Groundwater. Types of aquifers and determination of groundwater levels

Concept in geology

As a geological concept, the groundwater level is an arbitrary line below which the rock is completely saturated with water. After rain or snow melts, a large amount of water goes underground through pores in the soil. The level at which this water stops, since all the pores below are already filled with it, is the level of groundwater in its pure form.

The depth of this level largely depends on the terrain, as well as the presence of a river or lake nearby. In mountainous areas, the depth of groundwater can exceed 100 m, while in swampy lowlands it can become 1-2 m, and in some places only a few centimeters from the surface.

The groundwater level is not a static indicator, but can fluctuate depending on the time of year and the intensity of precipitation, and these fluctuations can be quite significant and reach several meters.

The lowest groundwater level is usually observed in winter.

It is in winter that it enters the ground minimal amount water. Frozen soil becomes impervious to precipitation. And the precipitation itself falls overwhelmingly in the form of snow, which does not melt until the spring warmth.

If we move away from the scientific definition, the groundwater level is the layer of water that is closest to the surface of the earth and is separated from the lower aquifers by a layer of rock or clay soil that prevents this water from seeping deeper.

It is clear that such a definition is imprecise, since geology distinguishes three types of groundwater:

• perched water, the depth of which is 2-3 m from the surface and which tends to disappear in winter and in dry weather;
• Gravity groundwater is the layer of water that lies underground above the first impervious layer. The level of such waters depends entirely on atmospheric precipitation and remains relatively stable, since there is no pressure in this layer of water;
• artesian water is a layer of water that is located between two impermeable layers. If you break through the upper water-resistant layer, then water from this layer will rise upward under pressure. Water from this aquifer is used to construct artesian wells.

But since it is groundwater that gives builders the most trouble when constructing pits for foundations and basements, it is by this layer that the groundwater level is determined. Therefore, for practical work this definition of groundwater level is quite suitable.

Groundwater

The construction of any structure that requires the construction of a foundation must begin with determining the groundwater level. There is a pattern: the higher the groundwater is located, the lower the bearing capacity of the soil becomes.

In some cases, it is better to abandon construction. For example, if between the waterproof layer and the soil surface there is a layer of fine-grained sand mixed with silt particles, then when groundwater enters it, it turns into floating material. If there is a layer of clay shale at this level, then when water gets into it, it softens and loses stability.

It is generally accepted that if groundwater is found at a depth of less than 2 m, then this high level groundwater. At this level, it is better to refuse any construction that requires the construction of a deep trench or foundation pit, since the costs of constructing a zero cycle will be disproportionately high. After all, in this case, groundwater will simply flood the dug pit, and it will be impossible to fill the foundation.

Even if you pump out the water and make reliable waterproofing, even then the problem is not completely eliminated. These measures are only a short time will give the necessary effect of lowering the groundwater level.

But the groundwater itself will not go away and after a short time will restore its original level, as a result of which the foundation or basement will be flooded.

That is why in construction there is a rule that from the base of the foundation to the occurrence of groundwater there must be a distance exceeding 0.5 m. Therefore, the groundwater level must be determined before the start of construction.

Level determination

There are several ways to determine the groundwater level. But there is general rule: measurements need to be taken in early spring, immediately after the snow melts, because during this period the groundwater levels are at their maximum.

The simplest, but at the same time the most accurate and effective method- determine it by the water level in the wells located near the site. Water in the depths of the well comes only from groundwater, therefore, by the distance from the top of the well to the water surface, you can accurately determine at what distance from the surface they are located. For a more accurate picture, it is better to carry out such measurements not in one, but in 2-3 wells.

The second method, which is often used in the construction of private houses, especially if there are no dug wells nearby, is drilling test wells. With this method, an ordinary garden auger is used as a working tool. With this drill, 3-4 test wells are drilled around the perimeter of the construction site to a depth of 2-2.5 m. If water does not appear in these wells for 1-2 days, this means that it is deep enough; during construction it can not be fear.

There are also old ways. For example, a piece of wool needs to be thoroughly washed and dried. Then you need to take this scrap, raw egg(necessarily freshly picked, still warm) and clay pot.

In a place chosen on the site, you need to carefully remove the turf, put wool on the bottom of the formed hole, put an egg on the wool and cover them with an inverted clay pot. The top of the pot should be carefully covered with a piece of removed turf.

