River runoff and its characteristics. Rivers as a natural resource

28.07.2015

Fluctuations of river flow and criteria for its assessment. River runoff is the movement of water in the course of its circulation in nature, when it flows down the river bed. River flow is determined by the amount of water flowing through the river channel for a certain period of time.
The runoff regime is influenced by numerous factors: climatic - precipitation, evaporation, humidity and air temperature; topographic - topography, 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 was found 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, measures to combat floods, roads, etc., the following main characteristics of river flow are determined.
1. Water consumption is the volume of water flowing through the section under consideration per unit of time. The average water consumption Qcp is calculated as the arithmetic mean of the costs for a given period of time T:

2. Runoff volume V is the volume of water that flows through a given section during the considered time interval T

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

Unlike the water discharge, the flow module is not associated with a specific section of the river and characterizes the flow from the basin as a whole. The average long-term runoff module M0 does not depend on the water content of individual years, but is determined only geographic location river basin. This made it possible to regionalize our country in hydrological terms and to construct a map of isolines of mean annual runoff modules. These maps are listed in the relevant regulatory literature. Knowing the catchment area of ​​a river and having determined the value M0 for it from the isoline map, it is possible to establish the average long-term water discharge Q0 of this river using the formula

For closely located river sections, the flow modules can be taken constant, that is

Hence, according to the known water flow rate in one section Q1 and famous squares catchments in these sections F1 and F2, the water flow rate in the other section Q2 can be set according to the ratio

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

Contour maps were compiled for the average long-term runoff layer h0 of the spring flood.
5. Modular flow coefficient K is the ratio of any of the above characteristics of the runoff to its arithmetic mean value:

These factors can be set for any hydrological characteristics (flow rates, levels, precipitation, evaporation, etc.) and for any flow periods.
6. Drainage coefficient η is the ratio of the runoff layer to the precipitation layer x:

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

Since at most gauging stations the number of observation years is usually less than 40, it is necessary to check whether this number of years is sufficient to obtain reliable values ​​of the flow rate Q0. For this, the root-mean-square error of the runoff rate is calculated 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 the annual runoff is primarily influenced by climatic factors: precipitation, evaporation, air temperature, etc. All of them are interrelated and, in turn, depend on a number of factors that are random in nature. Therefore, hydrological parameters characterizing 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 their exceeding. For example, in the hydraulic calculation of timber floating dams, it is necessary to establish 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(repeatability) and security (duration).
The frequency shows in 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 discharge in a given section of the river varied over a number of years of observation from 150 to 350 m3 / s, then it is possible to establish how many times the values ​​of this quantity 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 provision of any hydrological element is equal to the sum of the frequencies of the upstream intervals.
Frequency and availability can be expressed in the number of cases, but in hydrological calculations they are most often determined as a percentage of the total members of the hydrological series. For example, in the hydrological series there are twenty values ​​of the average annual water discharge, 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 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 the years for which the flow availability, that is, the average annual water flow Qg, is less than 50%, are high-water, and the years with the Qg availability of more than 50% are low-water. A year with a runoff rate of 50% is considered the year of average water availability.
Water availability during the year is sometimes characterized by its average frequency. For high-water years, the frequency of occurrence shows how often there are, on average, years of a given or higher water content, for low-water years, a given or lower water content. For example, the average annual consumption of a high-water year of 10% supply has an average recurrence rate of 10 times in 100 years or 1 time in 10 years; the average recurrence rate of a dry year of 90% availability also has a recurrence rate of 10 times in 100 years, since in 10% of cases the average annual costs will have lower values.
Years of a certain water content have a corresponding name. Table 1 for them the security and repeatability are given.

The relationship between the repeatability y and the security p can be written as follows:
for high-water years

for dry years

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

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

The procedure for constructing an empirical supply curve:
1) all members of the hydrological series are recorded in decreasing absolute value okay;
2) each member of the series is assigned 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.
But empirical supply 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. The calculated values ​​of the flow availability of 1 ... 2% are not reliable, since sufficiently substantiated results can be obtained only with the number of observations over 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 is most closely aligned with the Pearson curve of type III, the integral expression of which is the probability curve. Pearson obtained tables for plotting this curve. The security curve can be constructed with sufficient accuracy for practice in three parameters: the arithmetic mean of the members of the series, the coefficients of variation and asymmetry.
The arithmetic mean of the members of the series is calculated by the formula (19).
If the number of years of observations is less than ten, or observations were not carried out at all, then the average annual water discharge Qgcp is taken to be equal to the long-term average Q0, that is, Qgcp = Q0. The Q0 value can be set using the modular coefficient K0 or the flow modulus M0, determined from the contour maps, since Q0 = M0 * F.
The coefficient of variation Cv characterizes the variability of the runoff or the degree of its fluctuation relative to the mean value in a given series; it is numerically equal to the ratio of the mean square error to the arithmetic mean of the members of the series. The value of the coefficient Cv is affected by significant influence climatic conditions, type of river feeding and hydrographic features of its basin.
If observational data are available for at least ten years, the coefficient of variation of the annual runoff is calculated by the formula

The Cv value varies over a wide range: from 0.05 to 1.50; for timber floating rivers Cv = 0.15 ... 0.40.
With a short period of observations of the river flow 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, a map of isolines of the Cv coefficient is also used if the total area of ​​lakes is not more than 3% of the catchment area.
In the normative document SNiP 2.01.14-83, the generalized formula of K.P. Voskresensky:

Asymmetry coefficient Cs characterizes the asymmetry of the series of the considered random variable relative to its mean value. The smaller the number of members of the series exceeds the value of the runoff rate, 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 years of observations n> 100.
The asymmetry coefficient of unexplored rivers is established according to the Cs / Cv ratio for analogous rivers, and in the absence of sufficiently good analogs, the average Cs / Cv ratios for the rivers of a given area 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 unexplored rivers are taken for regulatory reasons: for river basins with a lacustrine ratio of more than 40%

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

To construct a theoretical productivity curve according to the above three parameters - Q0, Cv and Cs - use the method proposed by Foster - Rybkin.
From the above ratio for the modular coefficient (17) it follows that the average long-term value of the flow of a given supply - Qp%, Мр%, Vp%, hp% - can be calculated by the formula

The modular coefficient of the flow of a year of a given supply is determined by the dependence

Having determined a number of any runoff characteristics for a long-term period of different supply, it is possible to construct a supply curve based on these data. Moreover, 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 runoff distribution is expressed in the form of modular coefficients of the monthly runoff, representing the ratio of the average monthly flow rates Qm.av to the average annual Qg.av:

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

(33): Qm.cp = KmQg.av

Maximum water consumption. When designing dams, bridges, dams, measures to strengthen the banks, it is necessary to know the maximum water flow rates. Depending on the type of river feeding, the maximum water discharge of a spring flood or an autumn flood can be taken as the calculated maximum discharge. The estimated provision for these costs is determined by the capital class of hydraulic structures and is regulated by the relevant regulatory documents. For example, timber-floating dams of the III class of capital are designed to pass the maximum water flow rate of 2% availability, and IV class - 5% availability, bank protection structures should not collapse at flow rates corresponding to the maximum water flow rate of 10% availability.
The method for determining the value of Qmax depends on the degree of knowledge of the river and on the difference between the maximum flow rates of spring floods and floods.
If there are observational data for a period of more than 30 ... 40 years, then an empirical curve of the Qmax security is built, and for a shorter period, a theoretical curve. Calculations take: for spring floods Cs = 2Cv, and for rain floods Cs = (3 ... 4) CV.
Since observations of the regime of rivers are carried out at water measuring posts, then the supply curve is usually built for these sections, and the maximum water flow rates in the sections of the location of structures are calculated by the ratio

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

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

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

The hp% parameter is calculated from the dependency

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

The coefficient δ2 is determined by the ratio

The calculation of the maximum flow rates of spring floods is carried out in tabular form (Table 7).

Levels high waters(Air-blast) of the calculated supply are established according to the curves of water flow rates for the corresponding values ​​of Qmaxp% and calculated sections.
With approximate calculations, the maximum flow rate of rain flood water can be set according to the dependence

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

Annual runoff characteristics

Runoff is the movement of water along the surface, as well as in the thickness of soils and rocks during its cycle in nature. In calculations, runoff is understood as the amount of water flowing down from the catchment area over a period of time. This amount of water can be expressed as flow rate Q, volume W, module M, or drainage layer h.

Runoff volume W - the amount of water flowing down from the catchment for any period of time (day, month, year, etc.), - is determined by the formula

W = QT [m 3], (19)

where Q is the average water consumption for the calculated time period, m 3 / s, T is the number of seconds in the calculated time period.

Since the average water discharge was previously calculated as the annual flow rate, the volume of the river. Kegety per year W = 2.39 365.25 24 3600 = 31764096m 3.

Runoff module M - the amount of water flowing from a unit of catchment area per unit of time - is determined by the formula

M = 103Q / F [l / (sqm2)], (20)

where F is the catchment area, km 2.

Runoff module r. Kegety M = 10 3 2.39 / 178 = 13.42 l / (sqm 2).

