Within Africa, 4 hydrological regions have been identified with different intra-annual distribution river flow(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 hydrographs of rivers 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, 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 consumption occurred in the first years of the economic development of the 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 catchment areas 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 (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 flow, rivers have different type its intra-annual distribution, 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. So, 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 precipitation purely oceanic. 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.
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 period of time, m 3 / s, T is the number of seconds in billing period time.
Since the average water consumption was calculated earlier as the norm annual runoff, runoff volume 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 changes from K = 1.58 / 2.39 = 0.66 for the year from minimum consumption up to K = 3.26 / 2.39 = 1.36 for 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.
AT term paper it is necessary to determine the characteristics of the annual runoff for the considered basin, 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 that determine the intra-annual distribution of runoff and its total value are climatic. They determine the general nature (background) of the distribution of runoff in the year of a particular geographical area; territorial changes in runoff distribution follow climate change.
The factors influencing the distribution of runoff throughout the year include lakes, forest cover, waterlogging, the size of watersheds, the nature of soils and grounds, and the depth of occurrence. ground water, 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, a 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 as in the years with the most early term offensive, and with the most late deadline endings.
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 flow for the season, determined in terms of the inter-seasonal distribution of flow (Table 10), by the percentage of each month A% (Table 11), calculate the estimated flow 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
To determine the flow of the river depending on the area of the basin, the height of the sediment layer, etc. in hydrology, the following quantities are used: river flow, flow modulus, and flow coefficient.
River runoff call water consumption over a long period of time, for example, per day, decade, month, year.
Drain module they call the amount of water expressed in liters (y), flowing on average in 1 second from the area of the river basin in 1 km 2:
Runoff coefficient call the ratio of water flow in the river (Qr) to the amount of precipitation (M) on the area of the river basin for the same time, expressed as a percentage:
a - runoff coefficient in percent, Qr - annual runoff value in cubic meters; M is the annual amount of precipitation in millimeters.
To determine the runoff modulus, it is necessary to know the water discharge and the area of the basin upstream of the target, according to which the water discharge of the given river was determined. The area of a river basin can be measured from a map. For this, the following methods are used:
- 1) planning
- 2) breakdown into elementary figures and calculation of their areas;
- 3) measuring the area with a palette;
- 4) calculation of areas using geodetic tables
It is easiest for students to use the third method and measure the area using a palette, i.e. transparent paper (tracing paper) with squares printed on it. Having a map of the studied area of the map on a certain scale, you can make a palette with squares corresponding to the scale of the map. First, you should outline the basin of this river above a certain alignment, and then apply the map to the palette, on which to transfer the contour of the basin. To determine the area, you first need to count the number of full squares located inside the contour, and then add 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. To convert cubic meters to liters, we multiply the flow rate by 1000, S pool area, km 2.
To determine the river runoff coefficient, it is necessary to know the annual runoff of the river and the volume of water that has fallen on the area of a given river basin. The volume of water that fell on the area of this pool is easy to determine. To do this, you need to multiply the area of the basin, expressed in square kilometers, by the thickness of the layer of precipitation (also in kilometers). For example, the thickness will be equal to p if precipitation in a given area was 600 mm per year, then 0 "0006 km and the runoff coefficient will be equal to:
Qr is the annual flow of the river, and M is the area of the basin; multiply the fraction by 100 to determine the runoff coefficient as a percentage.
Determination of the river flow regime. To characterize the flow regime of the river, you need to establish:
a) what seasonal changes the water level undergoes (a river with a constant level, which becomes very shallow in summer, dries up, loses water in pores and disappears from the surface);
b) the time of high water, if any;
c) the height of the water during the flood (if there are no independent observations, then according to questionnaire data);
d) the duration of the freezing of the river, if it occurs (according to their own observations or according to information obtained through a survey).
Determination of water quality. To determine the quality of water, you need to find out whether it is cloudy or transparent, drinkable or not. The transparency of the water is determined by a white disk (Secchi disk) with a diameter of approximately 30 cm, summed up on a marked line or attached to a marked pole. If the disk is lowered on the line, then a weight is attached below, under the disk, so that the disk is not carried away by the current. The depth at which this disk becomes invisible is an indication of the transparency of the water. You can make a disk out of plywood and paint it white, but then the load must be hung heavy enough so that it falls vertically into the water, and the disk itself maintains a horizontal position; or plywood sheet can be replaced with a plate.
