Groundwater is formed as a result. Groundwater: its formation and classification. Groundwater Sources

Groundwater includes all waters located in the earth's crust, regardless of their state of aggregation.

Groundwater is formed mainly as a result of the infiltration of atmospheric precipitation, as well as through the condensation of water vapor penetrating with air into fractured and porous rocks. In addition, there are buried, or relict (lat. relictus -- abandoned), waters preserved from ancient sea basins and buried during the accumulation of thick layers of sediment, as well as thermal waters formed in the last stages of magmatic processes.

Water in rocks is found in different forms: in the form of free and sorbed molecules of water vapor, weakly sorbed polymolecular films, capillary water and, finally, water that can move under the influence of its own weight - gravitational water. The listed forms of water are closely related to different types of pores and cracks.

All rocks have porosity, which is measured by the ratio of the total volume of all types of pores to the total volume of the rock, expressed as a percentage. Rock porosity ranges from 20 to 30%.

An important property of rocks is their permeability - the ability to pass water through them. In rocks, gravitational water can move most actively, moving through the largest pores and cracks. Taking into account the possibility of its movement, water-permeable and water-impermeable rocks are distinguished. The former include sands, pebbles, fractured limestones and other rocks, while the waterproof ones include clays and massive crystalline rocks.

Permeable rock containing water is called an aquifer, or reservoir, and impervious rock is called an aquifer. The waterproof rock that overlies the waterproof horizon from above is called roofing, and the underlying one below is his sole.

The gravitational water filling the pores of the reservoir can be under pressure, and then they speak of pressure water, or pressure aquifers. If there is no pressure, then the aquifers are called non-confined. In this case, water can only move under the influence of its own gravity. Water under pressure is able to rise to a height that balances this pressure (the effect of communicating vessels).

The absolute height of the rise of pressure water is called the piezometric level. As a rule, the pressure in the aquifer is determined by the relatively high position of the horizon's recharge area. If such a horizon is opened by drilling, the water in the borehole will rise to the level at which the recharge area is located. Such waters were called artesian (after the name of the province of Artois in northwestern France, where such a well was first drilled).

A tectonic trough, in the geological structure of which there is one or usually several confined aquifers, is called an artesian basin.

An example is the Moscow artesian basin, in the cavernous limestones of Carboniferous age there are three confined aquifers of high quality fresh water, separated by impermeable clays.

The upper horizon of groundwater is called the groundwater horizon. This horizon has only an underlying aquifer layer and is formed due to the infiltration of atmospheric precipitation, which is retained on the aquiclude. Therefore, the surface (upper level) of groundwater is located at different depths depending on the terrain and the amount of precipitation.

Above the groundwater horizon during the period of rains or snow melting, due to the slow filtration of rain or spring melt water, a “hanging” (without aquitard) thin horizon of the so-called perched water may appear. This horizon exists for a short time during certain seasons of the year.

Groundwater confined to a system of aquifers separated by layers of impermeable rocks is called interstratal, or simply stratal. As noted earlier, they can be pressure or non-pressure.

In mountainous countries, there are fissure waters confined to fractured areas of crystalline massifs, as well as juvenile waters associated with post-volcanic processes. The sources of these waters, enriched with various mineral compounds and often possessing increased radioactivity, such as the sources of the Mineralnye Vody region in the North Caucasus, are used for medicinal and blebneological purposes.

In those places where aquifers come to the surface, springs are formed. Among them, a distinction is made between sources of groundwater and free-flowing interstratal waters, which are called downward, and sources of pressurized water, called upward.

On continents they form a continuous shell, which is not interrupted even in areas of dry steppes and deserts. Like surface waters, they are in constant motion and participate in the general water cycle in nature.

The construction and operation of most above-ground structures and all underground ones are associated with the need to take into account the movement of groundwater, its composition and condition. The physical and mechanical properties and condition of many rocks depend on groundwater. They often flood construction pits, ditches, trenches and tunnels, and when they come to the surface, they contribute to swamping of the area. Groundwater can be an aggressive environment in relation to rocks. They are the main cause of many physical and geological processes that occur in natural conditions, during the construction and operation of engineering structures.

There are:

Drinking water- water whose quality in its natural state or after treatment meets regulatory requirements and is intended for drinking and domestic human needs, or for the production of food products. This type of water also includes mineral natural table waters, which include underground waters with a total mineralization of no more than 1 g/dm3, which do not require water treatment or do not change their natural composition after water treatment.

