A
drainage basin is an extent of land where
waterWater is an ubiquitous chemical substance that is composed of hydrogen and oxygen and is essential for all known forms of life.In typical usage, water refers only to its liquid form or state, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam. Water covers 71%...
from
rainRain is liquid precipitation, as opposed to other kinds of precipitation such as snow, hail and sleet. On Earth, it is the condensation of atmospheric water vapor into drops heavy enough to fall, often making it to the surface...
or snow melt drains downhill into a body of water, such as a
riverA river is a natural watercourse, usually freshwater, flowing toward an ocean, a lake, a sea or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water...
,
lakeA lake is a terrain feature , a body of liquid on the surface of a world that is localized to the bottom of basin and moves slowly if it moves at all. Another definition is, a body of fresh or salt water of considerable size that is surrounded by land...
, reservoir,
estuaryAn estuary is a semi-enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries are thus subject to both marine influences, such as tides, waves, and the influx of saline water; and riverine influences, such as flows of...
,
wetlandA wetland is an area of land whose soil is saturated with moisture either permanently or seasonally. Such areas may also be covered partially or completely by shallow pools of water. Wetlands include swamps, marshes, and bogs, among others. The water found in wetlands can be saltwater, freshwater,...
,
seaA sea is any large amount of water filled with animals such as crabs, whales, sharks, and fish, but there is inconsistency as to its precise definition and application. Most commonly, a sea may refer to a large expanse of saline water connected with an ocean, but it is also used sometimes for a...
or
oceanAn ocean is a large body of saline water, and a principal component of the hydrosphere. Approximately 75% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...
. The drainage basin includes both the streams and rivers that convey the water as well as the land surfaces from which water drains into those channels, and is separated from adjacent basins by a drainage divide.
The drainage basin acts like a
funnelA funnel is a pipe with a wide, often conical mouth and a narrow stem. It is used to channel liquid or fine-grained substances into containers with a small opening. Without a funnel,spillage would occur....
, collecting all the water within the area covered by the basin and channelling it into a waterway. Each drainage basin is separated topographically from adjacent basins by a geographical barrier such as a
ridge300px|thumb|right|Stratigraphic ridge found in Northeastern [[Tennessee]]A ridge is a geological feature that features a continuous elevational crest for some distance. Ridges are usually termed hills or mountains as well, depending on size...
,
hillA hill is a landform that extends above the surrounding terrain, in a limited area. Hills often have a distinct summit, although in areas with scarp/dip topography a hill may refer to a particular section of scarp slope without a well-defined summit A hill is a landform that extends above the...
or
mountainA mountain is a large landform that stretches above the surrounding land in a limited area usually in the form of a peak. A mountain is generally steeper than a hill. The adjective montane is used to describe mountainous areas and things associated with them...
, which is known as a
water divideA drainage divide, water divide, divide or watershed is the line separating neighbouring drainage basins...
.
Other terms that are used to describe a drainage basin are
catchment,
catchment area,
catchment basin,
drainage area,
river basin,
water basin and
watershed. In the technical sense, a watershed refers to a divide that separates one drainage area from another drainage area. However, in the
United StatesThe United States of America is a federal constitutional republic comprising fifty states and a federal district...
and
CanadaCanada is a country occupying most of northern North America, extending from the Atlantic Ocean in the east to the Pacific Ocean in the west and northward into the Arctic Ocean...
, the term is often used to mean a drainage basin or catchment area itself. Drainage basins drain into other drainage basins in a
hierarchical patternIn mathematics, the Strahler number or Horton–Strahler number of a mathematical tree is a numerical measure of its branching complexity....
, with smaller
sub-drainage basins combining into larger drainage basins.
The
United States Environmental Protection AgencyThe U.S. Environmental Protection Agency is an agency of the federal government of the United States charged to regulate chemicals and protect human health by safeguarding the natural environment: air, water, and land...
launched the website
Watershed CentralWatershed Central is an Environmental Protection Agency website developed to organize information and tools relevant to watershed management from across the country....
for the US public to exchange information and locate resources needed to restore local drainage basins in that country.
Map
Drainage basins of the principal oceans and seas of the world. Grey areas are
endorheicAn endorheic basin is a closed drainage basin that retains water and allows no outflow to other bodies of water such as rivers or oceans. Normally the water accruing in drainage basins flows out through surface rivers or by underground diffusion through permeable rock to the oceans...
basins that do not drain to the ocean.
