The Woronora River.
A 'river' is a natural
waterway that transits
water through a
landscape from higher to lower elevations. It is an integral component of the
water cycle. The water within a river is generally from
precipitation through
surface runoff,
groundwater recharge (as seen at baseflow conditions / during periods of lack of precipitation) and release of stored water in natural reservoirs, such as a
glacier.
Origins of river water
A youthful river flowing over a slight change in topography
A river may have its
source in a
spring,
lake, from damp,
boggy landscapes where the
soil is
waterlogged, from glacial melt, or from
surface runoff of
precipitation. Almost all rivers are joined by other rivers and streams termed
tributaries the highest of which are known as
headwaters. Water may also originate from
groundwater sources. Throughout the course of the river, the total volume transported downstream will often be a combination of the free water flow together with a substantial contribution flowing through sub-surface rocks and gravels that underlie the river and its floodplain (called the ''
hyporheic zone''). For many rivers in large valleys, this unseen component of flow may greatly exceed the visible flow.
From their source, all rivers flow downhill, typically terminating in a
sea or in a lake, through a
confluence. In
arid areas rivers sometimes end by losing water to
evaporation. River water may also
infiltrate into the soil or
pervious rock, where it becomes
groundwater. Excessive
abstraction of water for use in industry, irrigation, etc., can also cause a river to dry before reaching its natural terminus.
The mouth, or lower end, of a river is known by hydrologists as its
base level.
The area drained by a river and its tributaries is called catchment, catchment basin,
drainage basin or watershed. The term "watershed" is also used to mean a boundary between catchments, which is also called a
water divide, or in some cases,
continental divide.
Topography
The water in a river is usually confined to a
channel, made up of a
stream bed between
banks. In larger rivers there is also a wider flood-plain shaped by flood-waters over-topping the channel. Flood plains may be very wide in relation to the size of the river channel. This distinction between river channel and flood-plain can be blurred especially in urban areas where the flood-plain of a river channel can become greatly developed by housing and industry.
The river channel itself typically contains a single stream of water but some rivers flow as several interconnecting streams of water, producing a
braided river. Extensive braided rivers are found in only a few regions worldwide, such as the South Island of New Zealand. They also occur on
peneplains and some of the larger river deltas. Anastamosing rivers are similar to braided rivers. They have multiple sinuous channels carrying large volumes of sediment. Due to the dynamics of this type of system, they are also quite rare.
A river flowing in its channel is a source of considerable energy which acts on the river channel to change its shape and form. In mountainous torrential zones this can be seen as erosion channels through hard rocks and the creation of sands and gravels from the destruction of larger rocks. In U shaped glaciated valleys, the subsequent river valley can often easily be identified by the V shaped channel that it has carved. In the middle reaches where the river may flow over flatter land, loops (
meanders) may form through
eroding of the river banks and deposition on the inside of bends. Sometimes the river will cut off a loop, shortening the channel and forming an
oxbow lake or
billabong. Rivers that carry large amounts of
sediment may develop conspicuous
deltas at their mouths, if conditions permit. Rivers, whose mouths are in saline
tidal waters, may form
estuaries. River mouths may also be
fjords or
rias.
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. (Examples:
Brazos River,
Trinity River,
Ebro River)
★ ''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. (Examples:
Mississippi River,
Ohio River,
River Thames)
★ ''Old river – ''a river with a low gradient and low erosive energy. Old rivers are characterized by flood plains. (Examples:
Ganges River,
Tigris River,
Euphrates River,
Indus River,
Nile River)
★ ''Rejuvenated river – ''a river with a gradient that is raised by
tectonic uplift.
It has been noted that on average, the air distance (euclidean distance) from the beginning to the end of most rivers is about one third their actual length. For rivers that flow in plain areas, this number is very close to
Pi;
Einstein wrote an explanation of why this is so.
[1][2]
Other types of rivers
Most rivers flow on the surface, however other rivers may flow underground in
caves or caverns. Such rivers can be found in
karst regions with
limestone geologic formations.
An ''intermittent river'' (or
ephemeral river) flows occasionally and can be dry for several years at a time. These rivers are found in regions with limited and highly variable rainfall.
