparent, tasteless, odorless, and , which is the main constituent of 's and the s of all known living organisms (in ...
, flowing towards an
ocean
The ocean (also the sea
The sea, connected as the world ocean or simply the ocean
The ocean (also the sea or the world ocean) is the body of salt water which covers approximately 71% of the surface of the Earth. ,
sea
The sea, connected as the world ocean or simply the ocean
The ocean (also the sea or the world ocean) is the body of salt water which covers approximately 71% of the surface of the Earth.

,
lake
A lake is an area filled with water, localized in a basin, surrounded by land
Land is the solid surface of Earth that is not permanently submerged in water. Most but not all land is situated at elevations above sea level (variable ove ...

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
A stream is a body of water
(Lysefjord) in Norway
Norway, officially the Kingdom of Norway,Names in the official and recognised languages: Bokmål
Bokmål (, ; literally "book tongue") is an official written standard for the No ...

, creek, brook, rivulet, and
rill
In hillslope geomorphology, a rill is a shallow Channel (geography), channel (no more than a few tens of centimetres deep) cut into soil by the erosion, erosive action of Overland flow, flowing water. Similar but smaller incised channels are kno ...
. 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
A burn is a type of injury
Injury, also known as physical trauma, is damage
Damage is any change in a thing, often a physical object, that degrades it away from its initial state. It can broadly be defined as "changes introduced into a ...
" 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
The water cycle, also known as the hydrologic cycle or the hydrological cycle, describes the continuous movement of water
Water is an Inorganic compound, inorganic, Transparency and translucency, transparent, tasteless, odorless, ...
. Water generally collects in a river from precipitation
In meteorology
Meteorology is a branch of the (which include and ), with a major focus on . The study of meteorology dates back , though significant progress in meteorology did not begin until the 18th century. The 19th century saw mod ...
through a drainage basin
A drainage basin is any area of land where precipitation collects and drains off into a common outlet, such as into a river, bay, or other body of water. The drainage basin includes all the surface water from surface runoff, rain runoff, snowm ...

from surface runoff
Surface runoff (also known as overland flow) is the flow of water
Water (chemical formula H2O) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydros ...
and other sources such as groundwater recharge
Groundwater recharge or deep drainage or deep percolation is a process, where moves downward from to . Recharge is the primary method through which water enters an . This process usually occurs in the below plant s and, is often expressed as ...
, 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 heli ...
, and the release of stored water in natural ice and snowpacks (e.g., from glacier
A glacier (; ) is a persistent body of dense ice
Ice is into a state. Depending on the presence of such as particles of soil or bubbles of air, it can appear transparent or a more or less bluish-white color.
In the , ice is abunda ...

s).
Rivers and streams 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
Major is a military rank of commissioned officer status, with corresponding ranks existing in many military forces throughout the world.
Background
When used unhyphenated, in conjunction with no other indicators, major is one rank senior to ...
are situated on the banks of rivers, as they are, or were, used as a source of water
Source or subsource or ''variation'', may refer to:
Research
* Historical document
* Historical source
* Source (intelligence) or subsource, typically a confidential provider of non open-source intelligence
* Source (journalism), a person, public ...

, for obtaining food
Food is any substance consumed to provide Nutrient, nutritional support for an organism. Food is usually of plant, animal or Fungus, fungal origin, and contains essential nutrients, such as carbohydrates, fats, protein (nutrient), proteins, vi ...

, for transport
Transport (in British English
British English (BrE) is the standard dialect
A standard language (also standard variety, standard dialect, and standard) is a language variety that has undergone substantial codification of grammar and ...
, as border
Borders are boundaries of or legal s, such as s, , , and other . Borders are established through agreements between political or social entities that control those areas; the creation of these agreements is called .
Some borders—such as mos ...

s, as a defensive measure, as a source of hydropower
Hydropower (from el, ὕδωρ, "water"), also known as water power, is the use of falling or fast-running water
Water (chemical formula H2O) is an , transparent, tasteless, odorless, and , which is the main constituent of 's and th ...
to drive machinery, for bathing
Bathing is the washing
Washing is a method of cleaning
Cleaning is the process of removing unwanted substances, such as dirt, infectious agents, and other impurities, from an object or environment. Cleaning occurs in many different contexts, ...

