ABRASION is the process of mechanical destruction by waves and currents of indigenous areas. Abrasion is especially intense near the shore under the influence of surf (roll-up). G. p. experience impact, corrosive destruction under the influence of impacts of stones and grains of sand, dissolution, and other influences. Underwater aeration occurs less intensely, although its effect on the bottom of seas and lakes extends to a depth of several tens of meters, and in the oceans to 100 m or more. A. should be distinguished from erosion, which destroys loose, often Holocene exc. This interpretation of aeration and erosion is used in oceanology. In general geology and geomorphology, abrasion is usually understood as the process of destruction of bedrock and loose soils. Peculiar abrasion processes occur on the shores of the polar regions, often formed by frozen soils, containing villages. ice. Under the influence of waves, frozen areas are thawed with complete or partial removal of the thawed material. The process of destruction of such shores by waves is called thermal abrasion.
Geological Dictionary: in 2 volumes. - M.: Nedra. Edited by K. N. Paffengoltz et al.. 1978 .
Abrasion
(from Latin abrasio - scraping, shaving * A. abrasion; n. Abrasion; f. abrasion; And. abrasion) - mechanical process. destruction and demolition of hydraulic structures in the coastal zone of water bodies (oceans, seas, lakes, reservoirs) by waves and surf, as well as by the influence of moving and suspended debris in the water. As a result, A. specific ones are created. relief forms: abrasion ledges (cliffs), wave-cut niches ("spurs"), underwater abrasion terraces or platforms (benches), etc. This process is often called. A. mechanical, as opposed to A. thermal (thermal abrasion), i.e. destruction of coasts composed of permafrost and ice, and A. chemical (destruction of coasts as a result of the chemical influence of water). The less stable the g.p., the larger the adjacent bottom zone and the greater the strength of the waves, the higher the speed of A. The most intense A. in the surf zone. The length of abrasion areas on the shores of reservoirs around the globe is approx. 400 thousand km (51% of the total length). On average, 3.45 billion m 3 per year of clastic material enters reservoirs from cliffs, and 7.4 billion m 3 per year from benches. Sand, gravel and larger material formed during A. make up an underwater accumulative terrace attached to the bench, and accumulative coastal and underwater (spits, bay-bars, etc.), with which coastal-marine deposits are connected and deposits are being built. materials. When developing coastal deposits of gravel and sand, it is necessary to coordinate the scale of their extraction with the rate of supply of clastic material. Sediments of abrasion origin suspended in water migrate along the shoreline or are carried by currents beyond the coastal zone and deposited in deeper parts of water bodies. Yu. F. Chemekov.
Mountain encyclopedia. - M.: Soviet Encyclopedia. Edited by E. A. Kozlovsky. 1984-1991 .
Synonyms:See what “Abrasion” is in other dictionaries:
- (from Latin abrasio scraping), destruction, grinding and demolition of rocks under the influence of wind, water or ice. Abrasion is most intense as a result of the action of surf and corrosion on the seashore (dissolution of rocks under the influence of chemical... ... Marine Dictionary
- (lat.). Painful irritation of the stomach from strong substances. Dictionary of foreign words included in the Russian language. Chudinov A.N., 1910. abrasion (lat. abrasio scraping) 1) geol. destruction of the shores of seas, lakes, large... ... Dictionary of foreign words of the Russian language
Scraping, destruction Dictionary of Russian synonyms. abrasion noun, number of synonyms: 5 scraping (7) ... Synonym dictionary
abrasion- Mechanical destruction of the shores of seas, lakes, rivers and reservoirs by waves. [Terminological dictionary of construction in 12 languages (VNIIIS Gosstroy USSR)] abrasion Mechanical destruction by waves and currents of bedrock and loose rocks of marine and... ... Technical Translator's Guide
A type of natural disaster in insurance. This is how the demolition, erosion and destruction by the water element, sea surf, of the land surface directly adjacent to the water is determined. Applies to seas, rivers, lakes and reservoirs. Dictionary… … Dictionary of business terms