Use of rivers
Man has been using rivers for navigation since the dawn of civilization. Rivers provide the cheapest means of transport. In this figure a country boat is seen plying over
Hooghly River at
Kolkata,
India.
Rivers have been used by man since the dawn of civilization as a source of water, for food, for transport, as a defensive barrier, as a source of power to drive machinery, and as a means of disposing of waste.
For thousands of years rivers have been used for navigation ''(The earliest evidence of navigation is found in the
Indus Valley Civilization, which existed in north-western
India around 3300 BC)''. Riverine navigation provides the cheapest means of transport and is still used extensively on major rivers of the world like the
Ganges, the
Nile, the
Mississippi, and the
Indus.
In some highly-forested countries like
Scandinavia and
Canada,
lumberjacks use the river to float felled trees downstream to lumber camps for further processing, saving much effort and cost by transporting the huge heavy logs by natural means.
Rivers have been a source of food since pre-history. Apart from being a rich source of
fish, rivers indirectly aid cultivation by supplying water for the crops. Rivers sustain their own
food chain. They are a major source of fresh water, hence, it is no surprise to find most of the major
cities of the world situated on the banks of rivers. Rivers also provide an easy (if unsanitary) means of disposing of waste.
Most riverbanks in Japan are used as places for playing, recreation and parties
The rocks and gravel generated and moved by rivers have been greatly used in construction. In more recent generations, the beauty of rivers and their wider habitats has contributed greatly to tourist income from areas well endowed with attractive riverine scenery.
In upland rivers,
rapids with
whitewater or even
waterfalls occur. Rapids are often used for recreational purposes (''see
whitewater kayaking''). Fast flowing rivers and waterfalls are harnessed as sources of energy, via
watermills and
hydroelectric plants.
Rivers have been important historically in determining political boundaries and defending countries. 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 and
Limpopo Rivers in Southern Africa form the boundaries between various provinces and countries along their routes.
The noted
Greek historian
Megasthenes (350BC-290BC) mentions about
River Ganga several times in his work Indika: ''"India, again, possesses many rivers both large and navigable, which, having their sources in the mountains which stretch along the northern frontier, traverse the level country, and not a few of these, after uniting with each other, fall into the river called the Ganges. Now this river, which at its source is 30 stadia broad, flows from north to south, and empties its waters into the ocean forming the eastern boundary of the Gangaridai, a nation which possesses a vast force of the largest-sized elephants."'' (Diodorus II.37.)
Biology
Main articles: Aquatic ecosystem
The
flora and
fauna of rivers have developed to utilise the very wide range of aquatic habitats available from torrential
waterfalls through to lowland mires. Although many organisms are restricted to the
fresh-water in rivers, some, such as
Salmon and
Hilsa have adapted to be able to survive both in rivers and in the sea.
Flooding
Main articles: Flood
Flooding is a natural part of a river's cycles. The majority of the erosion of river channels and the erosion and deposition on the associated
floodplains occur during flood stage. Human activity, however, has upset the natural way flooding occurs by walling off rivers, straightening their courses and by draining of natural
wetlands.
Flooding can be
mitigated.
Direction of flow
A misconception, is that most, or even all, rivers flow from north to south.
[3][4] Rivers in fact flow down gradient irrespective of direction, often in a complex
meandering path involving all directions of the compass.
[5][6][7]
As it happens, few major rivers in the continental US flow north, as most of the country is located in the watershed of the Pacific or Atlantic oceans or the Gulf of Mexico, with very few rivers flowing northward toward the Arctic Ocean, Great Lakes, or Hudson Bay. However, thousands of north-flowing rivers exist elsewhere, including such major watercourses as the
Nile,
Mackenzie,
Rhine,
Yenisei,
Nelson, and
Lena. Four of the ten
longest river systems of the world flow mainly north.
Studying the flows of rivers is one aspect of
hydrology.
[8]
Rate of water flow
Volumetric flow rate, also called volume flow rate and rate of water flow, is the volume of water which passes through a given volume per unit time, measured in cubic meters per second ( 1
m3/s = 35.31
ft3/s).
Management
Main articles: River engineering
Rivers are often 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 river water from flowing on floodplains or floodways.
★
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. The benefits sought through managing rivers may often be offset by the social and economic costs of mitigating the effects of such management. As an example, in many parts of the developed world, rivers have been confined within channels to free up flat flood-plain land for development. Subsequent extreme flood events can inundate such development at very high financial costs and often with loss of life.
