River

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For other uses, see River (disambiguation). River_sentence_0

"Rivers" redirects here. River_sentence_1

For other uses, see Rivers (disambiguation). River_sentence_2

"Riverine" redirects here. River_sentence_3

For riverine warfare, see Brown-water navy. River_sentence_4

A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. River_sentence_5

In some cases a river flows into the ground and becomes dry at the end of its course without reaching another body of water. River_sentence_6

Small rivers can be referred to using names such as stream, creek, brook, rivulet, and rill. River_sentence_7

There are no official definitions for the generic term river as applied to geographic features, although in some countries or communities a stream is defined by its size. River_sentence_8

Many names for small rivers are specific to geographic location; examples are "run" in some parts of the United States, "burn" in Scotland and northeast England, and "beck" in northern England. River_sentence_9

Sometimes a river is defined as being larger than a creek, but not always: the language is vague. River_sentence_10

Rivers are part of the hydrological cycle. River_sentence_11

Water generally collects in a river from precipitation through a drainage basin from surface runoff and other sources such as groundwater recharge, springs, and the release of stored water in natural ice and snowpacks (e.g., from glaciers). River_sentence_12

Rivers and streams are often considered major features within a landscape, however, they actually only cover around 0.1% of the land on Earth. River_sentence_13

They are made more obvious and significant to humans by the fact that many human cities and civilizations are built around the freshwater supplied by rivers and streams. River_sentence_14

Most of the major cities of the world are situated on the banks of rivers, as they are, or were, used as a source of water, for obtaining food, for transport, as borders, as a defensive measure, as a source of hydropower to drive machinery, for bathing, and as a means of disposing of waste. River_sentence_15

Potamology is the scientific study of rivers, while limnology is the study of inland waters in general. River_sentence_16

Topography River_section_0

A river begins at a source (or more often several sources), follows a path called a course, and ends at a mouth or mouths. River_sentence_17

The water in a river is usually confined to a channel, made up of a stream bed between banks. River_sentence_18

In larger rivers there is often also a wider floodplain shaped by flood-waters over-topping the channel. River_sentence_19

Floodplains may be very wide in relation to the size of the river channel. River_sentence_20

This distinction between river channel and floodplain can be blurred, especially in urban areas where the floodplain of a river channel can become greatly developed by housing and industry. River_sentence_21

Rivers can flow down mountains, through valleys (depressions) or along plains, and can create canyons or gorges. River_sentence_22

The term upriver (or upstream) refers to the direction towards the source of the river, i.e. against the direction of flow. River_sentence_23

Likewise, the term downriver (or downstream) describes the direction towards the mouth of the river, in which the current flows. River_sentence_24

The term left bank refers to the left bank in the direction of flow, right bank to the right. River_sentence_25

The river channel typically contains a single stream of water, but some rivers flow as several interconnecting streams of water, producing a braided river. River_sentence_26

Extensive braided rivers are now found in only a few regions worldwide, such as the South Island of New Zealand. River_sentence_27

They also occur on peneplains and some of the larger river deltas. River_sentence_28

Anastamosing rivers are similar to braided rivers and are quite rare. River_sentence_29

They have multiple sinuous channels carrying large volumes of sediment. River_sentence_30

There are rare cases of river bifurcation in which a river divides and the resultant flows ending in different seas. River_sentence_31

An example is the bifurcation of Nerodime River in Kosovo. River_sentence_32

A river flowing in its channel is a source of energy which acts on the river channel to change its shape and form. River_sentence_33

In 1757, the German hydrologist Albert Brahms empirically observed that the submerged weight of objects that may be carried away by a river is proportional to the sixth power of the river flow speed. River_sentence_34

This formulation is also sometimes called Airy's law. River_sentence_35

Thus, if the speed of flow is doubled, the flow would dislodge objects with 64 times as much submerged weight. River_sentence_36

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. River_sentence_37

A river valley that was created from a U-shaped glaciated valley, can often easily be identified by the V-shaped channel that it has carved. River_sentence_38

In the middle reaches where a river flows over flatter land, meanders may form through erosion of the river banks and deposition on the inside of bends. River_sentence_39

Sometimes the river will cut off a loop, shortening the channel and forming an oxbow lake or billabong. River_sentence_40

Rivers that carry large amounts of sediment may develop conspicuous deltas at their mouths. River_sentence_41

