River
A river is a large natural waterway. The source of a river may be a
lake, a spring, or a collection of small streams, known as
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, made up of a
stream bed between
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.
Encyclopedia
A
river is a large natural waterway. The source of a river may be a
lake, a spring, or a collection of small streams, known as
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, made up of a
stream bed between
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
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
deltas at their mouths. Rivers whose mouths are in saline
tidal waters may form
estuaries.
Over time, rivers cut away at their beds, eventually forming a more gentle gradient.
- 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.
Where a river descends quickly over sloped topography,
rapids with
whitewater or even
waterfalls occur. Rapids are often used for recreational purposes . 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, forming from
glacial meltwater, flowing from a body of water such as a
lake, or simply from damp,
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 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 watershed, catchment basin or
drainage basin.
Starting at the mouth of the river and following it upstream as it branches again and again, the resulting river network forms a dendritic structure that is an example of a natural random
fractal.
Geopolitical boundaries
Rivers have been important historically in determining political boundaries.
The
Orange River discharges into the
Atlantic ocean and forms the
International boundary between various provinces and countries along its route. The source of the Orange River is in the
Lesotho mountains. The
Lesotho Highlands Water Project was conceived to divert water from
Lesotho into the Vaal River system, itself a tributary of the Orange River, to supply the water needs of the
Gauteng province in
South Africa. Water from the Delivery tunnel is discharged into the Ash River. The spot has become a popular
Kayaking venue.
The
Danube was a long standing border of the
Roman Empire, and today forms most of the border between
Bulgaria and
Romania.
The Mississippi in North America, and the Rhine in Europe, are major east-west boundaries in those continents.
Rating systems
- International Scale of River Difficulty - The scale is used to rate rivers -- particularly those with rapids -- for navigation. Class I is the easiest and Class VI is the hardest.
- Strahler Stream Order - The Strahler Stream Order is a method to rank rivers based on the connectivity and hierarchy of contributing tributaries. Headwaters are first order while the Amazon River is twelfth order. Approximately 80 percent of the rivers and streams on Earth are of the first and second order.
Biology
The flora and fauna of rivers are much different from those of the ocean because the water is
fresh . 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.
Water quality
Human
pollution of rivers is common, and few rivers in the world are free 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 account for significant destruction of riparian biomes.
Heated water discharged into rivers by
power plants and
factories also affects river biota. Non-point source pollutants such as diffuse pollution from
agriculture, urbanisation,
logging, construction activity and
slash-and-burn techniques are all recognised as sources of sediment and other pollutants.
Techniques have been developed to analyze
dispersal of water pollutants in river systems. For example the
U.S. Environmental Protection Agency funded research to develop the
DSSAM Model to assess the transport of soluble
nitrogen, reactive
phosphorus,
total dissolved solids and
dissolved oxygen in the Truckee River, which flows through both
California and
Nevada.
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 and the 'weakening' of soil since plant roots no longer hold it together. As a result there is a reduced Infiltration capacity and greater infiltration . This leads to faster soil saturation and therefore greater
overland flow 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 Workshop , with the hope of mimicking natural logjams.
In wintertime, rivers can be subject to ice jams or dams. An ice dam can create flooding upstream. When the jam melts or breaks apart, it can lead to flash flooding downstream. Ice jams caused flooding in the Northeastern United States in 1996.
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 dredged to make it deeper for navigation or to prevent flooding.
- Dams or weirs may be built to control the flow, store water, or extract energy.
- Levees may be built to prevent flooding.
- 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.
These are average measurements.
- Nile
- Amazon
- Mississippi-Missouri
- Yangtze
- Yenisey-Angara
- Huang He
- Ob
...
-
Irtysh- Amur
- Congo .
- Lena
For a longer list see
Longest rivers. This also gives more information on measuring river lengths.
Well-known rivers
...
, the river that runs through
FlorenceThroughout history, Iran has been of great geostrategic [i] importance because of its centr ...
and
Iraq ...
, the principal river in northeast India and
Tibet ...
, the principal river of central and southeastern
Europe ...
, one of the twin principal rivers of
MesopotamiaThroughout history, Iran has been of great geostrategic [i] importance because of its centr ...
- The River Kaveri, the principal river of South India
- The Lena, the principal river of northeastern Siberia
- The Mackenzie River, the longest river in Canada
- The 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
- The Maas, the principal river of the southern provinces of the Netherlands and eastern Belgium
- The Mississippi River, the principal river of the 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 Niagara River, the river which flows between Lake Erie and Lake Ontario, and which flows over the Niagara Escarpment
- The 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, a major river in Central Europe
- The Ohio River, the largest river between the Mississippi and the Appalachian Mountains
- The Orinoco, the principal river of Venezuela
- The Paraná, a major river in South America
- The Paraguay, the principal tributary of the Parana river and an important river in Brazil, Bolivia, Paraguay and Argentina
- The Po, one of the principal rivers of Italy
- The Potomac River, the principal river of Washington, D.C. and the southern border of Maryland in the United States
- The Rhine, the principal river of northwestern Europe
- The 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
- The Sava, which flows through four countries—Slovenia, Croatia, Bosnia and Herzegovina and Serbia
