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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 ...

watercourse
, 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.
sea
,
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 ...

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 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 ...

stream
, 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 ...

drainage basin
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 ...

glacier
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 ...

source of water
, 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 ...

food
, 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 ...

border
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, ...

bathing
, 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 ...

waste
. 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 ...

drainage basin
, 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 ...

mouth
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 ...

confluence
,
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 ...

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 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 ...

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. 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 ...

plain
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 ...

canyons
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 ...

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 ...

New Zealand
. 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 ...

peneplain
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 ...

river delta
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 ...

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, 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 ...

meander
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 ...

oxbow lake
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 ...

billabong
. 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. ...

sediment
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 ...

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 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 ...

rafting
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 ...

canoe
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 ...

cave
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 ...

limestone
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 ...

ice sheet
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 ...

pressure
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 ...

Bournemouth
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 ...

Eastbourne
. 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 ...

evapotranspiration
. 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 ...

Amazon River
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, ...

Canada
, 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 ...

Manitoba
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 ...

Labrador
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 ...

Seine
'', 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 ...

Francophonie
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 ...

erode
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 ...

aggradation
. 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 ...

William Morris Davis
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 ...

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 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 ...

Mississippi
,
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 ...

Danube
,
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 ...

Ohio
,
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 ...

Ganges
,
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 ...

Tigris
,
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
{{Redirect category shell, {{R from move {{R from miscapitalisation {{R unprintworthy ...

Indus
and lower
Nile The Nile, , Bohairic , lg, Kiira , Nobiin Nobiin, or Mahas, is a Northern Nubian languages, Nubian language of the Nilo-Saharan languages, Nilo-Saharan language family. "Nobiin" is the genitive case, genitive form of ''Nòòbíí'' ("Nub ...

Nile
rivers. * Rejuvenated river: A river with a gradient that is raised by
tectonic Tectonics (; ) are the processes that control the structure and properties of the Earth's crust and its evolution through time. These include the processes of mountain building A mountain is an elevated portion of the Earth's crust, gen ...
uplift. Examples are the
Rio Grande The Rio Grande ( and ), known in Mexico as the Río Bravo del Norte and as the Río Bravo, is one of the principal river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another riv ...

Rio Grande
and
Colorado River The Colorado River ( es, Río Colorado) is one of the principal rivers (along with the Rio Grande) in the Southwestern United States and northern Mexico. The river drains an expansive, arid drainage basin, watershed that encompasses parts of ...

Colorado River
. The ways in which a river's characteristics vary between its upper and lower course are summarized by the
Bradshaw model The Bradshaw Model is an idealized geographical 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 Sout ...
. Power-law relationships between channel slope, depth, and width are given as a function of discharge by "
river regimeRiver regime can describe one of two characteristics of a reach of an alluvial river: * The variability in its discharge (hydrology), discharge throughout the course of a year in response to precipitation, temperature, evapotranspiration and drainage ...
".


Biotic classification of rivers: Crenon, Rhithron, Potamon

There are several systems of classification based on biotic conditions typically assigning classes from the most
oligotrophic The Trophic State Index (TSI) is a classification system designed to rate water bodies based on the amount of biological productivity they sustain. Although the term "trophic index" is commonly applied to lakes, any surface water body may be inde ...
or unpolluted through to the most
eutrophic Eutrophication (from Greek ''eutrophos'', "well-nourished") is a limnological term for the process by which a body of water ( Lysefjord) in Norway Norway ( nb, ; nn, ; se, Norga; smj, Vuodna; sma, Nöörje), officially the Ki ...
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 The Water Framework Directive 2000/60/EC is an EU directive which commits European Union The European Union (EU) is a political and economic union of Member state of the European Union, member states that are located primarily in Europ ...
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 This article details the geographical distribution of speakers of the French language French ( or ) is a Romance language The Romance languages, less commonly Latin or Neo-Latin languages, are the modern languages that evolved from ...
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.


Navigation difficulty classification

The
International Scale of River Difficulty The international scale of river difficulty is an American system used to rate the difficulty of navigating a stretch of river, or a single (sometimes whitewater) rapid. The scale was created by the American Whitewater Association to evaluate ...
is used to rate the challenges of navigation—particularly those with rapids. Class I is the easiest and Class VI is the hardest.


