Drainage system (geomorphology)

A river system (including river network ) is the set of all rivers which consists of a main river and its direct and indirect tributaries. Here, the water collects from a barely manageable number of flumes, which unite to form larger and larger rivers. The main strand of such a branching river system results, upriver considered in the many union points by the most voluminous, on average, more water-bearing river. This main line generally follows the naming historically grown, where it is, however, very many exceptions. After the particular dominant flow and the flow system is usually named. The dehydrated from the river system area, the catchment area is bounded by watersheds. River networks differ in characteristics such as water density, predominant historical pattern or typical topologies of their water network.

In contrast to the river system, which represents the totality of the real body of water of a drainage system, river network is on the hydrography and water management, the concept of a theoretical concept: So all standing water (lakes ) are used for modeling of river networks ignored and by passing through them waters axis replaced so that the water path (also waters strand or water route ) is continuous. For the river network is primarily the flow behavior of concern. The totality of water bodies ( water bodies in the true sense and groundwater bodies ), whose structure as a network of water bodies and the catchment area is referred to as water system ( hydroglogisches / hydrographic system ).

• 3.1 Examples of complex river systems 3.1.1 river system of the Amazon
• 3.1.2 Ganges-Brahmaputra river system
• 3.1.3 Flow System of the Pearl River
• 3.1.4 Flow System of the Rhine

Water system

Important flow strands and sources

The upstream mouth of all points in each water -rich strand is gewässerkundlich the main branch of a river system and mostly notably the main river. Deviations from such naming, there is often, by about the strand with the greater Konstanz retains the name instead of the umbilicus or the one river, whose valley was economically or culturally more important. Important strands can also be determined by other numerical criteria, such as by the larger catchment area or by the greater length, both of which were hardly to determine precisely at times without accurate maps. In disputes about the main source of a river (Rhein source Source of the Danube ) is often used for competitive criterion of greater water flow, the criterion of greater length.

In river systems with every mouth point clearly recognizable main line this also follows in general - language history often very old - River name. Most of this strand is also the longest flow path. But flow along two rivers of similar size here often share the main line and the longest strand.

Sometimes unite two similarly sized rivers and their common underflow wearing a third name. Then you call the confluent waters headwaters of the lower reaches; Headwaters are gewässerkundlich often of little concern. Examples of such three- name confluences, where sometimes the source river pairings are quite different ( sorted according to the volume at the confluence ):

• Amazon ( 28,400 m³ / s): from Marañón (10% water-rich ) and Ucayali (40 % longer )
• Rio Madeira ( 17,100 m³ / s): from Río Beni (8% water-rich ) and Río Mamoré (21% longer)
• Nil ( 2440 m³ / s): from Blue Nile (73% water-rich ) and the White Nile (113 % longer )
• Ganges ( 694 m³ / s): from Alaknanda (72% water-rich ) and Bhagirathi (79% longer)
• Weser (117 m³ / s): from Fulda (34% water-rich ) and Werra (36% longer)
• Rhine (113 m³ / s): from Hinter Rhine (11% water-rich ) and the Anterior Rhine (6% more)
• Trough ( 60.2 m³ / s): from the Freiberger Mulde (33% water-rich ) and Mulde (35 % longer )
• Regnitz (25 m³ / s): from Rednitz (27% richer in water, 1 % longer ) and Pegnitz
• Main ( 13.9 m³ / s): from White Main ( 96 % water-rich ) and the Red Main ( 16 % longer )
• Danube (9.3 m³ / s): from Breg (71% water-rich, 14 % longer ) and Brigach
• Saar ( 3.5 m³ / s): from Red Saar (16% richer in water, 1 % longer ) and White Saar

Examples in which the main strands below a confluence on the name of the - according to hydrological criteria - lead tributary, the article provides Creek.

In large river systems, defined according to the criteria of greater water flow, larger catchment area or of greater length strands of a river system often fall apart. Is favored this incongruity if the catchment areas of the headwaters extend over climate zones of different aridity. Notably, this is the case with the Blue and White Nile. Typical of this is also the situation in the basin of the Mississippi: the Namenssstrang draws here about the central axis of the river system, it starts a little above the Itascasees; however, the longest flow path begins in the low-rainfall west of the source of the Red Rock River and runs across the Missouri River; the main strand in turn arises in the rainy east to the source of the Allegheny and continues over the water rich Ohio to the Lower Mississippi.

Main line by Name

The highlighted by the historically grown naming flow path thus not always coincides with the main strand gewässerkundlich defined. In the rare case of not changing names in the course of the main river should be representative of the river system and its main branch necessarily just a river section name. For example, the section name Brahmaputra is usually also for the sections Tsangpo and Dihang in the upper reaches of the Jamuna and the lower reaches, but rarely also in the following passages Padma and Lower Meghna. In the case of the Mobile River, the name refers to only the muzzle close to collecting vein of a river system whose main line sequentially lists the names Cartecay, Coosawattee, Oostanaula, Coosa, Alabama and the Mobile River. River names are thus suitable only to a limited definition of major and minor rivers.