River lists
The world's ten longest rivers
Because rivers are approximately
fractal in nature 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.
#
Nile River (6,695 km)
#
Amazon River (6,400 km)
#
Jefferson-
Missouri-
Mississippi (6,270 km)
[9]
#
Yangtze (Chang Jiang) (6,245 km)
[10]
#
Yenisey-
Angara (5,550 km)
#
Huang He (Yellow) (5,464 km)
#
Ob-
Irtysh (5,410 km)
#
Amur (4,410 km)
#
Congo (4,380 km)
#
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)
★
Amazon – largest and ''possibly'' longest
[11] river in the world (in terms of volume and water cubic metres/second)
★
Amu Darya – longest river in central
Asia
★
Amur – principal river of eastern
Siberia and the border between Russia and China
★
Arkansas – a major tributary of the
Mississippi River
★
Arno – the river that runs through
Florence
★
River Boyne - principal river on the east coast of Ireland
★
Brahmaputra – principal river in northeast
India,
Bangladesh and
Tibet
★
Chao Phraya – principal river of
Thailand
★
River Clyde – runs through
Glasgow
★
Colorado – in
Argentina
★
Colorado – principal river of the
American Southwest
★
Columbia – principal river of the
Pacific Northwest
★
Congo – principal river of central
Africa
★
Damodar - the principal river of Chotanagpur plateau,
India and a primary tributary of
Hooghly River
★
Danube – principal river of central and southeastern
Europe
★
Detroit - acts as a brief boarder of the
USA and
Canada, part of the
Great Lakes Waterway
★
Dnieper – one of the main rivers of
Russia,
Belarus and
Ukraine.
★
Dniester – one of proncipal rivers in Eastern Europe, runs through
Ukraine and
Moldova into the
Black Sea.
★
Ebro – a river in northwestern
Spain
★
Elbe – a major
German river, running through the city of
Hamburg
★
Euphrates – one of the twin principal rivers of
Anatolia (
Turkey) and
Mesopotamia (
Iraq)
★
River Forth - runs between
Stirling and
South Queensferry
★
Ganges – principal river of
India and
Bangladesh
★
Gavenny – principal river of
Abergavenny
★
Godavari - principal river of
South India
★
Han – river that runs through
Seoul,
Korea
★
Helmand – principal river of
Afghanistan
★
Hooghly - the primary distributary of
Ganges, which runs through
Kolkata,
India
★
Hudson – principal river of
New York, USA
★
Indus – principal river of
Pakistan
★
Irvine - a principal river in
Ayrshire,
Scotland.
★
James – principal river of
Virginia in the USA, historically important.
★
River Jordan – principal river of
Israel,
Jordan, and the
West Bank.
★
Karun – principal navigable river of southern
Iran
★
Kaveri – principal river of
South India
★
Lena River – the principal river of northeastern
Siberia
★
River Liffey - runs through
Dublin,
Ireland.
★
Loire – the longest river of
France, an important natural reserve for wildlife preservation.
★
Mackenzie – longest river in
Canada
★
Magdalena – the principal river of
Colombia
★
Main – a river in
Germany which runs through
Frankfurt am Main
★
Mekong – a principal river of
Southeast Asia
★
River Mersey – near
Liverpool
★
Meuse – principal river of the southern provinces of the
Netherlands and eastern
Belgium
★
Mississippi – principal river of the central and southern
United States
★
Missouri – one of the principal rivers of the
Great Plains
★
Monongahela - one of the three rivers connected in Pittsburgh, PA
★
Murray – principal river of southeastern
Australia
★
Niagara – between
Lake Erie and
Lake Ontario, and which flows over the
Niagara Escarpment (better known as
Niagara Falls)
★
Niger – principal river of west
Africa
★
Nile – principal river of
Egypt and northeastern Africa
★
Ob – a large river of
Siberia
★
Oder – a major river in Central Europe
★
Ohio – largest river between
Mississippi River and
Appalachian Mountains
★
Orange – the longest river in
South Africa
★
Orinoco – principal river of
Venezuela
★
Paraná – one of the longest and most important rivers in
South America, running through
Brazil,
Paraguay and
Argentina
★
Po - the longest river of
Italy
★
Rhine – one of the longest and most important navigatable rivers in western
Europe, flowing from
Switzerland to the
Netherlands, and a natural border with
Liechtenstein,
Austria,
Germany, and
France.
