A river (from Old High German fluz , to fliozan “to flow”) is a natural, linearly flowing body of water on land surfaces. In general, however, only medium-sized flowing waters can be referred to as rivers ; A distinction is made between the larger rivers and the smaller brooks . These two terms are avoided in the geosciences because their delimitations vary regionally and historically and are therefore not generally applicable.
Land waters form systems of innumerable drainage lines that gradually merge. Within such a system, a river usually represents the main strand, which is usually followed by the name. Viewed upstream, this flow path leads to the greater amount of water at each point of its mouth. Its uppermost water outlet is usually considered to be the source of the river. Rivers mostly flow into the sea, or else they evaporate in dry, ultimately drain-free areas, often also in end lakes . The smaller rivers that flow into it are called tributaries . The longest flow path in the river system does not always coincide with the main branch and then runs over longer tributaries (but with poorer water supply). The naming can also differ from the main strand.
The characteristics of a river depend on several factors. In addition to the surface shapes in its catchment area, these are rock features such as strength and permeability or climatic factors such as the amount of precipitation or the duration of frost. Larger rivers in particular can have a significant impact on their region; not only for the ecosystem , but also for cultural history , traffic development and water supply .
Classification and demarcation
Rivers are bounded by banks, but their branches are unlimited. The number of source channels is hardly manageable; they unite to form ever larger streams and rivers. In addition to the main branch of a river system , other special flow paths can be identified, which can be defined at the mouths by features such as the greatest length, the larger catchment area or the greater constancy of the flow direction. The river system and the catchment area are usually named after the main river . Depending on the direction of flow, one speaks of left or right tributaries, these are sorted according to the number of connections until reaching the main river or, vice versa, starting from the sources.
Short- term stratified floods on rinsing surfaces in the tropically humid regions or during glacier courses are not counted as rivers . Estuaries such as the Río de la Plata or the Gironde are also not counted among the rivers . They are not considered to be flowing waters , but belong to the coastal waters . Long sea bays that continue the rivers below the mouth ( Obbusen , Rio Pará , Outer Weser ) are not counted as part of the respective river. Inconsistent, the handling at the beginning of some estuaries as at the Unterweser or the lower Elbe . Even water flowing underground is not called a river, but belongs to the groundwater . Rivers can be canalised , but artificial waterways that are not integrated into a natural drainage line are canals .
Quantitative characteristics of rivers
Rivers can be typified according to different characteristics. Examples are the water flow in various key figures, the length and the catchment area, or continuously width, depth and flow speed . All of these characteristics are changeable and not always easy to determine. The values in the specialist literature can therefore differ greatly from one another.
The heights of the water level are recorded by levels . Sufficient discharge measurements were carried out at many gauges in order to derive the respective flow rate from the gauges and thus enable predictions. This is important for flood protection, for example . The chemical and biological state of water is also recorded there and at other points ( water monitoring ).
Rivers have several characteristics that can be used to compare their size. The most obvious feature is the width, which, however, can vary greatly in space and time depending on the flow velocity and depth. It is essentially determined by the more regular water flow, which is usually given in cubic meters per second (m³ / s), the mean discharge (MQ) occasionally also in cubic kilometers per year (km³ / a). The water flow can change in the long term and is subject to typical annual fluctuations, which is why only mean values from long-term measurement series are meaningful. Discharge measurement causes technical problems, especially with large rivers, and is now also safeguarded by computational modeling of entire river systems . The discharge of the Amazon was estimated at 100,000 m³ / s around the middle of the 20th century and had to be corrected to 209,000 m³ / s in the meantime ( Rhine near Emmerich, Danube near Budapest: a good 2,300 m³ / s each).
In addition to the mean water flow, the mean low water flow (MNQ), which can be more typical for the normal state of a river, is often compared. After all, at Passau the Inn is the larger river after the mean water flow, but the Danube with its more balanced flow regime after the mean low water . The Blue Nile near Khartoum is on average larger than the White Nile, but the White Nile is larger at medium low tide. The Nile is also an example that the runoff value characterizing the river is not always the estuary value, because its natural runoff below the Atbara estuary is around 2,700 m³ / s, a good double that at the estuary. This applies even more to dwindling rivers, which are characterized more individually by the point of maximum discharge than by their final value zero. Other economically interesting discharge values are the mean flood (MHQ), flood values of certain annualities (around 10 or 100 years) and the previous extreme values (HHQ and NNQ).
