Analysis of the formation conditions and calculation of the main statistical characteristics of the flow of the Kegeta River. River characteristic
2.13. When determining the calculated hydrological characteristics of the annual river runoff, the requirements set forth in paragraphs. 2.1 - 2.12.
2.14. To determine the intra-annual distribution of water runoff in the presence of hydrometric observation data for a period of at least 15 years, following methods:
runoff distribution according to analogue rivers;
seasons layout method.
2.15. The intra-annual flow distribution should be calculated for water management years, starting from the high-water season. The boundaries of the seasons are assigned the same for all years, rounded to the nearest month.
2.16. The division of the year into periods and seasons is made depending on the type of river regime and the predominant type of runoff use. The duration of the high-water period should be determined so that its accepted boundaries include floods for all years. The period of the year and the season in which natural runoff can limit water consumption are taken as the limiting period and the limiting season. The limiting period includes two adjacent seasons, of which one is the most unfavorable in terms of runoff use (limiting season).
For rivers with spring floods, two dry seasons are taken as the limiting period: summer - autumn and winter. With the predominance of water consumption for agricultural needs, summer-autumn should be taken as the limiting season, and winter for hydropower and water supply purposes.
2.17. For high-mountain rivers with summer floods, with predominantly irrigation use of runoff, autumn-winter and spring are taken as the limiting period, and spring is taken as the limiting season.
When designing the diversion of excess water for flood control or when draining swamps and wetlands, the limiting period is the high-water part of the year (for example, spring and summer - autumn), and the limiting season is the most high-water season (for example, spring).
The estimated probability of exceeding the runoff for the year, for the limiting season and period is determined by the curves of the distribution of the annual probabilities of exceeding (empirical or analytical).
2.18. The intra-annual distribution of runoff for a particular year of observations is taken as a calculated one if the probability of excess runoff for this year and for the limiting period and season are close to each other and correspond to the annual probability of excess given by the design conditions.
2.19. The intra-annual distribution of runoff when calculating according to the layout method is determined from the conditions of equality of the probabilities of exceeding the runoff for the year, the runoff for the limiting period, and within it for the limiting season.
The runoff value of a season not included in the limiting period is determined by the difference between the runoff for the year and the runoff for this period, and the runoff values for a non-limiting season included in the limiting period are determined by the difference between the runoff of this period and the season.
2.20. With close values of the coefficients of variation and asymmetry of river runoff for the year and limiting the period and season, the calculated intra-annual distribution is determined as the average distribution of water runoff by months (decades) for all years as a percentage of the annual water runoff of the studied river.
2.21. With a slight change in water consumption during the year, it is allowed to replace the calendar distribution of water flow by seasons and months of the curve for the duration of daily water consumption for the year.
2.22. When the water flow changes under the influence of economic activity, it is necessary to bring it to the natural flow of the river water in accordance with the requirements of clause 1.6. Based on these data, the estimated intra-annual distribution of river water flow is determined, and appropriate changes are made to the calculation results.
Characteristics of the annual runoff
Runoff is the movement of water over the surface, as well as in the thickness of the soil and rocks during its cycle in nature. In calculations, runoff is understood as the amount of water flowing from the catchment for any period of time. This amount of water can be expressed as a flow rate Q, a volume W, a modulus M, or a runoff layer h.
Runoff volume W - the amount of water flowing from the catchment for any period of time (day, month, year, etc.) - is determined by the formula
W \u003d 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 calculated earlier as the annual flow rate, the flow volume of the r. Kegets per year W \u003d 2.39 365.25 24 3600 \u003d 31764096 m 3.
Runoff module M - the amount of water flowing from a unit catchment area per unit time - is determined by the formula
М=103Q/F [l/(sqm2)], (20)
where F is the catchment area, km 2.
Drain module Kegets М=10 3 2.39/178 = 13.42 l/(sqm 2).
Runoff layer h mm - the amount of water flowing from the catchment for 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)
The runoff layer for the river basin. Kegets h = 31764096/ (178 10 3) = 178.44 mm.
The dimensionless characteristics include the modulus factor and the runoff factor.
The modular coefficient K is the ratio of the runoff for any particular year to the runoff rate:
K \u003d Q i /Q 0 \u003d W i / W 0 \u003d h i / h 0, (22)
and for r. Kegets for the period under consideration K varies from K = 1.58 / 2.39 = 0.66 for a year with a minimum flow to K = 3.26 / 2.39 = 1.36 for a maximum flow.
Runoff coefficient - the ratio of the volume or layer of runoff to the amount of precipitation x that fell on the catchment area, which caused the occurrence of runoff:
The runoff coefficient shows how much of the precipitation goes to the formation of runoff.
In the course work, it is necessary to determine the characteristics of the annual runoff for the basin taken into consideration, taking the runoff rate from the section
Intra-annual runoff distribution
The intra-annual distribution of river runoff takes important place in the issue of studying and calculating runoff, both in practical and scientific terms, being at the same time the most challenging task hydrological research /2,4,13/.
The main factors determining the intra-annual distribution of runoff and its overall value, - climatic. They determine the general character (background) of runoff distribution in the year of one or another geographical area; territorial changes in runoff distribution follow climate change.
The factors influencing the distribution of runoff throughout the year include lakes, forest cover, swampiness, the size of watersheds, the nature of soils and soils, the depth of groundwater, etc., which to a certain extent should be taken into account in the calculations both in the absence and in the presence of observational materials.
Depending on the availability of hydrometric observation data, the following methods for calculating the intra-annual runoff distribution are used:
in the presence of 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 the seasons;
in the absence or insufficiency (less than 10 years) of observational data: a) by analogy with the distribution of the runoff of the studied analogue river; b) according to regional schemes and regional dependences of the parameters of the intra-annual distribution of runoff on physical and geographical factors.
The intra-annual flow distribution is usually calculated not by calendar years, but by water management years, starting from the high-water season. The boundaries of the seasons are assigned the same for all years, rounded to the nearest month.
The estimated probability of flow exceeding for a year, limiting the period and season, is assigned in accordance with the tasks of the water management use 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 distribution of runoff 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, the given percentage of supply P and division into periods and seasons.
The calculation is divided into two parts:
inter-seasonal distribution, which is of the greatest importance;
intra-seasonal distribution (by months and decades, established with some schematization.)
Interseasonal distribution. Depending on the type of intra-annual distribution of runoff, 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 limiting.
The limiting period (season) is the most stressful in terms of water use. For drainage purposes, the limiting period is high water; for irrigation, energy-shallow water.
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 (winter for energy use).
The calculation is carried out according to hydrological years, i.e. for years beginning with a high-water season. The dates of the seasons are assigned the same for all years of observations, rounded up to the nearest whole month. The duration of the high-water season is assigned so that the high water is placed within the boundaries of the season both in the years with the earliest onset and with 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). AT last year the costs for December are added to the costs for three months (I, II, III) of the first year.
When calculating according to the layout method, the intra-annual distribution of runoff is taken from the condition of equality of the probability of exceeding the runoff for the year, the runoff for the limiting period, and within it for the limiting season. Therefore, it is necessary to determine the costs of the security specified 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 supply 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 flow.
You can determine the estimated costs using the formulas:
annual runoff
Orasgod \u003d Kr "12Q 0, (26)
limiting period
Orasinter = KрQ0inter, (27)
limiting season
Oraslo \u003d Kr "Qlo (27)
where Kp", Kp, Kp" are the ordinates of the curves of the three-parameter gamma distribution, taken from the table, respectively, for C v - annual runoff. C v low flow and C v for summer-autumn.
Note. Since the calculations are based on average monthly expenses, the estimated expense for the year must be multiplied by 12.
One of the main conditions of the layout method is the equality
Orasgod = Orasses. However, this equality will be violated if the calculated runoff for non-limiting seasons is also determined from 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)
and for a non-limiting season (in the task-winter)
Oraszim = Orasmezh. - Qlo (29)
The calculation is more convenient to perform in the form of a table. ten.
Intra-seasonal distribution - is taken averaged over each of the three water content groups (high-water group, including years with runoff per season Р<33%, средняя по водности 33<Р<66%, маловодная Р>66%).
To identify the years included in separate water content groups, it is necessary to arrange the total costs for the seasons in descending order and calculate their actual supply. Since the calculated availability (Р=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 down the expenses by seasons, corresponding to the provision P> 66%, and in the column "Years" - write down the years corresponding to these expenses.
