What Is Soil Erosion?

Soil erosion refers to the process by which soil and its parent material are destroyed, eroded, transported, and deposited under the influence of external forces such as water power, wind power, freeze-thaw, or gravity. The amount of soil displacement caused by external forces is called the amount of soil erosion. The amount of erosion per unit area per unit of time is called the rate of soil erosion (or soil erosion rate); the amount of sediment that is transported out of a specific location in the amount of soil erosion is called the amount of soil loss. In a certain period of time, the total amount of sediment at a certain section of the exit through a small watershed is called the sediment yield of the watershed. The widely used term "soil and soil loss" refers to the process by which the surface layer of the soil and its parent material are eroded, washed away and transported under the action of water.

Chinese name: Soil Erosion
Foreign name: soil erosion
Definition: Destruction and erosion of soil and parent material

Soil loss: Amount of sediment transported out of a specific lot
River basin sediment production: Total amount of sediment measured on a section during a specific period
Types of: Hydraulic erosion, gravity erosion, wind erosion, etc.

Introduction to Soil Erosion

Soil erosion ^[1] is the process of erosion, destruction, separation, transportation and deposition of soil or other ground components under the action of external forces such as water power, wind power, freezing and thawing, and gravity. Narrow soil erosion refers only to the "soil" being separated, damaged, and moved by external forces. According to the types of external forces, soil erosion can be divided into hydraulic erosion, wind erosion, freeze-thaw erosion, gravity erosion, leaching erosion, flash flood erosion, debris flow erosion, and soil subsidence. The objects of erosion are not limited to the soil and its parent material, but also include the soil below the soil, cuttings and soft rock layers. Under the conditions of modern erosion, the impact of human activities on soil mantle erosion is increasing, and its stripping and destruction of soil and surface materials has become a very important external force. Therefore, the comprehensive and precise meaning of soil erosion should be: the process of soil, or other ground-based constituents being eroded, destroyed, separated, transported, and deposited under the action of natural forces or the combined action of natural forces and human activities. Soil erosion is sometimes used as a synonym for soil erosion in China. The water and soil loss referred to in the Law of the People's Republic of China on Soil and Water Conservation includes water loss and soil erosion.

Soil erosion type

The purpose of the classification of soil erosion is to reflect and reveal the characteristics of different types of erosion and their regional differentiation rules in order to take appropriate measures to prevent or mitigate erosion damage.

Soil erosion is classified according to the period of soil erosion

Ancient erosion ^[1]

Erosion occurred during a long geological period before human activities began to affect soil erosion, also known as geological erosion.

Modern erosion

Occurred after human activities began to affect soil erosion, human activities increased the intensity and speed of erosion and accelerated its development based on the original erosion.

Soil erosion by erosion capacity

Usually divided into hydraulic erosion, gravity erosion, freeze-thaw erosion and wind erosion. Among them, hydraulic erosion is the most important form. ^{[2] It is} customarily called soil erosion. Hydraulic erosion is divided into surface erosion and gully erosion, gravity erosion is manifested as landslide, collapse and mountain peeling, wind erosion is divided into suspended wind erosion and moving wind erosion. ^[3]

Hydraulic erosion

Hydraulic erosion or flowing water erosion refers to soil erosion caused by rainfall and runoff, referred to as water erosion for short. Including surface erosion, latent erosion, trench erosion and erosion.

1. Surface erosion or sheet erosion: Surface erosion is a relatively uniform erosion of the ground surface by flaky water or raindrops. It mainly occurs on sloping farmland or barren slopes without vegetation or reliable soil and water conservation measures. It is the most basic form of erosion in hydraulic erosion. Surface erosion is divided into layered, structural, gravel, and scaly surface erosion according to its external manifestations. The surface change caused by surface erosion is gradual and difficult to be noticed by people, but its rate of decline in ground power is amazing and the land area involved is often large.

Soil Erosion

2. Erosion: It is the surface erosion that infiltrates into the soil layer for mechanical erosion and dissolution. The karst karst landforms are all caused by the erosion, and it is also quite common in loess areas where vertical joints are very developed.

3. Gully erosion: Gully erosion is the erosion of the surface by concentrated linear water flow. ^[3] Cut into the ground to form a form of soil erosion, which can be subdivided into fine grooves, Shallow trench and cut trench erosion. Gully erosion develops from sheet erosion, but it is obviously different from sheet erosion, because once the erosion gully is formed, the land is completely destroyed, and due to the continuous expansion of the erosion gully, the area of arable land on the slope will shrink. Cut a piece of land once fragmented.

4. Erosion: It mainly refers to the erosion, transportation and sedimentation of soil by surface runoff. Erosion is the main process of soil erosion, and the sign of erosion is the formation of gullies of different sizes on the surface. Flash floods and debris flows are the result of extreme development of surface erosion ^[4] .

5. Splash erosion: mainly refers to the impact of raindrops on soil particles. In the case of sloping fields and heavy rain, splashing is very strong. Splashing is often a prelude to runoff erosion. Sputtering can change the surface soil structure and is beneficial to the development of surface runoff. According to related research, raindrops splashed on soil particles in the loess region

Soil Erosion , Up to 50 cm, up to 1 meter in one horizontal movement.

Gravity erosion

Gravity erosion refers to the unstable movement of weathered debris or unstable soil and rock mass on the steep walls of a slope under the action of gravity. Generally, it can be divided into types such as torrents, landslides, landslides, and debris flows. A serious form of soil erosion. Gravity erosion occurs mostly on high and steep slopes in deep trenches.