Flow of river

Studying the flows of rivers is one aspect of
hydrology Hydrology (from Ancient Greek, Greek wikt:ὕδωρ, ὕδωρ, ''hýdōr'' meaning "water" and wikt:λόγος, λόγος, ''lógos'' meaning "study") is the scientific study of the movement, distribution, and management of water on Earth and ...
.


Flow Characteristics


Flow 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 In mathematics Mathematics (from Greek: ) includes the study of such topics as numbers (arithmetic and number theory), formulas and related structures (algebra), shapes and spaces in which they are contained (geometry), and quantities a ...

fractal
pattern, or a pattern that is determined by weaknesses in the bedrock, such as faults,
fractures Fracture is the separation of an object or material into two or more pieces under the action of stress. The fracture of a solid usually occurs due to the development of certain displacement discontinuity surfaces within the solid. If a displa ...
, or more erodible layers.


Flow rate

Volumetric flow rate In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space and time, and the related entities of energy and force. ...
, 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 A cubic metre per second (m3s−1, m3/s, cumecs or cubic meter per second in American English American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States English or U.S. English, is the set of varieties of the English la ...
(cumec) or
cubic feet per second The cubic foot (symbol ft3)
, .
is an Imperial unit, imperial and United States customary units, US cus ...
(cfs), where 1 m3/s = 35.51 ft3/s; it is sometimes also measured in
litre The litre (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 ...

litre
s or
gallon The gallon is a unit Unit may refer to: Arts and entertainment * UNIT Unit may refer to: Arts and entertainment * UNIT, a fictional military organization in the science fiction television series ''Doctor Who'' * Unit of action, a discrete pie ...
s per second. Volumetric flow rate can be thought of as the mean velocity of the flow through a given cross-section, times that cross-sectional area. Mean velocity can be approximated through the use of the Law of the Wall. In general, velocity increases with the depth (or
hydraulic radiusThe Manning formula is an Empirical relationship, empirical formula estimating the average velocity of a liquid flowing in a conduit that does not completely enclose the liquid, i.e., open channel flow. However, this equation is also used for calcula ...
) and slope of the river channel, while the cross-sectional area scales with the depth and the width: the double-counting of depth shows the importance of this variable in determining the discharge through the channel.


Effects of flow


Fluvial erosion

In its youthful stage the river causes erosion in the water-course, deepening the valley.
Hydraulic actionis the erosion that occurs when the motion of water against a rock surface produces mechanical weathering. Most generally, it is the ability of moving water (flowing or waves) to dislodge and transport rock particles. This includes a number of speci ...
loosens and dislodges the rock which further erodes the banks and the river bed. Over time, this deepens the river bed and creates steeper sides which are then weathered. The steepened nature of the banks causes the sides of the valley to move downslope causing the valley to become
V-shaped Many shapes have metaphorical names, i.e., their names are metaphors: these shapes are named after a most common object that has it. For example, "U-shape" is a shape that resembles the letter U, a Gaussian function, bell-shaped curve has the shape ...

V-shaped
.
Waterfall A waterfall is a point in a or where water flows over a vertical drop or a series of steep drops. Waterfalls also occur where drops over the edge of a tabular or . Waterfalls can be formed in several ways, but the most common method of fo ...

Waterfall
s also form in the youthful river valley where a band of hard rock overlays a layer of soft rock. Differential erosion occurs as the river erodes the soft rock more readily than the hard rock, this leaves the hard rock more elevated and stands out from the river below. A plunge pool forms at the bottom and deepens as a result of hydraulic action and abrasion.


Flooding

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 stageFlood stage is the water level Water level, also known as gauge height or stage, is the elevation of the free surface of a sea, stream, lake or reservoir A reservoir (; from French language, French ''réservoir'' ) is most commonly an enlar ...
. 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
levee file:River Levee Cross Section Figure.svg, Components of a levee: file:Sacramento River Levee.jpg, The side of a levee in Sacramento, California A levee (), dike (American English), dyke (Commonwealth English), embankment, floodbank, or stop ...

levee
s, the straightening of channels, and the draining of natural
wetland A wetland is a distinct ecosystem An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles ...

wetland
s. 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.
Detention basin A detention basin or retarding basin is an excavated area installed on, or adjacent to, tributaries of river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some case ...
s finally also reduce the risk of flooding significantly by being able to take up some of the flood water.