, and as a means of disposing of waste
Waste (or wastes) are unwanted or unusable materials. Waste is any substance which is discarded after primary use, or is worthless, defective and of no use. A by-product
A by-product or byproduct is a secondary product derived from a produ ...

.
Potamology is the scientific study of rivers, while limnology
Limnology ( ; from Greek λίμνη, ''limne'', "lake" and λόγος, ''logos'', "knowledge") is the study of inland aquatic ecosystems.
The study of limnology includes aspects of the biology, biological, chemistry, chemical, physics, physical, ...
is the study of inland waters in general.
Topography
Source and drainage basin
A river begins at a source
Source or subsource or ''variation'', may refer to:
Research
* Historical document
* Historical source
* Source (intelligence) or subsource, typically a confidential provider of non open-source intelligence
* Source (journalism), a person, public ...
(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
** European watershed
* Drainage basin, ...
, drains all the streams in its drainage basin
A drainage basin is any area of land where precipitation collects and drains off into a common outlet, such as into a river, bay, or other body of water. The drainage basin includes all the surface water from surface runoff, rain runoff, snowm ...

, follows a path called a rivercourse (or just ''course'') and ends at either at a mouth
In animal anatomy
Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism
In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is ...

or mouths which could be a confluence
In geography
Geography (from Greek
Greek may refer to:
Greece
Anything of, from, or related to Greece
Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is ...

, river delta
A river delta is a landform
A landform is a natural or artificial feature of the solid surface of the Earth or other planetary body
A planet is an astronomical body
Astronomy (from el, ἀστρονομία, literally meaning the ...

, 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 Austr ...
, made up of a stream bed
A stream bed or streambed is the channel bottom of a stream
A stream is a body of water with surface water flowing within the stream bed, bed and Bank (geography), banks of a Channel (geography), channel. The flow of a stream is controlle ...
between banks
A bank is a financial institution
Financial institutions, otherwise known as banking institutions, are corporation
A corporation is an organization—usually a group of people or a company—authorized by the State (polity), stat ...
. In larger rivers there is often also a wider floodplain
A floodplain or flood plain or bottomlands is an area of land adjacent to 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 int ...
shaped by flood
A flood is an overflow of water that submerges land that is usually dry. In the sense of "flowing water", the word may also be applied to the inflow of the . Floods are an area of study of the discipline and are of significant concern in , a ...

-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. Likewise, the term downriver (or downstream) describes the direction towards the mouth of the river, in which the current
Currents or The Current may refer to:
Science and technology
* Current (fluid)
A current in a fluid
In physics, a fluid is a substance that continually Deformation (mechanics), deforms (flows) under an applied shear stress, or external force. ...
flows. The term left bank refers to the left bank in the direction of flow, right bank to the right.
River channel
Rivers can flow down mountains, through valleys
A valley is an elongated low area often running between hills or mountains, which will typically contain a river or stream running from one end to the other. Most valleys are formed by erosion
In earth science
Earth science or geos ...
(depressions
Depression may refer to:
Mental health
* Depression (mood), a state of low mood and aversion to activity
* Mood disorders characterized by depression are commonly referred to as simply ''depression'', including:
** Dysthymia
** Major depressive ...
) or along plain
In geography
Geography (from Greek
Greek may refer to:
Greece
Anything of, from, or related to Greece
Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population i ...

s, and can create canyons
A canyon (; archaic British English
British English (BrE) is the standard dialect of the English language
English is a West Germanic languages, West Germanic language first spoken in History of Anglo-Saxon England, early medieval En ...

or gorges. The river channel typically contains a single stream of water, but some rivers flow as several interconnecting streams of water, producing a braided river
A braided river, or braided channel, consists of a network of river s separated by small, often temporary, s called s or, in English usage, ''s'' or ''eyots''. Braided streams tend to occur in rivers with high loads and/or coarse grain sizes, and ...
. Extensive braided rivers are now found in only a few regions worldwide, such as the South Island
The South Island, also officially named , is the larger of the two major in surface area, the other being the smaller but more populous . It is bordered to the north by , to the west by the , and to the south and east by the . The South Island ...

of New Zealand
New Zealand ( mi, Aotearoa
''Aotearoa'' (; commonly pronounced by English
English usually refers to:
* English language
English is a West Germanic languages, West Germanic language first spoken in History of Anglo-Saxon Engl ...

