What is an Aquifer? , Type of Geological formation And Type of Aquifers

What is an Aquifer?

An underground body of rock ( or soil or sediment ) that serves as a storage reservoir for groundwater and also through which water can easily move.           

     

Ⅰ) Aquifer have good porosity ( can store water ) and good permeability ( water can travel in and out ).

Ⅱ) Aquifer material should have good amount of interconnected pores such as sand and gravels are example of some excellent aquifers.

Geological Formation:

Geological formation refer to natural formations and structures in the bedrock and soil, usually created by extremely slow geological processes of varying age.

Type of Geological Formation:

1. Aquifer: An aquifer refer to a geological formation, which can store and transmit groundwater in sufficient quantity so that the water can be economically utilized from the aquifer.The Geological formation which can store and discharge water. ( Porous + Permeable )

Example:- Sandy soil, Gravel, course silt, fine sand, etc.

2. Aquiclude: It is the geological formation which is porous but less permeable ( Highly porous + Non-Permeable ). Aquiclude have good volume of of pores, but they are not interconnected.

Example:- Clay

3. Aquitard: It is the geological formation which is porous but very less permeable. Aquitard have sufficient volume of pores, but limited interconnectedness of pores. Thus, they may transmit water only in certain direction.

Example:- Sandy Clay, Clayed Silt

4. Aquifuge: The geological formation which is neither porous and nor permeable. Aquifuge have negligible interconnection pores.

Example:- Rocks like Granite, Diorite etc.

Type of Aquifers:

Their are mainly four type of Aquifers:

1. Unconfined Aquifer: Also called Free Aquifer OR Non-Artesian Aquifer

The Aquifer which rest over impermeable layer, which could be either an aquiclude or aquifuge. Thus, here the aquifer can be recharged locally from the rainfall by infiltration and percolation of rainwater through interconnected pores reaching up to groundwater. The aquifer system is open to surface, air and water are in direct contact through interconnected pores to the water table.

2. Confined Aquifer: Also known as Artesian Aquifer

The Aquifer which lies between two impermeable layers. This impermeable layer could be an aquiclude or aquifuge. As it is lies between two impermeable layers, there is no direct local recharge to the aquifer. It receives recharge by lateral flow of groundwater from the recharge areas where the aquifer is exposed to surface ( as shown in Diagram below ).

3. Semi-confined Aquifer: Also known as Leaky confined Aquifer (or simple leaky aquifer).

A semi-confined aquifer is one that is either overlain or underlain by a semi-pervious materials, which is mostly an aquifers. Semi-confined Aquifer is a three-layer system, the top layer is semi-pervious and the bottom layer is impervious. Such leaky confined aquifers or semi confined aquifers has provision for water movement through the top semi pervious layers.

4. Perched Aquifer:

It is an Aquifer that occurs above the regional water table, in the vadose zone(zone of aeration). This occurs when there is an impermeable layer of rock or sediment ( aquiclude ) or relatively impermeable layer ( aquitard ) above the main water table but below the land surface.  

Important definition Related to Aquifers:

1. Artesian well: An artesian well is a water well that doesn't require a pump to bring water to the surface; this occurs when there is enough pressure in the Aquifer. In artesian well, water will flow to the surface naturally.

2. Non-Artesian well: An Non-Artesian well is a water well in which water not flowed naturally to the surface but has to be raised by pumping or other artificial means.