Why is a river called a river? Origin of the word "river". River names
general characteristics rivers
As we know, a river is a constant natural water flow flowing in a relief depression created by it. All rivers are divided into mountain and plain (according to the nature of the flow). The main characteristics of rivers are indicators such as: length of the river, slope and fall of the river, volume of annual river flow, type of river feeding, river flow speed.
Russia, due to the size of its territory and climate, has big amount rec. Scientists have calculated that more than $3 million rivers flow through the country. Their total length exceeds $10$ million km. The vast majority of rivers are typical lowland rivers.
Note 1
In terms of annual river flow, Russia is second only to Brazil.
Rivers are distributed very unevenly throughout the country. This is due to the characteristics of the climate and terrain. Let's look at these topics in more detail.
Rivers of the Arctic Ocean basin
The territory of the northern part of the East European Plain, Siberia and parts Far East has a surface slope to the north. Therefore, more than half of the country's territory belongs to the Arctic Ocean basin. The largest of them are the systems of the Ob, Yenisei, and Lena. In the European part of the country, the largest rivers of the Arctic Ocean basin are Northern Dvina and Pechora. The Lena River is the longest river in Russia (without tributaries). Its length is $4400$ km. The Yenisei is the deepest river in the basin and one of the deepest rivers in the world. The Ob River has the largest basin in terms of area.
Note 2
And if we measure the length of the Ob with its tributary Irtysh, then this particular system will be the longest in Russia - $5410$ km.
The rivers of the European part of the basin have a slow, calm flow. These are typically lowland rivers. They are significantly shorter than the rivers of Siberia. Siberian rivers originate far in the south, in the mountains Southern Siberia(Altai, Sayan Mountains, Transbaikalia). In the upper reaches they often have the character mountain rivers, have thresholds. In the middle and lower reaches there are lowland rivers.
The feeding type of northern rivers is snow and rain. Flood occurs in the spring, when spring rains coincide with snowmelt. Northern rivers freeze in winter. Ice melting occurs from south to north. Therefore, when meltwater comes to the north, and there is still ice there, river floods occur over large areas.
Northern rivers are rich in fish. And the Northern Dvina and Pechora in the old days were famous for their soft pearl fishing. Unfortunately, due to deterioration ecological situation soft pearls are no longer mined.
Siberian rivers have large energetic resources, so a number of powerful hydroelectric power stations were built there.
Rivers of the Pacific Ocean
The Pacific Ocean basin occupies approximately a fifth of Russia's territory. The largest river in this basin is the Amur. The rivers of the Amur basin are fed by rain, associated with monsoon climate Far Eastern coast. The Amur is one of the deepest rivers in the world. The rivers of the coast of the Okhotsk and Bering seas are short. They belong to snow-fed rivers. A number of hydroelectric power stations have been built on the rivers of the Amur system. The state border with China runs along the Amur, Ussuri, and Argun rivers.
Rivers of the Atlantic Ocean
The Atlantic Ocean basin is the smallest. It accounts for about $5$% of the country's area. The type of river feeding is mixed, with a predominance of rain. As a rule, rivers are full all year round. The Western Dvina, Neman, and Neva flow into the Baltic Sea. To the south, to Chernoe and Sea of Azov The Dnieper, Don and Kuban carry their waters. The water of these rivers is actively used in agriculture for irrigation. In ancient times, a legendary path ran along the river system of the East European Plain "from the Varangians to the Greeks."
Rivers of the internal drainage region (Aral-Caspian basin)
The Caspian Sea basin covers the interior regions of the East European Plain, the Southern Urals, and the eastern part of the Caucasus. It is called endorheic, since the Caspian does not communicate with the World Ocean and is a sea-lake. The most famous rivers of this basin - Volga, Ural, Araks, Terek.
The Volga basin occupies approximately $34% of the area of the East European Plain. When it flows into the Caspian Sea, the Volga forms a vast delta (about $80 branches). Today the Volga is actually a whole cascade of reservoirs.
The canal system made it possible to unite the navigable rivers of the East European Plain into a single transport system (Volga-Don Canal, White Sea-Baltic Canal).
Note 3
The rational use of rivers is today one of the most important areas of the state’s environmental policy. For improper economic activity can lead to global irreversible changes in nature, to the disappearance of many rivers, especially the so-called “small rivers”.
Rivers are natural water streams flowing in the depression they have created, the bed, and are fed by surface and underground runoff from their territory and basins. A “river basin” usually means an area bounded by a watershed line, the flow from which flows into the main river and its tributaries. Rivers have a source - the place where the river (lake, spring) begins and an estuary - the place where the river flows into another river, lake, sea (mouths can be “blind” or “dry”). The main river and its tributaries form a river system. Between river basins there is a border - a watershed. The set of all watercourses and reservoirs of a territory is called a hydrographic network.
The most important characteristics of a river include its water content, flow structure according to food sources, type water regime, length of the river, catchment area, slope and fall of the river, width and depth of the channel, cross-sectional area, water flow speed, its temperature, chemical composition water, etc.
All rivers are divided into mountain rivers with fast currents, flowing in narrow valleys, and lowland rivers with a characteristic slow flow and wide terraced valleys.
According to the sources of river nutrition and the distribution of their flow by season, 38 types of water regime are distinguished.
Rivers are characterized by a very uneven distribution of flow over time. The main phases of the water regime of rivers are high waters, floods and low water.
The natural mineralization of most rivers is relatively low - usually less than 200 mg/l. Their water would be quite suitable for drinking if it were not contaminated with waste from economic activities.
River- a natural constant water flow flowing in a depression created by it - a channel. In turn, the channel is only part river valley– a linearly elongated depression, along the bottom of which a river flows in accordance with the slope of the bed. In mountain rivers, the bottom of the valley is almost completely occupied by the river bed; in lowland rivers, it is occupied by the bed and floodplain. Channels most often have a meandering shape, but large rivers and rivers in the foothills can branch into branches. Channels of a relatively rectilinear shape are less common.
Every river has source- the place where the river originates, where the river bed acquires a clearly defined outline and a current is observed in it. Rivers can originate from springs, glaciers, or lakes. It is sometimes said that rivers are also formed by the confluence of two other rivers. In fact, a new river toponym, that is, a new name, can arise in this way, while the constituent rivers, no matter what they are called, have typical sources. Example: the rivers Biya and Katun give rise to the Ob. The Amur begins at the confluence of the Shilka and Argun rivers.
Estuary– a place where a river flows into another river, lake or sea. A river may have a “dry mouth”, i.e. it may end at a “blind end” if in the lower reaches the slopes of the territory through which the river flows are very small, the water consumption for evaporation, filtration into the ground or for irrigation is high (Chu Tarim rivers , Murgab, etc.).
Hydrographic network– a set of watercourses and bodies of land of natural origin (rivers, lakes, swamps) and reservoirs within a territory. River network– a set of rivers located within this territory; it is part of the hydrographic network.
The river network consists of river systems.
River system- the main river with its tributaries. For example, a significant part of European Russia is occupied by the Volga river system with its tributaries. Usually the longest and deepest river is considered the main one. But a number of names of the main rivers were strengthened historically; the main river became the one that people knew earlier and better. For example, the Volga is inferior in length to both the Oka and Kama from its source to its confluence with them; The Missouri is longer and deeper main river Mississippi. According to one classification, the tributaries of the main river are called tributaries of the first order, their tributaries are called tributaries of the second order, etc. According to another classification (by the American hydrologist Horton), a river of the first order (elementary river) is considered a river without tributaries, rivers of the second order are formed at the confluence of two rivers of the first order, rivers of the third order - at the confluence of two rivers of the second order, etc. Thus, the higher the order number of the river, the more complex nature has a river system. There are other approaches to classifying rivers.
River basin- Part earth's surface, which includes this river system. Most large swimming pool the Amazon has 7.2 million km 2. drainage basin- the area of land from which a river system collects its waters. It may be smaller than a river basin if there are drainage areas within the latter (for example, as in the Irtysh basin).
Watershed– a line on the earth’s surface dividing the drain atmospheric precipitation along two oppositely directed slopes. All Earth can be divided into two main slopes along which water flows from the continents: 1) into the Atlantic and North Arctic Ocean s; 2) in Quiet and Indian Oceans. Between these two slopes passes World watershed, or the Main Divide of the Earth. The watersheds between the peripheral areas and the internal drainage areas are called internal watersheds. Watersheds between oceans and seas separate areas of land, the flow from which is directed to different oceans or seas. River watersheds are the dividing lines of river systems. Watersheds are better defined in the mountains than on the plains.
Very rarely on accumulative plains it is impossible to draw watersheds at all, since the mass of water from one river is divided into two parts, heading to different river systems. This phenomenon of bifurcation of the flow is called river bifurcation. A striking example of a bifurcation is the bifurcation of the Orinoco River in the upper reaches: one of them. which retains the name Orinoco, flows into the Atlantic Ocean, the other, Casiquiare, flows into the Rio Negro River, a tributary of the Amazon. There are bifurcations of rivers flowing through the Primorsky lowlands of northeast Russia between the mouths of the Indigirka and Kolyma. A unique case of bifurcation is demonstrated by the Onega in its lower reaches, being divided into two branches by a huge island composed of bedrock. The branches diverge over a distance of up to 20 km and converge again near the mouth.
Each river has certain morphometric characteristics.
River length– the length of the river bed from source to mouth.
River meandering is determined by the coefficient of tortuosity of the river bed (K) - the ratio of the length of the river along the bed ( l) to the length of the river along the valley bottom (L). K= l/L. The tortuosity coefficient is usually calculated for individual river sections.
Density of the river network (D) is the ratio of the total length of all rivers of the river system to the river basin (F): D=ΣL/F km/km 2 .
Longitudinal profile The river is characterized by the longitudinal profile of the bed of the channel (it always looks like a wavy line) and the water surface (a smoother line). The fall of a river is the height difference between the source and the mouth of a river or the difference in heights of two points on the water surface along the length of the river ( h m).
River slope– the ratio of the magnitude of the river fall to the length of the river ( l) or to the length of a certain section of the river ( i=h/l). The slope of a river is a dimensionless quantity. Its values are very small, especially on lowland rivers. Thus, the slope of the Oka in the middle reaches is only 0.00009, so the slope is often replaced by a kilometer drop - a value physically identical to the slope, but expressed in m/km. The kilometric fall of the Oka is 0.09 m/km.