Arrange the average monthly expenses within the season in descending order, indicating the calendar months to which they relate (Table 11). Thus, the first will be the discharge for the most wet month, the last - for the low-water month.
For all years, summarize the costs 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 the name of the month that repeats most often. If there are no repetitions, write out any of those encountered, 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 interseasonal distribution of runoff (Table 10), by the percentage of each month A% (Table 11), calculate the estimated discharge for each month.
Horac v = Horaces A % v / 100% (30)
The data obtained are entered in table. 12 “Estimated expenses by months” and on graph paper, an estimated hydrograph R-80% of the river under study is built (Fig. 11).
Table 12. Estimated costs (m3/s) by months
INTRODUCTION
Tasks of hydrological calculations and their role in the development of the country's economy. Connection of hydrological calculations with other sciences. History of the development of hydrological calculations: the first works of foreign scientists in the 17th-19th centuries; works of Russian scientists of the late 19th - early 20th centuries; the first textbook of hydrology in Russia; Soviet period of development of hydrological calculations; All-Union hydrological congresses and their role in the development of methods for calculating river runoff; post-Soviet period of development of hydrological calculations. The main characteristics of river flow. Three cases of determining hydrological characteristics.
METHODS FOR ANALYSIS OF RIVER FLOW CHARACTERISTICS.
Genetic analysis of hydrological data: geographic and hydrological method and its special cases - methods of hydrological analogy, geographic interpolation and hydrological and hydrogeological. Probabilistic-statistical analysis: method of moments, maximum likelihood method, quantifier method, correlation and regression analysis, factor analysis, principal component method, discriminant analysis method. Methods of analysis of computational mathematics: systems of algebraic equations, differentiation and integration of functions, 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: construction principles, runoff determination reliability. Hydrological zoning of the territory: concept, boundaries of application, principles of zoning and approaches to zoning, methods for determining the boundaries of regions, homogeneity of regions. Graphic processing of hydrological data: rectilinear, exponential and exponential graphic dependences.
FACTORS OF RIVER FLOW FORMATION.
The importance of understanding the mechanism and degree of influence of physical and geographical factors on the regime and magnitude of river runoff. The equation water balance river basin. Classification of river runoff formation factors. 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 location, size, shape of the river basin, relief, vegetation, soils and rocks, permafrost, lakes, swampiness, glaciers and ice within the basin. The impact of economic activity on river flow: the creation of reservoirs and ponds, the redistribution of flow between river basins, the irrigation of agricultural fields, the drainage of swamps and wetlands, agroforestry activities in river catchments, water consumption for industrial and domestic needs, urbanization, mining.
STATISTICAL PARAMETERS OF RIVER FLOW.
RELIABILITY OF INITIAL HYDROLOGICAL INFORMATION.
The flow rate and the principles of its calculation. River runoff variability, its relative (coefficient of variation) and absolute (standard deviation) expression, connection with meteorological factors. Variability of intra-annual distribution of runoff, maximum runoff of spring floods and rain floods, minimum winter and summer runoff. Asymmetry coefficient. Degree of reliability of hydrological input information. Causes of errors in regime hydrological information.
FORMATION CONDITIONS AND CALCULATIONS OF ANNUAL FLOW RATE.
Annual runoff of rivers as the main hydrological characteristic. Conditions for the formation of annual runoff: precipitation, evaporation, air temperature. Influence of lakes, swamps, glaciers, ice floes, basin area, watershed height, forest and its clearing, creation of reservoirs, irrigation, industrial and municipal water consumption, drainage of swamps and wetlands, agroforestry measures on the formation of annual river flow. The concept of the representativeness of a series of hydrological data. Elements of cyclic fluctuations in runoff. Synchronicity, asynchrony, in-phase, out-of-phase fluctuations of the drain. Calculations of the annual flow rate in the presence, insufficiency and absence of observational data. Distribution of annual runoff across the territory of Russia.
FORMATION FACTORS AND CALCULATION
INTRA-ANNUAL DISTRIBUTION OF RIVER FLOW.
The practical significance of knowledge about the intra-annual distribution of runoff. The role of climate in the distribution of runoff during the year. Underlying surface factors that correct the intra-annual distribution of runoff: lakes, swamps, river floodplains, glaciers, permafrost, icing, forest, karst, river basin size, catchment shape. Influence of the creation of reservoirs and ponds, irrigation, agroforestry activities and drainage on the intra-annual distribution of river flow. Calculation of the intra-annual distribution of runoff in the presence, insufficiency and absence of observational data. Calculation of the daily distribution of runoff. Curves of duration of daily expenses. Coefficient of natural runoff regulation. Coefficient of intra-annual runoff unevenness.
FEATURES OF FORMATION AND CALCULATION OF THE MAXIMUM
RIVER FLOW DURING THE SPRING FLOOD PERIOD.
The concept of "catastrophic flood (flood)". 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 availability of maximum water flow rates depending on the capital class of a hydraulic structure. Quality of initial information on maximum water discharges. Conditions for the formation of flood runoff: snow reserves in the river basin and water reserves in the snow cover, evaporation losses from snow, intensity and duration of snowmelt, loss of melt water. Underlying surface factors: relief, slope exposure, dimensions, configuration, dissection of the basin, lakes and swamps, soils and soils. Anthropogenic factors in the formation of the maximum flow of floods. Genetic theory of formation of maximum runoff. Reduction of the maximum flow. Calculations of the maximum spring runoff in the presence, insufficiency and absence of observational data. Mathematical and physico-mathematical models of the processes of formation of melt water runoff.
MAXIMUM RIVER FLOW DURING RAIN FLOOD PERIOD.
Areas of distribution of high rain maxima. Difficulties in researching and generalizing the characteristics of rain runoff. Types of rain and their components. Features of the formation of rain floods: the intensity and duration of rain, the intensity of infiltration, the speed and time of rainwater runoff. The role of underlying surface factors and types of economic activity in the formation of rain runoff. Calculations of the maximum water discharges of rain floods in the presence, insufficiency and absence of observational data. Simulation of the runoff of rain floods.
FORMATION CONDITIONS AND CALCULATIONS OF THE MINIMUM SUMMER
AND WINTER DRAIN OF RIVERS.
The concept of low-water period and low-water runoff. The practical significance of knowledge about the minimum flow of rivers. The main design characteristics of the minimum and low flow of rivers. The duration of the winter and summer or summer-autumn low-water periods on the rivers of Russia. Types of low water and low water periods of Russian rivers. Minimum runoff formation factors: precipitation, temperature, evaporation, connection of aeration zone waters, groundwater, karst and artesian waters with the river, geological and hydrogeological conditions in the basin, lakes, swamps, forest, dismemberment and height of the terrain, river floodplain, depth of erosion cut river channels, areas of surface and underground watersheds, slope and orientation of the watershed, irrigation of agricultural lands, industrial and domestic consumption of river water, drainage, use of groundwater, 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 ANNUAL RUNOFF OF RIVERS
WITH INSUFFICIENCY AND ABSENCE OF OBSERVATION DATA.
TASK 1: Select a river basin with a catchment area of at least 2000 km² and not more than 50000km ² within the Tyumen region and extract from the publications of the WRC for this basin a number of observations of average annual discharges.
TASK 2: Determine the statistical parameters of the curve for the average annual flow of the selected river using the methods of moments, maximum likelihood, graph-analytical.
TASK 3: Determine the annual flow of the river with a security of 1%, 50% and 95%.
TASK 4: Calculate the average annual runoff of the same river using the isoline map of the module and runoff layer and evaluate the accuracy of the calculation.
THEORY: In the presence or insufficiency of observational data, the main statistical parameters of river runoff are determined by three methods: the method of moments, the maximum likelihood method, and the graph-analytical method.
METHOD OF MOMENTS.
To determine the parameters of the distribution curveQo, Cv and Cs 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 observation series of less than 30 years, instead of n, take (n - 1).
2) coefficient of variation
Cv \u003d ((Σ (Ki -1)²) / n)½, where
Ki - modular coefficient calculated by the formula
Ki \u003d Qi / Qo.
3) coefficient of asymmetry
Cs \u003d Σ (Ki - 1)³ / (n Cv³).
