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A drainage basin is any area of land where
precipitation In meteorology Meteorology is a branch of the atmospheric sciences which includes atmospheric chemistry and atmospheric physics, with a major focus on weather forecasting. The study of meteorology dates back millennia, though significant p ...

precipitation
collects and drains off into a common outlet, such as into 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 reaching another body of water ...

river
,
bay A bay is a recessed, coastal body of water that directly connects to a larger main body of water, such as an ocean The ocean (also the sea or the world ocean) is the body of salt water which covers approximately 71% of the surface ...
, or other
body of water ( Lysefjord) in Norway Norway ( nb, ; nn, ; se, Norga; smj, Vuodna; sma, Nöörje), officially the Kingdom of Norway, is a Nordic countries, Nordic country in Northern Europe whose mainland territory comprises the western and nort ...
. The drainage basin includes all the
surface water An example of surface water is Lake Kinney. Surface water is water Water is an Inorganic compound, inorganic, Transparency and translucency, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which ...
from rain runoff,
snowmelt In hydrology Hydrology (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 approxim ...
, hail, sleet and nearby streams that run downslope towards the shared outlet, as well as the
groundwater Groundwater is the water present beneath Earth's surface in rock and Pore space in soil, soil pore spaces and in the fractures of stratum, rock formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usabl ...

groundwater
underneath the earth's surface. Drainage basins connect into other drainage basins at lower elevations in a hierarchical pattern, with smaller sub-drainage basins, which in turn drain into another common outlet. Other terms for ''drainage basin'' are catchment area, catchment basin, drainage area, river basin, water basin, and impluvium. In
North America North America is a continent entirely within the Northern Hemisphere and almost all within the Western Hemisphere. It can also be described as the northern subcontinent of the Americas. It is bordered to the north by the Arctic Ocean, to ...

North America
, the term ''watershed'' is commonly used to mean a drainage basin, though in other English-speaking countries, it is used only in its original sense, that of a
drainage divide In topography, a drainage divide, water divide, divide, ridgeline, watershed, water parting or ''height of land'' is elevated terrain that separates neighboring drainage basins. On rugged land, the divide lies along topographical ridge A ...
. In a closed drainage basin, or
endorheic basin An endorheic basin (; also spelled endoreic basin or endorreic basin) is a drainage basin that normally retains water and allows no outflow to other external bodies of water, such as river A river is a natural flowing watercourse, usually ...
, the water converges to a single point inside the basin, known as a
sink A sink – also known by other names including sinker, washbowl, hand basin, wash basin, and simply basin – is a bowl-shaped plumbing fixture used for washing hands, dishwashing, and other purposes. Sinks have taps (faucets) that supply hot ...
, which may be a permanent lake, a
dry lake A dry lake, also known as a playa, is either a basin or depression that formerly contained a standing surface water body, which disappeared when evaporation processes exceeded recharge. If the floor of a dry lake is covered by deposits of alkali ...
, or a point where surface water is lost underground. The drainage basin acts as a
funnel Image:Roman Kitchen Funnel Saalburg.jpg, A ceramic Ancient Rome, Roman kitchen funnel (1st–3rd century AD) A funnel is a tube or pipe that is wide at the top and narrow at the bottom, used for guiding liquid or powder into a small opening. Fu ...

funnel
by collecting all the water within the area covered by the basin and channelling it to a single point. Each drainage basin is separated topographically from adjacent basins by a perimeter, the
drainage divide In topography, a drainage divide, water divide, divide, ridgeline, watershed, water parting or ''height of land'' is elevated terrain that separates neighboring drainage basins. On rugged land, the divide lies along topographical ridge A ...
, making up a succession of higher geographical features (such as a
ridge A ridge or a mountain ridge is a geographical feature consisting of a chain of mountains or hills that form a continuous elevated crest for some distance. The sides of the ridge slope away from narrow top on either side. The lines along the ...

ridge
,
hill A hill is a landform that extends above the surrounding terrain. It often has a distinct summit. Terminology The distinction between a hill and a mountain A mountain is an elevated portion of the Earth's crust, generally with steep s ...

hill
or
mountain A mountain is an elevated portion of the Earth's crust, generally with steep sides that show significant exposed bedrock. A mountain differs from a plateau in having a limited summit area, and is larger than a hill, typically rising at least ...

mountain
s) forming a barrier. Drainage basins are similar but not identical to hydrologic units, which are drainage areas delineated so as to nest into a multi-level hierarchical drainage system. Hydrologic units are defined to allow multiple inlets, outlets, or sinks. In a strict sense, all drainage basins are hydrologic units but not all hydrologic units are drainage basins.


