River

A river (from Old High German fluz to fliozan, "flow" ) is a natural, line by way of flowing water on land surfaces. But may be commonly referred to as flow even medium size rivers; distinguish them then the larger streams and the smaller streams. These two terms are in the geosciences but avoided because their definitions vary regionally and historically, and therefore are not generally valid.

Land waters form systems of numerous drainage lines that merge gradually. Within such a system, a flow is usually the main line represents the mostly follows the naming. This flow path leads up the river considered, at each point in each estuary, the greater amount of water. Its top water outlet is usually considered the source of the river. Rivers flow mostly into the sea, or they evaporate in dry, ultimately endorheic areas, often in Endseen. The joining smaller rivers are called tributaries. The longest flow path in the river system does not always coincides with the main line and then runs over longer ( on water management but poorer ) tributaries. The nomenclature may differ from the main line (see Creek ).

The characteristics of a flow are dependent on several factors. In addition to the surface shapes in its catchment area, these are rock characteristics such as strength and permeability or climatic factors such as the amount of rainfall or the frost period. Especially larger rivers can have a formative importance for their region; not only for the ecosystem, but also for the history of civilization, the transport infrastructure or the water supply.

4.1 Flow Networks
4.2 Flow curves
4.3 Characteristics and types of river beds

Classification and delimitation

The rivers of the earth set in its entirety is the part of the water cycle, in which the non- evaporated portion of the precipitation over land surfaces finally collected flows to the oceans.

Rivers are not clearly distinguishable. The number of Quellgerinne is hardly manageable; they unite to form larger and larger streams and rivers. In addition to the main strand of a river system can make more special flow paths, which may be defined at the mouth of points through features such as the largest length, whichever is greater catchment area or the greater constancy of the flow direction. After the main river and the river system and the catchment area is usually named. Depending on the direction of flow is referred to as the left or right tributaries, they are ordered by number of associations to reach the main flow, or, conversely, from the sources.

Not to be counted among the rivers brief sheet flow in polders on the humid tropics or at glacier runs. Also not counted among the rivers estuary ( estuaries such as the Río de la Plata or the Gironde). They are not running waters, but belong to the coastal waters. Also elongated bays coves below the mouth continue ( Obbusen, Rio Pará, Outer Weser ), are not counted in the rivers for each flow. Uneven is the handling at the beginning of some estuaries, such as on the lower Weser or the Lower Elbe. Even underground running water is not referred to as flow, but belongs to the groundwater. Although flows can be channeled in artificial waterways but that are not part of a natural drainage line is channels.

Quantitative characteristics of rivers

Flows can be classified according to various characteristics. Examples are the water levels in different ratios, the length and the catchment area, or continuously width, depth and flow rate. All these features are variable and not always easy to determine. The values in the literature can therefore vary greatly.

The height of the water level are recorded by level. At many levels, discharge measurements were carried out to derive the respective flow rate of the water levels and thus to predict sufficiently. This is important as for flood protection. Also, the chemical and biological status of surface waters is there and at other locations recorded ( water monitoring ).

Water management

Rivers have several characteristics by which their size can be compared. The most striking feature is the width, however, depending on the flow velocity and depth can vary widely in space and time. It is essentially determined by the regelhaftere water management, mostly in cubic meters per second (m³ / s) is specified, the mean discharge ( MQ ), occasionally, in cubic kilometers per year ( km ³ / a). The water flow can be long-term variable and subject to typical annual fluctuations, which is why only averages longtime series of measurements are meaningful. The discharge measurement prepares especially for large rivers technical problems and is now also backed by mathematical modeling entire river systems. Thus the outflow of the Amazon still in the mid- 20th century to 100,000 m³ / s appreciated and needed now to 209,000 m³ / s to be corrected ( Rhine at Emmerich, Danube in Budapest: the well 2,300 m³ / s).

In addition to the mean water flow and the mean low water flow ( MNQ ) is often compared, which may be typical for the normal state of a river. After all, in Passau the Inn of the average water supply of the larger river, according to the mean low water but the river Danube with its balanced flow regime. Also the Blue Nile at Khartoum is bigger in size than the White Nile, at mean low water, however, the White Nile is larger. The Nile is also an example that characterizes the river runoff value is not always the mouth of value, because his natural runoff is below the Atbara mouth with about 2,700 m³ / s still twice as large as at the mouth. A fortiori, this applies to drying up rivers that are identified individually by the point of maximum runoff than by its final value zero. More economically attractive outflow values are the mean high water ( MHQ ), high water levels of certain return periods ( about 10 - or 100 - year) and the recent extreme values ( HHQ and NNC ).