Based on the Cv and Cs values, the Cs / Cv ratio and the calculation errors of Qo, Cv and Cs are calculated:
1) Qo error
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%.
Maximum likelihood 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 value functions. This method is based on the use of statistics λ 1 , λ 2 , λ 3. Statistics λ 2 and λ 3 are connected with each other and their ratio changes from the change in Cv and the ratio of Cs / Cv. 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 \u003d Σ IgKi / (n - 1);
3) statistics λ 3
λ 3 = Σ Ki· IgКi /(n – 1).
The determination of the coefficient of variability Cv and the ratio Cs / Cv is carried out according to nomograms (see in the textbook. Practical hydrology. L .: Gidrometeoizdat, 1976, p. 137) in accordance with the calculated statistics λ 2 and λ 3 . On the nomograms, we find the point of intersection of the values of the 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 error Cv is determined by the formula:
Έ = (3 / (2n(3+ Cv²)))½ 100%.
GRAPH-ANALYTICAL METHOD .
With this method, the statistical parameters of the analytical endowment curve are calculated by three characteristic ordinates of the smoothed empirical endowment curve. These ordinates are Q
On the semi-logarithmic fiber of probabilities, the dependence Q = f (P) is built. To build a smoothed empirical supply curve, it is necessary to build a series of observations in descending sequence and for each ranked value of water consumption Q ub . assign the value of security P, calculated by the formula:
P \u003d (m / n + 1) 100%, where
m is the serial number of a member of the series;
n is the number of members of the series.
Provision values are plotted along the horizontal axis, the corresponding Q kill The intersection points are indicated by circles with a diameter of 1.5-2 mm and fixed with ink. A smoothed empirical security curve is drawn over the points with a pencil. Three characteristic ordinates Q are taken from this curve 5% ,Q 50% and Q 95% availability, thanks to which the value of the coefficient of skewness S of the supply 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 skewness factor. Therefore, according to the calculated value of S, the value of Cs is determined (see Appendix 3 in the textbook. Practical Hydrology. L .: Gidrometeoizdat, 1976, p. 431). According to the same application, depending on the obtained value of Cs, the difference of normalized deviations (Ф 5% - F 95% ) and normalized deviation Ф 50% . Next, calculate the standard deviation σ, the average long-term runoff Qо´, and the coefficient of variation Cv using the following formulas:
σ \u003d (Q 5% - Q 95% ) / (F 5% - F 95% ),
Qo ´ \u003d Q 50% - σ F 50%,
Сv = σ / Q´.
The analytical endowment curve is considered to be sufficiently consistent with the empirical distribution if the following inequality is satisfied:
IQo - Qo´I< 0,02·Qо.
The root mean square error Qо´ is calculated by the formula:
σ Qo´ = (Сv / n½) 100%.
Coefficient of variation error
Έ = ((1+ Сv²) / 2n)½ 100%.
CALCULATION OF THE EXPENSES OF THE GIVEN SECURITY .
The consumption of a given security is calculated by the formula:
Qр = Кр·Qо, where
Кр - modular coefficient of the given security p%, calculated by the formula
Kp \u003d Fr Cv + 1, where
Fr - normalized deviations of a given security from the average value of the ordinates of the binomial distribution curve, determined according to Appendix 3 of the training manual. Practical hydrology. L .: Gidrometeoizdat, 1976, p. 431.
Recommended for further hydrological calculations and design work, the statistical parameters for the river basin and its secured costs are obtained by calculating the arithmetic mean of those obtained by the above three methods Qо, Cv, Cs, Q 5% ,Q 50% and Q 95% security.
DETERMINATION OF THE VALUES OF AVERAGE ANNUAL RIVER FLOW
CARDS.
In the absence of observational data on runoff, one of the ways to determine it is maps of the isolines of the runoff modules and layer (see textbook. Practical Hydrology. L .: Gidrometeoizdat, 1976, pp. 169-170). The value of the modulus or runoff layer is determined for the center of the catchment area of the river. If the center of the watershed lies on the isoline, then the average value of the runoff of this watershed is taken from the value of this isoline. If the watershed lies between two isolines, then the runoff value for its center is determined by linear interpolation. If the watershed is crossed by several isolines, then the value of the runoff module (or runoff layer) for the center of the watershed 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 runoff values between adjacent isolines crossing the watershed;
f1, f2… - catchment areas between contour lines within the catchment area (in km² or in scale divisions).
28.07.2015
Fluctuations in river runoff and criteria for its assessment. River runoff is the movement of water in the process of its circulation in nature, when it flows down the river channel. River flow is determined by the amount of water flowing through the river channel for a certain period of time.
Numerous factors influence the flow regime: climatic - precipitation, evaporation, humidity and air temperature; topographic - terrain, shape and size of river basins and soil-geological, including vegetation cover.
For any basin, the more precipitation and less evaporation, the greater the flow of the river.
It has been established that with an increase in the catchment area, the duration of the spring flood also increases, while the hydrograph has a more elongated and “calm” shape. In easily permeable soils, there is more filtration and less runoff.
When performing various hydrological calculations related to the design of hydraulic structures, reclamation systems, water supply systems, flood control measures, roads, etc., the following main characteristics of the river flow are determined.
1. Water consumption is the volume of water flowing through the considered section per unit of time. The average water consumption Qcp is calculated as the arithmetic average of the costs for a given period of time T:
2. Flow volume V- this is the volume of water that flows through a given target for the considered period of time T
3. Drain module M is the flow of water per 1 km2 of catchment area F (or flowing from a unit catchment area):
In contrast to the water discharge, the runoff modulus is not associated with a specific section of the river and characterizes the runoff from the basin as a whole. The average multi-year runoff module M0 does not depend on the water content of individual years, but is determined only by the geographical location of the river basin. This made it possible to zonate our country in hydrological terms and to build a map of isolines of average long-term runoff modules. These maps are given in the relevant regulatory literature. Knowing the catchment area of a river and determining the value M0 for it using the isoline map, we can determine the average long-term water flow Q0 of this river using the formula
For closely spaced river sections, the runoff moduli can be taken constant, i.e.
From here, according to the known water discharge in one section Q1 and the known catchment areas in these sections F1 and F2, the water discharge in the other section Q2 can be established by the ratio
4. Drain layer h- this is the height of the water layer, which would be obtained with a uniform distribution over the entire basin area F of the runoff volume V for a certain period of time:
For the average multi-year runoff layer h0 of the spring flood, contour maps were compiled.
5. Modular drain coefficient K is the ratio of any of the above runoff characteristics to its arithmetic mean:
These coefficients can be set for any hydrological characteristics (discharges, levels, precipitation, evaporation, etc.) and for any periods of flow.
6. Runoff coefficient η is the ratio of the runoff layer to the layer of precipitation that fell on the catchment area x:
This coefficient can also be expressed in terms of the ratio of the volume of runoff to the volume of precipitation for the same period of time.
7. Flow rate- the most probable average long-term value of runoff, expressed by any of the above runoff characteristics over a multi-year period. To establish the runoff norm, a series of observations should be at least 40 ... 60 years.
The annual flow rate Q0 is determined by the formula
Since the number of observation years at most water gauges is usually less than 40, it is necessary to check whether this number of years is sufficient to obtain reliable values of the runoff norm Q0. To do this, calculate the root mean square error of the flow rate according to the dependence
The duration of the observation period is sufficient if the value of the root-mean-square error σQ does not exceed 5%.
The change in annual runoff is predominantly influenced by climatic factors: precipitation, evaporation, air temperature, etc. All of them are interconnected and, in turn, depend on a number of reasons that are random in nature. Therefore, the hydrological parameters characterizing the runoff are determined by a set of random variables. When designing measures for timber rafting, it is necessary to know the values of these parameters with the necessary probability of exceeding them. For example, in the hydraulic calculation of timber rafting dams, it is necessary to set the maximum flow rate of the spring flood, which can be exceeded five times in a hundred years. This problem is solved using the methods of mathematical statistics and probability theory. To characterize the values of hydrological parameters - costs, levels, etc., the following concepts are used: frequency(recurrence) and security (duration).
The frequency shows how many cases during the considered period of time the value of the hydrological parameter was in a certain interval. For example, if the average annual water flow in a given section of the river changed over a number of years of observations from 150 to 350 m3/s, then it is possible to establish how many times the values of this value were in the intervals 150...200, 200...250, 250.. .300 m3/s etc.
security shows in how many cases the value of a hydrological element had values equal to or greater than a certain value. In a broad sense, security is the probability of exceeding a given value. The availability of any hydrological element is equal to the sum of the frequencies of the upstream intervals.
