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

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

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

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

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

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

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

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

Q - water consumption, l. For translate cubic meters in liters we multiply the consumption by 1000, S the area of ​​​​the pool, km 2.

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

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

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

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

b) the time of high water, if any;

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

General characteristics of the river and its use. At general characteristics rivers need to find out:

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

b) degree of meandering.

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

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

Meander study It has great importance for timber rafting and shipping;

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

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

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

The river is shown in Figure 2.

m 3

Conclusion: During this practical lesson, as a result of calculations, we obtained the following values characterizing the flow of the river:

Drain module? = 177239 l / s * km 2

Runoff coefficient b = 34.5%.

Intra-annual runoff distribution

Systematic ( daily) observations of water levels were started in our country around 100 years back. Initially, they were conducted in a small number of points. At present, we have data on the flow of rivers for 4000 hydrological posts. These materials are of a unique nature, making it possible to trace changes in runoff over a long period, they are widely used in calculations of water resources, as well as in the design and construction of hydraulic engineering and other industrial facilities on rivers, lakes and reservoirs. For solutions practical issues it is necessary to have observational data on hydrological phenomena for periods of time from 10 before 50 years and more.

Hydrological stations and posts located on the territory of our country form the so-called state hydrometeorological network. It is administered by Roskomgidromet and is designed to meet the needs of all industries. National economy according to the data on the regime of water bodies. For the purpose of systematization, observation materials at posts are published in official reference publications.

First time data hydrological observations were summarized in the State Water Cadastre USSR (GVK). It included guides to water resources the USSR (regional, 18 volumes), information about water levels on rivers and lakes the USSR(1881-1935, 26 volumes), materials on the regime of rivers ( 1875-1935, 7 volumes). With 1936 materials of hydrological observations began to be published in hydrological yearbooks. Currently, there is a unified nationwide accounting system for all types of natural waters and their use on the territory of the Russian Federation.

Primary processing data on daily water levels, given in the Hydrological Yearbooks, is to analyze the intra-annual flow distribution and plot the fluctuations in water levels for the year.

The nature of the change in runoff during the year and the regime of water levels due to these changes mainly depend on the conditions for feeding the river with water. According to B.D. Zaikova rivers are divided into three groups:

With spring floods, formed as a result of snow melting on the plains and low mountains;

With high water in the warmest part of the year, arising from the melting of seasonal and perpetual mountain snows and glaciers;

With rainfall.

The most common are rivers with spring floods. This group is characterized by the following phases water regime: spring flood, summer low water, period of autumn water rise, winter low water.

During the period spring flood in the rivers of the first group, due to the melting of snow, the flow of water increases significantly, and its level rises. The amplitude of fluctuations in water levels and the duration of floods on the rivers of this group differ depending on the factors of the underlying surface and factors of a zonal nature. For example, the Eastern European type of intra-annual runoff distribution has a very high and sharp spring flood and low water discharges in the rest of the year. This is due to the low amount of summer precipitation and strong evaporation from the surface of the steppe basins of the Southern Trans-Volga region.

Western European type distribution is characterized by a low and extended spring flood, which is a consequence of the flat relief and severe waterlogging of the West Siberian lowland. The presence of lakes, swamps and vegetation within the boundaries of the drainage basin leads to the equalization of the flow throughout the year. This group also includes the East Siberian type of runoff distribution. It is characterized by relatively high spring floods, rain floods in summer autumn period and extremely low winter low water. This is due to the influence permafrost on the nature of the feeding of the river.

The amplitude of fluctuations in water levels at medium and big rivers Russia is quite significant. She reaches 18 m on the upper Oka and 20 m on the Yenisei. With such filling of the channel, vast areas of river valleys are flooded.

The period of low levels that change little over time during the summer is called the period summer low water when groundwater is the main source of river nutrition.

In autumn, surface runoff increases due to autumn rains, which leads to water rise and education summer-autumn rain flood. The increase in runoff in autumn is also facilitated by a decrease in evaporation during this period of time.

Phase winter low water in the river begins with the appearance of ice and ends with the beginning of the rise in water levels from spring snowmelt. During the winter low water in the rivers, a very small flow is observed, since from the moment of the onset of stable negative temperatures, the river is fed only by groundwater.