Length

The length information on the same river can be very different for several reasons:

The lengths of rivers themselves may be variable, particularly in the course sections in which they form free, changing meanders.
Often the small meanders are not measured at headwaters, but probably the larger in the lower reaches.
When branching is not always possible to decide which is the main branch of the river representing.
Occasionally, only the more stretched way is measured, the maximum flood would follow.

In addition, there are definitional problems with length information. Especially with gradually widening estuaries the views may differ greatly from each other to muzzle point. Total lengths of rivers are partly measured along the main river roll-call and optionally additionally along the greater or the longer of two source rivers. Lengths to single run sections of different names are rare, and say little about the size of the river. Rarely, the length measurement is taken along the upstream respectively largest flow ( hydrological main flow path ), most probably along the longest flow path. The most famous examples are: Red Rock River - Beaver Head - Jefferson - Missouri - Mississippi ( 6051 km ) and Lloquera - Callamayo - hornillos - Apurimac - Ene - Tambo - Ucayali - Amazon ( 6448 km ).

Especially to the length specifications ranking lists are common, which may motivate them to dubious lengths. So were a time far inflated values to the Missouri - Mississippi common, and were ( technically correct ) or 2008 values to the Amazon published, which also include on long possible way the neighboring estuary of the Tocantins.

Can also be in the branches that form many rivers at the end of their course, the most water and the longest arm determine the then generally received in the specified length of the whole river as with the source branches.

Catchment area

The river basin is characterized by a land surface (usually the mouth ) is inclined towards generally the same direction as the end point of the river, so the water flowing off the area leaves there to a receiving stream or the sea. It is limited to neighboring river basins towards by watersheds. Only with similar climatic conditions are the sizes of basins and the rivers draining them in comparable proportions. The amount of water that flows out of the river as a catchment area, is essentially an expression of the climatic situation. In humid climates such as the tropics or the temperate zone of the rivers are significantly greater than under arid climatic conditions of the subtropics at about the same catchment area. The ratio of drainage area and runoff is expressed in mean runoff ( Mq ).

The catchment area (AE) is to identify clearly on uneven relief above impermeable rock and humidem climate. Contrast, can move from water attack or outflow obstructions ( coastal marshes, tributaries of the Amazon or Orinoco region ) at a flat relief watersheds dependent. In permeable rocks ( sand, karst areas), the above-ground catchment ( AEO) has lost its influence largely to the underground catchment area ( AEU ). In arid regions many rivers do not reach the sea because they evaporate before. Such so-called undrained areas can be complicated interlocked with the catchment areas of major rivers such as the Nile and the Niger, whose surface can therefore be only approximately determined. Particularly large catchment areas may include several climatic zones, the effects then superimposed in the flow regime of a river.

Flow regime

The water flow is dependent on the non -evaporating rainfall and meltwater, which flow either directly or only seep and later emerge as groundwater sources. According to the climatic conditions of the water flow of a river typical is subject to fluctuations that are reflected from the mean seasonal course of the discharge values . Simple dependencies exist in rain regime, which represent approximately with a short delay the seasonal cycle of the runoff entering rainfall. If the precipitation as snow, the outflow is delayed until the snow melts and can be as nearly opposite hydrographs cause ( nivales regime ). Retarding effects over several decades can cause glaciers ( glaziäres regime ). The larger the catchment area is, the more likely it is to overlay this simple regime and effects that can cause very complex flow regime (see also flow regime ).

At times of low runoff may occur to the drying up of a river with drastic consequences on the ecosystem structure effect. It therefore differs from the perennial rivers or permanent water flow with constant periodic or intermittent rivers with seasonally limited water (only during the rainy season or snow melt). Perform this only occasionally water, it is called episodic rivers ( wadis, Creeks, torrents ).