Frequency and availability can be expressed in terms of the number of occurrences, but in hydrological calculations they are most often determined as a percentage of the total number of members of the hydrological series. For example, in the hydrological series there are twenty values of average annual water discharges, six of them had a value equal to or greater than 200 m3/s, which means that this discharge is provided by 30%. Graphically, changes in frequency and availability are depicted by curves of frequency (Fig. 8a) and availability (Fig. 8b).
In hydrological calculations, the probability curve is more often used. It can be seen from this curve that the greater the value of the hydrological parameter, the lower the percentage of availability, and vice versa. Therefore, it is generally accepted that years for which the runoff availability, that is, the average annual water discharge Qg, is less than 50% are high-water, and years with Qg more than 50% are low-water. A year with a runoff security of 50% is considered a year of average water content.
The availability of water in a year is sometimes characterized by its average frequency. For high-water years, the frequency of occurrence shows how often years of a given or greater water content occur on average, for low-water years - of a given or less water content. For example, the average annual discharge of a high-water year with 10% security has an average frequency of 10 times in 100 years or 1 time in 10 years; the average frequency of a dry year of 90% security also has a frequency of 10 times in 100 years, since in 10% of cases the average annual discharge will have lower values.
Years of a certain water content have a corresponding name. In table. 1 for them the availability and repeatability are given.
The relationship between repeatability y and availability p can be written as follows:
for wet years
for dry years
All hydraulic structures for regulating the channel or flow of rivers are calculated according to the water content of the year of a certain supply, which guarantees the reliability and trouble-free operation of the structures.
The estimated percentage of provision of hydrological indicators is regulated by the "Instruction for the design of timber rafting enterprises".
Provision curves and methods of their calculation. In the practice of hydrological calculations, two methods of constructing supply curves are used: empirical and theoretical.
Reasonable calculation empirical endowment curve can only be performed if the number of observations of the river runoff is more than 30...40 years.
When calculating the availability of members of the hydrological series for annual, seasonal and minimum flows, you can use the formula of N.N. Chegodaeva:
To determine the availability of maximum water flow rates, the S.N. dependence is used. Kritsky and M.F. Menkel:
The procedure for constructing an empirical endowment curve:
1) all members of the hydrological series are recorded in decreasing order in absolute value;
2) each member of the series is assigned a serial number, starting from one;
3) the security of each member of the decreasing series is determined by formulas (23) or (24).
Based on the results of the calculation, a security curve is built, similar to the one shown in Fig. 8b.
However, empirical endowment curves have a number of disadvantages. Even with a sufficiently long observation period, it cannot be guaranteed that this interval covers all possible maximum and minimum values of the river flow. Estimated values of runoff security of 1...2% are not reliable, since sufficiently substantiated results can be obtained only with the number of observations for 50...80 years. In this regard, with a limited period of observation of the hydrological regime of the river, when the number of years is less than thirty, or in their complete absence, they build theoretical security curves.
Studies have shown that the distribution of random hydrological variables most well obeys the type III Pearson curve equation, the integral expression of which is the supply curve. Pearson obtained tables for constructing this curve. The security curve can be constructed with sufficient accuracy for practice in three parameters: the arithmetic mean of the terms of the series, the coefficients of variation and asymmetry.
The arithmetic mean of the terms of the series is calculated by formula (19).
If the number of years of observations is less than ten or no observations were made at all, then the average annual water discharge Qgcp is taken equal to the average long-term Q0, that is, Qgcp = Q0. The value of Q0 can be set using the modulus factor K0 or the sink modulus M0 determined from the contour maps, since Q0 = M0*F.
The coefficient of variation Cv characterizes the runoff variability or the degree of its fluctuation relative to the average value in a given series; it is numerically equal to the ratio of the standard error to the arithmetic mean of the series members. The value of the Cv coefficient is significantly affected by climatic conditions, the type of river feeding, and the hydrographic features of its basin.
If there are observational data for at least ten years, the annual runoff variation coefficient is calculated by the formula
The value of Cv varies widely: from 0.05 to 1.50; for timber-rafting rivers Cv = 0.15...0.40.
With a short period of observations of the river runoff or in their complete absence the coefficient of variation can be established by the formula D.L. Sokolovsky:
In hydrological calculations for basins with F > 1000 km2, the isoline map of the Cv coefficient is also used if the total area of lakes does not exceed 3% of the catchment area.
In the normative document SNiP 2.01.14-83, a generalized formula K.P. is recommended for determining the coefficient of variation of unstudied rivers. Resurrection:
Skewness coefficient Cs characterizes the asymmetry of the series under consideration random variable about its average value. The smaller part of the members of the series exceeds the value of the runoff norm, the greater the value of the asymmetry coefficient.
The asymmetry coefficient can be calculated by the formula
However, this dependence gives satisfactory results only for the number of observation years n > 100.
The coefficient of asymmetry of unstudied rivers is set according to the Cs/Cv ratio for analogue rivers, and in the absence of sufficiently good analogues, the average Cs/Cv ratios for the rivers of the given region are taken.
If it is impossible to establish the Cs/Cv ratio for a group of analogous rivers, then the values of the Cs coefficient for unstudied rivers are accepted for regulatory reasons: for river basins with a lake coefficient of more than 40%
for zones of excessive and variable moisture - arctic, tundra, forest, forest-steppe, steppe
To build a theoretical endowment curve for the above three parameters - Q0, Cv and Cs - use the method proposed by Foster - Rybkin.
From the above relation for the modular coefficient (17) it follows that the average long-term value of the runoff of a given recurrence - Qp%, Мр%, Vp%, hp% - can be calculated by the formula
The modulus runoff coefficient of the year of a given probability is determined by the dependence
Having determined a number of any runoff characteristics for a long-term period of different availability, it is possible to construct a supply curve based on these data. In this case, it is advisable to carry out all calculations in tabular form (Tables 3 and 4).
Methods for calculating modular coefficients. To solve many water management problems, it is necessary to know the distribution of runoff by seasons or months of the year. The intra-annual distribution of runoff is expressed in the form of modular coefficients of monthly runoff, representing the ratio of the average monthly flow Qm.av to the average annual Qg.av:
The intra-annual distribution of runoff is different for years of different water content, therefore, in practical calculations, the modular coefficients of monthly runoff are determined for three characteristic years: a high-water year with 10% supply, an average year with 50% supply, and a low-water year with 90% supply.
Monthly runoff modulus coefficients can be established based on actual knowledge of average monthly water discharges in the presence of observational data for at least 30 years, according to an analogue river, or according to standard tables of monthly runoff distribution, which are compiled for different river basins.
The average monthly water consumption is determined based on the formula
(33): Qm.cp = KmQg.sr
Maximum water consumption. When designing dams, bridges, lagoons, measures to strengthen the banks, it is necessary to know the maximum water flow. Depending on the type of river feeding, the maximum flow rate of spring floods or autumn floods can be taken as the calculated maximum discharge. The estimated security of these costs is determined by the capital class of hydraulic structures and is regulated by the relevant normative documents. For example, timber rafting dams of class Ill of capitality are calculated for the passage of a maximum water flow of 2% security, and class IV - of 5% security, bank protection structures should not collapse at flow rates corresponding to the maximum water flow of 10% security.
The method for determining the value of Qmax depends on the degree of knowledge of the river and on the difference between the maximum discharges of the spring flood and the flood.
If there are observational data for a period of more than 30...40 years, then an empirical security curve Qmax is built, and with a shorter period - a theoretical curve. The calculations take: for spring floods Cs = 2Сv, and for rain floods Cs = (3...4)CV.
Since river regimes are monitored at water-measuring stations, the supply curve is usually plotted for these sites, and the maximum water discharges at the sites where structures are located are calculated by the ratio
For lowland rivers maximum flow of spring flood water given security p% is calculated by the formula
The values of the parameters n and K0 are determined depending on the natural zone and relief category according to Table. 5.