This kind of indicator will show the results the next morning, as soon as the sun will rise. You need to remove the turf, carefully remove the pot and pay attention to the dew that has formed under it. If there is dew not only on the wool, but also on the egg, then you can be sure that the water in this place is not very deep. If dew has formed only on the wool, but not on the egg, then it is at a decent depth. If, as a result, both the wool and the egg remain dry, then the water in this place is very deep, if there is any.

It is possible to determine that groundwater is close without conducting earthworks Location on. It is enough just to examine it carefully. If during a drought, thick green-emerald grass or a lot of moss grows on your site, and in the evenings you constantly see fogs over your site, although there is no river or lake near the site, then with a high probability it can be said that the waters are high.

You can also decide by the plants growing on the site. If hemlock, nettle, horse sorrel, foxglove, sedge, and reeds predominate among them, then the distance from the soil surface to the water is probably no more than 3 m. And if wormwood or licorice predominate, then you will not find moisture in less than 4-5 m.

So, there are many ways to determine the depth of groundwater. They are not all equally accurate, but general idea With their help, you can draw up information about the aquifers on your site. If you want to know the exact picture, then order a special geological survey of your site. After all accurate map groundwater can only be compiled with the help of well drilling performed by professionals.

Most houses have a centralized water supply. But due to the distance from settlement or for other reasons in some country cottages and dachas it is not available. The owners have to drill a well or equip a well.

To determine the horizon of the source, you have to seek the help of a professional. His services will not be cheap. The depth of groundwater can be determined independently. At the same time, it will be possible to significantly save money on the family budget for the arrangement of a water supply system. To do this, several simple approaches are used. Before starting work, it is necessary to consider the entire procedure in detail.

Type of groundwater

The depth of the groundwater level varies. The type of source depends on this indicator. It is taken into account when installing a water supply system. The layer closest to the surface is called perch. It is located at a depth of 2-3 m. This source is applicable only for technical purposes.

Next follow with a free surface. There are also interstratal free-flow and pressure artesian springs. The last variety is considered the purest and most drinkable. The chemical composition and quality are the highest among all sources. The layer of water can pass through sandy or gravel.

Features of groundwater

Before determining the depth of groundwater, it is necessary to learn about its characteristics. First of all, their location is influenced by the type of terrain. In the steppe, where the surface is flat, the layers lie evenly. At any point their depth is the same.

But in the presence of potholes and slides, the water is also located in a curved manner. Experts recommend taking into account such terrain features when creating a well. If water is needed for technical purposes, you can use the first layer. He comes closer than others to the surface.

For drinking purposes, it is necessary to use water from at least the second layer. If the area is hilly, it is better to drill a well on a hill. In this case, the soil layer will better filter such water.

In swampy areas, groundwater can approach the surface at a depth of only 1 m. When developing a well, you need to be prepared for this.

Groundwater of the Moscow region

Owners of their own homes should inquire about the characteristics of the layers of underground sources. For example, the depth of groundwater in the Moscow region is characterized by heterogeneity.

There are 5 main layers here. They are all unequally located and have different powers. The first three layers are characterized by low pressure. They are used for technical purposes. Water discharge occurs in small streams and rivers. This groundwater is replenished in the spring when the snow begins to melt.

Dolomite and limestone rocks contain the two lower layers. Their depth is about 100 m. These springs are suitable for drinking purposes. In the Moscow region, the central water supply is laid precisely from these sources.

Preparing for measurement

Moistening conditions and the depth of groundwater are quite closely related. When planning to take measurements, you need to choose the right time. There should be no drought or prolonged rains. All weather conditions affect the measurement results.

To determine the depth of groundwater, you must use one of simple ways. To do this, you need to prepare all available tools and materials. The tools you will need are a regular drill and a tape measure. You also need to prepare a long rope.

In addition to tools, you need certain chemical elements. This is sulfur and copper sulfate. Different techniques will require one or another available means.

Drilling

Determining the depth of groundwater is possible using several methods. The most reliable of them is drilling. In this case, it is possible to accurately determine how deep the underground source is, and whether there are any significant obstacles in the form of stones on the way to it.

A regular factory drill will do the job. If desired, additional blades are welded onto its blades. The tool cuts into soft ground. It is brought to the surface along with the soil. To soften the soil, water it.