Rivers whose mouths are in saline tidal waters may form estuaries. River_sentence_42

Throughout the course of the river, the total volume of water transported downstream will often be a combination of the free water flow together with a substantial volume flowing through sub-surface rocks and gravels that underlie the river and its floodplain (called the hyporheic zone). River_sentence_43

For many rivers in large valleys, this unseen component of flow may greatly exceed the visible flow. River_sentence_44

Subsurface streams River_section_1

Most but not all rivers flow on the surface. River_sentence_45

Subterranean rivers flow underground in caves or caverns. River_sentence_46

Such rivers are frequently found in regions with limestone geologic formations. River_sentence_47

Subglacial streams are the braided rivers that flow at the beds of glaciers and ice sheets, permitting meltwater to be discharged at the front of the glacier. River_sentence_48

Because of the gradient in pressure due to the overlying weight of the glacier, such streams can even flow uphill. River_sentence_49

Permanence of flow River_section_2

Main article: Intermittent river River_sentence_50

An intermittent river (or ephemeral river) only flows occasionally and can be dry for several years at a time. River_sentence_51

These rivers are found in regions with limited or highly variable rainfall, or can occur because of geologic conditions such as a highly permeable river bed. River_sentence_52

Some ephemeral rivers flow during the summer months but not in the winter. River_sentence_53

Such rivers are typically fed from chalk aquifers which recharge from winter rainfall. River_sentence_54

In England these rivers are called bournes and give their name to places such as Bournemouth and Eastbourne. River_sentence_55

Even in humid regions, the location where flow begins in the smallest tributary streams generally moves upstream in response to precipitation and downstream in its absence or when active summer vegetation diverts water for evapotranspiration. River_sentence_56

Normally-dry rivers in arid zones are often identified as arroyos or other regional names. River_sentence_57

The meltwater from large hailstorms can create a slurry of water, hail and sand or soil, forming temporary rivers. River_sentence_58

Classification River_section_3

Rivers have been classified by many criteria including their topography, their biotic status, and their relevance to white water rafting or canoeing activities. River_sentence_59

Topographical classification River_section_4

Rivers can generally be classified as either alluvial, bedrock, or some mix of the two. River_sentence_60

Alluvial rivers have channels and floodplains that are self-formed in unconsolidated or weakly consolidated sediments. River_sentence_61

They erode their banks and deposit material on bars and their floodplains. River_sentence_62

Bedrock rivers form when the river downcuts through the modern sediments and into the underlying bedrock. River_sentence_63

This occurs in regions that have experienced some kind of uplift (thereby steepening river gradients) or in which a particular hard lithology causes a river to have a steepened reach that has not been covered in modern alluvium. River_sentence_64

Bedrock rivers very often contain alluvium on their beds; this material is important in eroding and sculpting the channel. River_sentence_65

Rivers that go through patches of bedrock and patches of deep alluvial cover are classified as mixed bedrock-alluvial. River_sentence_66

Alluvial rivers can be further classified by their channel pattern as meandering, braided, wandering, anastomose, or straight. River_sentence_67

The morphology of an alluvial river reach is controlled by a combination of sediment supply, substrate composition, discharge, vegetation, and bed aggradation. River_sentence_68

At the start of the 20th century William Morris Davis devised the "cycle of erosion" method of classifying rivers based on their "age". River_sentence_69

Although Davis's system is still found in many books today, after the 1950s and 1960s it became increasingly criticized and rejected by geomorphologists. River_sentence_70

His scheme did not produce testable hypotheses and was therefore deemed non-scientific. River_sentence_71

Examples of Davis's river "ages" include: River_sentence_72

River_unordered_list_0

  • Youthful river: A river with a steep gradient that has very few tributaries and flows quickly. Its channels erode deeper rather than wider. Examples are the Brazos, Trinity and Ebro rivers.River_item_0_0
  • Mature river: A river with a gradient that is less steep than those of youthful rivers and flows more slowly. A mature river is fed by many tributaries and has more discharge than a youthful river. Its channels erode wider rather than deeper. Examples are the Mississippi, Saint Lawrence, Danube, Ohio, Thames and Paraná rivers.River_item_0_1
  • Old river: A river with a low gradient and low erosive energy. Old rivers are characterized by flood plains. Examples are the Yellow, lower Ganges, Tigris, Euphrates, Indus and lower Nile rivers.River_item_0_2
  • Rejuvenated river: A river with a gradient that is raised by tectonic uplift. Examples are the Rio Grande and Colorado River.River_item_0_3