Category I - rivers located within hilly and plateau-like uplands - Central Russian, Strugo-Krasnenskaya, Sudoma uplands, Central Siberian plateau, etc .;
II category - rivers, in the basins of which hilly uplands alternate with depressions between them;
Category III - rivers, most of the basins of which are located within the flat lowlands - Mologo-Sheksninskaya, Meshcherskaya, Belarusian woodland, Pridnestrovskaya, Vasyuganskaya, etc.
The value of the coefficient μ is set depending on the natural zone and the percentage of security according to Table. 6.
The hp% parameter is calculated from the dependency
The coefficient δ1 is calculated (for h0 > 100 mm) by the formula
The coefficient δ2 is determined by the relation
The calculation of the maximum water discharges during the spring flood is carried out in tabular form (Table 7).
Levels high waters(HWV) of design availability are established according to the curves of water discharges for the corresponding values of Qmaxp% and design ranges.
With approximate calculations, the maximum water flow of a rain flood can be set according to the dependence
In responsible calculations, the determination of the maximum water flow should be carried out in accordance with the instructions of regulatory documents.
River- a natural water stream that flows constantly in the recess (channel) formed by it.
Each river has its source, upper, middle, lower reaches and mouth. Source- the beginning of the river. Rivers begin at the confluence of streams that arise at the places of groundwater outlets or collecting water from atmospheric precipitation that has fallen to the surface. They flow from swamps (for example, the Volga), lakes and glaciers, feeding on the water accumulated in them. In most cases, the source of the river can only be determined conditionally.
From the source of the river begins its upper course.
AT top In the course of a river flow, it is usually less full of 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 flow and in the eroding activity of the flow. AT average In the course of the river, the river becomes more abundant, but the speed of the current decreases, and the flow carries mainly the products of erosion of the channel in the upper reaches. AT lower During the slow movement of the flow, the deposition of sediments brought by it from above (accumulation) predominates. The lower course of the river ends at the mouth.
mouth rivers - the place of its confluence with the sea, lake, another river. In a dry climate, where rivers consume a lot of water (for evaporation, irrigation, filtration), they can gradually dry up, not reaching their waters to the sea or to another river. The mouths of such rivers are called "blind". All the rivers flowing through a given territory form its river network, included together with lakes, swamps and glaciers in 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, it is very difficult to determine it in the middle and especially in the upper reaches. As signs of the main river, one can take the length, water content, axial position in the river system, relative age river valley(the valley is older than the tributaries). The main rivers of most major river systems do not meet all of these criteria at once, for example: the Missouri is longer and more full-flowing than the Mississippi; The Kama brings no less water into 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. The main river of the river system has historically become 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 sinuosity and the density of the river network. River length- the total length of all the rivers of the system, measured on a large-scale map. The degree of sinuosity of the river is determined tortuosity factor(Fig. 87) - the ratio of the length of the river to the length of a straight line connecting the source and mouth. Density of the river network- the ratio of the total length of all rivers of the considered river network to the area occupied by it (km/km2). On the map, even on a not very large scale, it is clear that the density of the river network in various natural areas 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 Caucasus Range, it is 1.49 km / km2, and on the plains of the Ciscaucasia - 0.05 km / km2.
The surface area 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 is made up of basins of tributaries of the first order, which in turn consist of basins of tributaries of the second order, etc. The 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) internal runoff area (area 32,035 thousand km2).
River basins have different sizes and very diverse shapes. There are symmetrical basins (for example, the Volga basin) and asymmetric ones (for example, the Yenisei basin).
The size and shape of the basin largely determine the magnitude and regime of the river flow. 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 belt.
Basins are limited by watersheds. In mountainous countries, they may be lines that generally coincide with the crests of the ridges. On the plains, especially flat and marshy ones, watersheds are not clearly defined.
In some places, it is impossible to draw watersheds at all, since the mass of water of one river is divided into two parts, heading to different systems. This phenomenon is called the bifurcation of the river (dividing it into two). A striking example bifurcations - the division of the upper reaches of the Orinoco into two rivers. One of them, which retains the name Orinoco, flows into Atlantic Ocean, the other - Casiquiare - flows into the Rio Negro, a tributary of the Amazon.
Watersheds limit the basins of rivers, seas, oceans. Main basins: Atlantic and Northern 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 through earth's surface in the longitudinal depressions they created - channels. Without a channel, there can be no river. The term "river" includes both stream and bed. In most rivers, the channel is cut into the surface over which the river flows. Ho there are many rivers, the channels of which rise above the plain they cross. These rivers have carved their channels in the sediments deposited by them. An example would be the Yellow River, Mississippi and Po in the lower reaches. Such channels move easily, often breaking through their side shaft, 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 there are stationary sections in the water section (with a speed of movement that is not captured by the instruments), they are called dead space. In this case, the living section will be less than the water one by the value, equal to the area dead space. The cross section of the channel 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 open area is related to the width (B) and the greatest depth (H) by the equation: F=2/3BH.
Hydraulic radius (R) - 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 shape of the channel in the cross section, 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 a river's cross section is determined by dividing its area by its width (B): Hcp = S/B. Width and maximum depth obtained by direct measurements.
All elements of the cross section change along with the change in the position of the river level. The level of the river is subject to constant fluctuations, observations of which are systematically carried out at special water-measuring posts.
The longitudinal profile of the river channel is characterized by dip and slope. Fall (Δh) - height difference 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 decimal- in meters per kilometer of fall, or thousandths (ppm - ‰).
The rivers of the plains have slight slopes, the slopes of mountain rivers are significant.
The greater the slope, the faster the flow of the river (Table 23).
Longitudinal profile of the channel bottom and longitudinal profile water surface differ: the first represents always wavy line, the second - a smooth line (Fig. 88).
The speed of the river flow. Water flow is characterized by turbulent movement. Its speed at each point is continuously changing both in magnitude and in direction. This ensures constant mixing of the water and promotes scouring activity.
The speed of the river flow is not the same in different parts live section. Numerous measurements show that the highest speed is usually observed near the surface. As we approach the bottom and the walls of the channel, the flow velocity gradually decreases, and in the near-bottom layer of water, only a few tens of millimeters thick, it sharply decreases, reaching a value close to 0 at the very bottom.
The lines of distribution of equal velocities along the living section of the river are isotachs. The wind blowing with the current increases 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 flow, which has the highest speed, is called its dynamic axis, the jet of the highest speed on the surface of the flow is called the rod. Under certain conditions, for example, when the wind is following the flow, the dynamic axis of the flow is on the surface and coincides with the rod.
The average velocity in the clear section (Vav) is calculated by the Chezy 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. Water particles in the stream move under the action of gravity along the slope. Their movement is delayed by the force of friction. In addition to gravity and friction, the character of the flow movement is affected by the centrifugal force that occurs at the turns of the channel, and the deflecting force of the Earth's rotation. These forces cause transverse and circular currents in the stream.
Under the action of centrifugal force at the turn, the flow is pressed against the concave bank. In this case, the greater the flow velocity, the greater the inertia force that prevents the flow from changing the direction of movement and deviating from the concave bank. The flow velocity near 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. Since the water is pressed against the concave bank, the surface of the stream receives a transverse slope from the concave to the convex bank. However, there is no movement of water on the surface along the slope from one coast to another. This is hindered by the centrifugal force, which forces the water particles, overcoming the slope, to move towards the concave shore. In the bottom layers, due to the lower speed of the current, the effect of centrifugal force is less pronounced, and therefore the water moves in accordance with the slope from the concave to the convex bank. The particles of water moving across the river are simultaneously downstream, and their trajectory resembles a spiral.
The deflecting force of the Earth's rotation causes 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 countercurrent that is clockwise (in the northern hemisphere) when looking downstream. Since this movement is also combined with the translational movement of particles, they move along the channel in a spiral.
In a straight section of the channel, where there are no centrifugal forces, the nature of the crossflow is determined mainly by the action of the deflecting force of the Earth's rotation. At the bends in the channel, the deflecting force of the Earth's rotation and the centrifugal force either add up or subtract, depending on which way the river turns, and the transverse circulation is strengthened or weakened.
Transverse 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 the formation of the channel, as we shall see below, is very great.
River flow and its characteristics. The amount of water passing through the living section of the river in 1 second is its flow. The flow rate (Q) is equal to the product of the open area (F) and the average speed (Vcp): Q=FVcp m3/sec.