Using a threaded, bushing connection, the drill is fastened to the pipes in order to go deep to the desired level. Next, measurements are taken using a rope. The well should be 0.5-1 m deeper than the paper. Attach paper to the rope and check at what level it gets wet.

Application of chemicals

If you don’t want to drill a well, there is an easier way to find out the depth of groundwater. To do this, dig a hole in the intended location with a shovel. It can be about 0.5 m deep. You need to install a clay pot in it.

In a vessel, mix quicklime, sulfur and copper sulfate in equal proportions. Next, the hole is buried and left for a day. After this, the pot is taken to the surface and weighed. The heavier it becomes, the closer the groundwater comes to the surface. This method is not accurate enough, but it has been used since ancient times. Only now it has been improved.

Barometer

Another reliable way to determine the depth of groundwater in a given area is to use a barometer. However, it should be noted that its use requires the presence of a reservoir in the area.

If there is one, you can start measuring. Each barometer division corresponds to 1 m of depth. First, you need to approach the reservoir with the device. Here the barometer readings are recorded.

This method is also not very accurate. The error distorts the real picture. But general principle you can understand.

Folk way

The depth of groundwater can be determined traditional methods. First of all, you need to pay attention to the vegetation. Where the source comes close to the surface, it is greener and brighter. Reeds, ivy, forget-me-nots and other moisture-loving representatives of the flora love to grow in such places.

The folk approach assumes the following. It is necessary to wash the wool in a soapy solution and dry it well. Vegetation is removed from the intended place for the experiment.

Wool is laid out on the ground. They lay on it a raw egg and cover everything with a frying pan. In the morning the result of the experiment is evaluated. If the egg and wool bedding are covered with drops of dew, it means the water is close to the surface. But this procedure must be carried out in dry weather.

Having considered how the depth of groundwater is determined, you can take measurements yourself. Depending on the chosen method, you can get a more accurate or approximate result. You can do all the work yourself. This will significantly save your family budget.

Groundwater - first from earth's surface, sustained in distribution, an aquifer located on the first aquifer from the surface. Aquifers are porous sedimentary rocks (sands, sandy loams, loams), fractured dense sedimentary or halogen rocks; waterproof (waterproof) - clays and dense sedimentary or hypogene massive rocks. There are also relative aquicludes with low water permeability, over which water can accumulate.

The areas of recharge and distribution of groundwater usually coincide. With a level bedding of aquitards, relatively thick aquifers can form; with a concave bedding, a groundwater pool is formed, and with an inclined bedding, their flows can arise.

The space between the earth's surface and the groundwater horizon is called the aeration zone. It contains moisture that saturates the capillary pores and has no connection with groundwater, which is called suspended (capillary) moisture, characteristic of soils. In the aeration zone, perched waters are often found - aquifers of small thickness and length located above aquitards. In addition to gravitational (free) and capillary moisture, there are sorbed, film (thin films several molecules thick) and loosely bound (thick water films around soil particles) moisture.

Sorbed and film moisture is inaccessible to plants due to its strong connection with soils; other forms are available. The mobility of moisture increases as its adhesion to particles weakens: sorbed moisture is almost immobile, film moisture is capable of slow movement under the influence of gravity. The moisture of the aeration zone and groundwater is dynamic: it evaporates, condenses, infiltrates, moving in the form of films, through capillaries, in the form of a ground flow, freezes and thaws. Depending on the influx or decrease of moisture, the groundwater level and the volumes of other forms of moisture fluctuate, and some forms transform into others.

Groundwater is formed mainly as a result of the infiltration of rain and melt water, which occurs frontally only on sandy rocks, or through so-called windows, usually confined to depressions in the relief. In porous rocks with temperature fluctuations a small amount of moisture (no more than 10–15%) is formed as a result of condensation from underground air. In some areas, groundwater can be of flow origin (inflow from the side) and deep - when rising (outpouring) from the depths of groundwater. Groundwater outlets to the surface in relief depressions or on slopes are called sources (springs, springs).

Close to the surface, groundwater is located in river valleys, where it can be very thick in thick sandy deposits. Distribution, proximity to the surface, and groundwater reserves increase with an increase in annual precipitation, a decrease in evaporation and outflow, and the presence of porous water-bearing rocks and good aquitards. On the contrary, a decrease in precipitation and increased drainage of the area are the main factors for lowering (deepening) the groundwater level and reducing its reserves.