Technical underground waters - waters of various chemical compositions (from fresh to brines), intended for use for industrial, technical and technological purposes, the quality requirements of which are established by state or industry standards, technical specifications or consumers.

Groundwater is also divided into:

Groundwater is mainly formed as a result of seepage (infiltration) of atmospheric precipitation and surface water into the earth's crust. Water passes through permeable rocks to the impervious layer and accumulates there, forming an underground pool or stream. This underground water is called infiltration. The amount of infiltration water depends on the climatic conditions of the area, relief, vegetation, composition of the rocks of the upper strata, their structure and texture, as well as the tectonic structure of the area. Infiltration groundwater is the most common.

Groundwater can also be formed by condensation of vaporous water constantly circulating in the pores of rocks. Condensation underground water is formed only in summer and partially in spring and autumn, and in winter it is not formed at all. By condensation of water vapor, A.F. Lebedev explained the formation of significant reserves of underground water in desert and semi-desert zones, where the amount of precipitation is negligible. Not only atmospheric water vapor can condense, but also water vapor released from magma chambers and other high-temperature zones of the earth's crust. Such groundwater is called juvenile .

Juvenile Groundwater is usually highly mineralized. During geological development, buried water basins may remain deep in the earth's crust. The water contained in the sedimentary strata of these basins is called relict.

The formation of groundwater is a complex process that begins with the accumulation of sediments and is closely related to the geological history of the area. Very often, groundwater of different origins mix with each other, forming mixed according to the origin of the water.

From the point of view of the distribution of groundwater, the upper part of the earth’s crust is usually divided into two zones: the aeration zone and the saturation zone. In the aeration zone, not all the pores of rocks are always filled with water. All water in the aeration zone is fed by precipitation, intensively evaporates and is absorbed by plants. The amount of water in this zone is determined by climatic conditions. In the saturation zone, regardless of climatic conditions, all the pores of rocks are always filled with water. Above the saturation zone there is a capillary humidification subzone. In this subzone, thin pores are filled with water, and large ones with air.

In the aeration zone, soil water and perched water are formed. Soil water lies directly at the surface of the earth. This is the only water that does not have an aquitard under it and is represented mainly by bound and capillary water. Soil water is in a complex relationship with animal and plant organisms. It is characterized by sharp temperature fluctuations, the presence of microorganisms and humus. Builders encounter soil water only in wetlands.

Verkhovodka forms in the aeration zone on waterproof lenses. High water is also called any temporary accumulation of water in the aeration zone. Atmospheric precipitation penetrating into this zone can be temporarily retained in low-permeability or compacted layers. Most often this happens in the spring during the snowmelt period or during periods of heavy rain. During dry periods, perennial water may disappear.

The characteristic features of perched water are its inconsistent existence, limited distribution, and low power. High water often creates difficulties for builders, since the presence or possibility of its formation is not always established during geotechnical surveys. The resulting perched water can cause flooding of engineering structures and swamping of areas.

Ground called water lying on the first permanent waterproof layer from the surface of the earth. Groundwater exists constantly. They have a free water surface called groundwater mirror, and a waterproof bed. The projection of the groundwater table onto a vertical plane is called groundwater level (U GV). The distance from the aquitard to the groundwater level is called capacity of the aquifer.

The groundwater level, and, consequently, the thickness of the aquifer, are variable values ​​and can change throughout the year depending on climatic conditions. Groundwater is recharged mainly from atmospheric and surface waters, but they can also be mixed, infiltration-condensation. The area of ​​the earth's surface from which surface and atmospheric water enters an aquifer is called nutrition area groundwater. The area of ​​groundwater recharge always coincides with the area of ​​its distribution. Groundwater, due to the presence of a free water surface, is free-flowing, i.e., the water level in the well is set at the same level at which the water is encountered.

Depending on the conditions of groundwater occurrence, groundwater flows and basins are distinguished. Ground flows have an inclined mirror and are in continuous movement towards the slope of the aquitard. Ground pools have a horizontal mirror and are much less common.

Groundwater, being in constant movement, has a close connection with surface watercourses and reservoirs. In areas where precipitation dominates evaporation, groundwater usually feeds rivers. underground drinking aquifer artesian

In arid areas, water from rivers often flows into groundwater, replenishing underground streams. There may also be a mixed type of connection, when on one bank groundwater feeds the river, and on the other, water from the river enters the groundwater flow. The nature of the connection may vary depending on climatic and some other conditions.

