River system
A river system (also river network ) is the totality of all rivers , which consists of a main river and its direct and indirect tributaries . The water collects from a barely manageable number of spring channels, which unite to form ever larger rivers . The main strand of such a ramified river system results, viewed upstream, at the many junction points through the more voluminous, on average more water-carrying river. This main line is generally followed by the historically grown naming , although there are very many exceptions. The river system is usually named after the river that dominates by name. The area drained by the river system, the catchment area , is bounded by watersheds . River networks differ in terms of features such as water density, prevailing flow patterns or typical topologies of their water network.
In contrast to the river system , which represents the entirety of the real water bodies of a drainage system, the term river network in hydrography and water management stands for a theoretical concept: For a modeling of river networks, all standing waters (lakes) are ignored and a water axis flowing through them is ignored replaced so that the water path (also water line or water route ) is continuous. The flow behavior is of primary importance for the river network. The totality of water bodies (water bodies in the actual sense and groundwater bodies), their structure as a water network and the catchment area are referred to as the water system (hydrological / hydrographic system) .
Water systematics
Important streams and sources
The stretch of water that is richer in water upstream across all estuaries is the main branch of a river system in terms of hydrology and is mostly also the main river by name. There are often deviations from such a naming if instead of the main strand, for example, the strand with the greater constancy of direction retains the name or the river whose valley was economically or culturally more important. Important strands can also be determined according to other quantitative criteria, such as according to the larger catchment area or according to the greater length, both of which could hardly be determined precisely at times without precise maps. In disputes about the main source of a river ( source of the Rhine , source of the Danube ), the criterion of greater length is often used in competition with the criterion of greater water flow .
In the case of river systems with a main line clearly recognizable at each point of its mouth, this is generally followed by the river name, which is often very old in terms of language history. Most of the time, this strand is also the longest flow path. But when two rivers of similar size flow together, it is not uncommon for the main strand and the longest strand to split here, seen upstream.
Sometimes two rivers of similar size come together and their common lower reaches have a third name. Then the confluent waters are called source rivers of the lower reaches; this special feature is, however, of little importance in terms of hydrology. Examples of such three-name confluences, in which the source flow pairings can be quite different, are (sorted according to the volume at the confluence):
- Amazon (28,400 m³ / s): from Marañón (10% more watery) and Ucayali (40% longer)
- Rio Madeira (17,100 m³ / s): from Río Beni (8% more watery) and Río Mamoré (21% longer)
- Nile (2440 m³ / s): composed of the Blue Nile (73% more watery) and the White Nile (113% longer)
- Ganges (694 m³ / s): from Alaknanda (72% more watery) and Bhagirathi (79% longer)
- Weser (117 m³ / s): from Fulda (34% more watery) and Werra (36% longer)
- Rhine (113 m³ / s): from Hinterrhein (11% more watery) and Vorderrhein (6% longer)
- Mulde (60.2 m³ / s): from Freiberg Mulde (33% more watery) and Zwickauer Mulde (35% longer)
- Regnitz (25 m³ / s): from Rednitz (27% more watery, 1% longer) and Pegnitz
- Main (13.9 m³ / s): from White Main (96% more watery) and Red Main (16% longer)
- Danube (9.3 m³ / s): from Breg (71% more watery, 14% longer) and Brigach
- Saar (3.5 m³ / s): from the Red Saar (16% more watery, 1% longer) and the White Saar
The article tributary offers examples in which main strands below a confluence continue to use the name of the tributary - according to hydrological criteria .
In the case of large river systems, the strands of a river system, which are defined according to the criteria of greater water flow, greater catchment area or greater length, often fall apart. This incongruence is favored when the catchment areas of the upper reaches extend over climatic zones of different aridity . This is particularly the case with the Blue and White Nile. The situation in the Mississippi river basin is also typical for this : the name string runs roughly along the central axis of the river system, it begins a little above Lake Itasca ; on the other hand, the longest river route in the west with little precipitation begins at the source of the Red Rock River and runs over the Missouri ; the main strand in turn arises in the rain- rich east at the source of the Allegheny and continues over the water-rich Ohio to the Lower Mississippi .
Main strand by name
The flow path highlighted by the historically evolved naming thus does not always coincide with the main branch defined in terms of water science. In the not uncommon case of changing names in the course of the main river, only one river section name has to represent the river system and its main strand. For example, the section name Brahmaputra usually also stands for the sections Tsangpo and Dihang in the upper reaches and Jamuna in the lower reaches, but more rarely also for the following sections Padma and Lower Meghna . In the case of the Mobile River , the name only refers to the collecting artery of a river system close to the mouth, the main strand of which is successively named Cartecay , Coosawattee , Oostanaula , Coosa , Alabama and Mobile River . River names are therefore only suitable to a limited extent for determining main and tributaries.