The suitability of groundwater for water supply and use by animals is limited mainly by the amount of dissolved organic matter(swamp waters), salinity and anthropogenic pollution.
The map is based on the following hierarchy of groundwater characteristics.

The main characteristic of groundwater is the depth of groundwater from the earth's surface, shown in color. Depth determines their role in nature; it reflects the climatic and geological-geomorphological conditions of their formation, the processes of leaching of mobile components from rocks, evaporative concentration, the genesis and dynamics of groundwater.

Mineralization and chemistry of groundwater are shown together with shading and icons. They are determined by the quantity, salinity of rocks, evaporation, and the duration of the migration path.
Groundwater is also distinguished according to the degree of acidity and oxygen-gley content, which is determined by the presence of oxygen in the water and is associated with the intensity of water exchange (from intensive to stagnant), the abundance of decomposing organic matter, and the activity of microorganisms.

Groundwater is divided according to its phase state as follows: in non-permafrost areas, permanently liquid groundwater is common, in areas of continuous permafrost - seasonally melted water, in areas of disconnected permafrost with taliks - predominantly seasonally melted water, in areas of island permafrost, permanently liquid water predominates, but there are also seasonal meltwaters.

Further, the forms of groundwater are distinguished according to their host rocks and relief conditions: on the plains, loose sedimentary rocks with formation waters located in them predominate; In the mountains, dense rocks with fissure waters predominate; formation waters are also found in deluvial deposits.
Groundwater contours with different water properties are grouped into 12 provinces that reflect natural zoning groundwater. The degree of drainage of the territory is superimposed on the zonal patterns. Groundwater mountain systems non-permafrost areas are azonal.

Soil properties. The special conditions for the existence of groundwater in the strata of loose rocks force us, first of all, to dwell on some physical properties these soils. Among these properties, the porosity of rocks, their moisture capacity, capillary properties and water permeability are of particular importance.

Soil porosity. The ratio of voids in the soil to the volume of total dry soil is called soil porosity. Porosity is usually expressed as a percentage. It can be defined as follows: a vessel with a volume of 1 l need to be filled with dry sand. Then carefully pour water from a beaker into a vessel with sand until all the sand is completely saturated with moisture. Let's say that this required 250 cm 3

water. The ratio 250/1000 = 0.25, or 25%, will precisely determine the porosity of the sand we take.

The porosity of different loose rocks is far from the same. So, for coarse river sand the porosity is approximately 15-25%, for gravel - 35%, for clay - 50-55%, for peat soil - 80%, etc. Soil moisture capacity.

Their moisture capacity, i.e., the ability of the rock to retain this or that amount of water, largely depends on the porosity of the rocks. Dense rocks have the lowest moisture capacity, and loose clastic rocks have the highest, as can be clearly seen from the table below.

Capillary properties of soils. A huge role in the life of groundwater is played by the size and shape of those grains (or particles) that make up the clastic rock. The larger the grains, the larger the gaps between them, and vice versa (Fig. 98). And the size of the gaps determines the capillary properties of the rock. It is known from physics that the height of water rising in a capillary tube is inversely proportional to the diameter of the tube. So, for a tube with a diameter of 1 mm the height of water rise (at 15° C) is 0.29 cm,- 29 mm with a diameter of 0.1 A huge role in the life of groundwater is played by the size and shape of those grains (or particles) that make up the clastic rock. The larger the grains, the larger the gaps between them, and vice versa (Fig. 98). And the size of the gaps determines the capillary properties of the rock.- 2 mm

Experiments carried out on various soils (Fig. 99) showed that the height of water rise in soils depends on the size of the grain (or, more precisely, on the size of the gaps that form between these grains). Thus, the height of water rise in clastic rocks, the grain diameter of which ranges from 1 to 0.5 mm, equal to 1.31 mm for grains with a diameter of 0.2-0.1 A huge role in the life of groundwater is played by the size and shape of those grains (or particles) that make up the clastic rock. The larger the grains, the larger the gaps between them, and vice versa (Fig. 98). And the size of the gaps determines the capillary properties of the rock.- 4,82 mm for grains with a diameter of 0.1-0.05 cm,- 10,5 cm etc.