Ocean basins
There are numerous drainage basins throughout the world in all sorts of places. The following is a list of some of the major ones:
- The Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about 106.4 million square kilometres , it covers approximately one-fifth of the Earth's surface and about one-quarter of its water surface area. The first part of its name refers to the Atlas of Greek...
drains approximately 47% of all land in the world. In North America, it directly drains the Saint Lawrence RiverThe Saint Lawrence River is a large river flowing approximately from southwest to northeast in the middle latitudes of North America, connecting the Great Lakes with the Atlantic Ocean. It is the primary drainage of the Great Lakes Basin...
and Great LakesThe Great Lakes are a collection of freshwater lakes located in eastern North America, on the Canada – United States border. Consisting of Lakes Superior, Michigan, Huron, Erie, and Ontario, they form the largest group of freshwater lakes on Earth. They are sometimes referred to as the "Third...
basins, the Eastern SeaboardAn Eastern seaboard can mean any easternmost part of a continent, or its countries, states and/or cities.Eastern seaboard may also refer to:*East Coast of the United States*East Coast of Australia*Eastern Seaboard of Thailand...
of the United States, the Canadian Maritimes, and most of Newfoundland and LabradorNewfoundland and Labrador is a province of Canada on the country's Atlantic coast in northeastern North America. This easternmost Canadian province comprises two main parts: the island of Newfoundland off the country's eastern coast, and Labrador on the mainland to the northwest of the island.A...
. It also directly drains nearly all of South AmericaSouth America is the southern continent of the Americas, situated entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere...
east of the AndesThe Andes are the world's longest exposed mountain range. They lie as a continuous chain of highland along the western coast of South America...
, most of Western and Central EuropeEurope is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally divided from Asia to its east by the water divide of the Ural Mountains, the Ural River, the Caspian Sea, the Caucasus Mountains , and the Black Sea to the southeast...
, and the greatest portion of western Sub-Saharan AfricaSub-Saharan Africa is a geographical term used to describe the area of the African continent which lies south of the Sahara, or those African countries which are fully or partially located south of the Sahara...
. The three major mediterranean seaIn oceanography, a mediterranean sea is a mostly enclosed sea that has limited exchange of deep water with outer oceans and where the water circulation is dominated by salinity and temperature differences rather than winds....
s of the world also flow to the Atlantic:
- The American Mediterranean Sea (the Caribbean Sea
The Caribbean Sea is a sea of the Atlantic Ocean situated in the tropics of the Western hemisphere, bounded to the south and west by the American landmass, with the North Atlantic Ocean proper to the northeast and the Gulf of Mexico to the northwest...
and Gulf of MexicoThe Gulf of Mexico is the ninth largest body of water in the world. Considered a smaller part of the Atlantic Ocean, it is an ocean basin largely surrounded by the North American continent and the island of Cuba. It is bounded on the northeast, north and northwest by the Gulf Coast of the United...
) basin includes most of the AmericanThe United States of America is a federal constitutional republic comprising fifty states and a federal district...
interior between the Appalachian and Rocky Mountain ranges, a small part of the CanadianCanada is a country occupying most of northern North America, extending from the Atlantic Ocean in the east to the Pacific Ocean in the west and northward into the Arctic Ocean...
provinces of AlbertaAlberta is one of Canada's prairie provinces. It became a province on September 1, 1905.Alberta is located in western Canada, bounded by the provinces of British Columbia to the west and Saskatchewan to the east, the Northwest Territories to the north, and the U.S. state of Montana to the south....
and SaskatchewanSaskatchewan is a prairie province in Canada, which has an area of and a population of 1,023,810 , mostly living in the southern half of the province. Of these, 233,923 live in the province's largest city, Saskatoon, while 194,971 live in the provincial capital, Regina...
, eastern Central AmericaManagua
Guatemala City
San Salvador
San Pedro Sula
Panama City
San José, Costa Rica
Santa Ana, El Salvador
León
San Miguel|-|}...
, the islands of the Caribbean and the Gulf, and a small part of northern South AmericaSouth America is the southern continent of the Americas, situated entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere...
.
- The European Mediterranean Sea
The Mediterranean Sea is a sea connected to the Atlantic Ocean surrounded by the Mediterranean region and almost completely enclosed by land: on the north by Anatolia and Europe, on the south by Africa, and on the east by the Levant. The sea is technically a part of the Atlantic Ocean, although it...
basin includes much of northern AfricaAfrica is the world's second-largest and second most-populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area. With a billion people in 61 territories, it accounts for about 14.8% of the...
