28.07.2015

Fluctuations in river runoff and criteria for its assessment. River runoff is the movement of water in the process of its circulation in nature, when it flows down the river channel. River flow is determined by the amount of water flowing through the river channel for a certain period of time.
Numerous factors influence the flow regime: climatic - precipitation, evaporation, humidity and air temperature; topographic - terrain, shape and size of river basins and soil-geological, including vegetation cover.
For any basin, the more precipitation and less evaporation, the greater the flow of the river.
It has been established that with an increase in the catchment area, the duration of the spring flood also increases, while the hydrograph has a more elongated and “calm” shape. In easily permeable soils, there is more filtration and less runoff.
When performing various hydrological calculations related to the design of hydraulic structures, reclamation systems, water supply systems, flood control measures, roads, etc., the following main characteristics of the river flow are determined.
1. Water consumption is the volume of water flowing through the considered section per unit of time. The average water consumption Qcp is calculated as the arithmetic average of the costs for a given period of time T:

2. Flow volume V- this is the volume of water that flows through a given target for the considered period of time T

3. Drain module M is the flow of water per 1 km2 of catchment area F (or flowing from a unit catchment area):

In contrast to the water discharge, the runoff modulus is not associated with a specific section of the river and characterizes the runoff from the basin as a whole. The average multi-year runoff module M0 does not depend on the water content of individual years, but is determined only by the geographical location of the river basin. This made it possible to zonate our country in hydrological terms and to build a map of isolines of average long-term runoff modules. These maps are given in the relevant regulatory literature. Knowing the catchment area of ​​a river and determining the value M0 for it using the isoline map, we can determine the average long-term water flow Q0 of this river using the formula

For closely spaced river sections, the runoff moduli can be taken constant, i.e.

From here, according to the known water discharge in one section Q1 and the known catchment areas in these sections F1 and F2, the water discharge in the other section Q2 can be established by the ratio

4. Drain layer h- this is the height of the water layer, which would be obtained with a uniform distribution over the entire basin area F of the runoff volume V for a certain period of time:

For the average multi-year runoff layer h0 of the spring flood, contour maps were compiled.
5. Modular drain coefficient K is the ratio of any of the above runoff characteristics to its arithmetic mean:

These coefficients can be set for any hydrological characteristics (discharges, levels, precipitation, evaporation, etc.) and for any periods of flow.
6. Runoff coefficient η is the ratio of the runoff layer to the layer of precipitation that fell on the catchment area x:

This coefficient can also be expressed in terms of the ratio of the volume of runoff to the volume of precipitation for the same period of time.
7. Flow rate- the most probable average long-term value of runoff, expressed by any of the above runoff characteristics over a multi-year period. To establish the runoff norm, a series of observations should be at least 40 ... 60 years.
The annual flow rate Q0 is determined by the formula

Since the number of observation years at most water gauges is usually less than 40, it is necessary to check whether this number of years is sufficient to obtain reliable values ​​of the runoff norm Q0. To do this, calculate the root mean square error of the flow rate according to the dependence

The duration of the observation period is sufficient if the value of the root-mean-square error σQ does not exceed 5%.
The change in annual runoff is predominantly influenced by climatic factors: precipitation, evaporation, air temperature, etc. All of them are interconnected and, in turn, depend on a number of reasons that are random in nature. Therefore, the hydrological parameters characterizing the runoff are determined by a set of random variables. When designing measures for timber rafting, it is necessary to know the values ​​of these parameters with the necessary probability of exceeding them. For example, in the hydraulic calculation of timber rafting dams, it is necessary to set the maximum flow rate of the spring flood, which can be exceeded five times in a hundred years. This problem is solved using the methods of mathematical statistics and probability theory. To characterize the values ​​of hydrological parameters - costs, levels, etc., the following concepts are used: frequency(recurrence) and security (duration).
The frequency shows how many cases during the considered period of time the value of the hydrological parameter was in a certain interval. For example, if the average annual water flow in a given section of the river changed over a number of years of observations from 150 to 350 m3/s, then it is possible to establish how many times the values ​​of this value were in the intervals 150...200, 200...250, 250.. .300 m3/s etc.
security shows in how many cases the value of a hydrological element had values ​​equal to or greater than a certain value. In a broad sense, security is the probability of exceeding a given value. The availability of any hydrological element is equal to the sum of the frequencies of the upstream intervals.
Frequency and availability can be expressed in terms of the number of occurrences, but in hydrological calculations they are most often determined as a percentage of the total number of members of the hydrological series. For example, in the hydrological series there are twenty values ​​of average annual water discharges, six of them had a value equal to or greater than 200 m3/s, which means that this discharge is provided by 30%. Graphically, changes in frequency and availability are depicted by curves of frequency (Fig. 8a) and availability (Fig. 8b).