- (from the Latin abrasio scraping), the process of destruction by breaking waves of rocks in the coastal zone of reservoirs (oceans, seas, lakes, reservoirs). The total length of the abrasion areas is 51% of the total length of the coastline of water bodies on the globe. WITH… … Modern encyclopedia
- (from Latin abrasio scraping) the process of destruction by waves and surf of the shores of seas, lakes and reservoirs ... Big Encyclopedic Dictionary
Destruction of shores and coastal sections of the seabed by sea waves... Geological terms
ABRASION, in geology, mechanical wear of rocks under the influence of mutual abrasion by rock fragments in contact with it. The main agents of abrasion are water flows, debris at the base of glaciers, as well as sand,... ... Scientific and technical encyclopedic dictionary
- (from Latin abrasio scraping), the erosive process of eroding the shores of seas and reservoirs under the influence of wave impacts, weathering or human economic activity. As a result, abrasion zones are created on shores exposed to erosion... ... Ecological dictionary
Books
- Life safety. Protection of territories and economic facilities in emergency situations, Onoprienko M.. Organizational, legal and technical issues of life safety are outlined, as well as the impact on the human body and its habitat of negative factors of natural,…
Abrasion of sea shores
Abrasion
Abrasion is the process of destruction of the shores of water bodies by waves and surf. Abrasion also extends to the bottom of reservoirs to a depth of several tens of meters, and in the oceans - up to 100 meters or more. Debris material moves along the coast, is carried away and deposited offshore where wave energy weakens, and in depressions of the bottom. As a result of abrasion, various forms of relief of the abrasion coast are created.
There are mechanical (basic), chemical and thermal abrasion.
Mechanical abrasion occurs under the influence of mechanical impact of waves and dragged debris.
Chemical abrasion is the destruction of shores composed of soluble rocks (carbonates, sulfates, halogens). Under the influence of salts and carbon dioxide contained in chemically aggressive sea water, dissolution and leaching of rocks occurs.
Thermal abrasion occurs mainly in the polar zones on the shores of seas composed of loose permafrost or ice. Here the coast is destroyed not only under the influence of the mechanical energy of waves, but also as a result of the fact that the temperature of sea water is higher than the temperature of frozen rocks, and the latter thaw, loosen and are more easily destroyed. Chemical and thermal abrasion are always accompanied by mechanical, which is ultimately the main one. Abrasion occurs most intensely on deep coastlines, i.e. where there is a steep underwater slope. Then the waves approach the shore without wasting their energy, as happens when waves overturn on shallow shores, and all the kinetic energy of the waves goes to destroy the shore. First, at the sea's edge, a depression is formed at the base of the coastal cliff - an abrasion or wave-breaking niche (in conditions of permanent permafrost, a thermal abrasion niche), and then with its further deepening and the collapse of the bedrock cornice overhanging it, a steep abrasion ledge, or cliff, is formed. The intensity and speed of abrasion depend not only on the energy of the waves, but also on the height of the coast, the composition and structure of the rocks composing it, i.e. on their resistance to erosion. Metamorphic, igneous, and cemented sedimentary rocks are durable and strong. If the coast is composed of soft rocks, then its destruction is especially intense and is often accompanied by sliding or subsidence of rock blocks with the formation of steep walls. In this case, the abrasion niche does not form (does not have time to form).
The average rate of abrasion on such shores is 0.6-1 m/year, although during strong storms the shore can retreat by 10 m at once. If the shore is composed of hard rocks, then large fragmentary material formed during their destruction remains at the foot of the cliff, and smaller ones are carried out to sea by reverse currents and deposited on an underwater slope, gradually forming an underwater accumulative terrace. As the cliff is destroyed and retreats inland, a slightly inclined seaward or horizontal abrasion platform - a bench - is formed in front of its foot. The surface of the bench articulates with an underwater accumulative terrace, forming an inclined abrasion-accumulative surface, which subsequently, being brought to the surface from the area of wave processes (as a result of uplifting the coast), forms a marine terrace.
