The speed of the rivers. Discharge and runoff of rivers

flow speed runoff water

The role of flowing water on earth is enormous and has always attracted the attention of man, not without reason, since ancient times, many rivers have been personified; and in the eyes of modern science, rivers are the most active element of physical geography. Some of them are calm, have a slow current and regular rises in water, which are easy to foresee; others - quickly and swiftly carry stormy waters, suddenly raise their level and just as suddenly lower it.

But rivers are not only a geographical factor in themselves, but in themselves, they are at the same time tirelessly working to change the earth; the results of this geological work of flowing water, summing up over the centuries, are so great that the countries completely lose their original appearance: where once high mountains rose, at present we find only an undulating plain, and, on the other hand, high plateaus turned into mountainous or hilly areas.

Human life is in such close connection with the regime of flowing waters that the high interest shown by a person in relation to rivers is self-evident. The great rivers are the cheapest natural means of communication in many countries, and in the far north they are often the only means of communication, not only in summer but also in winter, when their icy surface offers the best way. Even in desert countries, as, for example, in the Sahara, dry riverbeds determine the direction of caravan routes. From time immemorial, Amu Darya (ancient Oxus), Syr Darya (ancient Jaxart) determined the direction of trade routes through Central Asia. The rapid colonization of certain countries, such as Canada, the middle part of the United States of America, and Siberia, becomes intelligible only if one takes into account the location of the rivers in these countries. The conveniences that rivers provide as means of communication draw people to their banks and are one of the factors in the emergence of cities, especially at the intersections of river routes. Rivers are even more important as intermediaries between the ocean and the interior of countries, not without reason, not far from their mouths, the greatest trading cities such as London, Rotterdam, Antwerp, Hamburg, Alexandria, Calcutta, Shanghai, Montreal, Quebec, New Orleans, Montevideo, Leningrad, etc. .

On the other hand, the floods of certain rivers, such as the Nile, Tigris and Euphrates, made it possible to develop civilizations at the very borders of the desert. The importance of rivers in the life of a country is so great that in all civilized states special organizations have arisen for the study of hydrography, and a systematic study of rivers and their regime has long since begun. In France, the establishment of the Service nydrometrique de la Seine preceded the establishment of meteorological stations, in Germany a number of valuable monographs were published on the study of all large rivers, from the Rhine to the Vistula, in the United States of America, a systematic study of rivers is carried out by the Geological Survey. The strong and devastating floods of the Danube, and especially its tributaries the Tissa, Maros and others in Hungary, led to the creation of a whole network of hydrological institutions with a central station in Budapest. Of the CIS rivers, the Dnieper, Volga and a number of other rivers were subjected to a more detailed survey in the 19th century; at the end of the 19th century, in European Russia, in addition, a special expedition worked to survey the sources of the most important rivers, under the general leadership of A.A. Tillo, which provided valuable material on the hydrology of the upper reaches of your main water arteries. The most characteristic feature of each river is its regime, i.e., the change during the year of its levels: flow, sediment, temperature, chemistry, etc. To find out the regime of a river, it is necessary to determine the relationship that exists between the amount of precipitation that has fallen in its basin, and a mass of water flowing down the river.

To determine this latter, it is enough to know the cross-sectional area of ​​\u200b\u200bthe river (the so-called living section) and the average speed of its flow in a given place, since the product of these two magnitudes gives us the required amount of water flowing by the river in a certain unit of time, for example, per second, per minute, etc. However, determining the flow of water in a river over a more or less significant period of time, and especially a whole year, is not an easy task, since both the flow rate and the living section of the river are constantly changing throughout the year.

The determination of the speed of the current is carried out either with the help of simple floats, such as bottles, or with the help of more accurate devices called turntables.

Observations show that the speed of the flow in the river usually decreases from the headwaters downstream. The reason for this is that during its movement, water experiences friction, both externally against the bottom, shores and against the air, and internally, due to the unequal speed and different direction of movement of water particles. In the end, the obstacles experienced by water during its movement are so great that they absorb all the acceleration acquired by water when falling from the sources to the mouth.

Due to friction in a given living section of the river, the highest speed (in the case of a regular river diameter) is in the middle, but not on the surface, but at some shallow depth, since on the surface the water experiences friction against the air. In the case of an asymmetric living section, the highest speed will be over the deepest hollow of the river, closer to one of the banks. Connecting the points of the cross sections of the river, in which the current is the fastest, we get a winding line, which is called the core, or axis, of the river. A visual concept of the distribution of velocities in a given living section of the river can be obtained by connecting lines - isotachs - points that have the same speed. In the middle of the upper isotach runs the midstream of the river.

If there is no wind and the roughness of the bottom is normal, then on each individual vertical the maximum speed will be from the surface at a distance of approximately 1/5 of the depth of the vertical.

The position of the point with the highest speed is determined by the ratio between the surface and bottom velocities (the ratio of surface and longitudinal friction). An increase in the bottom roughness will entail a decrease in the bottom velocity and a corresponding approach of the point with the highest velocity to the surface.

The water level in the river is not always the same. During the rise (rise) of water, its horizon in the middle of the channel rises slightly, and during the decline it drops in the middle and rises near the banks. This is due to the fact that the bottom of the channel near the banks creates resistance to the movement of water.

Scheme of a living current during a decrease and with a sharp increase in water

With a sharp decrease in water, all objects floating on the river (logs, debris, etc.) are drawn into its middle part, in a straight section of the channel and closer to the concave bank at its bend. This is especially evident in the spring, when the flooded river enters the channel and individual ice floes and other floating objects move through the water, strictly outlining the ribbon-like contour of the rod.

During the rise of the water, various floating objects move along the banks, sliding off the water bulge formed in the middle of the stream. The splash is cut by the current, from which it becomes steep, the water has a dull yellow or dark color. With a decrease in water, the splash increases and becomes gentle.

The direction of the rod is especially pronounced where the current is strong, and its surface, wavy from the wind, is a light, clearly defined ribbon-like strip, interrupted in places.

Directions and velocities of currents can be determined by the navigator along the contours of the banks, based on the fact that the core passes close to the concave banks. If the coast is edged, then the current in the immediate vicinity of it is especially fast. The speed of the current is greater, the smaller the width of the channel and the greater its slope.

The direction and speed of the current can be determined by various coastal objects visible from the vessel: bushes, piles, stones, etc. At a high current speed, the water rises above these objects, forming a backwater.

The flooded bushes, under the pressure of the current, rhythmically sway, vibrate, and waves move away from rigid objects - pillars, piles, bridge supports. The greater the flow velocity, the sharper the angle of wave formation and the higher the wave. With a small current, a weak trace is visible below the object.

The direction and approximate speed of the current are determined by objects floating on the surface of the water, including those thrown into the water specially for this, and by the location of the angle of the rafts on which the buoys are installed. The stronger the current, the more the buoys and milestones tilt.

The headwind, increasing friction, reduces the surface speed and removes the highest speed from the surface. If the surface velocity is equal to the bottom one, the highest velocity will be in the middle of the vertical. In winter, under the ice, with a strongly rough bottom surface, the greatest speed moves closer to the bottom.

The wind blowing in the direction of the current will not slow down the surface layers of water, but will drive them, so the highest vertical speed will rise to the surface.

Thus, the flow velocity is determined by:

• 1) the slope of the river surface,
• 2) the shape of the channel,
• 3) the roughness of the channel.

In this case, it must be borne in mind that the speed is determined by the slope of the surface of the water in the river, and not by the slope of the channel. If the surface of the water is horizontal (for example, in front of a dam), then there will be no flow.

The Chezy formula, giving the dependence of the speed on the factors that determine it, makes it possible to foresee how the speed will change when these factors change.

Due to the unequal speeds of water movement in the living section, the surface of the river is not horizontal; as the river level rises, more water flows to the middle than to the edges, and the surface takes on a convex shape, which is very clearly seen, for example, in our rivers before the ice breaks up: due to the increase in water, ice also takes a convex shape towards the middle, and surface melt waters are collected near the shores, forming here long puddles, while the surface of the ice in the middle remains dry. When the waters subside, the largest amount of water flows down the middle of the river, and the surface of the river takes on a concave shape. The resulting level difference in the Mississippi reaches 2 m.

In addition, the transverse profile of the river is distorted by the centrifugal force, the Coriolis force resulting from the rotation of the earth, and the surge winds blowing across the river. There are two types of fluid motion - laminar and turbulent.

