Geographic features of the development and distribution of ravines. What is a ravine
Introduction
Ravine erosion is an active relief-forming process. The ravine, the topmost link in the erosion network, develops over hundreds of years and, as a rule, is not destroyed under the influence of annual anthropogenic pressure. The immediate cause of the formation of ravines is the violation (for any type of economic use of land) of the natural conditions for the formation of runoff on the slopes of river valleys, gullies, dry valleys, etc. A large number of ravines develop in cities, suburban areas, towns, during deforestation, mining and construction.
The negative role of ravines is determined to the greatest extent by the destruction of land, engineering facilities, and communications. In addition to the loss of area due to the formation of the ravines themselves, the loss of arable land causes damage to agriculture; their area is almost three times the area of the ravines themselves. Ravines destroy communal and industrial buildings, roads, power lines. At present, attention to the ravines in the territory of housing construction is increasing due to the environmental problems of the territories adjacent to the ravines. The ravines were used both earlier and are still being used now for industrial and domestic waste dumps, which is often a threat to human health.
Modern technical means aimed at combating erosion processes can significantly limit the manifestation of ravine erosion. At the same time, it is possible to use large ravine forms within the city for parks, recreational areas, in rural areas to create ponds in ravines and organize pond farming. However, this requires a scientifically based understanding of the patterns of development of ravines, which will make it possible to determine the need for application and an appropriate set of anti-erosion measures.
Of exceptional importance is the predictive assessment of the maximum dimensions that a ravine can reach in the course of its development, the growth rates of ravines in length at individual stages, as well as obtaining indicators of the maximum possible damming of territories. At present, territories have already been outlined where, with a large modern ravine, the potential for its development is practically exhausted and the emergence of new ravine forms is unlikely. These circumstances should be taken into account when organizing anti-erosion protection of lands. At the same time, gully formation should be given increased attention, since the natural prerequisites for the development of gully erosion are very high. Opportunities for the development of ravines are available in the forest zone, subject to the destruction of the vegetation and sod-soil cover there, which is confirmed by data on the active growth of ravines along clearings, ravines developing along forest belts in the forest zone, in the tundra during the development of oil and gas fields, in places of deer pastures and etc.
All these problems can be solved if there is data on the “potential” of the territory for the development of the ravine formation process. Therefore, the development of methods for assessing the potential of ravine erosion based on experimental data, field observations and a model of ravine erosion is the basis for designing anti-erosion measures, establishing their sequence and composition.
Formation and development of the ravine
Gullying is a modern relief-forming process carried out by temporary channel flows of rain and melt water, as a result of which specific negative linear forms appear on the land surface. The formation of ravines is currently associated, as a rule, with the violation of the existing natural complex under the influence of anthropogenic impact. However, their development itself occurs according to the laws of natural processes and depends on a combination of factors that largely determine the possibility of the emergence and activity of the subsequent development of ravines. This does not exclude the possibility of the beginning of the appearance and growth of a ravine without anthropogenic interference on large slope watersheds under the influence of natural processes (washing away a steep bank by a river, landslides, karst, etc.)
The main natural factors of gully formation are hydrometeorological and geological-geomorphological conditions: precipitation summer period and water reserves in the snow cover before snowmelt, horizontal and vertical dissection of the territory by a valley-beam network, soil erosion, steepness and shape of the slopes of river valleys, block, dry valleys, as the main centers of ravine formation.
The ravine differs from other linear erosion formations - hollows, ruts, gullies, beams in three main features:
1) characteristic dimensions;
2) typical shape transverse and longitudinal profile;
3) dynamic state.
The ravine is characterized by a longitudinal profile, in the top part having a slope significantly exceeding the slope of the slope, and in the lower part - much smaller, often reaching zero values. In the overwhelming majority of cases, if they reach the floodplain of a river or at the bottom of a ravine, the fans of ravine forms are a typical accumulative form that rises above the marks of the surrounding surface.
The transverse profile of the ravine changes both in length and in time over the period of development. With active growth, the ravine throughout its entire length has steep, crumbled, landslide slopes, devoid of vegetation, the slopes of which significantly exceed the angles of repose. As the ravine develops, starting from its mouth part, the slopes flatten and overgrow. This process is most characteristic of humid zones; in other conditions ravines long time retain steep bare slopes.
hallmark ravine is its dynamic state. A ravine remains a ravine as long as it is active or has not lost the possibility of activation due to changes in anthropogenic load or under the influence of natural factors. This distinguishes the ravine from the beams. When a developing erosion cut of considerable depth appears in a beam, often cutting through the entire area of its bottom, it is called, in contrast to the beam form, bottom; ravine, emphasizing that it is active development that is a distinctive feature of the ravine erosional form.
The activity of the development of the ravine on different stages is one of the problems, the solution of which is associated with the analysis of field and experimental data, which makes it possible to compose an algorithm for the development of such an erosional form. The emergence of a ravine usually begins with the formation of erosion funnels on a steep part of the slope, which then combine into a gully. It, in turn, moving regressively upwards by the near-top ledge, deepens, cleans the thalweg from soil material coming from the slope and eroded in the channel, and takes it to the lower parts of the slope or directly to the valley of larger links of the erosion network. Already at the very beginning of the formation of a ravine in the channel, a cascade of ledges is observed, moving up the channel. The development of the ravine is carried out by the conjugated activity of regressive and transgressive deep erosion with the removal of erosion products and elephant deformations. At the beginning of development, the channel of the ravine is a purely erosive form; then, as the ravine lengthens, deepens, and expands, alternation of erosion and accumulation zones begins in its channel. During the development of the longitudinal and transverse profiles, accumulative complexes form first in the mouth part of the ravine, and then the same complexes, but smaller, appear in the middle and even upper parts of the longitudinal profile. At the final stage of development, the flow velocities in the ravine are significantly reduced, approaching non-erosive and are insufficient to move the slope material.