Sometimes, when a rocky coast is destroyed and retreats, individual rocks - kekurs - remain in the coastal zone. As the bench expands and coarse material accumulates at the foot of the cliff, a continuous block or boulder, depending on the lithology of the rocks and the duration of their processing by the sea, a blind area or flooring is formed. This blind area protects the shore from erosion. The bench can be developed in clayey rocks, then there is no blind area. The surface of the bench is either flat, or ridged, or stepped, depending on the angle of inclination and the uniformity of the eroded rocks and their composition. According to the degree of development, cliffs are divided into modern, or active, currently being formed, dying and ancient, already extinct. Over time, the bench and accumulative underwater terrace expand, and the underwater slope flattens. Waves passing over the developing shallow water expend significantly more energy, and the abrasion gradually weakens and fades.
The underwater slope turns from deep to shallow, on which sediment accumulates and accumulative forms begin to form - underwater and surface levees. In this case, the bench, covered with sediments, becomes buried. Thus, the abrasive activity of the sea can naturally be replaced by accumulative activity. The processes of abrasion and accumulation in natural conditions lead to the leveling of the coast - the cutting off of capes protruding into the sea and the filling of bays with sediments.
The entire coastal strip of all reservoirs on the planet was formed to one degree or another under the influence of waves arising in these reservoirs. The process that occurs under the influence of waves and forms the coastline of reservoirs is called coastal abrasion. The word Abrasia is translated from Latin as Scraping. It is the mechanical destruction of the coastline of the seas, rivers and lakes of the planet due to the incessant impact of waves on it that determines the state of the shores of reservoirs that we observe today. The most intense coastal abrasion occurs near the coast, at shallow depths, where surf waves and water flows continuously rolling onto the rocks of the coast gradually destroy these rocks, forming peculiar terraces of the coastline at the water-land boundary. If the depth of influence of waves on the destruction of shores in lakes and rivers is relatively small (5-10 meters), then in oceans and seas the process of shore abrasion occurs to a depth of 50 - 100 meters. During the process of abrasion of the shore, breaking waves attacking it mechanically destroy them, undermining and carrying away the destroyed rock to the coastal zone of reservoirs. Thus, a wave-cut or abrasive terrace is formed directly at the shore of the reservoir. The shore above the water level is called a “cliff,” or “abrasive ledge.” The underwater part of the shore is a “bench”, which is actually an “abrasive terrace”.
Part of the destroyed shore of the reservoir in the form of pebbles, gravel and sand is carried by waves onto the abrasive terrace and settles on it in the form of coastal battery forms. The other part of the material is carried by waves further into the reservoir, where the so-called leaning battery terrace is formed. Coastal abrasion occurs until an abrasive terrace is formed over a sufficiently large area. When the area of the terrace becomes such that the breaking waves, when moving along it to the shore, lose their energy due to the friction of the waves on the bottom, coastal abrasion stops. In some areas of the shores of reservoirs, the length of abrasive terraces can reach 20–25 kilometers. The depth of the reservoir’s advancement deep into the coastline depends on two important factors:
- Strength and intensity of the breaking waves of the reservoir
- Hardness of coastline rocks.
In high latitudes, the coastal strip of the northern seas, in addition to mechanical abrasion of the coast, is also subject to thermal abrasion. Thermal abrasion of shores is the destruction of shore material under the influence of a difference in external temperatures from minus to positive values. Water entering at positive temperatures into cracks in the rocks that make up the material of the coastline freezes in the cracks when the temperature drops to minus values, thereby destroying the rock that makes up the shore of the reservoir. It should be noted that the rate of destruction of coastline rocks during thermal abrasion of the coast is quite high, and in some cases it is higher than in the case of wave-driven coastal abrasion.
In some cases, shore abrasion increases under the influence of the following factors:
1. Increasing the water level in the reservoir.
2. Land subsidence due to tectonic processes.
3. Increased speed of water flow in rivers or underwater coastal currents in lakes and seas in the event of an increase in the amount of seasonal precipitation.