If the speed at each point is depicted as a vector (an arrow giving the direction of the speed and its magnitude), then during laminar motion the speed vector at each given point will be constant and will not change. Such fluid motion is observed in narrow tubes at low velocities. In nature, the movement of groundwater through small pores approaches laminar. A special case of laminar motion will be parallel jet.

Turbulent motion is characterized by inconsistency, variability of the velocity vector at each given point of the live section or vertical. This variability is called pulsation. Thus, during turbulent motion, each individual particle of water, arriving at a given point, will pass through it in different directions and at different linear speeds. Turbulent motion is widespread in nature. All fairly fast-flowing surface waters are turbulent. It is safe to say that rivers have only turbulent flow. A special case of turbulent motion is vortex (whirlpools, funnels, etc.).

The velocity vector of turbulent motion can be decomposed into components - horizontal, vertical and lateral. The horizontal component characterizes the drift along the stream, and the vertical component characterizes the movement of water particles up or down.

The significance of the turbulence of the river flow is extremely high. It determines the mixing of river water and the transport of material in suspension.

The amount (volume) of water flowing through the living area per unit time is called the flow of the river. The flow over a long period of time is called runoff. Usually there are annual, monthly, daily runoff.

Knowing the mass of water flowing by the river at different times of the year, we can get an idea of ​​its regime. For clarity, the change in water flow can be expressed graphically, denoting the amount of water flowing at a given time with rectangles proportional to the corresponding masses of water. Since the determination of the discharge is associated with great difficulties and has been made for a small number of rivers, they are often limited only to observations on the water gauge over fluctuations in the level of the river, and on the basis of these fluctuations they also judge the change in discharge, obtaining empirical formulas for the dependence of the discharge on the height of the level. These formulas lose their meaning if the channel is unstable (washed out or covered).

Precipitates deposited on the surface are known to run off, dissolve, and percolate. The leaked water will sooner or later either evaporate or join the drain, therefore, on average, over a long period of time, it can be considered that the precipitated water partly evaporates and partly drains. If the runoff coefficient is 30%, then this means that out of the total amount of precipitation, 30% is glass, and the remaining 70% has evaporated.

The value of the runoff coefficient is determined by the general geographical situation - climate, relief, vegetation. So, for the rivers of northern Europe - the Neva, Northern Dvina, Pechora, etc. - the runoff coefficient is more than 60%, for the Don it is about 15%, for the Nile - about 4%, for the Amazon - about 30%. Huge evaporation in the Nile basin and weak in the north of Europe and gives such a sharp contrast. In different years, for the same river, the runoff coefficient varies depending on the amount of precipitation. In wet years, the runoff coefficient is greater, in dry years it is less.

In drainless areas, the runoff coefficient is zero.

Among the reasons that determine the runoff coefficient, the climate of the area must be put in the first place. Temperature influences the form of precipitation and the course of evaporation. High temperatures and low humidity reduce surface runoff and shut down shallow springs. During winter dormancy, the evaporation of vegetation stops, the frozen soil prevents the penetration of water into the depths. In areas with long cold winters, the snow that has fallen for the winter remains until spring. In the spring, the runoff coefficient is greatly increased by melt water.

The relief also affects the value of the runoff coefficient: a significant slope facilitates runoff even on permeable rocks. Mountain streams after rain carry an enormous amount of water, and in the absence of rain they almost dry up, not due to lack of precipitation, but due to the fact that their waters drain too quickly. Permeable rocks cause a more uniform runoff, impermeable rocks - the flow regime.

In mountainous areas, the forest has a beneficial effect on the regime of rivers, slowing down the flow of water and thereby protecting mountain slopes from erosion. In general, the forest has a regulating effect on river flow, reducing the size of the flood and maintaining moisture reserves by the beginning of summer. Swamps, contrary to popular belief, are unfavorable for feeding rivers. Peat, like a sponge, absorbs a lot of water in wet times, and evaporates a lot in hot weather. According to Oppokov's research, the drainage of swamps not only does not entail the shallowing of rivers, but contributes to their more proper nutrition.

In addition to the runoff coefficient, the runoff modulus is also used to characterize the runoff.

The runoff module is the amount of water, expressed in liters, flowing down on average in one second from 1 sq. km of basin area. Engineer Kocherin built a contour map of the runoff module for the European Union Territory. Knowing the average basin runoff modulus, one can calculate the annual runoff value by multiplying the runoff modulus by the number of seconds in a year and by the basin area. It is also clear that the runoff modulus is closely related to the amount of precipitation, evaporation, topography, vegetation, and surface character.

The slope of the river. The most characteristic feature of any river is that continuous movement of water from source to mouth, which is called flow. The reason for the flow is the inclination of the channel, along which, obeying the force of gravity, the water moves at a greater or lesser speed. As for the speed, it is directly dependent on the slope of the channel. The slope of the channel is determined by the ratio of the height difference of two points to the length of the section located between these points. So, for example, if from the source of the Volga to Kalinin 448 km, and the height difference between the source of the Volga and Kalin and nom is 74.6 m, then the average slope of the Volga in this section is 74.6 m, divided by 448 km, i.e. 0.00017. This means that for every kilometer of the length of the Volga in this section, the fall is 17 cm.

Longitudinal profile of the river. Let us plot along the horizontal line successively the length of the various sections of the river, and along the vertical lines, the heights of these sections. By connecting the ends of the verticals with a line, we get a drawing of the longitudinal profile of the river (Fig. 112). If you do not pay much attention to details, then the longitudinal profile of most rivers can be simplified as a falling, slightly concave curve, the slope of which progressively decreases from source to mouth.

The slope of the longitudinal profile of the river is not the same for different sections of the river. So, for example, for the upper section of the Volga, as we have already seen, it is 0.00017, for the section located between Gorky and the mouth of the Kama 0.00005, and for the section from Stalingrad to Astrakhan - 0.00002.

Approximately the same near the Dnieper, where in the upper section (from Smolensk to Orsha) the slope is 0.00011, and in the lower section (from Kakhovka to Kherson) 0.00001. In the section where the rapids are located (from Lotsmanskaya Kamenka to Nikopol), the average slope of the longitudinal profile of the river is 0.00042, i.e., almost four times greater than between Smolensk and Orsha.

The given examples show that the longitudinal profile of different rivers is far from the same. The latter is understandable: the longitudinal profile of the river reflects the relief, geological structure and many other geographical features of the area.

For example, consider the "steps" on the longitudinal profile of the river. Yenisei. Here we see sections of large slopes in the area of ​​​​the intersection of the Western Sayan, then the Eastern Sayan and, finally, at the northern tip of the Yenisei Ridge (Fig. 112). The stepped nature of the longitudinal profile of the river. The Yenisei indicates that uplifts in the areas of these mountains occurred (geologically) relatively recently, and the river has not yet had time to level the longitudinal curve of its channel. The same must be said about the Bureinsky mountains, cut through by the river. Cupid.

So far, we have been talking about the longitudinal profile of the entire river. But when studying rivers, it is sometimes necessary to determine the slope of the river in a given small area. This slope is determined directly by leveling.

Cross profile of the river. In the transverse profile of the river, we distinguish two parts: the transverse profile of the river valley and the transverse profile of the river itself. We already have an idea of ​​the transverse profile of the river valley. It is obtained as a result of conventional surveying of the terrain. To get an idea about the profile of the river itself, or, more precisely, the river channel, it is necessary to make measurements of the depths of the river.

Measurements are made either manually or mechanically. For measurements by hand, a basting or hand lot is used. The basting is a pole made of flexible and durable wood (spruce, ash, hazel) of round section with a diameter of 4-5 cm, length from 4 to 7 m.

The lower end of the basting is finished with iron (iron prevents splitting and helps with its weight). The basting is painted white and marked in tenths of a meter. Zero division corresponds to the lower end of the basting. With all the simplicity of the device, the basting gives accurate results.

Depth measurements are also made with a manual lot. With the flow of the river, the lot deviates from the vertical by a certain angle, which makes it necessary to make an appropriate correction.

Soundings on small rivers are usually made from bridges. On rivers reaching 200-300 m width, at a flow rate of not more than 1.5 m per second, measurements can be made from a boat along a cable stretched from one river bank to another. The rope must be taut. With a river width of more than 100 m it is necessary to anchor a boat in the middle of the river to support the cable.

On rivers with a width of more than 500 m, the sounding line is determined by the leading signs placed on both banks, and the sounding points are determined by goniometric instruments from the shore. The number of soundings along the alignment depends on the nature of the bottom. If the bottom topography changes rapidly, there should be more soundings; if the bottom is uniform, there should be fewer. It is clear that the more measurements, the more accurate the profile of the river.

