Rivers of Gorj County
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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 Co ...

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 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 o ...
. 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, is a biogeochemical cycle In ecology Ecology (from el, οἶκος, "house" and el, -λογία, label=none, "study of") is the study of the relationships ...
. 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 , transparent, tasteless, odorless, and , which is the main constituent of 's and the s of all known living organisms (in which it ac ...
and other sources such as
groundwater recharge Groundwater recharge or deep drainage or deep percolation is a Hydrology, hydrologic process, where water moves downward from surface water to groundwater. Recharge is the primary method through which water enters an aquifer. This process usually ...
,
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 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, publication, publishing institute or ...
(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 organisms and their parts. Anatomy is a branch of natural science which deals with the structural organization ...

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 (Lysefjord) in Norway Norway, officially the Kingdom of Norway,Names in the official and recognised languages: Bokmål Bokmål (, ; lit ...
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 tide Tides are the rise and fall of sea level Mean sea level (MSL) (often ...

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, a plain is a flat expanse of land that generally does not change much in elevation, and is primarily treeless. Plains occur as lowlands along valleys or at the base of mountains, as coastal plains, and as plateaus or Highland, up ...

plain
s, and can create
canyons A canyon (; archaic 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 a ...

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 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 ...
. 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 islands of New Zealand upright=1.25, Whakaari / White Island in the Bay of Plenty New Zealand consists of many islands, estimated around six hundred, mainly remnan ...

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 bifurcation (from la, furca, fork) occurs when a river flowing in a single stream A stream is a body of water (Lysefjord) in Norway Norway, officially the Kingdom of Norway,Names in the official and recognised languages: ...
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 Frisia Frisia (, ; ) is a cross-border cultural region 's map of native American cultural areas within the territory of the United States (1948) as defined by Melville J. Herskovit ...
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 erodes the sediment Sediment is a naturally occurring material that is broken down by processes of weath ...

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 File:rio-cauto-cuba.JPG, Meanders of the ''Cauto River, Rio Cauto'' at Guamo Embarcadero, Cuba A meander is one of a series of regular sinuous curves in the channel of a river o ...

oxbow lake
or
billabong A billabong ( ) is an Australian Australians, colloquially referred to as "Aussies", are the citizens Citizenship is a relationship between an individual and a state to which the individual owes allegiance and in turn is entitled to ...

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 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, be ...
). 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 outdoor activities Outdoor recreation or outdoor activity refers to recreation Recreation is an activity of leisure, leisure being discretionary time. The "need to do something for recreation ...

rafting
or
canoe A canoe is a lightweight narrow vessel, 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 paddle A paddle is a tool used for pushin ...

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 wit ...
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 v ...
s. Subglacial streams are the braided rivers that flow at the beds of glaciers and
ice sheet In glaciology Lateral moraine on a glacier joining the Gorner Glacier, Zermatt">Gorner_Glacier.html" ;"title="moraine on a glacier joining the Gorner Glacier">moraine on a glacier joining the Gorner Glacier, Zermatt, Swiss Alps. The moraine is ...

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#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 ...
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 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") ...
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 Evaporation is a type of that occurs on the of a as it changes into the gas phase. The surrounding gas must not be saturated with the evaporating substance. When the molecules of ...

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 centrifugal pump Centrifugal pum ...
of water, hail and sand or soil, forming temporary rivers.


Stream order classification of rivers: Fleuve and Rivière

The
Strahler Stream Order 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 and t ...
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 = Provinces and territories of ...

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 organiz ...

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 ...
,
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 The lithology of a Rock (geology), rock unit is a description of its physical characteristics visible at outcrop, in hand or core sample, core samples, or with low magnification microscopy. Physical characteristics include colour, texture, grain ...
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 branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Roman Re ...
. 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 or humanist whose area of study is geography Geography (from Greek Greek may refer to: ...

William Morris Davis
devised the "
cycle of erosion The geographic cycle, or cycle of erosion, is an idealized Scientific modelling, model that explains the development of Terrain#Relief, relief in landscapes. The model starts with the erosion that follows uplift of land above a base level and ends, ...
" 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 ...
,
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and rivers. * Old river: A river with a low gradient and low erosive energy. Old rivers are characterized by flood plains. Examples are the
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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
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. The ways in which a river's characteristics vary between its upper and lower course are summarized by the
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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 the process by which an entire body of water A body of water or waterbody (often spelled water body) is any significant accumulation of water, generally on a planet's surface. Th ...
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 member states to achieve good qualitative and quantitative status of all Body of water, water bodies (including marine ecosystem, marine waters up to one na ...
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
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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
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fractal
pattern, or a pattern that is determined by weaknesses in the bedrock, such as fault (geology), faults, fracture (geology), fractures, or more erodible layers.


