Classification of Subsurface Water | Hydrogeology

Subsurface water can be mainly divided into two zones viz.: 1. Zone of Aeration 2. Zone of Saturation.

1. Zone of Aeration:

In this zone the soil pores are partially filled with water. The space between the ground surface and the water table is the zone of aeration.

Zone of aeration can be further divided into three zones:

i. Soil Water Zone,

ii. Pellicular Water Zone and

iii. Capillary Water Zone.

i. Soil Water Zone:

It is adjacent to the ground surface consisting of the topsoil and the subsoil. In this zone water is lost to the atmosphere mainly due to evapotranspiration. The depth of this zone varies up to about 15 metres depending on the type of soil.

ii. Pellicular Water Zone:

This zone lies between the soil water zone and capillary water zone. In this zone water is held in place by capillary forces. Temporarily water moves downward in this belt as gravitational water. The water in this zone is also known as vadose water.

iii. Capillary Fringe:

This is the zone in which water is held by capillary action. This zone is situated between the gravitational zone and the saturated zone as shown in Fig. 7.3. The thickness of this zone may vary from few centimetres is about 600 metres or more depending on the type of soil.

2. Zone of Saturation or Ground Water Zone:

Voids are fully saturated with water. This zone may include loose, unconsolidated deposits of sand and gravel as well as porous rock formations like limestone and sandstone.