To draw the profile of the river, a horizontal line is drawn, on which the measurement points are plotted according to the scale. A perpendicular line is drawn down from each estrus, on which the depths obtained from measurements are also plotted on a scale. By connecting the lower ends of the verticals, we get a profile. Due to the fact that the depth of the rivers is very small compared to the width, when drawing a profile, the vertical scale is taken larger than the horizontal one. Therefore, the profile is distorted (exaggerated), but more visual.

Given the profile of the river bed, we can calculate the free area (or area of ​​the water section) of the river (fm 2 ), the width of the river (B), the length of the wetted perimeter of the river ( Rm) , greatest depth (hmaxm ), average depth of the river ( h cpm) and the hydraulic radius of the river.

A living cross section of the river called the cross section of a river filled with water. The profile of the channel, obtained as a result of measurements, just gives an idea of ​​the living section of the river. The area of ​​the living section of the river is mostly calculated analytically (less often it is determined from the drawing using a planimeter). To calculate the open area ( Fm 2) take a drawing of the transverse profile of the river, on which the verticals divide the area of ​​\u200b\u200bthe living section into a series of trapezoids, and the coastal sections look like triangles. The area of ​​each individual figure is determined by formulas known to us from geometry, and then the sum of all these areas is taken.

The width of a river is simply determined by the length of the top horizontal line representing the surfaces of the river.

wetted perimeter - this is the length of the river bottom line on the profile from one edge of the river bank to another. It is calculated by adding the length of all segments of the bottom line in the drawing of the living section of the river.

Hydraulic radius is the quotient of the open area divided by the length of the wetted perimeter ( R= F/R m).

Average depth is the quotient of the area of ​​the living section

rivers to the width of the river ( h Wed = F/ Bm).

For lowland rivers, the hydraulic radius is usually very close to the average depth ( R≈ h cp).

Greatest depth restored according to measurements.

River level. The width and depth of the river, the open area and other quantities given by us can remain unchanged only if the level of the river remains unchanged. In fact, this never happens, because the level of the river changes all the time. From this it is quite clear that in the study of a river, the measurement of fluctuations in the level of the river is the most important task.

For the gauging station, an appropriate section of the river with a straight channel is selected, the cross section of which is not complicated by shoals or islands. The observation of fluctuations in the level of the river is usually carried out using footstock. Footstock is a pole or rail, divided into meters and centimeters, installed near the shore. The lowest horizon of the river in a given place is taken as the zero of the footstock (if possible). The zero chosen once remains constant for all subsequent observations. The zero of the footstock is bound permanently rapper .

Level fluctuations are usually observed twice a day (at 8 and 20 hours). At some posts self-recording limnigraphs are installed, which give a continuous record in the form of a curve.

Based on the data obtained from observations of the footstock, a graph of fluctuations in levels is drawn for one or another period: for a season, for a year, for a number of years.

The speed of the rivers. We have already said that the speed of the river flow is directly dependent on the slope of the channel. However, this dependence is not as simple as it might seem at first glance.

Anyone who is even a little familiar with the river knows that the speed of the current near the banks is much less than in the middle. This is especially well known to boaters. Whenever the boatman has to go up the river, he keeps to the bank; when he needs to go down quickly, he keeps to the middle of the river.

More accurate observations made in rivers and artificial streams (having a regular trough-shaped channel) showed that the layer of water immediately adjacent to the channel, as a result of friction against the bottom and channel walls, moves at the lowest speed. The next layer already has a high speed, because it is not in contact with the channel (which is motionless), but with the slowly moving first layer. The third layer has an even higher speed, and so on. Finally, the highest speed is found in the part of the stream furthest from the bottom and walls of the channel. If we take the cross section of the flow and connect places with the same flow velocity with lines (isotachs), then we will get a diagram that clearly depicts the location of layers of different speeds (Fig. 113). This peculiar layered movement of the flow, in which the speed consistently increases from the bottom and walls of the channel to the middle part, is called laminar. Typical features of laminar motion can be briefly characterized as follows:

1) the speed of all particles of the flow has one constant direction;

2) the velocity near the wall (near the bottom) is always equal to zero, and with distance from the walls it gradually increases towards the middle of the flow.

However, we must say that in rivers where the shape, direction and character of the channel are very different from the regular trough-shaped channel of an artificial flow, regular laminar movement is almost never observed. Already with only one bend in the channel, as a result of the action of centrifugal forces, the entire system of layers abruptly moves towards the concave bank, which in turn causes a number of other

movements. In the presence of protrusions at the bottom and along the edges of the channel, eddy movements, countercurrents, and other very strong deviations arise, which further complicate the picture. Particularly strong changes in the movement of water occur in shallow places in the river, where the current breaks into fan-shaped jets.

In addition to the shape and direction of the channel, an increase in the speed of the current has a great influence. Laminar motion even in artificial flows (with the right channel) changes dramatically with increasing flow velocity. In fast-moving flows, longitudinal helical jets appear, accompanied by small vortex movements and a kind of pulsation. All this greatly complicates the nature of the movement. Thus, in rivers, instead of laminar movement, a more complex movement is most often observed, called turbulent. (We will dwell on the nature of turbulent motions later when considering the conditions for the formation of the flow channel.)

From all that has been said, it is clear that the study of the velocity of a river is a complex matter. Therefore, instead of theoretical calculations, one more often has to resort to direct measurements.

Measurement of flow velocity. The simplest and most accessible way to measure the flow velocity is to measure using floats. By observing (with a clock) the time it takes for the float to pass two points located along the river at a certain distance from each other, we can always calculate the desired speed. This speed is usually expressed in meters per second.

The method indicated by us makes it possible to determine the speed of only the uppermost layer of water. To determine the speed of deeper layers of water, two bottles are used (Fig. 114). In this case, the top bottle gives the average speed between both bottles. Knowing the average speed of the water flow on the surface (the first method), we can easily calculate the speed at the desired depth. If a V 1 there will be speed on the surface, V 2 - average speed, a V is the desired speed, then V 2 =( V 1 + V)/2 , whence the desired speed v = 2 v 2 - v 1 .

Incomparably more accurate results are obtained when measuring with a special device called turntables. There are many types of turntables, but the principle of their device is the same and is as follows. A horizontal axis with a bladed propeller at the end is movably fixed in a frame with a steering pen at the rear end (Fig. 115). The device, lowered into the water, obeying the rudder, rises just against the current,

and the bladed propeller begins to rotate along with the horizontal axis. The axis has an endless screw that can be connected to the counter. Looking at the clock, the observer turns on the counter, which begins to count the number of revolutions. After a certain period of time, the counter turns off, and the observer determines the flow rate by the number of revolutions.

In addition to these methods, measurement is also used with special bathometers, dynamometers, and, finally, chemical methods known to us from the study of the groundwater flow rate. An example of a bathometer is Prof. V. G. Glushkova, which is a rubber balloon, the opening of which is facing the flow. The amount of water that manages to get into the balloon per unit of time makes it possible to determine the flow rate. Dynamometers determine the force of pressure. The force of pressure allows you to calculate the speed.

When it is required to obtain a detailed idea of ​​the distribution of velocities in the cross section (living section) of the river, proceed as follows:

1. A transverse profile of the river is drawn, and for convenience, the vertical scale is taken 10 times larger than the horizontal one.

2. Vertical lines are drawn at the points where current velocities were measured at different depths.

3. On each vertical, the corresponding depth is marked on the scale and the corresponding speed is indicated.

By connecting points with equal velocities, we obtain a system of curves (isotochs), which gives a visual representation of the distribution of velocities in a given living section of the river.

Average speed. For many hydrological calculations, it is necessary to have data on the average flow rate of water in the living section of the river. But determining the average water velocity is a rather difficult task.

We have already said that the movement of water in a stream is not only complex, but also uneven in time (pulsation). However, based on a series of observations, we always have the opportunity to calculate the average flow velocity for any point in the river's flow area. Having the value of the average speed at the point, we can depict the distribution of speeds along the vertical we have taken on the graph. To do this, the depth of each point is plotted vertically (from top to bottom), and the flow velocity horizontally (from left to right). We do the same with other points of the vertical we have taken. By connecting the ends of the horizontal lines (depicting the velocities), we get a drawing that gives a clear idea of ​​the velocities of the currents at various depths of the vertical we have taken. This drawing is called the speed chart or speed hodograph.