Runoff layer h mm - the amount of water flowing down from the catchment over any period of time, equal to the thickness of the layer evenly distributed over the area of ​​this catchment, - is determined by the formula

h = W / (F 10 3) = QT / (F 10 3). (21)

Runoff layer for the river basin. Kegety h = 31764096 / (178 10 3) = 178.44 mm.

Dimensionless characteristics include modular coefficient and drain coefficient.

The modular coefficient K is the ratio of the flow for a particular year to the flow rate:

К = Q i / Q 0 = W i / W 0 = h i / h 0, (22)

and for p. Kegety for the period under consideration K varies from K = 1.58 / 2.39 = 0.66 for the year with the minimum discharge to K = 3.26 / 2.39 = 1.36 for the maximum discharge.

The runoff coefficient is the ratio of the volume or layer of runoff to the amount of precipitation x falling on the catchment area, which led to the occurrence of runoff:

The runoff coefficient shows how much of the precipitation goes to runoff formation.

V term paper it is necessary to determine the characteristics of the annual runoff for the basin accepted for consideration, taking the runoff rate from the section

Intra-annual runoff distribution

The intra-annual distribution of river runoff occupies an important place in the study and calculation of runoff both in practical and scientific terms, being at the same time the most difficult task of hydrological research / 2,4,13 /.

The main factors determining the intra-annual runoff distribution and its overall value are climatic. They determine the general nature (background) of the distribution of runoff in a year in a given geographical area; territorial changes in runoff distribution follow climate change.

Factors affecting the distribution of runoff throughout the year include lacustrine, forest cover, swampiness, catchment sizes, the nature of soils and grounds, groundwater depth, etc., which, to a certain extent, should be taken into account in calculations both in the absence and in the presence of observation materials.

Depending on the availability of hydrometric observation data, the following methods for calculating the intra-annual runoff distribution are used:

if there are observations for a period of at least 10 years: a) distribution by analogy with the distribution of a real year; b) the method of arranging seasons;

in the absence or insufficiency (less than 10 years) of observation data: a) by analogy with the distribution of the flow of the studied analogue river; b) according to regional schemes and regional dependences of the parameters of the intra-annual runoff distribution on physical and geographical factors.

The intra-annual runoff distribution is usually calculated not by calendar years, but by water management, starting from the high-water season. Season boundaries are assigned the same for all years, rounded to the nearest month.

The estimated probability of exceeding the flow for the year, the limiting period and season, is assigned in accordance with the tasks of the water management of the river flow.

In the course work, it is necessary to perform calculations in the presence of hydrometric observations.

Calculations of the intra-annual runoff distribution by the layout method

The initial data for the calculation are the average monthly water consumption and, depending on the purpose of using the calculation, a given percentage of supply P and division into periods and seasons.

The calculation is divided into two parts:

the most important off-season distribution;

intra-seasonal distribution (by months and decades, established with some schematization.)

Off-season distribution. Depending on the type of intra-annual runoff distribution, the year is divided into two periods: high-water and low-water (low water). Depending on the purpose of use, one of them is assigned as limiting.

The limiting period is the most intense period (season) in terms of water management. For dehumidification purposes, the limiting period is high water; for irrigation purposes, energy-shallow.

The period includes one or two seasons. On rivers with spring floods, for irrigation purposes, the following are distinguished: a high-water period (aka season) - spring and a low-water (limiting) period, which includes seasons; summer-autumn and winter, and the limiting season for irrigation is summer-autumn (for energy use, winter).

The calculation is carried out for hydrological years, i.e. over the years starting with the high-water season. The seasons are assigned the same for all observation years, rounded to the nearest whole month. The duration of the high-water season is set so that the high water is placed within the boundaries of the season both in the years with the earliest onset date and the latest end date.

In the task, the duration of the seasons can be taken as follows: spring - April, May, June; summer-autumn - July, August, September, October, November; winter - December and January, February, March next year.

The amount of runoff for individual seasons and periods is determined by the sum of average monthly discharges (Table 10). In the last year, expenses for three months (I, II, III) of the first year are added to the expense for December.

When calculating using the layout method, the intra-annual runoff distribution is taken from the condition of equality of the probability of exceeding the runoff for a year, runoff for the limiting period and within it for the limiting season. Therefore, it is necessary to determine the costs of the provision given by the project (in the task P = 80%) for the year, the limiting period and season. Therefore, it is required to calculate the parameters of the probability curves (О 0, С v and С s) for the limiting period and season (for the annual runoff, the parameters are calculated above). Calculations are made by the method of moments in table. 10 according to the scheme outlined above for the annual runoff.

You can determine the estimated costs using the formulas:

annual flow

Orasgod = Kp "12Q 0, (26)

limiting period

Orasmezh = KрQ0intermediate, (27)

limiting season

Oraslo = Kр "Qlo (27)

where Kр ", Kр, Kр" are the ordinates of the curves of the three-parameter gamma distribution, taken from the table, respectively, for С v - the annual runoff. С v low-water runoff and С v for summer-autumn.

Note. Since the calculations are performed on average monthly expenses, the estimated annual consumption must be multiplied by 12.

One of the basic conditions of the layout method is the equality

Orassgod = Orassus. However, this equality will be violated if the estimated runoff for non-limiting seasons is also determined by the supply curves (due to the difference in the parameters of the curves). Therefore, the estimated runoff for a non-limiting period (in the task - for the spring) is determined by the difference

Orasves = Orasgod - Orasmezh, (28)

but for a non-limiting season (in the winter task)

Oraszim = Orasmierz. - Qlo (29)

It is more convenient to perform the calculation in the form of a table. ten.

Intraseasonal distribution - taken as averaged over each of the three water content groups (high-water group, including years with flow availability for the season P<33%, средняя по водности 33<Р<66%, маловодная Р>66%).

To distinguish the years included in individual water content groups, it is necessary to arrange the total costs for the seasons in descending order and calculate their actual supply. Since the estimated supply (P = 80%) corresponds to the low-water group, further calculation can be made for the years included in the low-water group (Table 11).

For this in. in the column "Total flow" write out the costs by seasons, corresponding to the availability of P> 66%, and in the column "Years" - write down the years corresponding to these costs.

Arrange the average monthly expenditures within the season in descending order, indicating the calendar months to which they relate (Table 11). Thus, the first will be the flow rate for the most high-water month, the last for the low-water month.

For all years, sum up expenses separately for the season and for each month. Taking the amount of expenses for the season as 100%, determine the percentage of each month A% included in the season, and in the column "Month" write down the name of the month that is repeated most often. If there are no repetitions, write out any of the meeting, but so that each month included in the season has its own percentage of the season.

Then, multiplying the estimated discharge for the season, determined in terms of the off-season distribution of runoff (Table 10), by the percentage of each month A% (Table 11), calculate the estimated discharge for each month.

Oras v = Orasves A% v / 100% (30)

The data obtained are entered in table. 12 "Estimated expenses by months" and the calculated hydrograph P-80% of the studied river is built on graph paper (Fig. 11).

Table 12. Estimated flow rates (m3 / s) by months

INTRODUCTION

The tasks of hydrological calculations and their role in the development of the country's economy. Connection of hydrological calculations with other sciences. The history of the development of hydrological calculations: the first works of foreign scientists 17-19 centuries; works of Russian scientists of the late 19th - early 20th centuries; the first textbook of hydrology in Russia; the Soviet period of the development of hydrological calculations; All-Union hydrological congresses and their role in the development of methods for calculating river flow; post-Soviet period of development of hydrological calculations. Main characteristics of river flow. Three cases of determination of hydrological characteristics.

METHODS FOR ANALYSIS OF RIVER RUNOFF CHARACTERISTICS.

Genetic analysis of hydrological data: geographic-hydrological method and its special cases - methods of hydrological analogy, geographic interpolation and hydrological-hydrogeological. Probabilistic statistical analysis: method of moments, method of maximum likelihood, method of quantifiers, correlation and regression analysis, factor analysis, principal component analysis, discriminant analysis method. Methods for the analysis of computational mathematics: systems of algebraic equations, differentiation and function integration, partial differential equations, Monte Carlo method. Mathematical modeling of hydrological phenomena and processes, classes and types of models. System analysis.

METHODS FOR GENERALIZING HYDROLOGICAL CHARACTERISTICS.

Runoff contour maps: principles of construction, reliability of runoff determination. Hydrological zoning of the territory: concept, boundaries of application, principles of zoning and approaches to zoning, methods of determining the boundaries of areas, homogeneity of areas. Graphical processing of hydrological data: straight-line, power-law and exponential graphical dependencies.

RIVER RUNOFF FORMATION FACTORS.

The importance of understanding the mechanism and the degree of influence of physical and geographical factors on the regime and amount of river runoff. Equation of water balance of the river basin. Classification of factors in the formation of river runoff. Climatic and meteorological factors of river flow: precipitation, evaporation, air temperature. Influence of factors of the river basin and its underlying surface on the runoff: geographical position, size, shape of the river basin, relief, vegetation, soils and rocks, permafrost, lacustrine, swampiness, glaciers and ice within the basin. The impact of economic activities on river flow: the creation of reservoirs and ponds, redistribution of runoff between river runoff basins, irrigation of agricultural fields, drainage of swamps and wetlands, agroforestry measures in river catchments, water consumption for industrial and municipal needs, urbanization, mining mineral.

