Phreatic zone

Examples of different groundwater systems ( phreatic zone ; vadose zone and bottom water zone ; groundwater non-conductor ). Example (a) shows an untensioned (phreatic) aquifer, not hydraulically isolated from the surface, in a region with a humid climate . Example (b) is a similar groundwater system, but in a region with a semi-arid to arid climate . Example (c) shows a strained aquifer that is largely hydraulically isolated from the surface.

The phreatic zone (also called the saturated zone ) is the part of a water-conducting rock in the subsurface that lies below the groundwater level (i.e. an aquifer in the broader sense). There, the cavities in the rock ( intergrain spaces, solution cavities , fissures ) are largely completely filled with water. The water of the phreatic zone therefore represents the actual groundwater and the corresponding water-saturated rock form the actual aquifer.

Definition of terms

Above the phreatic zone is the vadose zone (also unsaturated zone ). In this, the cavities in the rock are partly filled with air and partly with water. In order to get into the actual groundwater, rainwater (meteoric water) has to cross the vadose zone (see also →  Infiltration , →  Groundwater recharge ). In the actual groundwater, i.e. in the phreatic zone, water of this origin is also referred to as vadose water . In addition to vadosem / meteoric water, the phreatic zone can also contain juvenile water , mostly at lower levels . The so-called capillary rim usually extends between the groundwater level and the actual vadose zone .

A distinction between vadose zone and phreatic zone only applies to unconstrained aquifers (also known as phreatic aquifers ). No vadose zone can exist under stressed groundwater conditions.

Terminological peculiarities in karst hydrology

Groundwater system in a karst area with a vados and phreatic zone. Karst cavities represent a special case of groundwater systems.

Due to seasonal or climatic shifts in the relationship between the amount of precipitation and evaporation , there are short and long-term fluctuations in the groundwater level, also known as karst water level in karst hydrology . In karst hydrology, however, only the area that is below the karst water level for a long time is referred to as a phreatic zone. The area within the vadose zone, which can briefly fall below the karst water level, is called the flood zone according to Bögli (1978) .

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• Werner Aeschbach-Hertig: Current and Transport in Groundwater. Physics of Aquatic Systems I (lecture notes), Ruprecht-Karls-Universität Heidelberg, 2005 ( PDF ( Memento from July 5, 2016 in the Internet Archive ) 520 kB)

Individual evidence

1. ↑ Note, however, that vadose waters in English literature often only refers to the water located in the vadose zone, see: Vadose water. Spectrum online encyclopedia of geosciences, accessed September 30, 2019
2. ↑ Bernward Hölting. Hydrogeology. Introduction to General and Applied Hydrogeology. 5th edition. Enke, Stuttgart 1996, ISBN 3-8274-1246-3 , p. 14.
3. ^ Alfred Bögli: Karst hydrography and physical caveology. Springer, Berlin 1978, ISBN 3-540-09015-0 ; see also: phreatic. Online geoglossary of the Martin Luther University Halle-Wittenberg, accessed on September 30, 2019