Water in soil Mantle is called sub-surface water. About 30% of the world’s fresh water resources exist in the form of ground water. It gives important input for the substance of life and vegetation in barren zones. So, studies on various aspects of this sub-surface water is very important.
Forms of Subsurface water:
Sub-surface water is considered in two zones.
1) Saturated zone.
2) Aeration zone.
1. Saturated zone:
In this zone all the interstices of soil are filled with water. Here, the water table forms its upper limit and marks a free surface, i.e. a surface having atmospheric pressure.
2. Zone of aeration:
Interstices in soil only partially saturated with water, in this zone which extends between the land surface and the water table. The thickness of zone of aeration depend upon the soil texture and moisture content and may very from region to region. Again, the zone of aeration has three sub zones:
a) Soil water zone
b) Capillary fringe
c) Intermediate zone