In hydrological calculations, the probability curve is more often used. It can be seen from this curve that the greater the value of the hydrological parameter, the lower the percentage of availability, and vice versa. Therefore, it is generally accepted that years for which the runoff availability, that is, the average annual water discharge Qg, is less than 50% are high-water, and years with Qg more than 50% are low-water. A year with a runoff security of 50% is considered a year of average water content.
The availability of water in a year is sometimes characterized by its average frequency. For high-water years, the frequency of occurrence shows how often years of a given or greater water content occur on average, for low-water years - of a given or less water content. For example, the average annual discharge of a high-water year with 10% security has an average frequency of 10 times in 100 years or 1 time in 10 years; the average frequency of a dry year of 90% security also has a frequency of 10 times in 100 years, since in 10% of cases the average annual discharge will have lower values.
Years of a certain water content have a corresponding name. In table. 1 for them the availability and repeatability are given.

The relationship between repeatability y and availability p can be written as follows:
for wet years

for dry years

All hydraulic structures for regulating the channel or flow of rivers are calculated according to the water content of the year of a certain supply, which guarantees the reliability and trouble-free operation of the structures.
The estimated percentage of provision of hydrological indicators is regulated by the "Instruction for the design of timber rafting enterprises".
Provision curves and methods of their calculation. In the practice of hydrological calculations, two methods of constructing supply curves are used: empirical and theoretical.
Reasonable calculation empirical endowment curve can only be performed if the number of observations of the river runoff is more than 30...40 years.
When calculating the availability of members of the hydrological series for annual, seasonal and minimum flows, you can use the formula of N.N. Chegodaeva:

To determine the availability of maximum water flow rates, the S.N. dependence is used. Kritsky and M.F. Menkel:

The procedure for constructing an empirical endowment curve:
1) all members of the hydrological series are recorded in decreasing order in absolute value;
2) each member of the series is assigned a serial number, starting from one;
3) the security of each member of the decreasing series is determined by formulas (23) or (24).
Based on the results of the calculation, a security curve is built, similar to the one shown in Fig. 8b.
However, empirical endowment curves have a number of disadvantages. Even with a sufficiently long observation period, it cannot be guaranteed that this interval covers all possible maximum and minimum values ​​of the river flow. Estimated values ​​of runoff security of 1...2% are not reliable, since sufficiently substantiated results can be obtained only with the number of observations for 50...80 years. In this regard, with a limited period of observation of the hydrological regime of the river, when the number of years is less than thirty, or in their complete absence, they build theoretical security curves.
Studies have shown that the distribution of random hydrological variables most well obeys the type III Pearson curve equation, the integral expression of which is the supply curve. Pearson obtained tables for constructing this curve. The security curve can be constructed with sufficient accuracy for practice in three parameters: the arithmetic mean of the terms of the series, the coefficients of variation and asymmetry.
The arithmetic mean of the terms of the series is calculated by formula (19).
If the number of years of observations is less than ten or no observations were made at all, then the average annual water discharge Qgcp is taken equal to the average long-term Q0, that is, Qgcp = Q0. The value of Q0 can be set using the modulus factor K0 or the sink modulus M0 determined from the contour maps, since Q0 = M0*F.
The coefficient of variation Cv characterizes the runoff variability or the degree of its fluctuation relative to the average value in a given series; it is numerically equal to the ratio of the standard error to the arithmetic mean of the series members. The value of the Cv coefficient is significantly affected by climatic conditions, the type of river feeding, and the hydrographic features of its basin.
If there are observational data for at least ten years, the annual runoff variation coefficient is calculated by the formula

The value of Cv varies widely: from 0.05 to 1.50; for timber-rafting rivers Cv = 0.15...0.40.
With a short period of observations of the river runoff or in their complete absence the coefficient of variation can be established by the formula D.L. Sokolovsky:

In hydrological calculations for basins with F > 1000 km2, the isoline map of the Cv coefficient is also used if the total area of ​​lakes does not exceed 3% of the catchment area.
In the normative document SNiP 2.01.14-83, a generalized formula K.P. is recommended for determining the coefficient of variation of unstudied rivers. Resurrection:

Skewness coefficient Cs characterizes the asymmetry of the series of the considered random variable with respect to its average value. The smaller part of the members of the series exceeds the value of the runoff norm, the greater the value of the asymmetry coefficient.
The asymmetry coefficient can be calculated by the formula