Determination of water temperature in the river. The temperature of the water in the river is determined by a spring thermometer, both on the surface of the water and at different depths. Keep the thermometer in water for 5 minutes. A spring thermometer can be replaced with a conventional wooden-framed bath thermometer, but in order for it to sink into the water at different depths, a weight must be tied to it.
You can determine the temperature of the water in the river with the help of bathometers: a bathometer-tachymeter and a bottle bathometer. The bathometer-tachymeter consists of a flexible rubber balloon with a volume of about 900 cm 3; a tube with a diameter of 6 mm is inserted into it. The bathometer-tachymeter is fixed on a rod and lowered to different depths to take water.
The resulting water is poured into a glass and its temperature is determined.
It is not difficult for a student to make a bathometer-tachymeter. To do this, you need to buy a small rubber chamber, put on it and tie a rubber tube with a diameter of 6 mm. The bar can be replaced with a wooden pole, dividing it into centimeters. The rod with the tachymeter bathometer must be lowered vertically into the water to a certain depth, so that the opening of the tachymeter bathometer is directed downstream. Having lowered to a certain depth, the bar must be rotated by 180 and held for about 100 seconds in order to draw water, and then again turn the bar by 180 °. runoff water regime river
It should be removed so that water does not spill out of the bottle. After pouring water into a glass, determine the temperature of the water at a given depth with a thermometer.
It is useful to simultaneously measure the air temperature with a sling thermometer and compare it with the temperature of the river water, making sure to record the time of observation. Sometimes the temperature difference reaches several degrees. For example, at 13 o'clock the air temperature is 20, the water temperature in the river is 18 °.
Study in certain areas on certain nature of the riverbed. When examining sections of the nature of the riverbed, it is necessary:
a) mark the main reaches and rifts, determine their depths;
b) when detecting rapids and waterfalls, determine the height of the fall;
c) draw and, if possible, measure the islands, shoals, middles, side channels;
d) collect information in which places the river is eroding and in places that are especially strongly eroded, determine the nature of the eroded rocks;
e) study the nature of the delta, if the estuarine section of the river is being investigated, and plot it on the visual plan; see if the individual arms correspond to those shown on the map.
General characteristics of the river and its use. With a general description of the river, you need to find out:
a) which part of the river is mainly eroding and which is accumulating;
b) degree of meandering.
To determine the degree of meandering, you need to know the tortuosity coefficient, i.e. the ratio of the length of the river in the study area to the shortest distance between certain points in the study part of the river; for example, river A has a length of 502 km, and the shortest distance between the source and the mouth is only 233 km, hence the tortuosity coefficient:
K - sinuosity coefficient, L - river length, 1 - shortest distance between source and mouth
Meander study is of great importance for timber rafting and shipping;
c) Non-squeezing river fans formed at the mouths of tributaries or produce temporary flows.
Find out how the river is used for navigation and timber rafting; if the hand is not navigable, then find out why, it serves as an obstacle (shallow, rapids, are there waterfalls), are there dams and other artificial structures on the river; whether the river is used for irrigation; what transformations need to be done to use the river in the national economy.
Determining the nutrition of the river. It is necessary to find out the types of river nutrition: groundwater, rain, lake or marsh from melting snow. For example, r. Klyazma is fed, ground, snow and rain, of which ground supply is 19%, snow - 55% and rain. - 26 %.
The river is shown in Figure 2.
m 3
Conclusion: In the course of this practical lesson, as a result of calculations, the following values were obtained, characterizing the flow of the river:
Drain module? = 177239 l / s * km 2
Runoff coefficient b = 34.5%.
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 erosion 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, the relative age of the river valley (the valley is older than that of 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 different natural zones is not the same.
In the mountains, the density of the river network is greater than on the plains, for example: on the northern slopes of the 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 first-order tributary basins, which in turn consist of second-order tributary basins, etc. River basins are included in the basins of the seas and oceans. All land waters are divided between the main basins: 1) the Atlantic and Arctic Oceans (area 67,359 thousand km2), 2) the Pacific and Indian Oceans (area 49,419 thousand km2), 3) the internal flow area (area 32,035 thousand km2). 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 zone.
