River

Samur River in Azerbaijan – In the natural landscape
Daugava river, Riga in Latvia – In the urban landscape

A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases a river flows into the ground and becomes dry at the end of its course without reaching another body of water. Small rivers can be referred to using names such as stream, creek, brook, rivulet, and rill. There are no official definitions for the generic term river as applied to geographic features,[1] although in some countries or communities a stream is defined by its size. Many names for small rivers are specific to geographic location; examples are "run" in some parts of the United States, "burn" in Scotland and northeast England, and "beck" in northern England. Sometimes a river is defined as being larger than a creek,[2] but not always: the language is vague.[3]

Rivers are part of the hydrological cycle. Water generally collects in a river from precipitation through a drainage basin from surface runoff and other sources such as groundwater recharge, springs, and the release of stored water in natural ice and snowpacks (e.g., from glaciers). Potamology is the scientific study of rivers, while limnology is the study of inland waters in general.

Topography

Melting toe of Athabasca Glacier, Jasper National Park, Alberta, Canada
The Loboc River in Bohol, Philippines
The Colorado River at Horseshoe Bend, Arizona

A river begins at a source (or more often several sources), follows a path called a course, and ends at a mouth or mouths. The water in a river is usually confined to a channel, made up of a stream bed between banks. In larger rivers there is often also a wider floodplain shaped by flood-waters over-topping the channel. Floodplains may be very wide in relation to the size of the river channel. This distinction between river channel and floodplain can be blurred, especially in urban areas where the floodplain of a river channel can become greatly developed by housing and industry.

Rivers can flow down mountains, through valleys (depressions) or along plains, and can create canyons or gorges.

The term upriver (or upstream) refers to the direction towards the source of the river, i.e. against the direction of flow. Likewise, the term downriver (or downstream) describes the direction towards the mouth of the river, in which the current flows.

The term left bank refers to the left bank in the direction of flow, right bank to the right.

The river channel typically contains a single stream of water, but some rivers flow as several interconnecting streams of water, producing a braided river.[4] Extensive braided rivers are now found in only a few regions worldwide,[citation needed] such as the South Island of New Zealand. They also occur on peneplains and some of the larger river deltas. Anastamosing rivers are similar to braided rivers and are quite rare. They have multiple sinuous channels carrying large volumes of sediment. There are rare cases of river bifurcation in which a river divides and the resultant flows ending in different seas. An example is the bifurcation of Nerodime River in Kosovo.

The River Cam from the Green Dragon Bridge, Cambridge (Britain)

A river flowing in its channel is a source of energy which acts on the river channel to change its shape and form. In 1757, the German hydrologist Albert Brahms empirically observed that the submerged weight of objects that may be carried away by a river is proportional to the sixth power of the river flow speed.[5] This formulation is also sometimes called Airy's law.[6] Thus, if the speed of flow is doubled, the flow would dislodge objects with 64 times as much submerged weight. In mountainous torrential zones this can be seen as erosion channels through hard rocks and the creation of sands and gravels from the destruction of larger rocks. A river valley that was created from a U-shaped glaciated valley, can often easily be identified by the V-shaped channel that it has carved. In the middle reaches where a river flows over flatter land, meanders may form through erosion of the river banks and deposition on the inside of bends. Sometimes the river will cut off a loop, shortening the channel and forming an oxbow lake or billabong. Rivers that carry large amounts of sediment may develop conspicuous deltas at their mouths. Rivers whose mouths are in saline tidal waters may form estuaries.

Throughout the course of the river, the total volume of water transported downstream will often be a combination of the free water flow together with a substantial volume flowing through sub-surface rocks and gravels that underlie the river and its floodplain (called the hyporheic zone). For many rivers in large valleys, this unseen component of flow may greatly exceed the visible flow.

Subsurface streams

Most but not all rivers flow on the surface. Subterranean rivers flow underground in caves or caverns. Such rivers are frequently found in regions with limestone geologic formations. Subglacial streams are the braided rivers that flow at the beds of glaciers and ice sheets, permitting meltwater to be discharged at the front of the glacier. Because of the gradient in pressure due to the overlying weight of the glacier, such streams can even flow uphill.

Permanence of flow

An intermittent river (or ephemeral river) only flows occasionally and can be dry for several years at a time. These rivers are found in regions with limited or highly variable rainfall, or can occur because of geologic conditions such as a highly permeable river bed. Some ephemeral rivers flow during the summer months but not in the winter. Such rivers are typically fed from chalk aquifers which recharge from winter rainfall. In England these rivers are called bournes and give their name to places such as Bournemouth and Eastbourne. Even in humid regions, the location where flow begins in the smallest tributary streams generally moves upstream in response to precipitation and downstream in its absence or when active summer vegetation diverts water for 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 of water, hail and sand or soil, forming temporary rivers.[7]