The longitudinal profiles of rivers are different depending on the properties of the rocks composing their beds and slopes. In most lowland rivers flowing through loose sediments, it has the appearance of a concave curve, flattening towards the mouth. In mountain rivers, the longitudinal profile of the channel is usually stepped, and the steps are associated with unequal erosion of the rocks composing the channel. In places where rocks are hard to erode, profile breaks are observed in the form of thresholds or steep ledges, which are associated with rapids or waterfalls, respectively. There are also rapids on lowland rivers, for example the famous Dnieper rapids, formed when the Dnieper crossed the crystalline ledges of the Ukrainian shield. The length of rivers flowing from lakes is typical of convex or convex-concave longitudinal profiles.
Water section of the river is the cross section of a riverbed filled with water.
Live cross section of the river– cross-sectional area of the flow. That part of the water cross-sectional area where there is practically no flow is called dead space.
The elements of the river’s water section are: its square (ω); channel width(IN); maximum depth (h max), average depth, which is calculated by the formula h medium = ω/V; wetted perimeter(P) – the length of the underwater contour of the river from the edge of one bank to the edge of the other bank; hydraulic radius(R) – ratio of the water cross-sectional area to the wetted perimeter: R= ω/P. The hydraulic radius characterizes the shape of the channel in cross section: for lowland rivers it is almost equal to the average depth. The width of the river and maximum depth are determined by direct measurements. Based on slopes, flow velocities and the general hydrological regime in rivers, three flow sections can be distinguished: upper, middle and lower.
The upper reaches of many rivers are mountainous, and even among lowland rivers they are most often located on hills. There are high current speeds, a rocky bottom, rapids, rapids, sometimes waterfalls, and low water temperatures are common. Mountain rivers have a similar character almost throughout their entire length, excluding where they cross intermountain depressions. In sections of the middle reaches of lowland rivers, flow speeds are lower; the bed is composed of sand, gravel, and pebbles. In the lower reaches of the river, they are characterized by low flow speeds, long floods, small sediments, and low banks.
Literature.
- Lyubushkina S.G. General Geography: Textbook. a manual for university students studying specialties. "Geography" / S.G. Lyubushkina, K.V. Pashkang, A.V. Chernov; Ed. A.V. Chernova. - M.: Education, 2004. - 288 p.
Inland waters - lakes, swamps, rivers, reservoirs, groundwater and glaciers - are the main source fresh water on the planet. They are very important for us, since people mainly use this type of water for their needs.
Inland waters are also a component of the landscape and are interconnected with its other components. In addition, they themselves can influence the landscape. Groundwater, for example, gradually erodes the soil and directly changes the surface topography; groundwater affects the formation of soils and vegetation. Rivers gradually wash away their bottoms and deepen, washing stones and making intricate patterns on the surface.
River Basins
Russia is very rich in river systems. They are very important for the economy. They are used for fishing, navigation, field irrigation, energy supply and water supply to populated areas.
Rivers are distributed unevenly, since their life sums up the climate regime, relief features and others. important features nature. They carry their waters to 14 seas washing the territory of our Motherland: 13 seas three oceans(Pacific, Atlantic and Arctic) and into the drainless Aral-Caspian basin, the boundaries of which run along plateaus, mountain systems, hills, among forests, swamps, steppes and semi-deserts.
The largest area of Russia occupies Arctic Ocean basin. Its area reaches 11.7 million m^2. It receives water from the rivers of the Urals, the East European Plain and Siberia. The largest rivers of Russia flow into it - Indigirka, Ob, Pechora, Yenisei, Lena, Northern Dvina, Kolyma. The longest river flowing into the basin is the Lena (4,400 km), the largest catchment area is the Ob River, 2,990 thousand square meters. km; The largest average annual flow at the mouth of the Yenisei is 630 cubic meters. km.
The eastern part of Russia is occupied by Pacific Ocean basin, with an area of 3.3 million km^2. From afar, the Amur carries water into the Tatar Strait, whose length reaches 2820 km. The remaining rivers are relatively short in length, since the watershed passes through the mountains and is close to the shores of the Pacific Ocean.
In the west is Atlantic Ocean basin. The rivers in this territory flow into 3 different seas - the Black, Azov and Baltic. The river systems of this basin have one peculiarity: they are located close enough to build canals.
In the northern part of the huge endorheic basin of Eurasia there is Endorheic Aral-Caspian basin, with an area of 4.9 million km^2. It, in turn, consists of three basins: Balkhash, Aral and Caspian. The largest area is occupied by the Caspian basin (3 million km^2, which is 60% of the total area). The largest rivers of the world flow into this basin from the north and south: the Volga (3530 km), Syr Darya (2660 km), Amu Darya (2540 km), Ural (2430 km), Kama (1805 km) and Kura (1360 km).
Nutrition of Russian rivers
Russian rivers receive water from rain, glaciers, underground drains and melting snow. Based on the sources of nutrition, there are several types: rain, snow and mixed with a predominance of snow, rain, ground and glaciers.
Most common snow food, or mixed with a predominance of snow. This type includes the rivers of the Black Sea and Caspian lowlands(80% of the annual flow), as well as the Volga, Yenisei, Ob, etc.
Rivers of this type are divided into 3 groups: with spring floods, with spring-summer and summer floods, and with flood regime. The most common rivers are those with spring floods, since Russia is covered with a stable snow cover. Less common are rivers with spring-summer and summer floods.
Floods in warm periods of the year are caused by rains and melting glaciers in mountainous areas. The least common are rivers with flood conditions. They are characterized by a sharp rise in water during heavy rains. In the areas of the Black Sea slope of the Caucasus, the climate is warm and there is a lot of moisture, so floods on the rivers occur throughout the year.
The rain feeds the rivers with a monsoon climate, such as Amur. Mountain rivers with modern glaciation are fed by glaciers. Absolutely all rivers receive a share of groundwater.
Thermal regime of rivers
The thermal regime of rivers depends on climate, temperature, groundwater that feeds the river, and the presence of permafrost, glaciers and lakes. On the Kola Peninsula and Karelia, the average temperature of river water in summer is +14 C0, and in the south in the lower reaches of the Volga, it reaches +24 C0. In the North-Eastern part of Siberia, the temperature of rivers in summer does not rise above +6 C0. Very low temperature (+1+2С0) of water at the sources of rivers that flow from under glaciers.
In winter, almost all Russian rivers freeze. On the Taimyr Peninsula, rivers are covered with ice already at the beginning of September, and by the end of September they already take on an icy appearance. The rivers in southwestern Russia are the last to become covered with ice.
According to the ice regime, rivers are divided into 4 groups. Most rivers have stable annual ice composition with varying durations; slightly fewer have unstable ice composition, which is not observed annually. There are also rivers where ice phenomena are observed, but there is no ice composition and absolutely no ice formations (places where winter time the air temperature is above 0).
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The material was found and prepared for publication by Grigory Luchansky
Source: Report "Movement along rivers". Types of riversOur country has a large number of rivers on which you can sail on tourist boats. All of them are different from each other and at the same time have common characteristics that allow them to be combined into types. Water tourists have developed at least five classifications. Their use allows you to correctly solve the problem that each tourist group sets for itself when choosing a route; where to go, when to go and why to go.
TERRAIN AND RIVER
This classification primarily reflects the nature of the river depending on the topography of the geographical area where it flows. According to this classification, rivers are divided into lowland, mountain-taiga (sometimes called foothill) and mountain.
Plain rivers. There are a lot of lowland rivers in Russia. They have wide valleys, with insignificant depth and steepness of the slopes, small slopes, their channels are, as a rule, tortuous and composed of soft sedimentary materials (sand and clay), the speed of water flow in the channel is low, as a rule, no more than 1 m/s , the banks are most often covered with forest or bushes. There are usually no rocks in the channel; obstacles are represented by sandbanks and riffles, as well as rubble from trees washed away or carried by water. This type of river is most clearly represented by the large rivers of the European part of the country - the Volga, Dnieper, Western Dvina and their tributaries, for example Vetluga, Desna, tributaries of the lower reaches of the Ob, for example Lyapin.
However, in the riverbeds of the European part, flowing through hills and mountain ranges, there are areas where bedrock comes to the surface, forming rapids. The most famous are the now flooded Dnieper rapids and the Migei rapids on the river. Southern Bug, Opechenskie rapids river. Msta. There are large numbers of rapids on the rivers of the Northern European part. The rapids alternate with long, calm, almost flowless reaches. These rivers belong to a special Karelian type, for example the river. Okhta in Karelia, r. Leather in the Arkhangelsk region.
Mountain taiga rivers. Rivers of old mountain regions, such as the Urals or the relatively low mountain systems of the Sayans, Eastern Siberia and the Far East, belong to this type. Rivers often flow in rocky banks, forming rapids, rifts, waterfalls, and cheeks. There are also rubble, as well as shallows and rifts made of large pebbles and cobblestones. The slopes of mountain taiga rivers reach 10 m/km, the flow speed in the rapids is 4 m/s. Mountain taiga rivers, as a rule, have fairly developed gorges and valleys; rapid areas are interrupted by rather long reaches and rapids. Typical mountain taiga rivers can be considered the river. Kozhim in the Urals, r. Kantegir in Sayany, r. Vitim in Transbaikalia.
Mountain rivers. These include rivers in the high mountain regions of the Caucasus, Tien Shan, Pamir-Alai, Pamir, and Altai. Compared to the mountain-taiga ones, they have an even steeper drop (up to 20 m/km), there are very few reaches, the rapids pass one into another often without interruption, the flow speed in the rapids reaches 6-7 m/s. Mountain river valleys are located at considerable heights and are often poorly developed. Examples of mountain rivers are Obihingou and Muksu in the Pamirs, Zeravshan in the Pamir-Alai, Nary in the Tien Shan, Shavla in Altai. Some steep rivers of the Carpathians, for example, the sources of the Cheremosh and Prut, belong to the same type.
It should be noted that the boundaries between the types of mountain and mountain-taiga rivers are somewhat blurred. In addition, the same river can belong to three or two types, usually in the upper, middle and lower reaches, respectively. Thus, Chulyshman, along almost its entire length, is a mountain river, Biya, which is, as it were, a continuation of Chulyshman below Lake Teletskoye, is a mountain-taiga river, and the Ob, one of the sources of which is Biya, is a plain river. Kosyu, a tributary of the Usa, is a mountain-taiga river in its upper reaches, and a flat river in its lower reaches. There are examples of reverse alternation. Thus, the Tsipa, a tributary of the Bitim, is a lowland river in the upper reaches, within the Bauntovskaya Basin, and a mountain taiga river in the lower reaches.