Major drainage basins of the world


Ocean basins

The following is a list of the major ocean basins: * About 48.71% of the world's land drains to the . In
North America North America is a continent entirely within the Northern Hemisphere and almost all within the Western Hemisphere. It can also be described as the northern subcontinent of the Americas. It is bordered to the north by the Arctic Ocean, to ...

North America
, surface water drains to the Atlantic via the
Saint Lawrence River The St. Lawrence River is a large river in the middle latitudes of North America, flowing from Lake Ontario in a roughly northeasterly direction into the Gulf of St. Lawrence, connecting the Great Lakes to the North Atlantic Ocean and forming the ...
and
Great Lakes upright=1.3, Location in North America The Great Lakes also called the Great Lakes of North America or the Laurentian Great Lakes, is a series of large interconnected freshwater lake A lake is an area filled with water, localized in a ...

Great Lakes
basins, the Eastern Seaboard of the United States, the
Canadian Maritimes The Maritimes, also called the Maritime provinces, is a region In geography, regions are areas that are broadly divided by physical characteristics ( physical geography), human impact characteristics ( human geography), and the interaction of h ...

Canadian Maritimes
, and most of
Newfoundland and Labrador Newfoundland and Labrador (; sometimes abbreviated as NL) is the easternmost province of Canada The Province of Canada (or the United Province of Canada or the United Canadas) was a British North America, British colony in North America f ...
. Nearly all of
South America South America is a continent A continent is one of several large landmasses. Generally identified by convention (norm), convention rather than any strict criteria, up to seven regions are commonly regarded as continents. Ordered fr ...

South America
east of the
Andes The Andes, Andes Mountains or Andean Mountains ( es, Cordillera de los Andes) are the List of mountain ranges#Mountain ranges by length, longest continental mountain range in the world, forming a continuous highland along the western edge of Sout ...
also drains to the Atlantic, as does most of
Western Western may refer to: Places *Western, Nebraska, a village in the US *Western, New York, a town in the US *Western Creek, Tasmania, a locality in Australia *Western Junction, Tasmania, a locality in Australia *Western world, countries that ide ...

Western
and
Central Europe Central Europe is an area of Europe between Western Europe and Eastern Europe, based on a common History, historical, Society, social and cultural identity. The Thirty Years' War between Catholic Church, Catholicism and Protestantism was a signifi ...
and the greatest portion of western
Sub-Saharan Africa Sub-Saharan Africa (commonly called Black Africa) is, geographically, the area of the continent of Africa that lies south of the Sahara. According to the United Nations, it consists of all list of sovereign states and dependent territories in ...

Sub-Saharan Africa
, as well as
Western Sahara Western Sahara ( '; ; ) is a disputed territory Controversy is a state of prolonged public dispute or debate, usually concerning a matter of conflicting opinion or point of view. The word was coined from the Latin ''controversia'', as a comp ...

Western Sahara
and part of
Morocco ) , image_map = Morocco (orthographic projection, WS claimed).svg , map_caption = Location of Morocco in northwest Africa Africa is the world's second-largest and second-most populous continent A con ...

Morocco
. The two major mediterranean seas of the world also flow to the Atlantic: ** The
Caribbean Sea The Caribbean Sea ( es, Mar Caribe; french: Mer des Caraïbes; ht, Lanmè Karayib; jam, Kiaribiyan Sii; nl, Caraïbische Zee; pap, Laman Karibe) is a sea of the Atlantic Ocean in the tropics of the Western Hemisphere. It is bounded by Mexico a ...
and
Gulf of Mexico The Gulf of Mexico ( es, Golfo de México) is an oceanic basin, ocean basin and a marginal sea of the Atlantic Ocean, largely surrounded by the North American continent. It is bounded on the northeast, north and northwest by the Gulf Coast of ...

Gulf of Mexico
basin includes most of the U.S. interior between the
AppalachianAppalachian may refer to: * The Appalachian Mountains, a major mountain range in eastern United States and Canada * The Appalachian Trail, a hiking trail in the eastern United States * The people of Appalachia and their culture ** Appalachian Americ ...
and
Rocky Mountains The Rocky Mountains, also known as the Rockies, are a major mountain range in western North America. The Rocky Mountains stretch in great-circle distance, straight-line distance from the northernmost part of British Columbia, in western Canada, ...