, east-central AfricaAfrica is the world's second-largest and second most-populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area. With a billion people in 61 territories, it accounts for about 14.8% of the...
(through the NileThe Nile is a major north-flowing river in Africa, generally regarded as the longest river in the world....
), southern, central, and eastern EuropeEurope is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally divided from Asia to its east by the water divide of the Ural Mountains, the Ural River, the Caspian Sea, the Caucasus Mountains , and the Black Sea to the southeast...
, TurkeyTurkey , known officially as the Republic of Turkey
, is a Eurasian country that stretches across the Anatolian peninsula in Western Asia and Thrace in the Balkan region of southeastern Europe...
, and the coastal areas of IsraelIsrael officially the State of Israel , is a developed state in Western Asia located on the eastern shore of the Mediterranean Sea. It borders Lebanon in the north, Syria in the northeast, Jordan in the east, and Egypt on the southwest, and contains geographically diverse features within its...
, LebanonLebanon , officially the Republic of Lebanon
[Republic of Lebanon is the most common term used by Lebanese government agencies...]
, and SyriaSyria , officially the Syrian Arab Republic , is a country in Western Asia, bordering Lebanon and the Mediterranean Sea to the west, Turkey to the north, Iraq to the east, Jordan to the south and Israel to the southwest....
.
- The Arctic Ocean
The Arctic Ocean, located in the Northern Hemisphere and mostly in the Arctic north polar region, is the smallest, and shallowest of the world's five major oceanic divisions.
The International Hydrographic Organization recognizes it as an ocean, although some...
basin drains most of Western and Northern CanadaCanada is a country occupying most of northern North America, extending from the Atlantic Ocean in the east to the Pacific Ocean in the west and northward into the Arctic Ocean...
east of the Continental DivideThe Continental Divide of the Americas, or merely the Continental Divide or Great Divide, is the name given to the principal, and largely mountainous, hydrological divide of the Americas that separates the watersheds that drain into the Pacific Ocean from, those river systems which drain into the...
, the north shore of AlaskaAlaska is the largest state of the United States of America by area; it is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...
and parts of North DakotaNorth Dakota is a state located in the Midwestern region of the United States of America; on the Canadian border halfway between the Pacific and Atlantic oceans. North Dakota is the 19th largest state by area in the U.S.; it is the 3
rd least populous, with just over 641,481 residents as...
, South DakotaSouth Dakota is a state located in the Midwestern region of the United States of America. It is named after the Lakota and Dakota Sioux American Indian tribes. South Dakota was carved out of the southern half of the Dakota Territory and admitted to the Union on November 2, 1889...
, MinnesotaMinnesota is a state in the Midwestern region of the United States. The twelfth largest state by area in the U.S., it is the twenty-first most populous, with 5.2 million residents. Minnesota was carved out of the eastern half of the Minnesota Territory and admitted to the Union as the...
, and MontanaMontana is a state in the Western United States. The western third of the state contains numerous mountain ranges; other 'island' ranges are found in the central third of the state, for a total of 77 named ranges of the Rocky Mountains. This geographical fact is reflected in the state's name,...
in the United States, the north shore of the Scandinavian peninsulaThe Scandinavian Peninsula is a geographic region in northern Europe, consisting of Norway and Sweden. The name Scandinavian is derived from Scania, a region at the southernmost extremity of the peninsula. The Scandinavian Peninsula is the largest peninsula in Europe.-Geography:The Scandinavian...
in Europe, and much of central and northern RussiaRussia , officially known as both Russia and the Russian Federation , is a country in northern Eurasia . It is a semi-presidential republic, comprising 83 federal subjects...
.
- The Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. Its name is derived from the Latin name Tepre Pacificum, "peaceful sea", bestowed upon it by the Portuguese explorer Ferdinand Magellan. It extends from the Arctic in the north to Antarctica in the south, bounded by Asia and...
drains just over 13% of the land in the world. Its basin includes much of ChinaChina is a cultural region, an ancient civilization, and, depending on perspective, a national or multinational entity extending over a large area in East Asia....
, southeastern RussiaRussia , officially known as both Russia and the Russian Federation , is a country in northern Eurasia . It is a semi-presidential republic, comprising 83 federal subjects...