STATISTICAL PARAMETERS OF THE RIVER RUNOFF.

RELIABILITY OF INITIAL HYDROLOGICAL INFORMATION.

Flow rate and principles of its calculation. River runoff variability, its relative (coefficient variations) and absolute (standard deviation) expression, relationship with meteorological factors. Variability of intra-annual runoff distribution, maximum spring flood and rainfall runoff, minimum winter and summer runoff. Asymmetry coefficient. The degree of reliability of hydrological baseline information. The reasons for the occurrence of errors in the regime hydrological information.

CONDITIONS FOR FORMATION AND CALCULATION OF ANNUAL STOCK RATE.

Annual runoff rivers as the main hydrological characteristic. Conditions for the formation of the annual runoff: precipitation, evaporation, air temperature. Influence of lakes, swamps, glaciers, icings, basin area, catchment height, forest and its cutting, creation of reservoirs, irrigation, industrial and communal water consumption, drainage of swamps and wetlands, agroforestry on the formation of annual river flow. The concept of the representativeness of a series of hydrological data. Elements of flow cyclical fluctuations. Synchronous, asynchronous, in-phase, asynphased drain fluctuations. Calculations of the annual runoff rate in the presence, insufficiency and absence of observational data. Distribution of the annual runoff over the territory of Russia.

FORMATION FACTORS AND CALCULATION

INTRA ANNUAL DISTRIBUTION OF RIVER RUNOFF.

Practical significance of knowledge about the intra-annual runoff distribution. The role of climate in the distribution of runoff throughout the year. Factors of the underlying surface that correct the intra-annual distribution of runoff: lakes, swamps, river floodplain, glaciers, permafrost, ice, forest, karst, the size of the river basin, the shape of the catchment area. The influence of the creation of reservoirs and ponds, irrigation, agroforestry and drainage on the intra-annual distribution of river flow. Calculation of the intra-annual runoff distribution in the presence, insufficiency and absence of observational data. Calculation of the daily runoff distribution. Curves of the duration of the daily expenditure. The coefficient of natural regulation of the flow. Coefficient of intra-annual runoff irregularity.

FEATURES OF FORMATION AND CALCULATION OF THE MAXIMUM

RIVER RUNOFF DURING SPRING FLOOR PERIOD.

The concept of "catastrophic flood (flood)". The practical and scientific significance of a reliable assessment of the statistical parameters of floods. Causes of catastrophic floods. Genetic groups of maximum water flow rates. Estimated provision of maximum water flow rates depending on the capital class of the hydraulic structure. The quality of the initial information on the maximum flow rates. Conditions for the formation of flood runoff: snow reserves in the river basin and water reserves in the snow cover, losses due to evaporation from snow, intensity and duration of snow melting, losses melt water... Subsurface factors: relief, slope exposure, size, configuration, dissection of the basin, lakes and marshes, soils and grounds. Anthropogenic factors of the formation of the maximum flood runoff. Genetic theory of the formation of the maximum flow. Reduction of the maximum flow. Calculations of the maximum spring runoff in the presence, insufficiency and absence of observational data. Mathematical and physical-mathematical models of the formation processes of melt water runoff.

MAXIMUM RIVER RUNOFF DURING THE PERIOD OF RAIN FLOOD.

Areas with high rainfall highs. Difficulties in the study and generalization of the characteristics of rainfall runoff. Types of rain and their components. Features of the formation of rainfall floods: the intensity and duration of rain, the intensity of infiltration, the speed and time of the running of rainwater. The role of underlying surface factors and types of economic activities in the formation of rainfall runoff. Calculations of the maximum water discharge of rainfall floods in the presence, inadequacy and absence of observational data. Modeling the runoff of rain floods.

CONDITIONS FOR FORMATION AND CALCULATION OF THE MINIMUM SUMMER
AND WINTER RIVER FLOW.

The concept of low-water period and low-water runoff. The practical significance of knowledge about the minimum flow of rivers. The main calculated characteristics of the minimum and low-water flow of rivers. The duration of the winter and summer or summer-autumn low-water period on the rivers of the territory of Russia. Types of low-water and low-water periods of Russian rivers. Factors of the formation of the minimum runoff: precipitation, temperature, evaporation, connection of the waters of the aeration zone, groundwater, karst and artesian waters with the river, geological and hydrogeological conditions in the basin, lakes, swamps, forest, dissection and height of the terrain, river floodplain, depth of the erosional incision of the river channel, areas of surface and underground catchments, slope and orientation of the catchment, irrigation of agricultural lands, industrial and domestic consumption of river water, drainage, use of underground waters, creation of reservoirs, urbanization. Calculations of the minimum low-water runoff for different volumes of initial hydrological information.

4. PRACTICAL WORKS.

PRACTICAL WORK No. 1.

CALCULATIONS OF THE ANNUAL RUNOFF OF RIVERS WITH A PRESCRIBED PERFORMANCE
IN THE INSUFFICIENT AND ABSENCE OF OBSERVATION DATA.

ASSIGNMENT 1: Choose a river basin with a catchment area of ​​at least 2000 km² and no more than 50,000 km ² within Tyumen region and to extract from the ORC publications for this basin a number of observations of average annual discharges.

TASK 2: Determine the statistical parameters of the curve of the provision of average annual flows of the selected river by the methods of moments, maximum likelihood, graphical-analytical.

TASK 3: Determine the annual flow of the river with 1%, 50% and 95% coverage.

TASK 4: Calculate the average annual runoff of the same river using the map of the isolines of the module and the runoff layer and evaluate the accuracy of the calculation.

THEORY: In the presence or inadequacy of observational data, the main statistical parameters of the river runoff are determined by three methods: the method of moments, the method of maximum likelihood, and the graphic-analytical method.

METHOD OF MOMENTS.

To determine the parameters of the distribution curveQо, Cv and Сs by the method of moments the following formulas are used:

1) average long-term value of water consumption

Qо = ΣQi / n, where

Qi - annual values ​​of water consumption, m³ / s;

n is the number of years of observations; for a series of observations less than 30 years, instead of n, take (n - 1).

2) coefficient of variation

Cv = ((Σ (Ki -1) ²) / n) ½, where

Ki - modular coefficient calculated by the formula

Ki = Qi / Qо.

3) coefficient of asymmetry

Cs = Σ (Ki - 1) ³ / (n · Cv³).

The Cv and Cs values ​​are used to calculate the Cs / Cv ratio and calculation errors for Qо, Cv and Cs:

1) error Qо

σ = (Cv / n½) * 100%;

2) Cv error should be no more than 10-15%

Έ = ((1 + Cv²) / 2n) ½ · 100%,

3) Cs error

έ = ((6 / n) ½ (1 + 6Cv² + 5Cv (½ / Cs) · 100%.

THE BIGGEST LIKELY METHOD .

The essence of the method is that the most probable is the value of the unknown parameter at which the likelihood function reaches the highest possible value. In this case, the members of the series, which correspond to greater importance functions. This method is based on the use of statistics λ 1, λ 2, λ 3. Statistics λ 2 and λ 3 are related to each other and their ratio changes with changes in Cv and the Cs / Cv ratio. Statistics are calculated using the formulas:

1) statistics λ 1 is the arithmetic mean of a series of observations

λ 1 = ΣQi / n;

2) statistics λ 2

λ 2 = Σ ІgКi / (n - 1);

3) statistics λ 3

λ 3 = Σ Кi · ІgКi / (n - 1).

Determination of the coefficient of variability Cv and the ratio Cs / Cv is carried out according to nomograms (see in study guide... Practical hydrology. L .: Gidrometeoizdat, 1976, p. 137) in accordance with the calculated statistics λ 2 and λ 3 ... On the nomograms, we find the intersection point of the values ​​of statistics λ 2 and λ 3 ... The Cv value is determined from the vertical curve closest to it, and the Cs / Cv ratio is determined from the horizontal curve, from which we proceed to the Cs value. The Cv error is determined by the formula:

Έ = (3 / (2n (3+ Cv²))) ½ · 100%.

GRAPHO-ANALYTICAL METHOD .

By this method, the statistical parameters of the analytical supply curve are calculated using three characteristic ordinates of the smoothed empirical supply curve. These ordinates are the quantities Q

The dependence Q = f (P) is plotted on the semilogarithmic fiber of the probability. To build a smoothed empirical supply curve, it is necessary to build a number of observations in a decreasing sequence and for each ranked value of water flow Q kill ... assign the value of security P, calculated by the formula:

Р = (m / n + 1) 100%, where

m is the ordinal number of a member of the series;

n is the number of members of the series.

The horizontal axis shows the values ​​of the security, along the vertical - the corresponding Q kill The intersection points are marked with circles with a diameter of 1.5-2mm and are fixed with ink. A smoothed empirical supply curve is drawn along the points with a pencil. Three characteristic ordinates Q are removed from this curve 5%, Q 50% and Q 95% security, due to which the value of the slope coefficient S of the security curve is calculated according to the following formula:

S = (Q 5% + Q 95% - 2 Q 50%) / (Q 5% - Q 95%).