The ways in which a river's characteristics vary between its upper and lower course are summarized by the Bradshaw model. River_sentence_73

Power-law relationships between channel slope, depth, and width are given as a function of discharge by "river regime". River_sentence_74

Biotic classification River_section_5

There are several systems of classification based on biotic conditions typically assigning classes from the most oligotrophic or unpolluted through to the most eutrophic or polluted. River_sentence_75

Other systems are based on a whole eco-system approach such as developed by the New Zealand Ministry for the Environment. River_sentence_76

In Europe, the requirements of the Water Framework Directive has led to the development of a wide range of classification methods including classifications based on fishery status A system of river zonation used in francophone communities divides rivers into three primary zones: River_sentence_77

River_unordered_list_1

  • The crenon is the uppermost zone at the source of the river. It is further divided into the eucrenon (spring or boil zone) and the hypocrenon (brook or headstream zone). These areas have low temperatures, reduced oxygen content and slow moving water.River_item_1_4
  • The rhithron is the upstream portion of the river that follows the crenon. It has relatively cool temperatures, high oxygen levels, and fast, turbulent, swift flow.River_item_1_5
  • The potamon is the remaining downstream stretch of river. It has warmer temperatures, lower oxygen levels, slow flow and sandier bottoms.River_item_1_6

Whitewater classification River_section_6

The International Scale of River Difficulty is used to rate the challenges of navigation—particularly those with rapids. River_sentence_78

Class I is the easiest and Class VI is the hardest. River_sentence_79

Stream order classification River_section_7

The Strahler Stream Order ranks rivers based on the connectivity and hierarchy of contributing tributaries. River_sentence_80

Headwaters are first order while the Amazon River is twelfth order. River_sentence_81

Approximately 80% of the rivers and streams in the world are of the first and second order. River_sentence_82

In certain languages, distinctions are made among rivers based on their stream order. River_sentence_83

In French, for example, rivers that run to the sea are called fleuve, while other rivers are called rivière. River_sentence_84

For example, in Canada, the Churchill River in Manitoba is called la rivière Churchill as it runs to Hudson Bay, but the Churchill River in Labrador is called le fleuve Churchill as it runs to the Atlantic Ocean. River_sentence_85

As most rivers in France are known by their names only without the word rivière or fleuve (e.g. la Seine, not le fleuve Seine, even though the Seine is classed as a fleuve), one of the most prominent rivers in the Francophonie commonly known as fleuve is le fleuve Saint-Laurent (the Saint Lawrence River). River_sentence_86

Since many fleuves are large and prominent, receiving many tributaries, the word is sometimes used to refer to certain large rivers that flow into other fleuves; however, even small streams that run to the sea are called fleuve (e.g. , "coastal fleuve"). River_sentence_87

Uses River_section_8

Rivers have been a source of food since pre-history. River_sentence_88

They are often a rich source of fish and other edible aquatic life, and are a major source of fresh water, which can be used for drinking and irrigation. River_sentence_89

Rivers help to determine the urban form of cities and neighbourhoods and their corridors often present opportunities for urban renewal through the development of foreshoreways such as river walks. River_sentence_90

Rivers also provide an easy means of disposing of waste water and, in much of the less developed world, other wastes. River_sentence_91

Rivers have been used for navigation for thousands of years. River_sentence_92

The earliest evidence of navigation is found in the Indus Valley Civilization, which existed in northwestern India around 3300 BC. River_sentence_93

Riverine navigation provides a cheap means of transport, and is still used extensively on most major rivers of the world like the Amazon, the Ganges, the Nile, the Mississippi, and the Indus. River_sentence_94

Since river boats are often not regulated, they contribute a large amount to global greenhouse gas emissions, and to local cancer due to inhaling of particulates emitted by the transports. River_sentence_95

Rivers have been important in determining political boundaries and defending countries. River_sentence_96

For example, the Danube was a long-standing border of the Roman Empire, and today it forms most of the border between Bulgaria and Romania. River_sentence_97

The Mississippi in North America and the Rhine in Europe are major east-west boundaries in those continents. River_sentence_98

The Orange and Limpopo Rivers in southern Africa form the boundaries between provinces and countries along their routes. River_sentence_99