, Japanis an island country in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, People's Republic of China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
, KoreaKorea is a civilization and formerly unified nation currently divided into two states. Located on the Korean Peninsula, it borders China to the northwest, Russia to the northeast, and is separated from Japan to the east by the Korea Strait....
, most of IndonesiaThe Republic of Indonesia is a country in Southeast Asia and Oceania. Indonesia comprises 17,508 islands. With an estimated population of around 237 million people, it is the world's fourth most populous country, with the world's largest population of Muslims.Indonesia is a republic, with an...
and MalaysiaMalaysia is a country in Southeast Asia that consists of thirteen states and three Federal Territories, with a total landmass of . The capital city is Kuala Lumpur, while Putrajaya is the seat of the federal government. The population stands at over 28 million inhabitants...
, the PhilippinesThe Philippines officially known as the Republic of the Philippines, is a country in Southeast Asia with Manila as its capital city. It comprises 7,107 islands in the western Pacific Ocean....
, all of the Pacific IslandsThe Pacific Islands comprise 20,000 to 30,000 islands in the Pacific Ocean. Those islands lying south of the tropic of Cancer are traditionally grouped into three divisions: Melanesia, Micronesia and Polynesia.-Oceania:...
, the northeast coast of AustraliaAustralia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the continental mainland , the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans...
, and the western parts of Canada, the United States (including most of AlaskaAlaska is the largest state of the United States of America by area; it is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...
), Central AmericaManagua
Guatemala City
San Salvador
San Pedro Sula
Panama City
San José, Costa Rica
Santa Ana, El Salvador
León
San Miguel|-|}...
, and South AmericaSouth America is the southern continent of the Americas, situated entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere...
.
- The Indian Ocean
The Indian Ocean is the third largest of the world's oceanic divisions, covering about 20% of the water on the Earth's surface. It is bounded on the north by South Asia ; on the west by Africa; on the east by Indochina, the Sunda Islands, and Australia; and on the south by the Southern Ocean...
drains around 13% of the Earth's land. It drains the eastern coast of Africa, the coasts of the Red SeaThe Red Sea is a seawater inlet of the Indian Ocean, lying between Africa and Asia. The connection to the ocean is in the south through the Bab el Mandeb strait and the Gulf of Aden. In the north, there is the Sinai Peninsula, the Gulf of Aqaba, and the Gulf of Suez,...
and the Persian GulfThe Persian Gulf, in the Southwest Asian region, is an extension of the Indian Ocean located between Iran and the Arabian Peninsula. Historically and commonly known as the Persian Gulf, this body of water is sometimes controversially referred to as the Arabian Gulf by most Arab states or simply The...
, the Indian subcontinentThe Indian subcontinent, also Indian Subcontinent and other terms, is a region of the Asian continent on the Indian tectonic plate south of the Himalayas, forming a peninsula which extends southward into the Indian Ocean...
, Burma, and most of AustraliaAustralia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the continental mainland , the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans...
.
- The Southern Ocean
The Southern Ocean, also known as the Great Southern Ocean, the Antarctic Ocean and the South Polar Ocean, comprises the southernmost waters of the World Ocean south of 60° S latitude. The International Hydrographic Organization has designated the Southern Ocean as an oceanic division encircling...
drains Antarctica| style="border-top:solid 1px #ccd2d9; padding:0.4em 1em 0.4em 0; vertical-align:top;" | 14,000,000 km
2 280,000 km
2 13,720,000 km
2 |-! style="border-top: solid 1px #ccd2d9; padding: 0.4em 1em 0.4em 0; vertical-align: top;...
. Antarctica comprises approximately eight percent of the Earth's land.
Largest river basins
The three largest river basins (by area), from largest to smallest, are the
AmazonThe Amazon River of South America is the largest river in the world by volume, with a total river flow greater than the next eight largest rivers combined. The Amazon, which has the largest drainage basin in the world, accounts for approximately one-fifth of the world's total river flow. During...
basin, the
CongoThe Congo River is the largest river in Western Central Africa. Its overall length of 4,700 km makes it the second longest in Africa .-Background:...
basin, and the
MississippiThe Mississippi River is the second longest river in the United States, with a length of from its source in Lake Itasca in Minnesota to its mouth in the Gulf of Mexico....
basin. The three rivers that drain the most water, from most to least, are the
AmazonThe Amazon River of South America is the largest river in the world by volume, with a total river flow greater than the next eight largest rivers combined. The Amazon, which has the largest drainage basin in the world, accounts for approximately one-fifth of the world's total river flow. During...
