The flow rate of water is the smallest where. Basics of hydrodynamics
The slope of the bed. Most characteristic sign every river is the continuous movement of water from the source to the mouth, which is called flow.The cause of the flow lies in the slope of the bed, which, obeying the power of gravity, the water moves with a greater or lesser speed. As for the speed, it is directly dependent on the slope of the bed. The bonding of the channel is determined by the ratio of the heights of two points to the length of the site located between these items. So, for example, if from the source of the Volga to Kalinina 448 km,and the height difference between the source of the Volga and Kalin and Mr. 74.6 m,the average bias of the Volga in this section is 74.6 m,divided by 448. km,i.e. 0.00017. This means that every kilometer of the length of the Volga on this site is drop - 17 cm.
Longitudinal profile of the river. We postpone along the horizontal line sequentially the length of different parts of the river, and along the vertical lines of the height of these areas. Connecting the ends of the vertical line, we get a drawing of the longitudinal profile of the river (Fig. 112). If you do not pay special attention to the details, then the longitudinal profile of most rivers can be simplified in the form of a drop-down, slightly concave curve, the slope of which is progressively decreased by the sources to the mouth.
The slope of the longitudinal profile of the river for various sections of the river of the neodynaks. For example, for the top section of the Volga, as we have already seen, it is equal to 0.00017, for the site located between the bitter and the mouth of the Kama 0.00005, and for the portion from Stalingrad to Astrakhan - 0.00002.
Approximately the same at the Dnipro, where in the upper section (from Smolensk to Orsha) is 0.00011, and in the lower portion (from Kakhovka to Kherson) 0.00001. In the area where the thresholds are located (from the pilots of the Lotsmannaya Kamenka to Nikopol), the average slope of the longitudinal profile of the river 0.00042, i.e., almost four times more than between Smolensk and Ors.
The examples showed that the longitudinal profile of various rivers is far from the same. The latter is understandable: the relief is reflected on the longitudinal profile of the river, geological structure And many other, geographical features of the area.
For example, consider the "steps" on the longitudinal profile of the r. Yenisei. Here, sections of large slopes we see in the area of \u200b\u200bintersection of Western Sayan, then East Sayan and, finally, at the northern tip of the Yenisei ridge (Fig. 112). Stage character of the longitudinal profile r. Yenisei suggests that raising in areas of these mountains occurred (geologically) relatively recently, and the river still did not have time to align the longitudinal curve. The same thing is to say about the Burein mountains cutting into the river. Amur.
Until now, we talked about the longitudinal profile of the whole river. But when studying rivers, it is sometimes necessary to determine the bonus of the river on a given small area. This slope is determined directly by levetling.
Transverse river profile. 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 \u200b\u200bthe transverse profile of the river valley. It turns out as a result of the usual shooting of the terrain. To obtain an idea of \u200b\u200bthe profile of the river itself or, more precisely, the river channel needs to produce the depths of the river.
Promes are produced or manually or mechanical. For measurements, the mark or manual lotter is used manually. The backbone of the flexible and durable tree (spruce, ash, nut) of the circular cross section with a diameter of 4-5 cm,4 to 7 m.
The lower end of the mark is cooled with iron (iron protects from splitting and helps its weight). The mark is painted white and placed on the tenths of the meter. The zero division corresponds to the lower end of the mark. With all the simplicity of the device, the mark gives accurate results.
Measuring depths are also made by manual lot. The flow of the lot is deviated from the vertical to some angle, which makes you make an appropriate amendment.
Simple rivers are usually produced from bridges. On rivers reaching 200-300 m.widths, at current speed not more than 1.5 m.in sec., Promers can be made from a boat on a cable stretched from one bank of the river to another. The cable should be tightly tightened. With the width of the river more than 100 m.it is necessary in the middle of the river to put a boat at anchor to maintain a cable.
On rivers whose width is more than 500 g, the line of the displacement is determined by the final the signs set on both shores and the points of the industrial are determined by the gear tools from the shore. The number of industrial displays depends on the nature of the bottom. If the relief of the bottom changes quickly, the forms should be greater, with the bottom of monotonia - less. It is clear that the more precruples, the more accurate the profile of the river.
To draw a river profile, a horizontal line is performed, on which the valves are postponed along the scale. From each flow down, a perpendicular line is carried out, on which the depth obtained from the precursors is also deposited along the scale. Connecting the lower ends of the verticals, we get a profile. Due to the depth of rivers compared to the width is very small, while drawing a profile, the vertical scale takes more horizontal. Therefore, the profile is distorted (exaggerated), but more visual.
Having a profile of the river bed, we can calculate the area of \u200b\u200bthe living cross section (or the area of \u200b\u200bthe water section) of the river (FM. 2 ), the width of the river (B), the length of the moistened perimeter of the river ( PM), The greatest depth (h Maxm. ), the middle depth of the river ( h CP. m) and hydraulic river radius.
Live cross section of the river they call the cross section of the river filled with water. The profile of the channel, obtained as a result of the industrial, is just gives an idea of \u200b\u200ba living cross section of the river. The area of \u200b\u200bthe living cross section of the river for the most part is calculated analytically (less often is determined by the drawing using a plan meter). To calculate the area of \u200b\u200bliving cross section ( F.m 2) take a drawing of the cross profile of the river, on which the verticals split the area of \u200b\u200bliving cross section into a number of trapezoids, and the coastal areas have the appearance of triangles. The area of \u200b\u200beach individual figure is determined by the formulas known to us from the geometry, and then the sum of all these areas is taken.
The width of the river is simply determined by the length of the upper horizontal line depicting the surface of the river.
Moistened perimeter - It is the length of the bottom line of the river on the profile from one bank of the river coast to another. It is calculated by adding the length of all the segments of the bottom line on the drawing of the living cross section of the river.
Hydraulic radius - It is a private from dividing the area of \u200b\u200bliving section for the length of the moistened perimeter ( R.= F./ R M).
Medium depth - This is a private from dividing the area of \u200b\u200bliving cross section
river river width ( h. cf. = F./ B.m).
For the plain rivers, the size of the hydraulic radius is usually very close to the magnitude of the middle depth ( R.≈ h CP.).
The greatest depth restores according to the Projects.
River level. The width and depth of the river, the area of \u200b\u200bthe living section and the other values \u200b\u200bgiven by us can remain unchanged only if the level of the river remains unchanged. In fact, this is never happening, because the river level changes all the time. From here it is clear that when studying the river, the measurement of the river level fluctuations is the most important task.
For a water supply, the corresponding area of \u200b\u200bthe river with a straight line is selected, the cross section of which is not complicated by grinders or islands. Observation of the river level fluctuations is usually conducted with footbath.Foots are a pole or rack, divided into meters and centimeters installed on the shore. For zero of the footbath (if possible), the lowest horizon of the river in this place is accepted. The chosen once zero remains constant for all subsequent observations. The footbath zero is constant reper .
Observation of level fluctuations is usually produced twice a day (at 8 and 20 hours). Some posts are installed authentic lymnigraphs that give a continuous recording in the form of a curve.
Based on the data obtained from the observations on the footbath, the graph of level fluctuations for one or another period is drawn: for the season, for a year, for a number of years.
The flow rate of rivers. We have already said that the flow rate of the river is directly dependent on the liner of the bed. However, this dependence is not so simple as it may seem at first glance.
Anyone who is at least a little familiar with the river knows that the flow rate off the coast is much less than in the middle. This is especially well known to boating. Whenever the boatman has to climb the river upwards, he keeps the shore; When he needs to quickly go down, he keeps the middle of the river.
More accurate observations produced in rivers and artificial flows (having the right trough-like bed) showed that the water layer directly adjacent to the channel, as a result of friction about the bottom and the wall of the channel moves at the lowest speed. The next layer is already greater than the speed, because it does not come into contact with the channel (which is still), but with slowly moving the first layer. The third layer has even more velocity, etc. Finally, the largest speed is found in the flow part, then the channel is all distinguished from the bottom and walls. If you take a cross-section of the flow and connect places at the same flow rate with lines (isothams), then we will have a scheme, a clearly depicting layout of the layers of different speeds (Fig. 113). This is a peculiar layered flow of flow, in which the speed consistently increases from the bottom and the walls of the bed to the middle part, called laminar.Typical laminar features can be briefly characterized as follows:
1) the speed of all flow particles has one constant direction;
2) The speed near the wall (at the bottom) is always zero, and with the removal from the walls smoothly increases to the middle of the stream.
However, we must say that in rivers, where the form, direction and nature of the channel differ greatly from the correct verge of artificial flow, the correct laminar movement is almost never observed. Already at only one bending of the bed, as a result of centrifugal forces, the entire system of layers is dramatically moved towards the concave shore, which in turn causes a number of others
movements. With the precompositions at the bottom and at the edges of the channel there are vortex movements, antiflays and others, very strong deviations, even more complicating the picture. Particularly strong changes in the water movement occur in small places of the river, where the flow is divided into jets located fan-forming.
In addition to the shape and direction of the bed, an increase in the flow rate has a great influence. Laminar movement Even in artificial streams (with the right channel) changes dramatically with an increase in the flow rate. In fast moving streams, longitudinal screw-like jets occur, accompanied by small vortex movements and a kind of ripple. All this largely complicates the nature of the movement. Thus, in rivers instead of a laminar movement, a more complex movement is most often observed, called turbulent. (More on the nature of turbulent movements, we will focus later when considering the conditions for the formation of the flow of flow.)