When designing and constructing engineering structures, it is necessary to take into account groundwater regime, i.e., changes over time in such indicators as fluctuations in groundwater levels, temperature and chemical composition. The level and temperature of groundwater are subject to the greatest changes. The reasons for these changes are very diverse and are often directly related to human construction activities. Climatic factors cause both seasonal and long-term changes in groundwater levels. Floods on rivers, as well as reservoirs, ponds, irrigation systems, canals, and drainage structures lead to changes in the groundwater regime.

The position of the groundwater table on maps is depicted using hydroisohypses and hydroisobaths. Hydroisohypses-- lines connecting points with the same absolute elevations of the groundwater level. These lines are similar to the contours of the relief and, like them, reflect the relief of the groundwater table. The hydroisohypsum map is used to determine the direction of groundwater movement and to determine the value of the hydraulic gradient.

The direction of movement of groundwater is always perpendicular to the hydroisohypses from higher to lower elevations. The directions along which groundwater moves during a steady, time-invariant movement are called current lines. If the streamlines are parallel to each other, then such a flow is called flat. The flow can also be converging or diverging. The smaller the distance between the hydraulic isohypses, the greater the hydraulic gradient of the ground flow. Hydroisobates-- lines connecting points with the same depth of groundwater.

Interlayer Groundwater refers to aquifers lying between two aquitards. They can be non-pressure or pressure.

Interstratal non-pressure waters are rare. The nature of their movement is similar to that of groundwater. Interlayer pressure waters are called artesian. The occurrence of artesian waters is very diverse, but the most common occurrence is synclinal.

Artesian water always fills the entire aquifer from the base to the roof and has no free water surface. The area of ​​distribution of one or more levels of artesian aquifers is called artesian pool. The areas of artesian basins are huge and measure in tens, hundreds, and sometimes thousands of square kilometers.

In each artesian basin, areas of feeding, distribution and discharge are distinguished. The feeding area of ​​artesian basins is usually located at greater distances from the center of the basin and at higher elevations.

It never coincides with the area of ​​their distribution, which is sometimes called the area of ​​pressure. Artesian waters experience hydrostatic pressure due to the difference in elevation between the feeding area and the discharge area, according to the law of communicating vessels. The level at which artesian water is installed in a well is called piezometric.

Its position is determined piezometric line, or a pressure line, a conditional straight line that connects the supply area with the discharge area. If the piezometric line passes above the surface of the earth, then when the aquifer is opened by wells, flowing will occur, and the pressure is called positive.

When the piezometric level is located below the surface of the earth, the pressure is called negative, and water does not flow out of the well. Artesian waters are generally more mineralized and less connected to surface watercourses and bodies of water than groundwater.

By fissure waters called groundwater confined to fractured igneous, metamorphic and sedimentary rocks. The nature of their movement is determined by the size and shape of the cracks. Fracture waters can be non-pressure or pressure. They are not constant and can change the nature of movement. The erosion and dissolution of rocks lead to the expansion of cracks, and the crystallization of salts and the accumulation of sediments lead to their narrowing. The flow rate of fissure water can reach 500 m3/h. Fissure waters create significant difficulties in the construction of underground structures.

Groundwater is water located below the surface of the earth. Their physical state can be anything, but for economic purposes it is liquid water reserves that are of interest. To make optimal use of this resource, an answer is required to how groundwater is formed and what types it comes in.

Groundwater is distributed unevenly. There is little moisture in the deepest layers, which consist of high-density rocks formed by igneous and metamorphic processes. Its main part is located in surface layers consisting of rocks of sedimentary origin.

The water reserves of the upper part are divided into three more layers. The moisture in the top layer is most often fresh and is used for a variety of needs. In the middle layer there are mineralized waters. Below are brines with high mineralization and a significant content of iodine, bromine and some other minerals.

Types of upper layer groundwater

The waters of the surface layer are divided into varieties.

1. The first type is perched water. It is located closest to the soil surface and is tied to the uppermost waterproof layer. The high water is not constant: during the dry period, with a lack of precipitation, it can disappear. Most often these are waters with low mineralization, but often containing organic contaminants and dissolved salts. As a source of water supply, perched water is not the best option.
2. Groundwater is located immediately above the upper aquifer. They have a relatively stable ratio of income and expense. This water accumulates in loose soils and various cracks. Changes in level are influenced by precipitation, human activity, topography, climate and other factors.
3. Artesian water has another name - pressure water. They are located between two layers of water-resistant rocks. They are subject to hydrostatic pressure due to differences in the level of nutrition and access to the surface. In artesian waters, feeding areas can be very far away, and their area is often enormous.