A big problem is created by the processes of coastal abrasion on artificial reservoirs (reservoirs, artificial seas and canals). The shores of such reservoirs are geomorphologically relatively young and unsettled. The material of the coastline in most cases is represented by sedimentary rocks, which are easily abraded. These circumstances lead to significant destruction of the coastline of artificial reservoirs in the process of bank abrasion, which leads to significant costs for bank protection measures. Coastal erosion leads to the loss of land and coastline, which inexorably goes under water. For example: In the northwestern part of the Russian section of the Black Sea coastline, about 1.5 meters of the coast goes under water annually. In some areas, the rate of absorption of the coastline by the Black Sea is 3.5 - 4.0 meters per year. This phenomenon becomes especially problematic within populated areas or industrial and transport infrastructure. To prevent the advance of the sea onto the shore, huge amounts of money are spent, which does not always lead to positive results, since the advance of the sea onto the land, in some cases, cannot be prevented. Therefore, scientists constantly monitor the condition of the coasts within populated areas to prevent emergencies.
Abrasion- the process of mechanical destruction by waves and currents of the shores of oceans, seas, lakes and reservoirs. Its intensity depends on the energy and impact force of the waves, which can reach 0.6 MPa, on their height and direction. The development of abrasion is strongly influenced by the magnitude of tides, speeds along coastal currents, the configuration and topography of the coastal zone (this exogenous geological process begins when the slopes of the coastal part of the reservoir are more than 0.01) and the geological structure of the shores. A general pattern can be identified: the weaker the soil, the more active its development. The characteristics of resistance to destruction of various soils are given in the table.
A high rate of abrasion is observed in reservoirs whose banks are composed of sand, weak clayey soils, and especially loess. In reservoirs it is called reservoir bank reworking. Partly, such intensive development is due to the fact that soils that are not adapted to interact with water find themselves in “hostile” conditions in a very short time.
In the area of development of permafrost soils, it is usually preceded by thawing of the soil by the heat of water masses. This process leads to erosion of the bases of slopes and disruption of their stability with the formation of landslides, landslides, and screes. The depth of action does not exceed the depth of action of waves. As a result, abrasion banks and other forms of coastal relief are formed; one of the most typical forms is a cliff. Due to the demolition of soil from collapsing banks below the water level, an underwater accumulative terrace is formed.
The speed and intensity of abrasion depend on the geological structure of the coast, its shape, bottom slope, direction and energy of wave action. Over time, the process gradually fades due to the formation of a strip of shallow water. Abrasion is especially intense near the shore under the influence of surf (rolling up). Then the soils experience wave shock, corrosive destruction under the influence of impacts of stones and grains of sand, dissolution and other actions.
Underwater abrasion occurs less intensely, although its impact on the bottom in seas and lakes extends to a depth of several tens of meters, in oceans up to 100 m or more.
The coast is the border between land and sea. Although this border is depicted as a line on maps, in reality we should talk about the coastal zone, i.e., a more or less wide strip within which the interaction of land and sea takes place. The coastal zone consists of the shore itself - its surface part, and from the underwater coastal slope. The boundaries of the coastal zone are sea waves, wave currents and tidal phenomena. In addition, some organisms, as well as rivers, take part in the formation of sea coasts. An important condition for the development of the coast is also the tectonic movements of the earth's crust and the geological structure of the coastal land and the underwater coastal slope. The formation of the modern coastal zone is associated with the post-glacial transgression of the World Ocean. The initial level from which it began is considered to be minus 110 m relative to the modern ocean level, characterizing the position of the level 17-18 thousand years ago. During the transgression, the sea covered the coastal areas of the former land.
