The catchment area (also drainage area , runoff area , in the narrower sense precipitation area , in the case of flowing waters also a river area , in the case of streams a river area ) is the area or the area from which a water system draws its runoff , i.e. the area within the watershed of the water.
A basic distinction must be made between the surface and the underground catchment area. The above-ground catchment area can usually be determined quickly through the topography of the site ( orography ). It is very time-consuming to determine subterranean catchment areas that may differ from this using groundwater flows , which is why this has not yet been done for most bodies of water. In addition, the catchment area is now often influenced by technical interventions (shipping canals, hydropower and drinking water supply).
The catchment area ( drainage basin, drainage area, catchment area, river basin ) is an "area with a common discharge for surface runoff ", including the groundwater . The discharge from the drainage area is its receiving water . A catchment area is framed by the watershed , so that the catchment area can also be defined as "an area that - with the exception of one point - is completely surrounded by watersheds". The area of the catchment area projected onto the plane is called the catchment area area .
The area is mainly determined by the topographical and geological conditions . The water balance of a catchment area includes surface and underground runoff . The latter, however, can also reach another valley and thus flow to the groundwater of another surface catchment area. In this case, the above-ground and underground catchment areas do not match.
Catchment areas always refer to a specific point, usually a gauge (if there is no gauge point, the reference point is called the area outlet ). The catchment area of a small river usually refers to the point at which the water flows into a water of higher order .
The source and catchment areas of streams and smaller rivers are always part of a larger catchment area - namely of the body of water into which they flow. If a brook flows directly into the sea, it belongs to its much larger catchment area (see also order of waters or tributary ). In contrast, the cirques and glaciers represent the beginning of the catchment areas in higher-lying areas of high mountains .
The effective catchment area results from the natural catchment area, taking into account the areas affected by inflows and outflows. It is particularly needed to calculate the discharge donations in order to ensure their comparability.
Harz and Elbe
In terms of the water hierarchy , for example, in the low mountain range of the Harz, each source river of the Bode has a certain catchment area that is part of the catchment area of the Bode. Their collecting basin is in turn part of the catchment area of the Saale , that of the Saale belongs to the catchment area of the Elbe . The latter is already 148,000 km² and is fed by several thousand source streams. That of the Volga is nine times larger and covers 13% of the area of Europe.
Danube / Rhine
The Danube has a catchment area of 817,000 km², more than four times that of the Rhine (185,000 km²). In the Black Forest , however, an exchange of around 2000 km² is looming: the steep upper course of the Wutach , which flowed to the Danube around 50,000 years ago, is eroding backwards to the sources of the Danube , and the Neckar's source rivers do the same from the north .
Through the artificially created Altmühlüberleiter water is transferred from the catchment area of the Danube into the catchment area of the Rhine. Another - albeit hidden - specialty can be found in the area of the so-called Danube infiltration . There, a considerable part of the Danube water flows underground to Lake Constance and thus to the Rhine and thus also overcomes the European watershed .
In the Silvretta , several tributaries of the Rosanna and Trisanna are captured and diverted across the European watershed into the Silvretta reservoir or the Kops reservoir and thus fed to the Ill . The effective catchment area of the Sanna (and subsequently the Inn and Danube) will be reduced by 164 km², that of the Ill and thus the Rhine increased by the same amount.
The Memel Basin has a catchment area of 97,928 km² and is 46.4% in Belarus and 47.7% in Lithuania. The eastern and southeastern border of the Memel Basin to the Dnepr Basin forms part of the main European watershed between the Baltic Sea and the Black Sea.
The Vistula basin has a catchment area of 194,424 km² and 89% of it is in Poland, which corresponds to 168,699 km². The eastern, southeastern and southern borders of the Vistula Basin form another part of the main European watershed.
Seas and inland seas also feed from one or more basins. The Black Sea is formed from the Danube Basin, Dniester Basin, Dnieper Basin, Don Basin, Kuban Basin, and Kızılırmak Basin.
Watersheds, canals and power plants
The catchment areas of different bodies of water that do not flow into one another are separated by watersheds, which mostly run along the ridge lines of the site. In some places, however, these can differ significantly from the course of the terrain surface due to geological features .
In the lowlands , the boundaries of the catchment area can also be overcome with the help of canals for the purposes of shipping , although due to the differences in altitude, it is usually not possible to do without locks or ship lifts . Due to such structures, there are also canal systems that overcome large differences in height, such as the Rhine-Main-Danube Canal .
While there is little net water exchange (through sluice and infiltration) with such traffic routes , it is the main concern in many projects in the mountains . Such transfers take place in storage power plants and for water management purposes . The often steep, natural boundaries of the catchment areas can be overcome by tunnel-like tunnels with pumping stations, but also with exposed water pipes (e.g. Roman aqueducts ). Locally limited height differences and valley crossings can be overcome with culverts .
- What is a stream and river catchment area , offers for pupils and teachers from the Bavarian State Office for the Environment
- Hans Bretschneider, Kurt Lecher, Martin Schmidt : Taschenbuch der Wasserwirtschaft , 6th edition, Paul Parey Verlag, Hamburg and Berlin, 1982, p. 110
- DE 0360 catchment area, drainage area, river area. Entry in the International Hydrological Glossary, published for UNESCO by Pierre Hubert, Ecole des Mines de Paris
- Federal Ministry of Agriculture, Forestry, Environment and Water Management (ed.): Hydrographisches Jahrbuch von Österreich 2010. 118th volume. Vienna 2012, p. XL, PDF (12.6 MB) on bmlrt.gv.at (2010 yearbook)
- Hydrographical Yearbook of Austria 2010 , p. OG 400.