The

phreatic ''Phreatic'' is a term used in hydrology to refer to aquifers, in speleology to refer to cave passages, and in volcanology to refer to a type of volcanic eruption. Hydrology The term phreatic (the word originates from the Greek , meaning "we ...

zone, saturated zone, or zone of saturation, is the part of an

aquifer An aquifer is an underground layer of water-bearing, permeable rock, rock fractures, or unconsolidated materials ( gravel, sand, or silt). Groundwater from aquifers can be extracted using a water well. Aquifers vary greatly in their characte ...

, below the

water table The water table is the upper surface of the zone of saturation. The zone of saturation is where the pores and fractures of the ground are saturated with water. It can also be simply explained as the depth below which the ground is saturated. T ...

, in which relatively all pores and fractures are saturated with water. Above the water table is the unsaturated or

vadose zone The vadose zone, also termed the unsaturated zone, is the part of Earth between the land surface and the top of the phreatic zone, the position at which the groundwater (the water in the soil's pores) is at atmospheric pressure ("vadose" is f ...

. The phreatic zone size, color, and depth may fluctuate with changes of season, and during wet and dry periods. Depending on the characteristics of soil particles, their packing and porosity, the boundary of a saturated zone can be stable or instable, exhibiting fingering patterns known as

Saffman–Taylor instability The Saffman–Taylor instability, also known as viscous fingering, is the formation of patterns in a morphologically unstable interface between two fluids in a porous medium, described mathematically by Philip Saffman and G. I. Taylor in a paper ...

. Predicting the onset of stable vs. unstable drainage fronts is of some importance in modelling phreatic zone boundaries. Dynamics of Drainage and Viscous Fingering
in ''Transport in Porous Media''
''Note that zones "behind" the drainage front are areas on the 'dry' (low-viscosity) (typically above / beyond the 'wet' zone).''

References

Aquifers Cave geology Hydrogeology Soil physics {{Hydrology-stub

See also

References