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, watersheds are generally impossible to draw, 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 of bifurcation is the division of the upper reaches of the Orinoco into two rivers. One of them, which retains the name Orinoco, flows into the Atlantic Ocean, the other - Casiquiare - flows into the Rio Negro, a tributary of the Amazon.
Watersheds limit the basins of rivers, seas, oceans. The main basins: the Atlantic and the Arctic Ocean (Atlantic-Arctic), on the one hand, and the Pacific and Indian, on the other, are limited by the main (world) watershed of the Earth.
The position of the watersheds does not remain constant. Their movements are associated with the slow incision of the upper reaches of the rivers as a result of the development of river systems and with the restructuring of the river network, caused, for example, by tectonic movements of the earth's crust.
Riverbed. Water streams flow along the earth's surface in the longitudinal recesses created by them - 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 free section will be less than the water section by an amount equal to the area of the 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 are 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 as a decimal fraction - 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).
The longitudinal profile of the bottom of the channel and the longitudinal profile of the water surface are different: the first is always a wavy line, the second is a smooth line (Fig. 88).
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 of the living 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 open 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 viewed 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 either in cubic meters or 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 in the formation of runoff. 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 the potential for 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, and in spring it moderates the intensity of snowmelt, which contributes to the infiltration 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), a zonal pattern is found. 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. In general, the influence of the forest on the runoff is water-regulating and water-protective.
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 great 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 the manifestation of latitudinal zonality in the distribution of runoff, which is especially pronounced 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 nutrition of which snowmelt waters play an important role, 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 occur in spring and summer in monsoonal climates, in autumn in equatorial climates, and in winter in Mediterranean climates. 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 sources of nutrition (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 supply, 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.
The natural combinations of different combinations of power sources with different variants of runoff distribution during the year allowed Lvovich to identify the types of river water regime. 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 the melt waters of polar ice and snow for a short period, but they freeze over most of the year. Rivers of the subarctic type are fed by melted snow waters, their underground feeding is very small. Many, even significant rivers freeze over. These rivers have the highest level in summer (summer flood). The reason is late spring and summer rains.
Rivers of 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 from direct solar radiation, the effective radiation of the water surface, the cost of heat for evaporation and its release during condensation, heat exchange with the atmosphere and the bed of the channel. The water temperature and its changes depend on the ratio of the 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 different 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. The chemical features of the water in the river depend on the sources of nutrition 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 the middle zone of the European part of Russia, in the South Caucasus and partially 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, one can cite the rivers of the Sea of \u200b\u200bAzov, some rivers of the 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 the flow of rivers, the chemical composition of 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, the chemical properties of river water 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. With an average land height of 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, stepwise, 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 of the 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 remain unchanged for a long time only under certain conditions, such as rocks that are difficult to erode and 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. At the same time, being reflected downstream, the flow hits the opposite bank, erodes it, is reflected again, etc. As a result, 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. Large 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 the 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. The water temperature is lower due to the absolute height of the place. 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 the branch of the national economy that first of all 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 of railways. Rivers have long been used for timber rafting. The importance of rivers in the water supply of the population (drinking and household), industry, and agriculture is great. All major cities are on the rivers. The population and the urban economy consume a lot of water (an average of 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, much attention is paid to the organization of fisheries with the creation of artificial reservoirs (ponds, reservoirs).
In areas with a large amount of heat and a lack of atmospheric moisture, river water is used in large quantities for irrigation (UAR, India, Russia - Central 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, on different continents is very different.
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 for industrial production in water (this is especially true for the chemical industry), with the increasing consumption of water for the needs of 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.
The water regime of rivers is characterized by a cumulative change in time in the levels and volumes of water in the river. Water level ( H) - the height of the water surface of the river relative to the constant zero mark (ordinary or zero of the graph of the water gauge station). Among the fluctuations in water levels in the river, long-term ones are identified, due to secular climate changes, and periodic: seasonal and daily. In the annual cycle of the water regime of rivers, several characteristic periods are distinguished, called the phases of the water regime. For different rivers, they are different and depend on climatic conditions and the ratio of food sources: rain, snow, underground and glacial. For example, the rivers of temperate continental climate (Volga, Ob, etc.) have the following four phases: spring flood, summer low water, autumn rise of water, winter low water. high water- a long-term increase in the water content of the river that repeats annually in the same season, causing a rise in the level. In temperate latitudes, it occurs in spring due to intensive snowmelt.
low water- a period of long-term low levels and flow of water in the river with the predominance of underground feeding ("low water"). Summer low water is due to intense evaporation and seepage of water into the ground, despite the greatest amount of precipitation at this time. Winter low water is the result of the lack of surface nutrition, rivers exist only due to groundwater.