It is clear from all that is clear that the study of the flow rate of the river is a difficult thing. Therefore, instead of theoretical calculations here more often have to resort to direct dimensions.
Measurement of the flow rate. The simplest and most affordable way to measure the flow rate is the measurement with floats.Watching (with a clock) time passing the float past two points located along the river at a certain distance against each other, we can always calculate the desired speed. This speed is usually expressed by the number of meters per second.
The method we specified makes it possible to determine the speed of only the most upper layer of water. To determine the speed of deeper water layers, two bottles consume (Fig. 114). In this case, the upper bottle gives the average speed between both bottles. Knowing the average water flow rate on the surface (first method), we can easily calculate the speed in the desired depth. If a V. 1 there will be speed on the surface, V. 2 - average speed, but V. - desired speed, then V. 2 =( V. 1 + V.)/2 where the desired speed v. = 2 v. 2 - v. 1 .
Inconsistently more accurate results are obtained when measured by a special device wearing name turntables.There are many types of turntables, but the principle of their device is the same and lies in the following. The horizontal axis with a paddle screw at the end is movably reinforced in the frame having a steering pen at the rear end (Fig. 115). The device, lowered into the water, obeying the steering wheel, gets up just against the current,
and the blade screw begins to rotate along with the horizontal axis. On the axis there is an infinite screw that can be connected to the meter. Looking at the clock, the observer includes a counter that begins to count the number of revolutions. After a certain period of time, the counter turns off, and the observer by the number of revolutions determines the flow rate.
In addition to these methods, we use another measurement by special tractors, dynamometers and, finally, chemical methods, known to us to study the velocity of the flow of groundwater. An example of a betometer can serve as a producer of prof. V. Glushkov,presenting a rubber cylinder, the hole of which is drawn towards the flow. The amount of water that has time to get into a balloon per unit of time makes it possible to determine the flow rate. Dynamometers determine the pressure force. Pressure force allows you to calculate speed.
When it is required to obtain a detailed idea of \u200b\u200bthe distribution of velocities in cross section (living section) of the river, are applied as follows:
1. The transverse profile of the river is drawn, and for convenience, the vertical scale takes 10 times more horizontal.
2. Vertical lines are carried out on those items in which the flow rates were measured at different depths.
3. On each vertical, the corresponding depth of scale is noted and the corresponding speed is indicated.
Connecting points with the same speeds, we will receive a system of curves (hinds), which gives a visual idea of \u200b\u200bthe distribution of speeds in a given live cross section of the river.
Average speed. Many hydrological calculations need to have data on mid speed The flow of water of the living cross section of the river. But the determination of the average water velocity is a rather complicated task.
We have already told that the movement of water in the stream is not only complex, but also unevenness, in time (pulsation). However, based on a number of observations, we always have the opportunity to calculate the average flow rate for any point of the live cross section of the river. Having the size of the average speed at the point, we can portray the distribution of speeds on the vertical we take. To do this, the depth of each point is postponed vertically (from top to bottom), and the flow rate horizontally (from left to right). We are doing the same with other points with us vertical. By connecting the ends of horizontal lines (depicting speeds), we will get a drawing that gives a clear idea of \u200b\u200bthe speeds of currents at various depths of the vertical we take. This drawing is called the chart of speeds or humograph of speeds.
According to numerous observations, it has been revealed that in order to obtain a complete view of the distribution of vertical flow rates, it suffices to determine the speeds at the next five points: 1) on the surface, 2) by 0.2h., 3) 0.6h., 4) 0.8h. and 5) at the bottom, counting h. - The depth of the vertical from the surface to the bottom.
The humor of the speed gives a clear idea of \u200b\u200bchanging the speeds from the surface to the bottom of the flow on the taking vertical. The smallest speed at the bottom of the flow is mainly due to friction. The larger the bottom roughness, the sharpness of the flow rates decrease. In winter, when the surface of the river is covered with ice, friction occurs also about the surface of the ice, which is also reflected at the flow rate.
Homes of speed allows us to calculate the average river flow rate on this vertical.
The average vertical flow vertical flow rate is easiest to determine by the formula:
where ώ is the area of \u200b\u200bthe yoke of speeds, and H is the height of this area. In other words, to determine the average flow rate of the vertical of the living section of the flow, the area of \u200b\u200bthe yoke of the velocity is divided into its height.
The area of \u200b\u200bthe yield of speeds is determined or using a plan meter or analytically (that is, breaking on simple figures - triangles and trapezoids).
The average flow rate is determined in various ways. Most simple way is the multiplication of the maximum speed (V Max) on the coefficient of roughness (P). The coefficient of roughness for mountain rivers can approximately be 0.55, for rivers with a river lined with gravel, 0.65, for rivers with uneven sandy or clay lies 0.85.
For accurate definition The average flow rate of the live cross section of the flow is used by various fortmiths. The most common is the Formula of Szi.
where v. - average speed of living flow cross section, R. - hydraulic radius, J. - Surface Flow Safety and FROM- Speed \u200b\u200bcoefficient. But here significant difficulties represent the determination of the speed coefficient.
The rate coefficient is determined by various empirical formulas (i.e., obtained on the basis of studying and analyzing a large number of observations). The simplest is the formula:
where p- coefficient of roughness, a. R. - Already familiar with the hydraulic radius.
Consumption. Number of water B. m,flowing through this living cross section of the river per second, called river flow(for this item). Theoretically flow (but)calculate simply: it is equal to the area of \u200b\u200bthe living cross section of the river ( F.), multiplied by the average flow rate ( v.), t. E. but= FV. So, for example, if the area of \u200b\u200bthe living cross section of the river is equal to 150 m 2,and speed 3. m / s, thenconsumption will be equal to 450 m 3.per second. When calculating the consumption per unit of water, a cubic meter is taken, and per unit of time - second.
We have already talked about the theoretically the consumption of the river for one or another item to calculate it is not difficult. Perform this task almost more complex things. Let us dwell on the simplest theoretical and practical methods that are most often used in the study of rivers.
There are many different ways to determine water consumption in rivers. But all of them can be divided into four groups: a bulk method, a method of mixing, hydraulic and hydrometric.
Volumeful way it is successfully used to determine the consumption of the smallest river (keys 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 driving and the water descends on the groove. A bucket or tank is installed under the chute (depending on the value of the stream). The volume of the vessel must be accurately measured. The time of the vessel filling is measured in seconds. Private from dividing the volume of the vessel (in meters) at the time of the filling of the vessel (in seconds) as. Once and gives a desired value. The volume method gives the most accurate results.
Method of mixing it is based on the fact that in a certain paragraph of the river, a solution of any salt or paint is admired. Determining the salt content or paint in the other, below located, the flow rate, calculate the water consumption (the simplest formula
where q. - consumption of hydrogen mortar, K 1 -Concentration of salt solution when issuing, to 2.- Salt solution concentration in the underlying point). This method is one of the best for turbulent mountain rivers.
Hydraulic method it is based on the use of various types of hydraulic formulas when water flowing both through natural channels and artificial waterfronts.
Let us give the simplest example of the waterproof method. A dam is built, the top of which has a thin wall (from wood, concrete). The wall is cut through a rectangle, with precisely defined sizes. Water overflows through the catchment, and the flow rate is calculated by the formula
(T. - the coefficient of waterproof, b. - Width of the threshold of waterproof, H. -Naps over the rib of the waters g. - Sustainment of gravity), with the help of hydrogen, can accurately measure costs from 0.0005 to 10 m 3 / s.It is especially widely used in hydraulic laboratories.
Hydrometric method it is based on measuring the area of \u200b\u200bliving cross section and flow rate. It is the most common. The calculation is conducted by the formula, which we have already spoken.
Stock. The amount of water flowing through this living cross section of the river per second, we call consumption. The amount of water flowing through this living cross section of the river for a longer period is called stock.The magnitude of the flow can be calculated per day, for the month, for the season, for the year and even in a number of years. Most often the stock is calculated for the seasons, because seasonal changes for most rivers are particularly strong and characteristic. Great importance in geography has the values \u200b\u200bof annual effluents and in particular the amount of the average annual flow (stock calculated from perennial data). The average annual runoff makes it possible to calculate the average river consumption. If the consumption is expressed in cubic meters per second, then the annual stock (in order to avoid very large numbers) is expressed in cubic kilometers.
Having expense information, we can get data and about the drain for one or another period of time (by multiplying the amount of the flow rate for the number of seconds of the time taken). The magnitude of the flow in this case is expressed volume. Flow of large rivers is expressed usually in cubic kilometers.
So, for example, the average annual stock Volga 270 km 3,Dnipro 52. km 3,Obi 400. km 3,Yenisei 548. km 3, Amazon 3787. kM, 3.etc.