Flow rate

Volumetric flow rate, also known as discharge, volume flow rate, and rate of water flow, is the volume of water which passes through a given cross-section of the river channel per unit time. It is typically measured in cubic metres per second (cumec) or cubic feet per second (cfs), where 1 m3/s = 35.51 ft3/s; it is sometimes also measured in litres or gallons per second. Volumetric flow rate 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 radius) 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 action 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 Valley, V-shaped. Waterfalls also form in the youthful river valley where a band of hard rock overlays a layer of soft rock. Weathering, 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 stage. In many developed areas, human activity has changed the form of river channels, altering magnitudes and frequencies of flooding. Some examples of this are the building of levees, the straightening of channels, and the draining of natural wetlands. In many cases human activities in rivers and floodplains have dramatically increased the risk of flooding. Straightening rivers allows water to flow more rapidly downstream, increasing the risk of flooding places further downstream. Building on flood plains removes flood storage, which again exacerbates downstream flooding. The building of levees only protects the area behind the levees and not those further downstream. Levees and flood-banks can also increase flooding upstream because of the back-water pressure as the river flow is impeded by the narrow channel banks. Detention basins 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 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 larvae. The products of these shredders are used by collectors, such as Hydropsychidae, and further downstream algae that create the primary production 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, with the highest density where the conditions are optimal. In rivers Ecological succession, 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, and 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, rapids with whitewater or even waterfalls 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 watermills and hydroelectric plants. Evidence of watermills shows them in use for many hundreds of years, for instance in Orkney at Dounby Click Mill. Prior to the invention of steam power, watermills for grinding cereals and for processing wool and other textiles were common across Europe. In the 1890s the first machines to generate power from river water were established at places such as Cragside in 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.


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. Rivers help to determine the urban design, urban form of cities and neighbourhoods and their corridors often present opportunities for urban renewal through the development of foreshoreways such as river walks. Rivers also provide an easy means of disposing of waste water and, in much of the less developed world, other wastes.


Navigation and transport

Rivers have been used for navigation for thousands of years. The earliest evidence of navigation is found in the Indus Valley Civilization, which existed in northwestern India around 3300 BC. Riverine navigation provides a cheap means of transport, and is still used extensively on most major rivers of the world like the Amazon River, Amazon, the Ganges River, Ganges, the
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Mississippi
, and the River Indus, Indus. Since river boats are often not regulated, they contribute a large amount to global greenhouse gas Greenhouse gas#Greenhouse gas emissions, emissions, and to local cancer due to inhaling of Atmospheric particulate matter, particulates emitted by the transports. In some heavily forested regions such as Scandinavia and
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Canada
, lumberjacks use the river to float felled trees downstream to lumber camps 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 was a long-standing border of the Roman Empire, and today it forms most of the border between Bulgaria and Romania. The Mississippi in North America and the Rhine in Europe are major east–west boundaries in those continents. The Orange River, Orange and Limpopo River, Limpopo Rivers in southern Africa 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 animism, eco-friendly belief as core of their religion. For example, the Indian religions, Indian-origin religions (Buddhism, Hinduism, Jainism, and Sikism) revere and preserve the Sacred groves of India, groves, List of Banyan trees in India, trees, Sacred_mountains#India, mountains and rivers as sacred. Among the most sacred rivers in Hinduism are the
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, Yamuna, Sarasvati River, Sarasvati rivers on which the rigvedic rivers flourished. The vedas and Gita, the most sacred of hindu texts were written on the banks of Sarasvati river which were codified during the Kuru Kingdom, Kuru kingdom in present-day Haryana. Among other secondary sacred rivers of Hinduism are Narmada and many more.


Management of rivers

Rivers are often managed or controlled to make them more useful or less disruptive to human activity. * Dams or weirs may be built to control the flow, store water, or extract energy. * Levees, known as dikes in Europe, may be built to prevent river water from flowing on floodplains or floodways. * Canals connect rivers to one another for Aqueduct (water supply), water transfer or 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, sluice, sluice mechanisms 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, as they are critical for many aquatic plant, aquatic and riparian zone, riparian plants, freshwater fish, resident and fish migration, migratory fishes, waterfowl, bird of prey, birds of prey, bird migration, migrating birds, and many mammals.


Concerns

Man-made causes, such as the Exploitation of natural resources, over-exploitation and Water pollution, pollution, are the biggest threats and concerns which are making rivers Dead zone (ecology), ecologically dead and drying up the rivers. Plastic pollution imposes threats on aquatic life and river ecosystems because of plastic's durability in the natural environment. Plastic debris may result in entanglement and ingestion by aquatic life such as turtles, birds, and 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 * "Ol' Man River, Old Man River" * ''The Riverkeepers'' (book) ;General * Drought * Fluvial * Salt tide * Water conflict ;Crossings * Bridge * Ferry * Ford (crossing) * Tunnel ;Habitats * Exposed riverine sediments * Riparian zone ;Lists * Lists of rivers * List of international border rivers * List of rivers by continent * List of rivers by discharge * List of rivers by length * List of waterways ;Transport * Barge * Raft * River transport * Riverboat * Sailing * Steamboat * Towpath * Yacht


References


Further reading

* * — a non-technical primer on the geomorphology and hydraulics of water. * {{Authority control Rivers, Bodies of water Fluvial landforms Geomorphology Sedimentology Water streams