According to numerous observations, it turned out that in order to obtain a complete picture of the distribution of flow velocities along the vertical, it is sufficient to determine the velocities at the following five points: 1) on the surface, 2) by 0.2h, 3) by 0.6h, 4) by 0.8hand 5) at the bottom, counting h - vertical depth from the surface to the bottom.

The hodograph of velocities gives a clear idea of ​​the change in velocities from the surface to the bottom of the stream on a given vertical. The lowest velocity at the bottom of the stream is mainly due to friction. The greater the roughness of the bottom, the sharper the decrease in current velocities. In winter, when the surface of the river is covered with ice, friction also occurs on the surface of the ice, which also affects the speed of the current.

The velocity hodograph allows us to calculate the average velocity of the river along a given vertical.

The average flow velocity along the vertical flow section is easiest to determine by the formula:

where ώ is the area of ​​the velocity hodograph, and H is the height of this area. In other words, to determine the average flow velocity along the vertical flow cross section, the area of ​​the velocity hodograph must be divided by its height.

The area of ​​the velocity hodograph is determined either using a planimeter or analytically (i.e., breaking it into simple figures - triangles and trapezoids).

The average flow rate is determined in various ways. The easiest way is to multiply the maximum speed (Vmax) on the roughness coefficient (P). The roughness coefficient for mountain rivers can be approximately considered 0.55, for rivers with a channel lined with gravel, 0.65, for rivers with an uneven sandy or clay bed, 0.85.

To accurately determine the average flow velocity of the living section of the flow, various formulas are used. The most common is the Chezy formula.

where v - average flow velocity, R - hydraulic radius, J- surface flow slope and With- speed factor. But here the determination of the velocity coefficient presents significant difficulties.

The velocity coefficient is determined by various empirical formulas (i.e., obtained from the study and analysis of a large number of observations). The simplest formula is:

where P- roughness coefficient, a R - already familiar to us hydraulic radius.

Consumption. The amount of water in m, flowing through a given living section of the river per second is called river flow(for this item). Theoretically consumption (a) easy to calculate: it is equal to the area of ​​​​the living section of the river ( F), multiplied by the average flow velocity ( v), i.e. a= fv. So, for example, if the area of ​​the living section of the river is 150 m 2, and speed 3 m/s, then consumption will be 450 m 3 per second. When calculating the flow rate, a cubic meter is taken per unit of water, and a second is taken per unit of time.

We have already said that it is not difficult to theoretically calculate the flow of a river for one or another point. To carry out this task in practice is much more difficult. Let us dwell on the simplest theoretical and practical methods most often used in the study of rivers.

There are many different ways to determine the flow of water in rivers. But all of them can be divided into four groups: volumetric method, mixing method, hydraulic and hydrometric.

Volumetric method successfully used to determine the flow of the smallest rivers (springs and streams) with a flow rate of 5 to 10 liters (0,005- 0,01 m 3) per second. Its essence lies in the fact that the stream is dammed and the water goes down the gutter. A bucket or tank is placed under the gutter (depending on the size of the stream). The volume of the vessel must be accurately measured. The filling time of the vessel is measured in seconds. The quotient of dividing the volume of the vessel (in meters) by the time it takes to fill the vessel (in seconds) as. times and gives the desired value. The volumetric method gives the most accurate results.

Mixing method is based on the fact that at a certain point in the river a solution of some kind of salt or paint is admitted into the stream. Determining the content of salt or paint in another lower flow point, the water flow is calculated (the simplest formula

where q - consumption of brine, k 1 - concentration of salt solution at release, to 2 is the concentration of the salt solution in the downstream point). This method is one of the best for stormy mountain rivers.

hydraulic method It is based on the use of various kinds of hydraulic formulas when water flows through both natural channels and artificial weirs.

We give the simplest example of the spillway method. A dam is being built, the top of which has a thin wall (made of wood, concrete). A weir in the form of a rectangle is cut in the wall, with precisely defined dimensions of the base. Water overflows through the weir, and the flow rate is calculated by the formula

(t - weir coefficient, b - weir threshold width, H- pressure over the edge of the spillway, g -acceleration of gravity), With the help of a spillway, it is possible to measure flow rates from 0.0005 to 10 m 3 / sec. It is especially widely used in hydraulic laboratories.

Hydrometric method is based on the measurement of the open area and the flow velocity. It is the most common. The calculation is carried out according to the formula, as we have already said.

Stock. The amount of water flowing through a given living section of the river per second, we call the flow. The amount of water flowing through a given living section of the river over a longer period is called drain. The amount of runoff can be calculated for a day, a month, a season, a year, and even a number of years. Most often, the flow is calculated for the seasons, because seasonal changes for most rivers are especially strong and characteristic. Of great importance in geography are the values ​​of annual flows and, in particular, the value of the average annual flow (flow calculated from long-term data). The average annual flow makes it possible to calculate the average flow of the river. If the discharge is expressed in cubic meters per second, then the annual flow (to avoid very large numbers) is expressed in cubic kilometers.

Having information about the flow, we can also obtain data on the flow for one or another period of time (by multiplying the flow rate by the number of seconds of the taken time period). The runoff value in this case is expressed volumetrically. The flow of large rivers is usually expressed in cubic kilometers.

So, for example, the average annual flow of the Volga is 270 km 3, Dnipro 52 km 3, Obi 400 km 3, Yenisei 548 km 3, Amazons 3787 km, 3 etc.

When characterizing rivers, the ratio of the magnitude of the runoff to the amount of precipitation falling on the area of ​​the basin of the river we have taken is very important. The amount of precipitation, as we know, is expressed by the thickness of the water layer in millimeters. Therefore, to compare the runoff with the amount of precipitation, it is necessary to express the runoff also by the thickness of the water layer in millimeters. To do this, the amount of runoff for a given period, expressed in volumetric measures, is distributed in a uniform layer over the entire area of ​​the river basin lying above the observation point. This value, called the height of the drain (A), is calculated by the formula:

BUT is the height of the drain, expressed in millimeters, Q - expense, T- period of time, 10 3 is used to convert meters to millimeters and 10 6 to convert square kilometers to square meters.

The ratio of the amount of runoff to the amount of precipitation is called runoff coefficient. If the runoff coefficient is denoted by the letter a, and the amount of precipitation, expressed in millimeters, - h, then

The runoff coefficient, like any ratio, is an abstract quantity. It can be expressed as a percentage. So, for example, for r. Neva A=374 mm, h= 532 mm; hence, a= 0.7, or 70%. In this case, the runoff coefficient p. Neva allows us to say that out of the total amount of precipitation falling in the basin of the river. Neva, 70% flows into the sea, and 30% evaporates. We observe a completely different picture on the river. Nile. Here A=35 mm, h =826 mm; hence a=4%. This means that 96% of all precipitation in the Nile basin evaporates and only 4% reaches the sea. Already from the examples given, it is clear what a huge value the runoff coefficient has for geographers.

Let us give as an example the average value of precipitation and runoff for some rivers of the European part of the USSR.

In the examples we have given, the amount of precipitation, runoff values, and, consequently, runoff coefficients are calculated as annual averages based on long-term data. It goes without saying that the runoff coefficients can be derived for any period of time: day, month, season, etc.

In some cases, the flow is expressed as the number of liters per second per 1 km 2 pool area. This flow rate is called drain module.

The value of the average long-term runoff can be put on the map with the help of isolines. On such a map, the sink is expressed in units of the sink. It gives an idea that the average annual runoff in the flat parts of the territory of our Union has a zonal character, with the magnitude of the runoff decreasing towards the north. From such a map one can see how great the relief is for the runoff.

River nutrition. There are three main types of river feeding: surface water feeding, groundwater feeding and mixed feeding.

Surface water supply can be divided into rain, snow and glacial. Rain feeding is characteristic of the rivers of tropical regions, most of the monsoon regions, as well as many areas of Western Europe, which have a mild climate. Snow nutrition is typical for countries where a lot of snow accumulates during the cold period. This includes most of the rivers of the territory of the USSR. In spring, they are characterized by powerful floods. It is especially necessary to single out the snows of the high mountainous countries, which give the greatest amount of water in late spring and in summer. This food, which is called mountain-snow food, is close to glacial food. Glaciers, like mountain snows, provide water mainly in the summer.

Groundwater is fed in two ways. The first way is the feeding of rivers by deeper aquifers that go out (or, as they say, wedged out) into the riverbed. This is a fairly sustainable food for all seasons. The second way is the supply of groundwater to alluvial strata directly connected with the river. During periods of high standing water, the alluvium is saturated with water, and after the decline of the waters, it slowly returns its reserves to the river. This diet is less sustainable.

