Solid waste definition. River flow is solid

The energy of the flow is spent on overcoming resistance from the bottom and banks, as well as on erosion and transfer of soil from the slopes of the drainage basin to the reservoir. The water level in the receiving water represents the river flowing into it erosion basis, those. the potential level up to which the watercourse will erode. The erosion basis characterizes the flow energy.

The erosion process includes four stages:

Rinsing of soil from the surface of the catchment area;

Erosion of the bottom and banks in the river bed and floodplain;

Transfer of soil particles along the watercourse;

Deposition or accumulation of particles.

The cause of erosion is the movement of masses of water (in the form of streams on the slopes or flow in the river), reaching a certain speed. The separation of soil particles and their rise - transition to a suspended state - in addition to the speed of water, depends on the size of the particles, their shape and density, as well as on relative position particles at the bottom.

On separate particle lying on the bottom, there is a force of frontal pressure and a lifting force that occurs when the particle flows around, caused by the difference in velocities on its upper and lower faces. According to Bernoulli's law, the pressure on top edge will be less than the bottom one. In addition, it is necessary to take into account the weight of the particle and the Archimedean (buoyant) force.

Another mechanism for the separation of particles from the bottom is the presence of vortices that arise during flow around various kinds obstacles. These vortices have an area of ​​low pressure on their axis and capture detached particles and lift them into the flow.

In cases where the lifting force is less than the force of gravity, the particle can move along the bottom by sliding and rolling. This movement is called sediment drag. Analysis of the stability of such a particle shows that the weights of the attracted particles are related as sixth powers of velocities (Ary's law). Thus, if the velocities of mountain and plain streams are related as 1:4, then the weights of sediment they carry are related as 1:4096.

The flow speed at which the initial imbalance of the particles of bottom sediments forming the channel occurs is called non-erosive speed, and at the beginning mass movement bottom particles – eroding speed. They depend on particle size, flow depth and cohesive forces (cohesive soils). The erosive speed is approximately 30...40% greater than the non-erosive one. It is used in determining sediment flow, and the non-erosive one is used in calculating the general and local erosion of the channel near a hydraulic structure.

It is known that particle transport occurs in the form of suspended and bottom sediments.

Bottom sediments are channel-forming, i.e. participating in the formation, movement and destruction of such channel forms as ridges, sideways, middles, etc.

Unlike them, suspended sediment, whose particles are in the flow most time and transferred to long distances. When the flow speed decreases, they can be deposited on the bottom and turn into bottom sediments. The size of suspended particles is approximately an order of magnitude smaller than bottom particles.

The product of average turbidity and flow rate characterizes it transport capacity, which decreases from the source to the mouth of the river, where sediment accumulation processes predominate.

Mass of particles carried by water through cross section watercourse in 1 sec is called suspended sediment flow, which is determined by the formula: G = 1000 * ρ * Q, kg/s. To characterize the volume of soil removed by river water, calculate the value solid waste per day, month, season and year. The greatest solid runoff is observed, as a rule, during periods of high water and floods.

Long-term average sediment volume calculated by the formula:

Vн = G * 86400*365 / γ = ρ * Q * 86400*365 / γ ,

where G is the average annual sediment flow rate or solid runoff rate, kg/s,

ρ - water turbidity, kg/m3,

γ – sediment density, kg/m3

End of work -

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Lecture notes for the course hydrology specialty: bridges and transport tunnels

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Characteristics and factors of runoff
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The energy of the flow is spent on overcoming resistance from the bottom and banks, as well as on erosion and transfer of soil from the slopes of the drainage basin to the reservoir. The water level in the receiving water represents the river flowing into it erosion basis, those. the potential level up to which the watercourse will erode. The erosion basis characterizes the flow energy.

The erosion process includes four stages:

Rinsing of soil from the surface of the catchment area;

Erosion of the bottom and banks in the river bed and floodplain;

Transfer of soil particles along the watercourse;

Deposition or accumulation of particles.

The cause of erosion is the movement of masses of water (in the form of streams on the slopes or flow in the river), reaching a certain speed. The separation of soil particles and their rise - transition into a suspended state - in addition to the speed of water, depends on the size of the particles, their shape and density, as well as on the relative position of the particles at the bottom.