Based on the results of field studies and laboratory experiments in the natural complex "slope catchment - ravine", the main relationships were identified, the interaction of which is the essence of the ravine-forming process. These are links - external, intercomponent and internal.
The external conditions of gully formation include a complex of natural factors and the degree of anthropogenic impact on the landscape, as well as processes accompanying gully formation - collapse and shedding of soil on slopes, landslides, karst, suffusion, etc. External links establish a relationship between the conditions in which ravines develop and their number, parameters, and growth activity. Of the natural factors, the main ones are: firstly, the factors affecting the active, acting force (storm and melt water flows) are precipitation, filtration properties of soils, morphometry of the drainage basin, i.e. its dimensions and configuration, depth of erosion bases, slope and shape of slopes; secondly, it is the susceptibility of soils to erosion, their anti-erosion properties.
Intercomponent relationships establish the relationship between the morphometric parameters of the ravine in the process of its development. Natural surveys of ravine-gully systems and individual ravines, even in large areas and in a wide range of natural characteristics of regions, do not provide sufficient material to analyze the relationships in the development of individual parameters of the ravine. Ravines, the development cycle of which, as a rule, exceeds a century, are in the development phase at the time of the survey, due to previous processes. Observation cycles of 10–15 years, which is considered a fairly long period, usually fall on one of the development phases, which does not allow us to identify the growth trend of individual parameters and extrapolate the patterns of their changes into the future.
Intra-component relationships describe the internal patterns of development of the ravine as an erosional form. The main pattern that determines the development of the ravine as a whole is the presence of ascending and descending branches of development in time. The ascending branch corresponds to the positive feedback during the period when the self-development of the ravine up to a certain point intensifies the process of growth of the ravine form. This is the period of formation of a linear incision, when a channel is formed, concentrating runoff from the catchment area, in connection with which the speed increases and, as a result, the eroding and transporting capacity of the flow. In the initial period, there is also a gradual increase in the catchment area drained by a linear incision, and, consequently, the flow of water entering the channel increases. The gradual formation of a single channel with less stepping, and, consequently, with a gradually decreasing roughness, belongs to the same time.
Under natural conditions, when the edge of the slope breaks, especially during periods of significant floods or during heavy rains, an unusually rapid development of a rut on the slope occurs, when in one season its length reaches 100-1500 m. Similar growth rates of linear cuts in length were recorded by a number of researchers not only in our country, but also abroad. IN scientific literature often noted the possibility of destruction of arable land for several years due to gully formation. The case of an exceptionally rapid growth of a linear incision during the spring flood was recorded by us on the slope catchment area of the river. Toyms (a tributary of the Kama River near the village of Tanaika). The consequences of the growth of the ravine were the destruction of the roadbed with an unpaved surface and the subsequent backfilling of the cut with soil, eroded and displaced from garden plots.
Changes in the growth trends of the ravine, its slowdown in all respects as the top moves up the slope, is primarily due to the transformations taking place on the slope catchment area due to the development of the ravine form itself, i.e. the ravine in the process of growth modifies the catchment that gave rise to it. As the linear form develops, the flow from the state of an active, eroding force is transformed into a transport artery with velocities close to non-erosive, capable of transporting sediment from the overlying catchment area without eroding the bottom of the ravine.
An analysis of the complex of external, intercomponent, and internal relationships that determine the patterns of formation of ravines made it possible to identify the stages of their development, which differ mainly in the growth rate. The main, integrating parameter in this case is the volume of the ravine, the changes in which correspond to changes in time in the volume of soil carried by the flow outside the developing erosional form. An important role in determining the stage is played by the determination of the length of the ravine in time. At the same time, the growth rate of the ravine is inseparable from its morphometric appearance and is largely due to the interrelationships of the parameters of the ravine in the process of its development. At the same time, the distinguished stages of development are inherent in both modern, in the overwhelming majority of cases, anthropogenic ravines, and natural modern erosional forms. There are four stages in the development of ravines.
Stage 1 - the ravine originates on a steep section of the slope catchment area in the form of sod breaks, the formation of erosion funnels, their confluence, the formation of a gully and the gradual concentration of the slope flow in a single channel. At this stage, the impact of anthropogenic factors, random intensification or cessation of linear erosion is great. The period from the formation of an erosion funnel to a ravine is difficult to determine by a time interval. The beginning of the gully-forming process is clearly recorded from the moment of breaking through the edge of the slope and turning the gully into a linear shape with a longitudinal profile typical of a ravine and dimensions that do not allow it to be destroyed by subsequent plowing.
Stage 2 - the most intensive growth of the ravine in all respects near the edge of the slope, especially its length and depth. The longitudinal profile of the bottom in the middle and mouth parts remains convex, which contributes to an increase in the speed, and, accordingly, the scouring and transporting capacity and turbidity of melt and rainwater flows.
Stage 3 - the development of the length of the ravine completely ends; the volume to the end of the stage is produced by 60-80%. The second and third stages are characterized by the most intense decrease in the rates of linear and volumetric growth, which is a consequence of a decrease in the near-top catchment area as the ravine regressively moves up the slope. At the same time, the average slope of the longitudinal profile of the ravine decreases and it flattens out, transforming from convex to straight and convex-concave.
This stage completes the period of the most active growth of the ravine, corresponding to 40% of the total time of gully formation.
Stage 4 - corresponds to the time of gradual formation of the longitudinal profile, its transformation from a straight and convex-concave into a "worked out", a time of slow and relatively calm development. This stage is characterized by alternation both in time and along the length of the ravine of processes and zones of erosion and accumulation. Erosion profile associated with intense floods or showers of rare frequency, on long years may become cumulative.