Rocky Mountains
, a small part of the Canadian provinces of
Alberta ("Strong and free") , image_map = Alberta in Canada 2.svg , Label_map = yes , coordinates = , official_lang = English , capital = Edmonton Edmonton () is the capital ci ...
and
Saskatchewan ("From Many Peoples Strength") , image_map = Saskatchewan in Canada 2.svg , Label_map = yes , coordinates = , official_lang = English language, English , capital = Regina, Sa ...
, eastern
Central America Central America ( es, América Central, , ''Centroamérica'' ) is a region of the Americas. It is bordered by Mexico to the north, Colombia to the south, the Caribbean Sea to the east, and the Pacific Ocean to the west. Central America consist ...
, the islands of the Caribbean and the Gulf, and a small part of northern South America. ** The
Mediterranean Sea The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western and Southern Europe and Anatolia, on the south by North Africa, and on the ...
basin includes much of
North Africa North Africa is a region encompassing the northern portion of the African continent. There is no singularly accepted scope for the region, and it is sometimes defined as stretching from the Atlantic shores of Mauritania in the west, to Egypt's ...

North Africa
, east-central
Africa Africa is the world's second-largest and second-most populous continent A continent is one of several large landmasses. Generally identified by convention (norm), convention rather than any strict criteria, up to seven regions are ...

Africa
(through the
Nile River 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'' ("Nubi ...
),
Southern The name Southern may refer to: * 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 earl ...

Southern
, Central, and
Eastern Europe Eastern Europe is the eastern region of Europe. There is no consistent definition of the precise area it covers, partly because the term has a wide range of geopolitical, geographical, ethnic, cultural, and socioeconomic connotations. Russia, loca ...
,
Turkey Turkey ( tr, Türkiye ), officially the Republic of Turkey, is a country located mainly on Anatolia in Western Asia, with a small portion on the Balkans in Southeast Europe. It shares borders with Greece and Bulgaria to the northwest; the B ...

Turkey
, and the coastal areas of
Israel Israel (; he, יִשְׂרָאֵל, translit=Yīsrāʾēl; ar, إِسْرَائِيل, translit=ʾIsrāʾīl), officially the State of Israel ( he, מְדִינַת יִשְׂרָאֵל, label=none, translit=Medīnat Yīsrāʾēl; ), is a ...

Israel
,
Lebanon Lebanon ( , ar, لُبْنَان, translit=lubnān, ), officially the Republic of Lebanon or the Lebanese Republic, is a country in Western Asia. It is located between Syria to Lebanon–Syria border, the north and east and Israel to Blue Line ...

Lebanon
, and
Syria Syria ( ar, سُورِيَا, ''Sūriyā''), officially the Syrian Arab Republic ( ar, ٱلْجُمْهُورِيَّةُ ٱلْعَرَبِيَّةُ ٱلسُّورِيَّةُ, al-Jumhūrīyah al-ʻArabīyah as-Sūrīyah), is a country in ...

Syria
. * The
Arctic Ocean The Arctic Ocean is the smallest and shallowest of the world's five major oceans. It spans an area of approximately and is also known as the coldest of all the oceans. The International Hydrographic Organization (IHO) recognizes it as an ocea ...

Arctic Ocean
drains most of
Western Western may refer to: Places *Western, Nebraska, a village in the US *Western, New York, a town in the US *Western Creek, Tasmania, a locality in Australia *Western Junction, Tasmania, a locality in Australia *Western world, countries that ide ...
and
Northern Canada Northern Canada, colloquially the North or the Territories, is the vast northernmost region of Canada variously defined by geography and politics. Politically, the term refers to the three territories of Canada The provinces and territories of ...

Northern Canada
east of the
Continental Divide A continental divide is a drainage divide on a continent A continent is one of several large landmasses. Generally identified by convention (norm), convention rather than any strict criteria, up to seven regions are commonly regarded as co ...
, northern
Alaska Alaska (; ale, Alax̂sxax̂; ; ems, Alas'kaaq; Yup'ik The Yup'ik or Yupiaq (sg & pl) and Yupiit or Yupiat (pl), also Central Alaskan Yup'ik, Central Yup'ik, Alaskan Yup'ik ( own name ''Yup'ik'' sg ''Yupiik'' dual ''Yupiit'' pl; rus ...
and parts of
North Dakota North Dakota () is a state in the Upper Midwest region of the United States The United States of America (USA), commonly known as the United States (U.S. or US), or America, is a country Contiguous United States, primarily located in ...
,
South Dakota South Dakota () is a U.S. state in the Upper Midwest region of the United States The United States of America (USA), commonly known as the United States (U.S. or US), or America, is a country Contiguous United States, primarily locate ...