In some heavily forested regions such as 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. River_sentence_100

Fast flowing rivers and waterfalls are widely used as sources of energy, via watermills and hydroelectric plants. River_sentence_101

Evidence of watermills shows them in use for many hundreds of years, for instance in Orkney at Dounby Click Mill. River_sentence_102

Prior to the invention of steam power, watermills for grinding cereals and for processing wool and other textiles were common across Europe. River_sentence_103

In the 1890s the first machines to generate power from river water were established at places such as Cragside in Northumberland and in recent decades there has been a significant increase in the development of large scale power generation from water, especially in wet mountainous regions such as Norway. River_sentence_104

The coarse sediments, gravel, and sand, generated and moved by rivers are extensively used in construction. River_sentence_105

In parts of the world this can generate extensive new lake habitats as gravel pits re-fill with water. River_sentence_106

In other circumstances it can destabilise the river bed and the course of the river and cause severe damage to spawning fish populations which rely on stable gravel formations for egg laying. River_sentence_107

In upland rivers, rapids with whitewater or even waterfalls occur. River_sentence_108

Rapids are often used for recreation, such as whitewater kayaking. River_sentence_109

Ecosystem River_section_9

Main article: River ecosystem River_sentence_110

The organisms in the riparian zone respond to changes in river channel location and patterns of flow. River_sentence_111

The ecosystem of rivers is generally described by the river continuum concept, which has some additions and refinements to allow for dams and waterfalls and temporary extensive flooding. River_sentence_112

The concept describes the river as a system in which the physical parameters, the availability of food particles and the composition of the ecosystem are continuously changing along its length. River_sentence_113

The food (energy) that remains from the upstream part is used downstream. River_sentence_114

The general pattern is that the first order streams contain particulate matter (decaying leaves from the surrounding forests) which is processed there by shredders like Plecoptera larvae. River_sentence_115

The products of these shredders are used by collectors, such as Hydropsychidae, and further downstream algae that create the primary production become the main food source of the organisms. River_sentence_116

All changes are gradual and the distribution of each species can be described as a normal curve, with the highest density where the conditions are optimal. River_sentence_117

In rivers succession is virtually absent and the composition of the ecosystem stays fixed . River_sentence_118

Chemistry River_section_10

Main article: River chemistry River_sentence_119

The chemistry of rivers is complex and depends on inputs from the atmosphere, the geology through which it travels and the inputs from man's activities. River_sentence_120

The chemical composition of the water has a large impact on the ecology of that water for both plants and animals and it also affects the uses that may be made of the river water. River_sentence_121

Understanding and characterising river water chemistry requires a well designed and managed sampling and analysis. River_sentence_122

Brackish water River_section_11

Further information: Brackish water River_sentence_123

Brackish waster occurs in most rivers where they meet the sea. River_sentence_124

The extent of brackish water may extend a significant distance upstream, especially in areas with high tidal ranges. River_sentence_125

Flooding River_section_12

Main article: Flood River_sentence_126

Flooding is a natural part of a river's cycle. River_sentence_127

The majority of the erosion of river channels and the erosion and deposition on the associated floodplains occur during the flood stage. River_sentence_128

In many developed areas, human activity has changed the form of river channels, altering magnitudes and frequencies of flooding. River_sentence_129

Some examples of this are the building of levees, the straightening of channels, and the draining of natural wetlands. River_sentence_130

In many cases human activities in rivers and floodplains have dramatically increased the risk of flooding. River_sentence_131

Straightening rivers allows water to flow more rapidly downstream, increasing the risk of flooding places further downstream. River_sentence_132

Building on flood plains removes flood storage, which again exacerbates downstream flooding. River_sentence_133

The building of levees only protects the area behind the levees and not those further downstream. River_sentence_134

Levees and flood-banks can also increase flooding upstream because of the back-water pressure as the river flow is impeded by the narrow channel banks. River_sentence_135

Detention basins finally also reduce the risk of flooding significantly by being able to take up some of the flood water. River_sentence_136

Flow River_section_13

Studying the flows of rivers is one aspect of hydrology. River_sentence_137

Direction River_section_14

Rivers flow downhill with their power derived from gravity. River_sentence_138

The direction can involve all directions of the compass and can be a complex meandering path. River_sentence_139