This stage occupies 60% of the total time of ravine formation and is characterized by the ravine reaching its maximum size. If the identification of stages 2 and 3 is due only to the intensity of the gully formation process and the nature of intercomponent bonds, then at the fourth stage, the characteristic dimensions of gully forms are most closely determined by a complex of external bonds. Natural factors of ravine erosion serve as arguments in dependencies for determining the dimensions of ravines at the final stage of development. They are the reason for the difference in the maximum possible damming of territories, different lengths of slope watersheds affected by ravines under close conditions and time of development of the regions.
In their totality, the identified stages of gully formation characterize the features of the process of self-development of the ravine. The change in the process in time, considered by intracomponent connections, is peculiar for each of the parameters of the ravine shape; it is prepared by the process of previous development and determines the nature of subsequent changes in the entire complex of parameters of the ravine - its length, width, depth, area and volume.
Spread of ravines
The distribution of ravines in almost all natural areas Russia is indicated in the works of most researchers of ravine erosion. The influence of natural characteristics on the appearance and development of ravines was studied under stationary conditions, during field surveys of territories, in laboratories, using cartographic materials and aerial photographs, using mathematical statistics methods and using all types of modeling. New data on ravines attract attention as a basis for anti-erosion measures, material for calibrating models of the gully formation process, and as a source of additional regional characteristics of the distribution of ravines, which specify the danger of their further development for specific conditions.
The formation of ravines is directly related to the development of larger links of the erosion network (rivers, gullies, dry valleys). An analysis of the morphometry of the slopes of the valley-gully network and the conditions of runoff formation in the watersheds of rivers, ravines, dry valleys makes it possible not only to reveal the influence of natural and anthropogenic factors on the current distribution of ravines, but also to obtain data to determine the development trend of the process. An analysis of the distribution of ravines on slope watersheds along river valleys and sides of gullies shows exceptional variability in the conditions of their occurrence and distribution. During field surveys of ravines conducted in 1970-1993. in the regions of the South of the Non-Black Earth Region (Oryol, Ryazan, Tula region), the Chernozem Center (Kursk, Voronezh regions), the Volga region (Kirov, Gorka, Saratov regions), Stavropol, Altai Territory, the structural features of the ravine network were noted and the place of ravines and the hierarchy of channel forms formed by temporary flows of rain and melt water on slope catchments were determined . An analysis of the topographic maps of these regions, with refinement and adjustment during field studies, showed that one hundred drainage basins of ravine forms are despite exceptional diversity. natural conditions have common features morphometric structure, which distinguish them from gully and river watersheds. This is manifested both in the relationship between the length and area of the watersheds, and in the configuration features (changes in width along the length) of erosional forms. The influence of the depths of local erosion bases on the planned characteristics of the drainage basins was also considered.
Patterns in the distribution of ravines on the territory of Russia were identified using maps compiled by the National Research Laboratory of Soil Erosion and Channel Processes, containing data on the density and density of modern ravines and the area of ravines in terms of the percentage of loss of land resources from the area of agricultural land. When calculating indicators, gully forms with a length of at least 70 m were taken into account. Analysis of the maps revealed features of the distribution of ravines, reflecting both the results of anthropogenic intervention in the conditions of formation of water runoff on slope catchments, and natural features regions. Studies have confirmed a number of well-known factors in the development of the ravine-forming process, the importance of natural factors and their anthropogenic disturbance. According to the degree of damming, the following types of territories are distinguished:
Territory with a low degree of congestion. Where ravines are extremely rare and only single ravine forms. The area of ravines, which is largely a function of their distribution in terms of density and density, is also extremely small in these areas. Similar ravine indicators are typical for the following two types of districts:
a) undeveloped or poorly developed lands with a flat or ridge-undulating relief; these are the northernmost regions of the European territory of the country - the tundra, forest-tundra zones and the northern part of the forest zone. However, in these territories there are also strongly ravine areas, which usually accompanies deforestation and anthropogenic development. Such areas are noted on the territory of the Malozemelskaya and Bolshezemeskaya tundras, Northern ridges, Vyatskiye ridges and in some other areas.
b) Flat lowlands with a very weak valley incision (the depth of dissection exceeds 10 m. Such territories include the Caspian lowland, Meshchera.
Areas with a moderate degree of damming. The area of these territories of ravine erosion does not exceed 0.5%. Against this background, small areas with higher levels of damming may occur. Such territories are predominantly characteristic of sparsely populated and poorly developed areas with a shallow dissection of the relief, as well as for the lowlands of populated areas. This is a significant part of the forest zone south of 57-58 N, separate areas in the more northern regions adjacent to the middle course of the river. Pechory, lower reaches of the river. Mezen, the middle course of the river. Sev. Dvina, flattened areas of the Smolensk and Central Russian Uplands, the Oka-Don Plain, the Kuban Lowland, a wide strip of population along the western spurs Ural mountains south of the river Kama and some other areas.
Territory with a high degree of damming. A significant part of the forest zone belongs to this type of gully dissection. These are predominantly well-developed areas with relatively favorable conditions for gully formation, including a rather dissected and rugged relief. Cover rocks are easily eroded and are provided by silty sandy loams and loams, less often by sands and loess-like loams. These regions include the central dissected areas of uplands and ridges (Central Russian, Volga, Verkhnekamsk, Northern ridges, etc.), as well as undulating plains (Oka-Don, western part of the Common Syrt, etc.)
Territory with a very high degree of damming. These are areas of the forest-steppe and steppe zones, long-standing and active agricultural development, almost completely plowed. They usually occupy deep dissected, rugged parts of uplands composed of silty and loess-like deposits. In these territories, there are areas with more than 1.5% of agricultural lands affected by ravine erosion. Within the steppe and forest-steppe zones, the following regions are distinguished: the south of the Central Russian and sections of the Volga and Kalach uplands, the highlands of the High Trans-Volga region and some other smaller territories. Within the southern part of the forest zone, the most trans-ravine basins are the basins of the Vyatka, Oka, Don, Kama rivers, as well as certain areas of the Smolensk-Moscow and Central Russian Uplands.