When the rivers characteristic is very important, the ratio of the amount of precipitation falling on the area of \u200b\u200bthe river with us is very important. The amount of precipitation, as we know, is expressed in a thickness of the water layer in millimeters. Therefore, to compare the value of the flow from the size of the precipitate, it is necessary to express the thickness of the water layer in millimeters as a thickness of the water layer. For this, the flow rate for this period, expressed in bulk measures, is distributed to a uniform layer over the entire area of \u200b\u200bthe river basin underlying the observation item. This value, called the height of the drain (A), is calculated by the formula:
BUT - this is the height of the drain, expressed in millimeters, Q. - Consumption, T.- The period of time, 10 3 serves as a translation of meters to millimeters and 10 6 to translate square kilometers into square meters.
The ratio of the amount of flow to the amount of precipitation of precipitation is called the flow factor.If the flow factor indicate the letter but,and the amount of precipitation expressed in millimeters - h.T.
The flow factor, as well as anything, is an abstract value. It can be expressed as a percentage. So, for example, for p. Neva A \u003d 374 mm, h. \u003d 532 mm; hence, but\u003d 0.7, or 70%. In this case, the flow coefficient r. Neva allows us to say that from the total amount of precipitation falling in the river basin. Neva, 70% flows into the sea, and 30% evaporates. We observe a completely different picture on r. Nile. Here A \u003d 35 mm, h. =826 mm;consequently a \u003d 4%. So, 96% of all sediments of the Nile basin evaporates and only 4% comes to the sea. Already from the above examples, it is clear what a huge value of the flow factor has for geographers.
We give as an example the average precipitation value and drain for some rivers of the European part of the USSR.
In the examples we provided the amount of precipitation, the values \u200b\u200bof the effluent, and, therefore, the drain coefficients are calculated as the average annual on the basis of perennial data. It goes without saying that the wastewater coefficients can be removed for any period of time: day, month, season, etc.
In some cases, the drain is expressed by the number of liters per second for 1 km 2. Pool area. This value of the drain is called module of flow.
The magnitude of the average long-term flow using an isolated isolines can be on the map. On such a stock map is expressed by modules of the drain. It gives an idea that the average annual stock on the plain parts of the territory of our union has a zonal character, and the magnitude of the flow decreases to the north. According to such a map, you can see what a lot of importance for the flow has a relief.
Nutrition rivers. There are three main types of nutrition of rivers: nutrition with surface waters, underground water and mixed nutrition.
Power supply surface waters can be divided into rain, snow and glacial. Rain food is characterized by rivers of tropical regions, most monsoon areas, as well as many districts Western EuropeA distinguished mild climate. Snow nutrition is characteristic of countries where a lot of snow accumulates during the cold period. This includes most of the rivers of the USSR. In the spring time, powerful floods are characterized. It is especially necessary to highlight the snow of the high mountain countries that are given the largest amount of water in the late spring and in the summer. This is a meal that is the name of the enemy, close to the glacial diet. Glaciers, like mountain snow, give water mainly in the summer.
Underground water is powered by two ways. The first way is the nutrition of rivers with deeper aquatic layers emerging (or, as they say, seduced) in the river bed. This is quite sustainable food for all seasons. The second way is the nutrition of the soil waters of alluvial thickness directly related to the river. During periods of high water standing, alluvius is saturated with water, and after the decline of water, the river slowly returns its own stocks. This power is less stable.
Rivers receiving their diet from some surface or alone groundwater are rare. Mixed nutrition rivers are significantly more common. In some periods of the year (spring, summer, the beginning of autumn), surface waters have predominant, to other periods (in winter or during drought periods), the soil nutrition becomes the only one.
It is possible to mention the rivers feeding with condensing waters that can be superficial and underground. Such rivers are more often found in mountainous areas, where the accumulations of blocks and stones on tops and slopes condense moisture in noticeable quantities. These waters can affect the increase in flow.
Power conditions of rivers at different times of the year. In winter, painthe neck of our rivers is supplied exclusively groundwater. This nutrition is quite evenly, so winter stock for most of our rivers can be characterized as the most uniform, very weakly decaying from the beginning of winter to spring.
In the spring of the character of the drain and in general, the entire river mode changes dramatically. The snowy precipitates in the form of snow quickly become quickly, and melting water in a huge amount merge into the river. As a result, it turns out a spring flood, which, depending on geographical Conditions The river basin lasts more or less for a long time. On the nature of the spring fellow we will talk a little later. In this case, we note only one fact: a huge number of spring tales snow waters are added to the ground power supply, which increases the stock many times. For example, for the chart, the average consumption in the spring exceeds the winter consumption of 12 and even 15 times, for the Oka 15-20 times; Dnipro's consumption at Dnepropetrovsk in spring time in some years exceeds the winter consumption of 50 times, the difference in small rivers is even more significant.
In the summer, the nutrition of the rivers (in our latitudes) is carried out, a row side, groundwater, on the other - the immediate rainwater runoff. According to the observations of Acad. Opokovain the upper dnipper pool, this immediate rainwater flow during the summer months reaches 10%. In mountainous areas where flow conditions are more favorable, this percentage increases significantly. But it reaches especially a great size in those areas that are distinguished by the widespread permafrost. Here, after each rain, the level of rivers quickly rises.
In autumn, as the temperature decreases, evaporation and transpiration gradually decrease, and surface stock (rainwater) increases. As a result, the fall in the fall, generally speaking, increases until the moment when liquid atmospheric precipitations (rain) are replaced by solid (snow). Thus, in the fall, like
we have a soil plus rain nutrition, and rainy gradually decreases and stops at the beginning of winter at all.
This is the course of food of ordinary rivers in our latitudes. In the highland countries, even the molten water of mountain snow and glaciers are added.
In the desert and dry-steppe areas, the molded water of mountain snow and ice play a dominant role (AMU-Daria, Cheese Daria, etc.).
Oscillation of water levels in rivers. We just talked about the conditions of nutrition of rivers at different times of the year and in connection with this noted how the stock changes at different times of the year. The most clearly of these changes shows the curve fluctuations in water levels in rivers. Here we have three graphics. The first chart gives an idea of \u200b\u200bfluctuations in the level of the forest zone of the European part of the USSR (Fig. 116). In the first chart (r. Volga) is characteristic
fast and high rise with a duration of about 1/2 months.
Now pay attention to the second schedule (Fig. 117), which is characteristic of the rivers of the Taiga Zone of Eastern Siberia. Here is a sharp rise in spring and a number of lifts in summer due to the rains and the presence of permafrost, increasing the speed of the flow. The presence of the same permafrost that reduces the winter soil power leads to a particularly low water level in winter.
On the third chart (Fig. 118), the curve of oscillations of the rivers of the Taiga zone of the Far East. Here in connection with the Marzlot, the same is very low in the cold period and continuous sharp level fluctuations in warm periods. They are determined by the spring of the beginning of the summer by melting snow, and later with rains. The presence of mountains and permafrost speeds up the stock, which is particularly sharply affected by level fluctuations.
The character of fluctuations in the levels of the same river in different years of unequal. Here we have the chart fluctuate levels r. Kama for different years (Fig. 119). As you can see, the river in different years has a very different character of oscillations. True, here the most sharp deviations from the norm are selected. But here is the second schedule of oscillations of levels p. Volga (Fig. 116). Here all oscillations of the same type, but the swing of oscillations and the duration of the spill is quite different.
In conclusion, it must be said that the study of fluctuations in river levels, in addition to scientific importance, also has a huge practical value. The demolished bridges, destroyed dams and coastal facilities, flooded, and sometimes completely destroyed and washed villages have long ago forced a person carefully treat these phenomena and study them. It is not difficult that observations of fluctuations in river levels are carried out with deep antiquity (Egypt, Mesopotamia, India, China, etc.). River shipping, road construction, and especially railways, demanded more accurate observations.
Observation of the oscillations of river levels in Russia began, apparently, for a very long time. In the chronicles, starting with XV c., We are often indicated on the height of spills p. Moscow and Oka. Observations over the oscillations of the level of the Moscow river were produced daily. First XIX. in. Daily observations were held on all major marins of all shipping rivers. From year to year the number of hydrometry stations continuously increased. In a pre-revolutionary time, we had more than a thousand watering posts in Russia. But these stations have achieved a special development in Soviet times, which is easy to see from the table.
Spring flood. During the spring melting of the snow, the water level in the rivers rises sharply, and the water, the interlayer usually flows, comes out of the banks and often floods the understanding. This phenomenon is characteristic of most of our rivers, is called spring flood.
The time of the underworld depends on the climatic conditions of the area, and the duration of the field of the flooder, in addition, from the size of the basin, the individual parts of which can be under different climatic conditions. So, for example, for p. Dnipro (according to observations in Kiev) The duration of flooding from 2.5 to 3 months, whereas for the tributaries of the Dnieper - Sula and Psöl - the duration of the flood is only about 1.5-2 months.
The height of the spring flood depends on many reasons, but the most important of them are: 1) the number of snow in the river basin to the top of melting and 2) the intensity of the spring melting.
Some significance also has the degree of saturation of the soil water in the river basin, a merzlot or soil tires, spring precipitation, etc.
For most major rivers of the European part of the USSR, spring water rise to 4 is characteristic of m.However, at various years, the height of the spring flood is susceptible to very strong fluctuations. So, for example, for the Volga in the city of Gorky water lifts reach 10-12 m,ulyanovsk until 14 m;for p. Dnieper for 86 years of observation (from 1845 to 1931) from 2.1 M.up to 6-7 and even 8,53 m.(1931).