Although many different classifications of shores have been proposed to date, none of them can be considered completely satisfactory. Perhaps the most widely known classification is that proposed by Johnson. While retaining two main groups in it - subsidence shores and uplift shores, defined in earlier works - he introduces new categories - neutral and complex shores. In the group of neutrals, Johnson includes shores, the formation of which is not directly related to the processes of subsidence or uplift, for example, the coastlines of deltas, alluvial and outwash plains, as well as shores predetermined by a fault structure. Complex coastlines simultaneously exhibit features shared by two or more of the major categories. This group includes shores with signs of both subsidence and uplift, which, for example, is observed in some areas of the east coast of North America. Complex coastlines are characterized by a coastline deeply dissected by bays, located behind a coastal bar, which, according to Johnson, is a sign of an uplift coast. A typical example of a complex coast is the southwestern part of the coast of New Zealand, indented by fjords, where signs of a submerged glacial topography and the straightness and steepness of a typical fault coast are found simultaneously. The main types of coasts identified by Johnson are divided as follows:
1. Shores of Dive
· rias shores
fjord shores
2. Rising shores
· shores of coastal plains bordered by a bar
3. Neutral shores
· delta shores
· shores of alluvial plains
· shores of outwash plains
· volcanic shores
· shores of coral reefs
fault banks
4. Complex banks - any combination of the types described above
The second group in Johnson's classification is perhaps the least satisfactory. In his category of uplift coasts, he recognizes only the uplift of a very slightly inclined section of the seabed, which causes the formation of a straight coastline. It is as a result of the very weak inclination of the coastal zone that coastal and island bars develop along coasts of this type, which are the main criterion for their identification, along with dunes, coastal lagoons and marshes. However, Johnson acknowledges that such forms do not necessarily have to be included in the group of uplift coasts he is considering: they can also form on a very flat coastal plain that has been subject to some flooding. However, it did not provide for the possibility of raising the steep bank.
The advantage of this classification is the genetic principle underlying it. When the classification is strictly applied, it is found that most shores fall into the category of complex. Only very few areas in the recent geological past were not affected by fluctuations in the level of the World Ocean due to the alternation of glacial and interglacial eras, as well as oscillatory movements of the earth's crust due to Alpine orogenesis. Some areas of the earth's crust do show a predominance of upward or downward movements, which allows them to be classified into one of Johnson's two main categories. As an example, we can take the southwestern rias coast of Ireland, which is characterized by deep dissection - the main criterion for a coast of this type. Fjord shores are also often clearly visible, but in this case the signs of subsidence are more doubtful, since there is a theoretical possibility of underwater glacial excavation of fjords, subsequently flooded by the sea when glaciers retreat under conditions of stable sea level. Johnson himself acknowledges this possibility.
Coastal abrasion
The degree of compliance of the abrasion bank varies greatly and depends on a number of the following factors:
1. Exposure:
· outline of the coastline in plan
exposure to dominant winds, waves and wave lengths
2. Tidal heights and tidal currents
3. Shore type:
· low bank with dunes
· high rocky coast, usually framed by cliffs
4. Composition of rocks composing the shore
5. Relief of the sea area of the beach
6. Sea level changes
7. The influence of artificial structures
8. Alongshore movement of coastal sediments
Let us move on to a brief consideration of the influence of these factors.
Exposition . Where the coastline has an irregular contour, the energy is concentrated mainly at the headlands, where, as a result, the beaches tend to erode. At the same time, capes are usually composed of harder rocks that better resist erosion compared to neighboring sections of the coast. It should be expected that windward shores will be destroyed more quickly by abrasion processes than leeward ones, although there are deviations from this rule.
Tidal phenomena. The influence of the tide is expressed in the fact that it helps to expand the zone of action of waves, facilitating the abrasion of cliffs. At high tide heights, the profile of the sea zone of the beach is usually smooth, which prevents the premature breaking of waves on underwater shafts with the neutralization of part of their energy. If the profile has the usual parabolic shape, the waves at high tide break closer to the shore and their energy is spent over the surface of the beach, which has a reduced width, which contributes to erosion of the coast.