As can be seen, the intensity of ravine erosion in all zones depends both on economic activity and on the natural conditions of the regions. The leading role in this case belongs to the anthropogenic factor. This is the reason for the intensive modern erosion of the forest-steppe and steppe zones, where the plowing of the territory is about 70-80% of the total area. Under natural conditions, the combination of natural characteristics of the steppe and forest-steppe zones (soils, vegetation cover) prevents the development of ravine erosion. Zonal natural factors contributed to the development of intense ravine erosion in these zones, since their landscape features caused the first stage of land development for arable land, which most contributed to the development of ravines. At the same time, the very structure of zonal factors turned out to be disturbed. The climate remained unchanged - the only factor that in itself contributes to the development of the erosion process is the stormy nature of precipitation, rapid snowmelt.
The most important role in the distribution of ravines belongs to the relief - the azonal factor. The main relief indicators that affect all aspects of the process of ravine formation include: the depths of local erosion bases, the shape and steepness of slopes, the areas of slope drainage basins, and slope exposure. The most expressive consequence of this influence is the maximum density and density of ravine dissection in elevated areas of the territory, for example, in the Central Russian and Volga Uplands. A detailed analysis of the influence of morphometry features of watersheds on the development of the ravine network is contained in almost all works devoted to the regional assessment of the ravine formation process.
Soil erosion has a great influence on the development of gully erosion, the spread of ravines over the territory, the intensity of the process, and the morphometric appearance of individual ravines. Often, eroding flow rates determine the very possibility of the development of ravines in the territory.
The main results of studying the distribution and development activity of ravines in different zones of the country are the following:
Ravines are common in all natural zones, which excludes the assumption that this process is typical for purely specific conditions, for example, the zonal nature of this phenomenon. It is well known that the forest-steppe and steppe zones are the most ravine, but in the tundra zone ravines are noted on Novaya Zemlya, Kolguev, Taimyr, Yamal, Bolshezemelskaya and Malozemelskaya tundra, in the Vorkuta region, especially in connection with the development of new oil and gas fields. In the forest zone, in almost all areas where lands previously in a natural state are being developed under a rural state, are being developed under Agriculture and industrial construction, gullying accompanies disturbances of the natural landscape. In the zones of deserts and semi-deserts along the river valleys on the Caspian lowland, on the Ustyurt, along the Amu Darya, ravines develop.
Despite the fact that ravines appear in all zones, their distribution is uneven. The prevailing amount, as noted by all researchers, corresponds to zones of active and long-standing agricultural development, and plowing of land is the cause of the most massive appearance of ravines in the south of the forest-steppe and steppe zones. The transformation of the natural complex in these zones under the influence of economic activity has led to "accelerated" linear erosion.
Of the natural factors of gully formation, the growth rate, size of ravines, their number and total length The greatest influence is exerted by azonal factors: the morphometry of water collections, the geological structure, and the dissection of the territory by a valley-gully network.
Ravine erosion is a complex relief-forming process. The emergence and activity of the development of ravine forms is determined by the whole complex of natural characteristics of the territories, i.e. there is no leading natural factor in the formation of ravines. The desire to single out such a factor among others is due to the difference in natural conditions in the regions. For example, in the case when the ravine of a region is characterized, which has different erosion or filtration capacity of soils and soils, other things being equal, one gets the impression of a “leading” influence of the geological factor. If we consider a region whose territory is dissected to varying degrees by a girder network, it is its presence that is considered as the main factor in the formation of ravines. The presence of elevated and flat territories in a particular region creates the impression of a “leading” geomorphological factor. At the same time, the general background of high damming of the region, associated, for example, with heavy precipitation or significant erosion of soils, can be relegated to the background. The diversity of natural conditions determines the variability of ravines within regions, and the quantitative characteristics of ravines (density and density of the network, the size of ravines) are a function of the totality of all natural characteristics of territories and the degree of anthropogenic impact.
The consequence of anthropogenic impact in different conditions and types of economic development are: the creation of additional runoff boundaries, concentrating the flows of melt and rainwater, the redistribution of runoff in the catchment area, the decrease in the filtration capacity of soils and soils, and the disturbance of natural vegetation. In the vast majority of cases, anthropogenic impact is a change in the parameters of all or part of the complex of natural factors of gully formation, the composition of which practically does not change. Thus, the complex of natural conditions - the factors of formation of ravines - is the main one that determines the characteristics of the region's damming.
Similar information.
Surely each of us had to see sharp slopes on the plains, which are usually overgrown with shrubs. It is about these slopes, which are called ravines, that we will talk about in our article.
What is a ravine, what are the geographic features of a ravine, and how are ravines formed?
Gullying
Ravines are linear landforms characterized by sharpness and steepness. They are formed due to the melting of snow and heavy rain, which literally wash the soil with stormy streams. The earth is eroded, so-called potholes are formed. Thus, the origin of ravines is associated with precipitation and atmospheric phenomena, including the wind, which carries out the washed-out land, thereby clearing the ravine and making it even deeper.
Usually, plants bloom in ravines that do not need a lot of sunlight.
It is worth noting that ravines have a detrimental effect on fertile lands. Usually people struggle with ravines, preventing them from deepening, planting trees and shrubs, thanks to the roots of which the surface layer of the earth receives at least some protection from atmospheric phenomena. The earth, which is held together by the root system of plants, is able to withstand the influence of rain. However, this may not be enough if there are no special furrows around the ravine. These furrows are made so that water flows along them, bypassing the ravine.
Ravines are most characteristic of the steppe, forest-steppe zones. Their formation occurs due to uneven precipitation and drying of the soil. As a rule, the formation of ravines requires the soil of rocks, namely clay, loess.
The anthropogenic factor also largely contributes to the formation of ravines. The plowing of slopes, as well as the destruction of vegetation and the destruction of the topsoil, is one of the main factors in the formation of ravines. Meanwhile, it is quite difficult to grow any crops in the ravines. Therefore, many countries seek to combat the formation of ravines by a variety of methods.