Water discharges in rivers are very variable. They are more stable on rivers regulated by lakes and reservoirs. On the rivers of the temperate zone, the greatest flow of water falls on the period of spring floods, the least - in the summer months. According to the data of daily expenses, graphs of changes in consumption are built - 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 volume of runoff is expressed in either cubic meters, or in cubic kilometers. Calculation of runoff over a number of years makes it possible to obtain its average long-term value (Table 24).
The flow of water characterizes the flow 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, the runoff module, runoff layer, and runoff coefficient are used.
Drain module(M) - the number of liters of water flowing from a unit of basin area (1 sq. km) per unit of time (in sec). If the average water flow in the river for a certain period of time is Q m3 / s, and the basin area is F sq. km, then the average runoff module for the same period of time is M = 1000 l / s * km2 (a factor of 1000 is necessary, since Q is expressed in cubic meters, and M - in l). M of the Neva - 10 l / s, Don - 9 l / s, Amazon - 17 l / s.
runoff layer- layer of water in millimeters, which would cover the catchment area with a uniform distribution of the entire volume of runoff over it.
Runoff coefficient(h) - the ratio of the size of the runoff layer to the size of the layer 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 flow coefficient of the Neva - 65%, Don - 16%, Nile - 4% , Amazons - 28%.
The runoff depends on the whole complex of physical and geographical conditions: on the climate, soils, geological structure of the zone, active water exchange, vegetation, lakes and swamps, as well as on human activities.
Climate refers to the main factors runoff formation. It determines the amount of moisture depending on the amount of precipitation (the main element of the incoming part of the water balance) and on evaporation (the main indicator of the outgoing part of the balance). The greater the amount of precipitation and the lower the evaporation, the higher the humidity must be and the greater the runoff can be. Precipitation and evaporation determine potential opportunities runoff. The actual flow depends on the whole complex of conditions.
The climate affects the runoff not only directly (through precipitation and evaporation), but also through other components of the geographical complex - through soils, vegetation, topography, 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 that determine river runoff, its surface and underground components, is occupied by soil cover, which plays the role of an intermediary between climate and runoff. The amount of surface runoff, water consumption for evaporation, transpiration and groundwater recharge depend on the properties of the soil cover. If the soil poorly absorbs water, the surface runoff is large, little moisture is accumulated in the soil, the consumption for evaporation and transpiration cannot be large, and there is little groundwater recharge. Under the same climatic conditions, but with a greater infiltration capacity of the soil, surface runoff, on the contrary, is small, a lot of moisture accumulates in the soil, the consumption for evaporation and transpiration is large, and groundwater is abundantly fed. In the second of the two cases described, the amount of surface runoff is less than in the first, but on the other hand, due to underground feeding, it is more uniform. The soil, absorbing precipitation water, can retain it and let it pass deeper beyond the zone available for evaporation. The ratio of water consumption for evaporation from the soil and for groundwater nutrition depends on the water-holding capacity of the soil. Soil that retains water well spends more water for evaporation and passes less water deep into the soil. As a result of waterlogging of the soil, which has a high water-retaining capacity, surface runoff increases. Soil properties are combined in different ways, and this is reflected in runoff.
Influence geological structures on river runoff is determined mainly by the permeability of rocks and is generally similar to the effect of soil cover. The occurrence of water-resistant layers in relation to the day surface is also important. The deep occurrence of aquicludes contributes to the preservation of infiltrated water from being spent on evaporation. The geological structure affects the degree of regulation of the runoff, the conditions for the supply of groundwater.
The influence of geological factors least of all others depends on zonal conditions and in some cases overlaps the influence of zonal factors.
Vegetation affects the amount of runoff both directly and through the soil cover. Its direct influence lies in transpiration. River runoff depends on transpiration in the same way as on evaporation from the soil. The greater the transpiration, the lower both components of the river runoff. Tree crowns retain up to 50% of the precipitation, which then evaporates from them. In winter, the forest protects the soil from freezing, in the spring it moderates the intensity of snowmelt, which contributes to the seepage of melt water and replenishment of groundwater reserves. The influence of vegetation on runoff through soil is due to the fact that vegetation is one of the factors of soil formation. Infiltration and water-retaining properties largely depend on the nature of the vegetation. The infiltration capacity of the soil in the forest is exceptionally 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, in the ratios between the runoff components (surface and underground), zonal pattern. In the forests of the forest zone, surface runoff is significant (higher humidity), although less than in the field. In the forest-steppe and steppe zones, there is practically no surface runoff in the forest, and all the water absorbed by the soil is spent on evaporation and groundwater recharge. AT general influence forests for runoff water regulation and water protection.
Relief affects the runoff differently depending on the size of the molds. The influence of mountains is especially great. The whole complex of physical and geographical conditions (altitude zonality) changes with height. As a result, the stock also changes. Since a change in the set of conditions with height can occur very quickly, the overall picture of runoff formation in high mountains becomes more complicated. With height, the amount of precipitation increases up to a certain limit, the runoff generally increases. The runoff increase is especially noticeable on the windward slopes, 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 peripheral ones. Relief is of great importance for the formation of runoff in connection with the distribution of snow cover. Significantly affects the 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 affect the intensity of the runoff, its fluctuations, but do not significantly affect the magnitude of the runoff.
lakes, evaporating the water accumulated in them, reduce the runoff and at the same time act as its regulators. The role of large flowing lakes is especially great in this respect. The amount of water in the rivers flowing from such lakes almost does not change during the year. For example, the flow of the Neva is 1000-5000 m3/s, while the flow of the Volga near Yaroslavl, before its regulation, fluctuated during the year from 200 to 11,000 m3/s.
has a strong effect on stock economic activity people, making big changes in natural complexes. The impact of people on the soil cover is also significant. The more plowed spaces, the more precipitation seeps into the soil, moistens the soil and feeds groundwater, the smaller part of it flows down the surface. Primitive agriculture causes destructuring of soils, a decrease in their ability to absorb moisture, and, consequently, an increase in surface runoff and a weakening of underground circulation. With rational agriculture, the infiltration capacity of soils increases with all the ensuing consequences.
The runoff is affected by snow retention measures aimed at increasing moisture entering the soil.
Artificial reservoirs have a regulating influence on the river runoff. Reduces runoff water consumption for irrigation and water supply.
The forecast of water content and regime of rivers is important for planning the use of the country's water resources. In Russia, a special forecasting method has been developed, based on an 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 isolines of runoff values are plotted - modules or annual runoff. The map shows a manifestation latitudinal zonality in the distribution of runoff, especially well expressed on the plains. The influence of the relief on the runoff is also clearly revealed.
River nutrition. There are four main sources of river nutrition: rain, snow, glacial, underground. The role of this or that food source, their combination and distribution in time depend mainly on climatic conditions. So, for example, in countries with a hot climate, there is no snow supply, rivers and deep groundwater do not feed, and rain is the only source of nutrition. In a cold climate, melt waters acquire the main importance in the nutrition of rivers, and ground waters in winter. In a temperate climate, various food sources are combined (Fig. 89).
The amount of water in the river varies depending on the feeding. 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 patterns in changes in the amount of water in rivers over time, their regime.
In the mode of rivers of a moderately cold climate, in the diet of which important role snowmelt waters play, four phases, or hydrological seasons, are clearly distinguished: spring flood, summer low water, autumn floods and winter low water. Floods, floods, and low water are characteristic of the regime of rivers that are also 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 time of onset and duration of floods in different conditions are different. The high water caused by snowmelt on the plains, in a temperate climate, comes in the spring, in a cold climate - in the summer, in the mountains it stretches into spring and summer. Rain-induced floods in monsoon climates take over spring and summer, equatorial climate they occur in autumn, and in the Mediterranean climate come in winter. The flow of some rivers during the flood is up to 90% of the annual flow.
Low water - the lowest standing water in the river with the predominance of underground nutrition. Summer low water occurs as a result of high infiltration capacity of soils and strong evaporation, winter - as a result of the lack of surface nutrition.
Floods are relatively short-term and non-periodic rises in the water level in the river, caused by the inflow 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. A flood can be viewed as a wave caused by the rapid flow of water into a channel.
A.I. Voeikov, who considered rivers as a "climate product" of their basins, created in 1884 a classification of rivers according to feeding conditions.