Sediment yield at outlet

Sediment yield is the total quantity of particulate matter (suspended or bedload) reaching the outlet of a drainage basin over a fixed time frame. Yield is usually expressed as kilograms per square kilometre per year. Sediment delivery processes are affected by a myriad of factors such as drainage area size, basin slope, climate, sediment type (lithology), vegetation cover, and human land use / management practices. The theoretical concept of the 'sediment delivery ratio' (ratio between yield and total amount of sediment eroded) indicates that not all of the sediment is eroded within a certain catchment that reaches out to the outlet (due to, for example, deposition on floodplains). Such storage opportunities are typically increased in catchments of larger size, thus leading to a lower yield and sediment delivery ratio.


Brackish water

Brackish waster occurs in most rivers where they meet the sea. The extent of brackish water may extend a significant distance upstream, especially in areas with high tidal ranges.


Ecosystem of rivers


River biota

The organisms in the
riparian zone A riparian zone or riparian area is the interface between land and 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 an ...
respond to changes in river channel location and patterns of flow. The ecosystem of rivers is generally described by the river continuum concept, which has some additions and refinements to allow for dams and waterfalls and temporary extensive flooding. The concept describes the river as a system in which the physical parameters, the availability of food particles and the composition of the ecosystem are continuously changing along its length. The food (energy) that remains from the upstream part is used downstream. The general pattern is that the first order streams contain particulate matter (decaying leaves from the surrounding forests) which is processed there by shredders like
Plecoptera Plecoptera is an order (biology), order of insects, commonly known as stoneflies. Some 3,500 species are described worldwide, with new species still being discovered. Stoneflies are found worldwide, except Antarctica. Stoneflies are believed to ...

Plecoptera
larvae. The products of these shredders are used by collectors, such as
Hydropsychidae The Hydropsychidae are a family In human society, family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of families is to mainta ...
, and further downstream algae that create the
primary production In ecology, primary production is the synthesis of organic compounds from atmospheric or aqueous carbon dioxide. It principally occurs through the process of photosynthesis, which uses light as its source of energy, but it also occurs through ch ...
become the main food source of the organisms. All changes are gradual and the distribution of each species can be described as a
normal curve In probability theory Probability theory is the branch of mathematics concerned with probability. Although there are several different probability interpretations, probability theory treats the concept in a rigorous mathematical manner by ex ...
, with the highest density where the conditions are optimal. In rivers succession is virtually absent and the composition of the ecosystem stays fixed .


River chemistry

The chemistry of rivers is complex and depends on inputs from the atmosphere, the geology through which it travels and the inputs from man's activities. The chemical composition of the water has a large impact on the ecology of that water for both plants and animals and it also affects the uses that may be made of the river water. Understanding and characterising river water chemistry requires a well designed and managed sampling and analysis.


Uses of rivers


Construction material

The coarse sediments,
gravel Gravel is a loose aggregation of rock fragments. Gravel occurs naturally throughout the world as a result of sedimentary and erosive geologic processes; it is also produced in large quantities commercially as crushed stone. Gravel is classifie ...

gravel
, and
sand Sand is a granular material composed of finely divided rock (geology), rock and mineral particles. Sand has various compositions but is defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer ...

sand
, generated and moved by rivers are extensively used in construction. In parts of the world this can generate extensive new lake habitats as gravel pits re-fill with water. In other circumstances it can destabilise the river bed and the course of the river and cause severe damage to spawning fish populations which rely on stable gravel formations for egg laying. In upland rivers,
rapid Rapids are sections of a river where the river bed has a relatively steep stream gradient, gradient, causing an increase in water velocity and turbulence. Rapids are hydrology, hydrological features between a ''run'' (a smoothly flowing part of ...

rapid
s with
whitewater Whitewater forms in a rapid context, in particular, when a river's Stream gradient, gradient changes enough to generate so much turbulence that air is trapped within the water. This forms an unstable current that foam, froths, making the wat ...

whitewater
or even
waterfall A waterfall is a point in a or where water flows over a vertical drop or a series of steep drops. Waterfalls also occur where drops over the edge of a tabular or . Waterfalls can be formed in several ways, but the most common method of fo ...

waterfall
s occur. Rapids are often used for recreation, such as whitewater kayaking.


