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What is Aquifer?

Meaning and Definition of Aquifer

The aquifer is an underground geological formation that works as a reservoir of water, fed by rain that seeps underground. They are rocks with porous and permeable characteristics capable of retaining and producing water. It supplies water to wells and springs in sufficient proportions, serving as profitable sources of supply.

To be considered an aquifer , a geological formation must contain open spaces or pores filled with water and allow water to move through them.

Types of Aquifer

Free or Phreatic

It is a geological formation with a permeable feature , partially saturated with water. Its base is made up of an impermeable layer like clay, or it can be semi-permeable. In this aquifer there is a free surface of water that is under atmospheric pressure.

In free aquifers , the water level varies depending on the amount of rainfall and is the most common type of aquifer and the most exploited by men. However, it is also the aquifers that present the greatest contamination problems .

Confined or Artesian

This type of aquifer occurs when groundwater is confined to a pressure higher than atmospheric pressure. It is due to the existence of an impermeable confining layer over the aquifer. Because the water is at a higher pressure than atmospheric pressure, when drilling a hole for its extraction, the water rises to the piezometric surface, giving rise to an artesian hole. Thus, the water reaches the surface in the form of a source, the artesian well is called an extraction hole .

Porous Aquifers

These types of aquifers have small empty spaces (pores), through which water circulates. They are associated with consolidated sedimentary rocks , sandy soils, and unconsolidated sediments. They represent the most important group of aquifers , due to the large volume of water they store and also because they are found in many areas.

Fractured or Fissured Aquifers

They are characterized by having open fractures that accumulate water. These fractures represent the result of a certain deformation suffered by a rock when it is subjected to tensile forces of a different nature. Fractured aquifers are associated with igneous and metamorphic rocks.

karst aquifers

They form in carbonate rocks. The fractures present in this type of aquifer can reach larger dimensions, due to the dissolution of carbon by the water. Therefore, they can form large underground rivers.

Importance of Aquifers

Aquifers play important roles in nature and fulfill various functions. Through them, surface watercourses are kept stable and excess water ( overflow ) is prevented through the absorption of rainwater.

Therefore, in regions like tropical Asia, characterized by a long hot season (9 months) and marked by heavy rains, aquifers are of great help.

The largest underground freshwater reserve in the world , called the Guarani Aquifer. It is considered one of the largest aquifers in existence, with approximately 1.2 million km², with most of the area occupied by the aquifer present in the subsoil of central-southwestern Brazil.

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