The highest water lifts lead to branches that cause great damage to the population. An example is the flood in Moscow 1908, when a significant part of the city and the Moscow-Kursk can railway Tens of kilometers were under water. A very strong flood has experienced a number of Volga cities (Rybinsk, Yaroslavl, Astrakhan, etc.) as a result of an unusually high rise of water r. Volga in spring 1926
On large Siberian rivers in connection with the congestion, water lifting reaches 15-20 or more than meters. So, on r. Yenisei to 16. m,and on r. Lena (U Bulun) to 24 m.
Floods. In addition to periodically recurring spring semilations, there are still sudden lifts of water caused by or losing heavy rains, or any other reasons. These sudden lifts of water in rivers, in contrast to periodically repeated spring seals, are called floods.Floods in contrast to the salons can occur at any time of the year. In the conditions of the plain areas, where the bias of the rivers are very small, these floods can cause sharp increases in 1 levels mainly in small rivers. In mountain conditions, the flood manifests itself on more large rivers. Especially strong floods are observed in our Far East, where, in addition to the mountain conditions, we have sudden prolonged livne, giving over one or two days more than 100 mM.precipitation. Here, summer floods often take the character of strong, sometimes destructive floods.
It is known that forests and nature of the runoff are at all in general, forests are enormous. First of all, they provide slow melting of snow, which lengthens the duration of the flood and reduces the flood height. In addition, the forest litter (fond of foliage, needles, mosses, etc.) retains moisture from evaporation. As a result, the coefficient of surface runoff in the forest is three or four times less than on arable land. Hence the flood height decreases to 50%.
In order to reduce spills and in general, we have special attention to the preservation of forests in the nutrition areas in the USSR. Resolution (from 2 /VII1936) provides for the preservation of forests on both shores of the rivers. At the same time, forest stripes in 25 in the upper flows of rivers should be maintained. kM widths, and in the lower flow 6 km.
The ability to further combat spills and the development of measures to regulate the surface runoff in our country can be said unlimited. Creating forest structures and reservoirs regulates stock on huge spaces. Creating a huge network of channels and colossal reservoirs is even more subordinating the effluent and the greatest benefit of a person of a socialist society.
Mezhny. In the period when the river lives almost solely at the expense of nutrition of groundwater in the absence of nutrition of rainwate, the river level is the lowest. This period of the lowest standing of the water level in the river is called meeting.The beginning of the center considers the end of the decline in the spring flood, and the end of the center is the beginning of the autumn lifting level. So, the intertaries or inter-period for most of our rivers corresponds to the summer period.
Frozening rivers. Rivers of cold and moderate countries in the cold period of the year are covered with ice. The freezing of rivers begins usually off the coast, where the weakest current. In the future, crystalline and ice needles appear on the surface of the water, which, gathering in large quantities, form the so-called "fat". As the water cooling further, ice floes appear in the river, the number of which is gradually increasing. Sometimes a solid autumn ice-drying continues for several days, and with quiet frosty weather, the river "gets up" rather quickly, especially on the turns where a large amount of ice floes accumulates. After the river was covered with ice, it turns into nutrition with groundwater, and the water level is often reduced, and the ice on the river begins.
Ice by increasing bottom, gradually thickens. The thickness of the ice cover depending on the climate conditions can be very different: from several centimeters to 0.5-1 1 m,and in some cases (in Siberia) to 1.5- 2 m.From melting and freezing the flow of snow can thicken on top.
The exits of a large number of sources that bring more warm water, in some cases lead to the formation of "crawl", i.e. the non-freezing site.
The process of freezing the river begins with the cooling of the upper layer of water and the formation of thin ice films "known as sala.As a result of the turbulent nature of the flow, water stirring occurs, which leads to the cooling of the entire mass of water. At the same time, the water temperature may be somewhat lower than 0 ° (on the r. Neva to - 0 °, 04, on the p. Yenisei -0 °, 1): The supercooled water creates favorable conditions for the formation of ice crystals, resulting in the so-called depth ice.The depth ice formed on the bottom is called bottom ice.Depth ice, which is in suspension, is called shugoy.Shuga may be in suspension, as well as float to the surface.
The bottom ice, gradually increasing, breaks away from the bottom and, by virtue of its lesser density, floats to the surface. At the same time, the bottom ice, taking off from the bottom, captures with you and part of the soil (sand, pebbles and even stones). The bottom ice that came to the surface is also called shigoy.
The hidden heat of the ice formation is rapidly spent, and the water of the river is all the time, up to the formation of ice cover, remains overcooked. But as soon as ice cover occurs, the weight loss in the air is largely ceased and the water is no longer hypochealed. It is clear that the formation of ice crystals (and, consequently, deep ice) stops.
With a significant flow rate, the formation of ice cover is very slowed down, which in turn leads to the formation of deep ice in huge quantities. As an example, you can specify the r. Hangar. Here Shuga. and. bottom ice, scoring the channel, form burgers. The blockage of the bed leads to a high rise in the water level. After the formation of ice cover, the process of forming deep ice is sharply reduced, and the river level is quickly reduced.
The formation of ice cover begins with the shores. Here, at a lower flow rate, ice (tackle) is formed. But this ice is often keen on the flow and, together with the mass of Shuga, determines the so-called Autumn ice drift.Autumn iceshirt is sometimes accompanied by turni.e. the formation of ice dams. Constitutions (like lighters) can cause significant water lifts. Constitis arise usually in the narrowed areas of the river, on steep turns, on the cargo, as well as artificial structures.
On large rivers current to north (Ob, Yenisei, Lena), the lower rivers freeze earlier, which contributes to the formation of particularly powerful congestion. Rising the level of water in some cases can create conditions for the occurrence of reverse currents in the lower sections of the tributaries.
Since the formation of ice cover, the river is entering the period of the ice cover. From this point on, the ice slowly increases from below. On the thickness of the ice cover, in addition to temperatures, snow cover has a large influence, protecting the surface of the river from cooling. On average, ice thickness in the USSR reaches:
Walkers. There are no cases when some areas of the river in the winter do not freeze. These sites are called cramps.The causes of their formation are different. Most often, they are observed in the plots of rapid flow, at the site of the release of a large number of sources, at the site of the descent of factory waters, etc. In some cases, such sections are also observed when the river out of the deep lake. So, for example, p. Angara when leaving Oz. Baikal kilometers by 15, and in some years even by 30, does not freeze at all (the hangar "suits" the warmer water of Baikal, which is not cooled and then cooled to the freezing point).
Opening rivers. Under the influence of spring sunlight, the snow on ice begins to melting, as a result of which the lens-like water clusters are formed on the surface of the ice. Water flows flowing from the shores, strengthen the melting of ice especially at the shores, which leads to the formation of clouds.
Usually before the start of the opening is observed ice progression.In this case, the ice begins to move, it stops. The moment of the movement is the most dangerous for structures (dams, dams, bridge underworld). Therefore, about the facilities the ice is smoking in advance. The beginning of the waters wake up ice, which ultimately leads to ice driving.
Spring Iceshop usually happens a lot more than autumn, which is determined by a much larger amount of water and ice. Ice congestion in spring are also more autumn. Especially large sizes they reach the northern rivers, where the opening of rivers begins on top. The Ice River Brought by the River is detained below the locations where ice is still strong. As a result, powerful ice dams are formed, which in 2-3 hours raise water level onseveral meters. The subsequent breakthrough of the dam causes very strong destruction. Let us give an example. Ove River is revealed from Barnaul at the end of April, and Salekhard at the beginning of June. Ice thickness at Barnaul about 70 cm, and in the lower reaches of about 150 cm.Therefore, the phenomenon of congestion is quite usually. When the congestion is formed (or, as they say, "Zazhkov") water level in 1 hour rises by 4-5 m.and just as quickly falling after the breakthrough of ice dams. Grand flows of water and ice can destroy the forests on large areas, destroy the shores, lay new channels. Consisters can easily destroy even the strongest facilities. Therefore, when planning structures, it is necessary to take into account the places of structures, especially since the congestion is usually on the same sites. To protect structures or winter parking of the river fleet, ice on these areas usually explodes.
Water lifting at obituats on OIS reaches 8-10 m, and in the bottoms of the r. Lena (in Buluna) - 20-24 m.
Hydrological year. The stock and other characteristic features of the river life, as we have already seen, are different at different times. However, the seasons in the life of the river do not coincide with the usual calendar times of the year. For example, the winter season for the river begins from the moment when the rain food stops and the river goes to winter soil nutrition. Within the territory of the USSR, this moment in the northern regions occurs in October, and in the southern in December. Thus, one exactly set point that is suitable for all the USSR rivers does not exist. The same must be said about 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 of transition of the river to exclusively soil nutrition. For various sites of the territory of even one of our state, the beginning of the hydrological year can not be the same. For most USSR rivers, the beginning of the hydrological year is from 15 /XIup to 15 / xII..