South Dakota
,
Minnesota Minnesota () is a U.S. state, state in the north central region of the United States. It is known as the "Land of 10,000 Lakes". Its official motto is , French for "The Star of the North". Of the U.S. state, U.S. states, Minnesota is the List ...

Minnesota
, and
Montana Montana () is a U.S. state, state in the Mountain states, Mountain West region of the United States. It is bordered by Idaho to the west; North Dakota and South Dakota to the east; Wyoming to the south; and by the Provinces and territories ...

Montana
in the United States, the north shore of the
Scandinavian peninsula The Scandinavian Peninsula ( sv, Skandinaviska halvön; no, Den skandinaviske halvøy (Bokmål Bokmål (, ; literally "book tongue") is an official written standard for the Norwegian language, alongside Nynorsk. Bokmål is the preferred writ ...
in Europe, central and northern Russia, and parts of
Kazakhstan Kazakhstan ( kk, Қазақстан, Qazaqstan; russian: Казахстан, Kazakhstan), officially the Republic of Kazakhstan,; russian: Республика Казахстан, Respublika Kazakhstan, link=no) is a country located mainly in ...

Kazakhstan
and
Mongolia Mongolia (, mn, Монгол Улс, Mongol Uls, Traditional Mongolian: '; lit. "Mongol Nation" or "State of Mongolia") is a landlocked country A landlocked country is a country A country is a distinct territory, territorial body ...

Mongolia
in
Asia Asia () is a landmass variously described as part of Eurasia Eurasia () is the largest continent A continent is any of several large landmasses. Generally identified by convention (norm), convention rather than any strict crite ...
, which totals to about 17% of the world's land. * Just over 13% of the land in the world drains to the
Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south and is bounded by the continents of Asia ...

Pacific Ocean
. Its basin includes much of China, eastern and southeastern Russia, Japan, the
Korean Peninsula Korea (officially the "Korean Peninsula") is a region in East Asia. Since 1945 it has been divided into the two parts which soon became the two sovereign states: North Korea North Korea (Korean language, Korean: /, McCune– ...
, most of Indochina, Indonesia and Malaysia, the Philippines, all of the
Pacific Islands This is a list of islands in the Pacific Ocean, collectively called the Pacific Islands. Three major groups of islands in the Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's oceanic divisions. It extends from the Arcti ...
, the northeast coast of
Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, smal ...

Australia
, and Canada and the United States west of the Continental Divide (including most of Alaska), as well as western Central America and South America west of the Andes. * The
Indian Ocean The Indian Ocean is the third-largest of the world's five oceanic divisions, covering or 19.8% of the water on Earth's surface. It is bounded by Asia to the north, Africa to the west and Australia (continent), Australia to the east. To the so ...

Indian Ocean
's drainage basin also comprises about 13% of Earth's land. It drains the eastern coast of Africa, the coasts of the
Red Sea The Red Sea ( ar, البحر الأحمر ''Al Baḥr al aḥmar''; Hebrew Hebrew (, , or ) is a Northwest Semitic languages, Northwest Semitic language of the Afroasiatic languages, Afroasiatic language family. Historically, it is regar ...

Red Sea
and the
Persian Gulf The Persian Gulf ( fa, خلیج فارس, translit=xalij-e fârs, lit=Gulf of Fars, ) is a mediterranean sea The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely en ...
, the Indian subcontinent, Burma, and most of Australia. * The
Southern Ocean The Southern Ocean, also known as the Antarctic Ocean or the Austral Ocean, comprises the southernmost waters of the World Ocean, generally taken to be south of 60th parallel south, 60° S latitude and encircling Antarctica. As such, i ...

Southern Ocean
drains
Antarctica Antarctica ( or ) is Earth's southernmost continent. It contains the geographic South Pole and is situated in the Antarctic region of the Southern Hemisphere, almost entirely south of the Antarctic Circle, and is surrounded by the Southern Oce ...

Antarctica
. Antarctica comprises approximately eight percent of the Earth's land.