Energy production

Fast flowing rivers and waterfalls are widely used as sources of energy, via
watermill A watermill or water mill is a mill that uses hydropower Hydropower (from el, ὕδωρ, "water"), also known as water power, is the use of falling or fast-running water to Electricity generation, produce electricity or to power machines. T ...

watermill
s and
hydroelectric plant Hydroelectricity, or hydroelectric power, is electricity produced from hydropower. In 2015, hydropower generated 16.6% of the world's total electricity and 70% of all renewable electricity,http://www.ren21.net/wp-content/uploads/2016/06/GSR ...
s. Evidence of watermills shows them in use for many hundreds of years, for instance in
Orkney Orkney (; sco, Orkney; on, Orkneyjar; nrn, Orknøjar), also known as the Orkney Islands, is an archipelago An archipelago ( ), sometimes called an island group or island chain, is a chain, cluster or collection of island A ...

Orkney
at Dounby Click Mill. Prior to the invention of steam power, watermills for grinding
cereal A cereal is any Poaceae, grass cultivated (grown) for the edible components of its grain (botanically, a type of fruit called a caryopsis), composed of the endosperm, cereal germ, germ, and bran. The term may also refer to the resulting grain ...

cereal
s and for processing
wool Wool is the textile A textile is a flexible material made by creating an interlocking bundle of yarn Yarn is a long continuous length of interlocked fibres, suitable for use in the production of textiles, sewing, crocheting, knitti ...
and other textiles were common across
Europe Europe is a continent A continent is any of several large landmass A landmass, or land mass, is a large region In geography Geography (from Greek: , ''geographia'', literally "earth description") is a field of scienc ...

Europe
. In the 1890s the first machines to generate power from river water were established at places such as
Cragside Cragside is a Victorian era, Victorian country house near the town of Rothbury in Northumberland, England. It was the home of William Armstrong, 1st Baron Armstrong, founder of the Armstrong Whitworth armaments firm. An industrial magnate, scien ...

Cragside
in
Northumberland Northumberland () is a ceremonial county The counties and areas for the purposes of the lieutenancies, also referred to as the lieutenancy areas of England and informally known as ceremonial counties, are areas of England to which lord-li ...

Northumberland
and in recent decades there has been a significant increase in the development of large scale power generation from water, especially in wet mountainous regions such as
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 Norwegian language Norwegian (Norwegian: ''norsk'') is a Nort ...

Norway
.


Food source

Rivers have been a source of food since pre-history. They are often a rich source of fish and other edible aquatic life, and are a major source of fresh water, which can be used for drinking and
irrigation Irrigation is the agricultural Agriculture is the practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary Image:Family watching television 1958.jpg, Exercise trends, Increases in seden ...

irrigation
. Rivers help to determine the urban form of cities and neighbourhoods and their corridors often present opportunities for
urban renewal Urban renewal (also called urban regeneration in the United Kingdom and urban redevelopment in the United States) is a program of land redevelopment often used to address urban decay in cities. Urban renewal is the clearing out of blighted area ...
through the development of
foreshoreway , a 4.7 km (2.9 mi) elevated linear park built on top of obsolete railway infrastructure in the 12th arrondissement of Paris, France France (), officially the French Republic (french: link=no, République française), is a countr ...
s such as river walks. Rivers also provide an easy means of disposing of
waste water Wastewater is any water Water is an Inorganic compound, inorganic, Transparency and translucency, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosph ...

waste water
and, in much of the less developed world, other wastes.


Navigation and transport

Rivers have been used for
navigation Navigation is a field of study that focuses on the process of monitoring and controlling the movement of a craft or vehicle from one place to another.Bowditch, 2003:799. The field of navigation includes four general categories: land navigation, ...

navigation
for thousands of years. The earliest evidence of navigation is found in the
Indus Valley Civilization The Indus Valley Civilisation (IVC), also known as the Indus Civilisation, was a Bronze Age The Bronze Age is a prehistoric that was characterized by the use of , in some areas , and other early features of urban . The Bronze Age is ...

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 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 ...

Amazon
, the
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 ...

