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River
*** Shopping-Tip: River
Image:Murray-Howlong.jpg frame|right|The [[Murray River in
Australia.]]
A '''river''' is a large natural
waterway. The source of a river may be a
lake, a
spring (water) spring, or a collection of small streams, known as
source (river or stream) headwaters. From their source, all rivers flow downhill, typically terminating in the
ocean. The mouth, or lower end, of a river is known as its
base level.
A river's water is normally confined to a
Channel (geography) channel, made up of a
stream bed between
stream bank banks. Most
rainfall on land passes through a river on its way to the
ocean. Smaller side streams that join a river are
tributaries. The scientific term for any flowing natural waterway is a
stream; so in technical language, the term river is just a shorthand way to refer to a large stream.
Topography
A river conducts water by constantly flowing perpendicular to the elevation curve of its bed, thereby converting the
potential energy of the water into
kinetic energy. Where a river flows over relatively flat areas, the river will
meander: start to form loops and snake through the plain by
erosion eroding the river banks. Sometimes the river will cut off a loop, shortening the channel and forming an
oxbow lake from the cut off section. Rivers that carry large amounts of
sediment develop conspicuous
river delta deltas at their mouths. Rivers whose mouths are in saline
tide tidal waters may form
estuary estuaries.
Over time, rivers cut away at their beds, eventually forming a more gentle gradient.
There are 4 main types of rivers:
*'''Youthful river - '''a river with a steep gradient that has very few tributaries and flows quickly. Its channels erode deeper rather than wider.
*'''Mature river - '''a river with a gradient that is less steep than those of youthful rivers and flows more slowly than youthful rivers. A mature river is fed by many tributaries and has more discharge than a youthful river. Its channels erode wider rather than deeper.
*'''Old river - '''a river with a low gradient and low erosive energy. Old rivers are characterized by flood plains.
*'''Rejuvenated river - '''a river with a gradient that is raised by the earth's movement.
Image:Waterval Ova Fedoz.jpg thumb|right|A [[waterfall on the Ova da Fedoz,
Switzerland.]]
Where a river descends quickly over sloped topography,
rapids with
whitewater or even
waterfalls occur. Rapids are often used for recreational purposes (''see
Whitewater kayaking''). Waterfalls are sometimes used as sources of energy, via
watermills and
hydroelectric plants.
Rivers begin at their
source in higher ground, either rising from a
spring (water) spring, forming from
glacier glacial meltwater, flowing from a body of water such as a
lake, or simply from damp,
bog boggy places where the
soil is
waterlogged. They end at their
base level where they flow into a larger body of water, the
sea, a lake, or as a
tributary to another (usually larger) river. In
arid areas rivers sometimes end by losing water to
evaporation and percolation into dry,
porous material such as
sand, soil, or
pervious rock. The area drained by a river and its tributaries is called its
drainage basin watershed or catchment basin. (Watershed is also used however to mean a boundary between catchment basins.)
Starting at the mouth of the river and following it upstream as it branches again and again, the resulting river network forms a dendritic (tree-like) structure that is an example of a natural random
fractal.
{{seealso|geography|transvasement|water cycle|watershed}}
Biology
The flora and fauna of rivers are much different from those of the ocean because the water is
fresh water fresh (non-salty). Living things in a river must be adapted to the current of the moving water. For a detailed look at these processes, see
Lotic System Ecology lotic system ecology.
Pollution
Human
water pollution pollution of rivers is common, and very few rivers in the world today are clean of man-made substances. The most common point source of pollutant is probably
sewage piped into rivers, but chemical pollution is also common, and industrial accidents (and/or negligence) account for significant destruction of riparian
biome biomes. Heated water dumped into rivers by
power plants and
factory factories also affects river life. Non-point source pollutants such as diffuse pollution from
agriculture, urbanisation and
forestry and now being recognised as one of the more damaging sources of pollutants in the developed world.