Main line by volume

Of the respective mouth point apparently larger flow is generally the larger the mean flow ( MQ ). The location resulting hydrological main strand of a river system therefore coincides mostly with the traditional naming in a river system. In many climates of the earth, however, the mean low-water discharge ( MNQ ) is just such a major influence on the appearance of a river. For example, the Saar at the confluence of the assemblies and the Danube at confluence of the Inn by the MNQ values, the larger rivers, but not after the MQ values ​​which the roll-call tributaries Assemblies and Inn to sections of the respective hydrological main strand in the Saar- or Danube system do (as a result of their greater flood shares).

Umbilicus on the length

The specified lengths of rivers are applied inconsistently. Side lengths reported only on the shorter roll-call flow path relate such as often the Orinoco or the Weser River, you will find, especially with the great rivers of the world, increasingly lengths reported refer to the longest flow path, which occurs in the associated river system. In branched, islands occluded history is, however, measured along the main channel. In estuary branches can be found partly measurements along the main channel, partly along the longest estuary arm. For example, exist for the Ganges lengths not only to the confluence with the Jamuna ( Brahmaputra ), but also including the longer Mündungsarms Hugli.

Main line by above-ground catchment area

The umbilicus with the upriver seen, each larger catchment area places a focus on the potential size of a river, regardless of the runoff and thus the current climatic situation. This area value is less variable than drainage and length. Uncertainties remain, where the watershed runs through a plane. In a large area Permeable rock is the above-ground catchment area of little consequence.

Demarcation of river systems

River systems are separated by watersheds, but their location is not always stable. In addition, neighboring systems can be linked together in different ways and interact.

Demarcation problems in planes

In alluvial plains can high water level of a river system cause water passes into an adjacent area, and vice versa. This occurs, for example, in several tributaries of the Amazon as well as in the area of the Upper Meghna in Bangladesh. The border between Lower Weser and Jadegebiet is variable in this way. In a few cases, the main river touches itself a watershed, which can lead to temporary or permanent flow splitting ( bifurcation ). The best known example is the Casiquiare which connects the river systems of the Orinoco and Amazon. But even in the river system of the Rhine estuary, the IJssel Bifurkationscharakter. From a bifurcation may be a long-lasting smooth change emerge ( Avulsionen based on its own dynamics, Flussanzapfungen rather by larger dynamics of adjacent river systems ).

Demarcation problems in areas with verkarstetem or loose rock

The Donauversinkung is an example of underground contact of river systems. The affected catchment area of about 900 square kilometers belongs overground to the river system of the Danube, during the several months of each year falling dry but in fact only to the river system of the Rhine. To a lesser extent, the watershed can be moved underground in loose sediments. Among the most dry valleys at the beginning of the southward draining to the All rivers in the southern heath the phreatic surface drops north to the lower-lying, facing the same valleys.

Climate induced variability

In seasonally dry climates, the temporal variability of river systems is obvious. For example, the river system of the Amur decays mostly into two subsystems, which unite only in rainy years. Then the usually ending in a lake Kerulen reached the Amur, the 4444 kilometers to 5052 km length increases so. The nearly 2,000 -kilometer-long river system from Río Salado del Oeste (or Río Desaguadero ) and Rio Colorado in Argentina can decay even in four or more active portions, in the 20th century, partly because of increasing use for irrigation farming, the confluence with the Colorado was almost always dry.

Variability caused by human intervention

Water engineering projects such as Kraftwerk leads, irrigation canals or shipping channels have greatly changed many river systems and their water balance. Streams such as the Colorado River, Nile, Niger or Oranje reached only with greatly reduced water flow of the sea, others like Amu Darya Tarim or dry increasingly earlier, bringing the active flow system decreases from the bottom.

In Germany for example, the average runoff of Isar and Loisach by the Walchenseekraftwerk have been greatly changed, and the North Sea-Baltic Canal has two divided the river system of the Eider. In the Netherlands, the North Sea was directly from flood protection reasons, the Meuse 1904-1970 were forwarded what they removed at this time from the river system of the Rhine and made into an independent power.

Hierarchisierungsmodelle

As a basis for the quantitative consideration of river systems, various systems have been developed from river ordinal numbers, first in a paper by Horton in 1945. He examined the organization of river systems and put on a set of guidelines, which became known as Hortonsches order system. Classifications used even today go back to this system, which was modified in the 1950s by spotlights.