Rivers that receive their nourishment from either surface water or groundwater alone are rare. Rivers with mixed feeding are much more common. In some periods of the year (spring, summer, early autumn), surface waters are predominant for them, in other periods (in winter or during periods of drought) groundwater nutrition becomes the only one.

We can also mention rivers fed by condensation waters, which can be both surface and underground. Such rivers are more common in mountainous regions, where accumulations of boulders and stones on the peaks and slopes condense moisture in noticeable quantities. These waters can influence the increase in runoff.

Feeding conditions of rivers at different times of the year. Pain in the winterMost of our rivers are fed exclusively by groundwater. This feeding is fairly uniform, so the winter runoff for most of our rivers can be characterized as the most uniform, decreasing very slightly from the beginning of winter to spring.

In spring, the nature of the runoff and, in general, the entire regime of rivers changes dramatically. Precipitation accumulated during the winter in the form of snow quickly melts, and large amounts of melt water merge into rivers. As a result, a spring flood is obtained, which, depending on the geographical conditions of the river basin, lasts for a more or less long time. We will talk about the nature of spring floods a little later. In this case, we note only one fact: in spring, a huge amount of spring melted snow water is added to the ground supply, which increases the runoff many times over. So, for example, for the Kama, the average flow in spring exceeds the winter flow by 12 and even 15 times, for the Oka by 15-20 times; the flow of the Dnieper near Dnepropetrovsk in the spring in some years exceeds the winter flow by 50 times, in small rivers the difference is even more significant.

In summer, rivers (in our latitudes) are fed, on the one hand, by groundwater, and on the other, by direct runoff of rainwater. According to the observations of acad. Oppokova in the basin of the upper Dnieper, this direct runoff of rainwater during the summer months reaches 10%. In mountainous regions, where runoff conditions are more favorable, this percentage increases significantly. But it reaches a particularly large value in those areas that are characterized by a wide distribution of permafrost. Here, after each rain, the level of the rivers rises rapidly.

In autumn, as temperatures decrease, evaporation and transpiration gradually decrease, and surface runoff (rainwater runoff) increases. As a result, in autumn, the runoff, generally speaking, increases until the moment when liquid precipitation (rain) is replaced by solid precipitation (snow). Thus, in autumn, like

we have soil plus rain nutrition, and the rain gradually decreases and stops altogether by the beginning of winter.

Such is the course of feeding of ordinary rivers in our latitudes. In high-mountainous countries, melt waters of mountain snows and glaciers are added in summer.

In the desert and dry steppe regions, the melt waters of mountain snows and ice play a dominant role (Amu-Darya, Syr-Darya, etc.).

fluctuations in water levels in rivers. We have just talked about the feeding conditions of rivers at different times of the year, and in connection with this we noted how the flow changes at different times of the year. These changes are most clearly shown by the curve of fluctuations in water levels in rivers. Here we have three charts. The first graph gives an idea of ​​fluctuations in the level of rivers in the forest zone of the European part of the USSR (Fig. 116). On the first graph (Volga River) is characteristic

fast and high rise with a duration of about 1/2 month.

Now pay attention to the second graph (Fig. 117), which is typical for the rivers of the taiga zone of Eastern Siberia. There is a sharp rise in the spring and a series of rises in the summer due to rains and the presence of permafrost, which increases the speed of the runoff. The presence of the same permafrost, which reduces winter ground feeding, leads to a particularly low water level in winter.

The third graph (Fig. 118) shows the fluctuation curve of river levels in the taiga zone of the Far East. Here, due to permafrost, the same very low level during the cold period and continuous sharp fluctuations in the level during warm periods. They are caused in spring and early summer by snowmelt and later by rain. The presence of mountains and permafrost accelerates runoff, which has a particularly sharp effect on level fluctuations.

The nature of fluctuations in the levels of the same river in different years is not the same. Here we have a graph of fluctuations in the levels of p. Kamas for different years (Fig. 119). As you can see, the river in different years has a very different pattern of fluctuations. True, the years of the most sharp deviations from the norm are selected here. But here we have the second graph of fluctuations in the levels of p. Volga (Fig. 116). Here, all fluctuations are of the same type, but the range of fluctuations and the duration of the spill are very different.

In conclusion, it must be said that the study of fluctuations in river levels, in addition to scientific significance, is also of great practical importance. Demolished bridges, destroyed dams and coastal structures, flooded, and sometimes completely destroyed and washed away villages have long made people pay attention to these phenomena and study them. It is no wonder that observations of fluctuations in river levels have been carried out since ancient times (Egypt, Mesopotamia, India, China, etc.). River navigation, road construction, and especially railways, required more accurate observations.

Observation of fluctuations in the levels of rivers in Russia began, apparently, a very long time ago. In chronicles, starting with XV in., we often meet indications of the height of the floods of the river. Moscow and Oka. Observations on fluctuations in the level of the Moskva River were already made daily. At first XIX in. daily observations were already carried out at all major piers of all navigable rivers. From year to year, the number of hydrometric stations has been continuously increasing. In pre-revolutionary times, we had more than a thousand water-measuring posts in Russia. But these stations reached a special development in Soviet times, which is easy to see from the table below.

Spring flood. During the period of spring snowmelt, the water level in the rivers rises sharply, and the water, usually overflowing the channel, overflows the banks and often floods the floodplain. This phenomenon, characteristic of most of our rivers, is called spring flood.

The time of the onset of the flood depends on the climatic conditions of the area, and the duration of the flood period, in addition, on the size of the basin, some parts of which may be under different climatic conditions. So, for example, for r. Dnieper (according to observations near Kyiv), the duration of the flood is from 2.5 to 3 months, while for the tributaries of the Dnieper - the Sula and Psyol - the duration of the flood is only about 1.5-2 months.

The height of the spring flood depends on many factors, but the most important of them are: 1) the amount of snow in the river basin at the beginning of the thaw and 2) the intensity of the spring thaw.

The degree of water saturation of the soil in the river basin, permafrost or thawed soil, spring precipitation, etc., is also of some importance.

Most large rivers of the European part of the USSR are characterized by a spring rise in water up to 4 m. However, in different years, the height of the spring flood is subject to very strong fluctuations. So, for example, for the Volga near the city of Gorky, water rises reach 10-12 m, near Ulyanovsk up to 14 m; for r. Dnieper for 86 years of observations (from 1845 to 1931) from 2.1 m up to 6-7 and even 8.53 m(1931).

The highest rises in water lead to floods, which cause great damage to the population. An example is the flood in Moscow in 1908, when a significant part of the city and the track of the Moscow-Kursk railway were under water for tens of kilometers. A number of Volga cities (Rybinsk, Yaroslavl, Astrakhan, etc.) experienced a very strong flood as a result of an unusually high rise in the water of the river. Volga in the spring of 1926

On large Siberian rivers, due to traffic jams, the rise of water reaches 15-20 meters or more. So, on the river Yenisei under 16 m, and on the river Lene (at Bulun) up to 24 m.

Floods. In addition to periodically recurring spring floods, there are also sudden rises in water, caused either by heavy rains, or by any other reasons. These sudden rises of water in the rivers, in contrast to the periodically repeated spring floods, are called floods. Floods, unlike floods, can occur at any time of the year. In the conditions of flat areas, where the slope of the rivers is very low, these floods can cause sharp increases in level 1, mainly in small rivers. In mountainous conditions, floods also occur on larger rivers. Particularly strong floods are observed in our Far East, where, in addition to mountainous conditions, we have sudden prolonged showers, giving more than 100 mm precipitation. Here, summer floods often take on the character of strong, sometimes destructive floods.

It is known that the height of floods and the nature of the runoff in general are greatly influenced by forests. They primarily provide slow snowmelt, which lengthens the duration of the flood and reduces the height of the flood. In addition, the forest floor (fallen leaves, needles, mosses, etc.) retains moisture from evaporation. As a result, the coefficient of surface runoff in the forest is three to four times less than in arable land. Hence, the height of the flood decreases to 50%.

In order to reduce floods and generally regulate the runoff, in our USSR the government has paid special attention to the preservation of forests in the areas where rivers feed. Resolution (dated 2/VII1936) provides for the conservation of forests on both banks of the rivers. At the same time, in the upper reaches of the rivers, forest strips of 25 km width, and in the lower reaches 6 km.