An individual particle lying at the bottom is subject to the force of frontal pressure and the lifting force that occurs when the particle flows, caused by the difference in velocities on its upper and lower faces. According to Bernoulli's law, the pressure on the upper face will be less than on the lower face. In addition, it is necessary to take into account the weight of the particle and the Archimedean (buoyant) force.

Another mechanism for the separation of particles from the bottom is the presence of vortices that arise when flowing around various types of obstacles. These vortices have an area of ​​low pressure on their axis and capture detached particles and lift them into the flow.

In cases where the lifting force is less than the force of gravity, the particle can move along the bottom by sliding and rolling. This movement is called sediment drag. Analysis of the stability of such a particle shows that the weights of the attracted particles are related as sixth powers of velocities (Ary's law). Thus, if the velocities of mountain and plain streams are related as 1:4, then the weights of sediment they carry are related as 1:4096.

The flow speed at which the initial imbalance of the particles of bottom sediments forming the channel occurs is called non-erosive speed, and at the beginning of the mass movement of bottom particles - eroding speed. They depend on particle size, flow depth and cohesive forces (cohesive soils). The erosive speed is approximately 30...40% greater than the non-erosive one. It is used in determining sediment flow, and the non-erosive one is used in calculating the general and local erosion of the channel near a hydraulic structure.

It is known that particle transport occurs in the form of suspended and bottom sediments.

Bottom sediments are channel-forming, i.e. participating in the formation, movement and destruction of such channel forms as ridges, sideways, middles, etc.

Unlike them, suspended sediment, whose particles are in the flow most of the time and are transported over long distances. When the flow speed decreases, they can be deposited on the bottom and turn into bottom sediments. The size of suspended particles is approximately an order of magnitude smaller than bottom particles.

The product of average turbidity and flow rate characterizes it transport capacity, which decreases from the source to the mouth of the river, where sediment accumulation processes predominate.

The mass of particles transferred by water through the cross-section of a watercourse in 1 second is called suspended sediment flow, which is determined by the formula: G = 1000 * ρ * Q, kg/s. To characterize the volume of soil removed by river water, calculate the value solid waste per day, month, season and year. The greatest solid runoff is observed, as a rule, during periods of high water and floods.

Long-term average sediment volume calculated by the formula:

Vн = G * 86400*365 / γ = ρ * Q * 86400*365 / γ ,

where G is the average annual sediment flow rate or solid runoff rate, kg/s,

ρ - water turbidity, kg/m3,

γ – sediment density, kg/m3

Water turbidity lowest values in Russia it reaches the forest zone in rivers. There is turbidity in the taiga river water usually less than 20 g/m3, which is a consequence of relatively low surface runoff in forest soils with high infiltration capacity. Another reason is that the forest soil cover is well protected from erosion; In this strip, arable lands are relatively rare, where conditions are most favorable for erosion processes. In some areas of the southern and Far Eastern taiga, turbidity increases to 50 g/m3, and in some areas up to 100 g/m3. An increase in water turbidity within the taiga zone is associated mainly with linear erosion in the river beds themselves or is caused by conditions mountainous terrain(Verkhoyansk district).

As you move south, the turbidity of the river water increases. This is typical for forest-steppe and steppe zones, where turbidity reaches 500 g/m3. This is mainly due to large area plowedness of this territory. On arable lands, especially in the past, high surface runoff was formed. In addition, the soil on the arable land is poorly protected from erosion. In some steppe and forest-steppe areas, increased water turbidity (up to 1000 g/m3) is due to rugged terrain or particularly intense rainfall in combination with the spread of loess that is easily eroded (for example, the lower reaches of the Don River).

In general, the distribution of river water turbidity throughout the country has a clearly defined zonal character. At the same time, the natural zonal features of turbidity distribution are enhanced by the anthropogenic factor.

Special conditions for the formation of turbidity are characteristic of mountainous regions. Here the main role is played by the relief and. Also essential climatic conditions: with decreasing humidity, the intensity of denudation processes, including erosion, increases. Important role Mountain forests also play a role, inhibiting the development of erosion processes.