Layout pattern of river systems

River systems are classified by the geometry of the associated rivers into the following main types ( see also: River ):

• Chaotic flow network
• Dendritic river network
• Parallel flow network
• Radial flow network
• Rectangular river network
• Trellis -like ( Appalachian ) river network

The names of the individual floor plan patterns have been set up in 1932 in the USA by Emilie R. Zernitz. Except for the dendritic river network, this historical pattern are mainly influenced by conditions of the subsurface.

Rivers that reach the sea on a shorter route than neighboring longer flow path, are more erosion and wear their catchment area in the middle from stronger. As a result of the edges of the basin increasingly situations where Flussanzapfungen can take place towards the lower-lying area. This results repeatedly run reductions and a tendency towards a nearly optimal outflow dendritic network.

Nevertheless, flow paths have a strong tendency to persist, since a flow is trapped in his valley, even if it is only just deep enough to dissipate the highest floods. Therefore, the course of rivers, the conditions to which they owe their existence, nor reflect, though, as by further cutting into the subsoil ( epigenesis ), since other conditions may be prevalent. The river system of the Rhine is an example of a growing flow system, the sooner the neighboring Danube belonging to the system parts are still recognizable good to their old drainage patterns.

Major river systems

Examples of complex river systems

River system of the Amazon

By far the largest river system in the world to the Atlantic Ocean to approximately 209,000 m³ / s. The western lowlands of the Amazon is a part of the foreshore sink east of the Andes. The transitions to the north and south adjacent levels of the same foreland sink are so imperceptibly that it has come not only in the north to Flussbifurkation the Orinoco; in the south there is a bifurcation at the border to the catchment area of the Río Paraguay.

In the estuary there are blurred transitions to the bay of Rio Pará, in the Rio Tocantins opens. Often both are added to the river system of the Amazon, which, given the narrow, essentially tidal particular compound channels but hardly tenable.

The river network is, except for the region with parallel Andean mountain chains, almost dendritic, but in the flat foreshore area shows transitions to a parallel structure.

Ganges-Brahmaputra river system

The approximately 37,500 m³ / s largest river system in Asia was divided a few centuries ago in the nearly independent systems of the Ganges and Brahmaputra. The Brahmaputra flowed further east into the Bay of Bengal. Today's joint mouth region is still called the Ganges delta. Since the relocation of the main streams in the 18th century, who produced the now 230 km long common main branch of Padma and Lower Meghna, is the relatively water-rich ( and longer ) Brahmaputra, the umbilicus of the system. For the monsoon season can form a common high water table, which can be fluent in the river basin boundaries in the border area between the Old Brahmaputra and Meghna Upper. Since secede from the Ganges before the unification estuaries ( with about 1000 m³ / s ), the entire water flow of the river system is nowhere united in a river bed.

The river network is characterized by the mountain bar of the Middle Himalayas, the bundle the outflow pathways to the lowlands in a few antecedent rift valleys, forcing the upper reaches of the Brahmaputra ( Tsangpo ) to a long detour. In the plains prevail almost parallel drainage pattern.

River system of the Pearl River

The river system of the Pearl River is named after the bay, in the three streams in a braided river network flow entirely or partially. The dominant current is the Xī Jiang ( West River ). This with an average of 7410 m³ / s China's second largest river reaches with his right arm of the sea directly and with his left arms right estuaries of the Bei Jiang ( North River, 1200 m³ / s), which in turn partially with the Dong Jiang ( East River, 800 m³ / s) flows together before both reach the Pearl River Bay. As the main arms of the North River reach the West River before and after the current bifurcation, it may be considered with good reason as a tributary of the West River. ( However, the outflow of information on the West River not connect it mostly a. ) The East River, however, has no direct contact with the West River and thus can also apply as a separate river system.

River system of the Rhine

The river system of the Rhine is characterized by numerous distinct change in direction of its major and minor strands, there are traces of today continuing strong expansion at the expense of the higher-lying upper Danube system ( ancient Danube ). About the largest tributary, the River Aare, the main strand of the system runs. The longest flow path begins with the Medelser Rhine and ends at the lock on the IJsselmeer dike 's degree. Prior to the commencement of the longest tributary, the Meuse, the Rhine loses a little smaller amount of water to the IJssel, the leaves in a bifurcation of the power network of the Rhine Delta to the north. So the river system of the Rhine around 2900 m³ / s of water of the North Sea leads though on average, which combines braided stream itself but nowhere more than 2450 m³ / s and a single current channel never more than the average 2300 m³ / s The outflow portions of the Rhine estuary arms are completely controlled by the Delta Works.

Examples former river systems

The river system of the Rhine was during the glacial sea level lows substantially greater than today and included the Thames. Its water flowed from the event marveling Nordic inland ice over the area of the dry lying in the English Channel and the Atlantic also took it on the Seine.

After a controversial hypothesis, the largest river system in the world could have been a Uramazonas which once flowed on the supercontinent Gondwana to the west and is split at its breakup in the river systems of the Niger and today's Amazon.