Low tide. Photo: pfly
Low banks . Low shores are protected from the sea only by sediment accumulations. These coasts include dune coasts, which, in particular, can resist destruction by waves if the dunes are high and well secured by vegetation. Some low banks are protected by marches, provided they are in a very well sheltered place. The very nature of such coasts suggests low vulnerability to storm waves. In the tropics, low shores are often protected by a belt of mangroves or colonies of corals; In the polar regions, ice shelves play a protective role. In all the examples given, the preservation of low-lying coasts is ensured by the environment. If any of the environmental conditions were disrupted - for example, sea level rise - these shores would undergo rapid changes, which would only be possible to slow down with serious human intervention.
Rocky shores . Rocky or cliff shores, in the absence of a protective beach, are directly exposed to abrasion, resistance to which depends mainly on the nature of the material composing them.
The exposure of these shores relative to wave attack and the alongshore movement of sediment are of secondary importance; they determine the presence or absence of a protective beach.
Relief of the sea zone of the beach. The relief of the sea zone of the beach plays a big role in the direction and intensity of abrasion. First of all, relief affects wave refraction; Due to this, wave energy is concentrated on individual sections of the coast.
On shores bordered by a wide shelf, the abrasive activity of waves is less than on steep shores, where significant depths are observed directly at the water's edge.
Changes in the relief of the sea zone near the coast can play an important role in the distribution of individual eroded areas of the bottom in different periods of time.
Sea level changes . Changes in sea level also affect the abrasion process. The decrease in level caused by regression will likely be expressed in a decrease in abrasion activity: the marine zone of the cliff will become shallower, which will lead to a decrease in the intensity of the impact of storm waves on the coast. Rising sea levels lead to a deepening of the sea zone of the beach, as a result of which the sphere of action of waves expands and their abrasive ability increases. In general, rising sea levels contribute to the acceleration of abrasion in those areas where this process has already begun, and on neutral shores - to its occurrence.
Artificial constructions. In some areas, coastal abrasion is caused by various artificial structures, in particular breakwaters or breakwaters. A breakwater built in an area where there is strong alongshore movement of material will impede this transfer, which will inevitably cause erosion of the coast on the “leeward” side of the breakwater.
In other cases, coastal erosion may begin in connection with the construction of a sea channel cutting through the coastal bar.
Along-shore movement. The movement of material along the shore directly or indirectly has a decisive influence on almost all processes of shore destruction.
Scientists especially emphasize the importance of alongshore sediment movement in protecting coasts. If erosion waves approach the shore at right angles, then the beach material moves a relatively short distance from the shore, from where it can again be returned to the beach by alluvial waves that occur during periods of calm weather. Therefore, the constant absence of a beach is explained only by alongshore processes, except in cases where the formation of a beach is prevented by the significant depth of the coastal part of the bottom. The most favorable conditions for the development of abrasion occur where the sediment consumption due to alongshore movement is greater than the supply of material to this area.
This phenomenon is often observed on capes, where sediment transport occurs in both directions from the cape. A coast with a flat coastline is also unstable in relation to abrasion due to the lack of obstacles to the free along-shore movement of material. The negative influence of alongshore movement is especially noticeable in such sections of the coast where the supply of material from the neighboring area excludes any protruding forms.
Along-shore movement of sediment is an extremely important factor determining the nature of coastal abrasion.
Shore abrasion speed
The rate of abrasion depends on many factors and is rarely constant. Typically, during a storm, much more coastal damage can occur within a few hours than during a long period of good weather. The presence and structure of cliffs is of great importance in determining the nature and rate of coastal erosion, greater than the exposure of the coast relative to the waves.
Apparently, there is some relationship between the height of the cliff and the rate of erosion of the shore, since height is one of the important factors of its stability. The nature of the rocks composing the cliff plays a significant role. The erosion rate is also affected by the position of protective structures.
Protection of the shore from abrasion
When considering the issue of protecting banks from abrasion, one should keep in mind only banks composed of rocks that are easily eroded. Shores composed of durable rocks do not require additional protection. The erosion resistance of these rocks is quite sufficient to withstand abrasion.