Other Languages
Acèh: Krueng
Afrikaans: Rivier
Alemannisch: Fluss
አማርኛ: ወንዝ
العربية: نهر
aragonés: Río
ܐܪܡܝܐ: ܢܗܪܐ
armãneashti: Arâu
অসমীয়া: নদী
asturianu: Ríu
Atikamekw: Sipi
Avañe'ẽ: Ysyry
Aymar aru: Jawira
azərbaycanca: Çay (coğrafiya)
বাংলা: নদী
Bahasa Banjar: Sungai
Bân-lâm-gú: Khe
башҡортса: Йылға
беларуская: Рака
беларуская (тарашкевіца)‎: Рака
भोजपुरी: नदी
български: Река
Boarisch: Fluss
བོད་ཡིག: ཆུ་རྒྱུན།
brezhoneg: Stêr
буряад: Гол мүрэн
català: Riu
Чӑвашла: Юхан шыв
Cebuano: Suba
čeština: Řeka
Chi-Chewa: Category:Mtsinje
chiShona: Rwizi
Cymraeg: Afon
dansk: Flod
Deitsch: Rewwer
Deutsch: Fluss
dolnoserbski: Rěka
eesti: Jõgi
Ελληνικά: Ποταμός
emiliàn e rumagnòl: Fiòmm
эрзянь: Лей
español: Río
Esperanto: Rivero
estremeñu: Ríu
euskara: Ibai
فارسی: رود
Fiji Hindi: Naddi
français: Rivière
Frysk: Rivier
furlan: Flum
Gaeilge: Abhainn
Gaelg: Awin
Gàidhlig: Abhainn
galego: Río
贛語:
客家語/Hak-kâ-ngî:
한국어:
Հայերեն: Գետ
हिन्दी: नदी
hornjoserbsce: Rěka
Ido: Rivero
Ilokano: Karayan
Bahasa Indonesia: Sungai
interlingua: Fluvio
ᐃᓄᒃᑎᑐᑦ/inuktitut: ᑰᒃ
Iñupiak: Kuuk
isiXhosa: Umlambo
isiZulu: Umfula
italiano: Fiume
עברית: נהר
Basa Jawa: Kali
ಕನ್ನಡ: ನದಿ
къарачай-малкъар: Суу (черек, къобан)
ქართული: მდინარე
қазақша: Өзен
Kinyarwanda: Uruzi
Kiswahili: Mto
коми: Ю
Kongo: Mubu
Kreyòl ayisyen: Rivyè
kurdî: Çem
Кыргызча: Дарыя
лезги: ВацI
Latina: Flumen
latviešu: Upe
Lëtzebuergesch: Floss
lietuvių: Upė
Limburgs: Reveer
lingála: Motíma
Livvinkarjala: Jogi
la .lojban.: rirxe
lumbaart: Fiüm
magyar: Folyó
македонски: Река
Malagasy: Renirano
മലയാളം: നദി
मराठी: नदी
მარგალური: წყარმალუ
مصرى: نهر
Bahasa Melayu: Sungai
Baso Minangkabau: Sungai
Mìng-dĕ̤ng-ngṳ̄: Ò̤
Mirandés: Riu
монгол: Гол мөрөн
မြန်မာဘာသာ: မြစ်
Nāhuatl: Atoyatl
Dorerin Naoero: Ekaw
Nederlands: Rivier
Nedersaksies: Revier
नेपाली: नदी
नेपाल भाषा: खुसि
日本語:
Napulitano: Sciummo
Nordfriisk: Struum
Norfuk / Pitkern: Riveh
norsk: Elv
norsk nynorsk: Elv
occitan: Riu
олык марий: Эҥер
ଓଡ଼ିଆ: ନଦୀ
oʻzbekcha/ўзбекча: Daryo
ਪੰਜਾਬੀ: ਦਰਿਆ
پنجابی: دریا
Papiamentu: Riu
پښتو: سيند
Patois: Riba
Plattdüütsch: Stroom (Water)
polski: Rzeka
português: Rio
Qaraqalpaqsha: Da'rya
română: Râu
Romani: Nasho
rumantsch: Flum
Runa Simi: Mayu
русиньскый: Ріка
русский: Река
саха тыла: Өрүс
ᱥᱟᱱᱛᱟᱲᱤ: ᱜᱟᱰᱟ
संस्कृतम्: नदी
Scots: River
Seeltersk: Äi
Sesotho sa Leboa: Noka
shqip: Lumi
sicilianu: Ciumi
සිංහල: ගඟ
Simple English: River
سنڌي: درياھ
slovenčina: Rieka
slovenščina: Reka
ślůnski: Rzyka
Soomaaliga: Webiyada
کوردی: ڕووبار
српски / srpski: Река
srpskohrvatski / српскохрватски: Rijeka
Basa Sunda: Walungan
suomi: Joki
svenska: Flod
Tagalog: Ilog
தமிழ்: ஆறு
tarandíne: Jume
татарча/tatarça: Елга
తెలుగు: నది
тоҷикӣ: Дарё
ᏣᎳᎩ: ᎤᏪᏴ
Tsetsêhestâhese: Ó'he'e
ತುಳು: ಸುದೆ
Türkçe: Nehir
Türkmençe: Derýa
українська: Річка
اردو: دریا
vèneto: Fiume
vepsän kel’: Jogi
Tiếng Việt: Sông
Võro: Jõgi
文言:
Winaray: Salog
Wolof: Dex
吴语: 河流
ייִדיש: טייך
Yorùbá: Odò
粵語:
Zazaki: Ro
žemaitėška: Opės
中文: 河流
Bahasa Hulontalo: Dutula
ГӀалгӀай: Дода хий
Kabɩyɛ: Pɔɔ
Lingua Franca Nova: Rio