. They also occur on peneplain
In geomorphology
incised into shale at the foot of the North Caineville Plateau, Utah, within the pass carved by the Fremont River (Utah), Fremont River and known as the Blue Gate. Grove Karl Gilbert, GK Gilbert studied the landscapes of this a ...

s and some of the larger river delta
A river delta is a landform
A landform is a natural or artificial feature of the solid surface of the Earth or other planetary body
A planet is an astronomical body
Astronomy (from el, ἀστρονομία, literally meaning the ...

s. 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 deltas such as the pictured delta of the Salween River in Myanmar">Salween_River.html" ;"title="River deltas such as the pictured delta of the Salween River">River deltas such as the pictured delta of the Salween River in Myanmar often show ...
in which a river divides and the resultant flows ending in different seas. An example is the bifurcation of Nerodime River
The Nerodimka ( sr-cyr, Неродимка; sq, Nerodimja, Nerodime) is a river in the Nerodimlje region of Kosovo
Kosovo, or ; sr-Cyrl, Косово officially the Republic of Kosovo,; sr, / is a international recognition of Koso ...
in Kosovo
Kosovo, or ; sr-Cyrl, Косово officially the Republic of Kosovo,; sr, / is a partially recognised state in Southeast Europe
Southeast Europe or Southeastern Europe () is a geographical subregion
A subregion is a part of a ...

.
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, the German hydrologist Albert Brahms
Albert Brahms (October 24, 1692 – August 3, 1758) was a Frisian Dijkgraaf (official), dike judge, an elected community leader responsible for maintaining the Levee, dikes that protected the area against the Wadden Sea, and a pioneer of hydraulic ...
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
A glacier ( or ) is a persistent body of dense ice that is constantly moving under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. Glaciers slowly deform and flow under str ...
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, meander
A meander is one of a series of regular sinuous curves in the channel of a river or other watercourse. It is produced as a watercourse the s of an outer, concave bank () and deposits sediments on an inner, convex bank which is typically a . Th ...

s 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 that forms when a wide meander of a river is Meander cutoff, cut off, creating a free-standing body of water. In south Texas, oxbows left by the Rio Grande are called ''resaca (channel), resacas''. In Australia ...

or billabong
A billabong ( ) is an Australian term for an oxbow lake, an isolated pond left behind after a river changes course. Billabongs are usually formed when the path of a creek or river
A river is a natural flowing watercourse, usually freshwat ...

. Rivers that carry large amounts of sediment
Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently sediment transport, transported by the action of wind, water, or ice or by the force of gravity acting on the particles. ...

may develop conspicuous deltas at their mouths. Rivers whose mouths are in saline waters may form estuaries
An estuary is a partially enclosed coastal body of brackish water
Brackish water, also sometimes termed brack water, is water occurring in a natural environment having more salinity
File:IAPSO Standard Seawater.jpg, upInternational Associatio ...