Intra-annual fluctuations in solid runoff are primarily associated with fluctuations in water flow: with an increase in water consumption, the consumption of suspended sediment increases. However, the intra-annual distribution of sediment runoff is more contrasting than that of water runoff. Thus, during floods, the maximum sediment discharge does not coincide with the peak of the flood, but precedes it; in the presence of several floods following one after another, greatest mass The first flood carries sediment, and each subsequent flood carries less and less sediment.

For the rivers with snow floods that predominate in Russia, which are characterized by regular periodicity, the solid flow regime is of a fairly regular periodic nature.

Runoff carries loose rocks into rivers - products of weathering. This creates solid waste- the mass of suspended substances drawn along the bottom and dissolved substances. Their number depends on the energy of moving water and the resistance of rocks to erosion. Solid drain divided by suspended And bottom. When the flow speed changes, these types of solid waste can transform into one another. The amount of solid waste may depend on river turbidity. IN large systems Solid runoff from rivers is measured in tens of millions of tons per year. For example, the solid runoff of the Amu Darya is 94 million tons; Volga - 25 million tons; Ob - 15 million tons; Don - 6 million tons; Yellow River - 1500 million tons; Indus - 450 million tons; Nile - 62 million tons.

The amount of runoff depends on a number of factors:

from climate . The more precipitation and less evaporation, the greater the runoff, and vice versa. The amount of runoff depends not only on the amount of precipitation, but also on its form and timing. For example: rains in a hot summer will produce less runoff than rains in a cool autumn; snow does not provide surface runoff in the cold months; it is concentrated during the short period of spring floods. The amount of runoff is also affected by the uniformity of precipitation: sharp changes in the amount of precipitation and the amount of evaporation cause uneven runoff, and during prolonged rains, precipitation infiltration into the ground is greater than during heavy rains;

from the terrain . From minor elevations, the runoff is greater than from the adjacent plains: on the Valdai Upland, the runoff modulus is 12 l/sec/km 2, and on the adjacent plains - 6. Even greater runoff (from 25 to 75) in the mountains, since in addition to the influence The relief here affects the amount of runoff and an increase in precipitation, as well as a decrease in evaporation in the mountains due to a decrease in temperature. Water flows quickly from elevated and mountainous areas, and slowly from lowland areas. For these reasons, lowland rivers have a more uniform regime, while mountain rivers react sensitively and violently to the weather;

from soil cover . In areas of excessive moisture, the soils are saturated with water most of the year and release it to rivers. In areas of insufficient moisture during snow melting, the soils are able to absorb all the melt water, so the flow in these areas is weak;

from vegetation cover . Research recent years carried out in connection with the planting of forest belts in the steppes, indicate their positive effect on runoff, since it is greater in forest zones than in steppe zones;

from the influence of swamps . It is different in zones of excess and insufficient moisture: in the forest zone, swamps are flow regulators, and in the forest-steppe zone they absorb surface and groundwater and evaporate them into the atmosphere, thereby disrupting the flow;

from large flowing lakes . They are powerful flow regulators.

Analyzing the above, it should be concluded that the amount of runoff is variable. The zone of the most abundant flow is the equatorial latitudes (runoff module -1500 mm per year). The largest annual flow of rivers South America. Subpolar latitudes Northern Hemisphere- zone of minimum flow (flow module - 200 mm per year). Maximum amount runoff in these latitudes occurs in spring and summer.

On every continent there are territories from which the flow does not flow into the ocean, but into inland bodies of water - lakes that have no connection with the World Ocean. Such territories are called areas of internal drainage , or drainless. The formation of runoff in these areas is associated with precipitation, as well as with the remoteness of inland areas from the ocean. The largest drainage areas are in Africa (40% of the entire territory) and Eurasia (29% of the entire territory).

So, the most important link in the water cycle in nature and the most important characteristic of a river is runoff.

It is characterized by a number of indicators (water flow, runoff module, runoff coefficient). The amount of runoff depends on a number of factors (climate, terrain, soil cover, vegetation cover, the influence of swamps and lakes). A widely used characteristic of a river is the amount of its annual flow. The Amazon has the largest annual flow, which is due to the huge area of ​​its river basin, located mainly in the zone of moist equatorial forests.