However, this dependence gives satisfactory results only for the number of observation years n > 100.
The coefficient of asymmetry of unstudied rivers is set according to the Cs/Cv ratio for analogue rivers, and in the absence of sufficiently good analogues, the average Cs/Cv ratios for the rivers of the given region are taken.
If it is impossible to establish the Cs/Cv ratio for a group of analogous rivers, then the values ​​of the Cs coefficient for unstudied rivers are accepted for regulatory reasons: for river basins with a lake coefficient of more than 40%

for zones of excessive and variable moisture - arctic, tundra, forest, forest-steppe, steppe

To build a theoretical endowment curve for the above three parameters - Q0, Cv and Cs - use the method proposed by Foster - Rybkin.
From the above relation for the modular coefficient (17) it follows that the average long-term value of the runoff of a given recurrence - Qp%, Мр%, Vp%, hp% - can be calculated by the formula

The modulus runoff coefficient of the year of a given probability is determined by the dependence

Having determined a number of any runoff characteristics for a long-term period of different availability, it is possible to construct a supply curve based on these data. In this case, it is advisable to carry out all calculations in tabular form (Tables 3 and 4).

Methods for calculating modular coefficients. To solve many water management problems, it is necessary to know the distribution of runoff by seasons or months of the year. The intra-annual distribution of runoff is expressed in the form of modular coefficients of monthly runoff, representing the ratio of the average monthly flow Qm.av to the average annual Qg.av:

The intra-annual distribution of runoff is different for years of different water content, therefore, in practical calculations, the modular coefficients of monthly runoff are determined for three characteristic years: a high-water year with 10% supply, an average year with 50% supply, and a low-water year with 90% supply.
Monthly runoff modulus coefficients can be established based on actual knowledge of average monthly water discharges in the presence of observational data for at least 30 years, according to an analogue river, or according to standard tables of monthly runoff distribution, which are compiled for different river basins.
The average monthly water consumption is determined based on the formula

(33): Qm.cp = KmQg.sr

Maximum water consumption. When designing dams, bridges, lagoons, measures to strengthen the banks, it is necessary to know the maximum water flow. Depending on the type of river feeding, the maximum flow rate of spring floods or autumn floods can be taken as the calculated maximum discharge. The estimated security of these costs is determined by the class of capital size of hydraulic structures and is regulated by the relevant regulatory documents. For example, timber rafting dams of class Ill of capitality are calculated for the passage of a maximum water flow of 2% security, and class IV - of 5% security, bank protection structures should not collapse at flow rates corresponding to the maximum water flow of 10% security.
The method for determining the value of Qmax depends on the degree of knowledge of the river and on the difference between the maximum discharges of the spring flood and the flood.
If there are observational data for a period of more than 30 ... 40 years, then an empirical security curve Qmax is built, and with a shorter period - a theoretical curve. The calculations take: for spring floods Cs = 2Сv, and for rain floods Cs = (3...4)CV.
Since river regimes are monitored at water-measuring stations, the supply curve is usually plotted for these sites, and the maximum water discharges at the sites where structures are located are calculated by the ratio

For lowland rivers maximum flow of spring flood water given security p% is calculated by the formula

The values ​​of the parameters n and K0 are determined depending on the natural zone and relief category according to Table. 5.

Category I - rivers located within hilly and plateau-like uplands - Central Russian, Strugo-Krasnenskaya, Sudoma uplands, Central Siberian plateau, etc .;
II category - rivers, in the basins of which hilly uplands alternate with depressions between them;
Category III - rivers, most of the basins of which are located within the flat lowlands - Mologo-Sheksninskaya, Meshcherskaya, Belarusian woodland, Pridnestrovskaya, Vasyuganskaya, etc.
The value of the coefficient μ is set depending on the natural zone and the percentage of security according to Table. 6.

The hp% parameter is calculated from the dependency

The coefficient δ1 is calculated (for h0 > 100 mm) by the formula

The coefficient δ2 is determined by the relation

The calculation of the maximum water discharges during the spring flood is carried out in tabular form (Table 7).

The levels of high waters (HWL) of the calculated supply are established according to the curves of water discharges for the corresponding values ​​of Qmaxp% and calculated sections.
With approximate calculations, the maximum water flow of a rain flood can be set according to the dependence

In responsible calculations, the determination of the maximum water flow should be carried out in accordance with the instructions of regulatory documents.

Water discharge is the volume of water flowing through the cross section of a river per unit time. Water flow is usually measured in cubic meters per second (m3/s). The average long-term water flow of the largest rivers of the republic, for example, the Irtysh, is 960 m/s, and the Syr Darya - 730 m/s.