SIZE OF RIVERS AND WATER CONTAINMENT
TO big rivers include rivers flowing within several geographical zones and having a basin area of more than 50,000 km 2, for example the Volga, Dnieper. Medium-sized rivers flow within one geographical area and have a basin area from 2,000 to 50,000 km 2, for example, the Kem, Meta, Sakmara, Obihingou, Chulyshman rivers. Small rivers include rivers with a basin area from 1,000 to 2,000 km 2, for example, the Sandalash and Ulug-O rivers.
NATURE OF NUTRITION AND WATER REGIME
Rivers with high spring floods. Most of the rivers in our country that flow in areas with abundant snow cover (East European Plain, West Siberian Lowland, Ural) belong to this type. Spring floods caused by melting snow provide up to 40-60%, and sometimes more, of the entire annual runoff. The flood passes into the summer low-water level, which can be low in dry summer, average in summers with average precipitation and high in rainy summers. The low water level is very stable and changes slowly.
Rivers with moderate spring floods and summer rain floods. These are the rivers of the Carpathians, the western foothills of the Caucasus and Transcaucasia, and the mountains of Southern Siberia. The fairly high spring flood, caused by snow melting, extends until the beginning of summer due to the height of the basins above sea level. Heavy summer rains cause flash floods. Due to the narrowness of the valleys and steep slopes, rainwater quickly flows into rivers. Therefore, the spring flood almost without interruption turns into summer floods, of which there are 8-10 per summer. Thus, the share of summer runoff increases, and the share of spring flow drops to 30-40%.
Rivers with low spring floods and predominant summer floods. This type includes rivers in the highlands of the Caucasus and the mountains of Central Asia and rivers located in the eastern regions of the country with a monsoon climate (most of Eastern Siberia and the Far East). On the rivers of the highlands, a stable summer flood is caused by the melting of glaciers; on the rivers of Eastern Siberia and the Far East, by monsoon rains. The share of spring runoff drops to 20-30, the share of summer runoff increases to 50-60%.
COMPLEXITY OF THE ALLOY
This classification is purely tourist. It is contained in the “List of Classified Tourist Routes” and is revised once every four years in connection with the emergence of new vessels, the development of water tourism technology, and the emergence of new means and methods of ensuring safety. It can also change depending on the water flow in the river (with high water flow during the flood or flood period, the difficulty of passing the river usually increases). This classification also depends on the class of vessels used: for kayaks, the river is usually more difficult.
All lowland rivers in their technical complexity do not exceed the first category, that is, they do not contain obstacles that are of an individual nature and require an individual approach (thresholds and rifts). The exception is Karelian-type rivers with routes up to the third category of difficulty inclusive.
The most typical obstacles on rivers of the first category of complexity are shoals, riffles and rubble, as well as artificial obstacles - low bridges, dams, etc. However, these same rivers pose an increased danger during the spring flood period.
Large rivers are interesting for water tourism, as a rule, in the upper reaches, significantly above the beginning of navigation. On medium and small mountain taiga and mountain rivers, routes from the second to the sixth category of difficulty are possible. It is safer to take routes along the rivers of the highlands in the spring before the start of the summer flood or in the fall after it ends.
MAIN ELEMENTS OF THE VALLEY AND RIVER BED
Rivers are natural, significant and continuous flows of water, fed mainly by precipitation (rain, melted snow water, glacial water), and are formed wherever the terrain has at least a slight slope. The river itself forms the channel along which it flows, and in this way it differs from artificial watercourses. The connection of rivers with each other, the totality of all rivers pouring their waters into one lake or sea, is called a river system. In each river system, there is a main river and its tributaries, which, in turn, can receive tributaries of the second, third order, etc.
Each river system collects surface and groundwater from the area it occupies, which is called the drainage area, or river basin. The basins of neighboring rivers are separated from each other by watersheds, usually passing through the most elevated places in the region. Occasionally, bifurcations occur, that is, the division of rivers into two streams, one of which flows into a river in another basin.
The place where the water forming a river first takes the form of a surface flow is called the source. A river can begin as a spring, flow out of a lake, swamp, or originate from the tongue of a glacier.
Some rivers are formed from the confluence of two rivers that are usually close in water content, for example, the Ob begins from the confluence of the Biya and Katun, the Northern Dvina - from the Sukhona and the South. In this case, when determining the length of the river, the longer of the component rivers is taken as the source.
The final section of a river where it flows into the sea, lake or other river is called the mouth. At the mouth, the speed of water flow slows down and most of the particles carried by the water are deposited opposite the mouth in the form of a shoal.
River Valley – These are narrow and elongated, mostly winding, hollow landforms formed as a result of the activity of a river flow. Valleys are limited by coastal slopes, or sides.
Rice. 1. Elements of a river valley:
1 - edge; 2 and 3 - left and right slopes (sides); 4 - floodplain; 5 - level during high water; 6 - level during low water; 7 - shore height; 8 is the width of the river at high water; 9 - river width at low water; 10-terrace; 11 - valley width
The lowest point of the valley is called the bottom, the upper edge of the coastal slope is called the edge. The bed of the river along which it flows into the low-water level is called the channel. During a flood, that is, with a rise in water, the river leaves the channel and floods the bottom of the valley - the floodplain.
The slopes of a river valley have the form of ledges or steps with more or less horizontal surfaces, which are called terraces. There may be several terraces. Each river terrace is a trace of an ancient, higher valley floor.
The classic form of a river valley with a full set of its elements is found only on lowland rivers. On mountain rivers there is often no floodplain and the river bed occupies the entire bottom of the valley and comes close to the bedrock bank.
In mountainous and mountain-taiga areas, rivers often flow in deep narrow valleys with steep slopes - canyons, which, depending on the hardness of the rocks, can be of one form or another. Rocky, steep high banks of a river (in mountain taiga regions) are called cheeks(Siberian name). Cliffs located opposite each other on both sides of the river are also called cheeks. A sheer rocky wall more than 5 m high in a narrow place in a river valley or a cape protruding into the river and making it difficult to walk along the shore is called bom.
The cross-section of a river bed is rarely symmetrical; it is especially asymmetrical at turns, where water circulation occurs along the surface from the convex bank to the concave one, and vice versa at the bottom. Therefore, the concave bank erodes at turns, gradually approaching the side of the valley, where it eventually reaches the bedrock bank, composed of more ancient rocks.
The highest, steepest and steepest part of the bedrock bank is called rage. The part of the ravine upstream of the river, connecting to a straight section of the bank, is called the upper arm of the ravine, and the downstream part of the ravine, connecting to a straight section of the bank, is called the lower arm.
The erosion products of the concave, or outer, bank are transported by the bottom current and deposited near the convex, or inner, bank, forming a low, gently sloping sandbank. The depth of the channel from the convex bank to the concave bank (ditch) increases slowly. Immediately beyond the end of the ravine, the sand becomes cut off, that is, the shore looks like a low wall with a depth sufficient for all tourist vessels near the shore. In the immediate vicinity of the ravine and cutting sand there is rod - line of highest water speed in a stream. Behind the lower shoulder of the ravine, the core passes to the opposite bank, therefore, near the ravine bank, the flow speed slows down and behind the lower shoulder of the ravine a a bit - underwater sandbank of relatively small size.
All river valleys, and especially the channels, are tortuous, that is, they consist of alternating turns, or meander. Meanders with closely converging beginning and end are called bows. A typical example is the famous Samara bow on the Volga in the region of Kuibyshev, which includes the Zhiguli Mountains. The path along the river between the beginning and the end Samara bow more than 7 times the shortest distance between them by land.
At the beginning of the Samara Luka the river flows into the Volga. The mustache flowing very close to the end of the bow at the village. Transfers. This made possible the well-known circular water route with a small portage of the first category of complexity “Zhigulevskaya Around the World”.
The river bed often meanders within the valley. Gentle meanders of the riverbed within the valley are called bends, steep and short ones are called knees. The meanders of the river channel within the valley often change, the river washes out a new channel, and an island is formed, washed by two channels. The shorter and straight channel becomes the main channel, the longer channel, which was previously a bend or elbow, is closed by sediments, first at the outlet, and then at the entrance, forming an elongated floodplain lake - an oxbow lake. The oxbow in high water connects with the river.
Rice. 2. Turns of the river bed and valley:
1 - gyrus; 2 - valley border; 3 - bend; 4 - bow
OBSTACLES ON RIVERS
Roll. A complex formation of two shallows growing from opposite banks towards each other. Riffles often exist in places where the direction of channel turns changes, that is, in places where the flow core passes from one bank to another. Rifles long time exist at the same place in the riverbed. There are three types of rifts: normal (Fig. 3), shifted and scattered. All riffles consist of upper and lower spits or shallows, between which there is the crest of the riffle, where the depth is smallest and the current speed is highest. In the crest of the riffle there is a trough - a channel with the greatest depths. From above, a pressure slope with a gradually decreasing depth leads to the crest of the riffle; immediately behind the ridge downstream there is a basement of the riffle with a sharp increase in depth.
The parts of the channel located above and below the crest of the riffle are called upper and lower reach valley.
On lowland rivers, all elements of a sandy riffle can be easily identified on the river by the color of the water - the deeper places are dark, in the shallower places yellow sand shines through. On mountain and mountain-taiga rivers there are also rifts, shallows and other elements described above, composed of products of channel erosion; they can be composed of both sand and pebbles of various sizes, up to cobblestones.
The shifted riffle (Fig. 4) is distinguished by the fact that the upper and lower reach valleys strongly overlap each other, each continuing along its own bank, while the ridge
The roll can be directed along the longitudinal axis of the river or even so that the direction of the flow in the trough will make an angle of more than 90° with the direction of the river flow. In a shifted riffle, swell currents appear across the ridge in addition to the trough, which can mislead the tourist and drag the ship aground. Placer rifts have several ridges, vaguely defined troughs and spits located in the channel without any visible pattern, so they are especially difficult to pass.
The tourist navigation guide classifies elements of the bed and water flow that are not found on navigable rivers and are characteristic mainly of small and medium-sized rivers on which sports tourist trips are carried out.
Threshold. A section of a river bed with a sharp increase in slope and flow speed relative to sections above and below the threshold. Rapids are formed in places where a river crosses rocky ridges, moraines, outcrops of hard-to-erode bedrock, accumulations of boulders, products of mountain falls and mudflows, and the consequences of human activity, such as blasting when laying roads (artificial or explosive rapids). In front of local rapids with a particularly steep drop, areas of calm water (reaches) sometimes form due to the damming of the river by the rapid.