Floods- short-term non-periodic rises in water levels and an increase in the volume of water in the river. Unlike floods, they occur in all seasons of the year: in the warm half of the year they are caused by heavy or prolonged rains, in winter - by melting snow during thaws, at the mouths of some rivers - due to the surge of water from the seas where they flow. In temperate latitudes, the autumn rise of water in rivers is sometimes called the flood period; it is associated with a decrease in temperature and a decrease in evaporation, and not with an increase in precipitation - there is less than in summer, although cloudy rainy weather is more common in autumn. Autumn floods along the Neva River in St. Petersburg are caused primarily by the surge of water from the Gulf of Finland by westerly winds; the highest flood of 410 cm occurred in St. Petersburg in 1824. Floods are usually short-term, the rise in water level is lower, and the volume of water is less than during floods.
One of the most important hydrological characteristics of rivers is river runoff, which is formed due to the inflow of surface and groundwater from the catchment area. A number of indicators are used to quantify the flow of rivers. The main one is the flow of water in the river - the amount of water that passes through the living section of the river in 1 second. It is calculated according to the formula Q=v*ω, where Q- water consumption in m 3 / s, v is the average speed of the river in m/s. ω - open area in m 2. Based on the data of daily expenses, a calendar (chronological) graph of fluctuations in water consumption is built, called a hydrograph.
The flow modification is the volume of runoff (W in m 3 or km 3) - the amount of water flowing through the living section of the river for a long period (month, season, most often a year): W \u003d Q * T, where T is a period of time. The volume of runoff varies from year to year, the average long-term runoff is called the runoff rate. For example, the annual flow rate of the Amazon is about 6930 km3, which is about >5% of the total annual flow of all rivers of the world, the Volga is 255 km3. The annual volume of runoff is calculated not for the calendar, but for the hydrological year, within which the full annual hydrological cycle of the water cycle is completed. In regions with cold snowy winters, November 1 or October 1 is taken as the beginning of the hydrological year.
Drain module(M, l / s km 2) - the amount of water in liters flowing from 1 km 2 of the basin area (F) per second:
(10 3 is a multiplier for converting m 3 into liters).
The river flow module allows you to find out the degree of water saturation of the basin area. He is zoned. The Amazon has the largest runoff module - 30,641 l / s km 2; near the Volga, it is 5670 l / s km 2, and near the Nile - 1010 l / s km 2.
runoff layer (Y) is the water layer (in mm) evenly distributed over the catchment area ( F) and flowing down from it for a certain time (annual runoff layer).
Runoff coefficient (To) is the ratio of the volume of water flow in the river ( W) to the amount of precipitation ( X) falling on the area of the basin ( F) for the same time, or the ratio of the runoff layer ( Y) to the precipitation layer ( X) that fell on the same area ( F) for the same period of time (immeasurable value or expressed in%):
K=W/(x*F)* 100%, or K=Y/x*100%.
The average runoff coefficient of all the Earth's rivers is 34%. i.e., only one third of the precipitation that falls on land flows into rivers. The runoff coefficient is zonal and varies from 75-65% in tundra and taiga zones to 6-4% in semi-deserts and deserts. For example, for the Neva it is 65%, and for the Nile it is 4%.
The concept of runoff regulation is related to the water regime of rivers: the smaller the annual amplitude of water discharges in the river and the water levels in it, the more the runoff is regulated.
Rivers are the most mobile part of the hydrosphere. Their runoff is an integral characteristic of the water balance of the land area.