Dams
In places where the elevation changes of a river are great,
dams for hydroelectric plants and other purposes are often built. This disrupts the natural flow of the river, and creates a lake behind the dam. Often the building of dams affects the whole of the river, even the part above the dam, as migrating
fish are hindered (see
fish ladder), waterflow is no longer bounded by seasonal changes and
sediment flow is blocked. Dams are useful in many ways, such as: providing hydro-electric power; acting as regulator of river flow so as to regulate the occurrence of flooding, which is especially important to wet-rice agriculture; and also to improve navigation and transport on the river. Often, dams such as
Hoover Dam along
Colorado River become famous tourist attractions. Critics of dams, especially 'green' advocates, argue that dams remove upper-river biodiversity such as through deforestation and forced migration of rural villages and indigenous tribes. Furthermore, trapping of river sediments behind the dams lead to salination and loss of nutrients for down-water fish. It also raises concern of earthquakes due to instablity of incompetent dams which have to support thousands of tonnes of sediments behind them. One very famous, and problematic, dam is the
Aswan High Dam in the
Nile.
Flooding
Flooding is a natural part of a river's cycles. Human activity, however, has upset the natural way flooding occurs by walling off rivers and straightening their courses. Removal of bogs, swamps and other
wetlands in order to produce farmland has reduced the absorption zones for excess water and made floods into sudden disasters rather than gradual increases in water flow. In ancient
Egypt, life was made possible through the floods of the
Nile and the accompanying
silt and
sediment which enriched the fields with fresh
nutrients. Nowadays, since people have built on these floodplains, floods are disasters, causing untold property loss each year.
Human interference in the form of
deforestation can also worsen conditions. The removal of
vegetation leads to a reduction in interception (vegetation stopping
precipitation (meteorology) precipitation) and the 'weakening' of soil since plant roots no longer hold it together. As a result there is a reduced
Infiltration capacity (how much water the soil can hold) and greater infiltration (precipitation going into the ground). This leads to faster
soil saturation and therefore greater
overland flow (also known as
surface run off) and therefore, there are
flash floods as the lag time decrease.
Logjams
Logjams are barriers within rivers, created by dead and uprooted
trees. Over time, the obstruction prevents further logs to bypass, resulting in the creation of new network channels. According to author David R. Montgomery in his book, ''King of Fish'', a logjam also causes water to buildup within a small space, forming peaceful pools within the main channel which provide shelter for young
salmon. The existence of these deep pools along with the complex web of channels creates an ideal salmon
habitat. Today, many believe that the rebuilding of salmon runs is contingent upon reproducing the same environment shaped by logjams. As a result, many
scientists have attempted to recreate artificial logjams. Marc Duboiski and Mike Ramsey of the Salmon Recovery Funding board staff, George Pess of the
National Marine Fisheries Service, and Kevin Bauersfeld of Washington Department of Fish and Wildlife have prepared the Report to the Salmon Recovery Funding Board On the Engineered Log Jam (ELJ) Workshop ([http://iac.wa.gov/Documents/SRFB/Log_Jam_Report.pdf#search='log%20jams%20and%20salmon']), with the hope of mimicking natural logjams.
image:Marshall-county-indiana-yellow-river.jpg thumb|200px|Small river in [[Marshall County, Indiana|rural Indiana, United States. Rivers of this size are often referred to as a "
creek (stream) creek."]]
Management
In its natural state a river may be inconvenient to man in a variety of ways. Rivers in inhabited areas have therefore been managed or controlled to make them more useful and less disruptive to human activity.
*The river channel may be
dredging dredged to make it deeper for navigation or to prevent flooding.
*Dams (see above) or
weirs may be built to control the flow, store water, or extract energy.
*
Levees may be built to prevent flooding.
*
sluice Sluice gates provide a means of controlling flow and adjusting river levels.
*
floodways may be added to draw off excess river water in times of flood.
*
Canals connect rivers to one another for water transfer or navigation.
*River courses may be modified to improve navigation, or straightened to increase the flow rate.
River management is an ongoing activity as rivers tend to 'undo' the modifications made by man. Dredged channels silt up, sluice mechanisms deteriorate with age, levees and dams may suffer seepage or catastrophic failure.
River lists
The world's ten longest rivers
It is difficult to measure the length of a river, mainly because rivers have a
fractal property, which means that the more precise the measure, the longer the river will seem. Also, it is difficult to determine exactly where a river begins or ends, as very often, upstream rivers are formed by seasonal streams, swamps, or changing lakes.
