Drainage divide

A watershed - or more precisely, the watershed line ( in contrast to a watershed point) - is the border between two adjacent river systems. So corresponds to the boundary between the basins of the effluent precipitation water from two rivers. A distinction must be aboveground and underground watersheds.

Forms of watersheds

Watersheds are, next to the waters themselves, the main objects of investigation of limnology, the riverine customer. The details in the groundwater flow investigated the hydrogeology.

Hierarchy and structure

Meeting, three watershed lines, the result is - similar to a triangle - a point of the watershed point is called. Here, the water flows in three different river systems. The dividing line trains of the large oceanic basins, the various seas, or large endorheischen hydrographic provinces, and flows (direct opening into the large standing waters rivers, river atomic number 1), but only a certain region are called watershed, form the associated main watershed points the most important hydrographic brands. The two main watershed points in Europe, for example, are 200 km west and 300 km north- west of Moscow, the most important watershed point outside of Russia is located on the Lunghin pass below the Piz Lunghin ( river systems of the Atlantic, Mediterranean and Black Sea ). Characteristic of endorheic areas is located in the Valley watershed point, which marks the center of the basin.

Upper and underground watershed

In most cases, represents a watershed represents a topographic ridge, where the dividing line of the basin consists primarily in a ridgeline. This ridge line indicates the aboveground watershed ( watershed or ridge ). Here the rainfall area covered by the catchment area. Also to the overground watersheds include the Talwasserscheide, which is the boundary line of the watershed on the valley floor here. Examples are the Kartitscher bridge in the Gail Valley in East Tyrol, which forms the watershed between the Drau and Gail, and the watershed in Dobbiaco San Candido and Dobbiaco field between in South Tyrol, where the Drava river drains into the Black Sea and the Rienz in the Adriatic Sea.

In Talwasserscheiden often originates in alpine settlements. Examples are Eben im Pongau, Kirchberg in Tirol or Waidring. Extremely flat Talwasserscheiden with heights of less than two meters there are in the northern German lowlands within the glacial valleys, eg between Havel and Finow in the Eberswalde glacial valley. In swamp deltas such as the Okavango Delta, the largest seepage area in the world, or in the Great Lakes areas such as the Finnish Lake District, the watershed can not be more useful to say. Another case is the bifurcation ( river separation), in the watershed of the river bed, a wetland or underground is. Largest watershed of this type is the bifurcation of the Orinoco River in the north of South America drained the main run in the Caribbean, but over the Brazo Casiquiare in the Amazon and thus in the South Atlantic.

However, there are watersheds that are not identifiable on the ground, as they are hidden in the ground, and thus depend on the geological structure of the subsurface. In this case of subterranean watershed (or basic watershed ) is spoken. Here, the actual catchment area be greater than the precipitation area, namely when the underground watershed passes over from a neighboring rainfall area. This is especially the case in sedimentary rock when the layers of the underground construction are supported so that dehydration takes place against the fall line of the slope underground. In geologically homogeneous surface (eg in igneous rock) to cover under - and above-ground watershed. The underground watershed is also referred to as the basic watershed. Underground and aboveground watersheds can have several layers. Thus, for example, is the watershed between the rivers Weser and Leine on Hohenhagen at an altitude of 310 m above sea level. NN depth of 40 meters, while the above-ground watershed some 100 meters east to 379 m above sea level. MSL.

Another special case is the icy watersheds, where (as in the Arctic) the water transport almost exclusively carried out by glaciers. There, ice streams can wander far beyond the lying in the deep underlying terrain sheaths of time. The melting watersheds are determined by the ever-changing surface of the ice and the glacier mills, the watershed appear again until the glacier.

Migration of the watersheds

Watersheds can, especially if they run on asymmetric terrain back, gradually gradually through increased denudation on the steep sloping side are shifted toward the shallow side, which reduces the local river basin - in favor of other, more sunken river system. But watersheds can change spacious also in geologically short periods of time. So the west has Wutach by headward erosion distracted ( during the Würm glacial period some 70,000 years ago) the faces east Feldberg Danube of today's city Blumberg south to the deeper the Rhine. This river system of the Rhine was enlarged so as it did in other similar cases along the watershed between the Rhine and the Danube. The abandoned valley east of the present Wutach knee is now drained to 18 km away remaining Danube, from the Aitrach.

Watersheds also be altered by human intervention, both in the construction of canals for shipping as well as in power stations. Examples include the Panama Canal between the Atlantic and Pacific (directs the water of the Chagres, the former watershed, crossing, and the Pacific to ) and the North Sea-Baltic Canal (punctuated the river system of the Eider ), or the Kaprun power plant in the Hohe Tauern south of Salzburg ( the meltwater Pasterze am Großglockner drains naturally to the south, but is now directed to the northern Alps to the power plant ).

Determination and significance of watersheds

The above-ground watershed can be determined from of large-scale topographic maps or aerial photographs. The determination of the underground watershed is more difficult. It can be approximated by means of tracer tests ( dyes, salts, etc.).

Watershed and catchment area are for all hydrographic aspects of the hydrology of concern. For the ecology of watersheds are of great importance because they are the boundaries by which one can estimate the entry of substances into the water. Also, various ecological regions are defined on the basis of the boundaries of a river basin. The hydrogeology and geomorphology determined the aboveground and underground watershed to carry out water balance studies, which are used for example for the modeling of flood events. The major watersheds of the mountains are also generally important climate sheaths.

Politically watersheds tends to be of minor importance, since geologically reasonable political boundaries orient usually in hard to be overcome geological features such as rivers, mountain ridges or lakes. Exceptions are political boundary curves in the region of some glaciers in mountainous regions such as the South American Andes between Argentina and Chile in the Campo de Hielo Sur or in the Alps, such as the border between Italy and Switzerland, which had to be corrected time and again at longer time intervals, most recently in March 2009.

Examples of important watersheds

• European watershed
• Watersheds in Germany
• Watersheds in the Alps
• North American Continental Divide

Triple watershed at the pass Lunghin in Maloja

Walk on the Carpathian watershed between Uschok Pass and Bieszczady

Watershed stone on the North Sea - Baltic Sea watershed in Wandlitz, Germany.

Church in Poppberg on the watershed in Birgland

Church roof ridge as part of the watershed - sign on the church in Poppberg, Amberg -Sulzbach