In view of such rivers in arid climate regions, a distinction in the hydro- geography characterized by the following flow regime and the flow path types:

Exorheischer River: The river flows into the sea.
Endorheischer River: The rivers rise in the edge region of a humid dry region, the water region lose when flowing through the arid (evaporation > precipitation) or lead into a terminal lake from which the water evaporates completely. The salts contained in the water accumulate and form agriculturally heavy or not usable salt crusts (eg many rivers on the edge of the Gobi Desert ).
Diarheischer flow: These rivers have their source and estuary in humid regions (precipitation > evaporation), but flow through under considerable water loss arid, desert-like areas ( eg Nile, Niger ). They are also referred to as an alien rivers or allochthonous rivers because the river flow does not correspond in the arid regions of the local climatic conditions.
Arheischer River: This episodic streams originate and end in arid areas (eg wadis in North Africa, Humboldt River in the Great Basin of the United States).

Structural and genetic characteristics of rivers

River networks

Depending on the origin of the land surface, the duration of development of the river network and thereby exposed rock structures arise occasionally typical pattern of drainage flow directions and gradients.

At a still low level of development of river networks indicate structural patterns, which may be parallel ( to young, wide -area sloping land surfaces ), radial ( to young, dom - or cone-shaped large molds ) or chaotic ( in young Aufschüttungslandschaften ). Responding to exposed structures of the subsurface layer as steps or combs, folds or meandering and river networks with ring-shaped gap pattern, nearly rectangular or trellis -like structures. The river network can Particularly evenly depletable rocks optimize the time and get a tree-shaped, dendritic structure. Here, the flow paths are almost minimized, however, which increases the risk of flooding. Stages on the way to a river network thus formed are Flussanzapfungen. Them can bifurcations precede bifurcations called On very flat watersheds. A product derived from numerous, very different ancient river diversions and therefore irregularly appearing drainage network characterized example of the river system of the Rhine.

Flow curves

The flowing through the earth's gravity water decreases with increasingly bundled running motion energy, thus bringing forth the first eroded, then to and depositing acting on the rock underground flow and landforms that for each river section ( upper reaches, middle reaches and lower reaches ) are typical. The first high gradient increases significantly from a regular way in the course, with the longitudinal profile of theoretical equilibrium lines between transport and erosion force approaches. The tectonic and climatic changes usually lead however to changing phases of landfill and erosion, which can be read on terraced remnants of former Talfüllungen and erosion edges. The changing conditions of transport and erosion performance give rise to typical forms of river beds. Various kind according to sections may merge into one another (see also: Valley Type ).

Straight River: He has a river bed and a river. A straight flow is mainly produced in large depth of erosion. Lateral erosion plays only a minor role. Material is deposited or only very occasionally. This flow type is mainly found in the mountains, mountain and hill countries in which the rivers have a pretty big gap.
Meandering river: He also has a river bed and a river, meanders, however. From meandering rivers is called from a so-called Sinuositätsindex of 1.3, with straight sections can be switched on. The lateral erosion outweighs the deep erosion significantly. The meandering curves move slowly and steadily and downriver toward the outer baffle shore. Occasionally, abbreviated Mäanderhalsdurchbrüchen. On the inside Gleitufer sediments are deposited in grobbogiger cross-bedding, in which the grain size decreases towards the top. In the river bed, there are only a few gravel and sand banks. The river is lined by natural embankments and flooded at high tide the water meadows. The slope is moderate to low.
Braided river: He has a riverbed, but several rivers. A wicked flow is characterized in that shift the rivers and spillways and often unsystematic. He leads a lot, mostly of sands and gravels existing sediment with it, which is mainly sold at low tide. The water flow is seasonally concentrated, eg on the snow melt, which leads to severe floods. The river bed sediments are layered horizontally and have no sorting by grain sizes. This flow type is common in high mountains and in arid and arctic regions. The gradient can be very different, but is often high.
Anastomosing river: He has several, interconnected river beds with a common floodplain. The anastomosing river is mainly sands and silts with it. Due to the low gradient it does not erode, but builds up. The sediments are layered horizontally. Furthermore, an anastomosing river is accompanied by extensive floodplains and has pronounced levees. The latter effect that tributaries flow long distances parallel before finally culminate either in the river or parallel to the sea. This type occurs in levels and in estuaries in appearance and has a very low gradient, which is why Vermoorungen are typical. Anastomosing rivers are often wrongly referred to as the Inland Delta, although branched dam shore flow is accurate.

At the mouth of the rivers into the sea outweighs either the forming deposited by river sediment that leaves a river delta arise, or rearranging the shaping by the tides, which expands the estuary to estuary. Intermediate forms can be found on the Rhine delta at the mouth of the Amazon.

Some rivers have formed upstream of the mouth under the sea flow channels ( Congo - channel ), which were partly eroded at times of Pleistocene marine lows, caused partly by suspension currents.