The amount of river flow and its distribution during the year is influenced by a complex of natural factors and human economic activity. Among natural conditions, the main one is climate, especially precipitation and evaporation. With heavy rainfall, the flow of rivers is large, but one must take into account their type and the nature of the fallout. For example, snow will provide more runoff than rain because there is less evaporation in winter. Heavy precipitation increases the runoff compared to continuous precipitation with the same amount. Evaporation, especially intense, reduces runoff. In addition to high temperature, wind and lack of air humidity contribute to it. The statement of the Russian climatologist A. I. Voeikov is true: “Rivers are a product of the climate.”
Soils affect runoff through infiltration and structure. Clay increases surface runoff, sand reduces it, but increases underground runoff, being a moisture regulator. The strong granular structure of soils (for example, in chernozems) contributes to the penetration of water deep into, and on structureless loose loamy soils, a crust often forms, which increases surface runoff.
The geological structure of the river basin is very important, especially the material composition of rocks and the nature of their occurrence, since they determine the underground feeding of rivers. Permeable rocks (thick sands, fractured rocks) serve as moisture accumulators. The flow of rivers in such cases is greater, since a smaller proportion of precipitation is spent on evaporation. The runoff in karst areas is peculiar: there are almost no rivers there, since precipitation is absorbed by funnels and cracks, but at their contact with clays or shale, powerful springs are observed that feed the rivers. For example, the karsted Crimean yaila itself is dry, but powerful springs gush at the foot of the mountains.
The influence of the relief (absolute height and slopes of the surface, density and depth of dissection) is great and varied. The runoff of mountain rivers is usually greater than that of flat rivers, since in the mountains on the windward slopes there is more abundant precipitation, less evaporation due to lower temperatures, due to the large slopes of the surface, the path and time for the precipitation to reach the river are shorter. Due to the deep erosive incision, underground nutrition is more abundant from several aquifers at once.
The influence of vegetation - different types of forests, meadows, crops, etc. - is ambiguous. In general, vegetation regulates runoff. For example, a forest, on the one hand, enhances transpiration, delays precipitation with tree crowns (especially coniferous forests snow in winter), on the other hand, more precipitation usually falls over the forest, under the canopy of trees the temperature is lower and evaporation is lower, snowmelt is longer, precipitation is better seeped into forest floor. It is very difficult to identify the influence of different types of vegetation in its pure form due to the joint compensating effect of various factors, especially within large river basins.
The influence of lakes is unequivocal: they reduce the flow of rivers, since there is more evaporation from the water surface. However, lakes, like swamps, are powerful natural flow regulators.
The impact of economic activity on the stock is very significant. Moreover, a person affects both the runoff directly (its value and distribution in the year, especially during the construction of reservoirs), and the conditions for its formation. When creating reservoirs, the regime of the river changes: during the period of excess water, they are accumulated in reservoirs, during the period of shortage, they are used for various needs, so that the flow of rivers is regulated. In addition, the flow of such rivers is generally reduced, because evaporation from the water surface increases, a significant part of the water is spent on water supply, irrigation, watering, and underground nutrition decreases. But these inevitable costs are more than offset by the benefits of reservoirs.
When water is transferred from one river system to another, the flow changes: in one river it decreases, in another it increases. For example, during the construction of the Moscow Canal (1937), it decreased in the Volga, and increased in the Moskva River. Other transport channels for water transfer are usually not used, for example, the Volga-Baltic, White Sea-Baltic, numerous channels of Western Europe, China, etc.
The activities carried out in the river basin are of great importance for the regulation of river flow, because its initial link is the slope flow in the catchment area. The main activities carried out are as follows. Agroforestry - forest plantations, irrigation and drainage - dams and ponds in beams and streams, agronomic - autumn plowing, snow accumulation and snow retention, plowing across the slope or contour on hills and ridges, grassing slopes, etc.
In addition to intra-annual runoff variability, there are long-term fluctuations, apparently associated with 11-year cycles of solar activity. On most rivers, high-water and low-water periods lasting about 7 years are clearly traced: for 7 years, the water content of the river exceeds the average values, floods and low water are high, for the same number of years the water content of the river is less than the average annual values, water discharges in all phases of the water regime are small.
Literature.
- Lyubushkina S.G. General geography: Proc. allowance for university students enrolled in special. "Geography" / S.G. Lyubushkina, K.V. Pashkang, A.V. Chernov; Ed. A.V. Chernov. - M. : Education, 2004. - 288 p.