Different states of water in soils. Water in soils can be in three main states: solid, liquid and gaseous. Solid water can only be found at temperatures below 0°. She

motionless and in this case is of little interest to us. Much more important is liquid and gaseous water, which is in motion.

Liquid water in soils can be in the form of film and gravitational water.

Film water, as we have already had occasion to mention, it envelops every particle of the soil. The thickness of the water film depends on the moisture content of the rock, but has a limit that is determined by the magnitude of molecular forces. (The minimum film thickness is equal to the diameter of a water molecule). Film water moves, like liquid, but its movement does not depend on gravity. Film water is held by each soil particle with great strength and can only be removed with difficulty (eg by evaporation).

Gravity water unlike film, it does not fall within the radius of effective action of molecular forces, but moves down under the influence of gravity through the pores located between the grains (or particles) of the rock. The speed of movement of gravitational water is many times greater than the speed of film water. Gravity water moves towards the slope of the surface of the impermeable layer and only under the influence of hydrostatic pressure can it have an upward movement.

It goes without saying that gravitational water is of greatest interest to us, since it precisely constitutes the main mass of underground streams, lakes, springs and wells.

Gaseous water can only be found in soil pores (in the gaps between rock grains). In cases where water vapor saturates the “underground atmosphere,” the elasticity of water vapor in the gaps and pores of wet rock will depend only on temperature. The last circumstance has great importance

in the process of moistening the soil by condensation of water vapor coming from the air. According to observations made in the vicinity of Odessa by prof. A. F. Lebedev, the soil receives from 15 to 25% per year in the indicated way precipitation that falls here. This value is so significant that it deserves great attention. In deserts and semi-deserts at night the conditions for condensation of vapors in the soil are especially favorable. Thus, it has been proven that a significant part of groundwater is formed not only from precipitation, but also by direct condensation of water vapor from the air in the soil.

As if the transition between liquid and gaseous water in soils is water hygroscopic. Hygroscopic water surrounds each rock particle with a non-continuous layer of isolated molecules.

In cases where there are a lot of water molecules, they merge into a continuous film, the thickness of which is equal to the diameter of one molecule.. This is the so-called maximum hygroscopicity, which is observed when relative humidity"underground atmosphere" at 100%. The transition of water vapor into hygroscopic water is accompanied by the release of heat. Hygroscopic water moves from some layers of the soil and others, only passing into a vapor state.

Vaporous and hygroscopic water is of particular interest for soil science.

Origin of groundwater. For a long time, man has widely used groundwater for economic purposes, and therefore, naturally, a very long time ago he began to think about its origin. The first “theories” of the origin of groundwater were purely fantastic. It was said, for example, that the earth “gives birth” to water, that there are special inexhaustible lakes in the earth from where water comes to the surface. There was even an opinion that ocean water penetrates into the soil of continents and produces groundwater. The latter view was especially widespread and remained in science almost until the beginning XVIII

V. Along with fantastic hypotheses, there were explanations that approached the truth. Thus, according to Aristotle, rain and snow waters are partly evaporated and partly absorbed rocks The first “theories” of the origin of groundwater were purely fantastic. It was said, for example, that the earth “gives birth” to water, that there are special inexhaustible lakes in the earth from where water comes to the surface. There was even an opinion that ocean water penetrates into the soil of continents and produces groundwater. The latter view was especially widespread and remained in science almost until the beginning and form sources. The Roman Marcus Vitruvius Pollinus came even closer to the truth, who said that groundwater is formed everywhere from atmospheric precipitation.

However, only at the beginning V. these explanations began to penetrate European science.V. (1686) the French physicist Marriott was the first, based on careful observations, to prove that groundwater comes from precipitation seeping into the ground. Mariotte's conclusions, supplemented and clarified by subsequent researchers, became more and more firmly established in science and can now be simplifiedly expressed in the following form. Water falling onto land in the form of precipitation, partly flows into streams and rivers, partly evaporates and partly seeps into the ground. Water that has penetrated into the soil reaches the waterproof layer, and here its movement in depth stops. Accumulating on the surface of the waterproof layer, it abundantly permeates the overlying rocks and forms the so-called aquifer. This theory, which explains the origin of groundwater through the seepage of atmospheric precipitation into the depths of the earth, is called