Possibilities for further fight against spills and development of measures to regulate surface runoff in our country are, one might say, unlimited. The creation of forest shelterbelts and reservoirs regulates runoff over vast areas. The creation of a huge network of canals and colossal reservoirs subordinates the flow to the will and the greatest benefit of the man of socialist society to an even greater extent.

Low water. During the period when the river lives almost exclusively due to the supply of groundwater in the absence of rainwater supply, the river level is at its lowest. This period of the lowest water level in the river is called low water. The beginning of the low water is considered the end of the recession of the spring flood, and the end of the low water is the beginning of the autumn rise in the level. This means that the low water period or low water period for most of our rivers corresponds to the summer period.

Freezing rivers. The rivers of cold and temperate countries are covered with ice during the cold season. The freezing of rivers usually begins near the banks, where the current is weakest. In the future, crystals and ice needles appear on the surface of the water, which, gathering in large quantities, form the so-called "lard". As the water cools further, ice floes appear in the river, the number of which gradually increases. Sometimes continuous autumn ice drift lasts for several days, and in calm frosty weather the river "gets up" quite quickly, especially at bends where a large number of ice floes accumulate. After the river is covered with ice, it switches to groundwater, and the water level often drops, and the ice on the river sags.

The ice, by growing from below, gradually thickens. The thickness of the ice cover, depending on the climate conditions, can be very different: from a few centimeters to 0.5-1 m, and in some cases (in Siberia) up to 1.5- 2 m From the melting and freezing of the fallen snow, the ice can thicken from above.

The outlets of a large number of sources that bring warmer water, in some cases lead to the formation of a "polynya", that is, an ice-free area.

The process of river freezing begins with the cooling of the upper layer of water and the formation of thin films of ice, known as fat. As a result of the turbulent nature of the flow, water is mixed, which leads to cooling of the entire mass of water. At the same time, the water temperature can be slightly below 0° (on the Neva river up to -0°.04, on the Yenisei river -0°.1): Supercooled water creates favorable conditions for the formation of ice crystals, resulting in the so-called deep ice. Deep ice formed at the bottom is called bottom ice. Deep ice in suspension is called sludge. The sludge can be in suspension, as well as float to the surface.

Bottom ice, gradually growing, breaks away from the bottom and, due to its lower density, floats to the surface. At the same time, the bottom ice, breaking away from the bottom, captures with it part of the soil (sand, pebbles and even stones). Bottom ice that floats to the surface is also called sludge.

The latent heat of ice formation is quickly consumed, and the water of the river remains supercooled all the time, until the formation of an ice cover. But as soon as the ice cover is formed, the loss of heat to the air largely stops and the water is no longer supercooled. It is clear that the formation of ice crystals (and, consequently, deep ice) stops.

With a significant current velocity, the formation of an ice cover is greatly slowed down, which in turn leads to the formation of deep ice in huge quantities. As an example, r. Angara. Here is the sludge. and. bottom ice, clogging the channel, form congestion. The blockage of the channel leads to a high rise in the water level. After the formation of the ice cover, the process of formation of deep ice is sharply reduced, and the level of the river decreases rapidly.

The formation of the ice cover starts from the shores. Here, at a lower current speed, ice is more likely to form (protect). But this ice is often carried away by the current and, together with the mass of sludge, causes the so-called autumn ice drift. Autumn ice drift is sometimes accompanied by congestion, i.e., the formation of ice dams. Blockages (as well as blockages) can cause significant rises in water. Traffic jams usually occur in narrowed sections of the river, on sharp turns, on riffles, as well as near artificial structures.

On large rivers flowing to the north (Ob, Yenisei, Lena), the lower reaches of the rivers freeze earlier, which contributes to the formation of especially powerful jams. The rising water level in some cases can create conditions for the occurrence of reverse currents in the lower parts of the tributaries.

From the moment of formation of the ice cover, the river enters a period of freeze-up. From this point on, ice slowly builds up from below. The thickness of the ice cover, in addition to temperature, is greatly influenced by snow cover, which protects the surface of the river from cooling. On average, the ice thickness on the territory of the USSR reaches:

polynyas. It is not uncommon for some sections of the river not to freeze in winter. These areas are called polynyas. The reasons for their formation are different. Most often they are observed in areas of fast flow, at the place where a large number of springs come out, at the place where factory waters drain, etc. In some cases, similar areas are also observed when a river leaves a deep lake. So, for example, r. Angara at the exit from the lake. Baikal does not freeze for 15 kilometers, and in some years even for 30 kilometers (the Angara “sucks in” the warmer water of Baikal, which cools down to the freezing point after a while).

River opening. Under the influence of spring sunlight, the snow on the ice begins to melt, as a result of which lenticular accumulations of water form on the surface of the ice. The streams of water flowing down from the shores intensify the melting of ice, especially near the shores, which leads to the formation of rims.

Usually, before opening, there is ice movement. In this case, the ice then starts to move, then stops. The moment of movement is the most dangerous for structures (dams, dams, bridge abutments). Therefore, near the structures, the ice breaks off in advance. The beginning rise of the waters breaks the ice, which ultimately leads to an ice drift.

The spring ice drift is usually much stronger than the autumn one, which is due to a much larger amount of water and ice. Ice jams in spring are also greater than in autumn. They reach especially large sizes on the northern rivers, where the opening of the rivers begins from above. The ice brought by the river lingers in the lower areas where the ice is still strong. As a result, powerful ice dams are formed, which in 2-3 hours raise the water level several meters. The subsequent break of the dam causes very severe destruction. Let's take an example. The Ob River breaks up near Barnaul at the end of April, and near Salekhard at the beginning of June. The thickness of the ice near Barnaul is about 70 cm, and in the lower reaches of the Ob about 150 cm. Therefore, the phenomenon of congestion is quite common here. With the formation of congestion (or, as they call it, “jammings”), the water level rises by 4-5 in 1 hour. m and just as quickly decreases after the breakthrough of ice dams. Grandiose flows of water and ice can destroy forests over large areas, destroy banks, lay new channels. Congestion can easily destroy even the strongest structures. Therefore, when planning structures, it is necessary to take into account the location of structures, especially since congestion usually occurs in the same areas. To protect structures or winter camps of the river fleet, the ice in these areas usually explodes.

The rise of water during traffic jams on the Ob reaches 8-10 m, and in the lower reaches of the river. Lena (near Bulun) - 20-24 m.

hydrological year. The flow and other characteristic features of the life of rivers, as we have already seen, are different at different times of the year. However, the seasons in the life of the river do not coincide with the usual calendar seasons. So, for example, the winter season for a river begins from the moment when the rain supply stops and the river passes to the winter ground supply. Within the territory of the USSR, this moment occurs in October in the northern regions, and in December in the southern regions. Thus, there is no one precisely established moment suitable for all the rivers of the USSR. The same must be said for the other seasons. It goes without saying that the beginning of the year in the life of the river, or, as they say, the beginning of the hydrological year, cannot coincide with the beginning of the calendar year (January 1). The beginning of the hydrological year is considered the moment when the river passes to exclusively ground feeding. For different places on the territory of even one of our states, the beginning of the hydrological year cannot be the same. For most of the rivers of the USSR, the beginning of the hydrological year falls on the period from 15/XIup to 15/XII.

Climatic classification of rivers. Already from what has been said about mode of rivers in different seasons, it is clear that climate has a huge impact on rivers. It is enough, for example, to compare the rivers of Eastern Europe with the rivers of Western and Southern Europe to notice the difference. Our rivers freeze for the winter, break up in the spring, and produce an exceptionally high rise in water during the spring flood. The rivers of Western Europe very rarely freeze and almost never spring floods. As for the rivers of Southern Europe, they do not freeze at all, and have the highest water level in winter. We find a still sharper difference between the rivers of other countries lying in other climatic regions. Suffice it to recall the rivers of the monsoonal regions of Asia, the rivers of northern, central and southern Africa, the rivers of South America, Australia, etc. All this taken together gave our climatologist Voeikov a basis for classifying rivers depending on the climatic conditions in which they are located. According to this classification (slightly modified later), all the rivers of the Earth are divided into three types: 1) rivers that are fed almost exclusively by melt water from snow and ice, 2) rivers that are fed only by rainwater, and 3) rivers that receive water in both ways indicated above .

The rivers of the first type are:

a) desert rivers bordered by high mountains with snowy peaks. Examples are: Syr-Darya, Amu-Darya, Tarim, etc.;

b) the rivers of the polar regions (northern Siberia and North America), located mainly on the islands.