The flow of water in rivers in a year is called the annual flow. For example, the annual flow of the Irtysh is 28,000 million m3. Water runoff determines surface water resources. The runoff is unevenly distributed throughout the territory of Kazakhstan, the volume of surface runoff is 59 km3. The amount of annual river flow depends primarily on the climate. In the flat regions of Kazakhstan, the annual runoff mainly depends on the nature of the distribution of snow cover and water reserves before the snow melts. Rainwater is almost completely used to moisten the topsoil and evaporate.

The main factor influencing the flow of mountain rivers is the relief. As the absolute height increases, the amount of annual precipitation increases. The moisture coefficient in the north of Kazakhstan is about one, and the annual flow is high, and there is more water in the river. The amount of runoff per square kilometer on the territory of Kazakhstan is on average 20,000 m3. Our republic is ahead of only Turkmenistan in terms of river flow. The flow of rivers varies with the seasons of the year. Plain rivers during the winter months provide 1% of the annual flow.

Reservoirs are built to regulate river flows. Water resources are equally used both in winter and in summer for the needs of the national economy. There are 168 reservoirs in our country, the largest of them are Bukhtarma and Kapchagai.

All solid material carried by the river is called solid runoff. The turbidity of the water depends on its volume. It is measured in grams of a substance contained in 1 m³ of water. The turbidity of lowland rivers is 100 g/m3, while in the middle and lower reaches it is 200 g/m3. The rivers of Western Kazakhstan carry a large amount of loose rocks, turbidity reaches 500-700 g/m3. The turbidity of mountain rivers increases downstream. Turbidity in the river is 650 g/m3, in the lower reaches of the Chu - 900 g/m3, in the Syr Darya 1200 g/m3.

Nutrition and river regime

Kazakhstani rivers have different nutrition: snow, rain, glacial and groundwater. There are no rivers with the same nutrition. The rivers of the flat part of the republic are divided into two types according to the nature of the supply: snow-rain and predominantly snow supply.

Snow-rain fed rivers include rivers located in the forest-steppe and steppe zones. The main ones of this type - Ishim and Tobol - overflow their banks in spring, 50% of the annual runoff falls in April-July. Rivers are first fed by melt water, then rain. Since the low water level is observed in January, at this time they feed on groundwater.

Rivers of the second type have exclusively spring flow (85-95% of the annual flow). This type of food includes rivers located in the desert and semi-desert zones - these are Nura, Ural, Sagyz, Turgay and Sarysu. The rise of water in these rivers is observed in the first half of spring. The main source of food is snow. The water level rises sharply in the spring when the snow melts. In the CIS countries, such a regime of rivers is called the Kazakhstani type. For example, 98% of its annual flow flows along the Nura River in a short time in spring. The lowest water level occurs in summer. Some rivers dry up completely. After the autumn rains, the water level in the river rises slightly, and in winter it drops again.

In the high-mountainous regions of Kazakhstan, rivers have a mixed type of food, but snow-glacier prevails. These are the Syrdarya, Ili, Karatal and Irtysh rivers. The level in them rises in late spring. The rivers of the Altai Mountains overflow their banks in spring. But the water level in them remains high until mid-summer, due to non-simultaneous snowmelt.

The rivers of the Tien Shan and Zhungarskiy Alatau are full-flowing in the warm season; In spring and summer. This is explained by the fact that in these mountains the melting of snow stretches until autumn. In spring, snowmelt begins from the lower belt, then during the summer, snow of medium height and highland glaciers melt. In the runoff of mountain rivers, the share of rainwater is insignificant (5-15%), and in low mountains it rises to 20-30%.

The flat rivers of Kazakhstan, due to low water and slow flow, quickly freeze with the onset of winter and are covered with ice at the end of November. The ice thickness reaches 70-90 cm. In frosty winters, the ice thickness in the north of the republic reaches 190 cm, and in the southern rivers 110 cm. second half of April.

The glacial regime of high mountain rivers is different. There is no stable ice cover in mountain rivers due to strong currents and groundwater supply. Coastal ice is observed only in some places. Kazakh rivers gradually erode rocks. Rivers flow, deepening their bottom, destroying their banks, rolling small and large stones. In the flat parts of Kazakhstan, the river flow is slow, and it carries solid materials.

To determine the flow of the river depending on the area of ​​the basin, the height of the sediment layer, etc. in hydrology, the following quantities are used: river flow, flow modulus, and flow coefficient.

River runoff call water consumption over a long period of time, for example, per day, decade, month, year.