infiltration. However, this method of origin of groundwater cannot be considered the only one. The works of our Russian scientists (A.F. Lebedev and others) have proven that groundwater can also be obtained by condensation of water vapor directly in the soil. Groundwater formed by condensation of atmospheric water vapor directly in the soil is called

condensation

We have already said that groundwater, having reached the aquifer, stops its movement in depth and, collecting on the surface of the aquifer, forms the so-called aquifer or aquifer. The aquifer from below is limited by the surface of the aquifer layer, the shape of which can be very different (Fig. 101). The upper surface of the aquifer is usually flat and is called the “mirror” of groundwater. We can see this “mirror” in any well. Strictly speaking, the groundwater table has a horizontal surface only in small, relatively homogeneous spaces. On large areas, with differences in species, differences geological structure and relief, the horizontality of the mirror is to a greater or lesser extent disrupted. Let's take

The reasons for this are quite complex: greater compaction of sands under dune crests creates different capillarity conditions, which contributes to higher groundwater levels; Different degrees of evaporation also have an impact, etc. We can see approximately the same thing, only in more complex forms, in other examples (Fig. 103). The latter must be taken into account both when looking for places to dig wells, and especially when constructing underground storage facilities, cellars, dugouts, etc.

Movement of groundwater. In cases where the aquifer layer has the shape of a vast concave basin, groundwater, filling the basin, takes on the character underground lake. It is clear that a number of wells dug in the area of ​​such a lake will have a mirror at the same level (Fig. 104). But much more often the waterproof layer is inclined in one direction or another. Under the conditions we noted, groundwater, obeying the force of gravity, slowly moves towards the slope, forming underground stream(Fig. 105). A number of wells dug along the stream have mirrors at different depths. It is clear that the more wells there are, the more accurately we can determine the direction and nature of the underground flow. In areas where there are no wells or their number is insufficient, boreholes are plugged, pipes are lowered into the wells, and the nature of the underground flow is determined by the height of the water in the pipes.

When studying underground flows, it is important to determine not only the direction, but also the speed of the flow. To determine the flow rate, ordinary table salt is used. It is thrown into a well at the top of an underground stream, and then it is determined how long it takes for salt water to appear in other, lower wells. Silver nitrate solution (AgNO 3 ) makes it possible to notice even an insignificant admixture of sodium chloride in the water of the wells being examined (a clear white precipitate of silver chloride is obtained). Sometimes to determine

To control the speed of the underground flow, bacteria are used instead of salt, which, due to their small size, easily pass through the pores of the soil. The speed of underground flows depends on the angle of inclination of the aquifer and even more on the nature of the soil. Thus, in fine sands the speed of the underground flow reaches approximately 1 m per day, in coarse sands 2-3 and even 5 m. In the thickness of pebbles, crushed stone and along cracks in hard rocks, underground flows move much faster, several kilometers per day. In clays, on the contrary, the rate of water penetration even deep does not exceed 20 cm per year, which allows us to consider the clay practically waterproof.

Sources. Springs are formed where underground streams exit to the earth's surface. Sources (keys, springs) can be very different in nature. In some cases these are barely noticeable keys, sometimes only moistening the soil. The locations of such sources can be identified by the nature of the vegetation (sedge, reed, horsetail, mosses). In other cases, these are large springs, the water of which is knocked out and immediately forms a significant stream. However, there are often cases when even large sources do not come to the surface, but continue to flow in the soil very close to the earth's surface. Such hidden sources can be detected by thickets of reeds, reeds and other aquatic plants. Indeed, if you dig a small depression in such a place, it fills with water quite quickly.

From ancient times to the present day, sources have been widely used by humans. This is completely understandable, for they provide the purest and healthiest water.

To protect the source from contamination, it is secured with a wooden frame, masonry or concrete structures.

In places where the main suppliers of water are springs, they are received in special indoor pools, from where they are sent through pipes to the places of their use. We can see examples of such complex structures on the southern coast of Crimea. Large springs that provide water to supply cities are used in approximately the same way, only the structures here are even more complex. The feeding area of ​​such sources is fenced off with a fence where livestock cannot enter. This measure guarantees healthy water sources. Underground streams, before reaching the earth's surface,

often do large and

1) difficult paths underground. Here, first of all, a distinction is made between downward and upward sources (Fig. 106). Based on water temperature, sources are divided into: ordinary,

whose temperature is approximately equal to the average

2) annual temperature given

3) places, cold,

The closer the underground flow is to the earth's surface, the more strongly it is affected by air temperature fluctuations. Thus, annual fluctuations reach 5-10°, and in some cases more.