Ravines are the initial form of valley formation. You can read about this form of relief in the article.
The formation of ravines, widespread in the steppe and forest-steppe zones, is the result of water erosion - the process of erosion of soils and loose rocks underlying them by streams of water flowing down slopes from rains and melting snow. The towering elements of the relief of the earth's surface form a hydrographic network - a system of interconnected paths for the flow of rain and melt water. The formation of water jets in some places, the volume of which increases with the growth of the area of the basins feeding them, causes erosion of the soil surface. Erosion processes begin to manifest themselves at a slope steepness of 0.5-2°, noticeably increase on slopes with a slope of 2-6° and develop significantly at a steepness of 6-10°.
In the process of their formation, ravines go through several regularly changing stages. At the first stage of erosion, a ravine, or rut, of triangular cross-section, is formed on a steep section of the slope; its bottom is almost parallel to the surface of the earth. At the second stage, the rut deepens with a decrease in the longitudinal slope of the bottom. A cliff 5-10 m high is created at the top. The pothole expands and becomes trapezoidal in cross section. By the end of the second stage, a smooth longitudinal profile is developed in the lower part of the ravine - a transit channel, within which the erosion is balanced by the inflow of soil. At the mouth of the ravine, where the water, spreading, loses speed, an alluvial cone is deposited. At the third stage, the ravine further grows towards the watershed and its cross section expands as a result of washing and shedding of the banks. Along the side thalwegs, through which water flows to the ravine, on the secondary basins, branching ravines - screwdrivers - begin to form.
The ravine continues to develop until it reaches uneroded ground layers, or the drainage basin feeding its top decreases close to the watershed to such an extent that erosion ceases. In the fourth stage, deep erosion and erosion of the banks gradually stop, the ravine stops growing. Its slopes take on a stable shape and are overgrown with grass. The ravine turns into a beam. The side slopes are steepest at the top. As we approach the mouth, the slopes of the ravine become flatter as a result of soil shedding and are covered with a soil layer.
To reduce and slow down the runoff of water from the catchment area, the most appropriate agrotechnical measures are plowing the soil in preparation for sowing crops across slopes, strip placement of crops, creating a grass cover on steep slopes, and growing shelterbelts. The top of the ravine is most intensively eroded. To slow down the inflow to the top of the water during showers, a system of earthen ramparts is sometimes arranged on the immediately adjacent strip, slowing down the runoff, delaying it, or distributing it among several channels, diverting it to nearby screwdrivers.
To hold inflowing water on the roadside, two or three water-retaining shafts are sometimes arranged with a height of 1 to 2 m and a crest width of 0.5 (narrow profile shafts) to 2.5 m. Shafts after compaction and precipitation should be 0.2- 0.5 m rise above the level of water that can accumulate behind them. Shafts are placed along horizontal lines, bending their end sections up the slope. Shafts are traced along straight line segments, their crest must be horizontal. Shafts can be protective (deaf), when water can leave the pond only after reaching the height of the crest of the shaft, and open, when a lowered place is arranged at the end of the bends to drain the water.
The water-retaining shaft closest to the top of the ravine is usually located at a distance of 10-15 m from the top of the ravine, and not closer than two or three depths of the ravine at the top. Every 100 m of the delay shafts, transverse spurs are made to interrupt the flow of water along the shaft.
There are 4 main stages.
First stage- the formation of a gully, or pothole, 30 - 50 cm deep. A characteristic feature of a gully is the parallelism of the longitudinal profile of its bottom to the surface of the slope on which the ravine was formed. In plan, the ravine has a linear shape; cross section - triangular or trapezoidal. On plowed areas and loose soils, the first stage proceeds very quickly (1 - 3 years).
Second stage- the formation of the apex cliff. The bank of the beam, being steeper than the catchment slope adjacent to its crest, is eroded to the depth faster than the slope, so a cliff is formed below the crest of the beam. The base of the cliff is washed away by the falling stream of water. The wall of the cliff collapses, blocks of soil are washed away by the water flow and carried away by the current. The height of the cliff above the bottom of the ravine at its top is from 2 to 10 m. The ravine grows in length with the collapse of its top, towards the water flow, crashing into the slope adjacent to the gully. At the same time, it deepens, but the mouth of the ravine does not yet reach the level of the bottom of the gully. The ravine, as it were, "hangs" above the bottom of the beam. The longitudinal profile of the bottom of the ravine has the form of a concave line and differs greatly from the surface profile of the eroded banks of the gully and adjacent slopes. The slopes of the ravine are bare, steep and unstable. The scree of soil at their base does not linger, as it is carried away by the water stream. The ravine at this stage grows both in depth and in width. As the bottom of the ravine deepens, its mouth falls lower and lower and, finally, reaches the level of the bottom of the gully. The ravine is entering a new stage of development.
Third stage- development of an equilibrium profile. It begins when the mouth of the ravine descends to the level of the bottom of the gully, i.e., reaches the local base of erosion. The bottom of the ravine above the mouth continues to deepen until its longitudinal slope corresponds to the slope of the equilibrium profile for the given soil. With this slope of the bottom, the speed of the water flow is so small that its strength will be balanced by the resistance of the soil. At this speed, the water flow is usually not able to carry large particles of solid runoff, so the equilibrium profile is characterized by deposition along the bottom of the sediment ravine. At the beginning of this stage of development, sediments are deposited at the mouth of the ravine, then the deposition zone increases, moving towards the top of the ravine as the bottom deepens and its slope decreases. The ravine in this stage grows in depth, width and length. Growth in width occurs as a result of erosion and collapse of the slopes of the ravine, since the water flow does not flow along the bottom in a straight line, but tortuously.