Main strand by volume
The apparently larger flow at the respective mouth is generally the one with the larger mean flow (MQ). The resulting main hydrological strand of a river system therefore mostly coincides with the traditional naming in a river system. In many of the world's climates, however, the mean low water discharge (MNQ) is just as important for the appearance of a river. For example, the Saar at the confluence of the Blies and the Danube at the confluence of the Inn are the larger rivers according to the MNQ values, but not according to the MQ values, which the named tributaries Blies and Inn form part of sections of the respective main hydrological strand in the Saar. or make the Danube system (due to their larger flood shares).
Main strand by length
The length specifications of rivers are handled inconsistently. In addition to length information that only relate to the shorter named flow path, as is often the case with the Orinoco or the Weser , one increasingly finds length information, especially for the great rivers of the earth, that refer to the longest flow path that occurs in the associated river system. In the case of a branched course that includes islands, measurements are taken along the main channel. In the case of orifices, measurements can be found partly along the main channel and partly along the longest branch of the mouth. For example, there are length specifications for the Ganges not only up to the confluence with the Jamuna (Brahmaputra), but also including the longer Hugli estuary .
Main line to the above-ground catchment area
The main strand with the larger catchment area, seen upstream, focuses on the potential size of a river, regardless of the discharge and thus the current climatic situation. This area value is less variable than runoff and length. Blurs remain where the watershed runs through a plane. With large areas of permeable rock, the surface catchment area is of little concern.
Delimitation of river systems
River systems are separated by watersheds, but their location is not always stable. In addition, neighboring systems can be linked and interacted with one another in various ways.
Demarcation problems in levels
In alluvial plains, high water levels in one river system can cause water to cross into a neighboring area and vice versa. This occurs, for example, in several tributaries of the Amazon region as well as in the area of the Upper Meghna in Bangladesh. The boundary between the Lower Weser and Jade regions can also be changed in this way. In a few cases the main river itself touches a watershed, which can lead to a temporary or permanent stream division ( bifurcation ). The best known example is the Casiquiare , which connects the river systems of the Orinoco and Amazonas. But the IJssel estuary also has a bifurcation character in the Rhine river system . A permanent change in course can result from a bifurcation ( avulsions due to its own dynamics, river taps rather due to greater dynamics of neighboring river systems).
Delimitation problems in areas with karstified or loose rock
The sinking of the Danube is an example of underground contact between river systems. The affected catchment area of around 900 square kilometers belongs above ground to the river system of the Danube, but during the several months of annual dryness it actually belongs to the river system of the Rhine. To a lesser extent, the watersheds can also be shifted underground in loose sediments. Under most of the dry valleys at the beginning of the rivers of the Südheide , which drain south to the Aller , the groundwater surface drops to the north to the lower valleys facing the Elbe .
Climatic variability
The temporal variability of river systems becomes obvious in climates with changing humidity. For example, the Amur river system mostly divides into two subsystems that only unite in years with high rainfall. Then the Kerulen , which usually ends in a lake, reaches the Amur, which increases in length from 4,444 kilometers to 5,052 kilometers. The almost 2000 kilometer long river system from the Río Salado del Oeste (or Río Desaguadero) and Río Colorado in Argentina can even split up into four or more active parts, with the confluence with the Colorado in the 20th century, also because of the increasing use for irrigated agriculture was almost always dry.
Changeability through human intervention
Hydraulic engineering projects such as power plant supply lines, irrigation canals or shipping canals have greatly changed many river systems and their water balance. Currents such as the Colorado River , Nile, Niger or Oranje only reach the sea with greatly reduced water flow, while others such as Tarim or Amu Darja are drying up earlier, which reduces the active river system from below.
In Germany, for example, the mean outflows from the Isar and Loisach have been significantly changed by the Walchensee power plant , and the Kiel Canal has divided the Eider river system in two. In the Netherlands, for flood protection reasons, the Meuse was fed directly to the North Sea from 1904 to 1970, which it detached from the river system of the Rhine during this time and made it an independent river.
Hierarchization models
Various systems of flow order numbers have been developed as a basis for the quantitative consideration of river systems , first in a publication by Horton in 1945. He examined the organization of river systems and established a series of guidelines which became known as the Horton's order system . The divisions used today also go back to this system, which was modified by emitters in the 1950s .
