Groundwater corresponds to the surface of the underground bodies of Water, which separates the soil saturated zone from the aerated zone. They form in areas of permeable soils and can be shallower or deeper depending on elements such as the region's rainfall, topography and the presence or absence of vegetation cover. The water table is important for domestic supply and for economic activities, in addition, of course, to being responsible for feeding rivers, lakes and oceans.
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Topics in this article
- 1 - Summary on the water table
- 2 - What is water table?
- 3 - What are the characteristics of the water table?
- 4 - Aquifers
- 5 - What is the importance of the water table?
- 6 - Outcrop of the water table
- 7 - Lowering of the water table
- 8 - Groundwater in Brazil
- 9 - Environmental problems in the water table
- 10 - Solved exercises on the water table
Summary on the water table
Groundwater table is the surface that separates an underground body of water from the unsaturated zone of soil.
The type of soil, the climate of the region and its respective hydrological regime, the relief and the presence of vegetation cover are decisive for the volume and depth at which the water level is found.
Aquifers are subsurface rock formations capable of storing water.
The water table is important for the recharge of rivers, lakes and oceans, in addition to providing water for domestic supply and for carrying out agricultural and industrial activities.
They are important sources of water in areas with a dry climate, where precipitation is scarce, since the evaporation process is slower and the losses are smaller.
Upwelling happens when water reaches the surface.
Lowering the water table consists of making the water level deeper and may be necessary for the execution of works.
The main environmental problem of groundwater is the pollution, which occurs through the irregular disposal of garbage, construction of cemeteries in inappropriate places and excessive use of pesticides, for example.
What is groundwater?
Water table, also called water level or water table, is the name given to a water surface that delimits the unsaturated zone of a soil, or aeration zone, which corresponds to the area where water infiltration occurs, and the underground reserve itself, which can be called saturated or phreatic zone. In other words, the water table corresponds to the upper limit of groundwater.
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What are the characteristics of the water table?
The water table is often described as a water reserve itself, since, as we saw above, it delimits two distinct areas of the same homogeneous body of ground. Above the water table the soil is composed of pores (air) and spaces filled with water, while below it the soil is saturated, that is, filled with water.
For the formation of this water level and consequently of the reservoir to be possible, it is necessary that the substrate is permeable, thus allowing the infiltration of water and its storage in the layers lower.
The water that feeds and replenishes the underground reserves and maintains the water table comes from the rains. For this reason, in humid regions where rainfall is high, the water level tends to be more shallow, and the reservoirs, more voluminous, since the amount of water that percolates into the soil is larger. The opposite happens in areas with a dry climate, where the water table is at greater depth and indicates a lower volume of groundwater.
Other aspects that are decisive for the depth of the water table are the relief of the area where the reservoir is formed and the presence or absence of vegetation, which interfere with the infiltration of water into the soil.
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aquifers
The aquifers are geological units subsurface formed by porous and/or highly permeable rocks, as sedimentary rocks, which allow the infiltration and storage of water.|1|
The recharge of aquifers is carried out by surface waters, mainly rainwater, which penetrates the soil through its pores or fractures and discontinuities in the rocks. The waters retained in these reservoirs tend to be of higher quality than surface waters, since they are protected at depth.
the aquifers can be classified as confined or free.. Confined aquifers are also called artesian, characterized by the reserve of water between two layers of impermeable or poorly permeable rock.2| This body of water is located in an area of high pressure, so it is common for water to flow to the surface when drilling artesian wells.
On the other hand, the free aquifer has the porous zone of the soil over it, the surface that separates it from this area called the water table.
How important is the water table?
The water table is of great importance for the recharge of surface water bodies, as is the case with rivers, lakes and even the oceans.
They are very popular in regions with arid climates and semiarid for obtaining water intended for human consumption, as they are reservoirs of superior quality to the reservoirs surface due to soil filtration and deep storage, in addition to less evaporative losses. For this reason, the extraction of water from groundwater has been seen as a viable alternative to alleviate the effects of scarcity in different regions of the planet.
A survey carried out by the University of São Paulo (USP) with the Trata Brasil Institute and published in year 2019 revealed the great importance of groundwater for the supply of the territory national.|3| Among the main consumers of this type of water, usually extracted through artesian wells, are ordinary citizens (domestic supply) and the activity agricultural. In addition, the country appears in the list of the ten nations that most extract groundwater for consumption.