.
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
A floodplain or flood plain or bottomlands is an area of land adjacent to 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 int ...
(called the hyporheic zone
The hyporheic zone is the region of sediment and porous space beneath and alongside a stream bed
A stream is a body of water
( Lysefjord) in Norway
Norway ( nb, ; nn, ; se, Norga; smj, Vuodna; sma, Nöörje), officially the ...
). For many rivers in large valleys, this unseen component of flow may greatly exceed the visible flow.
Types and ratings of rivers
Rivers have been classified by many criteria including their topography
Topography is the study of the forms and features of land surface
Relief map of Sierra Nevada, Spain
Terrain or relief (also topographical
Topography is the study of the forms and features of land surfaces. The topography of an ...
, 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 l ...
status, and their relevance to white water rafting
Rafting and whitewater rafting are recreational which use an inflatable to navigate a or other body of water. This is often done on or different degrees of rough water. Dealing with risk is often a part of the experience.
This activi ...

or canoe
A canoe is a lightweight narrow , typically pointed at both ends and open on top, propelled by one or more seated or kneeling paddlers facing the direction of travel and using a single-bladed .
In , the term "canoe" can also refer to a , while ...

ing activities.
Subsurface rivers: Subterranean and Subglacial
Most but not all rivers flow on the surface. Subterranean river
A subterranean river is 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 without r ...
s flow underground in cave
A cave or cavern is a natural void in the Earth#Surface, ground, specifically a space large enough for a human to enter. Caves often form by the weathering of rock and often extend deep underground. The word ''cave'' can also refer to much small ...

s or caverns. Such rivers are frequently found in regions with limestone
Limestone is a common type of carbonate
In chemistry, a carbonate is a salt
Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of Salt (chemistry), salts; salt in its na ...

geologic formation
A geological formation, or formation, is a body of rock having a consistent set of physical characteristics (lithology
as seen in southeastern Utah
The lithology of a Rock (geology), rock unit is a description of its physical characteristics vis ...
s. Subglacial streams are the braided rivers that flow at the beds of glaciers and ice sheet
In , an ice sheet, also known as a continental glacier, is a mass of that covers surrounding terrain and is greater than . The only current ice sheets are in and ; during the at (LGM) the covered much of , the ice sheet covered and the c ...

s, permitting meltwater to be discharged at the front of the glacier. Because of the gradient in pressure
Pressure (symbol: ''p'' or ''P'') is the force
In physics, a force is an influence that can change the motion (physics), motion of an Physical object, object. A force can cause an object with mass to change its velocity (e.g. moving fr ...

due to the overlying weight of the glacier, such streams can even flow uphill.
Permanence of flow: Perennial and Ephemeral
An intermittent river (or ephemeral
Ephemerality (from the Greek language, Greek word , meaning 'lasting only one day') is the concept of things being transitory, existing only briefly. Typically the term ephemeral is used to describe objects found in nature, although it can descr ...
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 Bournemouth
Bournemouth () is a coastal resort town on the south coast of England. At the 2011 census, the town had a population of 183,491. With Poole to the west and Christchurch, Dorset, Christchurch in the east, Bournemouth is part of the South East Do ...

and Eastbourne
Eastbourne () is a town and seaside resort in East Sussex
East Sussex is a county in South East England on the English Channel
The English Channel,, "The Sleeve"; nrf, la Maunche, "The Sleeve" ( Cotentinais) or (Jèrriais), (Guer ...

. Even in humid regions, the location where flow begins in the smallest tributary
A tributary, or affluent, is a stream or river that flows into a larger stream or main stem (or parent) river or a lake. A tributary does not flow directly into a sea or ocean. Tributaries and the main stem river drain the surrounding drainage ba ...
streams generally moves upstream in response to precipitation and downstream in its absence or when active summer vegetation diverts water for evapotranspiration
Evapotranspiration (ET) is the sum of water evaporation and transpiration from a surface area to the Atmosphere of Earth, atmosphere. Evaporation accounts for the movement of water to the air from sources such as the soil, canopy interception, and ...