Natural protection
Where the coast is potentially susceptible to destruction due to low height or poor stability of the rocks, a sufficiently developed beach provides a natural protection against abrasion. It absorbs wave energy and prevents waves from crashing directly onto the walls of the cliffs or onto the surface of the bench. On a low coast in the absence of cliffs, the best natural protection is dunes composed of sand coming from the beach and secured by the roots of psammophyte plants. Vegetation is of great importance as the primary trap for sand in the process of dune formation.
Artificial protection
Since the best natural defense of a shore is a wide and high beach, any method of artificially reproducing this form seems most desirable in seeking ways to prevent or stop abrasion. An artificial beach can be built in two ways. First of all, a beach can be created using sea booms. However, these structures are not always safe for the shore. Buoys, usually built at almost right angles to the shoreline, have the purpose of trapping sediment moving along the shore in order to raise the level of the beach surface. The danger of groynes, as well as breakwaters and some other structures, is that the “leeward” area may experience a sediment deficiency due to the interception of material, which helps to accelerate the erosion process.
Speaking about the significance of the groynes, it is worth noting that their location and character must correspond to the selected section of the coast, since it is impossible to make final conclusions and recommendations on these characteristics of the groynes in advance. Their length must correspond to the width of the sediment flow zone; where this zone is narrow, the groins must be made shorter, but taking into account that all the small amount of sediment available can accumulate in the upper part of the beach, where this is especially necessary. On pebble beaches, the groins should only be short, ending only a few yards from where the beach becomes sandy.
As for the height of the groynes, it should not exceed the maximum height of the level to which sediment accumulation on the beach is expected. The buna should be gently inclined, going under the level of the beach with its lower end; the angle of its inclination must correspond to the slope of the beach surface, which depends on the mechanical composition of the material composing it. As for the distance between the groins, it should be equal to their length. Longer groins can be spaced one and a half lengths apart.
Another way to protect low banks is to construct an artificial embankment located on the inside of the bank.
In some areas, the only possible method of protecting the coast and structures is the construction of coastal wave walls. Such walls can simultaneously be used for walks by vacationers. In other areas, coastal walls are needed to protect low-lying land from flooding during storm surges. This purpose can be served by earthen embankments, similar to those that fence many rivers, protecting their banks from tidal waves, floods or wave erosion.
The walls also help build up the beach. A concrete wall is an extremely strong structure that can withstand the blows of the surf. The force of the reverse surf flow is especially high due to the absence of water loss due to filtration. The drift of material towards the sea, which increases with strong sea winds, contributes to the destruction of the beach directly at the foot of the wall. There are no sand reserves necessary to cushion and stabilize the upper part of the beach. Reducing the height and width of the beach leads to the concentration of wave energy in a narrower zone, which increases their destructive power.
There is another method of shore protection that deserves mention. This is a method of artificial recovery of material washed from the beach, widely used in the United States and called “bypassing”.
Bypassing comes down to the fact that the sediment deficit in any area is replenished by transferring this sediment to it from a neighboring accumulation area.
The scooping of sand from the burring zone initially caused intense erosion of the beach in its “leeward” part, which once again indicates the need to intervene with great caution in the natural process of alongshore sediment movement. The material needed for beach restoration may come from some areas of the shore that are upwind of the scour obstructions or from an entirely different source unrelated to sediment flow. If the initial ratio between the inflow and outflow of material is achieved, the process of sand deposition will be generally equivalent to its loss during erosion and the coast will acquire stability. In order to correctly determine what the material should be, careful collection and examination of samples of sediment currently composing the beach is necessary, including collection of samples from all areas of the beach. The results of these analyzes must be compared with the nature of the material used for filling. The mechanical composition of sediments used to form the beach must be within the limits of changes in the mechanical composition of the material of natural beaches. To obtain an optimal result, the filling material should be somewhat larger than the natural sediment, not altered by erosion, and better sorted.