Drain module they call the amount of water expressed in liters (y), flowing on average in 1 second from the area of ​​​​the river basin in 1 km 2:

Runoff coefficient call the ratio of water flow in the river (Qr) to the amount of precipitation (M) on the area of ​​the river basin for the same time, expressed as a percentage:

a - runoff coefficient in percent, Qr - annual runoff value in cubic meters; M is the annual amount of precipitation in millimeters.

To determine the runoff modulus, it is necessary to know the water discharge and the area of ​​the basin upstream of the target, according to which the water discharge of the given river was determined. The area of ​​a river basin can be measured from a map. For this, the following methods are used:

• 1) planning
• 2) breakdown into elementary figures and calculation of their areas;
• 3) measuring the area with a palette;
• 4) calculation of areas using geodetic tables

It is easiest for students to use the third method and measure the area using a palette, i.e. transparent paper (tracing paper) with squares printed on it. Having a map of the studied area of ​​the map on a certain scale, you can make a palette with squares corresponding to the scale of the map. First, you should outline the basin of this river above a certain alignment, and then apply the map to the palette, on which to transfer the contour of the basin. To determine the area, you first need to count the number of full squares located inside the contour, and then add these squares, partially covering the basin of the given river. Adding the squares and multiplying the resulting number by the area of ​​one square, we find out the area of ​​the river basin above this alignment.

Q - water consumption, l. To convert cubic meters to liters, we multiply the flow rate by 1000, S pool area, km 2.

To determine the river runoff coefficient, it is necessary to know the annual runoff of the river and the volume of water that has fallen on the area of ​​a given river basin. The volume of water that fell on the area of ​​this pool is easy to determine. To do this, you need to multiply the area of ​​​​the basin, expressed in square kilometers, by the thickness of the layer of precipitation (also in kilometers). For example, the thickness will be equal to p if precipitation in a given area was 600 mm per year, then 0 "0006 km and the runoff coefficient will be equal to:

Qr is the annual flow of the river, and M is the area of ​​the basin; multiply the fraction by 100 to determine the runoff coefficient as a percentage.

Determination of the river flow regime. To characterize the flow regime of the river, you need to establish:

a) what seasonal changes the water level undergoes (a river with a constant level, which becomes very shallow in summer, dries up, loses water in pores and disappears from the surface);

b) the time of high water, if any;

c) the height of the water during the flood (if there are no independent observations, then according to questionnaire data);

d) the duration of the freezing of the river, if it occurs (according to their own observations or according to information obtained through a survey).

Determination of water quality. To determine the quality of water, you need to find out whether it is cloudy or transparent, drinkable or not. The transparency of the water is determined by a white disk (Secchi disk) with a diameter of approximately 30 cm, summed up on a marked line or attached to a marked pole. If the disk is lowered on the line, then a weight is attached below, under the disk, so that the disk is not carried away by the current. The depth at which this disk becomes invisible is an indication of the transparency of the water. You can make a disk out of plywood and paint it white, but then the load must be hung heavy enough so that it falls vertically into the water, and the disk itself maintains a horizontal position; or plywood sheet can be replaced with a plate.

Determination of water temperature in the river. The temperature of the water in the river is determined by a spring thermometer, both on the surface of the water and at different depths. Keep the thermometer in water for 5 minutes. A spring thermometer can be replaced with a conventional wooden-framed bath thermometer, but in order for it to sink into the water at different depths, a weight must be tied to it.

You can determine the temperature of the water in the river with the help of bathometers: a bathometer-tachymeter and a bottle bathometer. The bathometer-tachymeter consists of a flexible rubber balloon with a volume of about 900 cm 3; a tube with a diameter of 6 mm is inserted into it. The bathometer-tachymeter is fixed on a rod and lowered to different depths to take water.

The resulting water is poured into a glass and its temperature is determined.

It is not difficult for a student to make a bathometer-tachymeter. To do this, you need to buy a small rubber chamber, put on it and tie a rubber tube with a diameter of 6 mm. The bar can be replaced with a wooden pole, dividing it into centimeters. The rod with the tachymeter bathometer must be lowered vertically into the water to a certain depth, so that the opening of the tachymeter bathometer is directed downstream. Having lowered to a certain depth, the bar must be rotated by 180 and held for about 100 seconds in order to draw water, and then again turn the bar by 180 °. runoff water regime river

It should be removed so that water does not spill out of the bottle. After pouring water into a glass, determine the temperature of the water at a given depth with a thermometer.

It is useful to simultaneously measure the air temperature with a sling thermometer and compare it with the temperature of the river water, making sure to record the time of observation. Sometimes the temperature difference reaches several degrees. For example, at 13 o'clock the air temperature is 20, the water temperature in the river is 18 °.