The length specifications for the same river can be very different for several reasons:
- The lengths of rivers themselves can be variable, especially in the stretches of the river where they form free, changing meanders .
- Often the small meanders are not measured on the upper reaches, but the larger ones on the lower reaches.
- In the case of branches, it is not always necessary to decide which is the main branch that represents the river.
- Occasionally, only the stretched path is measured that would be followed by a maximum flood.
In addition, there are definitional problems with length specifications. Particularly in the case of gradually widening funnel mouths, the views on the mouth point can differ greatly from one another. Total lengths of rivers are partly measured along the main river by name and, if necessary, also along the larger or the longer of two source rivers. Details of the length of individual sections of the river with different names are rarer and say little about the size of the river. The length measurement is seldom carried out along the largest river upstream ( main hydrological flow path), most often along the longest flow path. The most famous examples are: Red Rock River - Beaverhead - Jefferson - Missouri - Mississippi (6,051 km) and Lloquera - Callamayo - Hornillos - Apurímac - Ene - Tambo - Ucayali - Amazonas (6,448 km).
Ranking lists are particularly widespread for length information, which can motivate people to give dubious length information. For a while, values for the Missouri-Mississippi were far too high, and in 2008 (technically correct) values for the Amazon were published, which include the neighboring estuary of the Tocantins by the longest possible route .
As in the case of the spring branches, the branches that many rivers form at the end of their course can be determined as the most water-rich and the longest arm, which is then usually included in the length of the entire river.
The catchment area of a river is characterized by a land surface that is generally inclined in the same direction towards the end point of the river (mostly the mouth), which is why the draining water leaves the area there to a receiving water or to the sea. It is limited to neighboring catchment areas by watersheds . Only under similar climatic conditions are the sizes of catchment areas and the rivers draining them in a comparable relationship. The amount of water that flows out of a catchment area as a river is essentially an expression of the climatic situation. In humid climates such as the tropics or the temperate zone , the rivers are significantly larger with the same catchment area than under arid climatic conditions such as the subtropics . The ratio of the catchment area to the runoff is expressed in the mean discharge rate (Mq).
The catchment area (A E ) is to be clearly determined in the case of uneven relief over impermeable rock and humid climate. On the other hand, in the case of a flat relief, watersheds can shift depending on the amount of water or flow obstacles (coastal marshes , tributaries in the Amazon or Orinoco region ). In the case of permeable rocks (sand, karst areas), the surface catchment area (A EO ) has largely lost its influence to the underground catchment area (A EU ). In arid areas, many rivers do not reach the sea because they evaporate beforehand. Such so-called drainless areas can be interlinked in a complicated way with the catchment areas of large rivers such as the Nile or the Niger , the area of which can therefore only be determined approximately. Particularly large catchment areas can include several climate zones , the effects of which then overlap in the discharge regime of a river.
The water flow depends on the non-evaporating precipitation and meltwater, which either run off directly or seep away first and later emerge as groundwater in springs . Depending on the climatic conditions, the water flow of a river is subject to typical fluctuations, which are reflected in the mean seasonal course of the discharge values. There are simple dependencies in the case of rain regimes , which approximate the annual course of the amount of precipitation reaching the runoff with a slight delay. If the precipitation falls in the form of snow, the runoff is delayed until the snow melts and can thus cause almost opposing runoff curves ( nival regime ). Glaciers can cause delaying effects over several decades ( glacial regime ). The larger the catchment area, the more likely it is that these simple regimes and effects will overlap, which can lead to very complex runoff regimes.
Differentiation according to water flow
At times of low discharge, a river can dry up, with far-reaching consequences for the ecosystem. A distinction is therefore made:
- Perennial or permanent rivers: constant water flow
- intermittent , periodic or seasonal flows: seasonally limited water flow (during the rainy season or snowmelt).
Differentiation according to flow path
In hydrogeography, a distinction is made between the following types characterized by the flow path:
- Exorheic river : the river flows into the sea.
- Endorheic river : The rivers originate in the humid marginal area of a dry region, lose the water when flowing through the arid region (evaporation larger precipitation) or flow into an end lake from which the water evaporates completely. The salts contained in the water accumulate and form salt crusts that are difficult or impossible to use for agriculture (e.g. many rivers on the edge of the Gobi desert ).