Largest river basins

The five largest river basins (by area), from largest to smallest, are the basins of 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 L ...
(7M km), the Congo (4M km), the
Nile The Nile ( ar, النيل, an-Nīl, , Bohairic , lg, Kiira , Nobiin: Áman Dawū) is a major north-flowing river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In som ...
(3.4M km), the
Mississippi Mississippi () 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 ...

Mississippi
(3.22M km), and the
Río de la Plata The Río de la Plata (, "river of silver"), called River Plate in British English and the Commonwealth of Nations, Commonwealth and La Plata River (occasionally Plata River) in other English-speaking countries, is the estuary formed by the confl ...

Río de la Plata
(3.17M km). The three rivers that drain the most water, from most to least, are the Amazon,
Ganga The Ganges ( ) or Ganga ( , ) is a trans-boundary river of Asia Asia () is Earth's largest and most populous continent, located primarily in the Eastern Hemisphere, Eastern and Northern Hemisphere, Northern Hemisphere of the Earth, He ...

Ganga
, and Congo rivers.


Endorheic drainage basins

Endorheic drainage basins are inland basins that do not drain to an ocean. Around 18% of all land drains to endorheic lakes or seas or sinks. The largest of these consists of much of the interior of
Asia Asia () is a landmass variously described as part of Eurasia Eurasia () is the largest continent A continent is any of several large landmasses. Generally identified by convention (norm), convention rather than any strict crite ...
, which drains into the Caspian Sea, the
Aral Sea The Aral Sea (Aral ; kk, Aral teńizi, Арал теңізі, uz, Orol dengizi, Орол денгизи, kaa, Aral ten'izi, Арал теңизи, russian: Аральское море) was an endorheic lake lying between Kazakhstan Kaza ...

Aral Sea
, and numerous smaller lakes. Other endorheic regions include the
Great Basin The Great Basin is the largest area of contiguous endorheic watersheds in North America North America is a continent entirely within the Northern Hemisphere and almost all within the Western Hemisphere. It can also be described as the ...
in the United States, much of the
Sahara Desert The Sahara (, ; ar, الصحراء الكبرى, ', 'the Greatest Desert') is a desert on the African continent. With an area of , it is the largest hot desert upright=1.5, alt=see caption, Sand dunes in the Rub' al Khali ("Empty ...

Sahara Desert
, the drainage basin of the
Okavango River The Okavango River (formerly spelled Okovango or Okovanggo) is a river in southwest Africa. It is the fourth-longest river system in southern Africa, running southeastward for . It begins at 1,300 m altitude in the sandy highlands of Angola, wher ...

Okavango River
(
Kalahari Basin The Kalahari Basin, also known as the Kalahari Depression or the Okavango Basin, is an endorheic basin and large lowland area covering over 2.5 million km2 covering most of Botswana and Namibia, as well as parts of Angola, South Africa, Zambia, a ...
), highlands near the
African Great Lakes The African Great Lakes ( sw, Maziwa Makuu) are a series of lakes constituting the part of the Rift Valley lakes in and around the East African Rift. They include Lake Victoria, the List of lakes by area, second-largest fresh water lake in the wo ...

African Great Lakes
, the interiors of
Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, smal ...

Australia
and the
Arabian Peninsula The Arabian Peninsula (; ar, شِبْهُ الْجَزِيرَةِ الْعَرَبِيَّة, , "Arabian Peninsula" or , , "Island of the Arabs The Arabs (singular Arab ; singular ar, عَرَبِيٌّ, ISO 233: , Arabic pronunciati ...
, and parts in
Mexico Mexico ( es, México ; Nahuan languages: ), officially the United Mexican States (; EUM ), is a List of sovereign states, country in the southern portion of North America. It is borders of Mexico, bordered to the north by the United States; ...

Mexico
and the
Andes The Andes, Andes Mountains or Andean Mountains ( es, Cordillera de los Andes) are the List of mountain ranges#Mountain ranges by length, longest continental mountain range in the world, forming a continuous highland along the western edge of Sout ...
. Some of these, such as the Great Basin, are not single drainage basins but collections of separate, adjacent closed basins. In endorheic bodies of standing water where evaporation is the primary means of water loss, the water is typically more saline than the oceans. An extreme example of this is the
Dead Sea The Dead Sea ( he, יָם הַמֶּלַח lit. Sea of Salt; ar, البحر الميت , lit. ''the Dead Sea'',The first article ''al-'' is unnecessary and usually not used. or Buhayrat, Bahret or Birket Lut, ''lit.'' "Lake/Sea of Lot") is a s ...
.