. Normally dry rivers in arid zones are often identified as arroyos or other regional names.
The meltwater from large hailstorms can create a slurry
A slurry is a mixture of denser solids suspended in liquid, usually water. The most common use of slurry is as a means of transporting solids, the liquid being a carrier that is pumped on a device such as a . The size of solid particles may vary ...
of water, hail and sand or soil, forming temporary rivers.
Stream order classification of rivers: Fleuve and Rivière
The Strahler Stream Order
In mathematics, the Strahler number or Horton–Strahler number of a mathematical tree (graph theory), tree is a numerical measure of its branching complexity.
These numbers were first developed in hydrology by and ; in this application, they are ...
ranks rivers based on the connectivity and hierarchy of contributing tributaries. Headwaters are first order while the Amazon River
The Amazon River (, ; es, Río Amazonas, pt, Rio Amazonas) in South America
South America is a entirely in the and mostly in the , with a relatively small portion in the . It can also be described as the southern of a single con ...

is twelfth order. Approximately 80% of the rivers and streams in the world are of the first and second order.
In certain languages, distinctions are made among rivers based on their stream order. In French, for example, rivers that run to the sea are called ''fleuve'', while other rivers are called ''rivière''. For example, in Canada
Canada is a country in the northern part of North America
North America is a continent
A continent is any of several large landmasses. Generally identified by convention (norm), convention rather than any strict criteria, ...

, the Churchill River in Manitoba
Manitoba ( ) is a Provinces and territories of Canada, province of Canada at the Centre of Canada, longitudinal centre of the country. It is Canada's Population of Canada by province and territory, fifth-most populous province, with a population o ...

is called ''la rivière Churchill'' as it runs to Hudson Bay
Hudson Bay ( iu, text=ᑲᖏᖅᓱᐊᓗᒃ ᐃᓗᐊ, translit=Kangiqsualuk ilua or iu, text=ᑕᓯᐅᔭᕐᔪᐊᖅ, translit=Tasiujarjuaq; french: baie d'Hudson), sometimes called Hudson's Bay (usually historically), is a large body of sal ...
, but the Churchill River in Labrador
, nickname = "The Big Land"
, etymology =
, subdivision_type = Country
, subdivision_name = Canada
, subdivision_type1 = Province
A province is al ...

is called ''le fleuve Churchill'' as it runs to the . As most rivers in France are known by their names only without the word ''rivière'' or ''fleuve'' (e.g. ''la Seine
)
, mouth_location = Le Havre
Le Havre (, ; nrf, Lé Hâvre) is an urban French commune
A commune is an intentional community of people sharing living spaces, interests, values, beliefs, and often property
Property (''lati ...

'', not ''le fleuve Seine'', even though the Seine is classed as a ''fleuve''), one of the most prominent rivers in the Francophonie
The Organisation internationale de la Francophonie (OIF; sometimes shortened to the Francophonie, french: La Francophonie , but also called International Organisation of La Francophonie in English-language context) is an international organiza ...

commonly known as ''fleuve'' is ''le fleuve Saint-Laurent'' (the Saint Lawrence River
The St. Lawrence River is a large 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 c ...
).
Since many ''fleuves'' are large and prominent, receiving many tributaries, the word is sometimes used to refer to certain large rivers that flow into other ''fleuves''; however, even small streams that run to the sea are called ''fleuve'' (e.g. '' fleuve côtier'', "coastal ''fleuve''").
Topographical classification: Bedrock and Alluvial rivers
Rivers can generally be classified as either alluvial
Alluvium (from the Latin
Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of t ...
, bedrock
Bedrock in geology
Geology (from the γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is a branch of concerned with both the liquid and , the of which it is composed, and the processes by which they cha ...
, or some mix of the two. Alluvial rivers have channels and floodplains that are self-formed in unconsolidated or weakly consolidated sediments. They erode
Erode () is a city in the Indian state of Tamil Nadu. The seventh largest urban agglomeration in the state, after Chennai, Coimbatore, Madurai, Tiruchirapalli, Tiruppur and Salem, Tamil Nadu, Salem. It is also the administrative headquarters of ...

their banks
A bank is a financial institution
Financial institutions, otherwise known as banking institutions, are corporation
A corporation is an organization—usually a group of people or a company—authorized by the State (polity), stat ...
and deposit material on bars and their floodplain
A floodplain or flood plain or bottomlands is an area of land adjacent to 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 int ...
s.
Bedrock rivers
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 particularly hard lithology
as seen in southeastern Utah
The lithology of a Rock (geology), rock unit is a description of its physical characteristics visible at outcrop
An outcrop or rocky outcrop is a visible exposure of bedrock
Bedrock in geology
Geology (fr ...
causes a river to have a steepened reach that has not been covered in modern alluvium
Alluvium (from the Latin
Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of t ...
. 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 sub-types: Youthful, Mature, Old and Rejuvenated
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 bed aggradation
Aggradation (or alluviation) is the term used in geology
Geology (from the γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is a branch of concerned with both the liquid and , the of which it is composed, a ...