Ganges
, the
Nile The Nile, , Bohairic , lg, Kiira , Nobiin Nobiin, or Mahas, is a Northern Nubian languages, Nubian language of the Nilo-Saharan languages, Nilo-Saharan language family. "Nobiin" is the genitive case, genitive form of ''Nòòbíí'' ("Nub ...

Nile
, 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 ...

Mississippi
, and the
Indus#REDIRECT Indus River
{{Redirect category shell, {{R from move {{R from miscapitalisation {{R unprintworthy ...
. Since river boats are often not regulated, they contribute a large amount to global
greenhouse gas A greenhouse gas (GHG or GhG) is a gas that Absorption (electromagnetic radiation), absorbs and Emission (electromagnetic radiation), emits radiant energy within the thermal infrared range, causing the greenhouse effect. The primary greenhou ...
emissions, and to local cancer due to inhaling of
particulates Particulates – also known as atmospheric aerosol particles, atmospheric particulate matter, particulate matter (PM), or suspended particulate matter (SPM) – are microscopic The microscopic scale (from , ''mikrós'', "small" and σκοπ ...
emitted by the transports. In some heavily forested regions such as
Scandinavia Scandinavia; Sami Places * Sápmi, a cultural region in Northern Europe * Sami, Burkina Faso, a district of the Banwa Province * Sami District, Gambia * Sami, Cephalonia, a municipality in Greece * Sami (ancient city), in Elis, Greece * Sa ...

Scandinavia
and
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, ...

Canada
,
lumberjack Lumberjacks are mostly North American workers in the logging industry who perform the initial harvesting and transport of trees for ultimate processing into forest products. The term usually refers to loggers in the era (before 1945 in the Unite ...

lumberjack
s use the river to float felled trees downstream to
lumber camp A logging camp (or lumber camp) is a transitory work site used in the logging industry. Before the second half of the 20th century, these camps were the primary place where lumberjacks would live and work to fell trees in a particular area. Many p ...
s for further processing, saving much effort and cost by transporting the huge heavy logs by natural means.


Political borders

Rivers have been important in determining political boundaries and defending countries. For example, the
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 ...

Danube
was a long-standing border of the
Roman Empire The Roman Empire ( la, Imperium Rōmānum ; grc-gre, Βασιλεία τῶν Ῥωμαίων, Basileía tôn Rhōmaíōn) was the post-Republican Republican can refer to: Political ideology * An advocate of a republic, a type of governme ...

Roman Empire
, and today it forms most of the border between
Bulgaria Bulgaria (; bg, България, Bǎlgariya), officially the Republic of Bulgaria ( bg, Република България, links=no, Republika Bǎlgariya, ), is a country in Southeast Europe. It is bordered by Romania to the north, Serbia ...

Bulgaria
and
Romania Romania ( ; ro, România ) is a country at the crossroads of Central Central is an adjective usually referring to being in the center (disambiguation), center of some place or (mathematical) object. Central may also refer to: Directions ...

Romania
. The Mississippi in
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, up to seven geographical regions are commonly regarded as continen ...

North America
and the
Rhine ), Surselva Surselva Region is one of the eleven administrative districts Administrative division, administrative unitArticle 3(1). , country subdivision, administrative region, subnational entity, first-level subdivision, as well as many s ...

Rhine
in Europe are major east–west boundaries in those continents. The
Orange Orange most often refers to: *Orange (colour), occurs between red and yellow in the visible spectrum *Orange (fruit), the fruit of the tree species '' Citrus'' × ''sinensis'' ** Orange blossom, its fragrant flower *Some other citrus or citrus-li ...
and
Limpopo Limpopo is the northernmost Provinces of South Africa, province of South Africa. It is named after the Limpopo River, which forms the province's western and northern borders. The capital and largest city in the province is Polokwane (formerly ...
Rivers in
southern Africa Southern Africa is the south South is one of the cardinal directions or compass points. South is the opposite of north and is perpendicular to the east and west. Etymology The word ''south'' comes from Old English ''sūþ'', from earlier Pr ...
form the boundaries between provinces and countries along their routes.


Sacred rivers

Sacred rivers and their reverence is a phenomenon found in several religions, especially religions which have as core of their religion. For example, the Indian-origin religions (
Buddhism Buddhism (, ) is the world's fourth-largest religion Religion is a social Social organisms, including humans, live collectively in interacting populations. This interaction is considered social whether they are aware of it or not, and ...