- Diarheischer River : These rivers have their source and estuary in humid regions (precipitation greater than evaporation), but flow through arid, desert areas (e.g. Nile , Niger ) with considerable water loss . They are also called stranger rivers or allochthonous rivers ( give a wiki. Ἄλλος Allos "different", "different" and χθών khthṓn "earth", so as "foreign", "away team"), since their water supply is not the local in the arid regions climatic Conditions.
- Arheic River : These watercourses arise and end in arid areas, are episodic in terms of their water flow (e.g. wadis in North Africa, Humboldt River in the Great Basin of the USA).
Structural and genetic features of rivers
Depending on the formation of the land surface, the development time of the river network and the exposed rock structures, typical patterns of drainage directions and river courses occasionally emerge.
Structural patterns that can be parallel (on young, widely sloping land surfaces), radial (on young, dome-shaped or cone-shaped large forms) or chaotic (in young landfill landscapes) indicate a still low degree of development of the river networks . River networks with ring-shaped , almost right-angled or trellis-shaped structures react to exposed structures of the subsurface such as strata or ridges, folds or fault and crevice patterns . The river network can optimize itself over time and acquire a tree-shaped, dendritic structure, especially over rocks that can be removed evenly . The flow paths are almost minimized, which, however, increases the risk of flooding. Stages on the way to such a shaped river network are river taps . On very shallow watersheds, they can be preceded by bifurcations , known as bifurcations . A drainage network that emerged from numerous, very differently old river diversions and therefore appears irregularly characterizes the river system of the Rhine .
That by the earth's gravity draining water takes increasingly bundled running kinetic energy and brings so in the first eroded , then rebuilt and depositing acting on the bedrock flow and landforms produce that for each river section are typical (upper reaches, middle reaches and lower reaches) . The initially high gradient usually decreases significantly over the course, whereby the longitudinal profile approaches theoretical equilibrium lines between transport and erosion forces. However, the tectonic and climatic changes mostly lead to alternating phases of backfill and erosion, which can be seen in the terraced remains of former valley fillings and erosion edges. The changing ratios of transport and erosion performance give rise to typical forms of river beds. Different sections of this type can merge into one another (see also: valley shape ).
- Straight river: It has a river bed and a river course. A straight river is created especially when there is great deep erosion. Side erosion only plays a subordinate role. Material is not deposited or only very sporadically. This type of river is found mainly in mountains, mountainous and hilly countries, where the rivers have a fairly large gradient.
- Meandering river: It also has a river bed and a river course, but meanders . One speaks of meandering rivers from a so-called sinuosity index of 1.3, whereby straight sections can be switched on. The side erosion clearly outweighs the deep erosion. The meander arcs shift slowly and steadily downstream and in the direction of the outer banks . Occasionally there are shortened meander neck openings. On the inner glide bank , sediments are deposited in coarse - arched oblique stratification , with the grain size decreasing towards the top. There are only a few gravel and sand banks in the river bed. The river is bordered by natural walls and floods the floodplains when the water is high. The gradient is medium to low.
- Intertwined river : it has one riverbed but several courses. An intertwined river is characterized by the fact that its courses and channels shift frequently and unsystematically. It carries a lot of sediment, mostly consisting of sand and gravel, which is mainly deposited at low tide. The water flow is seasonally concentrated, for example on the snowmelt, which leads to strong floods. The river bed sediments are stratified horizontally and are not sorted according to grain size. This type of river is common in high mountains as well as in arid and arctic areas. The gradient can be very different, but is often high.
- Anastomosing river: It has several interconnected ( anastomosis ) river beds with a common flood plain. The anastomosing river mainly carries sands and silts with it. Due to the slight gradient, it does not erode, but builds upwards. The sediments are layered horizontally. Furthermore, an anastomosing river is accompanied by extensive floodplains and has pronounced embankments. The latter cause tributaries to flow in parallel for longer stretches before they finally flow either into the river or into the sea parallel to it. This type appears in plains and estuary areas and has a very low gradient, which is why bogs are typical. Anastomosing rivers are often incorrectly referred to as inland deltas , although branching dam bank river is more accurate.
At the confluence of rivers into the sea, either the formation by deposited river sediment , which creates a river delta , or the surrounding formation by the tides , which expands the river mouth to an estuary , predominates. Intermediate forms can be found at the Rhine delta and at the mouth of the Amazon.
Some rivers have formed river channels under the sea in front of the mouth ( Congo channel ), some of which were eroded during the ice age sea depression, and some of which are created by suspension flows .