This is an average measurement.
#
Nile (6,690 km)
#
Amazon River Amazon (6,452
kilometre km)
#
Yangtze River Yangtze (Chang Jiang) (6,380 km)
#
Mississippi River Mississippi-
Missouri River Missouri (6,270 km)
#
Ob River Ob-
Irtysh River Irtysh (5,570 km)
#
Yenisey River Yenisey-
Angara River Angara (5,550 km)
#
Huang He (Yellow) (5,464 km)
#
Amur (4,410 km)
#
Congo River Congo (4,380 km or 4,670 km). (The source of this river is disputed.)
#
Lena (4,260 km)
For a longer list see
Longest rivers. This also gives more information on measuring river lengths.
Well-known rivers (in alphabetic order)
* The '''
Amazon River''', the largest river in the world (in terms of volume and water cubic metres/second)
* The '''
American River''', the site of
Sutter's Mill
* '''
Amu Darya'''
* The '''
Amur''', the principal river of eastern
Siberia and the border between Russia and China,
* The '''
Arkansas River''', a major tributary of the
Mississippi River
* The '''
Arno River Arno''', the river that runs through
Florence
* '''The
Shatt al-Arab Arvandrud (Shatt al-Arab)''', the river that borders
Iran and
Iraq
* '''
Brahmaputra''', the principal river in North East India and
Tibet
* The '''
Chao Phraya River Chao Phraya''', the principal river of
Thailand
* The '''
River Clyde''', which runs through
Glasgow
* The '''
Colorado River (Argentina) Colorado River''' (in
Argentina)
* The '''
Colorado River (U.S.) Colorado River''' (in the
United States), the principal river of the
American West
* The '''
Columbia River''', the principal river of the
Pacific Northwest
* The '''
Congo River Congo''', the principal river of central
Africa
* The '''
Danube''', the principal river of central and southeastern
Europe
* '''
RÃo de la Plata De la Plata''', the widest river in the world
* The '''
Ebro''', a river in northwestern
Spain
* The '''
Elbe''', a major
Germany German river,
Hamburg is situated on it
* The '''
Euphrates''', one of the twin principal rivers of
Mesopotamia (
Iraq)
* The '''
Ganges''', the principal river of
India
* '''
Han River (Korea) Han-gang''', the river that runs through
Seoul
* The '''
Helmand River''', the principal river of
Afghanistan
* The '''
Huang He''' (or Yellow River), one of the principal rivers of
China
* The '''
Hudson River''', the principal river of
New York
* The '''
Indus River''', the principal river of
Pakistan
* The '''
Jordan River River Jordan''', the principal river of
Israel
* '''
Karun''', the principal navigable river of southern
Iran
* The '''
River Kaveri''', the principal river of
South India
* '''
Lena''', the principal river of northeastern
Siberia
* The '''
Mackenzie River''', the longest river in
Canada
* '''
Magdalena River Magdalena''', the principal river of
Colombia
* The '''
Main''', a river in
Germany
* The '''
Mekong''', a principal river of
Southeast Asia
* The '''
River Mersey''', the river on which sits the English city of
Liverpool
* '''
Maas''', the principal river of the southern provinces of the
Netherlands and eastern
Belgium
* The '''
Mississippi River''', the principal river of central and southern
United States
* The '''
Missouri River''', one of the principal rivers of the
Great Plains
* The '''
Murray River''', the principal river of southeastern
Australia
* The '''
Niger River Niger''', the principal river of west
Africa
* The '''
Nile''', The longest river in the world, principal to
Egypt and northeastern Africa
* The '''
Ob''', a large river of
Siberia
* The '''
Oder River Oder''', a major river in Central Europe
* The '''
Ohio River''', the largest river between
Mississippi and the
Appalachian Mountains
* The '''
Orinoco''', the principal river of
Venezuela
* The '''
Parana River Parana''', a major river in
South America
* The '''
Paraguay River Paraguay''', the principal tributary of the Parana river and an important river in
Brazil,
Bolivia,
Paraguay and
Argentina
* The '''
Po River Po''', one of the principal rivers of