Cold springs are rare, and then mainly in the mountains, where they are fed by meltwater from snow and glaciers.

Warm springs are most often associated with places of recent volcanism.

A special place is occupied by the so-called artesian wells. Boreholes drilled to great depths provide outlets for deep-lying groundwater (Fig. 107). These waters, being under strong hydrostatic pressure, often erupt in fountains and produce a lot of water (the strongest - up to 10-15 m 3 in a minute).

Mineral springs. During its underground movements, groundwater encounters various substances on its way that can dissolve in water. K such substances include limestones, gypsum, table salt, carbon dioxide, hydrogen sulfide and many others. The most common types of soil found are limestone (CaCO3) and gypsum (CaSO 4 ). Water containing gypsum or lime in the solution almost does not change the taste, but differs in that it dissolves soap poorly (does not lather well). People in the hostel call this kind of water “hard.” When boiling, lime is released from the water and forms the so-called “scale” on the walls of the vessel, which is well known to everyone.

Groundwater, coming into contact with saline soils (in dry steppes and deserts) or with deposits of table salt, dissolves this salt and acquires a salty taste. Salty springs and wells are very common and are good indicators of the salt content in the soil layers of a particular area. Examples include salty springs and wells of Solikamsk, Berezniki, Iletskaya Zashchita and many others.

Iron salts, sodium carbonate, carbon dioxide, hydrogen sulfide, etc. are often dissolved in groundwater.

The amount of salts and gases dissolved in water may vary. In cases where there are few dissolved salts and gases, the taste and smell of water does not change and the water in these cases is called fresh. In the same cases when solutions at 1 l waters contain at least 1 G salts or gases that give water different tastes and odors - water is called mineral, springs that produce mineral water - mineral springs. Depending on the chemical composition mineral springs they are divided into groups:

Groundwater in permafrost conditions. Beyond the Arctic Circledepth 50-100 cm Usually there is a frozen horizon, impermeable to water. Under these conditions, the aquifer is located above the frozen horizon, i.e., at the very surface of the soil. Such a high groundwater position creates exceptional favorable conditions for swamping, which is observed in the tundra on a wide scale.

However, permafrost horizons are found not only in the Arctic Circle. Thus, in Siberia (beyond the Yenisei) they are known south of the 60th and even 50th parallel. Permafrost in Siberia occurs at different depths, but most often at a depth of 2-4 m. Thus, the groundwater here also lies very shallow, which naturally leads to swampiness even with very little precipitation (Fig. 108).

Peat mosses, sedges, dwarf birches and willows, larches and gnarled birches typically grow in wetlands. By the distribution of this vegetation, in many cases one can judge the presence of permafrost in a given place. IN winter time

When soils freeze from above, groundwater becomes sandwiched between two impermeable horizons. This position of groundwater leads to a number of very peculiar phenomena. Thus, on slopes, especially in their lower parts, water experiences enormous hydrostatic pressure, as a result of which water breaks through the frozen soil with cracks and pours out. Due to the fact that these phenomena occur during severe frosts, water pouring out of cracks freezes. The outpouring of water and its subsequent freezing is repeated several times, which leads to an increase in the thickness of the ice to 4-5 meters or more. As a result, huge ice mounds grow, known as aufeis

(Fig. 109). Ice dams are particularly damaging to roads. Along the Amur-Yakut highway alone (728 km) for the winter of 1927-1928. Over a hundred aufeis have been registered. Of these, 24 aisles had areas greater than 1 km 2.

The thickness of the ice reaches 3-5 meters or more. Due to the fact that soil freezing (from above) gradually increases towards the end of winter, the amount of ice accumulation also increases. According to observations made in the area of ​​the same Amur-Yakutsk highway, 110 aufeis formed in December, 150 in January, 350 in February, 575 in March, 500 in April. (Not a single one formed in May.)