Fourth stage- attenuation of the growth of the ravine. This stage begins after the development of the equilibrium profile of the bottom of the ravine. There is no further deepening of the bottom. The growth in width continues due to erosion and collapse of slopes, as a result of which the bottom of the ravine expands. Gradually, the slopes of the ravine reach the angle of a natural, stable slope for a given soil, and become overgrown with vegetation. The ravine turns into a hollow or a beam.
It is quite possible to observe all stages of development on the same ravine, since in the listed sequence they spatially move towards the flow of the water flow: a ravine, a cliff, areas with an equilibrium profile, areas of attenuation (near the mouth). When the top of the ravine reaches the watershed, further growth in length stops, the cliff at its top flattens out. The growth of a ravine can be stopped at any stage of development by stopping the flow of water into it or by fixing the top and bottom with a spillway.
At the first two stages of development, water enters the primary ravine mainly through its top, and subsequently through the runoff-shock edge, i.e., facing the upper part of the catchment slopes. This feature must be taken into account when fixing and afforesting such ravines.
Let us consider the reasons for the formation and features of the growth of secondary ravines. The description of the stages of development of primary ravines showed that a water flow with the same destructive force develops such a longitudinal profile of the bottom of the ravine, which corresponds to the profile of equilibrium between erosion and soil deposition. As a result, the ravine fades and turns into a beam.
It can be assumed that the longitudinal profiles of the bottom of all links of the hydrographic network, which has developed in the process of geological erosion, correspond to the equilibrium profile for the normal flow regime, i.e., undisturbed by human economic activity. This is all the more likely that before the economic development of land, all links of the hydrographic network were covered with forest or grassy vegetation, depending on the zone. Many of them are now covered with vegetation.
At present, a significant part of the hydrographic network has. The reason for their formation, apparently, is the discrepancy between the new, increased surface runoff and the previous equilibrium profile of the bottom of beams, hollows, etc. Their slopes did not change, therefore, the speed of water flow along their bottom could not change. Therefore, the increase in the kinetic energy of the flow can be explained at a constant speed only by an increase in the mass of water flowing down from the slopes of the catchment area. Increased surface runoff cannot be explained by an increase in precipitation, since in historical time The earth's climate has not changed. The increase in surface runoff can only be explained by the improper use of land, deforestation and increased plowing of the land with a simultaneous deterioration in the water-physical properties of the soil.
Growth of bottom ravines begins, in fact, with the development of a new equilibrium profile corresponding to a new increased water flow. Fundamentally not different from the third stage of development of primary ravines, the growth of secondary ravines also has a number of features. First comes the destruction ("renewal") of the bottom, and then the banks of the network. The formation of a bottom ravine can begin in a gully link, and then in hollows and hollows flowing into this gully as the top of the bottom gully moves towards the upper reaches of the gully. This process can also start simultaneously in several links of the beam system or only at the top of the beam. Everything will depend on which part of the hydrographic network the most intense discharge of surface water runoff takes place.
The third stage of development of the bottom ravine ends with a complete renewal of the bottom and banks of the ancient hydrographic network. These ravines, as a rule, have many peaks, according to the number of former hollows and hollows. The fourth stage - the attenuation of the ravine, proceeds as described above. The ravine gradually turns into a new beam. Figuratively speaking, if ravines are fresh wounds on the body of the earth, then beams are scars from old wounds. A feature of the growth of bottom ravines is the fact that they inherit from the former hydrographic network their catchment areas. Water enters these ravines not only through the top, but also from the adjacent slopes of the catchment through the edges of the gullies (hollows). With increased water runoff, which actually causes the appearance of a secondary ravine, the banks of the ravines are cut through by jet washouts even before they are renewed.
Secondary gully growth
Features of the geological structure of a particular area affect the speed of passage of individual stages and appearance ravines.
The formation of ravines is most rapid on loess deposits and loose soils.
The older the agricultural areas, the more ravines there are. With the growth of ravines, a lot of developed land is lost. But the harm from ravines is not only this. They reduce the level of groundwater, increase the area of the evaporating surface and thereby cause the drying up of the territory, as pointed out by V. V. Dokuchaev. In addition, ravines, dividing the arable land into small pieces, make it inconvenient for cultivation. The removal of solid runoff from ravines and its deposition in river floodplains lead to shallowing of rivers and swamping of floodplains. Gully erosion causes great and almost irreparable damage to the land. This creates an urgent need to study this phenomenon and development of measures to protect the earth from destruction.