The rivers of the second group are distinguished Far Eastern and Tien Shan types of intra-annual runoff distribution. The first of them has a low, strongly stretched, comb-like flood in the summer-autumn period and a low runoff in the cold part of the year. The Tien Shan type is distinguished by a smaller amplitude of the flood wave and a secure runoff in the cold part of the year.

Near the rivers of the third group ( Black Sea type) rain floods are evenly distributed throughout the year. The amplitude of fluctuations in water levels is strongly smoothed near rivers flowing from lakes. In these rivers, the boundary between high water and low water is hardly noticeable, and the volume of runoff during high water is comparable to the volume of runoff during low water. For all other rivers, the main part of the annual flow passes during the flood.

The results of observations over the levels for the calendar year are presented as level fluctuation chart(Fig. 3.5). In addition to the course of levels, the phases of the ice regime are shown on the graphs with special symbols: autumn ice drift, freeze-up, spring ice drift, as well as the values ​​of the maximum and minimum navigational water levels are shown.

Usually, the graphs of fluctuations in water levels at a hydrological post are combined for 3-5 years on one drawing. This makes it possible to analyze the river regime for low-water and high-water years and to trace the dynamics of the onset of the corresponding phases of the hydrological cycle over given period time.

28.07.2015

fluctuations river flow and criteria for its evaluation. 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 geographic location river basin. This made it possible to zonate our country in hydrological terms and to build a map of isolines of the 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, it is possible to determine the average long-term water discharge 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 flow in one section Q1 and famous squares watersheds in these sections F1 and F2, the water discharge in another 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- most probable average long-term value 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 have random character. 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 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 discharge 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 defined as a percentage of total number 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, on average, years of a given or greater water content occur; for low-water years, 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 to regulate the channel or runoff of rivers, they are calculated according to the water content of the year of a certain supply, which guarantees the reliability and trouble-free operation of 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 written in descending order absolute value okay;
2) each member of the series is assigned serial number, starting from one;
3) the security of each member of the decreasing series is determined by formulas (23) or (24).
Based on the results of the calculation, a security curve is built, similar to the one shown in Fig. 8b.
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 river runoff. 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 Pearson curve equation III type, whose integral expression is the security 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 coefficient of variation of the annual runoff 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 asymmetry coefficient 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 supply curve for the above three of its 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 probability - 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 as 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 natural area and relief categories 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;
III category - 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.

Within Africa, 4 hydrological regions have been identified with different intra-annual distribution of river runoff (Fig. 6.1). At the same time, significant territories in the Northern, Eastern and South- West Africa remained outside these areas, although on map No. 28 "Intra-annual distribution of runoff" in the Atlas of the MVB, more than 30 histograms are shown within them, corresponding to sections on rivers with specific features water regime. These primarily include the White Nile, the flow of which is regulated by lakes Victoria, Kyoga, Albert, as well as the marshes of the Sadd region, and Zambezi, the flow of which is regulated by the Kariba and Cabora Bassa reservoirs. In addition, we did not use gauges on frequently drying rivers of semi-desert and desert regions, where the available river hydrographs are not representative enough due to the strong variability of the intra- and inter-annual distribution of river runoff.

• 1. West African region (watersheds of the Senegal, Niger, Shari, Ubangi (right tributary of the Congo), Volta and other rivers of the northern coast of the Gulf of Guinea), where low low water lasts the first half of the year, and in the high-water second half of the year, the maximum runoff usually occurs in September-October . The lower reaches of the Blue Nile and the Nile below this tributary, assigned to this area, are currently sections of the river network that have been transformed into the downstream of the cascade of irrigation and energy hydroelectric complexes of Sudan and the Aswan hydroelectric complex with one of the largest reservoirs in the world, Nasser. The flow regime here is determined only by water management needs. According to the classification of M.I. Lvovich, the water regime of the rivers of this region belongs to the RAy type and is characterized by low natural regulation (the average value
• 2. South African region, including the basins of the Kasai (left tributary of the Congo), Limpopo, Orange and southeastern slopes of the Dragon Mountains on the mainland and the island of Madagascar, where the flood lasts from December to April with a maximum in January

Rice. 6.1.