The skew factor is a function of the skew factor. Therefore, the calculated value of S determines the value of Cs (see Appendix 3 in the textbook. Practical Hydrology. L .: Gidrometeoizdat, 1976, p. 431). According to the same application, depending on the obtained Cs value, the difference between the normalized deviations (Ф 5% - Ф 95% ) and the normalized deviation Ф 50% ... Next, the standard deviation σ, the mean long-term runoff Qо´ and the coefficient of variation Cv are calculated according to the following formulas:

σ = (Q 5% - Q 95%) / (Ф 5% - Ф 95%),

Qо ´ = Q 50% - σ · Ф 50%,

Сv = σ / Q´.

The analytical supply curve is considered to be sufficiently consistent with the empirical distribution if the following inequality is satisfied:

ІQо - Qо´І< 0,02·Qо.

The root mean square error Qо´ is calculated by the formula:

σ Qо´ = (Сv / n½) · 100%.

Coefficient of variation error

Έ = ((1+ Сv²) / 2n) ½ · 100%.

CALCULATION OF EXPENSES OF THE GIVEN SECURITY .

The consumption of a given security is calculated by the formula:

Qр = Кр Qо, where

Кр - modular coefficient of a given provision р%, calculated by the formula

Кр = Фр Cv + 1, where

Фр - normalized deviations of the given provision from the average value of the ordinates of the binomial distribution curve, determined according to Appendix 3 of the textbook. Practical hydrology. L .: Gidrometeoizdat, 1976, p. 431.

The statistical parameters for the river basin and its guaranteed costs recommended for further hydrological calculations and design work are obtained by calculating the arithmetic mean of the Qо, Cv, Cs, Q obtained by the three above methods 5%, Q 50% and Q 95% of the security.

DETERMINATION OF THE VALUES OF THE AVERAGE ANNUAL FLOW OF RIVERS BY

CARDS.

In the absence of observational data on the runoff, one of the ways to determine it is the maps of the isolines of the modules and the runoff layer (see the tutorial. Practical hydrology. Leningrad: Gidrometeoizdat, 1976, pp. 169-170). The value of the module or layer of the runoff is determined for the center of the catchment area of ​​the river. If the center of the catchment lies on the isoline, then the mean value of the runoff of the given catchment is taken according to the value of this isoline. If a catchment lies between two contours, then the flow value for its center is determined by linear interpolation. If several isolines cross the catchment, then the value of the runoff modulus (or runoff layer) for the center of the catchment is determined by the weighted average method according to the formula:

Мср = (М 1 f 1 + М 2 f 2 +… М n f n) / (f 1 + f 2 +… f n), where

M 1, M 2 ... - average values ​​of runoff between adjacent isolines crossing the catchment;

f 1, f 2 ... - the catchment area between isolines within the catchment area (in km² or in palette divisions).

River- a natural water stream that constantly flows in the depression (channel) formed by it.
In each river, a source, upper, middle, lower reaches and mouth are distinguished. Source- the beginning of the river. Rivers begin at the confluence of streams that arise in places where groundwater flows out or that collect water from atmospheric precipitation that has fallen to the surface. They flow out of swamps (for example, the Volga), lakes and glaciers, feeding on the water accumulated in them. In most cases, the source of the river can be determined only conditionally.
Its upper course begins from the source of the river.
V upper In the course of the river flow, there is usually less abundant water than in the middle and lower reaches, the slope of the surface, on the contrary, is greater, and this is reflected in the speed of the current and on the erosion activity of the flow. V average During the course of the river, the river becomes abundant, but the speed of the current decreases, and the flow carries mainly the products of the erosion of the channel in the upper course. V lower during the slow movement of the flow, the deposition of sediments brought by it from above (accumulation) prevails. The lower course of the river ends with the mouth.
Estuary rivers - the place where it flows into the sea, lake, into another river. In a dry climate, where rivers consume a lot of water (for evaporation, irrigation, filtration), they can gradually dry up without bringing their waters to the sea or to another river. The mouths of such rivers are called "blind". All rivers flowing through a particular territory form it river network entering together with lakes, swamps and glaciers into hydrographic network.
The river network consists of river systems.
The river system includes the main river (whose name it bears) and tributaries. In many river systems, the main river is clearly distinguished only in the lower reaches, in the middle and especially in the upper reaches it is very difficult to determine it. Length, water content, axial position in the river system, relative age of the river valley (the valley is older than that of the tributaries) can be taken as signs of the main river. The main rivers of most large river systems do not meet all of these characteristics at once, for example: The Missouri is longer and fuller than the Mississippi; The Kama brings no less water to the Volga than the Volga carries at the mouth of the Kama; The Irtysh is longer than the Ob and its position is more consistent with the position of the main river of the river system. Historically, the main river of the river system was the one that people knew earlier and better than other rivers of this system.
The tributaries of the main river are called tributaries of the first order, their tributaries are called tributaries of the second order, etc.

The river system is characterized by the length of its constituent rivers, their tortuosity and the density of the river network. Length of rivers- the total length of all rivers in the system, measured on a large-scale map. The degree of tortuosity of the river is determined tortuosity coefficient(Fig. 87) - the ratio of the length of the river to the length of the straight line connecting the source and the mouth. River network density- the ratio of the total length of all rivers of the considered river network to the area it occupies (km / km2). On the map, even on a not very large scale, it can be seen that the density of the river network in different natural zones is not the same.
In the mountains, the density of the river network is greater than on the plains, for example: on the northern slopes of the Caucasian ridge it is 1.49 km / km2, and on the plains of the Ciscaucasia - 0.05 km / km2.
The area of ​​the surface from which water flows into the same river system is called the basin of this river system or its catchment. The basin of the river system consists of the basins of the tributaries of the first order, which in turn consist of the basins of the tributaries of the second order, etc. River basins are included in the basins of the seas and oceans. All land waters are divided between the main basins: 1) the Atlantic and Arctic oceans (area 67 359 thousand km2), 2) the Pacific and Indian oceans (area 49 419 thousand km2), 3) the area of ​​internal flow (area 32 035 thousand km2) km2).
River basins are of various sizes and very varied shapes. There are symmetrical basins (for example, the Volga basin) and asymmetric (for example, the Yenisei basin).
The size and shape of the basin largely determine the size and flow regime of the river. The position of the river basin is also important, which can be located in different climatic zones and can stretch in the latitudinal direction within the same zone.
Pools are bounded by watersheds. In mountainous countries, they can be lines that generally coincide with the crests of ridges. On the plains, especially flat and swampy, the watersheds are not clearly expressed.
In some places, watersheds cannot be drawn at all, since the mass of water from one river is divided into two parts, heading to different systems. This phenomenon is called bifurcation of the river (dividing it into two). A striking example of bifurcation is the division of the upper reaches of the Orinoco into two rivers. One of them, for which the name Orinoco is retained, flows into the Atlantic Ocean, the other, the Casiquiare, flows into the Rio Negro, a tributary of the Amazon.
Watersheds limit the basins of rivers, seas, oceans. The main basins: the Atlantic and Arctic Ocean (Atlantic-Arctic), on the one hand, and the Pacific and Indian, on the other, are limited by the main (world) watershed of the Earth.
The position of the watersheds does not remain constant. Their movements are associated with the slow incision of the upper reaches of the rivers as a result of the development of river systems and with the restructuring of the river network, caused, for example, by tectonic movements of the earth's crust.
Riverbed. Water streams flow along the earth's surface in longitudinal depressions created by them - channels. There can be no river without a channel. The concept of "river" includes both a stream and a channel. In most rivers, the channel is cut into the surface along which the river flows. But there are many rivers, the channels of which rise above the plain they cross. These rivers have laid their channels in the sediments deposited by them. An example would be the Yellow River, Mississippi and Po rivers downstream. Such channels are easy to move, their lateral wall breaks often occur, threatening floods.
The cross section of a channel filled with water is called the water section of a river. If the entire water section is a section of a moving stream, it coincides with the so-called living section. If in the water section there are fixed sections (with a speed of movement not captured by the devices), they are called dead space. In this case, the free area will be less than the water area by an amount equal to the area of ​​the dead space. The channel cross-section is characterized by area, hydraulic radius, width, average and maximum depth.
The cross-sectional area (F) is determined as a result of depth measurements over the entire cross-section at certain intervals, taken depending on the width of the river. According to V.A. Appolov, the area of ​​the free cross-section is related to the width (B) and the greatest depth (H) by the equation: F = 2 / 3BH.
Hydraulic radius (R) is the ratio of the cross-sectional area to the wetted perimeter (P), i.e., to the length, of the line of contact of the flow with its bed:

The hydraulic radius characterizes the cross-sectional shape of the channel, as it depends on the ratio of its width and depth. In shallow and wide rivers, the wetted perimeter is almost equal to the width; in this case, the hydraulic radius is almost equal to the average depth.
The average depth (Hcp) of the cross-section of the river is determined by dividing its area by the width (B): Hcp = S / B. Width and maximum depth are obtained by direct measurements.
All cross-sectional elements change with the change in the position of the river level. The level of the river is subject to constant fluctuations, which are systematically monitored at special gauging stations.
The longitudinal profile of the river bed is characterized by a dip and a slope. Fall (Δh) - difference in heights of two points (h1-h2). The ratio of the fall to the length of the section (l) is called the slope (i):

The fall is expressed in meters, the slope is shown as a decimal fraction - in meters per kilometer of fall, or in thousandths (ppm - ‰).
The rivers of the plains have small slopes, the slopes of the mountain rivers are significant.
The greater the slope, the faster the river flows (Table 23).