Solid runoff is solid particles carried by river waters. Forming factors; climatic (wet areas, soil composition, vegetation..), azonal (relief, local soil differences, slopes..), anthropogenic (agroforestry measures, deforestation, fires). The intensity of erosion varies according to climatic zones (in zones of excess and sufficient moisture, the soils are held together by grass and forest cover, slope erosion is difficult, sediments are formed during the erosion of river beds; in the zone of insufficient moisture, soil dryness increases, forest cover decreases). Sediment is divided into suspended (most of them are transit, size 1-3 mm), attracted (they move along the bottom by rolling, jumping or in the form of bottom ridges, they are taken into account in the reshaping of the channel. Erie’s law P = kU6 (the weight of transported particles is proportional to the 6th power of the flow speed => mountain rivers can move large stones, lowland rivers can move small fractions). For example, soil washout from the slopes of the forest and steppe zones of the European part of Russia, 60 and 1000 t/km2, respectively, in North Africa 5000 t/km2. In southern Asia 20,000 t/km2. ρ is the density of sediment in water. Turbidity is the amount of suspended sediment containing a unit volume of a mixture of water and TV particles. For the zone of excess and supply. humidity - from small values ​​to 50 g/m³, in the forest-steppe zone - increases to 100 g/m³, in the steppe zone - 500 g/m³, in the dry desert zone the turbidity increases, in mountainous areas of an arid climate it can exceed 10,000 g/ m³.Turbidity-suspended sediment in the practice of hydrological analysis. The sediment flow rate (R) is directly measured - the amount of sediment in weight units carried by the river through the cross section per unit time R=P/T kg/s.

9. Thermal regime of rivers. Thermal balance of water bodies.

The thermal regime of rivers and streams is formed under the influence of numerous heat sources that contribute to the heat exchange of the water mass with the atmosphere and the watercourse bed.

10. Channel process. Elements of channels, floodplains, etc.

Channel processes are a set of phenomena and processes that occur under the influence of a complex of various natural and anthropogenic factors, and are expressed in changes in the shape and parameters of river channels. The distribution of depths in river beds depends on the distribution of erosion-accumulative formations in them - channel forms. Small ridges are widely distributed, the dimensions of which are incommensurate with the size of the channel. Small forms of channel formations determine the degree of bottom roughness. On many lowland rivers there are ridges, the dimensions of which are comparable to the dimensions of the stream bed. Some of them are located at a certain angle to the flow axis, others are single formations that occupy almost the entire width of the channel. These are the so-called ribbon ridges. Another type of sand ridges are middles. They are powerful accumulations of sediment in the middle part of the channel in the form of sandbanks or moving islands. The middles are usually stretched along the river and separated from the banks by channels. During the low-water period, the sedges dry out. More complex forms of channel formations are riffles and floodplains. Rifles are formed where there are favorable conditions for sediment accumulation. Such conditions are created when the transporting capacity of the flow decreases under the influence of either a decrease in flow velocities or a sharp local increase in solid runoff. A decrease in flow speeds is observed in places where mountain rivers enter the plain, in places of a sharp expansion of the flow channel, as a result of backwater under the influence of narrowing of the valley, the confluence of large tributaries. An increase in solid runoff is most clearly manifested at the confluence of tributaries carrying a large amount of sediment (rifts in this case occur below the confluence of the tributaries), as well as in the case of sediment removal by ravines. Periodic fluctuations in bottom marks on the rifts reach large values. Erosion of the ridges of rapids occurs not only during the summer low-water period, but also in winter during freeze-up, especially if the latter formed at low levels.

\\\ River valley is a morphological formation, an element of a river basin; a relatively narrow and elongated, sinuous, sloping landform. Watershed space is the distance from the watershed to the edge of the valley. The width of the valley is the distance between the edges. Terraces are horizontal platforms located on ledges within the slopes of the valley. The bottom of the valley is a relatively flat horizon part, including the riverbed and floodplain. The gorge has almost vertical slopes, the bottom is occupied by a riverbed. Potsma is a part of the valley bottom, raised above the low water level in the river, covered with vegetation and flooded during floods and floods.