Characteristic elements of a rapid are weirs, water holes or barrels, and standing waves.
Spillways. They are divided into waterfalls (angle of incidence more than 45°), waterfalls (angle of incidence about 45°) and simply plums (angle of incidence less than 45°). Gentle drains usually have the shape of a triangle formed by the line of greatest inflection of the longitudinal profile of the river bed and oblique streams from the rocks limiting the drain at the base. Converging oblique jets lead to the appearance of a standing wave or a track of standing waves behind the vertex of the triangle. Steep drains, waterfalls and waterfalls usually form immediately behind the drain a water hole, or barrel - an area of reverse flow along the surface, and behind it a system of standing waves. In this case, a triangle is not formed. A rapid may have one drain the entire width of the river; it can also be divided by protruding rocks and stones into several drains of varying widths and thicknesses.
The threshold may also consist of several successive discharges. If in a threshold one discharge or successive discharges of the threshold occur one after another with an interval not exceeding the length of the vessel, the threshold is called single-stage. If between successive discharges of the threshold the ship can freely maneuver to move from one bank to the other, the threshold is called multi-stage. If between two successive discharges it is possible to moor to the shore on a raft, it is advisable to consider these discharges as belonging to different rapids. If the line of greatest inflection of the longitudinal profile of the river bed in the drainage is perpendicular to the direction of water flow, then the drainage is called straight. The drain is called oblique when the angle between the inflection line of the longitudinal profile and the flow is acute. Sometimes in a narrow oblique drain on the line of inflection of the longitudinal profile, the depth of the channel near the banks is very different, then the drain will be twisted, or helical.
Standing waves, or waves. They are formed during the movement of water in drains due to the addition of longitudinal, transverse and reverse local velocities of water in the flow, which arise when water encounters heterogeneities in the cross-section of the channel. A standing wave is formed below the inhomogeneity to which it owes its birth. Waves are called standing waves because they are motionless relative to the shores, in contrast to moving wind and tidal waves. The height of standing waves reaches several meters and depends on the water flow in the river, the speed of the current, the depth of the river and the bottom topography.
Standing waves whose crests are perpendicular to the direction of water flow are called straight waves, waves whose crests are located at an acute angle to the flow are called oblique. The sources of direct standing waves are, as a rule, distortions in the flow cross-section at the river bottom, for example, a ridge of underwater rocks. Oblique standing waves are most often formed due to distortions of the coastline, for example, near coastal ledges. Standing waves also occur when two streams merge, for example at the confluence of a large tributary. In such places, a system of many steep point standing waves sometimes appears. An important characteristic of a standing wave is the length of its slope, which is compared with the length of a tourist ship. Waves can be steep, or short, when the slope is less than half the length of the tourist vessel, and flat, or long, when the wave slope is equal to or greater than the length of the tourist vessel. Very short standing waves have a reverse crest, like a water peak, directed against the current.
Water holes or barrels. They form behind very powerful and steep plums (Fig. 5). They are characterized by a strong reverse flow of water at the surface. A barrel can be considered small if its size is less than half the length of the vessel, and large if it is larger. Water in barrels often contains a lot of air, so it has less specific gravity and holds the ship worse.
Shivera. A rocky section of a river bed with a fast current, shallow depths and randomly scattered underwater and protruding stones in the riverbed. On rifts, due to the high flow speed, standing waves, reverse currents, and sometimes water holes (barrels) appear in the stream. Unlike thresholds, shivers do not have clean, powerful drains; in a shiver, the drains are local, the connection between successive drains with each other is poorly visible, so it is difficult to identify the line of predominant water flow - the jet. The length of the rift varies from several tens of meters to several kilometers. Rapids often begin and end with shivers.
Clamps. On fast-flowing rivers, pressure often forms, that is, piles of water on the steep, most often rocky, outer bank of the river bend under the influence of centrifugal forces. Clamps are formed at very sharp turns, since at turns the flow core is located close to the outer bank of the turn, a significant mass of water falls on it, and directly near the shore various distributions of velocities are created across the flow. If the river's water content is significant and the turn is very sharp, breaker shafts are formed near the shore. The distribution of currents in the clamp in this case will have the form shown in Fig. 6b. When the river's water content is high, but at a less sharp turn, as well as when the bank has a negative steepness under water, a breaker shaft may not occur. Then the distribution of flows in the clamp will have the form shown in Fig. 6 a. A similar picture occurs in the clamp at a fairly sharp turn in a flow with low water flow. Clamps with a breaker shaft are easily recognized on the river by their breaker shaft, clamps without a breaker shaft are much more difficult to recognize, and the suction to the shore in them is much stronger.
Catches. On fast-flowing rivers, countercurrents can form in planes parallel to the river bottom - catches (Fig. 7). Their occurrence is associated with the separation of the flow from
banks for one reason or another (bank protrusion, tributary confluence, etc.). Catches are created at pressure points, near riffles, during sharp expansions of the channel, on shallows and during sharp accelerations of individual parts of the flow (jet), for example, when two channels merge. It can sometimes be difficult to get out of a catch, since you need to have time to leave the stream that forms the catch, crossing it in a short time.
Boundary of opposing currents or currents with different speeds. It occurs when tributaries flow into a river (especially if the tributaries are comparable in water flow to the main river), when the flow flows around large surface obstacles (stones, rocks, slabs). These boundaries are very small in length (sometimes the length of the transition from one speed to another is 30-50 cm) and are dangerous because a tourist vessel, having the speed of one stream, suddenly, in its individual parts, falls into a stream with other speeds, instantly experiencing the action of various forces . To avoid capsizing the vessel when crossing the border of opposing currents, it is necessary to use a variety of technical techniques.
A blockage or a crease. Characteristic obstacles characteristic of lowland rivers of the taiga zone and mountain taiga rivers are formed by tree trunks placed on the top of the island, at the entrance to a small channel, on the outer bank of a river bend. During the flood, the rubble is carried away, but when the water recedes, they appear again, they also appear during summer floods, and on small and narrow taiga rivers they can exist and increase in size for years. The blockage is a very dangerous obstacle; it is difficult to recognize, since from a distance it seems to be part of the shore and only in the immediate vicinity does a strong current begin to be felt, sucking under the blockage. On mountain taiga rivers, a great danger is posed by trees located on the outer banks of the river's bends that are being washed away, partially washed away but not yet fallen, and bent low over the water. Such trees are especially dangerous for ships with relatively high rowers - rafts and catamarans.
On rivers flowing in populated areas, there are artificial, that is, created by people, obstacles.
Bridges. There are often transport and pedestrian bridges and footbridges. Bridges are installed on supports standing in the riverbed. The supports pose the same danger to a tourist vessel as single surface rocks in an area with a fast current; the width of the passage between the supports and the direction of the current matter. Near modern reinforced concrete bridges, there are usually a lot of concrete blocks and reinforcement in the riverbed. Pedestrian bridges often have wooden supports located closer together and low decks. Near modern, new bridges in the riverbed there may be remains of supports or piles of old bridges located nearby.
Dams. There are mainly two types of dams - modern reinforced concrete operating dams and ancient stone-wood mill dams or regulating flow for timber rafting. Dams of the second type are in various stages of destruction and represent spillways of varying steepness and height, and are clogged to varying degrees. Often these spillways are passable, especially for kayaks. Reinforced concrete dams require demolition.
Stabs. Fences made of wooden stakes driven into the river bottom, blocking the entire river. The piers have narrow gates where tops for catching fish are installed. Stakes are mostly found as remains on small rivers, but stakes can pose a hazard to the hull of vessels.
Cables. The cables of ferry crossings hanging over the water pose a danger to tourist ships. Typically, these cables are raised high above the water near the banks of the river, where you should pass under them. It is very important to notice this cable in time.
Mole alloy. Although moth rafting of timber is almost no longer used, tourists may still have to encounter it. During rafting, tourists are not allowed to go out onto the river. Mole rafting usually begins immediately after the flood. On small rivers it ends quickly, on medium rivers it can last until the middle, and on large rivers until the end of summer. The rivers along which timber rafting has been carried out for many years are usually clogged with driftwood logs, one end of which lies at the bottom of the river, and the other end is shallow under the surface of the water. This end of the log is invisible, and encountering it while moving, especially against the current, ends in damage to the shell, and sometimes even damage to the frame of the vessel.
Zapani. On the rivers where timber rafting is carried out, all summer long there are dam systems made of narrow, several-log rafts, held by steel cables and blocking individual river channels in order to direct the rafted timber into the main channel. There are also storage pits that block the entire channel in order to accumulate timber for rallying or transshipment to the shore. As an obstacle, a jam is similar to a blockage—a drawing current goes under it, but you can’t get through it.
The trap can be passed under a high bank, where the cable is raised high above the water, and the logs do not reach the shore. You can also, while on the tank, temporarily separate or submerge the links of the tank. Storage areas usually always have a lot of forest, so they need to be surrounded.
Rye walls. On small rafting rivers (this is especially typical for the rivers of the European North and the Carpathians) there are often row walls made of logs, located on the concave outer banks of the channel bends, held from the inside by log cages with stones. The ryazhevy wall as an obstacle is similar to the clamp, but flakes from logs and metal staples holding the logs together often protrude from it.
The last type of artificial obstacles includes the general cluttering of the riverbed with a variety of objects, including sharp ones, within populated areas.
MAIN CHARACTERISTICS OF THE RIVER DETERMINING
COMPLEXITY OF THE ALLOY
Water consumption. An important characteristic of a river for a water tourist is water flow, that is, the volume of water flowing through the cross section of the stream per unit of time (m 3 /s). Water consumption depends on the size of the basin, its water content, the nature of the relief, geological structure, soil cover and vegetation of the area. Water flow is directly proportional to the area of the basin, therefore, the further downstream, the more water the river has, as more and more tributaries flow into it. The exceptions are rivers flowing through the desert, and rivers, part of the water of which is spent on irrigation, for example, Amu Darya, Syr Darya, Kuban, Terek.
The relief of the basin affects the amount of precipitation - the higher the mountains, the more precipitation, and the rate at which melt and rainwater enters the riverbed - the steeper the mountains, the faster the river collects melt and rainwater, the sharper the peaks of summer rain floods. The rate of entry of melt and rainwater into the river is also influenced by the nature of vegetation. Snow melts more slowly in the forest, the forest retains melt and rainwater longer; The steppe and desert quickly give water to the river.