.
At the start of the 20th century William Morris Davis
William Morris Davis (February 12, 1850 – February 5, 1934) was an American geographer
A geographer is a physical scientist, social scientist and humanist whose area of study is geography, the study of Earth's natural environment and human ...

devised the "cycle of erosionThe geographic cycle, or cycle of erosion, is an idealized model that explains the development of relief
Relief is a sculptural technique where the sculpted elements remain attached to a solid background of the same material. The term ''wikt:rel ...
" method of classifying rivers based on their "age". Although Davis's system is still found in many books today, after the 1950s and 1960s it became increasingly criticized and rejected by geomorphologists. His scheme did not produce testable hypotheses and was therefore deemed non-scientific. Examples of Davis's river "ages" include:
* 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
The Christian
Christians () are people who follow or adhere to Christianity, a monotheistic Abrahamic religion based on the life and teachings of Jesus in Christianity, Jesus Christ. The words ''Christ (title), Christ'' and ''Christian ...
and Ebro
, name_etymology =
, image = Zaragoza shel.JPG
, image_size =
, image_caption = The Ebro River in Zaragoza
, map = SpainEbroBasin.png
, map_size =
, map_caption = The Ebro r ...

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
Mississippi () is a U.S. state, state in the Southeastern United States, Southeastern region of the United States, bordered to the north by Tennessee; to the east by Alabama; to the south by the Gulf of Mexico; to the southwest by Louisiana; a ...

, Saint Lawrence
Saint Lawrence or Laurence ( la, Laurentius, lit. "laurelled"; 31 December AD 225 – 10 August 258) was one of the seven deacons of the city of Rome
, established_title = Founded
, established_date = 753 BC
, founder ...
, Danube
The Danube ( ; ) is the List of rivers of Europe#Longest rivers, second-longest river in Europe, after the Volga in Russia. It flows through much of Central Europe, Central and Southeastern Europe, from the Black Forest into the Black Sea. It ...

, Ohio
Ohio () is a state
State may refer to:
Arts, entertainment, and media Literature
* ''State Magazine'', a monthly magazine published by the U.S. Department of State
* The State (newspaper), ''The State'' (newspaper), a daily newspaper in Co ...

, Thames
The River Thames ( ), known alternatively in parts as the River Isis, is a river that flows through southern England
Southern England, or the South of England, also known as the South, is an area of England consisting of its southernm ...
and rivers.
* Old river: A river with a low gradient and low erosive energy. Old rivers are characterized by flood plains. Examples are the Yellow
Yellow is the color between green and Orange (colour), orange on the Visible spectrum, spectrum of visible light. It is evoked by light with a dominant wavelength of roughly 575585 Nanometre, nm. It is a primary color in subtractive color syst ...
, lower Ganges
The Ganges ( ) (in India: Ganga ( ); in Bangladesh: Padma River, Padma ( )). "The Ganges Basin, known in India as the Ganga and in Bangladesh as the Padma, is an international river to which India, Bangladesh, Nepal and China are the riparian ...

, Tigris
The Tigris () is the easternmost of the two great rivers that define Mesopotamia, the other being the Euphrates. The river flows south from the mountains of the Armenian Highlands through the Syrian Desert, Syrian and Arabian Deserts, and empti ...

, Euphrates
The Euphrates () is the longest and one of the most historically important rivers of Western Asia. Tigris–Euphrates river system, Together with the Tigris, it is one of the two defining rivers of Mesopotamia (the "Land Between the Rivers"). O ...
, Indus#REDIRECT Indus River
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and lower