The longitudinal profile of the channel bottom and the longitudinal profile of the water surface are different: the first is always a wavy line, the second is a smooth line (Fig. 88).
River flow speed. The water flow is characterized by turbulent motion. Its speed at each point is continuously changing both in magnitude and in direction. This ensures constant mixing of the water and promotes erosion activity.
The speed of the river flow is not the same in different parts of the living section. Numerous measurements show that the highest speed is usually observed near the surface. As it approaches the bottom and the walls of the channel, the current velocity gradually decreases, and in the bottom layer of water, only a few tens of millimeters thick, it sharply decreases, reaching a value close to 0 at the very bottom.
Lines of distribution of equal velocities along the free cross-section of the river - isotachs. The wind blowing with the current increases the speed on the surface; the wind blowing against the current slows it down. Slows down the speed of water movement on the surface and the ice cover of the river. The jet in the stream that has the highest speed is called its dynamic axis, the jet of the highest speed on the surface of the stream is the rod. Under some conditions, for example, when the wind is passing the current, the dynamic axis of the flow is on the surface and coincides with the rod.
The average speed in the open area (Vav) is calculated by the Shezy formula: V = C √Ri, where R is the hydraulic radius, i is the slope of the water surface at the observation site, C is a coefficient depending on the roughness and shape of the channel (the latter is determined using special tables).

The nature of the flow. Particles of water in the stream are moved by gravity along the slope. Their movement is delayed by the friction force. In addition to gravity and friction, the nature of the flow is influenced by the centrifugal force that occurs at the bends of the channel, and the deflecting force of the Earth's rotation. These forces cause cross and circular flow in the flow.
Under the action of centrifugal force at the turn, the stream is pressed against the concave bank. In this case, the greater the speed of the current, the greater the force of inertia that prevents the flow from changing the direction of movement and deviating from the concave coast. The current velocity at the bottom is less than on the surface; therefore, the deviation of the bottom layers towards the coast opposite to the concave one is greater than that of the surface layers. This contributes to the occurrence of a current across the channel. As the water is pressed against the concave bank, the surface of the stream receives a lateral slope from the concave to the convex bank. However, the movement of water on the surface along the slope from one bank to another does not occur. This is hindered by centrifugal force, which forces water particles, overcoming the slope, to move towards the concave coast. In the bottom layers, due to the lower current velocity, the influence of the centrifugal force is less pronounced, and therefore the water moves in accordance with the slope from the concave to the convex bank. Particles of water moving across a river are simultaneously related downstream, and their trajectory resembles a spiral.
The deflecting force of the Earth's rotation forces the stream to press against the right bank (in the northern hemisphere), which is why its surface (as well as at a turn under the influence of centrifugal force) acquires a transverse slope. The slope and varying degrees of force on the water particles at the surface and at the bottom cause an internal counter-current flowing clockwise (in the northern hemisphere) when viewed downstream. Since this movement is also combined with the translational movement of particles, they move along the channel in a spiral.
On a straight section of the channel, where centrifugal forces are absent, the nature of the cross-flow is determined mainly by the action of the deflecting force of the Earth's rotation. At bends in the channel, the deflecting force of the Earth's rotation and centrifugal force are either added or subtracted depending on where the river turns, and the lateral circulation is increased or decreased.
Cross circulation can also occur under the influence of different temperatures (unequal density) of water in different parts of the cross section, under the influence of the bottom topography and other reasons. Therefore, it is complex and varied. The influence of transverse circulation on channel formation, as we will see below, is very large.
River runoff and its characteristics. The amount of water passing through the cross-section of the river in 1 second is its consumption. The flow rate (Q) is equal to the product of the free area (F) and the average speed (Vcp): Q = FVcp m3 / s.
Water flows in rivers are highly variable. They are more stable on rivers regulated by lakes and reservoirs. On the rivers of the temperate zone, the highest water discharge occurs during the spring flood, the lowest - in the summer months. According to the data of daily expenditures, graphs of changes in expenditure are plotted - hydrographs.
The amount of water passing through the living section of the river for a more or less long time is the flow of the river. The runoff is determined by summing up the water consumption for the period of interest (day, month, season, year). The flow volume is expressed in either cubic meters or cubic kilometers. Calculation of the runoff over a number of years makes it possible to obtain its average long-term value (Table 24).

The flow of water is characterized by the water content of the river. River flow depends on the amount of water entering the river from the area of ​​its basin. To characterize the runoff, in addition to the flow rate, the runoff module, runoff layer, runoff coefficient are used.
Drain module(M) - the number of liters of water flowing down from a unit area of ​​the pool (1 sq. Km) per unit of time (in seconds). If the average flow rate in the river for a certain period of time is Q m3 / sec, and the area of ​​the basin is F sq. km, then the average flow modulus for the same period of time is M = 1000 l / s * km2 (the factor 1000 is necessary, since Q is expressed in cubic meters, and M - in l). M Neva - 10 l / sec, Don - 9 l / sec, Amazon - 17 l / sec.
Runoff layer- a layer of water in millimeters that would cover the catchment area if the entire volume of runoff is evenly distributed over it.
Runoff coefficient(h) - the ratio of the runoff layer to the amount of precipitation that fell on the same area over the same period of time, expressed as a percentage or in fractions of a unit, for example: the runoff coefficient of the Neva - 65%, Don - 16%, Nile - 4% , Amazon - 28%.
The runoff depends on the whole complex of physical and geographical conditions: on climate, soil, geological structure of the zone, active water exchange, vegetation, lakes and swamps, as well as on human activities.
Climate refers to the main factors in the formation of runoff. It determines the amount of moisture, depending on the amount of atmospheric precipitation (the main element of the input part of the water balance) and on the evaporation rate (the main indicator of the expenditure part of the balance). The greater the amount of precipitation and the lower the evaporation, the higher the moisture should be and the more significant the runoff can be. Precipitation and volatility determine the potential for runoff. The actual flow depends on the whole complex of conditions.
The climate influences the runoff not only directly (through precipitation and evaporation), but also through other components of the geographic complex - through soils, vegetation, relief, which to one degree or another depend on the climate. The influence of climate on runoff, both directly and through other factors, is manifested in zonal differences in the magnitude and nature of runoff. The deviation of the values ​​of the actually observed runoff from the zonal one is caused by local, intrazonal physical and geographical conditions.
A very important place among the factors determining the river runoff, its surface and underground components, is occupied by the soil cover, which plays the role of an intermediary between climate and runoff. The value of surface runoff, water consumption for evaporation, transpiration and recharge of groundwater depend on the properties of the soil cover. If the soil weakly absorbs water, the surface runoff is large, little moisture accumulates in the soil, the consumption for evaporation and transpiration cannot be large, and there is little groundwater supply. Under the same climatic conditions, but with a greater infiltration capacity of the soil, the surface runoff, on the contrary, is small, a lot of moisture accumulates in the soil, the consumption for evaporation and transpiration is high, and the supply of groundwater is abundant. In the second of the two described cases, the surface runoff is less than in the first, but due to underground recharge it is more uniform. Soil, absorbing water from atmospheric precipitation, can retain it and let it go deeper beyond the zone available for evaporation. The ratio of water consumption for evaporation from the soil and for recharge of groundwater depends on the water-holding capacity of the soil. Soil, which holds water well, consumes more water for evaporation and allows less water to flow into the depths. As a result of waterlogging of the soil, which has a high water-holding capacity, the surface runoff increases. Soil properties are combined in different ways and this is reflected in the runoff.
Influence geological structure on river runoff is determined mainly by the water permeability of rocks and is generally similar to the effect of soil cover. The occurrence of waterproof layers in relation to the day surface is also important. The deep bedding of the aquicludes contributes to the preservation of the infiltrated water from being consumed for evaporation. The geological structure influences the degree of flow regulation, the conditions of groundwater recharge.
The influence of geological factors less than all others depends on zonal conditions and in some cases overrides the influence of zonal factors.
Vegetation affects the amount of runoff both directly and through the soil cover. Its immediate effect is transpiration. River runoff depends on transpiration in the same way as it does on soil evaporation. The more transpiration, the less both components of the river flow. The crowns of trees retain up to 50% of the precipitation, which then evaporate from them. In winter, the forest protects the soil from freezing, in the spring the intensity of snow melting moderates, which contributes to the seepage of melt water and replenishment of groundwater reserves. The influence of vegetation on runoff through the soil is due to the fact that vegetation is one of the factors of soil formation. Infiltration and water retention properties largely depend on the nature of vegetation. The infiltration capacity of the soil in the forest is extremely high.
The runoff in the forest and in the field generally differs little, but its structure is significantly different. In the forest there is less surface runoff and more reserves of soil and groundwater (underground runoff), which are more valuable for the economy.
In the forest, a zonal regularity is found in the ratios between the components of the runoff (surface and underground). In the forests of the forest zone, the surface runoff is significant (higher moisture content), although less than in the field. In the forest-steppe and steppe zones in the forest, surface runoff is practically absent and all the water assimilated by the soil is spent on evaporation and feeding of groundwater. In general, the influence of the forest on the runoff is water-regulating and water-protecting.
Relief affects the drain differently depending on the size of the molds. The influence of the mountains is especially great. The whole complex of physical and geographical conditions (altitudinal zonation) changes with height. In this regard, the runoff also changes. Since the change in the complex of conditions with height can occur very quickly, the overall picture of the formation of runoff in high mountains becomes more complicated. With altitude, the amount of precipitation increases to a certain limit, and the runoff generally increases. The increase in runoff on the windward slopes is especially noticeable, for example, the runoff modulus on the western slopes of the Scandinavian mountains is 200 l / s * km2. In the interior, parts of the mountainous regions, the runoff is less than in the re-riper regions. The relief is of great importance for the formation of runoff in connection with the distribution of the snow cover. Significantly affects runoff and microrelief. Small depressions in the relief, in which water collects, contribute to its infiltration and evaporation.
The slope of the terrain and the steepness of the slopes have an impact on the intensity of the runoff, on its fluctuations, but do not significantly affect the amount of runoff.
Lakes by evaporating the water accumulating in them, they reduce the runoff and at the same time are its regulators. The role of large flowing lakes is especially great in this respect. The amount of water in rivers flowing from such lakes hardly changes during the year. For example, the discharge of the Neva is 1000-5000 m3 / s, while the discharge of the Volga near Yaroslavl before its regulation fluctuated during the year from 200 to 11,000 m3 / s.
Has a strong effect on runoff economic activity people, making big changes in natural complexes. The impact of people on the soil cover is also of great importance. The more plowed areas, the greater part of atmospheric precipitation seeps into the soil, moistens the soil and feeds groundwater, the less part of it flows down the surface. Primitive agriculture causes destructuring of soils, a decrease in their ability to assimilate moisture, and, consequently, an increase in surface runoff and a weakening of groundwater flow. With rational farming, the infiltration capacity of soils increases with all the ensuing consequences.
Snow retention measures aimed at increasing the moisture entering the soil affect the runoff.
Artificial reservoirs have a regulating effect on river runoff. Reduces runoff water consumption for irrigation and water supply.
Forecasting the flow and regime of rivers is important for planning use. water resources country. In Russia, a special forecasting method has been developed, based on the experimental study of various methods of economic impact on the elements of the water balance.
The distribution of runoff in the territory can be shown using special maps, on which the isolines of runoff values ​​- modules or annual runoff are plotted. The map shows the manifestation of latitudinal zoning in the distribution of runoff, which is especially pronounced on the plains. The influence of the relief on the runoff is also clearly seen.
Rivers feeding. There are four main sources of river power: rain, snow, glacial, underground. The role of one or another power source, their combination and distribution in time depend mainly on climatic conditions. So, for example, in countries with hot climates, snow supply is absent, rivers and deep-lying groundwater do not feed, and the only source of food is rainwater. In cold climates, melt water is of primary importance in the feeding of rivers, and groundwater in winter. In temperate climates, various food sources are combined (Fig. 89).