Ravine (top, peak, waterhole, yar, log, hollow, rut, ditch, abyss). The water that has fallen from the atmosphere, escaping in the form of streams along an inclined surface, is capable, under certain conditions, of eroding the land. This is how all the elongated ruts of erosion occurred - most of the river valleys, beams and ravines, of which the latter represent only the youngest or first stage of the process of erosion or, as geologists say, the formation of negative landforms. Under favorable conditions, i.e., with a significant slope of the terrain, with looseness of the soil and soil, in the absence of forests, etc., sometimes the most insignificant reason is enough to start the formation of O., for example, furrows along the slope, paths trodden by cattle, cracks in the soil, etc. The most common reasons for the emergence of O. are the following (according to the report of Mr. Kern): 1) reduction of forest or shrubs growing along O. and uprooting of stumps; 2) plowing large soddy slopes with a dip angle of 20 degrees or more, depending on the soil and the geological structure of the lake walls; 3) carrying out boundary furrows towards O., lowlands and hollows; 4) digging ditches, quarrying stone, and in general any violation of the integrity of the sod cover on a steep slope; 5) grazing cattle on steep slopes and especially driving them along one path; 6) solar heat and very coldy giving cracks in the soil; 7) plowing up the so-called "saucer-shaped hollows" in the steppe; 8) formation of railway embankments and cuts; 9) vestments for lowering forests in mountainous areas; 10) landslides and failures that appeared due to geological reasons. In a number of these factors, the most prominent place is undoubtedly occupied by deforestation along the slopes. As an instructive example, one can point to O. in the upper reaches of the Oka, between the village of Verkhnyaya Morozikha and the village of Voronets. According to S. N. Nikitin, all O. here have the same geological structure along the entire path, but their fate and development are strictly dependent on the distribution of forest areas. Near the village of Morozikha, ravines produce terrible destruction on arable land, while in the nearby forest area we see them only overgrown, with completely inactive peaks. But now, closer to the village of Voronets, vast areas of forest were cleared several years ago, and waterholes, powerful destruction, and cliffs of loess have already begun in the peaks of these overgrown and decayed lakes. Usually, quickly passing through the stage of a ditch and rut, O. vigorously begins to deepen and grow with its top. Sometimes the O.'s walls are made flatter, covered or overgrown with forest, and the O. freezes and turns into a beam. But more often O. remains active, creates conditions on its walls for the formation of new O. branches, and then, in a relatively a short time, the country is covered with a dense and intricate network of O. Particularly significant erosion of their surface is distinguished by areas lined with loose material - the steppe zone of Russia, Turan, China, some states of North America, Spain, etc. In order to judge the ravine nature of southern Russia, it is enough to look at the attached piece of a three-verst map of the Poltava province, which can still be considered average in terms of ruggedness of O. (Fig. 2). There are areas in the south where the area under O. occupies 15-20% of the entire area. In the counties of Zadonsky, Nizhnedvitsky, Korotoyaksky and Bogucharsky, the area of \u200b\u200buncomfortable land is about 120 thousand acres, of which a significant part should be attributed to the steep slopes of O. There is reason to think that people found the relief of the southern Russian steppes already at a dormant stage, i.e. . with tinned or forested beams, and only later plowing up the slopes and clearing forests brought the country to the sad state in which it is now. And at the present time it is not uncommon to meet at the bottom of a once tinned beam a secondary acting O., up to 15 meters or more deep. There are few indications in the literature about O.'s growth rate. O. at Gorishny Mlyny, near the town of Kobelyak, grew at its peak, from 1872 to 1888, by 320 feet, that is, it grew at a rate of about 3 fathoms per year. In the Lebedyansky district of the Tambov province, on the site of a drained pond in 1862, an O. (Prince) was formed, which over the next 6 years lengthened by 70 sazhens and formed a branch 30 sazhens long. After 30 years (in 1892) it grew by another 250 sazhens and deepened by 3 sazhens. Over the past 24 years, water has carried away at least 2,400 cubic meters. fathoms of earth, forming a gaping abyss, an area of about 2 acres. On the basis of all such indications, one can take the average growth rate of O., equal to about 3 fathoms per year. For the most part, the upper O. is a cauldron-shaped or cirque-shaped abyss, with completely sheer walls. From them in the spring and after showers, vertical columns of earth are separated, fall into the cauldron, are ground and carried out by water. Further, towards the mouth of the O. it becomes wider, the walls are laid back; there is a mass of landslides, landslides and screes; finally, at a certain angle of incidence of the slope, the lake freezes, i.e., becomes soddy. The looser the surface rocks, the longer, deeper, and steeper the lake. O. our steppe belt can be divided into two large type- O. of the southwestern steppe, loess, and O. of the eastern steppe, clayey. The former are characterized by their considerable size and steepness of the walls, which are usually vertical in the upper O.. The latter are wider and have more gentle slopes. Here, the descent to the O. sometimes begins a mile or more from the riverbed, while in the loess steppe, completely flat terrain almost suddenly breaks into some kind of O. The character of the O. is also reflected in the physiognomy of the steppe: while East End the steppe strip appears as a whole system of ridges, bulges, - the southwestern one seems to be a boundless, smooth plain, pitted with furrows - enemies. The average size of Poltava O. is as follows: length 7.4 versts, width 23.6 fathoms, depth 5.6 fathoms. However, in the same province there are O. 70 versts in length, 140 fathoms in width, 8 or more fathoms in depth. With such a considerable length, lakes can cut watersheds, thus connecting various river systems. The connection can occur either directly, by the direct growth of O. up to the neighboring valley, or by means of the closure of two, going towards each other. Thus, in Zenkovsky Uyezd, there are O.-beams belonging to the Psyola system, which, with their peaks, come very close to the right bank of the Vorskla. Connections of the second kind, by means of bows, are rich, for example, in the watershed Psel - Goltva - Vorskla (Volchek, B. Krivaya Ruda, etc.). In this way, there was even a change in the course of the river, the movement of watersheds, etc. So, according to Sokolov, beams in the Alexandria district of the Kherson province (Bogdanovka, Chumyannaya, Chernoleska, etc.) belonged earlier to the Tyasmina river basin and only later were captured by the Ingulets river, as a result which was the movement of the watershed to the north and the change in the flow of waters in the direction opposite to the previous one. O.'s value in economy of the nature is huge. Generally speaking, the process of ocean formation leads to the leveling of the surface of the globe by washing out the convex parts and filling the sea depressions with solid material. In particular, on each given piece of land, this process leads to extreme furrowing of the surface, and this circumstance is the highest degree unfavorable for humans. Here are the main consequences of the growth of oceans: 1) Wash-off and removal of soil into rivers and seas. In this way, many thousands of acres of rich black soil are taken from the South Russian farmer every year, which, in turn, clogs the river channels. Partial shallowing of rivers is due mainly to this circumstance. 