Features and Types of river beds

The cross section of a river is divided into the water, the river bed and the banks to the slope top. Extensive riparian areas in a flood plain are also referred to as flood plains and are used in the natural case as flooding surface at high tide.

Almost every river transported to the river bed of crushed rocks, called fluvial sediment or river sediment. Amount and traveling speed are dependent, among other things, of the drag force of the river. The key for this flow rate depends on slope, soil and water volume. (You can for example be reduced by a gravel barrier and increased by an attachment of the river bank. ) Within the section of the river, the flow rate is different. It is on the river bed at its lowest, a few inches below the water surface, the latter with a bend in the river moves the line of maximum velocity, the current line to the outside.

A special form of river bed molding can represent Waterfalls: If processes predominate, which accentuate a gradient step, there can be interrupted to balance the river longitudinal profile of the general tendency.

Ecological aspects

Most rivers carry fresh water, and are home to a corresponding freshwater flora and fauna. In limnology and hydrology flows are divided into habitat regions, which approximately corresponds to the legal division into fish fishing regions. Below the source region ( Krenal ) follows the creek region ( Rhithral ) corresponding to the region of trout and grayling region below the top. The flow region ( potamal ) is divided into the barbel region ( Epipotamal ), the Brachsenregion ( Metapotamal ) and the ruffe flounder region ( Hypopotamal ). Determining for the habitat properties are the water temperature, the oxygen content, the flow rate and particularly of the nutritional content.

Rivers are in an area the natural main propagation lines of new species. So many species on the rivers and valleys are again immigrated in Central Europe about after the ice ages.

The water pollution is mainly determined by the saprobic and divided into water quality classes.

Terms and etymology

Large, which opens into the sea flows are referred to as current. Occasionally inconsistent and are approximate boundaries named (about 500 km in length, more than 100,000 square kilometers of catchment area or 2,000 m³ / s mean water ). In earlier centuries, the term was also used for other navigable rivers. Smaller rivers are called creek, but also without a defined boundary. Sometimes the navigability of drainage are (less than 20 m³ / s) or the width ( less than 5 m) used as a criterion.

The names of rivers belong to the oldest stratum of Geographical Names. Many river names in the German language area have as part of their name or accessory Au (s ) derived from the Germanic * awjo meaning " island ", " floodplain ", " belonging to the waters ." The Upper German equivalent is Ache ( to Old High German aha "river" ) or Ohe, the Westphalian is Aa. The integrated at the German North Sea coast in a network of drainage canals and tidal waters, rivers are also called low.

The linguistic origin of the river name often follows the grammatical gender in German. Thus, the Rhine is ( from the old- reinos ) male, the same ( from the Latin albia ) ago female. A general rule does not exist. In rivers outside Germany also follows the use is not necessarily the grammatical gender in the original language. Thus, the Rhone is in French masculine (le Rhône).

Economic use

Economically rivers are mainly for transportation (see also: transport ), used for drinking water, to generate electricity in running power plants and for cooling of conventional and nuclear power stations. Often waste water is not sufficiently clarified or introduced. Especially in dry climates flows can be widely used for irrigation, which can then lead to land use conflicts with downstream riparians and also to the salinisation of soils.

In addition to the width and uniform flow rate is for the inland waterways, the water depth critical as this determines the maximum draft. For this purpose, many rivers have been converted into a series of impoundments, which the system of hydropower plants allowed, but also the construction (or upgrading ) of fish ways necessitated. Other sections of the river are held open with dredges. There are different types of ships that have been adapted to a river. For example, the Great Rhine, which is adapted to the navigation locks on tributaries of the Rhine or Danube. Other ship types are the Rhine -sea or pushed convoys.

Governmental framework

In Germany, some rivers are considered as federal waterways. The German Waterways and Shipping Offices take the bound thereto tasks; these include the setting up of navigational aids, monitoring of inland waterways order and the shipping lanes - order, inter alia,
Federal Waterways
Measures for flood protection
Environmental protection measures and agreements, see, eg, International Commission for the Protection of the Rhine

The 10 longest rivers in the world

For more " longest rivers ", see: List of longest rivers of the earth

The 10 longest rivers that flow through Germany

For more German rivers see: List of rivers in Germany

The six longest rivers that flow through Switzerland

For more Swiss rivers see: List of rivers in Switzerland Category: River in Switzerland

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