Outcrop of the water table
The upwelling of the water table happens when groundwater reaches the surface. When this outcrop has a perennial character and is followed by the formation of a river or watercourse, it is called a spring. Other types of natural outcrops are called Olho d’água or Mina d’água, as determined in the new Forest Code of Brazil.
Lowering of the water table
The lowering of the water table is a practice often necessary to carry out works in infrastructure and engineering, since the presence of water in a small depth can harm its execution. The main, but not the only, technique used for this is pumping water vertically to deeper layers of the soil.
Although common, the lowering of the water table is harmful to the soil structure and buildings and buildings in the surrounding areas, causing cracks and even collapse.
Groundwater in Brazil
As a country with humid and semi-humid climates and a substrate prone to the formation of underground reserves, the Brazil has extensive aquifers, which are among the largest and most important in the South America and also of the world. We will specifically talk about two aquifer systems that are responsible for the recharge of springs and urban and domestic supply:
Greater Amazon Aquifer System (Saga): formerly known as Alter do Chão, the Saga is spread over the North region of the country between the states of Acre, Amazonas, Roraima, Pará and Amapá, comprising four large watersheds South American. Its area is estimated to be 162,520 km², which would make it the largest in the world. |4|
Guarani Aquifer System (SAG): is one of the main aquifers in South America, extending through Paraguay, Argentina, Uruguay and Brazil. Its Brazilian portion corresponds to 70% of the total of more than 1,200 km² of extension, comprising eight states in the regions Midwest, Southeast and South from the country.
Environmental problems in the water table
Inadequate management of the soil and agricultural practice, the irregular disposal of garbage and other urban-industrial waste and the lack of urban planning can cause serious problems to the water table, such as water pollution, compromising its quality and, in the medium and long term, its use.
Some of The main causes of groundwater pollution are as follows:
landfills or garbage dumps in inappropriate places, which can lead to substances such as slurry derived from waste penetrating the soil and reaching the water table;
cemeteries where the sheet is shallow, generating water contamination by necrochorume;
pesticides and other pesticides that infiltrate the substrate.
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Solved exercises on the water table
question 1
Regarding the process of formation of water tables, mark the correct alternative.
a) They are formed only in regions with a humid climate.
b) Its supply takes place through rainwater.
c) Occur in soils with low permeability and high degree of slope.
d) The phenomena that originate the water tables are not part of the hydrological cycle because they occur in part underground.
e) They form inside impermeable rocks, such as sandstones.
Resolution: Alternative B
Groundwater reservoirs and therefore groundwater are replenished by rainwater. In some cases, recharge can also occur through river water.
question 2
(UFPB) Groundwater are important reservoirs found below the earth's surface, in porous and permeable rocks. These reservoirs, called aquifers, are found at different depths, and their exploitation has increased considerably in recent years.
Considering the above and the literature on groundwater, it is correct to say:
a) Groundwater is always potable and free from any type of surface contamination.
b) Excessive use of groundwater in agriculture can raise the level of the aquifer and compromise soil fertility.
c) Aquifers can be exploited, without the need for authorization from the competent body, by any citizen, as long as he/she is the owner of the land.
d) The rupture of fuel tanks and residential septic tanks is incapable of contaminating aquifers, as the depth prevents the contact of these contaminants.
e) Agricultural activities carried out on the surface, such as excessive fertilization and the use of pesticides, can contaminate aquifers.
Resolution: Alternative E
The indiscriminate and excessive use of pesticides and other agricultural pesticides can make these substances seep into the soil and reach the water table, contaminating the water reserves underground.
Grades
|1|KARMANN, Ivo. Water: cycle and geological action. In: EIXEIRA, Wilson.; FAIRCHILD, Thomas Rich.; TOLEDO, Maria Cristina Motta de; TAIOLI, Fabio. (Eds.) deciphering the earth. São Paulo, SP: Companhia Editora Nacional, 2009, 2nd ed. P. 186-209.
|2| Idem.
|3| HIRATA, Ricardo et al. The silent revolution of groundwater in Brazil: an analysis of the importance of the resource and the risks caused by the lack of sanitation. [São Paulo]: Instituto Trata Brasil. Available here.
|4| MADEIRO, Charles. The world's largest aquifer is located in Brazil and would supply the planet for 250 years. UOL Notícias, 21 Mar. 2015. Available here.
By Paloma Guitarrara
Geography teacher