To compare different drainage basins with respect to the amount of runoff, the value of the runoff module is introduced, that is, the ratio of water flow in a given river section to the area of the basin above this section. The runoff module is the amount of water in liters that the river receives from each square kilometer of the basin in one second, measured in l/km 2 *s. The greatest flow is in the mountains. On the northern slope of the Caucasus it reaches 50, and in Western Transcaucasia 75 l/km 2 *s. Large flowing lakes are among the most powerful flow regulators. If there are many lakes in the river basin, then all flood peaks will be smoothed out, extended in time and small in amplitude.
Water consumption is also influenced by climatic factors: temperature and distribution of precipitation by season.
High water. This is the phase of the highest standing water in the river. On lowland rivers of a temperate climate it is caused by the melting of snow (spring flood), on mountain rivers by the melting of glaciers and snow (summer flood).
Flood. A relatively short-term rise in water in the river as a result of heavy rains. Usually it has a pronounced peak - the highest level, which moves along the river at the average speed of its flow, forming a flood wave. Before the peak passes, the water rises, after passing - it decreases. A flood peak can be caused artificially, for example, by opening a reservoir dam in the upper reaches of a river, or by breaking a dam (ice or ground) holding a lake in the upper reaches of a mountain river.
Flood rise (Fig. 8a) is characterized by a higher water level at the core and its transverse circulation along the surface from the middle to the shores (small debris floats near the shores). The decline of the flood (Fig. 8b) is characterized by a higher water level near the banks and its transverse circulation along the surface from the banks to the middle (small debris floats in the middle of the channel). A flood, and especially a flood, is also characterized by muddy, dirty water. The flood may also be caused by the melting of glaciers in the river basin.
Low level. The summer season in the vast majority of tourist areas of the country corresponds to the low-water level - the lowest water level, when there is no significant influx of snow and rain water into the river. In the highlands and the Far East, the low-water period shifts to autumn. The average low-water level corresponds to the average year for climatic conditions. During low-water periods, the river seems to be in a steady state, channel processes hardly occur, and the channel most fully corresponds to the water flow flowing in it. However, in case of rainier summers, tourists face high water.
This is not a flood, but simply a larger than average influx of water into the river, that is, a higher low-water level. The water, as a rule, is clear, there are no sharp fluctuations in level, it comes close to the coastal bushes, flooding the pebble shallows and almost all the islands.
In a dry summer, a tourist may encounter low water - standing below the average low-water level. A characteristic sign of low water is a significant difference in flow speeds on reaches, rapids and rifts. You can hardly feel the current on the reaches. There are many pebble shallows and islands on the river, steeply plunging into the water. With a steady change in weather, a transition from high or low water to an average low-water level may be observed. Unlike sharp flood declines and rises, this transition lasts for one to two weeks and occurs in clear water.
Slope. A very important characteristic of a river is expressed by the ratio of the difference between the water edges of the beginning and end of a given section of the river to its length (measured in m/km or written as a dimensionless decimal). The slope of the river is a parameter that largely determines the speed of the flow. A river as a whole or a large section of it may be characterized by an average slope, but navigation conditions in small sections will be determined, among other factors, by the local slopes of these small sections.
Longitudinal profile of the river. A graph in which the water edges are plotted along the vertical axis, and the distances of the corresponding points from the source or mouth of the river along the horizontal axis. On the longitudinal profile it is easy to identify areas with different slopes. Typically, a river with a well-developed channel develops a longitudinal profile in the form of a parabola - it is called an equilibrium profile. On average, the slope gradually decreases from source to mouth.
In the upper reaches the slope can be significantly higher than average, but the river is low-water. Water velocities are high, the river often flows in one channel, and erosive (erosive) water activity predominates. In the middle course, the slope is close to average, the water content of the river increases, channels and islands appear, the eroding and accumulating activities of the river are approximately balanced. In the lower reaches, the slope is below average, the water content of the river has increased significantly, there are many channels and islands, the river mainly deposits material washed up higher. But all this is true on average. In practice, in any course of a mountain or mountain-taiga river there may be sections with both a small and a large slope. Some rivers in the upper reaches flow along swampy watershed plateaus and have a small slope, while they have a large slope only in the middle reaches, breaking through the bordering ridges (for example, such Siberian rivers as Tsipa, Temnik).
RIVER PASSABILITY
Water tourists are primarily interested in the river's passability - that basic and not easily perceptible characteristic, which consists of many factors and which is different for different types of rivers and different classes ships.
The passability of lowland rivers is determined mainly by sufficient water flow at the starting point of the rafting and the number of long-term impassable blockages on the river. The passability of mountain taiga rivers depends on the water flow at the starting point of the rafting, the slope and speed of the flow, as well as the nature of the valley. The blockage is of secondary importance. When mountain rivers are passable, especially with a predominance of glacial feeding, it is necessary to consider not only the minimum required water flow at the starting point of the rafting, but also the maximum allowable for safe rafting (on medium rivers).
In an average year in terms of climatic conditions, the country's lowland rivers flowing in the forest zone can be considered accessible for kayaking at a distance of at least 40 km from the source (according to a 1:1,000,000 scale map) or from the source itself, if the river serves as the only drainage lakes with an area of at least 80 km2. This corresponds to a low-water flow rate of 3-6 m 3 /s. On mountain taiga and mountain rivers, the minimum water flow at the starting point of the rafting should be 7-12 m 3 /s, depending on the slope, flow speed, and the nature of the valley. On mountain rivers fed by glaciers, such flow can be reached 10-15 km from the source (on rivers of Central Asia, sometimes directly from the glacier), on most mountain taiga rivers - 20-30 km. The greater the slope and speed of the current, the greater the water consumption required to begin swimming. However, to ensure the proper level of safety, all these characteristics are limited from above, and with the improvement of rafting technology, rafting means and means of insurance, this level is gradually increasing. For the most versatile modern vessels - multi-seat catamarans - rivers are now available with an average slope of up to 20 m/km and maximum slopes of individual short sections (3-5 km) of up to 40 m/km with water flow rates from 10 m 3 /s to 60 m 3 /With. For catamarans with an increased reserve of buoyancy and modern rafts with inflatable elements, these values can be taken higher by 10%, for frame-inflatable kayaks - lower by 20%, for rigid-frame kayaks - lower by 30-40%.
However, the slope itself mainly affects only the speed of the river. To determine its passability, it is much more important to know the degree of development of the channel and valley, which is determined by the slope of the river and water flow taken together, depending on the hardness and heterogeneity of the rocks of the channel and valley. A small stream and a large river, passing through the same level difference, make various jobs Therefore, with the same material, the channels and valleys are eroded differently. Where there is little water, the level difference is hard rocks will be triggered by steps, waterfalls, unsuitable for swimming; where there is more water, one can expect, even in hard rocks, the formation of a more uniform channel, possibly suitable for swimming. Therefore, from the point of view of cross-country ability, it is important to know the material and degree of development of the river bed and valley.
Rivers with poorly developed canyon-like gorges are less accessible for navigation. A poorly developed gorge indicates the hardness of the rocks or insufficient flow power: in both cases, in a poorly developed gorge one can expect difficult or impassable obstacles in the form of waterfalls and steep, high drainages. In a poorly developed gorge, it is also difficult to organize reconnaissance and insurance; the passage of rivers with such gorges is only possible for well-prepared and specially equipped groups.
Various forces act on a river flow, primarily gravity. The magnitude of its component affecting the water in the direction of flow depends on the slope of the river. The greater the slope, the greater this component, the higher the water speed. The speed of the current is ultimately the main factor determining the complexity and danger of the river for tourists. The gravity component is opposed by the friction force of water on the banks and bottom of the river and the force of internal friction between layers of water. These forces are determined by the degree of roughness of the material of the river bottom and banks, the depth and width of the riverbed. The larger the particles that make up the bottom and shores, the greater the friction force.
The water in the river is also affected by centrifugal force (at turns in the riverbed) and the Coriolis force caused by the rotation of the Earth. The centrifugal force acts from the center along the radius of rotation; the Coriolis force in the northern hemisphere is always directed to the right along the flow. These forces cause transverse currents in the river (the current caused by the Coriolis force can be ignored in tourist practice). There is a certain average flow velocity and local velocity. The local velocity is zero at the bottom and shores and is maximum at a certain line below the water surface (the corresponding line on the water surface is called the core).
According to the distribution of velocities in the flow cross-section, flows are distinguished as laminar, turbulent and with a spatial regime. Laminar flows, characterized by parallel movement of layers of liquid, are rarely encountered in tourist practice: they can only exist at very low depths, water velocities and channel slopes. Thus, with a river depth of 20 cm, laminar flow can exist at a flow speed of no more than 1 cm/s. A tourist almost always deals with a turbulent flow, characterized by the formation of vortices in the flow volume, that is, by the fact that different parts of the fluid have not only longitudinal, but also transverse velocity components. The vortices that arise at the bottom and shores break off and move toward the center of the flow. In a turbulent flow, the line of maximum local speeds is also below the flow surface, but the speed increases unevenly with distance from the bottom. At the very bottom there is a very thin layer of zero and low velocities, and then the velocities quickly increase and can reach, for example, already at a depth of one tenth 40-50% of the maximum speed, and at half the depth - 80-90% of the maximum speed. For turbulent flow, the maximum speed can be calculated. It is directly proportional to the slope and depth of the river and inversely proportional to the bottom roughness (the half-diameter of the particles that make up the bottom) to varying degrees. Below are graphs of the dependence of the maximum speed v on the slope i at various depths H and the roughness of the channel D, (Fig. 9) and on the depth at various slopes (Fig. 10), provided that the channel is assumed to be rectangular.
In Fig. 11 shows a graph of constant speeds with changes in slope, river depth, and constant channel roughness. If we take some kind of limit speed, for example 2 m/s, then we can determine at what combinations of slope, depth and bottom roughness the current speed will be higher or lower than the limit speed. Knowing that the flow speed largely determines the complexity and danger of the river, it is possible, by setting certain boundary speeds, for example 1.5 m/s, 3 m/s, to obtain from this graph approximate data on the slopes and depths at which the river will be uncomplicated , complex and very complex.