Rivers flowing downhill, from river source to river mouth, do not necessarily take the shortest path. River_sentence_140

For alluvial streams, straight and braided rivers have very low sinuosity and flow directly down hill, while meandering rivers flow from side to side across a valley. River_sentence_141

Bedrock rivers typically flow in either a fractal pattern, or a pattern that is determined by weaknesses in the bedrock, such as faults, fractures, or more erodible layers. River_sentence_142

Rate River_section_15

Main article: Streamflow River_sentence_143

Volumetric flow rate, also known as discharge, volume flow rate, and rate of water flow, is the volume of water which passes through a given cross-section of the river channel per unit time. River_sentence_144

It is typically measured in cubic metres per second (cumec) or cubic feet per second (cfs), where 1 m/s = 35.51 ft/s; it is sometimes also measured in litres or gallons per second. River_sentence_145

Volumetric flow rate can be thought of as the mean velocity of the flow through a given cross-section, times that cross-sectional area. River_sentence_146

Mean velocity can be approximated through the use of the Law of the Wall. River_sentence_147

In general, velocity increases with the depth (or hydraulic radius) and slope of the river channel, while the cross-sectional area scales with the depth and the width: the double-counting of depth shows the importance of this variable in determining the discharge through the channel. River_sentence_148

Fluvial erosion River_section_16

In its youthful stage the river causes erosion in the water-course, deepening the valley. River_sentence_149

Hydraulic action loosens and dislodges the rock which further erodes the banks and the river bed. River_sentence_150

Over time, this deepens the river bed and creates steeper sides which are then weathered. River_sentence_151

The steepened nature of the banks causes the sides of the valley to move downslope causing the valley to become V-shaped. River_sentence_152

Waterfalls also form in the youthful river valley where a band of hard rock overlays a layer of soft rock. River_sentence_153

Differential erosion occurs as the river erodes the soft rock more readily than the hard rock, this leaves the hard rock more elevated and stands out from the river below. River_sentence_154

A plunge pool forms at the bottom and deepens as a result of hydraulic action and abrasion. River_sentence_155

Sediment yield River_section_17

Sediment yield is the total quantity of particulate matter (suspended or bedload) reaching the outlet of a drainage basin over a fixed time frame. River_sentence_156

Yield is usually expressed as kilograms per square kilometre per year. River_sentence_157

Sediment delivery processes are affected by a myriad of factors such as drainage area size, basin slope, climate, sediment type (lithology), vegetation cover, and human land use / management practices. River_sentence_158

The theoretical concept of the 'sediment delivery ratio' (ratio between yield and total amount of sediment eroded) captures the fact that not all of the sediment is eroded within a certain catchment that reaches out to the outlet (due to, for example, deposition on floodplains). River_sentence_159

Such storage opportunities are typically increased in catchments of larger size, thus leading to a lower yield and sediment delivery ratio. River_sentence_160

Management River_section_18

Main article: River engineering River_sentence_161

Rivers are often managed or controlled to make them more useful or less disruptive to human activity. River_sentence_162

River_unordered_list_2

  • Dams or weirs may be built to control the flow, store water, or extract energy.River_item_2_7
  • Levees, known as dikes in Europe, may be built to prevent river water from flowing on floodplains or floodways.River_item_2_8
  • Canals connect rivers to one another for water transfer or navigation.River_item_2_9
  • River courses may be modified to improve navigation, or straightened to increase the flow rate.River_item_2_10

River management is a continuous activity as rivers tend to 'undo' the modifications made by people. River_sentence_163

Dredged channels silt up, sluice mechanisms deteriorate with age, levees and dams may suffer seepage or catastrophic failure. River_sentence_164

The benefits sought through managing rivers may often be offset by the social and economic costs of mitigating the bad effects of such management. River_sentence_165

As an example, in parts of the developed world, rivers have been confined within channels to free up flat flood-plain land for development. River_sentence_166

Floods can inundate such development at high financial cost and often with loss of life. River_sentence_167

Rivers are increasingly managed for habitat conservation, as they are critical for many aquatic and riparian plants, resident and migratory fishes, waterfowl, birds of prey, migrating birds, and many mammals. River_sentence_168

See also River_section_19

See also: geography, water cycle, and drainage basin River_sentence_169

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Credits to the contents of this page go to the authors of the corresponding Wikipedia page: en.wikipedia.org/wiki/River.