Depending on the nutrition, the amount of water in the river changes. These changes are manifested in fluctuations in the level of the river (the height of the water surface). Systematic observations of the level of rivers make it possible to find out the patterns in changes in the amount of water in rivers over time, their regime.
In the regime of rivers of a moderately cold climate, in the feeding of which melted snow waters play an important role, four phases, or hydrological seasons, are clearly distinguished: spring flood, summer low water, autumn floods and winter low water. High water, high water, and low water are characteristic of the regime of rivers that are in other climatic conditions.
High water is a relatively long and significant increase in the amount of water in the river, which is repeated annually in the same season, accompanied by a rise in the level. It is caused by the spring melting of snow on the plains, the summer melting of snow and ice in the mountains, and heavy rains.
The onset and duration of floods are different in different conditions. High water caused by the melting of snow on the plains in temperate climates occurs in spring, in cold climates - in summer, in the mountains stretches into spring and summer. High waters caused by rains in monsoon climates include spring and summer, in equatorial climates they occur in autumn, and in Mediterranean climates they occur in winter. The runoff of some rivers during the flood period is up to 90% of the annual runoff.
Low water is the lowest water standing in the river with a predominance of underground recharge. Summer low water occurs as a result of high infiltration capacity of soils and strong evaporation, winter - as a result of lack of surface nutrition.
Floods are relatively short-term and non-periodic rises in the water level in the river, caused by the flow of rain and melt water into the river, as well as by the passage of water from reservoirs. The height of the flood depends on the intensity of rain or snowmelt. The flood can be considered as a wave caused by the rapid flow of water into the channel.
A.I. Voeikov, who considered the rivers as a "product of the climate" of their basins, created in 1884 a classification of rivers according to their feeding conditions.
The ideas underlying the Voeikov river classification were taken into account in a number of classifications. The most complete and precise classification was developed by M.I. Lvovich. Lvovich classifies rivers depending on the source of supply and on the nature of the distribution of runoff throughout the year. Each of the four sources of food (rain, snow, glacial, underground) under certain conditions can be almost the only (almost exclusive), accounting for more than 80% of the total food supply, can have a predominant value in the river feeding (from 50 to 80%) and can prevail (> 50%) among other sources that also play a significant role in it. In the latter case, the river's feeding is called mixed.
The runoff is spring, summer, autumn and winter. Moreover, it can be concentrated almost exclusively (> 80%) or predominantly (from 50 to 80%) in one of the four seasons, or it can occur at all seasons of the year, dominating (> 50%) in one of them.
Natural combinations of various combinations of power sources with different options for the distribution of runoff throughout the year allowed Lvovich to identify the types water regime rivers. Based on the main regularities of the water regime, its main zonal types are distinguished: polar, subarctic, temperate, subtropical, tropical and equatorial.
Rivers of the polar type are fed by melt waters of polar ice and snow for a short period, but they freeze over most of the year. Rivers of the subarctic type are fed by melted snow waters, their underground feeding is very insignificant. Many, even significant rivers freeze over. These rivers have the highest level in summer (summer flood). The reason is late spring and summer rains.
Rivers of the temperate type are divided into four subtypes: 1) with a predominance of feeding due to the spring melting of the snow cover; 2) with a predominance of rainwater supply with a small runoff in spring, both due to the abundance of rains and under the influence of snow melting; 3) with a predominance of rainfall in winter with a more or less uniform distribution of precipitation throughout the year; 4) with a predominance of rainfall in summer due to heavy monsoon rains.
Rivers of the subtropical type are fed mainly by rainwater in winter.
Rivers of the tropical type are characterized by low runoff. Summer rainfall predominates, with little precipitation in winter.
Rivers of the equatorial type have abundant rainfall throughout the year; the largest runoff occurs in the fall of the corresponding hemisphere.
The rivers of mountainous regions are characterized by regularities of vertical zonation.
Thermal regime of rivers. The thermal regime of the river is determined by the absorption of heat from direct solar radiation, the effective radiation of the water surface, the cost of heat for evaporation and its release during condensation, heat exchange with the atmosphere and the bed of the channel. The water temperature and its changes depend on the ratio of the input and output parts of the heat balance.
In accordance with the thermal regime of rivers, they can be divided into three types: 1) rivers are very warm, without seasonal temperature fluctuations; 2) rivers are warm, with noticeable seasonal temperature fluctuations, not freezing in winter; 3) rivers with large seasonal temperature fluctuations, freezing in winter.
Since the thermal regime of rivers is determined primarily by the climate, large rivers flowing through different climatic regions have a different regime in different parts... The rivers of temperate latitudes have the most difficult thermal regime. In winter, when the water is cooled slightly below its freezing point, the process of ice formation begins. In a calmly flowing river, first of all, there are banks. Simultaneously with them or somewhat later, a thin layer of small ice crystals - tallow - forms on the surface of the water. The fat and the banks freeze into the continuous ice cover of the river.
At fast movement water, the freezing process is delayed by stirring it and the water can be supercooled by a few hundredths of a degree. In this case, ice crystals appear in the entire water column and intra-water and bottom ice is formed. Intra-bottom and bottom ice that has surfaced on the surface of the river is called sludge. Sludge accumulates under the ice and creates gaps. Sludge, fat, wet snow, broken ice floating on the river form an autumn ice drift. At the bends of the river, in the narrowing of the channel during ice drift, there are jams. The establishment of a continuous, stable ice cover on a river is called freeze-up. Small rivers freeze like poison earlier than large ones. The ice cover and the snow falling on it protect the water from further cooling. If heat loss continues, ice builds up from below. Since, as a result of freezing of water, the cross-section of the river decreases, water under pressure can pour out onto the surface of the ice and freeze, increasing its capacity. The thickness of the ice cover on the lowland rivers of Russia is from 0.25 to 1.5 m and more.
The freezing time of rivers and the length of the period during which the ice cover remains on the river are very different: Lena is covered with ice on average 270 days a year, Mezen - 200, Oka - 139, Dnieper - 98, Vistula near Warsaw - 60, Elbe near Hamburg - 39 days and even then not annually.
Under the influence of abundant groundwater outflows or due to the inflow of warmer lake water, some rivers may retain polynyas throughout the winter (for example, on the Angara).
River opening begins near the banks under the influence of solar heat of the atmosphere and melt water entering the river. The influx of melt water causes a rise in the level, ice floats up, breaking away from the coast, and along the coast a strip of water without ice stretches - the rim. The entire mass of ice begins to move downstream and stops: first, the so-called ice movements occur, and then the spring ice drift begins. On rivers flowing from north to south, ice drift is more calm than on rivers flowing from south to north. In the latter case, the coverage begins from the upper reaches, while the middle and lower reaches of the river are ice-bound. A wave of spring floods moves down the river, with congestions formed, water level rises occur, ice, not yet starting to melt, breaks up and is thrown onto the shore, powerful ice drifts are created that destroy the banks.
On rivers flowing from lakes, two spring ice drifts are often observed: first, river ice, then lake ice.
River water chemistry. River water is a solution with a very low salt concentration. The chemical characteristics of the water in the river depend on the sources of nutrition and on the hydrological regime. According to dissolved minerals (according to the equivalent prevalence of the main anions), river waters are divided (according to A.O. Alekin) into three classes: hydrocarbonate (CO3), sulfate (SO4) and chloride (Cl). The classes, in turn, are divided by the predominance of one of the cations (Ca, Mg, or the sum of Na + K) into three groups. In each group, three types of waters are distinguished according to the ratio between total hardness and alkalinity. Most of the rivers belong to the hydrocarbonate class, to the group of calcium waters. Hydrocarbonate waters of the sodium group are rare, in Russia mainly in Central Asia and Siberia. Among carbonate waters, weakly mineralized waters (less than 200 mg / l) prevail, waters of medium mineralization (200-500 mg / l) are less common - in middle lane The European part of Russia, the South Caucasus and partly in Central Asia. Highly mineralized hydrocarbonate waters (> 1000 mg / l) are very rare. Rivers of the sulfate class are relatively rare. As an example, we can cite the rivers of the Azov region, some rivers North Caucasus, Kazakhstan and Central Asia. Chloride rivers are even less common. They flow in the space between the lower reaches of the Volga and the upper reaches of the Ob. The waters of rivers of this class are highly mineralized, for example, in the river. Turgai water mineralization reaches 19000 mg / l.
During the year due to changes in river flow chemical composition water changes so much that some rivers "pass" from one hydrochemical class to another (for example, the Tejen river belongs to the sulfate class in winter, and to the hydrocarbonate class in summer).
In areas of excessive moisture, the salinity of river waters is insignificant (for example, Pechora - 40 mg / l), in areas of insufficient moisture - high (for example, Emba - 1641 mg / l, Kalaus - 7904 mg / l). When passing from the zone of excess to the zone of insufficient moisture, the composition of salts changes, the amount of chlorine and sodium increases.
Thus, Chemical properties river waters show zonal character. The presence of readily soluble rocks (limestone, salt, gypsum) can lead to significant local features in the salinity of river water.
The amount of dissolved substances carried in 1 second through the flow area of ​​the river is the consumption of dissolved substances. The flow of dissolved substances, measured in tons (Table 25), is formed from the sum of expenditures.

