Thephreatic zone,saturated zone, orzone of saturation, is the part of anaquifer, below thewater table, in which relatively all pores and fractures are saturated with water. The part above the water table is thevadose zone (also called unsaturated zone).
The phreatic zone size, color, and depth may fluctuate with changes of season, and during wet and dry periods.[1][2] Depending on the characteristics of soil particles, their packing andporosity, the boundary of a saturated zone can be stable or instable, exhibiting fingering patterns known asSaffman–Taylor instability. Predicting the onset of stable vs. unstable drainage fronts is of some importance in modelling phreatic zone boundaries.[3]