Features and types of river beds
The cross-section of a river is divided into the water body , the river bed and the bank up to the top of the embankment. Extensive bank areas in a flood plain are also known as forelands and, in the natural case, serve as flood plains during floods.
Virtually any flow transported on the river bed of crushed rock, called fluviales sediment or river sediment . The amount and speed of transport depend , among other things, on the drag of the river. The decisive flow speed for this depends on the gradient, the subsoil and the water volume. (It can be reduced , for example, by a rubble barrier and increased by fortifying the river bank.) The flow speed varies within the river section. It is lowest at the bottom of the water and highest a few centimeters below the surface of the water, whereby a bend in the river shifts the line of greatest speed, the current line , outwards.
Waterfalls can represent a special form of river bed formation: if processes prevail that accentuate a gradient, the general tendency to equalize the longitudinal profile of the river can be interrupted.
Most rivers carry fresh water and are the habitat of corresponding freshwater flora and fauna . In limnology and hydrology , rivers are divided into habitat regions , which roughly correspond to the division into fish regions under fishing law . Below the source region ( Krenal ) follows the stream region ( Rhithral ), which corresponds to the trout region above and the grayling region below . The river region ( Potamal ) is divided into the barbel region (Epipotamal), the bream region (Metapotamal) and the ruddy flounder region (Hypopotamal). The water temperature, the oxygen content, the flow rate and especially the nutrient content are decisive for the habitat properties.
At the beginning of 2018 the West Indonesian 300 km long Citarum on Java is considered to be the “dirtiest river in the world”. In addition to household waste and animal faeces, it also carries large amounts of the toxic heavy metal mercury , the poison arsenic and z. For example, a thousand times more lead than the US standard for “safe drinking water” allows, after around 2,000 textile factories in the region dispose of untreated wastewater in it. At the end of the 1970s it was still used as bathing water , now, according to the Indonesian government, its water should be drinkable again by 2025.
Terms and Etymology
Large, opening out into the sea flows are as current designated. Occasionally and inconsistently, approximate limits are named (about 500 km in length, over 100,000 km² of catchment area or 2,000 m³ / s mean discharge). In earlier centuries the term was also used for other navigable rivers. Smaller rivers are as Bach called, but also without a defined boundary. Sometimes navigability, runoff (less than 20 m³ / s) or width (less than 5 m) are used as criteria.
The names of rivers belong to the oldest layer of geographical names . Many river names in the German-speaking area have Au (e) as a component or addition to their name , derived from the Germanic * awjo meaning “island”, “Flussaue”, “belonging to the body of water”. The Upper German equivalent is Ache (in Old High German aha "river") or Ohe , the Westphalian is Aa . The rivers on the German North Sea coast, which are integrated into a network of drainage canals and tidal waters , are also known as deep .
The linguistic origin of a river name is often followed by the grammatical gender in German . The Rhine (from the old Germanic reinos ) is male, the Elbe (from the Latin albia ) is female. There is no general rule. In rivers outside Germany, the usage does not necessarily follow the grammatical gender in the original language. The Rhone is masculine in French ( le Rhône ).
In addition to the natural functions mentioned, rivers are used in a variety of economic ways. Important functions are:
- Drinking water supply
- Transport route
- Energetic use in mills and run-of-river power plants
- Water supplier for
- Shipping channels
- agricultural irrigation
- industrial production processes (washing, process, cooling water)
- and for pumped storage power plants
- Receiving water for - if possible treated - wastewater
- Leisure uses (sport, games, art)
Depending on the natural or economic framework, these uses can lead to major changes in rivers and to problems. Especially in dry climates , rivers can be used very heavily for irrigation, which can then lead to conflicts of use with those below and also to the salinization of the soil. In addition to the width and steady flow speed, the water depth is decisive for inland navigation , as this determines the maximum draft . For this purpose, many rivers were converted into a series of reservoirs , which was beneficial to the construction of hydropower plants , but also required the construction (or retrofitting) of fish ladders. Other river sections are kept open with dredgers .
However, there are also types of ships that have been adapted to the respective river. For example the Great Rhine Ship , which is adapted to the locks on tributaries of the Rhine or Danube. Other types of ship are the Rhine-Sea ship or push convoys .
- In Germany, some rivers are considered federal waterways . The German waterways and shipping authorities perform the related tasks; this includes the setting up of navigation signs , the monitoring of the inland waterways order and the sea waterway order and the like . a.