a- network of registered 73 observation points (shown by dots) and boundaries of regions; b- averaged hydrographs within districts {1-4). Monthly shares of runoff (% of its annual value) are shown in bars from January

to December or February, less often in March. Winter low water - from June to September, which corresponds to the type of river regime Rey. Natural regulation on average for the rivers of this region is moderate (f = 0.33). The sediment runoff module is slightly higher than in region 7, although it is just as variable from one catchment to another - from 50 to 500 t / (km 2 -year) and more on mountain steppe slopes developed for agriculture and pastures, where overgrazing is not uncommon livestock. In the Orange basin, where there are observations of sediment runoff over several decades, the average long-term module is 890 t/(km 2 year) on the main river and up to 1000 - 2000 t/(km 2 * year) on its small tributaries. A sharp increase in sediment discharge occurred in the first years economic development territory by the colonists. With the development of flow regulation by reservoirs, there has been a reduction in the turbidity of RWM.

3. The East African region covers the upper reaches of the Congo-Lualaba basin, the watersheds of lakes Tanganyika, Rukva, Eyasi and the river. Rufiji is the main river of Tanzania. In it, the maximum flow of rivers is observed in autumn (in March-May), and low water - from June to December (the type of water regime is RAy, as in region 7, but located in the Northern Hemisphere). The regulation of river flow here is on average the same as in the area 2 (f = 0.33). Variation in river turbidity is as large and variegated as in region 2, but mainly from 20 to 200 t/(km 2 - year), and on arrays of row crops (corn, wheat) on the plateau of Central Tanzania, the erosion modulus reaches 1500 t / (km 2 - year) .

In the Atlas Mountains, due to the large spatial variability of the conditions for the formation of river runoff, the rivers have a different type of its intra-annual distribution, which is inherent in the rivers of the three hydrological regions considered above (see Fig. 6.1). The rivers of the northern and northwestern slopes are the most abundant, and the water content of the rivers flowing to the Sahara is, on average, 100 times less. Downstream, they gradually turn into temporary streams. This is facilitated not only by evaporation, but also by the karst common here. On the separate sections rivers flow underground, turning into springs in the foothills with a flow rate of up to 1-1.5 m 3 / s.

4. The Central African region occupies a flat alluvial surface of the basin of the ancient lake. Busir, which existed until the late Pleistocene. It is filled with deposits of the river. Congo and its tributaries. This area also includes the watersheds of the rivers flowing into it, located between it and the eastern coast of the Gulf of Guinea. The rivers of the region are distinguished by the most uniform flow throughout the year with a long, on average 8-month high-water summer-autumn period without a clearly defined flow maximum and with a reduced flow in July-October (Ray). Due to the presence of lakes and vast swamps under the canopy of dense equatorial forests in the center of the Congo basin, the intensity of slope and channel erosion does not exceed 10 t / (km 2 - year). Therefore, on the peripheral slopes of this basin, turbid RSMs in the upper links of the river network in its central part become clearer as suspended matter sediments. Since the main role in the nutrition of these rivers is played by rain water of local origin, mineralization of RWM is very low. Thus, judging by the values ​​of the specific electrical conductivity of water (3–4 μS/cm) in some rivers of the Shaba region (former Katanga) on the southeastern margin of the Congo basin in the Mitumba mountains, the mineralization of water is half that in atmospheric precipitation of purely oceanic origin. This is evidence of an intense intra-regional (in the Congo Basin) moisture cycle, which not only causes the washing and desalination of soils and soils in their aeration zone, but also the distillation of atmospheric and river water involved in this cycle.

Due to the very short winter-spring period of low water content in the Central African hydrological region, the coefficient cp = 0.28 indicates the supposedly low natural regulation of the river flow, which is lower, for example, than in the East African region. At the same time, the maximum monthly runoff in April in the area 4 only three times the minimum in September, while in the region 3 the difference in extreme monthly runoff values ​​in the same months is 8-fold, i.e. the intra-annual distribution of runoff there is much more uneven. Thus, the coefficient of natural runoff regulation (used to characterize the runoff of Russian rivers, where the low water is longer than the flood) is not informative enough to judge the intra-annual variability of the runoff of equatorial rivers.

• The Ecology and Utilization of African inland Waters. - Nairobi: UNEP, 1981.