2) Rapid runoff of atmospheric precipitation. Hence the strong waterfields in spring and after rainstorms, the shallow water of rivers in the rest of the time and the low flow of water into the subsoil horizons. 3) Drainage of the terrain and lowering the level of groundwater. The phenomenon is especially pronounced when O. cut through a suite of water-bearing rocks and rests on the bottom of water-resistant rocks. The desiccation of the steppe, agricultural hardships must be attributed, to a large extent, to this factor. 4) The increase in the evaporating surface, in some places by 25-50% of the entire area of the earth, also plays a significant role in the drying up of the area. 5) The drift of cultural areas with sand almost always occurs when O. cuts through the thickness of the sand, which is blown out of the channel. 6) Cutting O. roads is a common and ruinous phenomenon. Between Alatyr and Ardatov, for 22 versts, in the second half of the fifties there were three bridges across the O., but now there are 42 of them. and in defense of O. (Krasnov, Mertvago). Literature. Kipriyanov, "Notes on the spread of ravines in southern Russia" ("Journal of the Head of the Department of Communications", 1857); V. Dokuchaev, "O. and their meaning" ("Proceedings of the Imperial Free Economic Society", 1887, vol. III); N. Sumtsov "Ravines" (popular essay, Kharkov, 1894); E. Kern, "Ravines, their fixation, afforestation and damming" (3rd ed., M., 1897). In addition, many separate chapters and information about O. are scattered in various "Works" of natural history expeditions, geological works, etc. P. Ototsky. Strengthening ravines. O. does not form equally quickly on all soils; their formation requires, on the one hand, the periodic appearance of masses of water that cannot be absorbed by the soil, and, on the other, a certain tendency. soil to erosion, due to the low connectivity of its particles. The strongest influence of periodically flowing waters can be observed on the slopes of mountains, the tops of which are covered with eternal snow, then on the slopes of more or less extensive plateaus (for example, Yayla in the Crimea); in these cases the destructive power of the water is increased to an extraordinary degree by the rapidity of its flow over a more or less steep slope, so that the most coherent soils are easily eroded. Only the presence of the forest weakens the rate of runoff of water and protects the soil of the slopes from erosion. In flat areas, periodically appearing waters do not acquire such significant speed and such destructive power; in addition, a significant part of the slowly flowing water can be absorbed by the soil. Therefore, erosion is not always observed in the plains: the presence of a grassy cover (turf), like the presence of a forest on the slopes of mountains, weakens the rate of runoff of water and, in addition, increases the connectivity of the upper soil layer, in which the roots of herbaceous plants branch abundantly. The destruction of the herbaceous cover that held the soil together is often sufficient for the destructive power of water to manifest itself and soil erosion to appear. The destruction, or rather weakening, of the herbaceous cover occurs most often under the influence of grazing, which, moreover, tramples the topsoil, thereby weakening its coherence. To a large extent also contributes to the formation of gullies plowing soil. Arable land, however, absorbs water much more strongly than unploughed soil, and on a completely flat place it can even stop the flow of periodically appearing waters [One of the rare exceptions can be observed in our steppes, where late snow often falls on the soil that has already frozen and the resulting when it melts, its water flows down the frozen soil without seeping into it.]; but the cohesion of the soil is so diminished by ploughing, that the slightest roughness, an insignificant hollow, is enough to reveal the erosion of the soil. The more the lake grows, the stronger the destructive power of water is manifested in it, washing away the slopes and carrying the washed earth to the mouth of the lake; these takeaways (in the Caucasus they are called mudflows) or are deposited in places flooded with water, forming undesirable sediments, or, falling into rivers, contribute to the formation of shallows in them, which impede navigation. Therefore, continuing to expand, or, as they are called, long O. present certain dangers to the underlying places, and their strengthening may be of national interest. O. of small extent, which have begun to form recently, usually calm down on their own, as soon as the influence of the cause that caused their formation is eliminated, that is, cattle grazing, plowing of slopes, etc., cease; the slopes of such an O. are overgrown with grass, and sometimes with forest, and it passes into the category inactive or calm. The plowing of slopes or increased grazing of livestock can again cause erosion of the calm O. and cause its further growth, which is expressed in the formation of new branches or so-called screwdrivers. Thus, preventive measures in relation to O. are reduced to the protection of the grassy cover available on the slopes and on the tops. The fight against active waterways consists in artificially strengthening them, followed by either afforestation of slopes or damming of waterways to form a permanent reservoir. The technique of work carried out to strengthen the O. is borrowed from the practice of fortifying and afforesting mountain slopes, which developed in France and, later, in Austria. It goes without saying that much weaker structures are sufficient to strengthen O. than those that have to be resorted to to weaken the destructive power of mighty mountain streams. The latter are restrained by stone dams, sometimes erected with cement masonry, while in O. they arrange barriers made of wood, most often of brushwood. Weirs are built to slow down the flow of water and make it deposit behind the dam those particles of soil and stones that it carries with it. Behind each dam, eventually, a layer of sediments is formed and the slope provided with them turns into a system of terraces with a very slight fall, in which the flowing water cannot acquire a destructive force. The system of such dams made of fascines is shown in the attached table. Strengthening the slope with fascinian dams. To determine the number and nature of dams, it is necessary, first of all, to determine the basin of a given lake, that is, to determine the area from which water flows down its channel. For such a definition, the terrain plan expressed in horizontal lines (Fig. 3) is best of all, on which the watershed lines that limit the O.'s basin can be easily marked. However, depending on the properties of the soil and the state of its surface, a larger or smaller part of the basin will absorb water that falls on it, which, therefore, will not drain into O. For given soil properties, the boundaries of such a safe part of the basin will be determined by a certain limiting angle of inclination of the surface . But an accurate determination of the area of the basin is important in regulating mountain streams, where a large basin with steep slopes requires the construction of permanent dams, while the barriers built in O., despite all their ease, usually turn out to be more than sufficient. These barriers are made of stakes and brushwood, which are either tied into fascines or braided between stakes driven into the ground. In especially dangerous places, such barriers are made double or even triple (Fig. 4), but in the vast majority of cases they are limited to single ones. A section of a dam of braided brushwood is shown in Fig. 5, fascinated - in Fig. 6. If fresh willow brushwood or fresh willow stakes are used for such dams, then they easily take root in the earth applied to the dams, give new shoots and a living dam is obtained, which is especially durable. Such a living dam is shown in Fig. 7 [FIG. 5-7 shows the dimensions of individual parts of the dams in meters.]. Installation