Climate classification of rivers. Already from what was said aboutriver mode at different times of the year, it is clear that the climate has a huge impact on the river. 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, open in spring and give an exceptionally high water lift during the spring flood. The Rivers of Western Europe very rarely freeze and almost do not give spring spills. As for the Southern Europe rivers, they do not freeze at all, and the most high level Waters have in winter. We find an even more sharp difference between the rivers of other countries lying in other climatic areas. Enough to recall the rivers of the monsoon regions of Asia, the river Northern, Central and South Africa, rivers South America, Australia, etc. All this together gave the basis of our climatologist Warikov to classify rivers depending on the climatic conditions in which they are. According to this classification (somewhat changed later), all rivers of the Earth are divided into three types: 1) rivers that feed on almost exclusively by the waters of snow and ice, 2) rivers that feed on only rainwater, and 3) rivers receiving water in both methods indicated above .
The first-type rivers include:
a) Rivers of the desert, bordered by high mountains with snowy vertices. Examples can serve: Cheese Daria, AMU-Daria, Tarim et al.;
b) the rivers of polar regions (Northern Siberia and North America), which are mainly on the islands.
The second-type rivers include:
a) rivers of Western Europe with more or less uniform rain powders: hay, Main, Moselle, etc.;
b) Rivers of Mediterranean countries with winter spill: Rivers of Italy, Spain, etc.;
c) rivers of tropical countries and monsoon areas with summer spills: Gang, Ind, Neil, Congo, etc.
The rivers of the third type, eating both mole and rainwater, belong:
a) the rivers of the Eastern European, or Russian, Plain, Western Siberia, North America and others with the Spring Spill;
b) Rivers receiving nutrition from high mountains, with spring and summer spill.
There are other newer classifications. Among them should be noted classification M. I. Lvovich,which based on the same classification of Waikova, but in order to clarify not only high-quality, but also quantitative indicators of power supply sources and seasonal drainage distribution. For example, it takes the magnitude of the annual flow and determines which percentage of the flow is determined by one or another power source. If the value of the flow of a source is more than 80%, then this source is given an exceptional value; If the flow rate is from 50 to 80%, then the predominant; Less than 50%-processed. As a result, it obtains 38 groups of water regime, which are combined in 12 types. These types are as follows:
1. Amazon type - almost exclusively rain nutrition and the predominance of autumnal flow, i.e. in those months, which are considered autumn (Amazon, Rio-Negro, Blue Neal, Congo, etc.).
2. Nigerian type - predominantly rain nutrition with the predominance of autumnal drain (Niger, Lualab, Neil, etc.).
3. Mekong type is almost exclusively rain nutrition with a predominance of summer runoff (Mekong, Topper Madeira, Maranyon, Paraguay, Parana, etc.).
4. Amur - predominantly rain nutrition with a predominance of summer runoff (Cupid, Vitim, Topper Olekma, Yana, etc.).
5. Mediterranean - exclusively or predominantly rain nutrition and domination of winter runoff (Moselle, Rur, Thames, Agry in Italy, Alma in Crimea, etc.).
6. Oderian - the predominance of rain food and spring drain (software, tess, Oder, Morava, Ebro, Ohio, etc.).
7. Volzhsky - mostly snow meals with a predominance of spring runa (Volga; Mississippi, Moscow, Don, Ural, Tobol, Kama, etc.).
8. Yukonsky - prevailing snow nutrition and dominance of summer runoff (Yukon, Cola, Athastka, Colorado, Vilyui, Phacina, etc.).
9. Nurinsky - the predominance of snow nutrition and almost exclusively spring stock (Nura, Eccerlan, Buzuluk, B. Ugeny, Inguletz, etc.).
10. Greenlandic - exclusively glacial nutrition and short-term flow in the summer.
11. Caucasian - prevailing or predominantly glacial nutrition and dominance of summer runoff (Kuban, Terek, Ron, Inn, Aara, etc.).
12. Loanian - exceptional or preferential nutrition due to groundwater and uniform distribution of the flow during the year (r. Loa in the northern part of Chile).
Many rivers, especially those that have a greater length and large area, may be separate in various groups. For example, the rivers Katun and Biya (from the merger of which are formed by OB) feed on the main water of mountain snow and glaciers with water lifting in summer. In the taiga zone, Ob tributaries feed on thawed snow and rainwater with spills in spring. In the lower reaches of the entrances are treated to the rivers of the cold belt. The Irtysh River itself has a complex character. All this, of course, must be considered.
- A source-
Polovinkin, A.A. Fundamentals of general land / A.A. Polovinkin .- M.: State Educational and Pedagogical Publishing House of the Ministry of Education of the RSFSR, 1958.- 482 p.
POST Views: 55
Movement of fluid on pipes.
The dependence of the fluid pressure from the speed of its flow
Stationary fluid flow. EXTRACTION EQUATION
Consider the case when the unusual liquid flows along a horizontal cylindrical tube with a changing cross section.
The flow of fluid is called stationaryIf at each point of the space occupied by liquid, its speed does not change over time. With a stationary flow through any cross-section of the pipe in equal periods of time, the same fluid volumes are transferred.
Fluid practically non-residents, i.e. it can be assumed that this mass of the liquid always has a constant volume. Therefore, the same fluid volumes passing through different pipe cross sections means that the flow rate of the fluid depends on the cross section of the pipe.
Let the speed of the stationary flow of fluid through the pipe cross section S1 and S2 are equal to the V1 and V2. The volume of the fluid flowing over the time t through the cross section S1 is V1 \u003d S1V1T, and the volume of the fluid flowing over the same time through the section S2 is V2 \u003d S2V2T. From equality v1 \u003d v2 it follows that
Relationship (1) call the equation is inseparable. It follows from it that
Hence, with the stationary flow of the fluid, the speed of its particles through different cross sections of the pipe is inversely proportional to the areas of these sections.
Pressure in the moving fluid. Bernoulli law
An increase in the flow rate of the fluid during the transition from the pipe area with a larger cross-sectional area into the pipe area with a smaller cross-sectional area means that the liquid moves with acceleration.
According to the second law of Newton, the cause of acceleration is power. This force in this case is the difference of pressure forces acting on the current fluid in the wide and narrow parts of the pipe. Consequently, in a wide part of the pipe, the pressure of the fluid should be greater than in a narrow. This can be directly observed by experience. In fig. It is shown that in the sections of a different cross section S1 and S2 into the pipe along which the liquid flows, pressure gauges are inserted.
As observations show, the level of fluid in the pressure gauge tube in the S1 section of the pipe is higher than that of the cross section S2. Consequently, the pressure in the liquid flowing through the section with a larger area S1 is higher than the pressure in the liquid flowing through the section with a smaller S2 area. Hence, with the stationary flow of fluid in those places where the flow rate is less, the pressure in the liquid is greater and, on the contrary, where the flow rate is greater, the pressure in the liquid is less. For the first time, Bernoulli came to this conclusion, so this law is called bernoulli law.
Disassembling problems:
Task 1. Water flows in a horizontally located tube of alternating section. The flow rate in a wide part of the pipe is 20 cm / s. Determine the flow rate of water in a narrow part of the pipe, the diameter of which is 1.5 times less than the diameter of the wide part.
Task 2. In a horizontally located pipe, a liquid flows with a cross section of 20 cm2. In one place, the pipe has a narrowing section of 12 cm2. The difference in fluid levels in the pressure gauges installed in the wide and narrow parts of the pipe is 8 cm. Determine the volume flow rate for 1 s.
Task 3. To the piston of the fringe, located horizontally, the force is applied 15 N. Determine the expiration rate of water from the script tip if the piston area is 12 cm2.
Hydrology 2012.
Lecture 8. Special issues of hydrology of rivers and water bodies
Questions:
Water movement in rivers
Movement of nanos in rivers
Digital processes
Thermal and ice river and reservoirs
Lakes and their morphometric characteristics
1. Movement of water in rivers.
The movement of water in rivers occurs under the action of gravity in the presence of a longitudinal slope or pressure. The flow rate depends on the ratio of the horizontal component of the gravity, determined by the slope and the difference of heads, and the friction force determined by the interaction between the particles inside the stream and the particles and the bottom.
For rivers, the turbulent mode of water movement is characteristic, the distinctive feature of which is the rate ripple or change it in time at each point by value and direction relative to the average value.
Due to the uneven losses on the width of the flow rate of the flow, unevenly distributed in the river stream: the highest speeds are observed on the surface of the flow over the most deep part of the bed, the smallest - at the bottom and shores. In the most common conditions, the regular distribution of the flow rates (distribution chart) of mean velocities in the depth of the river flow has a maximum (u max) near the surface, the speed close to the middle vertical - at a depth of 0.6h from the bottom (H - the full depth ) and a minimum (u min), not equal to zero, - at the bottom (Fig. 8.1, and ).
Fig. 8.1. Vertical distribution of flow rates in the river stream:
but - typical; 6-under ice cover; in - under the layer of intravel ice (shumbers); g - with a passing and counter wind; d- with the influence of vegetation; e - with the influence of the irregularities of the bottom; 1-library cover; 2 layer of shuga; V-direction of the wind; u max - maximum flow rate; -and - reverse
However, under the influence of ice cover, wind, vegetation, irregularities of the bottom and shores, this distribution of velocities is broken (Fig. 8.1, b -e.).
The average flow rate in cross section V is calculated according to the well-known consumption of water - q and cross-sectional area - by formula: V \u003d Q / .