Methods of groundwater formation

The creation of groundwater reserves is carried out in several ways. One of the main ones is the seepage of surface moisture and precipitation from the surface into depth. This method is called infiltration. In addition to precipitation, water from all surface sources participates in this process. The amount of penetrating moisture depends significantly on the characteristics of the soil. If we consider precipitation, then about twenty percent of the moisture goes deep. All this is part of the global process of the water cycle.

Penetrating water descends deep into a layer of waterproof rock. There it lingers and begins to saturate the surrounding rocks, which have pores and cracks. The result is an aquifer.

The seepage process depends on the characteristics of the surface soil, which can be permeable, semi-permeable or impermeable. Sandy, gravel, pebble and coarse rocks are permeable to water. Rocks created by magma or metamorphic processes, such as granite and clay, are waterproof. Clay sands, sandstones with a loose structure and some others are relatively permeable.

The volume of penetrating moisture depends not only on the characteristics of the soil. This indicator is also influenced by the relief (the greater the slope, the more precipitation flows off without penetrating into the ground), the amount and characteristics of vegetation, and some others.

In many areas, it is infiltration that ensures the formation of groundwater. However, we should not forget about other methods, despite their small share. Groundwater is formed by the precipitation of water vapor in rock cavities. Another way is the formation of juveniles, i.e. primary waters They occur when magma separates and solidifies. However, pure juvenile waters practically do not exist, because they immediately mix with the others.

Groundwater is constantly being formed, so it can be considered an inexhaustible water resource. However, care should be taken when using. Once contaminants penetrate into the impermeable horizon, it is very difficult to correct the situation.

Groundwater is formed by filtration into the soil of atmospheric precipitation and water penetrating from open reservoirs.

As well as condensate of water vapor formed in the soil from the atmosphere. During filtration, a slow destruction of the soil occurs - the washing out of small particles (suffusion). In hydrogeology, there are 2 types of it:

1. Mechanical suffusion is the separation of small particles of rock by a stream of water and their removal, in suspension, into the pores of another layer of rock.
2. Chemical suffusion is the dissolution of salts and carbonates in the soil. In this regard, the mineralization of groundwater increases.

As a result of prolonged filtration, the soil settles, forming sinkholes.

Aquiferous soil is considered to be soil that, when opened by a mine, is capable of releasing water. Waterproof - soil through which water does not filter.

There are practically no waterproof soils, since each layer contains voids that are gradually filled with water filtered from atmospheric precipitation.

This is how groundwater is formed. This especially happens during the period of melting snow and prolonged rains.

Soils such as gravel, limestone, pebbles, sand and weathered rocks have high permeability. Clay layers and non-weathered rocks are considered waterproof. Semi-permeable rocks include loams, loess, clayey sands, and marls.

Regardless of water permeability, each upper layer of rock is a roof for the layer located below. A decrease in groundwater reserves occurs in the absence of precipitation in the form of rain or winter with little snow and the presence of vegetation cover. If there is a slope in the area, then the vegetation cover delays its flow and it, filtering into the ground, replenishes water supplies.

Classification

Classification is carried out:

• according to the method of occurrence,
• on mineralization,
• by chemical composition.

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Method of occurrence

Verkhodka scheme.

Verkhodka is soil moisture. Groundwater is formed and replenished due to precipitation and recharge from nearby reservoirs. In dry years, due to lack of precipitation, it practically disappears. Usually it is located above the first waterproof layer of soil. It cannot be used to supply drinking water to the population, as it is contaminated with organic suspensions. In places where the first impermeable layer ends, the perched water disappears, flowing into the lower horizons. If the waterproof layer comes to the surface, then the possibility of swamp formation arises. Reclamation of this area is necessary.

When the voids in the soil are completely saturated with water, layers of soil water are created:

1. Groundwater is partially polluted and occupies the first aquifer from the surface of the earth.
2. Interstratal waters. They lie in aquiferous soil, between two waterproof layers: the underlying and the roof.
3. Artesian groundwater.
4. Soil water completely fills all the voids in the aquifer and, when it is opened by a mine, rises in it above the opening mark. This level established in the well is called piezometric. If high pressure is created, groundwater is ejected from the mine like a fountain.

When carrying out search work, it is determined in the spring, when it is highest and snow melting occurs intensively. It is mainly determined by measuring the distance from the soil surface to the water surface in the nearest wells and boreholes.

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Determination of mineralization

To determine the physicochemical properties of groundwater, color, smell, taste, temperature and impurities are examined.

Before assigning the studied groundwater to any class, a study is carried out for the presence of bicarbonate, sulfate, chloride anions and cations of calcium, magnesium, sodium and potassium.

