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River

2007 Schools Wikipedia Selection. Related subjects: Geology and geophysics

   River upstream of an Australian trout farm
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   River upstream of an Australian trout farm

   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 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. Rivers throughout history have been the source and
   support for civilization, and many major cities today are near a river
   of some sort.

Topography

   A river flowing over a slight change in topography
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   A river flowing over a slight change in topography
   Bridges are a popular way of crossing rivers, as seen here at the
   Buller River, West Coast, New Zealand
   Enlarge
   Bridges are a popular way of crossing rivers, as seen here at the
   Buller River, West Coast, New Zealand

   A river conducts water by constantly flowing perpendicular to the
   elevation curve of its bed, thereby converting the 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 especially in the steeper
   headwater regions, eventually forming a more gentle gradient. Although
   the following classes are a useful simplified way to visualize rivers,
   it is important to recognize there are other factors at work here.
   Gradient is controlled largely by tectonics, but discharge is
   controlled largely by climate and sediment load is controlled by
   various factors including climate, geology in the headwaters, and the
   stream 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 (see Whitewater kayaking). Waterfalls are
   sometimes used as sources of energy, via watermills and hydroelectric
   plants.
   The beginning of a mountain river (Reichenbach in Grosse Scheidegg)
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   The beginning of a mountain river (Reichenbach in Grosse Scheidegg)
   The "mouth", where this river comes out of the melting ice (also
   visible in the previous photo)
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   The "mouth", where this river comes out of the melting ice (also
   visible in the previous photo)

   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 (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 watershed, catchment basin or drainage basin. (Watershed
   is also used however to mean a boundary between drainage 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.

Geopolitical boundaries

   Rivers have been important historically in determining political
   boundaries. For example, the Danube was a longstanding 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. The Orange River forms
   the boundary between various provinces and countries along its route in
   Africa.

Rating systems

     * International Scale of River Difficulty - The scale is used to rate
       the challenges of navigation—particularly those with rapids. 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 (non-salty).

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 habitat. Today, many believe that the rebuilding of salmon runs
   is contingent upon reproducing the same environment shaped by logjams.
   In wintertime, rivers can be apart, it can lead to flash flooding
   downstream. Ice jams caused flooding in the Northeastern United States

Flow

   A common misconception, particularly amongst schoolchildren and college
   students in North America, is that most, or even all, rivers flow from
   north to south. Rivers in fact flow downhill. Sometimes downhill is
   from north to south, but equally it can be from south to north, and
   usually is a complex meandering path involving all directions of the
   compass.

   Studying the flows of rivers is one aspect of hydrology.

Management

   In its natural state a river can be managed or controlled to make them
   more useful and less disruptive to human activity.
     * Dams (see above) or weirs may be built to control the flow, store
       water, or extract energy.
     * Levees may be built to prevent run-off of 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 Amazon River near Manaus in Brazil.
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   The Amazon River near Manaus in Brazil.

The world's ten longest rivers

   It is difficult to measure the length of a river, the more precise the
   measurement, the longer the river will seem. Also, it is difficult to
   determine where a river begins or ends, as very often, upstream rivers
   are formed by seasonal streams, swamps, or changing lakes.

   These are average measurements.
    1. Nile (6,690 km)
    2. Amazon (6,452 km)
    3. Mississippi-Missouri (6,270 km)
    4. Yangtze (Chang Jiang) (6,245 km)
    5. Yenisey- Angara (5,550 km)
    6. Huang He (Yellow) (5,464 km)
    7. Ob- Irtysh (5,410 km)
    8. Amur (4,410 km)
    9. Congo (4,380 km)
   10. 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)

   Zambezi and Victoria Falls (Zambia/Zimbabwe, Africa)
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   Zambezi and Victoria Falls (Zambia/Zimbabwe, Africa)
     * 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 longest river in central Asia
     * 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, the river that runs through Florence
     * The Arvandrud (Shatt al-Arab), the river that borders Iran and Iraq
     * The Brahmaputra, the principal river in northeast India and Tibet
     * The Chao Phraya, the principal river of Thailand
     * The River Clyde, which runs through Glasgow
     * The Colorado River (in Argentina)
     * The Colorado River (in the United States), the principal river of
       the American Southwest
     * The Columbia River, the principal river of the Pacific Northwest
     * The Congo, the principal river of central Africa
     * The Danube, the principal river of central and southeastern Europe
     * Río de la Plata, the widest river in the world
     * The Ebro, a river in northwestern Spain
     * The Elbe, a major German river, running through the city of Hamburg
     * The Euphrates, one of the twin principal rivers of Anatolia
       (Turkey) and Mesopotamia (Iraq)
     * The Ganga, the principal river of India
     * 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 James River. the principal river of Virginia, historically
       important.
     * The River Jordan, the principal river of Palestine, Jordan, and
       Israel
     * Karun, the principal navigable river of southern Iran
     * 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 (better known
       as Niagara Falls)
     * 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 Rhine, one of the longest and most important rivers in Europe
     * 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 (making its northern border) and Serbia—and
       was therefore one of the symbols of former Yugoslavia
     * The Savannah River, a major river in the southeastern United
       States, forming most of the border between the states of Georgia
       and South Carolina
     * The Seine, the river that runs through 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
     * The Susquehanna River, the principal river of Pennsylvania and the
       Chesapeake Bay
     * Tajo, the largest river in the Iberian Peninsula
     * The River Tay, the largest river in Scotland
     * The Tennessee River, an important tributary of the Mississippi that
       flows through Eastern/Western Tennessee, Northern Alabama, and
       Kentucky
     * The Thames, the river that runs through London
     * The Tiber, the river that runs through Rome
     * The Tigris, one of the twin principal rivers of Anatolia (Turkey)
       and Mesopotamia (Iraq)
     * Tonegawa, one of the 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 Wabash River, the principal river of Indiana
     * The Yangtze (Chang Jiang), the longest river in China
     * The Yenisei, a large river in Siberia
     * The 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 of Oceania
               o List of rivers of New Zealand
     * 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 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 (the five rivers of Hades); and the Eridanus
     * Virginia's Nancy River alleged to have had mystical healing powers
     * the Alph, an underground river imagined by various mystics and
       mentioned in Coleridge's poem Kubla Khan
     * Zora's River in Ocarina of Time
     * the Tamanawis River in David James Duncan's "The River Why?"
     * the Anduin in J.R.R Tolkien's The Lord Of The Rings

   Retrieved from " http://en.wikipedia.org/wiki/River"
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   with only minor checks and changes (see www.wikipedia.org for details
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