If the obstacle is underwater and has a smooth ridge (a large stone, an underwater ridge, a channel ledge, a dam), then the disruption of the flow structure occurs mainly in the vertical plane. Depending on the speed of the current and the relative (to the depth of the river) height of the obstacle behind it, either a system of standing waves is formed, parallel to the crest of the obstacle, or a vertical whirlpool zone with the movement of the surface layer of water opposite to the flow (a water hole, or a barrel - Fig. 5). Sometimes in tourist reports the complexity and danger of a river are assessed by such a parameter as the product of water flow and slope. This parameter to some extent gives an idea of the maximum speed of the river, since it is proportional to the slope to the power of one-half, and the water flow is proportional to the speed of the current. The attractiveness of this parameter is that both the slope and water flow can be obtained from tables of the main hydrological characteristics of the river. But it must be used carefully. More accurate results are obtained by calculating the maximum speed of the river. The maximum river speed during low-water periods is also shown on topographic maps. The speed of the current is affected by obstacles in the riverbed. The extent of their influence can be calculated. For example, massive protrusions in a channel with a diameter of 1 m, following each other at intervals of 5 m, reduce the flow speed by approximately 1.8 times, and dense aquatic vegetation from the bottom to the surface of the water by up to 10 times.
The river bed is designed in such a way that the least amount of energy is expended to move water. This condition is usually met on rivers with a well-developed channel and during low water periods. Rivers with insufficiently developed channels (in young mountainous regions), as well as during floods, carry many particles of different sizes, and the patterns indicated above do not always apply (so-called channel processes take place, that is, the formation of a channel). These patterns do not apply in places where the river narrows. In such cases, a completely different type of flow with a spatial structure can be observed, characterized by a strong displacement of the line of maximum speeds in depth, as well as the presence of a stable transverse flow along the surface of the river from the banks to the middle of the channel and along the bottom from the middle to the banks. This structure has no visible distinctive features and can be found in rapids, canyons, cheeks, and generally in poorly developed channels with high water flow. The tourist recognizes this flow structure when the ship is strongly pulled into the stream, when exiting the stream requires significant effort from the crew. The spatial flow regime is one of the cases of stable transverse velocity of water flow in the channel. Transverse velocities, reaching 30-40% of the maximum current speed and directed from the shore to the middle of the river, also arise due to vortex formation near the banks of the turbulent flow. These speeds have a random distribution in time and space.
A stable transverse velocity occurs at a river bend due to centrifugal force. There is always a circulation flow at a turn. On the surface, water shifts from the inner bank of the bend to the outer bank. At the outer bank, the water velocity is directed from the surface to the bottom, and along the bottom the water moves from the outer bank of the turn to the inner bank (Fig. 8c). The maximum value of the transverse speed is quite high (it can reach 30-50% of the average flow speed) and this must be taken into account when negotiating turns. The transverse velocity leads to a displacement of the flow core towards the outer bank of the turn.
The circulation current at the bends causes erosion of the outer bank and the formation of shoals near the inner bank. On mountain rivers with high flow speeds at sharp turns, the circulation current causes water to pile up on the outer rocky bank (pressure). Due to the circulation flow at sharp turns of high-speed rivers, a noticeable transverse slope of the water surface is formed. Noticeable transverse velocities also occur during rapid flood rise or fall of water. When the water rises, the river seems to swell, the middle of the flow rises, and the transverse flow along the surface is directed from the middle of the channel to the banks. When the water recedes, the middle of the flow collapses, the transverse flow along the surface is directed from the banks to the middle of the river (Fig. 8 a, b).
When flowing around obstacles in the channel, areas of transverse and even reverse flows are also formed. Flow around obstacles, like flow in a channel, can be laminar or turbulent. Laminar flow without disturbing the flow structure with smooth expansion and closure of the jets is observed either at very low flow velocities or with an ideally streamlined obstacle shape. Both cases are almost never encountered in tourist practice. Turbulent flow around obstacles is characterized by disruption of the flow structure.
If an obstacle protrudes above the water (a rock, a shore ledge), then the flow structure is disrupted mainly in the horizontal plane. A zone of high pressure is formed in front of the obstacle, due to which a water “cushion” appears (the water rises and a transverse flow is created along the frontal part of the obstacle). A zone appears behind the obstacle low blood pressure(the so-called whirlpool zone) due to the fact that the jet breaks away from the obstacle. Depending on the flow speed, shape and size of the obstacle, the jet is disrupted from the side or almost from the frontal surface of the obstacle. The length of the whirlpool zone can exceed the diameter of the obstacle by 10 times. Behind large protrusions of the coast, the whirlpool zone sometimes forms an area with regular circular movement of water - a catch already familiar to us (Fig. 7). When the jet stalls early, oblique standing shafts appear near the frontal part of the obstacle, diverging to the sides from it. The area of standing water behind an above-water rock is often called the high-velocity area, or simply the “shadow” of the rock.
Reverse currents can also occur under the influence of external forces, such as wind or tide. There is a known wind surge of water at the mouth of the Neva, causing floods, as well as tidal waves that turn the rivers back at the mouth for 30-50 km (on some rivers of the European North, flowing into the White and Barents Seas). Such features of rivers should be clarified when preparing a trip.
A river flowing in its channel, on the one hand, erodes it, and on the other, deposits erosion material in places where the flow slows down. The greater the slope, the higher the flow speed, the more the erosive activity of the river during a flood prevails over the accumulating activity. We can assume that for a certain section of the river, where the slope is greater than the average, erosive activity predominates, and where the slope is less than the average, accumulative activity predominates. Areas with a predominance of erosive activity are characterized by thresholds, cheeks, and shivers. Areas with a predominance of accumulative activity are characterized by rifts, alluvial rifts and especially blockages. This is not a mandatory rule, but the prevailing trend.
When a river breaks through a mass of homogeneous rocks, cheeks are formed, not only in soft rocks, but also in fairly hard ones. There are known shale cheek canyons in the Eastern Caucasus, cheeks of the Tuvan Ka-Khem river in a lava massif and others. Usually the cheeks are replete with rapids, because in the mass of one rock there are many heterogeneities. In addition, there are frequent collapses in the cheeks, which also contribute to the appearance of thresholds. Rapids, cheeks and rifts found in sections of the river with a large slope have an individual character, and the line of movement in them should be determined depending on the structure of each obstacle after its reconnaissance.
In areas with a lower slope, with a predominance of the accumulating activity of the river, it is already possible to identify some patterns of the formation and structure of obstacles that clearly determine the choice of the route of movement. The river transports material of various sizes - from sand suspended in the water to the so-called transportable sediment (stones up to 1-2 m in diameter). The patterns of deposition of such sediments are similar: they are all deposited in places where flow slowdowns occur.
Where are these places in the riverbed? If there is an island on the river, then the current slows down when the channels separate and the streams from the channels are knocked together, that is, at the head and tail of the island, where elongated sandbanks are formed. If two channels are of unequal length, then the flow in the longer one is slower, because it has less slope. This means that it is more clogged with sediment, and there should be less water in it, since the river gradually clogged it. It can be expected that the outlet of the longer channel will be the most clogged: it is at the outlet that its water is strongly inhibited by the backwater of a longer channel. fast water short duct. Often, especially on mountain rivers, a longer channel ends in a steep and very shallow decline of pebbles deposited by water. A lot of sediment is carried by tributaries, especially steeply falling ones, and this sediment falls at the mouth of the tributary - where its flow is slowed down by the backwater of the main river. Alluvial rifts or shoals are usually created at the confluence of tributaries.
The areas noted above with a large slope (predominance of erosive activity) and with a smaller slope (predominance of accumulating activity) are clearly distinguishable on the map and on the ground. They differ primarily in the character of the valley. In areas with a large slope, the valley is narrow, like a gorge, and there is usually only one channel, without channels. In areas with a lower slope, the valley is wide, and the river is often divided into channels. The places of transition from one area to another and the place where the profile breaks are also clearly visible on the ground. At the point of transition from a higher slope to a smaller one, the flow slows down, so at the end of a difficult section with a high slope you can expect a long drift. Slowing down of water before a threshold such as a simple step can also lead to the formation of a pre-threshold alluvial rift.
IMPACT OF FLOW ON A FLOATING VESSEL
Let us briefly consider the effect of flow on a sailing ship. The influence of the flow on a floating object occurs within the depth of its immersion. Any free-floating object moves at the speed of flowing water or faster. The greater the mass of an object, the slope of the river and the smaller the area of contact of its surface with water, the more its speed differs from the speed of water.
The most interesting for a tourist are the effects on a single-hull vessel of the already mentioned oppositely directed currents (the boundary between the catch and the stream, currents in standing waves, etc.). The general rule is that the smaller the vessel’s draft and the larger its size, the weaker the impact of local currents on it. In the area of standing waves, this effect is expressed in the appearance (due to the different directions of surface currents on the slopes of standing waves) of a torque tending to place the vessel across the current (lag), that is, in the position of least stability for a single-hull vessel. Similar forces arise when the stern and bow enter areas of currents with different or even opposite velocities. In this case, the moment of forces acting oppositely on the bow and stern may be sufficient not only to turn with the lag, but also to overturn a narrow and long low-stability vessel, such as a kayak. Double-hulled (catamarans) and multi-hulled (rafts) vessels are much more stable in these cases. The vertical components of the current, for example in whirlpools, submerge and heel ships depending on which part of them is affected by the vertical current. Very large eddies can capsize small boats. In flows with a spatial structure, the vessel is drawn into the region of maximum speeds (into the jet) under the influence of the transverse component of the current speed.
River - natural water flow flowing in a mined-out depression. Its work is manifested in erosion, that is, in the destruction of rocks through which the river flows. As a result, river valleys are formed.
river valley
river valley- a linearly elongated depression along the bottom of which a river flows. The following elements of a river valley are distinguished: bed, floodplain, terraces, bedrock bank (Fig. 178).
Rice. 178. Structure of a river valley
A depression in a river valley, but into which river waters constantly flow, is called river bed.
The river bed usually has a meandering shape. The smooth bends of a river bed are called bends, or meanders(Fig. 179).
At a certain stage of development, the river can straighten its course. The remains of former river channels form oxbow lakes - oblong, winding or horseshoe-shaped lakes.
Rice. 179. River meanders: a - initial stage; b - growth and displacement of the meander; c - straightening of the river bed and the formation of a residual reservoir - oxbow lake
Rice. 180. Fairway, reach and roll
The lines of greatest depth of the river bed are called fairway(Fig. 180).
The river bed is characterized by alternating deeper sections (plesyov) with smaller ones (rolls)(see Fig. 180). There may also be waterfalls - a drop of water flow from a pronounced ledge.