,
CongoThe Congo River is the largest river in Western Central Africa. Its overall length of 4,700 km makes it the second longest in Africa .-Background:...
, and Ganges Rivers.
Endorheic drainage basins
Endorheic drainage basins are inland basins that do not drain into an ocean; around 18% of all land drains to endorheic lakes or seas. The largest of these consists of much of the interior of
AsiaAsia is the world's largest and most populous continent, located in the eastern and northern hemispheres. It covers 8.6% of the earth's total surface area and with approximately 4 billion people, it hosts 60% of the world's current human population.Asia is traditionally defined as part of the...
, and drains into the
Caspian SeaThe Caspian Sea is the largest enclosed body of water on Earth by area, variously classed as the world's largest lake or a full-fledged sea. It has a surface area of 371,000 square kilometres and a volume of 78,200 cubic kilometres...
and the
Aral SeaThe Aral Sea is an endorheic basin in Central Asia; it lies between Kazakhstan in the north and Karakalpakstan, an autonomous region of Uzbekistan, in the south...
. Other basins include the
Great BasinThe Great Basin is a large, arid region of the western United States. Its boundaries vary depending on how it is defined, but it is most commonly defined as the contiguous endorheic basin roughly between the Wasatch Mountains and the Sierra Nevada mountains. Culturally, the Great Basin is home to...
in the
United StatesThe United States of America is a federal constitutional republic comprising fifty states and a federal district...
, much of the Sahara Desert, the watershed of the
Okavango RiverThe Okavango River is a river in southwest Africa. It is the fourth-longest river system in southern Africa, running southeastward for 1,600 km . It begins in Angola, where it is known as the Cubango River...
(
Kalahari BasinThe Kalahari Basin is a large lowland area covering over 2.5 million km² covering most of Botswana and parts of Namibia, South Africa, Angola, Zambia, and Zimbabwe. The outstanding physical feature in the basin is the large Kalahari Desert, taking up most of the area.-Ecology:Despite its aridity,...
), highlands near the
African Great LakesThe Great Lakes of Africa are a series of lakes in and around the geographic Great Rift Valley formed by the action of the tectonic East African Rift. They include Lake Victoria, the second largest fresh water lake in the world in terms of surface area, and Lake Tanganyika, the world's second...
, the interiors of
AustraliaAustralia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the continental mainland , the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans...
and the
Arabian PeninsulaThe Arabian Peninsula , Arabia, Arabistan, and the Arabian subcontinent is a peninsula in Southwest Asia at the junction of Africa and Asia...
, and parts in
MexicoThe United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...
and the
AndesThe Andes are the world's longest exposed mountain range. They lie as a continuous chain of highland along the western coast of South America...
.
In endorheic
bodies of standing waterBodies of Water is a band from the Highland Park neighborhood of Los Angeles, California, signed to independent record label Secretly Canadian. The core group consists of married couple David and Meredith Metcalf. However, the band often plays LA shows with five or more additional musicians, such...
where evaporation is the primary means of water loss, the water is typically more saline than the oceans. An extreme example is the
Dead SeaThe Dead Sea is a salt lake in Jordan to the east and in the West Bank and Israel to the west. Its surface and shores are below sea level, the lowest elevation on the Earth's surface on dry land. The Dead Sea is deep, the deepest hypersaline lake in the world. It is also one of the world's...
.
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
EnglishEngland is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west and the North Sea to the east, with the English Channel to the south separating it from continental...
crown gave the
Hudson's Bay CompanyThe Hudson's Bay Company , abbreviated HBC, is the oldest commercial corporation in North America and is one of the oldest in the world...
a monopoly on the
fur tradeThe fur trade is a worldwide industry dealing in the acquisition and sale of animal fur.-Russian fur trade:Before the colonization of the Americas, Russia was a major supplier of fur-pelts to Western Europe and parts of Asia. Fur was a major Russian export as trade developed in the early Middle...
in the entire
Hudson BayHudson Bay is a large body of water in northeastern Canada. It drains a very large area that includes parts of Ontario, Quebec, Saskatchewan, Alberta, most of Manitoba, southeastern Nunavut, as well as parts of North Dakota, South Dakota, Minnesota, and Montana. A smaller offshoot of the bay,...
watershed, an area called
Rupert's LandRupert's Land, also sometimes called "Prince Rupert's Land", was a territory in British North America, consisting of the Hudson Bay drainage basin, that was owned by the Hudson's Bay Company for 200 years from 1670 to 1870. The area once known as Rupert's Land is now mainly a part of Canada, but a...