Buddhism
,
Hinduism Hinduism () is an Indian religion Indian religions, sometimes also termed Dharmic religions or Indic religions, are the religions that originated in the Indian subcontinent. These religions, which include Hinduism, Jainism, Buddhism, ...

Hinduism
,
Jainism Jainism (), traditionally known as ''Jain Dharma'', is an ancient Indian religion. It is one of the oldest Indian religions. The three main pillars of Jainism are ''Ahimsa in Jainism, ahiṃsā'' (non-violence), ''anekāntavāda'' (non-absolut ...

Jainism
, and Sikism) revere and preserve the groves,
trees In botany Botany, also called , plant biology or phytology, is the science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific method, builds and Taxonomy (general), organiz ...
,
mountains A mountain is an elevated portion of the Earth's crust 350px, Plates in the crust of Earth Earth's crust is a thin shell on the outside of Earth, accounting for less than 1% of Earth's volume. It is the top component of the lithosphere, a ...

mountains
and rivers as sacred. Among the most sacred rivers in Hinduism are the
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 ...

Ganges
,
Yamuna The Yamuna (Hindustani language, Hindustani: ) is the second-largest tributary river of the Ganga by discharge and the longest tributary in List of major rivers of India, India. Originating from the Yamunotri Glacier at a height of on the ...

Yamuna
,
Sarasvati Saraswati ( sa, सरस्वती, ) is the Hindu goddess of knowledge, music, art, speech, wisdom, and learning. She is a part of the trinity ('' Tridevi'') of Saraswati, Lakshmi Lakshmi (; ''IAST, Lakṣmī'', ), also known a ...

Sarasvati
rivers on which the rigvedic rivers flourished. The
vedas upright=1.2, The Vedas are ancient Sanskrit texts of Hinduism. Above: A page from the '' Atharvaveda''. The Vedas (, , ) are a large body of religious texts originating in ancient India. Composed in Vedic Sanskrit, the texts constitute the o ...

vedas
and
Gita The ''Bhagavad Gita'' (; sa, भगवद्गीता।, : ' /bɦɐɡɐʋɐd ɡiːtäː/, lit. "The Song of "), often referred to as the ''Gita'', is a 701- scripture that is part of the ' (chapters 23–40 of ), dated to the second ce ...
, the most sacred of
hindu texts Hindu texts are manuscripts and voluminous historical literature which are related to any of the diverse traditions within Hinduism Hinduism () is an Indian religion and ''dharma'', or way of life. It is the Major religious groups, world' ...
were written on the banks of Sarasvati river which were codified during the
Kuru kingdom Kuru ( sa, कुरु) was a Vedic Indo-AryanIndo-Aryan refers to: * Indo-Aryan languages ** Indo-Aryan superstrate in Mitanni or Mitanni-Aryan * Indo-Aryan peoples, the various peoples speaking these languages See also *Aryan invasion theory ...
in present-day
Haryana Haryana (; ) is a in India located in the northern-part of the country. It was carved out of the former state of on 1 November 1966 on a basis. It is ranked 21st in terms of area, with less than 1.4% () of India's land area. The state capital ...

Haryana
. Among other secondary sacred rivers of Hinduism are
Narmada The Narmada River, also called the Reva and previously also known as ''Narbada'' or anglicised as ''Nerbudda'', is the 5th longest river and overall longest west-flowing river in India, and largest flowing river of the state of Madhya Pradesh ...

Narmada
and many more.


Management of rivers

Rivers are often managed or controlled to make them more useful or less disruptive to human activity. *
Dam A dam is a barrier that stops or restricts the flow of surface water An example of surface water is Lake Kinney. Surface water is water Water is an Inorganic compound, inorganic, Transparency and translucency, transparent, tast ...

Dam
s or
weir A weir or low head dam is a barrier across the width of a river that alters the flow characteristics of water and usually results in a change in the height of the river level. They are also used to control the flow of water for outlets of lakes ...

weir
s may be built to control the flow, store water, or extract energy. *
Levee file:River Levee Cross Section Figure.svg, Components of a levee: file:Sacramento River Levee.jpg, The side of a levee in Sacramento, California A levee (), dike (American English), dyke (Commonwealth English), embankment, floodbank, or stop ...

