Types of Aquifers

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Zones of Soil

The earth’s crust is lithosphere consisting of rocky materials such as granite, sandstone, limestone etc.
Basically soil profile is divided into 2 zones
·         Zone of aeration (Suspended Water)
·         Zone of Saturation (Water under pressure)
Now as cleared from its name aeration zone would be upper than the saturation zone. Zone of aeration consists of 3 parts
  •        Soil moisture zone                               
  •         Intermediate belt/Vadoze zone            
  •     Capillary  fringe 





Image courtesy: Anonymous

Now these 3 parts are arranged from surface to inner level of the Earth. Soil moisture is that part that consists of water supplied externally to ground by man (irrigation) or naturally (floods/rain……etc.).This moisture is available to plants roots for their growth.
Next come the intermediate belt more commonly known as vadose zone which consists of soil and rocks and gravels. So this zone is also consisting of blocked air, which does not allow the water to saturate this area, leading to the blocking of air molecules inside the vadose zone. That’s why this zone is known as aeration zone.
Next comes the part that consists of water rose from the groundwater know as capillary fringe. Now the water from this zone is rose and is available for plants up taking.

Zone of Saturation as the name suggests that this zone is fully saturated with water so it is understood that groundwater is a part of this zone. Above the groundwater level there is capillary fringe (in zone of aeration) resulting in the rising of the water from the groundwater level naturally.



Aquifers or Ground water reservoirs or water bearing formations  



Same terms used for the extracting groundwater which can be used beneficially due to its purity (but now even groundwater has begun to pollute main reason involving the usage of pesticides which enters the surface to meet the groundwater along with infiltrating water).

Aquifers types:

  •     Unconfined/Phreatic Aquifer
  •     Confined Aquifer
  •     Semi-Confined Aquifer
  •     Perched Well


Unconfined/Phreatic Aquifer:  An unconfined aquifer is permeable bed, only filled with water lying over a relatively impervious layer. Its boundary is formed by a free, water table or phreatic level. It is also known as a free, water table or non-artesian aquifer.
The upper boundary of zone of saturation is known as water table. At water table the hydrostatic pressure=atmospheric pressure.



Confined Aquifer: An aquifer lying between two impermeable layers is said to be confined aquifer. It is also called artesian aquifer. Because of presence of the upper impermeable layer the water in this aquifer not being in contact to atmosphere is at a greater pressure than atmospheric pressure.
          Image courtesy: Anonymous

When a hole I drilled in this aquifer the water rises to a certain level due to the high pressure, the level to which water rise is known as piezometric level. An imaginary surface representing the hydrostatic pressure of the confined aquifer is known as piezometric surface.
The hydrostatic pressure of the aquifer can sufficiently large enough to cause water to rise up to ground surface level. (As in case of Gurdaspur, Punjab)


Semi-Confined Aquifer: It is also known as leaky aquifer. It is formation in which water is present between 2 layers. Upper layer is a semi-pervious layer and bottom one by either semi-pervious or impervious layer. Semi-pervious layer is a layer that transmits low yet measurable hydraulic conductivity. In this aquifer the peizometric and phreatic level are at same level. But after pumping starts, the piezometric level begins to fall due to vertical uplifting of water. Along with the fall in piezometric level, there is a fall in the phreatic level also.


·         Semi-Confined Aquifer with prompt yield: When phreatic level is lowered almost simultaneously with piezometric level.
·         Semi-Confined Aquifer with delayed yield: When there is sufficient time lag between the lowering of the two levels.

 Perched Well: A special case of a localised water body in an unconfined aquifer is the perched            water table. It is a water body which has been retarded the downward flow due to the                     presence of     some earthy materials at some distance above the water table.
The upper surface of the ground water in such a water body is known as perched water table.


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