Study in certain areas on certain nature of the riverbed. When examining sections of the nature of the riverbed, it is necessary:

a) mark the main reaches and rifts, determine their depths;

b) when detecting rapids and waterfalls, determine the height of the fall;

c) draw and, if possible, measure the islands, shoals, middles, side channels;

d) collect information in which places the river is eroding and in places that are especially strongly eroded, determine the nature of the eroded rocks;

e) study the nature of the delta, if the estuarine section of the river is being investigated, and plot it on the visual plan; see if the individual arms correspond to those shown on the map.

General characteristics of the river and its use. With a general description of the river, you need to find out:

a) which part of the river is mainly eroding and which is accumulating;

b) degree of meandering.

To determine the degree of meandering, you need to know the tortuosity coefficient, i.e. the ratio of the length of the river in the study area to the shortest distance between certain points in the study part of the river; for example, river A has a length of 502 km, and the shortest distance between the source and the mouth is only 233 km, hence the tortuosity coefficient:

K - sinuosity coefficient, L - river length, 1 - shortest distance between source and mouth

Meander study is of great importance for timber rafting and shipping;

c) Non-squeezing river fans formed at the mouths of tributaries or produce temporary flows.

Find out how the river is used for navigation and timber rafting; if the hand is not navigable, then find out why, it serves as an obstacle (shallow, rapids, are there waterfalls), are there dams and other artificial structures on the river; whether the river is used for irrigation; what transformations need to be done to use the river in the national economy.

Determining the nutrition of the river. It is necessary to find out the types of river nutrition: groundwater, rain, lake or marsh from melting snow. For example, r. Klyazma is fed, ground, snow and rain, of which ground supply is 19%, snow - 55% and rain. - 26 %.

The river is shown in Figure 2.

m 3

Conclusion: In the course of this practical lesson, as a result of calculations, the following values ​​were obtained, characterizing the flow of the river:

Drain module? = 177239 l / s * km 2

Runoff coefficient b = 34.5%.

Water resources are one of the most important resources of the Earth. But they are very limited. Indeed, although ¾ of the planet's surface is occupied by water, most of it is the salty World Ocean. Man needs fresh water.

Its resources are also mostly inaccessible to people, as they are concentrated in the glaciers of the polar and mountain regions, in swamps, underground. Only a small part of the water is suitable for human use. These are fresh lakes and rivers. And if in the first the water lingers for decades, then in the second it is updated about once every two weeks.

River flow: what does this concept mean?

This term has two main meanings. First, it refers to the entire volume of water flowing into the sea or ocean during the year. This is its difference from the other term "river flow", when the calculation is carried out for a day, hours or seconds.

The second value is the amount of water, dissolved and suspended particles carried by all rivers flowing in a given region: mainland, country, region.

Surface and underground river runoff is distinguished. In the first case, we mean the waters flowing into the river along the A underground - these are springs and springs that gush under the bed. They also replenish the water supply in the river, and sometimes (during the summer low water or when the surface is ice-bound) they are its only source of food. Together, these two species make up the total river runoff. When people talk about water resources, they mean it.

Factors affecting river flow

This issue has already been studied enough. Two main factors can be named: the terrain and its climatic conditions. In addition to them, several additional ones stand out, including human activity.

The main reason for the formation of river flow is the climate. It is the ratio of air temperature and precipitation that determines the evaporation rate in a given area. The formation of rivers is possible only with excessive moisture. If evaporation exceeds the amount of precipitation, there will be no surface runoff.

The nutrition of rivers, their water and ice regime depend on the climate. provide moisture replenishment. Low temperatures reduce evaporation, and when the soil freezes, the flow of water from underground sources is reduced.

The relief influences the size of the river catchment area. It depends on the shape of the earth's surface in which direction and at what speed the moisture will flow. If there are closed depressions in the relief, not rivers, but lakes are formed. The slope of the terrain and the permeability of rocks affect the ratio between the parts of precipitation that flow into water bodies and seep into the ground.

The value of rivers for humans

The Nile, the Indus with the Ganges, the Tigris and the Euphrates, the Yellow River and the Yangtze, the Tiber, the Dnieper… These rivers have become the cradle for different civilizations. Since the dawn of mankind, they have served for him not only as a source of water, but also as channels of penetration into new unexplored lands.

Thanks to river flow, irrigated agriculture is possible, which feeds almost half of the world's population. High water consumption also means rich hydropower potential. River resources are used in industrial production. Particularly water-intensive are the production of synthetic fibers and the production of pulp and paper.