The rivers of the second type are:

a) the rivers of Western Europe with more or less uniform rainfall: the Seine, the Main, the Moselle, and others;

b) the rivers of the Mediterranean countries with a winter flood: the rivers of Italy, Spain and others;

c) rivers of tropical countries and monsoon regions with summer floods: Ganges, Indus, Nile, Congo, etc.

The rivers of the third type, fed by both melt and rain water, include:

a) rivers of the East European, or Russian, plain, Western Siberia, North America and others with a spring flood;

b) rivers fed from high mountains, with a spring and summer flood.

There are other newer classifications. Among them is the classification M. I. Lvovich, who took the same Voeikov classification as a basis, but for the sake of clarification, took into account not only qualitative, but also quantitative indicators of river sources of nutrition and the seasonal distribution of runoff. So, for example, he takes the value of the annual runoff and determines what percentage of the runoff is due to this or that source of food. If the value of the runoff of any source is more than 80%, then this source is given exceptional importance; if the runoff is from 50 to 80%, then it is predominant; less than 50% - predominant. As a result, he gets 38 groups of river water regime, which are combined into 12 types. These types are:

1. Amazonian type - almost exclusively rain fed and the predominance of autumn runoff, that is, in those months that are considered autumn in the temperate zone (Amazon, Rio Negro, Blue Nile, Congo, etc.).

2. Nigerian type - predominantly rain fed with a predominance of autumn runoff (Niger, Lualaba, Nile, etc.).

3. Mekong type - almost exclusively rain fed with a predominance of summer runoff (Mekong, the upper reaches of Madeira, Maranyon, Paraguay, Parana, etc.).

4. Amursky - predominantly rain-fed with a predominance of summer runoff (Amur, Vitim, upper reaches of the Olekma, Yana, etc.).

5. Mediterranean - exclusively or predominantly rain-fed and the dominance of winter runoff (Mosel, Ruhr, Thames, Agri in Italy, Alma in the Crimea, etc.).

6. Oderian - the predominance of rain feeding and spring runoff (Po, Tisza, Oder, Morava, Ebro, Ohio, etc.).

7. Volzhsky - mainly snow-fed with a predominance of spring runoff (Volga; Mississippi, Moscow, Don, Ural, Tobol, Kama, etc.).

8. Yukon - the predominant snow supply and the dominance of summer runoff (Yukon, Kola, Athabasca, Colorado, Vilyui, Pyasina, etc.).

9. Nurinsky - the predominance of snow nutrition and almost exclusively spring runoff (Nura, Eruslan, Buzuluk, B. Uzen, Ingulets, etc.).

10. Greenland - exclusively glacial food and short-term runoff in summer.

11. Caucasian - predominant or predominantly glacial nutrition and dominance of summer runoff (Kuban, Terek, Rhone, Inn, Aare, etc.).

12. Loan - exclusive or predominant supply from groundwater and uniform distribution of runoff throughout the year (R. Loa in northern Chile).

Many rivers, especially those that are long and have a large feeding area, may be separate parts of themselves in different groups. For example, the Katun and Biya rivers (from the confluence of which the Ob is formed) are fed mainly by melt water from mountain snows and glaciers with a rise in water in summer. In the taiga zone, the tributaries of the Ob are fed by melted snow and rain waters with floods in spring. In the lower reaches of the Ob, tributaries belong to the rivers of the cold zone. The Irtysh River itself has a complex character. All this, of course, must be taken into account.

- Source-

Polovinkin, A.A. Fundamentals of general geography / A.A. Polovinkin.- M.: State Educational and Pedagogical Publishing House of the Ministry of Education of the RSFSR, 1958.- 482 p.

Post Views: 444

River flow velocities (or flow kinematics) are studied in detail in the hydraulics course. Here, we will pay attention only to those features of the flow kinematics that are necessary to know in order to understand the main sections of hydrology.

Water in rivers moves under the influence of gravity. The flow velocity depends on the ratio between the magnitude of the gravity component parallel to the line of the longitudinal slope of the flow and the resistance force arising in the flow as a result of the friction of the moving mass of water between the bottom and the shore. The magnitude of the longitudinal component of gravity depends on the slope of the channel, and the resistance force - on the degree of roughness of the channel. If the resistance is equal to the driving force, then the movement of water becomes uniform. If the driving force exceeds the resistance force, the movement acquires acceleration; when the ratio of these forces is reversed, the movement slows down. There are two categories of water movement - laminar and turbulent.

The laminar motion is a parallel jet motion. Laminar motion is distinguished by the following features: 1) All flow particles move in the same general direction without experiencing transverse deviations; 2) the water flow rate gradually increases from zero near the channel wall to a maximum on the free surface; 3) the flow velocity is directly proportional to the slope of the free surface and depends on the viscosity of the liquid.

Turbulent motion has the following features: 1) flow velocities pulsate, i.e., the direction and magnitude of the velocity at each point fluctuate all the time; 2) The flow velocity from zero on the wall increases rapidly within the thin bottom layer; further, towards the water surface, the speed increases slowly; 3) the speed of water flow does not depend or almost does not depend on the viscosity of the liquid and, in the absence of the influence of viscosity, is proportional to the square root of the slope .; 4) water particles move not only along the flow, but also vertically and transversely, i.e. the entire flowing mass of water is displaced.

Thus, in turbulent motion it has been established that in open flows the amplitude of pulsations increases from the surface to the bottom. In the cross section of the flow, the pulsation amplitude increases from the flow axis to the banks.

Due to the tortuosity and various forms of channels, the flow of water in rivers is almost never parallel to the banks, and the water flow is divided into separate so-called internal currents. These currents erode the channel, carry erosion products (sediments) and deposit them in the channel, resulting in spits, middle bars, rifts, passes and other underwater obstacles.

In the river flow, there are the following internal currents: 1) the current caused by the curvature of the channel; 2) the flow that occurs when the earth rotates around its axis; 3) rotational (vortex) movement of water, due to insufficient streamlining of channel forms.

Distinguish between instantaneous speed and local speed at a point in the flow. Instant speed (U) (see Fig. 1) is the speed at a given point in the flow at a given moment. In a rectangular coordinate system, the instantaneous velocity has a longitudinal component directed horizontally along the longitudinal axis of the flow and a vertical component directed along the vertical axis of the flow.

In practical calculations, as a rule, one has to deal with flow velocities averaged over time. The flow velocity at a point of flow, averaged over a sufficiently long period of time, is called the local velocity and is determined by the expression

(1)

where is the area of ​​the velocity pulsation graph within the time period T(Fig. 1).

Rice. 1. Graph of pulsations of the longitudinal component of the water flow velocity.

Velocity distribution in a river flow.

The distribution of water flow velocities in a river flow is varied and depends on the type of river (flat, mountainous, etc.), morphometric features, roughness of the channel, and the slope of the water surface. With all the diversity, there are some general patterns in the distribution of velocities in depth and width of the river.

Consider the distribution of longitudinal velocities at various vertical depths. If the values ​​of velocities are set aside from the direction of the vertical and their ends are connected by a smooth line, then this line will be a velocity profile. The figure bounded by the velocity profile, the direction of the vertical, the lines of the water surface and the bottom, is called the velocity diagram (Fig. 2). As can be seen from Figure 2, the highest speed (in an open stream) is usually observed on the surface (U sur). The speed at the bottom of the stream is called the bottom speed (U d).

If we measure the area of ​​the velocity diagram and divide it by the depth of the vertical, we get a value called average vertical speed and is expressed by the formula

(2)

The average velocity on the vertical of an open stream is located at a depth from the surface equal to approximately 0.6h.

The normal view of the velocity profile shown in Fig. 2, in the conditions of natural watercourses, it can be distorted by the influence of various factors: bottom irregularities, aquatic vegetation, wind, ice formations, etc.

With significant bottom roughness, the speed at the bottom can decrease sharply, approximately as shown in Fig. 3.

With downstream wind, surface velocities may increase, and the water level may decrease slightly; when the wind is upstream, the reverse picture is observed (Fig. 4).

Like velocity diagrams on the verticals, one can construct a velocity diagram along the width of the river (Fig. 5), for example, surface or average velocities on the verticals, the outlines of the plot usually follow the outlines of the bottom; the location of the greatest speed approximately coincides with the position of the greatest depth.

In the presence of an ice cover, the influence of the roughness of the lower surface of the ice causes a shift in the maximum velocity to a certain depth from the surface, usually by (0.3–0.4)h (Fig. 6a). If there is under-ice slush, then the downward shift of the maximum velocity can be even more significant, up to (0.6-0.7)h (Fig. 6b).

