River source
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The headwaters of a stream or river are referred to when the source of the watercourse cannot be clearly located or extends over a larger area, e.g. if the geological subsoil is suitable.
This is often the case in alpine high valleys such as the Engadine (upper reaches of the Inn). Sometimes even a whole region is designated as a headwaters area - for example Graubünden for the Vorder- and Hinterrhein.
While such source areas - often caused by waterlogging sediments under permeable surfaces - usually have a rather two-dimensional extension, the source area of many karst springs can be described as clearly three-dimensional.
Numerous examples can be found in the karst of the Balkan Peninsula, in Slovenia, but also in the Limestone Alps. The Tote Gebirge in Upper Austria knows underground spring areas that are dozens of square kilometres in size before the river they feed finally emerges. At the Pießling source, one of the strongest karst springs in Austria near Spital am Pyhrn, the water-rich stream only flows into the Teichl after 7-8 km and later into the river Steyr.
Other extensive source areas can be moor landscapes, which are then often - such as the Schwenninger Moos, source area of the Neckar - declared protected areas. Larger areas in which the supply of drinking water cannot rely on localised springs are often also worthy of protection.
See also: Catchment area