River transport is not the fastest, but it is cheap. It is best suited for the transportation of bulk cargo: timber, ores, oil products, etc.

A lot of water is taken for domestic needs. Finally, rivers are of great recreational importance. These are places of rest, restoration of health, a source of inspiration.

The most full-flowing rivers in the world

The largest volume of river flow is in the Amazon. It is almost 7000 km 3 per year. And this is not surprising, because the Amazon is full of water all year round due to the fact that its left and right tributaries overflow at different times. In addition, it collects water from an area almost the size of the entire mainland of Australia (more than 7000 km 2)!

In second place is the African Congo River with a flow of 1445 km 3. Located in the equatorial belt with daily showers, it never becomes shallow.

Following in terms of total river flow resources: the Yangtze is the longest in Asia (1080 km 3), Orinoco (South America, 914 km 3), Mississippi (North America, 599 km 3). All three spill heavily during the rains and pose a considerable threat to the population.

The 6th and 8th places in this list are the great Siberian rivers - the Yenisei and the Lena (624 and 536 km 3, respectively), and between them is the South American Parana (551 km 3). The top ten is closed by another South American river Tocantins (513 km 3) and the African Zambezi (504 km 3).

Water resources of the countries of the world

Water is the source of life. Therefore, it is very important to have its reserves. But they are distributed across the planet extremely unevenly.

The provision of countries with river runoff resources is as follows. The top ten countries richest in water are Brazil (8,233 km 3), Russia (4.5 thousand km 3), USA (more than 3 thousand km 3), Canada, Indonesia, China, Colombia, Peru, India, Congo .

Territories located in a tropical dry climate are poorly provided for: North and South Africa, the countries of the Arabian Peninsula, Australia. There are few rivers in the inland regions of Eurasia, therefore, among the low-income countries are Mongolia, Kazakhstan, and the Central Asian states.

If the number of people using this water is taken into account, the indicators change somewhat.

Availability of river runoff resources

The largest		Least
Countries	security	Countries	security
french guiana	609 thousand	Kuwait	Less than 7
Iceland	540 thousand	United Arab Emirates	33,5
Guyana	316 thousand	Qatar	45,3
Suriname	237 thousand	Bahamas	59,2
Congo	230 thousand	Oman	91,6
Papua New Guinea	122 thousand	Saudi Arabia	95,2
Canada	87 thousand	Libya	95,3
Russia	32 thousand	Algeria	109,1

The densely populated countries of Europe with full-flowing rivers are no longer so rich in fresh water: Germany - 1326, France - 3106, Italy - 3052 m 3 per capita, with an average value for the whole world - 25 thousand m 3.

Transboundary flow and problems associated with it

Many rivers cross the territory of several countries. In this regard, there are difficulties in the joint use of water resources. This problem is especially acute in areas where almost all water is taken to the fields. And the neighbor downstream may not get anything.

For example, belonging in its upper reaches to Tajikistan and Afghanistan, and in the middle and lower reaches to Uzbekistan and Turkmenistan, in recent decades it has not carried its waters to the Aral Sea. Only with good neighborly relations between neighboring states can its resources be used to the benefit of all.

Egypt receives 100% of river water from abroad, and a reduction in the flow of the Nile due to water intake upstream can have an extremely negative impact on the state of the country's agriculture.

In addition, along with water, various pollutants “travel” across the borders of countries: garbage, factory runoff, fertilizers and pesticides washed off the fields. These problems are relevant for the countries lying in the Danube basin.

Rivers of Russia

Our country is rich in large rivers. There are especially many of them in Siberia and the Far East: the Ob, Yenisei, Lena, Amur, Indigirka, Kolyma, etc. And the river flow is the largest in the eastern part of the country. Unfortunately, so far only a small fraction of them have been used. Part goes for domestic needs, for the operation of industrial enterprises.

These rivers have a huge energy potential. Therefore, the largest hydroelectric power plants are built on Siberian rivers. And they are indispensable as transport routes and for timber rafting.

The European part of Russia is also rich in rivers. The largest of them is the Volga, its flow is 243 km 3. But 80% of the country's population and economic potential are concentrated here. Therefore, the lack of water resources is sensitive, especially in the southern part. The flow of the Volga and some of its tributaries is regulated by reservoirs; a cascade of hydroelectric power stations has been built on it. The river with its tributaries is the main part of the Unified Deep Water System of Russia.

In the conditions of the growing water crisis all over the world, Russia is in favorable conditions. The main thing is to prevent pollution of our rivers. Indeed, according to economists, clean water can become a more valuable commodity than oil and other minerals.