. Today, bioregional democracy can include agreements of states in a particular drainage basin to defend it. One example of this is the
Great Lakes CommissionThe Great Lakes Commission is an eight-state compact United States agency established in 1955 through the Great Lakes Basin Compact, in order to "promote the orderly, integrated and comprehensive development, use and conservation of the water resources of the Great Lakes Basin," which includes the...
.
Hydrology
In
hydrologyHydrology is the study of the movement, distribution, and quality of water throughout Earth, and thus addresses both the hydrologic cycle and water resources...
, the drainage basin is a logical unit of focus for studying the movement of water within the hydrological cycle, because the majority of water that discharges from the basin outlet originated as
precipitationIn meteorology, precipitation is any product of the condensation of atmospheric water vapor that is deposited on the Earth's surface. The main forms of precipitation include rain, snow, ice pellets, and graupel...
falling on the basin. A portion of the water that enters the
groundwaterGroundwater is water located beneath the ground surface in soil pore spaces and in the fractures of lithologic formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water. The depth at which soil pore spaces or fractures and voids in...
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 gaugeA stream gauge, or stream gage, refers to a site along a stream where measurements of volumetric discharge are made.-Measurement of discharge:...
located at the basin's outlet.
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 meanIn mathematics and statistics, the arithmetic mean of a list of numbers is the sum of all of the list divided by the number of items in the list. If the list is a statistical population, then the mean of that population is called a population mean...
method will give good results. In the Thiessen polygon method, the watershed 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 isohyetal 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.
Geomorphology
Drainage basins are the principal hydrologic unit considered in
fluvialFluvial is used in geography and Earth science to refer to the processes associated with rivers and streams and the deposits and landforms created by them...
geomorphologyGeomorphology is the scientific study of landforms and the processes that shape them...
. A drainage basin is the source for water and
sedimentSediment is any particulate matter that can be transported by fluid flow, and which eventually is deposited.Sediments are most often transported by water transported by wind and glaciers...
that moves through the river system and reshapes the channel.
Ecology
Drainage basins are important elements to consider also in
ecologyEcology is the interdisciplinary scientific study of the interactions between organisms and the interactions of these organisms with their environment....
. As water flows over the ground and along rivers it can pick up nutrients, sediment, and
pollutantsWater pollution is the contamination of water bodies such as lakes, rivers, oceans, and groundwater. All water pollution affects organisms and plants that live in these water bodies and in almost all cases the effect is damaging either to individual species and populations but also to the natural...
. Like the water, they get 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 usage of artificial fertilizers, containing nitrogen, phosphorus, and potassium, has affected the mouths of watersheds. The minerals will be carried by the watershed to the mouth and accumulate there, disturbing the natural mineral balance. This can cause 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. stateA U.S. state is any one of 50 federated states of the United States of America that share sovereignty with the federal government . Because of this shared sovereignty, an American is a citizen both of the federal entity and of his or her state of domicile...
of
MinnesotaMinnesota is a state in the Midwestern region of the United States. The twelfth largest state by area in the U.S., it is the twenty-first most populous, with 5.2 million residents. Minnesota was carved out of the eastern half of the Minnesota Territory and admitted to the Union as the...
, governmental entities that perform this function are called
watershed districtWatershed districts are special government entities in the U.S. state of Minnesota that monitor and regulate the use of water in watersheds surrounding various lakes and rivers in the state. The districts cover the natural regions of the watersheds, rather than politically-defined regions...
s. 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 process of creating and implementing plans, programs, and projects to sustain and enhance watershed functions that affect the plant, animal, and human communities within a watershed boundary...
.
In
BrazilBrazil , officially the Federative Republic of Brazil , is a country in South America. It is the fifth largest country by geographical area, occupying nearly half of South America, the fifth most populous country, and the fourth most populous democracy in the world. Bounded by the Atlantic Ocean...
, the National Policy of Water Resources, regulated by Act n° 9.433 of 1997, establishes the drainage basin as territorial division of Brazilian water management.