Floor plan patterns of river systems
River systems are subdivided into the following main types according to the geometry of the associated rivers (see also: River ):
- chaotic river network
- dendritic river network
- parallel river network
- radial flow network
- right-angled river network
- Espalier-like ( Appalachian ) river network
The names of the individual floor plans were drawn up in 1932 in the USA by Emilie R. Zernitz . Except for the dendritic river network, these course patterns are predominantly influenced by the conditions of the subsoil.
Rivers that reach the sea by a shorter distance than neighboring rivers with a longer flow path are more erosive and on average wear their catchment area more heavily. As a result, there are more and more situations at the edges of the catchment area where river taps can take place in the lower lying area. This repeatedly results in shortened courses and a tendency towards a dendritic network that is almost optimal for drainage.
Nevertheless, flow paths have a strong tendency to persist because a river is trapped in its valley even if it is only just deep enough to carry away the highest floods. Therefore, river courses can still reflect the conditions to which they owe their formation, although, for example, by further cutting into the subsurface ( epigenesis ), other conditions may now prevail. The river system of the Rhine is an example of a growing river system, the parts of which formerly belonged to the neighboring Danube system can still be recognized by their old flow patterns.
Major river systems
| Name of the main river | Length [km] |
Catchment area [km²] |
Discharge at maximum point [m³ / s] |
|---|---|---|---|
| Africa | |||
| Congo | 4835 | 3,779,000 | 41,800 |
| Nile (longest river on earth) | 6852 | 3,255,000 | 2660 |
| Niger | 4184 | 2,262,000 | 6000 |
| Zambezi | 2574 | 1,325,000 | 7070 |
| Orange | 2360 | 973,000 | 370 |
| Okavango | 1800 | 721,000 | 475 a |
| America | |||
| Amazon (most water-rich river on earth) | 6448 | 6,112,000 | 206,000 |
| Mississippi | 6051 | 2,981,000 | 18,400 |
| Río Paraná | 3998 | 2,583,000 | 17,300 |
| Mackenzie | 4260 | 1,743,000 | 10,700 |
| Nelson River | 2671 | 1,093,000 | 3490 |
| St. Lawrence River b | 2421 | 1,030,000 | 10,400 |
| Orinoco | 3010 | 954,000 | 35,000 |
| Yukon | 3185 | 854,700 | 6430 |
| Rio Sao Francisco | 3199 | 618,000 | 2940 |
| Asia | |||
| If | 5410 | 2,972,000 | 12,500 |
| Yenisei | 5500 | 2,554,000 | 19,600 |
| Lena | 4295 | 2,307,000 | 17,100 |
| Amur d | 4444 | 1,930,000 | 11,400 |
| Meghna c | 3450 | 1,722,300 | 36,500 |
| Yangtze River | 6380 | 1,722,200 | 31,900 |
| Shatt al-Arab | 3596 | 1,125,000 | 1750 |
| Indus | 3180 | 1,082,000 | 7160 |
| Ganges (subsystem of the Meghna system) | 2620 | 1,016,000 | 13,000 |
| Mekong | 4500 | 795,000 | 15,000 |
| Huang He ("Yellow River") | 4845 | 752,000 | 2570 |
| Brahmaputra (In the lower Jamuna , main stream of the Meghna system) | 3100 | 651,000 | 21,200 |
| Australia | |||
| Murray | 3672 | 1,059,000 | 748 |
| Europe | |||
| Volga | 3534 | 1,360,000 | 8064 |
| Danube | 2857 | 817,000 | 6900 e |
| Dnieper | 2201 | 532,000 | 1670 |
| Ural | 2428 f | 244,000 | 297 |
| Rhine | 1239 | 218,300 | 2450 |
Examples of complex river systems
River system of the Amazon
By far the largest river system in the world supplies the Atlantic with around 206,000 m³ / s. The western lowlands of the Amazon are part of the foreland depression east of the Andes . The transitions to the north and south bordering plains of the same foreland depression are so imperceptible that the Orinoco river bifurcated not only in the north ; also in the south there is a bifurcation on the border with the catchment area of the Río Paraguay .
In the estuary there are blurred transitions to the Rio Pará bay , into which the Rio Tocantins flows. Often both are added to the river system of the Amazon, but this is hardly tenable in view of the narrow connecting channels , which are largely determined by the tides .
The river network is almost dendritic, except for the area with parallel Andes mountain ranges, but shows transitions to a parallel structure in the flat foreland area.