Levee
s, known as dikes in Europe, may be built to prevent river water from flowing on floodplains or floodways. *
Canal Canals are waterways channels 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 * ...

Canal
s connect rivers to one another for water transfer or
navigation Navigation is a field of study that focuses on the process of monitoring and controlling the movement of a craft or vehicle from one place to another.Bowditch, 2003:799. The field of navigation includes four general categories: land navigation, ...

navigation
. * River courses may be modified to improve navigation, or straightened to increase the flow rate. River management is a continuous activity as rivers tend to 'undo' the modifications made by people. Dredged channels silt up, deteriorate with age, levees and dams may suffer seepage or catastrophic failure. The benefits sought through managing rivers may often be offset by the social and economic costs of mitigating the bad effects of such management. As an example, in parts of the developed world, rivers have been confined within channels to free up flat flood-plain land for development. Floods can inundate such development at high financial cost and often with loss of life. Rivers are increasingly managed for
habitat conservation Habitat conservation is a management practice that seeks to conserve, protect and restore habitat Ibex in an alpine habitat In ecology Ecology (from el, οἶκος, "house" and el, -λογία, label=none, "study of") is the ...
, as they are critical for many
aquatic Aquatic means relating to water Water (chemical formula H2O) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known li ...
and
riparian A riparian zone or riparian area is the interface between land and 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 grou ...
plants, resident and migratory fishes,
waterfowl Anseriformes is an order (biology), order of birds that comprise about 180 living species in three families: Anhimidae (the 3 screamers), Anseranatidae (the magpie goose), and Anatidae, the largest family, which includes over 170 species of water ...
,
birds of prey Birds of prey, also known as raptors, include species of bird Birds are a group of s constituting the Aves , characterised by s, toothless beaked jaws, the of eggs, a high rate, a four-chambered , and a strong yet lightweight . Bi ...
,
migrating birds Bird migration is the regular seasonal movement, often north and south along a flyway, between Breeding in the wild, breeding and wintering grounds. Many species of bird migrate. Animal migration, Migration carries high costs in predation and mo ...
, and many
mammal Mammals (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to be i ...
s.


Concerns

Man-made causes, such as the
over-exploitation Overexploitation, also called overharvesting, refers to harvesting a renewable resource File:Global Vegetation.jpg, Global vegetation A renewable resource, also known as a flow resource, is a natural resource which will replenish to replace the ...
and
pollution Pollution is the introduction of s into the natural environment that cause adverse change. Pollution can take the form of any substance (solid, liquid, or gas) or energy (such as radioactivity, heat, sound, or light). s, the components of po ...

pollution
, are the biggest threats and concerns which are making rivers ecologically dead and drying up the rivers.
Plastic pollution Plastic pollution is the accumulation of plastic Plastics are a wide range of syntheticA synthetic is an artificial material produced by organic chemistry, organic chemical synthesis. Synthetic may also refer to: In the sense of both ...
imposes threats on aquatic life and river ecosystems because of
plastic Plastics are a wide range of syntheticA synthetic is an artificial material produced by organic chemistry, organic chemical synthesis. Synthetic may also refer to: In the sense of both "combination" and "artificial" * Synthetic chemical or s ...

plastic
's durability in the natural environment. Plastic debris may result in entanglement and ingestion by aquatic life such as
turtle Turtles are an of s known as Testudines, characterized by a developed mainly from their ribs. Modern turtles are divided into two major groups, the s and which differ in the way the head retracts. There are 360 living and recently extinct ...

turtle
s,
bird Birds are a group of warm-blooded vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With ...

bird
s, and
fish Fish are aquatic Aquatic means relating to water Water (chemical formula H2O) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the ...

fish
, causing severe injury and death. Human livelihoods around rivers are also impacted by plastic pollution through direct damage to shipping and transport vessels, effects on tourism or real estate value, and the clogging of drains and other hydraulic infrastructure leading to increased flood risk.


See also

;Arts, entertainment, and media * " Old Man River" * '' The Riverkeepers'' (book) ;General *
Drought A drought is an event of prolonged shortages in the water supply, whether atmospheric (below-average precipitation In meteorology Meteorology is a branch of the (which include and ), with a major focus on . The study of meteorolog ...

