Overflow source

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An overflow source is a source where the groundwater emerging from the surface of the earth does not simply flow downwards following the force of gravity, but reaches the source through a geological structure in the subsoil, which has a water-retaining effect and forces the moving groundwater to rise. Overflow sources are a source type in the classification systems according to Stiny (1933), there also called overflow sources , and according to Prinz and Kampe (1934).

Since this classification is based on the conditions in the geological subsurface and is not visible on the surface of the earth in terrain mapping, it is not used in hydrobiologically and ecologically oriented source mapping.

Overflow sources can develop in both pore aquifers and karst aquifers. What they have in common is that dammed and thus rising groundwater creates a reservoir in the pore or crevice space of the aquifer, which overflows in the spring. Overflow sources in pore aquifers usually have a relatively persistent spring discharge, while those in karst aquifers often dry up quickly and are directly dependent on the precipitation in the catchment area. In the simplest case, aquifers surrounded by impermeable, non-conductive layers form a saddle and trough structure, in the trough of which the groundwater accumulates until it overflows at the deepest point of the edge formed in this way. However, not all overflow sources are tied to ideal-typical troughs. It is sufficient if the cross-section or the permeability of a groundwater-conducting layer is significantly reduced, for example by using a clay lens in a sand layer with a high pore volume. Due to the rising water pressure, the groundwater can be forced to rise and reach the surface of the ground as an overflow source.

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  • J. Stiny: The sources: The geological foundations of source studies for engineers of all disciplines as well as for students of the natural sciences. Julius Springer Verlag, Vienna 1933. Overflow sources p. 133 ff.
  • E. Prinz & R. Kampe: Handbook of hydrology. Second volume: springs (fresh water and mineral springs). Springer Verlag, Berlin and Heidelberg, 1934. Overflow sources p. 50 ff.
  • LAWA working group groundwater measurement (publisher): Groundwater, guidelines for observation and evaluation. Part 4, sources. LAWA regional working group on water, 1995.
  • Hilmar Zetinigg (1998): Comments on classification systems for sources. Communications geology and palaeontology at the Landesmuseum Joanneum, special issue 2: 371–386.

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