The most simple patterns are observed with a uniform movement of fluid in line, close to straight. In this case, the average flow rate in line can be described by the Formula of the Swazy.
,
(8.1)
where C is the coefficient of the coefficient;
h cp - middle depth in line, m;
I - the slope of the water surface.
During a co-channel width (c) and middle depth (H cf), less than 10 instead of H, the hydraulic radius R \u003d / ( is the area of \u200b\u200bliving cross section, a moistened perimeter).
The coefficient of the Swazy is calculated by empirical formulas, among which are the most common
manning formula (for rivers):
C \u003d H CP 1/6 / N. (8.2)
formula Pavlovsky (for artificial watercourses - canals, canvas):
C \u003d (1 / N) r y / n (8.3)
y \u003d 0.37 + 2.5 
- 0,75(
-0,1)
,
where N is the coefficient of roughness, which is found according to special tables (in Russia - on the tables of the Slim, Carasev, in the United States - Tables of Bralli).
For smooth neglected beds with a sandy bottom n \u003d 0.020 - 0.023; For winding beds with an uneven bottom N \u003d 0.023-0.033; For understanding, overgrown with shrubs, n \u003d 0.033 - 0.045.
The Formula of the Swazy shows that the flow rate in the river stream is the greater, the greater the depth of the riverbed and the slope of the water surface and the less roughness of the bed.
By multiplying both parts of the coaching area to the cross-sectional area , taking into account formula (8.1), it is possible to obtain a formula for determining water consumption:
.
(8.4)
If the morphometric characteristics of the river stream change along the length of the river, the river flux movement will be uneven and the flow rate will vary along the river. On a small area of \u200b\u200bthe river, where the consumption does not change from the law of preserving the mass of the substance, you can record the continuity equation
1 v. 1 = 2 v. 2 = Q.= const.. (8.5)
It follows that an increase in cross-sectional area along the river (from the stem 1 to the stem 2) will entail a decrease in the flow velocity in this section of the flow rate, as, for example, into a cross-sectional area, a decrease in the cross-sectional area along the river will increase on this site The speed of the flow, as, for example, in the carmine on the ride.
In the case of uneven motion, the bias of the aqueous mirror will no longer be equal to the bottom of the bottom, therefore the phenomenon of the backpage can be observed along the river (increasing the depth of water with increasing distance) or the decay phenomenon (reduction of depth with increasing distance). The cause of uneven movements can be various structures, built in the river bed - dams, dams, bridge transitions, hidden and clearing River River.
More complex cases of movement occur at the turn of the bed, where, along with the strength of gravity, the centrifugal force is influenced by the flow rate. The centrifugal force is influenced. It is possible to deviate the flow in the surface layers in the direction of the concavened coast, which creates a cross-moving water level. As a result of an excess of hydrostatic pressure, the concave coast in the bottom layers arises within the convex coast. Folding out with the main longitudinal transfer of water in the river, multidirectional flows on the surface and at the bottom create a spiral movement of water on the bend of the river bed - transverse circulation (Fig. 8.2).
Fig.8.2. The transverse circulation circuit on the bend of the river stream in terms of (a) and the cross section (b) and the scheme of the current forces (B):
1 - superficial jets; 2) Cutton jets.
Transverse bias I. pop = sin. ), which occurs on the rotation of the bed, can be determined by the formula
.
(8.6)
where v.-If flow rate;
g - acceleration of free fall, m / s2;
r. - radio bend radius.
The magnitude of the level of level between both shores ( H. pop) Equal
H. pop = I. Pop IN, (8.7)
where IN- The width of the bed.
Example. At a speed V \u003d 1 m / s, r \u003d 100 m, b \u003d 50 m, the amount I. Pop=0,001, H. pop = 0.05 m.
Along with the power of gravity, the force of friction and the centripetal force on the liquid particles there is a deflecting force of rotation of the Earth.
Due to the daily rotation of the Earth with an angular velocity \u003d 2 / 86400 \u003d 0.0000729 rad / s, every material point, moving relative to the Earth at a rate of V, is experiencing an additional acceleration (). The signal corresponding to this acceleration is called Coriolis (F Coriol), and equal
F Coriol \u003d M r \u003d 2 Mvsin. (8.8)
Coriolis force is directed in the northern hemisphere at a right angle to the right to the direction of movement of the particle, in the southern hemisphere - to the left.
The transverse bias caused by Coriolis is equal to
I Coriol \u003d V SIN / 67200, (8.9)
For the northern latitude \u003d 45 sin \u003d 0.707 i Coriol \u003d V / 95000, at V \u003d 1 m / s i Coriol \u003d 1.0510 -5. With the river width B \u003d 50 m, the level difference h \u003d 0.00052 m (0.05 cm), which is 100 times less slope due to centrifugal force. The most strongly influence of the Coriolis force is manifested for large rivers (Volga, Dnieper, Yenisei, Ob, etc.), which was at one time discovered by the Russian academician, the scientist K. Bar. However, due to its smallness, the strength of the Corriolis is not taken into account in hydraulic calculations.
Movement of nanos in rivers
Along with water in the rivers, masts and soluble impurities are moving. The main sources of admission of nanos in the rivers are the surface of the catchment, exposed to erosion or the process of the destruction of soils and soils by flowing water and wind during the rain and snowmock, and the river beds themselves, blurred by the river stream.
Erosions of the surface of the catchment - the process is complex, depending on both the eroding ability to flow on its surface of rain and melting, and from the anti-erosion stability of soils and soils of the catchment. The erosion of the surface of the catchment (and the arrival of its products in the river) is usually the greater the longer the rains and intensively snowing, the more irregularity of the relief, the roar of the soil (the most easily exposed erosion of alloy soils), vegetable cover is less developed, stronger slopes. The erosion of the river beds is the more stronger than the speed of the flow in rivers and less stable soil, the foundation bottom and coast. A part of the nanos enters the river bed during abrasion (wave destruction) of the banks of reservoirs and river shores on wide splashes. Nanos, foundation bottom rivers, are called bottom sedimentsor alluvia.
The most important characteristics of the nanos are as follows:
geometric sizeexpressing through the diameter of the particles of the nanos (D mm);
hydraulic sizei.e., the rate of precipitation of particles of motions in fixed water (W, mm / s, mm / min);
density of particles(PN, kg / m 3), equal to the most common quartz sands2650 kg / m 3;
deposit density (the density of the soil) (p rally, kg / m 3), depending on the density of the particles and the soil porosity according to the formula (the density of liquid deposits at the bottom of the rivers is usually an average of 700-1000 kg / m 3, sandy 1500-1700, shans 1000-1500 kg / m 3);
concentration (the contents) of the deposits in the stream, which can be represented as in relative values \u200b\u200b(the ratio of the mass or volume of the injuries to the mass or volume of water), gas and in absolute values; In the latter case, the concept of water turbidity (S, g / m 3, kg / m 3) is used, which is calculated by the formula
where M is the mass of the nanos in the water sample; V- Water sample volume. The turbidity is determined by filing the water and weighing filters selected with the help of pitometers.
The largest concentration of nanos (turbidity of water) has rivers with flooding regime and flowing in conditions of arid climate and light-impaired soils. The most muddy rivers on Earth - Terek, Sulak, Kura, Amudarya, Gang, Huanghe. The average annual turbidity of the Terek rivers, Amudarya and Juanhe in the conditions of the natural regime was, for example, 1.7; 2.9 and 25.8 kg / m 3, respectively. In the flood, the turbidity of water Juanhe reached 250 kg / m 3! Currently, the turbidity of the listed rivers has become noticeably less. For comparison, we present data on the average annual turbidity of water in the Volga in its lower reaches: before registering the river, it was equal to about 60 g / m 3, and after the regulation, it decreased to 25-30 g / m 3.
By the nature of moving in rivers, the nanos are divided into two main types - weighted and inhaled. Intermediate type are chilling moving jumpsome in the bottom layer; The applications of this intermediate group are conventionally combined with inhibitory.
Inhalesable injuries -these are nanos moving by the river stream in the bottom layer and moving with sliding, rolling or by hydration. By attracting along the bottom, the largest particles of the nanos (sand, gravel, pebbles, boulders) are moved.
Thus, the criterion for the beginning of the movement of inhabitants in rivers is a condition
(8.11)
where U bottom is the actual bottom flow rate.
Between "initial speed" and the volume or weight of moving particles:
F G ~ D "~ U 6 bottom0. (8.12)
This formula was the name of the ERI law, which claims that the weight of the inlets proportional to the sixth degree of flow rate. From the formula of the ERI it follows that an increase in the flow rate, for example, in 2, 3, 4 times, leads to an increase in the weight moving along the bottom of the particles of the nanos, respectively, at 64, 729, 4096 times. This explains why the stream can be transferred on the low rivers with low flow rates on the bottom, and on the mountains with high speeds, pebbles and even murmur. For moving along the bottom of the sand, the bottom flow rates of at least 0.10-0.15 m / s are needed, gravel - at least 0.15-0.5, pebbles - 0.5-1.6, boulders - 1.6- 5 m / s. The average flow rate should be even more.