The ideas underlying the classification of the Voeikov rivers were taken into account in a number of classifications. The most complete and clear classification was developed by M. I. Lvovich. Lvovich classifies rivers depending on the source of supply and on the nature of the distribution of flow during the year. Each of the four food sources (rain, snow, glacial, underground) under certain conditions may turn out to be almost the only (almost exclusive), accounting for more than 80% of the total food, may have a predominant role in feeding the river (from 50 to 80%) and may prevail (>50%) among other sources that also play a significant role in it. In the latter case, the feeding of the river is called mixed.
The runoff is spring, summer, autumn and winter. At the same time, it can be concentrated almost exclusively (> 80%) or predominantly (from 50 to 80%) in one of the four seasons or occur at all seasons, prevailing (> 50%) in one of them.
Natural combinations of various power supply combinations with different options distribution of runoff during the year allowed Lvovich to distinguish types water regime rec. Based on the main patterns 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 water for a short period polar ice and snow, but most of the year they freeze. Rivers of the subarctic type are fed by melted snow waters, their underground feeding is very small. Many, even significant rivers freeze over. highest level these rivers have summer (summer flood). The reason is late spring and summer rains.
Rivers of a moderate type are divided into four subtypes: 1) with a predominance of nutrition due to the spring melting of snow cover; 2) with a predominance of rain supply with a small runoff in spring, both due to the abundance of rains and under the influence of snow melt; 3) with a predominance of rain supply in winter with a more or less uniform distribution of precipitation throughout the year; 4) with a predominance of rain supply in summer due to continuous rains of monsoon origin.
Subtropical rivers are fed mainly by rainwater in winter.
Tropical rivers are characterized by low flow. Summer rainfall predominates, with little precipitation in winter.
Rivers of the equatorial type have abundant rainfall throughout the year; the greatest runoff occurs in the autumn of the corresponding hemisphere.
The rivers of mountainous areas are characterized by patterns of vertical zonality.
Thermal regime of rivers. The thermal regime of the river is determined by the absorption of heat by the direct solar radiation, effective radiation of the water surface, heat consumption 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 incoming and outgoing parts of the heat balance.
In accordance with the thermal regime of the rivers, they can be divided into three types: 1) the rivers are very warm, without seasonal temperature fluctuations; 2) rivers are warm, with a noticeable seasonal temperature fluctuation, not freezing in winter; 3) rivers with large seasonal temperature fluctuations that freeze in winter.
Since the thermal regime of rivers is determined primarily by climate, large rivers flowing through different climatic regions have an unequal regime in various parts. Rivers of temperate latitudes have the most difficult thermal regime. In winter, when water cools 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 - lard - forms on the surface of the water. Salo and zaberezhi freeze into a continuous ice cover of the river.
With the rapid movement of water, the freezing process is delayed by its mixing and the water can be supercooled by several 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. Accumulating under the ice, sludge creates blockages. Sludge, lard, sleet, broken ice floating on the river form the autumn ice drift. At the turns of the river, in the narrowing of the channel during the ice drift, traffic jams occur. The establishment of a stable stable ice cover on a river is called freeze-up. Small rivers freeze, like poison, before large ones. The ice cover and the snow lying on it protect the water from further cooling. If heat loss continues, ice builds up from below. Since, as a result of the freezing of water, the free cross section of the river decreases, water under pressure can pour out onto the surface of the ice and freeze, increasing its thickness. The thickness of the ice cover on the flat rivers of Russia is from 0.25 to 1.5 m or more.
The time of freezing of the rivers and the duration of the period during which the ice cover remains on the river are very different: the Lena is on average covered with ice 270 days a year, the Mezen - 200, the Oka - 139, the Dnieper - 98, the Vistula near Warsaw - 60, the Elbe near Hamburg - 39 days and then not annually.
Under the influence of abundant outflows of groundwater or due to the inflow of warmer lake water, polynyas may remain on some rivers throughout the winter (for example, on the Angara).
The opening of rivers begins near the banks under the influence of the solar heat of the atmosphere and the melt water entering the river. The influx of melt water causes a rise in the level, ice floats, breaking away from the coast, and a strip of water without ice stretches along the coast - rims. The ice begins to move downstream with its entire mass and stops: first, the so-called ice shifts occur, and then the spring ice drift begins. On rivers flowing from north to south, ice drifts more calmly than on rivers flowing from south to north. In the latter case, the covering begins from the upper reaches, while the middle and lower reaches of the river are ice-bound. The wave of the spring flood moves down the river, while jams are formed, the water level rises, the ice, not yet starting to melt, is broken and thrown ashore, powerful ice drifts are created that destroy the banks.
On rivers flowing from lakes, two spring ice drifts are often observed: first there is river ice, then lake ice.
Chemistry of river waters. River water is a solution with a very low salt concentration. Chemical features The waters in the river depend on the sources of food and on the hydrological regime. According to dissolved mineral substances (according to the equivalent predominance of the main anions), river waters are divided (according to A.O. Alekin) into three classes: hydrocarbonate (CO3), sulfate (SO4) and chloride (Cl). Classes, in turn, are divided into three groups according to the predominance of one of the cations (Ca, Mg or the sum of Na + K). In each group, three types of water 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 the carbonate waters, weakly mineralized waters (less than 200 mg/l) predominate, waters of medium mineralization (200-500 mg/l) are less common - in middle lane European part of Russia, in the South Caucasus and partly in Central Asia. Highly mineralized hydrocarbonate waters (>1000 mg/l) are a very rare phenomenon. Rivers of the sulfate class are relatively rare. As an example, the rivers of the Sea of \u200b\u200bAzov can be cited, some rivers North Caucasus, Kazakhstan and Central Asia. Chlorine rivers are even rarer. 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 in winter belongs to the sulfate class, in summer - to the hydrocarbonate class).
In zones of excessive moisture, the mineralization of river waters is insignificant (for example, Pechora - 40 mg / l), in zones of insufficient moisture - high (for example, Emba - 1641 mg / l, Kalaus - 7904 mg / l). When moving from a zone of excess to a zone of insufficient moisture, the composition of salts changes, the amount of chlorine and sodium increases.
Thus, Chemical properties river waters show a zonal character. The presence of easily soluble rocks (limestone, salts, gypsum) can lead to significant local features in the mineralization of river water.
The amount of dissolved substances carried in 1 second through the living section of the river is the consumption of dissolved substances. From the amount of expenses, a runoff of dissolved substances is added, measured in tons (Table 25).
The total amount of dissolved substances carried by rivers from the territory of Russia is about 335 * 106 tons per year. About 73.7% of the dissolved substances are carried out into the Ocean and about 26.3% - into the water bodies of the internal runoff.
Solid stock. Solid mineral particles carried by river flow are called river sediment. They are formed due to the removal of rock particles from the surface of the basin and erosion of the channel. Their number depends on the energy of moving water and on the resistance of rocks to erosion.
River sediments are divided into suspended and traction, or bottom. This division is conditional, since when the flow velocity changes, one category of sediments 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 (jumping) sediments.
The amount of suspended sediment carried by the flow through the living section of the river per unit time (second) is the flow rate of suspended sediment (R kg/m3). The amount of suspended sediment carried through the living section of the river over a long period of time is the flow of suspended sediment.
Knowing the flow of suspended sediments and the flow of water in the river, it is possible to determine its turbidity - the number of grams of suspensions 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 differ in 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 flow of suspended sediments of some rivers is given in Table 26.
During the year, the flow of suspended sediments is distributed depending on the regime of water flow and is maximum on the large rivers of Russia during the spring flood. For the rivers of the northern part of Russia, spring runoff (suspended sediments is 70-75% of the annual runoff, and for the rivers of the central part of the Russian Plain - 90%.
Dragged (bottom) sediments make up only 1-5% of the amount of suspended sediments.
According to Erie's law, the mass of particles moved by water along the bottom (M) is proportional to the velocity (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 able to carry will increase by 729 times. From this it is clear why calm lowland rivers move only woods, while mountainous ones move boulders.
At high speeds, traction (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 dramatically. Therefore, sand waves form at the bottom of the river.
The total amount of sediment (suspended and bottom) carried through the living section 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.
Flow energy. A stream of water moving in a 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 in a section with a length of L km at a fall of 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/sec, the power of the river in this section is 1000 QH/103 = 9.7 QH kW. The rivers of the Earth annually carry 36,000 cubic meters to the Ocean. km of water. At medium height land 875 m, the energy of all rivers, (A) is 31.40 * 1000v6 kgm.