Importance


Geopolitical boundaries

Drainage basins have been historically important for determining territorial boundaries, particularly in regions where trade by water has been important. For example, the
English English usually refers to: * English language English is a West Germanic languages, West Germanic language first spoken in History of Anglo-Saxon England, early medieval England, which has eventually become the World language, leading lan ...

English
crown gave the
Hudson's Bay Company The Hudson's Bay Company (HBC; french: Compagnie de la Baie d'Hudson ''CBH'') is a Canadian retail business group. A fur trade, fur trading business for much of its existence, HBC now owns and operates retail stores in Canada and the United St ...
a monopoly on the
fur trade The fur trade is a worldwide industry dealing in the acquisition and sale of animal fur Fur is a thick growth of hair Hair is a protein filament that grows from follicles found in the dermis. Hair is one of the defining characte ...
in the entire
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 salt ...
basin, an area called
Rupert's Land Rupert's Land (french: Terre de Rupert), or Prince Rupert's Land, was a territory in British North America comprising the Hudson Bay drainage basin, a territory in which a commercial monopoly was operated by the Hudson's Bay Company for 200 ...
. Bioregional political organization today includes agreements of states (e.g., international
treaties A treaty is a formal legally binding written agreement between actors in international law. It is usually entered into by sovereign states and international organizations, but can sometimes include individuals, business entities, and other Leg ...

treaties
and, within the US,
interstate compact In the United States The United States of America (USA), commonly known as the United States (U.S. or US), or America, is a country Contiguous United States, primarily located in North America. It consists of 50 U.S. state, states, a Washin ...
s) or other political entities in a particular drainage basin to manage the body or bodies of water into which it drains. Examples of such interstate compacts are the Great Lakes Commission and the Tahoe Regional Planning Agency.


Hydrology

In
hydrology Hydrology (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 approximately 10.7 mill ...
, the drainage basin is a logical unit of focus for studying the movement of water within 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, ...
, because the majority of water that discharges from the basin outlet originated as
precipitation In meteorology Meteorology is a branch of the atmospheric sciences which includes atmospheric chemistry and atmospheric physics, with a major focus on weather forecasting. The study of meteorology dates back millennia, though significant p ...
falling on the basin. A portion of the water that enters the
groundwater Groundwater is the water present beneath Earth's surface in rock and Pore space in soil, soil pore spaces and in the fractures of stratum, rock formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usabl ...

groundwater
system beneath the drainage basin may flow towards the outlet of another drainage basin because groundwater flow directions do not always match those of their overlying drainage network. Measurement of the discharge of water from a basin may be made by a
stream gauge A stream gauge, streamgage or stream gauging station is a location used by hydrologists Hydrology (from Greek: ὕδωρ, "hýdōr" meaning "water" and wikt:λόγος, λόγος, "lógos" meaning "study") is the scientific study of the movem ...
located at the basin's outlet. Depending on the conditions of the drainage basin, as rainfall occurs some of it seeps directly into the ground. This water will either remain underground, slowly making its way downhill and eventually reaching the basin, or it will permeate deeper into the soil and consolidate into groundwater aquifers. As water flows through the basin, it can form tributaries that change the structure of the land. There are three different main types, which are affected by the rocks and ground underneath. Rock that is quick to erode forms dendritic patterns, and these are seen most often. The two other types of patterns that form are trellis patterns and rectangular patterns. Rain gauge data is used to measure total precipitation over a drainage basin, and there are different ways to interpret that data. If the gauges are many and evenly distributed over an area of uniform precipitation, using the
arithmetic mean In mathematics and statistics, the arithmetic mean (, stress on first and third syllables of "arithmetic"), or simply the mean or the average (when the context is clear), is the sum of a collection of numbers divided by the count of numbers in the ...
method will give good results. In the Thiessen polygon method, the drainage basin is divided into polygons with the rain gauge in the middle of each polygon assumed to be representative for the rainfall on the area of land included in its polygon. These polygons are made by drawing lines between gauges, then making perpendicular bisectors of those lines form the polygons. The
isohyet A contour line (also isoline, isopleth, or isarithm) of a function of two variables is a curve In mathematics, a curve (also called a curved line in older texts) is an object similar to a line (geometry), line, but that does not have to be ...

isohyet
al method involves contours of equal precipitation are drawn over the gauges on a map. Calculating the area between these curves and adding up the volume of water is time-consuming.
Isochrone map An isochrone map in geography Geography (from Greek: , ''geographia'', literally "earth description") is a field of science devoted to the study of the lands, features, inhabitants, and phenomena of the Earth and planets. The first pers ...
s can be used to show the time taken for runoff water within a drainage basin to reach a lake, reservoir or outlet, assuming constant and uniform effective rainfall.