The total amount of dissolved substances carried out by rivers from the territory of Russia is about 335 * 10 6 tons per year. About 73.7% of dissolved substances are carried out into the Ocean and about 26.3% - into the water bodies of the area of ​​internal flow.
Solid drain. The solid mineral particles carried by the river flow are called river sediments. They are formed due to the drift of rock particles from the surface of the basin and erosion of the channel. Their number depends on the energy of the moving water and on the resistance of the rocks to erosion.
River sediments are divided into suspended and transported, or bottom. This division is arbitrary, since with a change in the speed of the current, one category of sediment quickly passes into another. The higher the flow rate, the larger the suspended particles can be. With a decrease in speed, larger particles sink to the bottom, becoming entrained (moving abruptly) sediments.
The amount of suspended sediment carried by the flow through the cross-section of the river per unit of time (second) is the suspended sediment discharge (R kg / m3). The amount of suspended sediment carried through the cross-section of the river over a long period of time is the suspended sediment runoff.
Knowing the flow rate of suspended sediment and water flow in the river, it is possible to determine its turbidity - the number of grams of suspended matter in 1 m3 of water: P = 1000 R / Q g / m3. The stronger the erosion and the more particles are carried into the river, the greater its turbidity. The rivers of the Amu Darya basin are distinguished by the highest turbidity among the rivers of Russia - from 2500 to 4000 g / m3. Low turbidity is typical for northern rivers - 50 g / m3.
The average annual runoff of suspended sediment in some rivers is shown in Table 26.

During the year, the runoff of suspended sediments is distributed depending on the water runoff regime and is maximum on large rivers of Russia during the spring flood. For rivers in the northern part of Russia, spring runoff (suspended sediment is 70-75% of the annual runoff, and for rivers in the central part of the Russian Plain - 90%.
Traction (bottom) sediment is only 1-5% of the amount of suspended sediment.
According to Airy's law, the mass of particles transported by water along the bottom (M) is proportional to the speed (F) to the sixth power: M = AV6 (A is the coefficient). If the speed is increased by 3 times, the mass of particles that the river is capable of carrying will increase by 729 times. Hence, it is clear why calm flat rivers move only forests, while mountain rivers roll boulders.
At high speed, the drawn (bottom) sediments can move in a layer up to several tens of centimeters thick. Their movement is very uneven, since the speed at the bottom changes sharply. Therefore, sand waves are formed at the bottom of the river.
The total amount of sediment (suspended and bottom) carried through the free area of ​​the river is called its solid runoff.
The sediments carried by the river undergo changes: they are processed (abraded, crushed, rolled), sorted by weight and size), and as a result, alluvium is formed.
Stream energy. The stream of water moving in the channel has energy and is capable of doing work. This ability depends on the mass of the moving water and on its speed. The energy of the river on a section L km long at a drop in Nm and at a flow rate of Q m3 / s is equal to 1000 Q * H kgm / s. Since one kilowatt is equal to 103 kgm / s, the capacity of the river in this section is 1000 QH / 103 = 9.7 QH kW. The rivers of the Earth carry 36,000 cubic meters to the Ocean annually. km of water. With an average land height of 875 m, the energy of all rivers, (A) is equal to 31.40 * 1000w6 kgm.

The energy of the rivers is spent on overcoming friction, on erosion, on the transfer of material in a dissolved, suspended and entrained state.
As a result of the processes of erosion (erosion), transfer (transportation) and deposition (accumulation) of sediments, a river bed is formed.
River channel formation. The stream constantly and directly cuts into the rocks through which it flows. At the same time, it seeks to develop a longitudinal profile, in which its kinetic force (mv2 / 2) will be the same throughout the river, and an equilibrium will be established between erosion, transfer and sedimentation in the channel. This channel profile is called the equilibrium profile. With a uniform increase in the amount of water in the river downstream, the equilibrium profile should be a concave curve. It has the greatest slope in the upper part, where the mass of water is smallest; downstream, with an increase in the amount of water, the slope decreases (Fig. 90). In the rivers of the desert, which are fed in the mountains, and in the lower reaches that lose a lot of water for evaporation and filtration, an equilibrium profile is formed, which is convex in the lower part. Due to the fact that the amount of water, the amount and nature of sediments, the speed along the course of the river change (for example, under the influence of tributaries), the equilibrium profile of rivers has unequal curvature in different sections, it can be broken, stepwise, depending on specific conditions.
The river can develop an equilibrium profile only under conditions of prolonged tectonic rest and unchanged position of the erosion base. Any violation of these conditions leads to a violation of the balance profile and to the resumption of work on its creation. Therefore, in practice, the equilibrium profile of a river is not achievable.
Unworked longitudinal profiles of rivers have many irregularities. The river intensively erodes the ledges, fills the depressions in the channel with sediments, trying to level it. At the same time, the channel is incised according to the position of the base of erosion, spreading up the river (retreating, regressive erosion). Due to the irregularities of the longitudinal profile of the river, waterfalls and rapids often appear in it.
Waterfall- the fall of the river flow from a pronounced ledge or from several ledges (cascade of waterfalls). There are two types of waterfalls: Niagara and Yosemite. The width of the Niagara-type waterfalls exceeds their height. Niagara Falls is divided by the island into two parts: the width of the Canadian part is about 800 m, the height is 40 m; the width of the American part is about 300 m, the height is 51 m. Waterfalls of the Yosemite type are high in height and relatively small in width. Yosemite Falls (Merced River) is a narrow stream of water falling from a height of 727.5 m. This type includes the highest waterfall on Earth - Angel (Angela) - 1054 m (South America, Churun ​​River).
The ledge of the waterfall is continuously collapsing and receding up the river. In the upper part it is washed away by the flowing water, in the lower part it is vigorously destroyed by the water falling from above. Waterfalls recede especially quickly in cases where the ledge is composed of easily eroded rocks, covered only from above with layers of persistent rocks. It is such a structure that the Niagara ledge has, receding at a rate of 0.08 m per year in the American part and 1.5 m per year in the Canadian part.
In some areas, there are “waterfall lines” associated with long-distance ledges. Often, "waterfall lines" are associated with fault lines. At the foot of the Appalachians, when passing from mountains to plains, all rivers form waterfalls and rapids, the energy of which is widely used in industry. In Russia, the line of waterfalls runs in the Baltics (the precipice of the Silurian plateau).
Thresholds- sections of the longitudinal river bed, in which the fall of the river increases and, accordingly, the speed of the river flow increases. Rapids are formed for the same reasons as waterfalls, but at a lower ledge height. They can occur at the site of a waterfall.
Developing a longitudinal profile, the river cuts in its upper reaches, pushing back the watershed. Its basin increases, an additional amount of water begins to flow into the river, which contributes to cutting. As a result, the upper reaches of one river can come close to another river and, if the latter is located higher, capture it and include it in its own system (Fig. 91). Turning on new river into the river system will change the length of the river, its runoff and affect the formation of the channel.