The flow of a certain land area is measured by indicators:

• water flow - the volume of water flowing per unit of time through the living section of the river. It is usually expressed in m3/s. The average daily water discharges make it possible to determine the maximum and minimum discharges, as well as the amount of water flow per year from the basin area. Annual flow - 3787 km a - 270 km3;
• drain module. It is called the amount of water in liters, flowing per second from 1 km2 of area. It is calculated by dividing the runoff by the area of ​​the river basin. The tundra and rivers have the largest module;
• runoff coefficient. It shows what proportion of precipitation (in percent) flows into rivers. Rivers of the tundra and forest zones have the highest coefficient (60-80%), while in the rivers of the regions it is very low (-4%).

Loose rocks - products are carried by runoff into rivers. In addition, the (destructive) work of rivers also makes them a supplier of loose . In this case, a solid runoff is formed - a mass of suspended, drawn along the bottom and dissolved substances. Their number depends on the energy of moving water and on the resistance of rocks to erosion. Solid runoff is divided into suspended and bottom runoff, but this concept is arbitrary, since when the flow velocity changes, one category can quickly move into another. At high speed, bottom solid runoff can move in a layer up to several tens of centimeters thick. Their movements are very uneven, since the speed at the bottom changes dramatically. Therefore, sandy and rifts can form at the bottom of the river, hindering navigation. The turbidity of the river depends on the value, which, in turn, characterizes the intensity of erosion activity in the river basin. In large river systems, solid runoff is measured in the tens of millions of tons per year. For example, the runoff of elevated sediments of the Amu Darya is 94 million tons per year, the Volga river is 25 million tons per year, - 15 million tons per year, - 6 million tons per year, - 1500 million tons per year, - 450 million tons per year, Nile - 62 million tons per year.

Flow rate depends on a number of factors:

• first of all from . The more precipitation and less evaporation, the more runoff, and vice versa. The amount of runoff depends on the form of precipitation and their distribution over time. The rains of a hot summer period will give less runoff than a cool autumn period, since evaporation is very large. Winter precipitation in the form of snow will not provide surface runoff during the cold months, but is concentrated in the short spring flood period. With a uniform distribution of precipitation throughout the year, the runoff is uniform, and sharp seasonal changes in the amount of precipitation and evaporation rate cause uneven runoff. During prolonged rains, the infiltration of precipitation into the ground is greater than during heavy rains;
• from the area. When the masses rise along the slopes of the mountains, they cool down, as they meet with colder layers, and water vapor, so here the amount of precipitation increases. Already from insignificant hills, the flow is greater than from adjacent ones. So, on the Valdai Upland, the runoff module is 12, and on the neighboring lowlands - only 6. An even greater volume of runoff in the mountains, the runoff module here is from 25 to 75. The water content of mountain rivers, in addition to an increase in precipitation with height, is also affected by a decrease in evaporation in the mountains due to the lowering and steepness of the slopes. From the elevated and mountainous territories, water flows quickly, and from the plains slowly. For these reasons, lowland rivers have a more uniform regime (see Rivers), while mountainous ones react sensitively and violently to;
• from cover. In areas of excessive moisture, soils are saturated with water for most of the year and give it to rivers. In zones of insufficient moisture during the snowmelt season, the soils are able to absorb all the melt water, so the runoff in these zones is weak;
• from vegetation cover. Studies of recent years, carried out in connection with the planting of forest belts in, indicate their positive effect on runoff, since it is more significant in forest zones than in the steppe;
• from influence. It is different in zones of excessive and insufficient moisture. Bogs are regulators of runoff, and in the zone their influence is negative: they suck in surface and water and evaporate them into the atmosphere, thereby disrupting both surface and underground runoff;
• from large flowing lakes. They are a powerful flow regulator, however, their action is local.

From the above brief review of factors affecting runoff, it follows that its magnitude is historically variable.

The zone of the most abundant runoff is, the maximum value of its module here is 1500 mm per year, and the minimum is about 500 mm per year. Here, the runoff is evenly distributed over time. The largest annual flow in .

The zone of minimum runoff is the subpolar latitudes of the Northern Hemisphere, covering. The maximum value of the runoff module here is 200 mm per year or less, with the largest amount occurring in spring and summer.

In the polar regions, the runoff is carried out, the thickness of the layer in terms of water is approximately 80 mm in and 180 mm in.

On each continent there are areas from which the flow is carried out not into the ocean, but into inland water bodies - lakes. Such territories are called areas of internal flow or drainless. The formation of these areas is associated with fallout, as well as with the remoteness of inland territories from the ocean. The largest areas of drainless regions fall on (40% of the total territory of the mainland) and (29% of the total territory).