★
Rhône – one of the most important navigatable rivers of Western
Europe, going from
Switzerland to
France
★
Río de la Plata – widest river in the world
★
Rio Grande – forms part of the border between the
United States and
Mexico
★
Sabarmati – flows through
Ahmedabad,
India
★
Saint Lawrence – drains the
Great Lakes
★
Saint Mary's - acts as a brief boarder of the
USA and
Canada, connects
Lake Superior to
Lake Huron, and contains the world's busiest
Lock the
Soo Locks
★
São Francisco River – longest river wholly within
Brazil
★
Sava – 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
★
Savannah – a major river in the southeastern United States, forming most of the border between
Georgia and
South Carolina
★
Seine – river that runs through
Paris, France
★
Segura – a river in southeastern
Spain
★
Seti – river in
Nepal
★
River Severn – longest river in
Great Britain
★
River Shannon - longest river in
Ireland
★
Shatt al-Arab – the river that borders
Iran and
Iraq
★
Shinano-gawa – longest river in
Japan
★
Snake – largest tributary of the Columbia River in
Washington
★
Susquehanna River – principal river of
Pennsylvania and the
Chesapeake Bay
★
Tagus – longest river in the
Iberian Peninsula
★
River Tay – largest river in
Scotland
★
Tennessee – an important tributary of the Mississippi that flows through Eastern/Western
Tennessee,
Northern Alabama, and
Kentucky
★
River Thames – the primary river of
England, which runs through
London
★
Tiber – river that runs through
Rome
★
Tietê – river that runs through
São Paulo towards the centre of the continent
★
Tigris – one of the twin principal rivers of
Anatolia (
Turkey) and
Mesopotamia (
Iraq)
★
Tone – one of the largest rivers in
Japan
★
Vistula – principal river of
Poland
★
Vltava – river that runs through
Prague
★
Volga – principal river of
Russia and the longest river in
Europe
★
Volta – large river in
Western Africa, runs through
Burkina Faso
★
Wabash – principal river of
Indiana
★
Yangtze – longest river in
China and
Asia
★
Yellow – one of the principal rivers of
China
★
Yenisei – a large river in
Siberia
★
Yukon – principal river of
Alaska
★
Zambezi – principal river of southeastern
Africa
Other lists
★
List of rivers of Africa
★
List of rivers of the Americas
★
List of rivers of Asia
★
List of rivers of Europe
★
List of rivers of Oceania
★
List of waterways
★
List of river name etymologies
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
Amazon River is twelfth order. Approximately 80 percent of the rivers and streams on Earth are of the first and second order.
See also
★
Aqueduct
★
Canal
★
Drought
★
List of river name etymologies
★
Mainstem (hydrology)
★
River cruise
★
Water dispute
★
Baer's law
★
Rock-cut basin
Crossings
Rivers may be crossed by:
★
Bridges
★
Ferries
★
Fords
★
Tunnels.
Transport
★
Barge
★
Riverboat
★
Sailing
★
Towpath
References
1. http://www.dailytimes.com.pk/default.asp?page=story_10-12-2002_pg3_8
2. Fermat's last theorem, Simon Singh, 1997
3. Children's Misconceptions about Science
4. Earth Science Misconceptions William C. Philips
5. Do All Rivers Flow South? Matt Rosenberg
6. Rivers Flowing North: Rivers Only Flow Downhill; Rivers Do Not Prefer to Flow South Matt Rosenberg
7. Re: What determines the direction of river flow? Elevation, Topography, Gravity?? Nezette Rydell
8. How a River Flows Cristi Cave
9. Missouri
10. Chang
11. http://news.bbc.co.uk/1/hi/world/americas/6759291.stm
Further reading
★ Beyond the Bridges Life on American Rivers told by Riverlorian, Jerry Hay.
[1]for more information
★
A View of the River, Luna B. Leopold, , , Harvard University Press, , ISBN — a non-technical primer on the
geomorphology and
hydraulics of water
★
Water Encyclopaedia
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