River interceptions- the phenomenon is not uncommon, for example, p. Pinega (the right tributary of the Northern Dvina) was an independent river and was one with the r. Kuloi, which flows into the Mezen Gulf. One of the tributaries of the Northern Dvina intercepted most Pinegi and took her waters to the Northern Dvina. The Psel River (a tributary of the Dnieper) intercepted another tributary of the Dnieper - Khorol, r. Merty - upstream p. The Moselle (which belonged to the Meuse), the Rhone and Rhine are parts of the upper Danube. It is planned to intercept the Danube by the rivers Neckar and Rutach, etc.
Until the river develops an equilibrium profile, it intensively erodes the bottom of the channel (deep erosion). The less energy is spent on erosion of the bottom, the more the river erodes the banks of the channel (lateral erosion). Both of these processes, which determine the formation of the channel, occur simultaneously, but each of them becomes leading at different stages.
The river very rarely flows straight. The initial deviation may be due to local obstacles caused by geological structure and terrain. The meanders formed by the river are preserved long time unchanged only under certain conditions, which are difficult to erode rocks, a small amount of sediment.
As a rule, gyri, regardless of the cause of their occurrence, continuously change and move downstream. This process is called meandering, and the convolutions formed as a result of this process - meanders.
A water flow that, for whatever reason (for example, due to the emergence of bedrock on its way), the direction of movement, approaches at an angle to the channel wall and, intensively eroding it, leads to a gradual retreat. Reflecting downstream, the stream hits the opposite bank, erodes it, is reflected again, etc. As a result, the eroded areas "pass" from one side of the channel to the other. Between two concave (eroded) sections of the coast, there is a convex section - the place where the bottom cross current, coming from the opposite shore, deposits the erosion products carried by it.
As the tortuosity increases, the meandering process intensifies, however, up to a certain limit (Fig. 92). An increase in tortuosity means an increase in the length of the river and a decrease in the slope, which means a decrease in the speed of the current. The river loses its energy and can no longer erode the banks.
The curvature of the meanders can be so great that a breakthrough of the isthmus occurs. The ends of the severed gyrus are filled with loose deposits, and it turns into an oxbow.
The strip within which the river meanders is called the meander belt. Big rivers, meandering, form large meanders, and their meander belt is wider than that of small rivers.
Since the stream, eroding the coast, approaches it at an angle, the meanders do not just increase, but gradually move downstream. Over a long period of time, they can move so much that the concave section of the channel will be in place of the convex one, and vice versa.

Moving in the meander belt, the river erodes rocks and deposits sediments, as a result of which a flat depression lined with alluvium is created, along which the river bed meanders. During floods, the water overflows the channel and fills the depression. This is how a floodplain is formed - a part of a river valley that is flooded.
During floods, the river is less meandering, its slope increases, depths increase, speed becomes greater, erosion activity intensifies, large meanders are formed, which do not correspond to meanders formed during low-water periods. There are many reasons for eliminating the tortuosity of the river, and therefore meanders often have a very complex shape.
The relief of the bottom of the channel of a meandering river is determined by the distribution of the current. The longitudinal flow, due to the force of gravity, is the main factor in bottom erosion, while the lateral flow determines the transfer of erosion products. At the washed-out concave bank, the stream washes out a depression - a stretch, and the cross current carries mineral particles to the convex bank, creating a sandbank. Therefore, the cross-sectional profile of the channel at the bend of the river is asymmetric. On the straight section of the channel, located between two streams and called the roll, the depths are relatively shallow, and there are no sharp fluctuations in depth in the transverse profile of the channel.
The line connecting the deepest points along the channel - the fairway - runs from stretch to stretch through the middle part of the rift. If a roll crosses fairways that do not deviate from the main direction, and if its line runs smoothly, it is called normal (good); a roll in which the fairway makes a sharp bend will be shifted (bad) (Fig. 93). Bad rifts make navigation difficult.
The formation of the channel topography (formation of streams and rifts) occurs mainly in spring during floods.

Life in the rivers. Living conditions in fresh waters differ significantly from living conditions in oceans and seas. In the river, they are of great importance for life fresh water, constant turbulent mixing of water and relatively shallow depths accessible to sunlight.
The flow has a mechanical effect on organisms, provides an inflow of dissolved gases and the removal of decay products of organisms.
According to the living conditions, the river can be divided into three sections, corresponding to its upper, middle and lower reaches.
In the upper reaches of mountain rivers, water moves at the highest speed. There are often waterfalls and rapids here. The bottom is usually stony, with almost no silty deposits. The water temperature is lowered due to the absolute height of the place. V general conditions less favorable for the life of organisms than in other parts of the river. Aquatic vegetation is usually absent, plankton is poor, invertebrate fauna is very scarce, fish food is not provided. The upper reaches of the rivers are poor in fish both in the number of species and in the number of individuals. Only some fish can live here, for example, trout, grayling, marinka.
In the middle reaches of mountain rivers, as well as in the upper and middle reaches of plain rivers, the speed of water movement is less than in the upper reaches of mountain rivers. The water temperature is higher. Sand and pebbles appear at the bottom, and silt in the backwaters. Living conditions here are more favorable, but far from optimal. The number of individuals and species of fish is greater than in the upper reaches, in the mountains; fish such as ruff, eel, burbot, barbel, roach, etc. are widespread.
The most favorable living conditions in the lower reaches of rivers: low flow velocity, muddy bottom, a large number of nutrients... Mainly fish such as smelt, stickleback, river flounder, sturgeon, bream, crucian carp, carp are found here. Fish that live in the sea, into which rivers flow: sea flounder, sharks, etc., penetrate. Not all fish find conditions for all stages of their development in one place, the breeding and habitats of many fish do not coincide, and fish migrate (spawning, forage and wintering migrations).
Channels. The canals are artificial rivers with a peculiar regulated regime, created for irrigation, water supply and navigation. The peculiarity of the canal mode is small fluctuations in the level, but if necessary, the water from the canal can be completely drained.
The movement of water in the canal has the same laws as the movement of water in the river. To a large extent, the water of the canal (up to 60% of all the water consumed by it) is used for infiltration through its bottom. Therefore, the creation of anti-infiltration conditions is of great importance. This task has not yet been solved.
Possible average flow rates and bottom velocities should not exceed certain limits, depending on the resistance of the soil to erosion. For ships moving along the channel, the average current speed of more than 1.5 m / s is already unacceptable.
The depth of the canals should be 0.5 m more than the draft of the vessels, the width should not be less than the width of two vessels + 6 m.
Rivers like natural resource. Rivers are one of the most important water resources that have been used by people for a variety of purposes for a long time.
Shipping was the branch of the national economy for which the study of rivers was required first of all. Connecting rivers with canals allows you to create complex transport systems... The length of river routes in Russia currently exceeds the length railways... Rivers have long been used for timber rafting. The importance of rivers in the water supply of the population (drinking and household), industry, Agriculture... All major cities are on the rivers. The population and municipal economy consume a lot of water (on average 60 liters per day per person). Any industrial product cannot do without irretrievable consumption of a certain amount of water. For example, for the production of 1 ton of pig iron, 2.4 m3 of water is needed, for the production of 1 ton of paper - 10.5 m3 of water, for the production of 1 g of fabric from some polymer synthetic materials - more than 3000 m3 of water. On average, one head of cattle accounts for 40 liters of water per day. The fish wealth of the rivers has always been of great importance. Their use contributed to the emergence of settlements along the coast. Currently, rivers are a source of valuable and nutritious product- fish are underutilized; much more important is marine fisheries. In Russia great attention paid to the organization of fisheries with the creation of artificial reservoirs (ponds, reservoirs).
In areas with a large amount of heat and a lack of atmospheric moisture, the water of rivers in a large number goes for irrigation (UAR, India, Russia - middle Asia). The energy of rivers is being used more and more widely. The total hydropower resources on Earth are estimated at 3750 million kW, of which Asia accounts for 35.7%, Africa - 18.7%, North America - 18.7%, South America - 16.0%, Europe - 6. 4%, Australia - 4.5%. The degree of use of these resources in different countries, on different continents is very different.
The use of rivers is currently very large and will undoubtedly increase in the future. This is due to the progressive growth of production and culture, with the continuously increasing demand of industrial production for water (this is especially true for chemical industry), with an increasing consumption of water for the needs of agriculture (an increase in yield is associated with an increase in water consumption). All this raises the question not only of the protection of river resources, but also of the need for their expanded reproduction.