Types of aquifers

Aquifers are geological formations with hydraulic properties that allow the free storage and transmission of water through their pores or cracks. Among the parts of an aquifer , can be distinguished:

• The water table.
• The saturation zone.
• The waterproof layer.

The groundwater is located in the saturation zone, below the water table, which is the upper limit of this area. The deeper the saturated zone, the higher the water pressure. Since the stored water flows to areas of lower pressure, it naturally emanates to the surface through upwellings ( coals ), springs, springs or river beds. In addition, depending on the type of aquifer, there is an impermeable area that prevents the passage of water.

The recharge of the aquifers takes place through the infiltration-percolation process of precipitated water. In it they intervene: gravity and lithology.

• On the one hand, gravity is the force that draws water towards the center of the earth, allowing it to circulate vertically, from the earth’s surface to the different depths of the subsoil.
• On the other hand, lithology determines the degree of porosity or compaction of the geological materials that make up the aquifer. Depending on this, water can accumulate and circulate more or less easily.

If you want to know in more detail what an aquifer is and how it is formed , here is another summary of AgroCorrn. There are different criteria to classify the aquifers that exist. This article establishes four types of classifications.

Depending on the lithological behavior against groundwater , 4 hydrogeological systems are differentiated : aquifers, aquitards, aquicluids and aquifuges.

• According to their geological formations, aquifers can be considered excellent (made up of clean gravel), fair-good (made up of clean sands, gravel and sand or fine sand), or poor (fine sand, silty sand and fractured limestone) for storage and groundwater transmission. In general, this system is characterized by a high capacity to store, drain and transmit water.
• Aquitards , made up of silts, silty sands and clays, have a high capacity to store water but present problems for its drainage (medium-low capacity) and its transmission (low capacity). It is an intermediate term between what is an aquifer and an aquicluid.
• Despite having a high porosity, the characteristic formations of aquicluids are impervious to the passage of water (marl, clay or pumice stone). Therefore, its storage, drainage and transmission capacity is nil.
• Aquifuges are geological formations that cannot store or transmit water. Some examples are igneous rocks that are neither fissured nor fractured. Here you can learn more about the types of igneous rocks and their characteristics .

The location of the aquifers, their hydrological behavior and the characteristic geology, give rise to three different types of aquifers : free, confined and semi-confined.

• Free, unconfined or groundwater aquifers do not present impermeable formations. In them, the unsaturated zone is located between the ground surface and the water table and the water is in contact with air and at atmospheric pressure.
• Confined, captive, pressurized or loaded aquifers, unlike free aquifers, are not in contact with the atmosphere due to the presence of impermeable or confining materials. In a captive or confined aquifer, the water completely saturates the pores or cracks, so that when drilling it rises until the hydraulic pressure is balanced with the atmospheric one.
• Semi-confined aquifers are also pressurized aquifers, like confined ones, but unlike the latter, there is greater permeability in them (they are considered aquitards).

Lithology allows us to distinguish two types of aquifers: detrital and carbonate (or karst):

• Detrital aquifers are free aquifers in contact with rivers, which are mainly made up of clay materials, very little permeable. They may also contain accumulations of highly permeable and porous detrital materials, sand and gravel. This makes its permeability variable.
• Karst or carbonate aquifers are formed by limestone and dolomatic materials, which allow the accumulation of rain and runoff, due to their dissolution (high permeability).

According to the properties of their texture, aquifers can be: porous or fissured .

• In porous aquifers, water saturates the interconnected pores, which confers permeability and the ability to transmit water. This varies depending on the training material.
• In fissured aquifers , the water is located in the fissures of the rocks, which are also communicated. The circulation of water, being cracks and not pores, is less predictable and more heterogeneous.

Now that you know the different classifications of the types of aquifers, we encourage you to learn more about inland waters: what they are, characteristics and importance with this other AgroCorrn article.

If you want to read more articles similar to Types of aquifers , we recommend that you enter our category of Other environment .