K At the end of winter, the ground above freezes so much that the upper frozen layer often combines with the lower one, and the groundwater completely freezes. In the northern regions this phenomenon occurs earlier, in the southern regions later. Due to continuous freezing, the water in springs and wells dries up, which creates great difficulties for residents. It is also clear that the nutrition of rivers in winter period in areas of permafrost distribution it decreases very sharply. In the summer

On the contrary, after every heavy rain the rivers overflow. Groundwater of volcanic areas. Solidified lavas, due to their fracturing and porosity, allow water to pass through well. Volcanic tuffs, consisting of loose eruption products, allow water to pass through even better. Due to this circumstance precipitation

, even with a large number of them, are often completely absorbed by volcanic formations and do not produce surface drainage. As a result, the surface of lava sheets usually looks like a lifeless desert, devoid of water and vegetation. The dark or even black color of the lavas enhances the bleakness of the picture opening before the viewer.

Water penetrating into the thickness of volcanic rocks finally reaches the waterproof underlying rocks and forms significant accumulations of groundwater here. With the great power of volcanic formations, groundwater is very deep, and in order to get to it, you have to dig wells in

tens of meters deep. These groundwaters usually appear along the edges of lava plateaus in the form of clean, sometimes very rich springs... Juvenile waters. Magma penetrating into the thickness earth's crust, releases a large amount of water vapor, which, condensing underground, gives the so-called

juvenile water. Juvenile waters form springs that are especially widespread in areas of recent volcanism. Juvenile springs are most often hot or warm and often mineral. A special place among hot springs is occupied by geysers. Geysers periodically boil violently and emit jets hot water

Groundwater is that which is located at a depth of up to 25 meters from the surface of the earth. It is formed due to various reservoirs and precipitation in the form of rain and snow. They seep into the ground and accumulate there. Groundwater differs from underground water in that it has no pressure. In addition, their difference is that ground ones are sensitive to changes in the atmosphere. The depth at which groundwater can be found does not exceed 25 meters.

Ground water level

Groundwater is located in close proximity to the surface of the earth, however, its level can vary depending on the terrain and time of year. It will rise in high humidity, especially when walking heavy rains and the snow melts. And the level is also affected by nearby rivers, lakes, and other bodies of water. During drought periods, the groundwater level decreases. At this time he is considered the lowest.

Groundwater levels are divided into two types:

• low when the level does not reach 2 meters. Buildings can be built on such terrain;
• high - level over 2 meters.

If you make incorrect calculations of the depth of groundwater, this can lead to flooding of the building, destruction of the foundation and other problems.

Groundwater occurrence

To find out exactly where groundwater lies, you can first make simple observations. When the depth of occurrence is shallow, the following signs will be visible:

• the appearance of fog in the morning in certain areas of the earth;
• a cloud of midges “hovering” above the ground in the evening;
• an area where moisture-loving plants grow well.

And you can also use another folk way. Pour some desiccant material (for example, salt or sugar) into a clay pot. Then weigh it carefully. Wrap it in a piece of cloth and bury it in the ground to a depth of 50 centimeters. A day later, open it up and weigh it again. Depending on the difference in weight, it will be possible to know how close the water is to the surface of the earth.

You can also find out about the presence of groundwater from a hydrogeological map of the area. But the most effective way is exploratory drilling. The most commonly used method is the core method.

Characteristics

When groundwater appears naturally, then it is suitable for drinking. The pollution of the liquid is influenced by the villages and towns located nearby, as well as the proximity of the water to the surface of the earth.

Groundwater is divided into types that differ in their mineralization, so they are as follows:

• fresh;
• slightly salty;
• salty;
• salty;
• pickles.

The hardness of groundwater is also distinguished:

• general. It is divided into five types: very soft water, soft ground water, moderately hard water, hard water, very hard ground water;
• carbonate;
• non-carbonate.

In addition, there is groundwater, which contains a lot of harmful substances. Such water is usually found near landfills with chemical or radioactive waste.

Disadvantages of groundwater

Groundwater also has its disadvantages, for example:

• various microorganisms (and pathogenic ones too) in the water;
• rigidity. This affects the reduction in the lumen of the pipes through which water is supplied, since specific deposits are deposited on them;
• turbidity, due to the fact that the water contains certain particles;
• impurities in groundwater various substances, microorganisms, salts and gases. All of them are capable of changing not only the color, but also the taste of water, its smell;
• a large percentage of minerals. It changes the taste of water, causing a metallic taste;
• seepage of nitrates and ammonia into groundwater. They are very dangerous to human health.

To make water much better, it needs to be carefully treated. This will help rid it of various contaminants.