- Federal Institute for Hydraulic Engineering
- Measures for flood protection
- Environmental protection measures and agreements, see e.g. B. International Commission for the Protection of the Rhine
- Specific legislation (For example, New Zealand declared a river, the Whanganui River , to be a legal entity (under trustee protection) for the first time in 2017. Māori had requested this since the 1870s.)
The following 19 countries have no rivers: Bahamas , Bahrain , Yemen , Qatar , Kiribati , Comoros , Kuwait , Libya , Maldives , Malta , Marshall Islands , Monaco , Nauru , Oman , Saudi Arabia , Tonga , Tuvalu , Vatican City and United Arab Emirates .
The 10 longest rivers on earth
|6,670 km||Nile : Luvironza - Ruvuvu - Ruvusu - Kagera - White Nile - Nile||Africa|
|6,448 km||Amazon : Apurimac - Ene - Tambo - Ucayali - Amazon||South America|
|6,380 km||Yangtze River||Asia|
|6,051 km||Missouri-Mississippi||North America|
|5,476 km||Yenisei : Tuul - Orkhon - Selenga - Angara - Yenisei||Asia|
|5,410 km||Ob : Irtysh - Ob||Asia|
|5,052 km||Amur : Kerulen - (connection only in rainy years) Argun - Amur||Asia|
|4,845 km||Huáng Hé (Yellow River)||Asia|
The 10 longest rivers that flow through Germany
|2,852 km||647 km||Danube|
|1,233 km||865 km||Rhine|
|1,165 km||727 km||Elbe|
|866 km||187 km||Or|
|751 km||751 km||Weser (of which Werra 300 km)|
|545 km||242 km||Moselle|
|524 km||524 km||Main|
|510 km||218 km||Inn|
|413 km||413 km||Saale|
|382 km||382 km||Spree|
The 6 longest rivers that flow through Switzerland
|length||of which in
|1,233 km||376 km||Rhine||North Sea|
|812 km||264 km||Rhône||Mediterranean Sea|
|510 km||104 km||Inn||Danube|
|453 km||74 km||Doubs||Saone|
|288 km||288 km||Aare||Rhine|
|248 km||91 km||Ticino||Po|
- List of lists of rivers (directory of the river lists available in Wikipedia or those to be created)
- River landscape of the year
- River code number (Germany)
- Water code
- River construction , river straightening , river morphology , towing force
- Earth / dates and numbers
- orographic left and right (definition of the left and right side of the river)
- Uwe A. Oster (Ed.), Rivers in Germany. A cultural history, Darmstadt 2007.
- Lexicon of Geosciences, Akademischer Verlag Heidelberg-Berlin, Vol. 1 (2000), p. 179 (Definition Bach)
- Geoffrey Lean: Death of the world's rivers ( Memento from April 22, 2013 in the web archive archive.today ), on archive.org ( The Independent , March 12, 2006 - At a UN conference from March 14 to 22, 2006 in Mexico -City or the world Water Day on 22 March 2006, during the outgoing UNEP - Executive Director Klaus Toepfer was presented a frightening report on the state of the rivers in the world;. cf. world Water Assessment program (WWAP) , on unesco.org)
- Living rivers: How are our rivers (BUND), on bund.net
- Measurement by the Brazilian Instituto Nacional de Pesquisas Espaciais (INPE) in the Amazon and Tocantins estuary: (measurement path: red line) .
- Indonesia - Dirtiest river in the world should get clean . In: Deutschlandfunk . ( deutschlandfunk.de [accessed on March 17, 2018]).
- Indonesia aims to banish toxic waste from lifeline river. In: Reuters . March 2, 2018, accessed April 19, 2019 .
- current ; Enzyklo Online encyclopedia, on enzyklo.de
- Definition of Bach according to outflow: Lexicon of Geosciences, Akademischer Verlag Heidelberg-Berlin, Vol. 1 (2000), p. 179.
- Definition of brook by width: 2nd: Importance in flowing waters (State Institute for Development of Agriculture and Rural Areas), on lel-bw.de
- The dictionary of origin , Au, Duden Volume 7, Mannheim 1989.
- Bastian Sick : Why is the Rhine male and the Elbe female? In: Spiegel Online from July 7, 2005.
- New Zealand Made River Person orf.at, March 16, 2017, accessed March 16, 2017.
- Length of the Rhine (Update 2015) (KHR), river length in sections, on chr-khr.org