Geomorphology

Drainage basins are the principal hydrologic unit considered in
fluvial In geography and geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Earth, the rock (geology), rocks of which it is composed, an ...
geomorphology incised into shale at the foot of the North Caineville Plateau, Utah, within the pass carved by the Fremont River and known as the Blue Gate. GK Gilbert studied the landscapes of this area in great detail, forming the observational foundation f ...

geomorphology
. A drainage basin is the source for water and
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. F ...

sediment
that moves from higher elevation through the river system to lower elevations as they reshape the channel forms.


Ecology

Drainage basins are important in
ecology Ecology (from el, οἶκος, "house" and el, -λογία, label=none, "study of") is the study of the relationships between living organisms, including humans, and their physical environment. Ecology considers organisms In biology ...
. As water flows over the ground and along rivers it can pick up nutrients, sediment, and
pollutants A pollutant is a substance or energy introduced into the environment that has undesired effects, or adversely affects the usefulness of a resource. A pollutant may cause long- or short-term damage by changing the growth rate of plant or animal spec ...

pollutants
. With the water, they are transported towards the outlet of the basin, and can affect the ecological processes along the way as well as in the receiving water source. Modern use of artificial fertilizers, containing nitrogen, phosphorus, and potassium, has affected the mouths of drainage basins. The minerals are carried by the drainage basin to the mouth, and may accumulate there, disturbing the natural mineral balance. This can cause
eutrophication Eutrophication (from Greek ''eutrophos'', "well-nourished") is a limnological term for the process by which a body of water becomes progressively enriched with mineral In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth" ...

eutrophication
where plant growth is accelerated by the additional material.


Resource management

Because drainage basins are coherent entities in a hydrological sense, it has become common to manage water resources on the basis of individual basins. In the
U.S. state In the United States The United States of America (USA), commonly known as the United States (U.S. or US), or America, is a country Contiguous United States, primarily located in North America. It consists of 50 U.S. state, states, a W ...
of
Minnesota Minnesota () is a U.S. state, state in the north central region of the United States. It is known as the "Land of 10,000 Lakes". Its official motto is , French for "The Star of the North". Of the U.S. state, U.S. states, Minnesota is the List ...

Minnesota
, governmental entities that perform this function are called " watershed districts". In New Zealand, they are called catchment boards. Comparable community groups based in Ontario, Canada, are called conservation authorities. In North America, this function is referred to as "
watershed managementWatershed management is the study of the relevant characteristics of a watershed aimed at the sustainable distribution of its resources and the process of creating and implementing plans, programs and projects to sustain and enhance watershed funct ...
". In
Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, ...
, the National Policy of Water Resources, regulated by Act n° 9.433 of 1997, establishes the drainage basin as the territorial division of Brazilian water management. When a river basin crosses at least one political border, either a border within a nation or an international boundary, it is identified as a
transboundary river A transboundary river is a river that crosses at least one political border, either a border within a nation or an international boundary. Bangladesh has the highest number of these rivers, including two of the world's largest rivers, the Ganges and ...
. Management of such basins becomes the responsibility of the countries sharing it. Nile Basin Initiative, for
Senegal River ,french: Fleuve Sénégal) , name_etymology = , image = Senegal River Saint Louis.jpg , image_size = , image_caption = Fishermen on the bank of the Senegal River estuary at the outskirts of Saint-Louis, Senegal ...
,
Mekong River Commission The Mekong River Commission (MRC) is an "...inter-governmental organisation that works directly with the governments of Cambodia, Laos, Thailand, and Vietnam , image_map = , map_caption = , capital ...

Mekong River Commission
are a few examples of arrangements involving management of shared river basins. Management of shared drainage basins is also seen as a way to build lasting peaceful relationships among countries.