Increased injuries can move along the bottom of the rivers or a solid layer or in the form of clusters, i.e. discretely. The second nature of movement for rivers is most typical. The accumulations of inlets are represented by bottom ridges of various sizes (Fig. 8.3). The nans are moved by a layer on the riding slope of the ridge and roll along the lower slope (its slope is close to the corner of the natural slope) in the basement of the ridge. Here, the nanoson particles can be "buried" by the impending grocery and come into motion only after the ridge offset until its full length.
Fig.8.3. Bottom ridges at the bottom of the river in two consecutive time (1 and 2).
Weighted nans are transferred to the thicker of the river stream. The condition for such movement is the ratio
u + Z W, (8.13)
where U + Z is the vertical component of the flow velocity vector at this flow point; W - hydraulic particle size of the particle of the nanos.
The most important characteristics in the movement of suspended nanos in rivers are the turbidity of the water S, determined by the formula (8.10), and the flow rate of weighted applications:
R \u003d 10 -3 SQ, (8.14)
where R in kg / s, s in g / m 3, q \u200b\u200bin m 3 / s.
Weighted nanos are unevenly distributed in the river stream: in the bottom layers, the turbidity is maximum and decreases towards the surface, and for suspended nansions of larger fractions faster, for small fractions.
Along with the drain of water in hydrology, the stock of the nanos is determined. The river nanos are determined by the stock of weighted and flow of inlets, the main role usually belongs to suspended behavisions. It is believed that there are only 5-10% of the design of the weighted rivers of rivers, with an increase in the size of the river, with an increase in the size of the river, this share is usually reduced.
The limiting total consumption of both weighted and injected nans, which can carry the river under these conditions, are called the transporting ability of the R Tr. According to the theoretical I. experimental studies R tr depends primarily on the flow rates and water consumption:
(8.15)
where s. Tr. - the turbidity of water corresponding to the transporting ability of the stream;
v. -If flow rate;
h. CP. - middle depth;
w.- Medium hydraulic particle size of the particles of the nanos.
In our country and abroad, many different formulas of the form (8.15) were proposed. In this case, the turbidity of the water Sel, corresponding to the transporting ability of the flow (i.e., the maximum possible turbidity under data of hydraulic conditions) is often expressed as the function of the average flow rate: s. rP. = aV. n. where but and n. - Parameters, and n. varies from 2 to 4.
In real conditions, the actual flow rate of the river in the river and the transporting ability of the flow may not coincide that it becomes the cause of the channel deformations.
The stock of the river nanos (primarily suspended nans) is usually calculated based on the measurements of water consumption and weighted expenditures R \u003d F (Q). This connection has two important features: it is nonlinear, and R grows faster than q; Very approximately this dependence can sometimes be written in the form of a power equation:
R \u003d KQ M, (8.15)
where, according to N. I. Makkaveev, n. = 2 3 .
Very often the connection between R and Q is ambiguous (loop-shaped). This is due to the mismatch of changes in the rivers of water flow rivers and the expenditures in time in time (Fig. 6.18). The maximum turbidity of water in the rivers (and maximum deposits of the nanos also) is usually ahead of the maximum water consumption, since the most active washing of soils from the surface of the catchment goes during the raising flood or flood.
Fig. 8.4. Typical graphs change water consumption and suspended nanos (a) and links between them (b): 1 - flood lift; 2 - Sweep flood
Using the communication schedule R.= f.(Q.) At known average daily values \u200b\u200bof Q it is easy to determine the corresponding values \u200b\u200bof R.
The average nanos spending for any period R is defined in the same way as the average water costs. The stock of the nanos is calculated by the formula:
W H \u003d RT, (8.16)
where is the stock of nanos W n, kg; Middle consumption of nanos R, kg / s; time interval t, s.
The stock of the nanos is more convenient to present more convenient in kilograms, but in tons or even in millions of tons. In these cases, formulas are used.
W H (T) \u003d RT 10 -3, (8.17)
If we are talking about annual values, then write down
W H (million T) \u003d R 31,510 -3. (8.18)
The setting module of the nanos is called the stock of nanos in tons with 1 km 2 of the area of \u200b\u200bthe catchment (A):
M H \u003d WF / a. (8.19)
For annual values \u200b\u200bof the drain of the nanos, we will get M N, T / km 2:
M n \u003d R31,510 3 / f. (8.20)
The module of the set of nanos characterizes the erosion activity of river streams (we will remind, however, that the actual denudation in the river basins many times the module of the design of the nanos, calculated by the described methods, since the huge amount of washed from the slopes of the nanos does not fall into the river, and retains at the foot slopes, in the mouth of beams, ravines, small tributaries, on floodplains.
The module of the weighted nanos and the average turbidity of the water of the rivers, as well as the water flow module is unevenly distributed across the territory. So, in the north of the European territory of Russia (Tundra, the forest area) he often does not exceed 1-2 t / km 2 per year, in the northern and western parts European plains rises to 10-20 tons / km 2. In the south of the European territory of the former USSR, it reaches 50-100 tons / km 2, and in a number of areas of the Caucasus - even 500 m / km 2 per year. For pools of some rivers of the world, the module of the balance of weighted applications in natural flow conditions was: Volga - 10.3 t / km 2, Danube- 63.6, Terek - 350, Huanghe- 1590 t / km 2 per year. Turbidity river Pretty naturally distributed over the territory. So, for example, the average annual turbidity of rivers in the north of the European part of Russia is very small - 10-50 g / m 3, in the Oka basins, Dnieper, don increases to 150-500 g / m 3, in the North Caucasus sometimes exceeds 1000 g / m 3.
From the total annual flow of the nansos of all rivers of the world (15700 million T) The largest share in vivo accounted for Amazon (1200 million tons), Juanhe (1185 million tons), Ganges with Brahmaputra (1060 million tons), Yangtze (471 million tons), Mississippi (400 million tons) (see Tab. 6.1). Among the most muddy rivers on the planet - Huanghe (the average annual turbidity of water is more than 25 kg / m 3, and the maximum is 10 times more), Ind, Gang, Yangtze, Amudarya, Terek.
Hydraulic resistance.
During the fluid on the pipes, it has to spend energy to overcome the forces of external and internal friction. In direct areas of pipes, these resistance strengths operate along the entire length of the flow and the overall loss of energy on their overcoming is directly proportional to the length of the pipe. Such resistances are called linear. Their value (pressure loss) depends on the density and viscosity of the fluid, as well as from the diameter of the pipe (the smaller the diameter, the greater the resistance), the flow rate (the increase in speed increases the loss) and the purity of the inner surface of the pipe (the greater the roof of the walls, the more resistance ).
In addition to friction in direct areas, there are additional resistance in the pipelines in the form of turns of the stream, changes in the section, cranes, branches, etc. In these cases, the flow structure is broken and its energy is spent on rebuilding, swirls, blows. Such resistances are called local. Linear and local resistances are two types of so-called hydraulic resistances, the definition of which is the basis for calculating any hydraulic systems.
Fluid flow regimes .. In practice, two characteristic fluid flow modes are observed: laminar and turbulent.
When laminar mode, elementary stream streams flow parallel, without stirring. If you enter the stream of the painted liquid into such a stream, it will continue its current in the form of a fine thread among the thread of an unpainted liquid, not blurring. This flow mode is possible at very low flow rates. With an increase in the speed above a certain limit, the flow becomes turbulent, vortine, in which the liquid within the transverse section of the pipeline is intensively mixed. With a gradual increase in the speed, the colored stream in the stream first begins to fluctuate relative to its axis, then breaks appear in it due to stirring with other jets and then as a result of this, the entire flow receives a uniform color.
The presence of one or another flow mode depends on the value of the ratio of the kinetic energy flow 1 1
(■ P-GPI2 \u003d Ch-Rui2) to the work of the forces of inside-rhenium friction (/ 7 \u003d p "5 ^ /) - see (2.9).
This is a dimensionless attitude
^ -pvv21 (p, 5 ^ /) can be simplified having in mind that DB is proportional to V. values \u200b\u200b1 and a / g also have the same dimension, and they can be reduced, and the ratio of volume V to cross section 5 is linear size th.
Then the ratio of kinetic energy to the work of internal friction forces with an accuracy of constant multipliers can be characterized by a dimensionless complex:
which is called the number (or criterion) of Reynolds in honor of the English physics of Osborne Reynolds, at the end of the last century experimentally observed the presence of two flow modes.
Small values \u200b\u200bof Reynolds numbers indicate the predominance of the work of the internal friction forces in the fluid flow and correspond to laminar flow. Large values \u200b\u200bof ye correspond to the predominance of kinetic energy and turbulent flow regime. The border of the start of the transition of one mode to another is the critical number of Reynolds - is 1? ECR \u003d 2300 for round pipes (the diameter of the pipe is taken as the characteristic size).
In the technique, including diesel locomotive, hydraulic (including air and gas) systems usually takes place turbulent current liquids. The laminar regime is only viscous liquids (for example, oil) at low flow rates and in thin channels (flat tubes of the radiator).
Calculation of hydraulic resistance. Linear pressure losses are determined by the Darcy Weisbach formula: 
where X ("Lambda") is the linear resistance coefficient, depending on the number of Reynolds. For a laminar stream in a round tube, I, \u003d 64 / EE (depending on the speed), for turbulent flows, the value of little depends on the speed and, mainly, is determined by the roughness of the pipe walls.