Drought
*
Fluvial 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 ap ...
* Salt tide *
Water conflict Water conflict is a term describing a conflict between countries, states, or groups over water the rights to access water resources. The United Nations recognizes that water disputes result from opposing interests of water users, public or privat ...
;Crossings *
Bridge A bridge is a structure A structure is an arrangement and organization of interrelated elements in a material object or system A system is a group of Interaction, interacting or interrelated elements that act according to a set of rules t ...

Bridge
*
Ferry A ferry is a vessel used to carry passengers, and sometimes vehicles and cargo, across a body of water. A passenger ferry with many stops, such as in Venice Venice ( ; it, Venezia ; vec, Venesia or ) is a city in northeastern It ...

Ferry
*
Ford (crossing) A ford is a shallow place with good footing where 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 ...
*
Tunnel A tunnel is an underground passageway, dug through the surrounding soil/earth/rock and enclosed except for entrance and exit, commonly at each end. A pipeline Pipeline may refer to: Electronics, computers and computing * Pipeline (comput ...

Tunnel
;Habitats * Exposed riverine sediments *
Riparian zone A riparian zone or riparian area is the interface between land and 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 an ...
;Lists *
Lists of rivers This is a comprehensive list of lists of rivers, organized primarily by continent and country. General lists * List of drainage basins by area (including rivers, lakes, and endorheic basins) * List of largest unfragmented rivers * List of longe ...
* List of international border rivers * List of rivers by continent *
List of rivers by discharge A ''list'' is any set of items. List or lists may also refer to: People * List (surname)List or Liste is a European surname. Notable people with the surname include: List * Friedrich List (1789–1846), German economist * Garrett List (1943 ...
*
List of rivers by length This is a list of the longest rivers on Earth. It includes river systems over . Definition of length There are many factors, such as the identification of the source, the identification or the definition of the mouth, and the scale of measureme ...
* List of waterways ;Transport *
Barge A barge is a shoal A tidal sandbar connecting the islands of Waya and Wayasewa of the Yasawa Islands, Fiji In oceanography Oceanography (from the Ancient Greek Ancient Greek includes the forms of the Greek language used in a ...

Barge
*
Raft '' A raft is any flat structure for support or transportation over water. It is usually of basic design, characterized by the absence of a Hull (watercraft), hull. Rafts are usually kept afloat by using any combination of buoyant materials such as ...

Raft
* River transport *
Riverboat A riverboat is a watercraft Watercraft, also known as water vessels or waterborne vessels, are vehicles A vehicle (from la, vehiculum) is a machine A machine is any physical system with ordered structural and functional propertie ...
*
Sailing Sailing employs the wind—acting on sail A sail is a tensile structure by Vladimir Shukhov (during construction), Nizhny Novgorod, 1895 in Kings Domain, Melbourne A tensile structure is a construction of elements carrying only tension ...
*
Steamboat upright=1.35, Dutch river steam-tugboat ''Mascotte II'' A steamboat is a boat that is propelled primarily by steam power from Stott Park Bobbin Mill, Cumbria, England A steam engine is a heat engine In thermodynamics Thermod ...

Steamboat
*
Towpath A towpath is a road A road is a wide way leading from one place to another, typically one with a specially prepared surface which vehicles and bikes can use. Roads consist of one or two roadway A carriageway (British English ...
*
Yacht A yacht is a sailing or power vessel used for pleasure, cruising, or racing. There is no standard definition, so the term applies to such vessels that have a cabin with amenities that accommodate overnight use. To be termed a , as opposed to a , ...

Yacht


References


Further reading

* * — a non-technical primer on the
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 area in great detail, ...

geomorphology
and
hydraulics Hydraulics (from Greek#REDIRECT 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 ap ...
of water. * {{Authority control
Bodies of water {{See also, Limnology Compare to :Landforms and :Wetlands Bodies of water may exist within land areas or within other bodies of water and may be natural, man-made or a combination. Water Physical geography Hydrography Natural resources, +Water A ...
Fluvial landforms
Geomorphology Geomorphology (from the Greek words ''Ge'' = earth, ''morfe'' = form and ''logos'' = study) is the science of surface features and landforms including the forces and processes that create them. Geomorphology has strong ties to geologic structure, ...
Sedimentology Water streams