» new types of water. Visiting today - The groundwater. We will talk about what groundwater is, where it comes from and where it goes. Along the way, we’ll dispel a couple of common misconceptions on the topic of groundwater.

Groundwater is the collective name for various deposits of water underground. Water underground can be fresh, very fresh, brackish, salty, super-salty (for example, in cryopegs, which we touched on in the article “Diversity of water in the world”).

Common to all types of groundwater: they are located above an impervious layer of soil. Impermeable soil is soil that contains a large amount of clay (does not allow water to pass through) or soil that is solid rock with a minimum number of cracks.

If you go outside and spread a sheet of polyethylene on the ground, you will get nothing more than a model of a waterproof layer of soil. If you pour water onto polyethylene, it will collect in depressions and flow from higher places to lower ones. A model of groundwater distribution will be obtained. And if you make several holes of different sizes in polyethylene, you will get a model of the penetration of upper waters into the underlying horizons.

Similarly, groundwater reserves are formed where the impervious layer creates depressions. Underground rivers are formed from higher to lower depressions. In places where the waterproof layer is interrupted, the upper waters descend to the lower level.

In the form of a picture it can be represented like this:

Now about where groundwater comes from.

Main source: rain. Rain falls and soaks into the ground. Water penetrates through the loose upper loose layers of soil and accumulates in the depressions of the upper waterproof layer of the earth. This type of water is called "overwater". It depends heavily on the weather - if it rains often, there is water. If it rains less often, there is little or no water. This is also the most contaminated layer of underground water, since filtration through the ground was minimal, and the water contains everything - petroleum products, fertilizers, pesticides, etc. and so on. The depth of this type of water is generally from 2 to 10 meters.

Further, where the upper impervious layer breaks, rainwater enters lower aquifers. Their number is different, the depth of their occurrence is also very different. So, the upper limit starts from 30 meters and can reach 300 and deeper. By the way, for example, in Ukraine, private individuals are prohibited from using water deeper than 300 meters, since this is the country’s strategic reserve.

An interesting pattern is that the deeper the aquifer is located, the less often it contains places of connection with the upper layers. For example, in the Sahara Desert they use groundwater that fell underground in Europe. Another pattern is that the deeper the water, the cleaner it is and the less dependent it is on precipitation.

It is often believed that groundwater is located in voids. This happens, but mostly groundwater is a mixture of sand, gravel, other minerals and a lot of water.

It was said where groundwater comes from and how it moves, but it was not said where it goes. And they either disappear even deeper underground, or pour out to the surface in the form of springs, springs, geysers, springs and other similar phenomena. So, for example, the Dnieper originates from underground somewhere in Belarus. Near Cape Aya (Crimea, not far from Sevastopol), there is a source of fresh water flowing into the sea. I haven’t seen it myself (it’s kept secret:), but a diver told me: you dive with a bottle, open it underwater with the neck down, fresh water fills in.

In addition to natural types of groundwater outlets, there are also artificial ones. These are wells. And such an interesting phenomenon as artesian water is associated with wells. A long time ago, in France, in Artez, they drilled a well in search of water. And water began to flow from the well like a fountain. That is, artesian waters are waters that rise from underground without the help of pumps. There are few such cases, most often there are free-flow wells.

So, like everything in nature, groundwater has a beginning, a change and an end - it falls underground with rain, travels underground from layer to layer and eventually pours out to the surface.

The underground water cycle, so to speak :)

The volume of groundwater exceeds the volume of surface water on land. Water in the earth's crust can be found not only in liquid form, but also in gaseous form and in the form of ice. Water turns into ice in frozen rocks.

The reason for the formation of groundwater is the seepage of atmospheric precipitation through the rocks of the earth's crust. There are rocks that allow water to pass through, and there are those that do not. The former are called water-permeable, and the latter water-resistant.

Rainwater that falls on the surface of the earth seeps through permeable layers until it encounters a waterproof layer. As a result, just above the aquifer layer, rocks are saturated with water and turn into aquiferous rocks.

Rocks permeable to water include sand, pebbles, gravel, limestone, sandstone, and shale. These rocks are either loose or have cracks. Clays and hard rocks that do not have cracks are waterproof.

Water underground flows the way the surface is inclined - from higher places to lower ones.

Groundwater can be groundwater or interstratal. Groundwater is located closer to the surface of the earth, just below the permeable layers. Interstratal layers are located deeper, between water-resistant layers. Water gets here in those places where their aquifers come to the surface. This happens, for example, in river beds.