Ganges-Brahmaputra river system
With around 37,500 m³ / s, the most water-rich river system in Asia was only a few centuries ago divided into the almost independent systems of the Ganges and Brahmaputra . The Brahmaputra flowed further east into the Bay of Bengal . Today's common estuary is still called the Ganges Delta . Since the shifts of the main streams, especially in the 18th century, which gave rise to the 230 km long common main branch from Padma and Lower Meghna , the more watery (and longer) Brahmaputra has been the main strand of the system. During the monsoon season , a common high water level can form in the border area of the Old Brahmaputra and Upper Meghna, which makes the river basin boundaries fluid. Since estuary arms split off from the Ganges in front of the union (with a good 1000 m³ / s), the entire water flow of the river system is nowhere united in one river bed.
The river network is characterized by the mountain bars of the Front Himalayas , which bundle the drainage routes to the lowlands in a few antecedent breakthrough valleys and force the upper reaches of the Brahmaputra (Tsangpo) to take a long detour. Almost parallel drainage patterns prevail in the plains.
River system of the Pearl River
The river system of the Pearl River is named after the sea bay into which three streams in an intertwined network of water flow partly or completely. The dominant stream is the Xī Jiāng (West River). This river in China with an average of 7410 m³ / s, the second richest in water, reaches the sea directly with its right arm and the right mouth of the Bei Jiang (north river, 1200 m³ / s), which in turn partly joins the Dong Jiang (east river, 800 m³ ) with its left arms / s) flows together before they both reach Pearl River Bay. Since the main arms of the North River reach the West River before and after its bifurcation, it can be considered a tributary of the West River with good reason. (However, the discharge information for the west river mostly does not include it.) The east river, on the other hand, has no direct contact with the west river and can therefore also be regarded as a separate river system.
River system of the Rhine
The river system of the Rhine is characterized by numerous clear changes in direction of its main and secondary branches; there are traces of the strong expansion that has continued to this day at the expense of the higher-lying upper Danube system ( Urdonau ). The main branch of the system runs over the largest tributary, the Aare . The longest flow path begins with the Medelser Rhine and ends at the IJsselmeer locks - the closing dike . Before taking up the longest tributary, the Maas , the Rhine loses a similar amount of water to the IJssel , which leaves the river network of the Rhine delta in a bifurcation to the north. The river system of the Rhine supplies an average of around 2900 m³ / s of water to the North Sea, but the interwoven stream itself nowhere combines more than 2450 m³ / s and a single channel never more than an average of 2300 m³ / s. The discharge shares of the Rhine estuary are completely controlled by the Delta Works .
Examples of former river systems
The river system of the Rhine was much larger than it is today during the Ice Age sea level depressions and also included the Thames . In the event of a damming Nordic inland ice, its water flowed over the area of the dry English Channel into the Atlantic and also took in the Seine .
According to a controversial hypothesis , the largest river system in the world to date could have been an Uramazonas that once flowed west on the supercontinent of Gondwana and split into the river systems of the Niger and today's Amazon when it broke up.
See also
literature
- Frank Ahnert: Introduction to Geomorphology . 1st edition. Verlag Eugen Ulmer, Stuttgart 1996, ISBN 3-8252-8103-5 , p. 260 ff .
Web links
- Figure of river systems in Germany ( Memento from May 28, 2016 in the Internet Archive )
- Interactive map of Germany's river systems , calculated from data from OpenStreetMap .
References and comments
- ↑ cf. Hydrological system. Entry in GeoDataZone , Universidad national de Jujuy, geodz.com.
- ↑ Geoscientific map of the natural space potential of Lower Saxony and Bremen 1: 200,000, Part 4 - Groundwater Basics, Hanover, 1981.
- ↑ Note: The Meuse and Rhine are still administratively divided into two river basin units.
- ↑ Frank Ahnert: Introduction to Geomorphology. 1996, p. 257.
- ↑ RE Horton: Erosional development of streams and their drainage basins, hydrophysical approach to quantitative morphoplogy . In: Bulletin of the Geological Society of America . tape 52 , 1945, p. 275-370 .
- ↑ A. Strahler: Quantitative analysis of watershed geomorphology . In: Transactions of the American Geophysical Union . tape 38 , 1957, pp. 913-920 .
- ↑ Frank Ahnert: Introduction to Geomorphology. 1996, p. 260 f.
- ^ Emilie R. Zernitz: Drainage patterns and their significance . In: Journal of Geology . tape 40 , 1932, pp. 498-521 .
- ^ Harald Sioli : Studies in Amazonian waters. 9-50. In: Atas do Simpósio sôbre a Biota. 1967.
- ↑ Note: Nevertheless, Peruvian and Brazilian scientists measured the length of the Amazon by the longest possible route beyond the neighboring Rio Pará, claiming that the Amazon is the longest river in the world. (Instituto Nacional de Pesquisas Espaciais (INPE): Estudo do INPE indica que o rio Amazonas é 140 km mais extenso do que o Nilo. )