Catchment factors

The catchment is the most significant factor determining the amount or likelihood of
flooding Flash flooding caused by heavy rain falling in a short amount of time. 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 ...

flooding
. Catchment factors are:
topography Topography is the study of the forms and features of land surfaces. The topography of an area could refer to the surface forms and features themselves, or a description (especially their depiction in maps). Topography is a field of geoscience ...
, shape, size,
soil File:Stagnogley.JPG, Surface-water-Gley soil, gley developed in glacial till, Northern Ireland. Soil is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Earth's body of soil, called the pedosphere ...

soil
type, and
land use Land use involves the management and modification of natural environment or wilderness Wilderness or wildlands (usually in the plural), are natural environments on Earth that have not been significantly modified by human activity or any nonur ...
(paved or
roof A roof is the top covering of a building A building, or edifice, is a structure with a roof and walls standing more or less permanently in one place, such as a house or factory. Buildings come in a variety of sizes, shapes, and functions, ...

roof
ed areas). Catchment topography and shape determine the time taken for
rain Rain is liquid water in the form of drop (liquid), droplets that have condensation, condensed from atmosphere, atmospheric water vapor and then precipitation (meteorology), become heavy enough to fall under gravity. Rain is a major component ...

rain
to reach the river, while catchment size, soil type, and development determine the amount of water to reach the river.


Topography

Generally, topography plays a big part in how fast runoff will reach a river. Rain that falls in steep
mountain A mountain is an elevated portion of the Earth's crust, generally with steep sides that show significant exposed bedrock. A mountain differs from a plateau in having a limited summit area, and is larger than a hill, typically rising at least ...

mountain
ous areas will reach the primary river in the drainage basin faster than flat or lightly sloping areas (e.g., > 1% gradient).


Shape

Shape will contribute to the speed with which the runoff reaches a river. A long thin catchment will take longer to drain than a circular catchment.


Size

Size will help determine the amount of water reaching the river, as the larger the catchment the greater the potential for flooding. It is also determined on the basis of length and width of the drainage basin.


Soil type

Soil type will help determine how much water reaches the river. The runoff from the drainage area is dependent on the soil type. Certain soil types such as
sand Sand is a granular Granularity (also called graininess), the condition of existing in granules or grains A grain is a small, hard, dry seed A seed is an embryonic plant enclosed in a protective outer covering. The formation of th ...

sand
y soils are very free-draining, and rainfall on sandy soil is likely to be absorbed by the ground. However, soils containing
clay Clay is a type of fine-grained natural soil File:Stagnogley.JPG, Surface-water-Gley soil, gley developed in glacial till, Northern Ireland. Soil is a mixture of organic matter, minerals, gases, liquids, and organisms that together support ...

clay
can be almost impermeable and therefore rainfall on clay soils will run off and contribute to flood volumes. After prolonged rainfall even free-draining soils can become saturated, meaning that any further rainfall will reach the river rather than being absorbed by the ground. If the surface is impermeable the precipitation will create surface run-off which will lead to higher risk of flooding; if the ground is permeable, the precipitation will infiltrate the soil.


Land use

Land use can contribute to the volume of water reaching the river, in a similar way to clay soils. For example, rainfall on roofs, sidewalk, pavements, and roads will be collected by rivers with almost no absorption into the
groundwater Groundwater is the water present beneath Earth's surface in rock and Pore space in soil, soil pore spaces and in the fractures of stratum, rock formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usabl ...

groundwater
.


See also

* * * * * * * * * * *Catchment hydrology


References


Citations


Sources

* DeBarry, Paul A. (2004). ''Watersheds: Processes, Assessment and Management.'' John Wiley & Sons.


External links


Instructional video: Manual watershed delineation is a five-step process

Instructional video: To delineate a watershed you must identify land surface features from topographic contours

Science week catchment factsheet

Catchment Modelling Toolkit

Water Evaluation And Planning System (WEAP) - modeling hydrologic processes in a drainage basin

New Mexico State University - Water Task Force



Watershed Condition Classification Technical Guide
United States Forest Service
''Science in Your Watershed''
USGS
''Studying Watersheds: A Confluence of Important Ideas''

''Water Sustainability Project'' Sustainable water management through demand management and ecological governance, with the POLIS Project at the University of Victoria

Map of the Earth's primary watersheds
World Resources Institute, WRI
What is a watershed and why should I care?

Cycleau - A project looking at approaches to managing catchments in North West Europe


* [http://web.mit.edu/star/hydro StarHydro – software tool that covers concepts of fluvial geomorphology and watershed hydrology]
EPA Surf your watershed

Florida Watersheds and River Basins - Florida DEP
{{Authority control Drainage basins, Fluvial landforms Freshwater ecology Geomorphology Hydrology Rivers Water and the environment Water streams