Italy
* The '''
Potomac River''', the principal river of the
Washington, D.C. and the border between
Maryland and
Virginia in the
United States
* The '''
Rhine''', the principal river of northwestern
Europe
* The '''
Rhone River Rhône''', the principal river of southern
France
* The '''
Rio Grande''', the river that forms part of the border between the
United States and
Mexico
* The '''
Saint Lawrence River''', which drains the
Great Lakes (North America) Great Lakes
* The '''
Seine''', the river that runs through
Paris, France Paris
* The '''
Segura''', a river in southeastern
Spain
* The '''
River Severn''', the longest river in
Great Britain
* '''
Shinano-gawa''', the longest river in
Japan
* The '''
Snake River''', the largest tributary of the Columbia river in
Washington (State) Washington
* '''
Tajo''', the largest river in the
Iberian Peninsula
* The '''
River Tay''', the largest river in
Scotland
* The '''
River Thames Thames''', the river that runs through
London
* The '''
Tiber''', the river that runs through
Rome
* The '''
Tigris''', one of the twin principal rivers of
Mesopotamia
* '''
Tone River Tonegawa''', one of largest rivers in
Japan
* The '''
Vistula''', the principal river of
Poland
* The '''
Vltava''', the river that runs through
Prague
* The '''
Volga River''', the principal river of
Russia
* The '''
Yangtze River Yangtze''' (Chang Jiang), the longest river in
China
* The '''
Yenisei River Yenisei''', a large river in
Siberia
* The '''
Yukon River Yukon''', the principal river of
Alaska and the
Yukon Territory
* The '''
Zambezi''', the principal river of southeastern
Africa
Other lists
*
List of waterways
*
List of rivers by continent
**
List of rivers of Europe
***
Rivers of the United Kingdom
**
List of rivers of Asia
**
List of rivers of Africa
**
List of rivers of Antarctica
**
List of rivers of Australia
**
List of rivers of New Zealand
**
List of rivers of the Americas
**
List of rivers of Oceania
*
List of river name etymologies
Rivers in myth and fiction
Real rivers
*The Thames in
Edward Rutherfurd's ''London''.
*The Thames in
Jerome K. Jerome's ''Three Men in a Boat''.
*The Thames and the Congo in
Joseph Conrad's ''
Heart of Darkness''.
*The
Mississippi River Mississippi in
Mark Twain's ''
Huckleberry Finn''.
*The
River Liffey through Dublin in
James Joyce's
Finnegans Wake.
Mythological rivers
*In
Greek mythology, the
Acheron,
Cocytus,
Phlegethon,
Lethe and
Styx (mythology) Styx (the five rivers of
Hades); and the
Eridanos (mythology) Eridanus.
*The
Alph, an underground river imagined by various mystics and mentioned in
Samuel Taylor Coleridge Coleridge's poem ''
Kubla Khan''.
*The
Sambation river stops flowing every Saturday.
Fictional rivers
*River
Ankh (river) Ankh traversing the city of
Ankh-Morpork in
Terry Pratchett's ''
Discworld'' series.
*
Chocolate river in ''
Willy Wonka and the Chocolate Factory''.
*River Djel in the country of
Djelibeybi in
Terry Pratchett's ''
Discworld'' series.
*The River in the
Riverworld novels of
Philip José Farmer.
*
List of Middle-earth rivers Rivers of Middle-earth in various works of
J. R. R. Tolkien.
See also
*
Aquaduct
*
Canal
*
Drought
*
Water dispute
Crossings
Rivers may be crossed by:
*
bridges
*
ferry ferries
*
ford (river) fords
*
tunnels.
Transport
*
barge
*
riverboat
*
sailing
*
towpath
Further reading
*
Luna Leopold Luna B. Leopold, ''A View of the River'', Harvard University Press (1994), hardcover, 298 pages, ISBN 0674937325 A non-technical primer on the
geomorphology and
hydraulics of the river. Luna B. Leopold, Emeritus Professor of Geology at the University of California was Chief Hydrologist for the
U.S. Geological Survey. Measurements are in traditional English units.
External links
-
Management: River Basin Commissions.
Category:Bodies of water
Category:Geomorphology
Category:Rivers
Category:Hydrology
an:RÃo
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*** Shopping-Tip: River