The place where the river originates, from which there is a constant flow of water in the channel, is called source. They can be a lake, a swamp, a glacier, or a spring.
The place where a river flows into another river, lake, sea or ocean is mouth River mouths can vary in shape; For example, delta or estuary.
Delta - a low-lying plain in the lower reaches of a river, composed of river alluvium and cut through a network of streams. Formed near quietly flowing rivers that carry out into shallow seas a large number of solid precipitation.
Estuary- a funnel-shaped bay, tapering towards the top, formed as a result of flooding of the lower reaches of a river valley under the influence of wave, river and tidal factors. Low-water desert rivers sometimes end in blind mouths, that is, they do not reach the reservoir (Murgab, Tedzhent, Kupere Creek).
The part of a river valley that fills with water during periods of floods is floodplain The width of the floodplains of lowland rivers can reach 40 km. The edge of the floodplain is often marked by a steep slope, on the edge of which there are sometimes alongshore ramparts.
Rising above the floodplain slopes of the river valley. They can be high or low, steep or flat. The steepness of both slopes of the valley is identical or various (asymmetrical). In asymmetrical valleys of the Northern Hemisphere, the right one is often steeper (the action of the Coriolis force).
Valley slope often has a stepped shape. These steps are called terraces. Most often they arise as a result of the eroding activity of the river: the riverbed descends, cutting through the floodplain, which becomes a terrace. Occasionally, terraces arise when the earth's surface is distorted, caused by tectonic movements, as well as due to climate change.
The lowest river terrace is the floodplain, it is called floodplain terrace, other - above the floodplain.
Depending on the geological structure, the following terraces are distinguished:
- erosive(the alluvium composing the terrace is of small thickness);
- basement(there is a lot of alluvium, and bedrock is exposed only in the lower part of the valley sides);
- accumulative(the river cuts through only ancient alluvium).
Terraces can also be longitudinal, transverse and radical.
The shapes of river valleys can be varied, because their formation is influenced by many factors: terrain; rock composition; erosion processes, etc.
Based on the shape of the transverse profile, the following types of river valleys are distinguished (Fig. 181): gap (canyon), gorge, gorge, U-shaped valley, trough-shaped valley, trapezoidal valley, box-shaped valley, unclearly defined valley. According to their plan outline, valleys are divided into straight, meandering (meandering) and valleys with lake-like extensions (bead-shaped).
Rice. 181. Types of transverse profiles of river valleys: a - gap (canyon); b - gorge, gorge; c - U-shaped valley; d - trough-shaped valley; d - trapezoidal valley; e - box-shaped valley; g - unclearly defined valley
They differ greatly from each other mountain And lowland valleys. The former are characterized by significant depth with a relatively small width and an uneven fall in the longitudinal profile. The latter, as a rule, are wide, have insignificant depth and steep slopes, small slopes, etc.
The main river and its tributaries form river system. The main river is usually considered to be the longest and deepest river, but a number of names of the main rivers have been strengthened historically. In this case, the main river became the one that people knew before, longer and better. For example, the Missouri River is longer and deeper than the main Mississippi River. Along with river ones there are lake-river systems. They are formed in areas where rivers flow through lakes, for example the river. The Neva flows through Lake Ladoga.
Each river has certain characteristics, including length, drainage basin area, annual flow, maximum and average water flow, and a number of other indicators.
River length - the length of a river from source to mouth.
River basin
River basin (drainage basin rivers) - the territory of the earth's surface from which all surface and groundwater flows into the river and its tributaries. The river basin includes surface and underground watersheds. Surface catchment is an area of the earth's surface from which water flows into a given river system or a specific river. The underground catchment area is formed by layers of loose sediments, from which water flows into the river network. But since it is very difficult to determine the boundaries of the underground catchment area, only the surface catchment area is taken as the size of the river basin.
Table 30. The largest rivers in the world
|
Name |
Length, km |
|
|
Neil (with Kagera) |
||
|
Amazon (with Ucayali) |
||
|
Mississippi - Missouri |
||
|
Ob (with Irtysh) |
||
|
Parana (from the origins of Paranaiba) |
||
|
Amur (from the sources of Argun and) |
||
The largest drainage basin on Earth has the river. Amazon - 7.2 million km 2. Next in order are the basins of the Congo and Mississippi rivers (Table 31).
Table 31. The largest rivers in the world by basin area
|
Name |
Basin area, thousand km 2 |
|
|
Amazon |
||
|
Mississippi |
||
The basins of individual rivers are separated by watersheds.
Watershed - border between river basins. It is better expressed in the mountains than on the plains.
Density of the river network is determined by the ratio of the total length of all rivers to the area of the drainage basin.
A fall - height difference between source and mouth.
River slope- the ratio of the fall to the length of the river, measured in meters per kilometer (m/km).
River flow
River flow(in a broad sense) is the movement of water in the form of a stream along a river bed. It is influenced by many factors.
The statement of the Russian climatologist A.I. Voeikov is true: “Rivers are a product of climate.” Thus, during heavy rainfall, the river flow is large, but one must take into account the type and nature of the precipitation: snow gives more flow than rain, rainfall increases the flow compared to regular precipitation with the same amount. But evaporation, especially intense, reduces runoff.
Very important geological structure river basin, especially the chemical composition of rocks and the nature of their occurrence, as they determine the underground feeding of rivers. Permeable rocks (thick sands, fractured rocks) are moisture accumulators, river flow in such cases is greater, since a smaller proportion of precipitation is spent on evaporation, and it is regulated.
The flow in karst areas is peculiar: there are few rivers there, since sediments are absorbed by sinkholes and cracks, but at their contact with clays or shales in river valleys and foothills, powerful springs feeding the rivers are observed. For example, the dry Crimean yayla, but powerful springs at the foot of the mountains.
Influence relief to river flow ( absolute altitude and surface slopes, density and depth of dissection) is large and varied. The flow of mountain rivers is usually greater than that of lowland rivers, since in the mountains on windward slopes heavier precipitation, less evaporation due to lower temperature, etc.
River flow is also influenced by human activities. First of all, this applies to rivers, the water flow in which is regulated by created reservoirs. The flow of such rivers is generally reduced, as evaporation from the water surface increases, a significant part of the water is spent on water supply, irrigation, watering, and underground recharge decreases.
When water is transferred from one river system to another, the flow changes: in one river it decreases, in another it increases. For example, during the construction of the Moscow Canal (1937) in the river. In the Volga it has decreased, and in the river. Moscow - increased.
To regulate river flow, activities are carried out in the river basin, since its initial link is slope flow in the catchment area. The main activities carried out are as follows: agroforestry - forest plantations, etc., drainage - dams and ponds on ravines and streams, etc., agronomic - autumn plowing, snow accumulation and retention, plowing across the slope or along the slopes on hills and ridges, grassing of slopes, etc.
In a narrow sense, river flow is the flow of water in a river over a certain period (usually a year).
Water consumption- the amount of water that flows through the living section of the river per unit of time. Typically, the flow rate is usually expressed in cubic meters per second (m 3 /s), and low flow rates (less than 0.1 m 3 / s) - in liters per second (l/s).
Live cross section of the river - cross-sectional area of the water flow.
Annual flow- the amount of water flowing through the river mouth per year (Table 32).
Table 32. 10 largest rivers in the world by annual flow
|
River name |
The continent on which the river is located |
Volume of annual runoff per year. km 3 |
|
Amazon |
South America |
|
|
South America |
||
|
Mississippi |
North America |
|
|
South America |
||
|
Tocantins |
South America |
|
The movement of water in the river continuously changes in magnitude and direction, which leads to horizontal and vertical mixing of water. The river flow is characterized speed. It can be determined by floats or special devices - hydrothermal turntables. It is expressed in meters per second.
When the water surface is open in calm weather, the lowest speeds are observed near the shores and bottom, which is caused by friction, and increase towards the surface and middle of the river. With a tailwind, the maximum speed occurs on the surface; with a headwind and in winter, in the presence of ice cover, the maximum speed is observed at a certain depth.
Moving water is capable of producing work, that is, it has energy. They call her the living power of the river. It is directly proportional to the mass of water and speed.
In addition to water, rivers transport large amounts of solids. They are conventionally divided into suspended - moving along with the water in the thickness of the stream, and drawn - moved along the bottom by rolling and dragging.
Masses of suspended, transportable and dissolved chemical and biogenic substances and rocks that are carried away by surface runoff are called solid waste. Solid runoff is measured in tons carried by the river over a certain period of time (day, month, season, year) through the living (cross-section) section of the river. IN large rivers the volume of solid waste reaches tens and even hundreds of millions of tons per year.
The river ranks first in the world in terms of volume of solid runoff. Yellow River (translated into Russian as “yellow river”). Its name refers to the abundance of transported solids, which give the water a yellow tint (1300 million tons/year). The Chinese say that such water is too thick to drink, but too thin to plow. River bed The Yellow River is quickly silting up.
When a river exits to the sea or flows into another river, the solid runoff material forms alluvial fans or deltas, usually with fertile lands.
The turbidity of the water in the river depends on the amount of solid runoff.
Water turbidity - the amount of suspended particles contained in 1 m 3 of water (g/m 3) or in a liter of water (mg/l).
One of the most muddy rivers world is r. Yangtze. This is facilitated by the weak stability of the rocks through which the river flows, elevated and mountainous terrain, intense rains, deforestation and plowing of land.
Many rivers in Eurasia and Canada have low turbidity, where they have sedimentation lakes “strung” on them, natural vegetation is well preserved, the soil is bound by permafrost, and low-lying coastal plains predominate.
In addition to solid particles, river waters contain small amounts of dissolved substances. They enter rivers through surface and underground runoff. In general, the mineralization of river waters is low (usually less than 200 mg/l, but can reach up to 500 mg/l), since surface water flows from well-washed interfluve soils, and rapid water changes occur in rivers. In areas of excessive moisture, calcium waters are found in rivers. Sulfates appear in the waters of steppe rivers, and chlorides appear in transit rivers of semi-deserts and deserts. The lowest mineralization is in mountain rivers fed by glacial and snow waters, the highest is in rivers fed primarily by groundwater (for example, the rivers of Kazakhstan: Ishim - 12 g/l, Emba - 16 g/l, Turgai - 19 g/l) . In addition to minerals, river water always contains nutrients necessary for life in the rivers themselves.