I must say right away that only general principles are written here. Everything is more complicated than that, fish stops change depending on the combination of changes in the water level and water temperature. However, for simplicity, it's better in order. And yet do not forget that everything must be considered as a whole.

Let's try to figure out what happens in the river when the water level changes. If you imagine theoretically a river with an absolutely flat bottom, like a gutter, then everything is simple. With a decrease in the volume of water, the flow gradually slows down. In practice, everything is more difficult.

All rivers have a rather complex relief. Deep pits and stretches are replaced by rapid rifts. The main channel of the river winds from one bank to another, forming clamps and catches. Large stones often stand in the channel, forming complex swirls of the water flow.

Therefore, a change in the water level in the river creates a variety of changes in the speed of the current in different parts of the river. Important: the higher the water level, the more uniform the flow. The lower the water level, the greater the difference in the speed of the current, depending on the topography of the river bed.

The speed of the current in a particular section of the river is different at different depths. For example, at the surface of the water, the current velocity will be maximum, and at the bottom, where even medium-sized stones create eddies of water, the current velocity will be relatively small.

Let's now try to look for fish stops at different water levels. Basic search rules:

1. Comfortable depth. The fish will stop where it feels safe. You know the saying - the fish is looking for where it is deeper, and the man - where is better? So she will look for places with depths of at least 1.5 m and deeper. Although in small rivers with a pebbly bottom and shallow depths in the channel, it can rise in shallower places, but in any case, it will be somewhat deeper there than nearby. The larger the fish, the more depth it will try to occupy in the river.
2. Flow speed. The fish will stop where the current is not very strong, it saves energy. On the other hand, the current must be sufficient to provide the fish with a good oxygen regime. This is where the problems begin. Such places are difficult to find in deep rivers with complex bottom topography. Even in the raging rapids there are rocky fissures where the fish can get up and feel great. From the shore, such places can be very difficult to detect. There are other difficulties associated with the difference in current speed at different depths. It is necessary to constantly study the relief of the bottom of the river - this is best done at low water levels. And you should never jump to conclusions. You are not a fish, but it still sees much better where to stand. We must constantly experiment - everything is far from what we see from the shore.
3. Reverse flow. Fish can often stand in places with a reverse current, i.e. head down in relation to the main course of the river. The difficulty is that such streams are not always visible from the shore. It’s just that there is a convenient and comfortable reverse trickle, so it stands there, and it doesn’t bother her at all. And you?
4. Large stones in the riverbed. Fish are magically attracted to large stones in the riverbed. They create strong eddies in the water. In front of such a stone, the current most often washes out a small hole, these are the favorite parking places for salmon. If there is no such hole in front of the stone or it is occupied, the fish can stand on the side of the stone. It rarely stands directly behind a stone - sand is washed there, which forms a mound. There most often can be extraneous fish - brown trout, grayling or salmon motley. In deep rivers with high water levels, such stones may not be visible - this is another reason to study the riverbed in low water.
5. Deep holds near the shore. The proximity of the shore does not scare the fish at all. She can stand in the clamp half a meter from the water's edge, if there is sufficient depth and flow speed. Therefore, it is worth approaching a point with a decent depth near the shore carefully and, God forbid, immediately climb waist-deep into the water and smack the fly with all your might into the middle of the river.

So let's go point by point. Imagine that the water level first falls from high to low levels, and then rises again.

1. Comfortable depth. Everything is pretty simple here. The water level has dropped and the depth has not become large enough - the fish leaves this place for deeper points. When the water rises, fish will appear here again.
2. Flow speed. Here everything is much more complicated. The change in the current velocity in one way or another depends on the diversity of the bottom topography. Consider three fundamentally different sections of the river:



Underground pit. Let's imagine a roll or a threshold that flows into a pit. At a high level, huge masses of water rush into the pit at high speed and create a long "tail" of the current in it, in the absence of it near the banks of the pit. The fish can stand a little to the side of such a tail and under the jet, but the distance from the entrance of the jet into the pit to the fish stop will vary depending on the water level. The lower the level - the smaller the masses of water enter the pit, the "tail" of the current in the pit becomes shorter, respectively, the fish stops will mix up [closer to the beginning of the pit - there is created a comfortable for the fish (current speed. When the water level rises, the current will intensify and | the fish will move away from the start of the hole.






A small rift in a deep stretch of the river. In big water, this place does not stand out at all. It's just that the river flows uniformly (at least its surface layers). Fishing here at a high water level is useless - the fish can stand anywhere. You can only shoot at some pebbles, although, again, you need to know them - at a high water level they are not visible. The uniformity of the flow at high water levels is caused by

I "strong backwater. With a decrease in the water level, everything becomes much more interesting - the difference in current speeds, depending on the bottom topography, increases. Various trickles begin to appear, the river current forms interesting potential parking lots for salmon. In deep places up and [downstream from the rift weakened, and the salmon will [look for places with a stronger current.






Plums in front of the threshold. Plums can be deep and shallow.

In deep sinks, the fish will always stand, moving a little closer or farther from it, depending on the comfortable speed of the current. Directly at the drain, you can most often meet medium-sized fish. Krupnyak will stand a little further from the drain, where the depth is greater.

IB small plums, the fish stops only at a very high water level, with a drop in the level, it leaves these places, with an increase, it returns.

3. Reverse flow. At high water levels, the river often forms reverse currents. It occurs at the confluence of the pit, in the clamps near the shore. With a decrease in the water level, the force of the reverse flow weakens. However, there are places where there is a reverse flow even at low water levels. Fish often stand on the return lines. But if the return line is too weak, the fish leaves it. Yes, and a fly in a very weak return line will have to be dragged with strips, i.e. pull the line slightly towards you for better fly performance.
4. Large stones in the riverbed. Fish stand near them at almost any water level, if the strength of the current and the depth of the river allow (we should not forget about the depth of comfort). At high water levels, not all of these stones are visible. You can't even see the breakers from them. Here you need to know the river. When the water level is low, most of these stones are already visible. At a certain level of water, a powerful noisy breaker forms over some stones. Semga doesn't like him. And how do you feel about the noisy renovation of the neighbors on the floor above? The fish will move away and find a new stop nearby. When conditions become more favorable, the place at the once noisy stone will again be occupied by fish.
5. Deep holds near the shore. With a high water level in the fast sections of the rivers, these are quite promising places. When the water level in the clamps drops too much, the current weakens too much and the fish have nothing to do there.

Well, I think some clarity is coming? However, everything written is complete nonsense, if you do not consider the topic in conjunction with the dynamics of changes in the temperature regime of water in the river. To do this, we read about

The Amazon is moving at a speed of 15 km/h

The Amazon River is considered the fastest river in the world, already having several titles of the “most-most”. Among them, such titles as the most full-flowing (7,180,000 km 2), the deepest (its depth in some places reaches 135 meters), the longest (7,100 km) and the widest (in some places the Amazon delta has a width of 200 km) . In the lower reaches of the Amazon, the average water flow is approximately 200-220 thousand cubic meters, which corresponds to a river flow speed of 4.5-5 m/s or 15 km/h! In the rainy season, this figure increases to 300 thousand m 3.

The course of each river consists of the upper, middle and lower reaches. At the same time, the upper course is characterized by large slopes, which contributes to its greater erosive activity. The lower course is distinguished by the largest water mass and lower speed.

How is the flow rate measured?

The units used to measure the speed of a river are meters per second. At the same time, one should not forget that the speed of the water flow is not the same in different parts of the river. It gradually increases, originating from the bottom and walls of the channel and gaining the greatest power in the middle part of the stream. The average flow velocity is calculated on the basis of measurements made in several sections of the channel. Moreover, at least five spot measurements are carried out on each section of the river.

To measure the speed of the water current, a special measuring device is used - a hydrometric turntable, which descends to a certain depth strictly perpendicular to the surface of the water and after twenty seconds you can take readings from the device. Given the mean velocity of the river and its approximate cross-sectional area, the water discharge of the river is calculated.

Reverse flow of the Amazon

In addition, the Amazon River is the owner of a reverse current that occurs during ocean tides. Water flows with great speed - 25 km / h or 7 m / s, are driven back to the mainland. Waves at the same time reach 4-5 meters in height. The farther a wave passes on land, the less its destructive effect becomes. The tides stop at a distance of up to 1,400 kilometers upstream of the Amazon. Such a natural phenomenon was called "pororoka" - thundering water.