The energy of rivers is spent on overcoming friction, on erosion, on the transfer of material in dissolved, suspended and entrained states.
As a result of the processes of erosion (erosion), transfer (transportation) and deposition (accumulation) of sediments, the riverbed is formed.
Formation of the river bed. The stream constantly and directly cuts into the rocks over which it flows. At the same time, he 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, transport and sedimentation in the channel. Such a channel profile is called an 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 the smallest; downstream, with an increase in the amount of water, the slope decreases (Fig. 90). At the rivers of the desert, fed in the mountains, and in the lower reaches losing a lot of water to evaporation and filtration, an equilibrium profile is formed, convex in the lower part. Due to the fact that the amount of water, the amount and nature of sediments, the speed throughout the course of the river change (for example, under the influence of tributaries), the balance profile of rivers has unequal curvature in different segments, it can be broken, stepped depending on specific conditions.
A river can develop an equilibrium profile only under conditions of prolonged tectonic quiescence and an unchanged position of the erosion basis. Any violation of these conditions leads to a violation of the equilibrium profile and to the resumption of work on its creation. Therefore, in practice, the equilibrium profile of the river is not achievable.
The undeveloped longitudinal profiles of the rivers have many irregularities. The river intensively erodes ledges, fills depressions in the channel with sediment, trying to level it. At the same time, the channel is incised according to the position of the erosion base, propagating up the river (reversing, 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 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. Yosemite-type waterfalls have a large height with a relatively small width. Yosemite Falls (Merced River) - a narrow jet 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 falls is continuously eroding and receding upriver. 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 rapidly in those cases when the ledge is composed of easily eroded rocks, covered only from above with layers of resistant rocks. It is this structure that has the Niagara ledge, 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 "fall lines" associated with ledges that stretch for long distances. Often "waterfall lines" are confined to fault lines. At the foot of the Appalachians, when moving 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 Baltic (cliff of the Silurian plateau).
thresholds- sections of the longitudinal channel of the river, on 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 the waterfall.
Developing a longitudinal profile, the river cuts into the upper reaches, pushing the watershed away. Its basin increases, an additional amount of water begins to flow into the river, which contributes to cutting. As a result of this, the upper reaches of one river can come close to another river and, if the latter is located higher, capture it, include it in its system (Fig. 91). The inclusion of a new river in the river system will change the length of the river, its flow and will affect the process of channel formation.
River interceptions- a frequent phenomenon, for example, r. Pinega (the right tributary of the Northern Dvina) was an independent river and was one with the river. Kuloem, which flows into the Mezensky Bay. One of the tributaries of the Northern Dvina intercepted most Pinega and diverted its waters to the Northern Dvina. The Psel River (a tributary of the Dnieper) intercepted another tributary of the Dnieper - Khorol, r. Merty - upper course p. Mosel (belonging to the river Meuse), Rhone and Rhine - 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 rarely flows straight. The reason for the initial deviation may be local obstacles due to the geological structure and terrain. The meanders formed by the river are preserved long time unchanged only under certain conditions, such as rocks that are difficult to erode, a small amount of sediment.
As a rule, meanders, regardless of the reasons for their occurrence, are continuously changing and shifting downstream. This process is called meandering, and the convolutions formed as a result of this process - meanders.
A water flow that changes the direction of movement for whatever reason (for example, due to the outcropping of bedrock in its path), approaches the channel wall at an angle and, intensively washing it out, leads to a gradual retreat. Reflecting at the same time downstream, the flow hits the opposite bank, erodes it, is reflected again, etc. As a result of this, the areas being washed away "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 near-bottom transverse current coming from the opposite coast deposits the erosion products carried by it.
As the tortuosity increases, the process of meandering intensifies, however, to a certain limit (Fig. 92). An increase in meandering means an increase in the length of the river and a decrease in slope, and hence a decrease in the speed of the current. The river loses energy and can no longer erode the banks.
The curvature of the meanders can be so great that the isthmus breaks through. The ends of the detached gyrus are filled with loose deposits, and it turns into an old woman.
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 shift 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 strip of the meander belt, the river erodes the rocks and deposits sediment, resulting in a flat depression lined with alluvium, along which the riverbed meanders. During floods, water overflows the channel and floods the depression. This is how a floodplain is formed - a part of the river valley, flooded into floods.
In high water, the river is less winding, its slope increases, the depths increase, the speed becomes greater, the eroding activity intensifies, large meanders are formed that do not correspond to meanders formed during low water. There are many reasons for eliminating the sinuosity of the river, and therefore the 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 current, due to gravity, is the main factor in bottom erosion, while the transverse one determines the transfer of erosion products. At the eroded concave shore, the stream washes out a depression - a stretch, and the transverse current carries mineral particles to the convex shore, creating a shallow. Therefore, the transverse profile of the channel at the bend of the river is not symmetrical. In the straight section of the channel, located between two stretches and called a rift, the depths are relatively small, and there are no sharp fluctuations in depth in the transverse profile of the channel.
The line connecting the deepest places along the channel - the fairway - runs from stretch to stretch through the middle part of the rift. If the roll is crossed by fairways that do not deviate from the main direction, and if its line goes smoothly, it is called normal (good); the roll, on which the fairway makes a sharp bend, will be shifted (bad) (Fig. 93). Bad rifts make navigation difficult.
The formation of the relief of the channel (the formation of stretches and rifts) occurs mainly in spring during floods.
Life in the rivers. Living conditions in fresh waters differ significantly from living conditions in the oceans and seas. In the river, fresh water, constant turbulent mixing of water and relatively shallow depths accessible to sunlight are of great importance for life.
The flow has a mechanical effect on organisms, provides an influx of dissolved gases and removal of decay products of organisms.
According to the conditions of life, 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, rapids. The bottom is usually rocky, silt deposits are almost absent. Water temperature due to altitude reduced places. In general, conditions for the life of organisms are less favorable 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 course of the rivers is poor in fish both in terms of the number of species and the number of individuals. Only some fish can live here, such as trout, grayling, marinka.
In the middle reaches of mountain rivers, as well as in the upper and middle reaches of flat 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, 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; common fish such as ruff, eel, burbot, barbel, roach, etc.
The most favorable living conditions in the lower reaches of the rivers: low flow rate, muddy bottom, a large amount of nutrients. Here are found mainly such fish as smelt, stickleback, river flounder, sturgeon, bream, crucian carp, carp. Fish living 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 winter migrations).
Channels. Canals are artificial rivers with a peculiar regulated regime, created for irrigation, water supply and navigation. A feature of the channel mode is small level fluctuations, but if necessary, the water from the channel can be completely drained.
The movement of water in a canal follows the same patterns as the movement of water in a river. The canal water to a large extent (up to 60% of all water consumed by it) goes to infiltration through its bottom. Therefore, the creation of anti-infiltration conditions is of great importance. So far, this problem has not yet been solved.
Possible average flow velocities and bottom velocities should not exceed certain limits, depending on the resistance of the soil to erosion. For ships moving along the canal, an average flow velocity of more than 1.5 m / s is no longer permissible.
The depth of the channels should be more than the draft of the vessels by 0.5 m, the width - not less than the width of two vessels +6 m.
Rivers as a 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 that industry National economy, which first required the study of rivers. Connecting rivers with canals makes it possible 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 domestic), industry, Agriculture. All major cities are on the rivers. The population and urban economy consume a lot of water (on average 60 liters per day per person). Any industrial product cannot do without the irretrievable consumption of a certain amount of water. For example, to produce 1 ton of cast iron, 2.4 m3 of water is needed, to produce 1 ton of paper - 10.5 m3 of water, to produce 1 g of fabric from some polymeric synthetic materials - more than 3000 m3 of water. On average, 40 liters of water per day per 1 head of livestock. The fish wealth of the rivers has always been of great importance. Their use contributed to the emergence of settlements along the banks. At present, rivers as a source of a valuable and nutritious product - fish are not used enough; marine fisheries are much more important. In Russia great attention is given 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, river water in in large numbers goes for irrigation (UAR, India, Russia - middle Asia). The energy of rivers is being used more and more. The total hydropower resources on Earth are estimated at 3,750 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 is very different on different continents.
The scale of river use 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 need of industrial production for water (this is especially true for chemical industry), with increasing water consumption for agriculture (an increase in productivity 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.
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