Thermal regime of rivers depends on climate and food sources. By thermal conditions There are three main types of rivers:
- with constantly warm water without seasonal temperature fluctuations: Amazon, Congo, Niger, etc.;
- with seasonal fluctuations in water temperature, but not freezing in winter: Seine, Thames, etc.;
- with large seasonal temperature fluctuations, freezing in winter: Volga, Amur, Mackenzie, etc. in temperate and subarctic climate zones.
In the warm half of the year, the temperature of the water across the live section varies little due to mixing. The change in temperature along the length of the river depends on the direction of the flow: it is less for latitudinal rivers than for rivers flowing in the meridional direction. For rivers flowing from north to south, the temperature rises from source to mouth (Volga, etc.), for rivers flowing from south to north, on the contrary (Ob, Yenisei, Lena, Mackenzie). These rivers carry huge reserves of heat into the Arctic Ocean, easing ice conditions there in the spring, and shifting the boundaries of natural zones to the north.
IN winter period There are three main phases of freezing rivers: freezing, freeze-up, and break-up.
The freezing of rivers begins at an air temperature slightly below 0 °C with the appearance of crystals - needles, then lard And pancake ice. During heavy snowfalls, water forms Snowflake At the same time, stripes of ice appear off the coast - take care. On riffles (rapids), bottom ice may form, which then floats up, forming an autumn ice drift together with pancake ice, snow and ice floes that have broken away from the banks.
Ice cover on rivers is established mainly as a result of ice jams - the accumulation of ice floes in shallow waters, in winding and narrow places and their freezing with each other and with the banks. Small rivers freeze before large ones.
The duration of freeze-up and ice thickness vary and depend on climatic conditions. For example, R. The Volga in its middle reaches is covered with ice for 4-5 months and the ice thickness is up to 1 m, river. Lena in the middle reaches - 6-7 months with ice thickness up to 1.5-2 m. The thickness and strength of the ice determine the possibility and duration of river crossings and movement on their ice - on winter roads. During freeze-up on rivers, phenomena such as polynyas can be observed: dynamic - in rapid sections of the riverbed, thermal - in places where warm groundwater comes out or where technical water is discharged.
In areas with permafrost and severe frosts, river aufeis are common - ice build-ups in the form of flat-convex ice bodies when river water pours onto the surface due to a narrowing of the flow cross-section. The thickness of the ice dams is on average 3-5 m. Along the length of the river they are usually located in chains for tens of kilometers, sometimes narrowing, sometimes widening depending on the shape of the river valley. There are known cases when naledi “captured” villages. The largest ice dam in the world (according to V.M. Kotlyakov) - Bolshaya Momskaya (more than 100 km 3) exists in the valley of the river. Moma, the right tributary of the Indigirka. It has a length of 40 km and a thickness of 3-8 m. The flow of groundwater is involved in its formation. Often on rivers you can see side by side seemingly antagonistic phenomena - polynyas and ice fields. In fact, they are closely related to each other: aufeis with their upper edge are adjacent to polynyas in places where relatively powerful warm springs emerge.
On rivers there are also gluttons - blockage of the living section of the river by the mass of in-water and bottom broken ice. They complicate the operation of hydroelectric power plants, as ice clogs the water intake openings of the dams. Finally, complete freezing of rivers is possible (in northeastern Siberia and Alaska).
The opening of rivers in spring occurs 1.5-2 weeks after the air temperature passes through O °C due to solar heat and arrival warm air. The melting of ice begins under the influence of melted snow waters entering the river, stripes of water appear along the banks - edges, and when snow melts on the ice surface - thawed patches. Then the ice moves, it collapses, and spring ice drift and floods occur. On rivers flowing from lakes, in addition to the main river one, secondary ice drift is observed, caused by the removal of lake ice. The height of the flood depends on the annual amount of snow reserves in the catchment area, the intensity of spring snowmelt and rainfall during this period. On rivers flowing from north to south, ice drift and flood in different sections occur at different times, starting from the lower reaches, there are several peaks of floods, and in general everything passes calmly, but extended over time (Dnieper, Volga, etc.).
Water regime of rivers characterized by a cumulative change over time in the levels and volumes of water in the river.
Water level— the height of the river’s water surface relative to a certain zero level.
Characteristic periods with certain levels and volumes of water in the river are called phases of the water regime. They are different for different rivers and depend on climatic conditions and the ratio of food sources: rain, snow, underground and glacial.
The main phases of the water regime are flood And low water.
High water - a high and prolonged rise in the water level in the river, repeated annually in the same season, accompanied by flooding of the floodplain. During this period, the rivers have the highest water content. Floods account for most of the annual river flow (up to 60-80%). Floods are caused by the spring melting of snow on the plains, the summer melting of snow and ice in the mountains and polar regions, and long-term heavy rains in the warm season. Depending on what is the cause of the flood, this period on different rivers occurs in different seasons of the year, for example, in the summer on the river. Ganges, Indus, Yangtze, Mekong due to monsoon summer rains and melting glaciers in the mountains; in winter on the rivers of the Mediterranean (Guadiana, Guadalquivir, etc.) due to winter rains.
Table 33. Distribution of the main types of river feeding sources by continent and part of the world
|
Predominant power source |
Dominant flow |
Continents and parts of the world |
|||||
|
North America |
South America |
Australia |
|||||
|
Snegovoe |
|||||||
|
Rain |
|||||||
|
Underground |
|||||||
|
Glacial |
|||||||
|
Internal drainage areas |
|||||||
e - areas of internal drainage of a large area.
Low water(low water) - a period of prolonged low levels and flows of water in the river with a predominance underground supply. Summer low water is caused by intense evaporation and seepage of water into the ground, despite greatest number precipitation at this time. Winter low water is the result of a lack of surface nutrition. At this time, rivers exist only due to groundwater.
A sudden short-term non-periodic rise in water level in a river is called flood Unlike floods, floods occur in all seasons of the year: in summer they can be caused heavy rains; in winter - by melting snow during thaws; at the mouths of some rivers due to the surge of water from the seas (autumn floods on the Neva River in St. Petersburg are caused by a surge of water from the Gulf of Finland by westerly winds).
The autumn rise of water in rivers, sometimes called leash period, is associated with a decrease in temperature and a decrease in evaporation, and not with an increase in precipitation - there is less of it than in summer, although in autumn the weather is more often cloudy.
The forecast of water content of rivers and their regime during the year has great importance to address issues of reasonable use water resources countries It is very important to forecast runoff during floods, which in some years can be extremely high and lead to negative consequences.
According to feeding conditions and water regime, rivers are divided into separate groups. The first such classification was created by A. I. Voeikov(1842-1916) in 1884. It was later improved by M.I. Lvovich in 1964 through a quantitative assessment of the role of individual river feeding sources and the seasonal distribution of flow. They identified six zonal types of water regime of lowland rivers.
Rivers of the equatorial type have abundant rain nutrition, large and relatively uniform runoff throughout the year, a slight increase is observed in the autumn of the corresponding hemisphere. These are the Amazon, Congo, etc. rivers.
Rivers tropical type. The flow of these rivers is formed due to monsoon summer rains in the subequatorial climate zone and mainly summer rains on the eastern coasts of the tropical zone, so the flood is summer. The rivers Niger, Orinoco, and Nile belong to this type.
Rivers subtropical type in general, they are predominantly fed by rain, but according to the seasonal distribution of runoff, two subtypes are distinguished: on the western coasts of continents in a Mediterranean climate, the main flow is winter (the rivers Guadiana, Guadalquivir, Duero, Tajo, etc.), on the eastern coasts in a monsoon climate - summer (tributaries of the Yangtze and Yellow Rivers).
Rivers moderate type. Within moderate climate zone Four subtypes of rivers are distinguished based on their sources of nutrition and seasonal distribution of flow. On the western coasts in a maritime climate, rivers are predominantly fed by rain with a uniform distribution of runoff throughout the year with a slight increase in winter due to reduced evaporation (Seine, Thames, etc.); in areas with a transitional climate from sea to continental
mental rivers have a mixed supply with a predominance of rain over snow, with low spring floods (Elbe, Oder, Vistula); in areas of continental climate near rivers there are predominantly snow and spring floods (Volga, Ob, Yenisei, Lena); on the eastern coasts with a monsoon climate, the rivers are mainly fed by rain and summer floods.
Rivers subarctic type They have predominantly snow nutrition with an almost complete absence of underground nutrition due to permafrost. During the cold season (8-9 months), these rivers freeze to the bottom and have no flow. The flood on rivers of this type is summer, as they open in late May - early June (Yana, Indigirka, Khatanga, etc.).
Rivers polar type During a short period of summer they have snow and glacier feeding and runoff, but for most of the year they are frozen.
Similar types and subtypes of water regime are characteristic of rivers, the flow of which is formed under more or less similar climatic conditions. The regime of large transit rivers crossing several natural and climatic zones is more complex. It is even more complex for rivers in mountainous regions, which are characterized by patterns of vertical zonation. As the height of the mountains near the rivers increases, the share of snow and then glacial feeding increases. Therefore, rivers that begin in the mountains and are additionally fed by snow and glaciers are characterized by summer floods (Amu Darya, Syr Darya, etc.). Summer floods are especially intense and even catastrophic on rivers that begin high in the mountains, and in the middle and lower reaches are abundantly fed by monsoon rains: Indus, Ganges, Brahmaputra, Mekong, Irrawaddy, Yangtze, Yellow River, etc.
Economic importance and protection of rivers
Rivers are of great economic importance. The formation and development of human society is associated with them. Since historical times, rivers have been used as sources of fresh drinking water, means of communication, for fishing and fish farming, timber rafting, irrigation and water supply, and water supply to the population. They are used to supply water industrial enterprises, obtaining electricity.
Rivers are of great aesthetic and recreational importance, being places of recreation and various sports activities. They serve as collectors and water intakes during drainage reclamation of wetlands.
The widespread involvement of rivers in economic circulation has become disastrous for them. Unfortunately, many rivers are heavily polluted by industrial and domestic wastewater, pesticides and mineral fertilizers from fields and wastewater from livestock enterprises. Water protection zones do not exist everywhere along river banks. Many of the rivers, especially those flowing in the southern regions where the need for irrigation is high, are heavily damaged. For this reason, the Amu Darya and Syr Darya practically no longer flow into the Aral Sea, and it is rapidly drying up. Rivers need to be protected and supported by their natural water regime and its reasonable improvement through the creation of reservoirs, canals and various works in the river bed and basin.