Local pressure losses are also considered proportional to the square of speed and are determined as follows:
where £ ("zeta") is the coefficient of local resistance, depending on the type of resistance (rotation, expansion, etc.) and on its geometrical characteristics.
The coefficients of local resistance are set by an experimental way, their values \u200b\u200bare given in reference books.
The concept of calculating hydraulic systems. When calculating any hydraulic system, one of two tasks is solved: determining the required pressure drop (pressure) to skip this fluid flow or determination of fluid flow in the system with a given pressure drop.
In any case, a complete pressure loss in an AN system must be determined, which is equal to the sum of the resistance of all sections of the system, i.e. the sum of linear resistances "of all direct portions of pipelines and local resistances of other elements of the system:
If in all parts of the pipeline, the average flow rate of the same, equation (2.33) is simplified:
Typically, the system has sections, flow rates in which differ from each other. In this case, it is convenient to bring equation (2.33) to another form, given that fluid consumption is constant for all elements of the system (without branches). Substituting in the condition (2.33) values \u200b\u200band \u003d c) / 5, we obtain
hydraulic characteristic, or a common system resistance coefficient.
It must be borne in mind that the calculation of pipelines is not solving the problem with one specific answer. Its results depend on the selection of the size of the diameters of the pipeline or velocities in them. Indeed, it can be taken in the calculation of the low speed values \u200b\u200band get small pressure losses. But then at a given flow rate of pipelines (diameters) must be large, the system is bulky and heavy. Having accepted high flow rates in the pipes, we reduce their transverse dimensions, but at the same time, the pressure losses and energy costs to work the system will increase significantly (proportional to the square square). Therefore, when calculating is usually given by some mean, "optimal", values \u200b\u200bof fluid flow rates. For water systems, the optimal speed has an order of about 1 m / s, for low pressure air systems - 8-12 m / s.
The hydraulic blow is a phenomenon occurring in a fluid flow with a rapid change in the speed of its flow (for example, with a sharp closure of the valve in the pipeline or stopping the pump). In this case kinetic energy The stream instantly passes into the potential energy and the pressure of the flow before the lifting increases sharply. The area of \u200b\u200bincreased pressure is then propagated from the valve to the side of the non-stroken stream at a speed close to the speed of sound and in this medium.
A sharp increase in pressure leads if not to destruction, then to the elastic deformation of the elements of the pipeline, which reduces the force of impact, but enhances fluid pressure fluctuations in the pipe. The magnitude of the pressure jump at a complete stream of fluid flow that had vehicle V is determined by the formula of the outstanding Russian scientist - Professor N. E. Zhukovsky, obtained by him in 1898: Dr \u003d Raa, where p is the liquid density.
In order to prevent shock phenomena in large hydraulic systems (for example, plumbing networks), the locking devices are performed so that their closure occurs gradually.
The flow rate in the rivers of unequal at various points of flow: they change in depth, and in the width of the living section. The smallest speeds are observed at the bottom, which is due to the influence of the roughness of the bed. From the bottom to the surface, the rate of speed first occurs quickly, and then slows down, and the maximum in open streams is achieved at the surface or at a distance of 0.2h from the surface. Vertical speeds change curves are called yearographs or epuras speeds. The distribution of vertical velocities is greatly influenced by irregularities in the embossed of the bottom, ice cover, wind and water vegetation. If there is at the bottom of the irregularities (elevations, boulders), the speed in the stream before the obstacle sharply decreases to the bottom. Speed \u200b\u200bin the bottom layer decreases in the development of water vegetation, significantly increasing the roughness of the bottom of the bed. In winter, under the influence of additional friction about the rough surface of the speed of the speed of the speed. Maximum speed shifts to the middle of depth and sometimes to the bottom. In the wind, against the surface of the velocity, the surface decreases, and the position of the maximum is shifted to a greater depth compared to its position in the windless weather.
At the shores the speed is less, in the center of the stream more. Lines connecting points on the surface of the river with the highest speeds are called stregging. Knowledge of the position of Stregging has great importance When using rivers for water transport and leoplava purposes. A visual idea of \u200b\u200bthe distribution of speeds in a living section can be obtained by building izoud- Lines connecting points with the same speeds.
To calculate the average flow rate in the absence of direct measurements, the cozi formula is widely used. We highlight the volume of water limited by two cross sections ω. The magnitude of the volume V \u003d ωΔx, where Δx is the distance between sections. The volume is influenced by the equal power of the hydrodynamic pressure P, the action of the gravity F 'and the resistance force (friction) T. The force of the hydrodynamic pressure P \u003d 0, since the pressure of P 1 and P 2 with the equality of the cross sections and the constant slope is backed. So., V cf \u003d C, where h is the average depth, I is a slope. - Szi equation. Formula Maning :. Formula N. N. Pavlovsky:, where N is the coefficient of roughness, is located on special tables M. F. Sriban.
Water movements in rivers. Types of movement.
Water in rivers is moving under the action of gravity F '. This force can be decomposed into two components: parallel bottom F 'X and normal to the bottom f' y. The force f 'y is equalized by the reaction by the bottom of the bottom. The force F 'x, depending on the slope, causes the movement of water in the stream. This force, acting constantly, should cause an acceleration of movement. This does not occur, as it is equalized by the power of the resistance arising in the stream as a result of internal friction between water particles and the friction of the moving mass of water about the bottom and the coast. The change in the slope, roughness of the bottom, the narrowing and expansion of the channel causes changes in the ratio of the driving force and the resistance force, which leads to a change in the flow rates along the length of the river and in a living section.
Types of movement in streams:
1) uniform,
2) uneven,
3) unidentified.
For uniform Movement of the flow rate, a living section, the wave consumption is constant along the length of the stream and do not change over time. This kind of movement can be observed in channels with a prismatic cross section. With uneven bias, speeds, the living section do not change in this section in time, but change along the length of the stream. This type of movement is observed in rivers during the period of interactions with stable water consumption in them, as well as in the conditions of the subjoil formed by the dam. Unidentified movement is such in which all hydraulic elements of the flow (slopes, speeds, a living section area) are changed and in time, and in length. Unidentified movement is characteristic of rivers during the passage of seals and floods.
With uniform movement of the flow surface I. equal to the slope of the bottom i. and water bottle parallel to the aligned surface of the bottom. Uneven movement can be slow and accelerated. When slowing down the river, the curve curve of the free water surface takes the form of the sub-curve. Surface slope becomes less lowering bottom ( I. ), and the depth increases towards the flow. With an accelerating flow, the curve of the free surface of the flow is called the recession curve; Depth decreases along the stream, speed and bias are increasing ( I\u003e I.).
Reynolds Number One of the similarity of criteria for the flows of viscous liquids and gases, which characterizes the ratio between the inertial forces and viscosity forces: Re.\u003d R. vl/ m, where R is the density, M is the dynamic viscosity coefficient of fluid or gas, v - Characteristic flow rate, l. - Characteristic linear size. So, when in round cylindrical pipes, usually take l.= D.where d - pipe diameter, and v.= V. CP, where v. CP. - average flow rate; when flowing around the phone / - length or transverse body size, and v. = v. ¥, where v. ¥ - The speed of the unperturbed flux by the body. Named by name O. Reynolds.
R. h. The mode of fluid flow, characterized by critical R. h, also depends. Re. kr . For R.<Re. kr is possible only a laminar flow of fluid, and when Re.> Re. KR Current can be turbulent. Value Re. KR depends on the type of flow. For example, for the flow of viscous fluid in a round cylindrical tube Re. Kr \u003d 2300.
Distribution of flow rates in the river stream.
One of the features of the movement of water particles in rivers is irregular random changes in speeds. Continuous changes in the direction and values \u200b\u200bof the speeds at each point of the turbulent flow are called pulsation. The greater the speed, the greater the turbulent ripple. Then at each point of the flow and at each moment of time the instantaneous flow rate is a vector. It can be decomposed into components in the rectangular coordinate system (υ x, υ y, υ z,), they will also be pulsating. Most hydrometric devices are measured by a longitudinal component of the speed (υ x), averaged for some time interval (in practice 1-1.5 minutes).
Speed \u200b\u200bchanges in the depth and width of the live cross section of the river. On each single vertical, the smallest speed is noted at the bottom, which depends on the roughness of the bed. To the surface, the speed increases to the value of the average vertical at a depth of 0.6h, and the maximum is noted on the surface or at a distance of 0.2h from the surface, in the open line. The chart of changing the speed of depth is called the hodographic (velocity pulp).
The distribution of the depth rate depends on the bottom relief, the presence of ice cover, wind and aqueous vegetation. The presence of boulders, large stones and aqueous vegetation at the bottom leads to a sharp decrease in the speed in the bottom layer. Ice cover and shuga also reduce the speed, but in the layer of water under the ice. The average speed per vertical is determined by dividing the area of \u200b\u200bthe plot to the depth of the vertical.
In the width of the flow, the speed repeats basically a change in depth - from the shores the speed increases by the middle. The line connecting points with the highest speeds along the length of the river is called the neck (line of the largest depths).
The distribution of speeds in the plan can be reflected by the outflows - lines connecting points with equal speeds in the living section.
The line connecting along the river point of individual living sections with maximum speeds is called a dynamic axis of flow.