Catchment factors
The catchment is the most significant factor determining the amount or likelihood of flooding.
Catchment factors are:
topographyTopography is the study of Earth's surface shape and features or those ofplanets, moons, and asteroids...
, shape, size,
soilSoil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics. It is composed of particles of broken rock that have been altered by chemical and...
type and
land useLand use is the human modification of natural environment or wilderness into built environment such as fields, pastures, and settlements. The major effect of land use on land cover since 1750 has been deforestation of temperate regions. More recent significant effects of land use include urban...
(paved or
roofA roof is the covering on the uppermost part of a building. A roof protects the building and its contents from the effects of weather. Structures that require roofs range from a letter box to a cathedral or stadium, dwellings being the most numerous....
ed areas). Catchment topography and shape determine the time taken for
rainRain is liquid precipitation, as opposed to other kinds of precipitation such as snow, hail and sleet. On Earth, it is the condensation of atmospheric water vapor into drops heavy enough to fall, often making it to the surface...
to reach the river, Catchment size, soil type and development determine the amount of water to reach the river.
Topography
Topography determines the speed with which the runoff will reach a river. Clearly rain that falls in steep
mountainA mountain is a large landform that stretches above the surrounding land in a limited area usually in the form of a peak. A mountain is generally steeper than a hill. The adjective montane is used to describe mountainous areas and things associated with them...
ous areas will reach the river faster than flat or gently sloping areas.
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.
Soil type
Soil type will help determine how much water reaches the river. Certain soil types such as
sandSand is a naturally occurring granular material composed of finely divided rock and mineral particles.As the term is used by geologists, sand particles range in diameter from 0.0625 to 2 millimeters. An individual particle in this range size is termed a sand grain...
y soils are very free draining and rainfall on sandy soil is likely to be absorbed by the ground. However, soils containing
clayClay is a naturally occurring material composed primarily of fine-grained minerals, which show plasticity through a variable range of water content, and which can be hardened when dried and/or fired...
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
saturatedSaturation or saturated may mean:* Dew point, which is a temperature that occurs when atmospheric humidity reaches 100% and the air is saturated with moisture...
, meaning that any further rainfall will reach the river rather than being absorbed by the ground.
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,
pavementA sidewalk , pavement , footpath , platform or footway is a path for pedestrians that is situated alongside a road or a paved...
s and
roadA road is an identifiable route, way or path between places.
s will be collected by rivers with almost no absorption into the
groundwaterGroundwater is water located beneath the ground surface in soil pore spaces and in the fractures of lithologic formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water. The depth at which soil pore spaces or fractures and voids in...
.
See also
- Drainage system
*In geomorphology, a drainage system is the pattern formed by the streams, rivers, and lakes in a particular watershed. They are governed by the topography of the land, whether a particular region is dominated by hard or soft rocks, and the gradient of the land...
- Drainage system (Geomorphology)
In geomorphology, a drainage system is the pattern formed by the streams, rivers, and lakes in a particular drainage basin. They are governed by the topography of the land, whether a particular region is dominated by hard or soft rocks, and the gradient of the land.-Types of drainage...
- Mainstem
In rivers and hydrology, the main stem is defined as the principal channel within a given drainage basin, into which all of the tributary streams in a drainage basin flow. Viewed in terms of the Strahler stream order system, the main stem would be the highest order stream amongst the streams in a...
- Reservoir
- Integrated catchment management
Integrated catchment management is a subset of environmental planning which approaches sustainable resource management from a catchment perspective, in contrast to a piecemeal approach that artificially separates land management from water management....
- International Journal of River Basin Management
JRBM is the International Journal of River Basin Management. The journal issued for the first time at the Third World Water Forum in Kyoto, March 2003. It is published in four issues per year in print and electronic format, and is co-published by IAHR with IAHS and INBO....
(JRBM)
- Catchment Management Authority
The Catchment Management Authorities were established in Victoria, Catchment and Land Protection Act 1994.Originally known as Catchment and Land Protection Boards, the CMA's were changed to their present name in 1997....
- River Basin Management Plans
River basin management plans are a management tool in Integrated Water Resources Management. They generally contain descriptions of the water resources in a drainage basin and water allocation plans.-Europe:...
- Time of Concentration
Time of concentration is a concept used in hydrology to measure the response of a watershed to a rain event. It is defined as the time needed for water to flow from the most remote point in a watershed to the watershed outlet...
External links