Freeze-thaw erosion

It is mainly distributed in the high and cold regions of western China. On the slopes of some loose deposits, the soil freezes in winter with large amounts of soil moisture or groundwater seepage. The surface layer in the spring melts first, while the lower part still freezes, forming a water barrier. The upper part The soil infiltrated with water is in a fluid state and flows down the slope, creeps, or collapses, forming a mudslope slope or mudditch. Therefore, this form mainly occurs in some areas with more soil moisture, especially on shady slopes. For example, in the late spring and early summer on some alpine slopes in eastern Qinghai, some northern slopes in northern Shanxi and northern Shaanxi, tongue-like mudslides are often seen, but the scope is generally small.

Wind erosion

Under relatively dry and sparse vegetation conditions, when the wind is greater than the resistance of the soil

During erosion, soil particles are suspended in the airflow and lost. This phenomenon of soil erosion caused by wind is wind erosion, or wind erosion for short. Wind erosion occurs in a wide area. Except for some well-vegetated places and paddy fields, it can occur in plains, plateaus, mountains, and hills, but the degree is different. Wind erosion intensity is closely related to wind strength, soil properties, vegetation coverage and topographical features. It is also affected by temperature, precipitation, evaporation and human activity. In particular, the soil moisture condition is a very important factor affecting wind erosion intensity. The higher the soil moisture content, the stronger the bonding between soil grains, and the better the general vegetation, the stronger the wind erosion resistance.

Man-made erosion

Man-made erosion means that people have moved a lot in the process of transforming and using nature and developing the economy.

The soil body, without paying attention to soil and water conservation, directly or indirectly exacerbates erosion and increases river sand transport. At present, it is mainly manifested in the process of mining, construction of various buildings, highways, railways, water conservancy, etc., which destroys arable land and wastes. Some are dumped directly into the river bed, and some are piled into small hillsides. erosion. The harm caused by man-made erosion on the Loess Plateau cannot be ignored, especially the mining of a large number of open-pit coal mines, which has caused the soil erosion in some areas to have a significant trend in recent years. The quantitative index for measuring soil erosion mainly uses the soil erosion modulus, that is, the amount of soil loss per square kilometer per year. Divide the soil erosion intensity according to the soil erosion modulus.

Soil erosion is classified by soil erosion intensity and hazard degree

Natural erosion

It is also called normal erosion or normal erosion. ^[1] It is an erosion process caused by natural action, and is not affected by human activities. Under normal circumstances, its progress is very slow, and the amount of erosion produced is usually equal to or less than the mass formed by soil formation. Therefore, it can form a "normal" soil appearance, that is, the complete A, B, and C layers are arranged in harmony. Soil profile.

Accelerated erosion

This is an erosion process caused by human unreasonable production activities or ^[1] sudden natural disasters disrupting ecological balance. Its erosion rate is much faster than the rate of soil formation, resulting in thinning of soil layers and degradation of fertility, causing great harm to human beings.

Distribution and harm of soil erosion

Soil erosion distribution

Globally, the main distribution area of water erosion is between 50 ° N ~ 40 ° S ^[1] . Water erosion areas in China are mainly distributed between 20 ° ~ 50 ° N. Wind erosion mainly occurs in grasslands and deserts. The United States, China, Russia, Australia, India and other countries are the main distribution countries of soil erosion, and some countries in South America and Africa also have large areas. Soil erosion in China is mainly distributed in the northwest loess plateau, the southern mountainous and hilly areas, the northern mountainous and hilly areas, and the northeast low mountain and hilly hilly areas, the Sichuan Basin and the surrounding mountainous and hilly areas. Wind erosion areas in China are mainly distributed in the dry and semi-arid regions of northeast, northwest and north China, as well as coastal sandy land.

China is one of the countries with the most severe soil erosion in the world, and its scope covers all parts of the country. The causes of soil erosion are complex and serious. The main types of erosion are hydraulic erosion, wind erosion, gravity erosion, freeze-thaw erosion and glacial erosion. According to a survey conducted by the Remote Sensing Center of the Ministry of Water Resources in 1990, the country's soil erosion area reached 4.92 million km2, accounting for 51% of the country's land area, of which hydraulic erosion area was 1.79 million km2, wind erosion area was 1.88 million km2, and freeze-thaw erosion area was 1.25 million km2. Gravity erosion is distributed to different extents in the above three types of soil erosion.

China's mountainous hills have a wide area ^[1] , large terrain fluctuations, deep and loose ground composition, heavy rainfall intensity, a long history of reclamation, and low vegetation coverage. Different combinations of many factors determine the type, extent, regional distribution, and potential danger of soil erosion.

Soil erosion hazards

Destruction of soil resources

Due to soil erosion, a large amount of soil resources have been eroded and destroyed, the gully is increasingly intensified, and the soil layer has become thinner.

Soil Erosion A large area of land was cut into pieces, and the area of cultivated land continued to shrink. With the development of soil erosion year after year, it is bound to erode the fertile soil layers on which human beings depend. According to statistics, the total area of soil and water loss in the country reaches 1.5 million square kilometers (excluding wind erosion area), accounting for almost 1/6 of the total land area. The total area of the Loess Plateau is 530,000 square kilometers, and the area of soil and water loss is 430,000 square kilometers, accounting for 81% of the total area. According to information, in Jin, Shaanxi, Gan and other provinces, there are more than 50 trunks and trunk ditches per square kilometer, and the length of the channel can reach more than 5-10km. The area of the valley can account for 50-60% of the drainage area.

2. Decreased soil fertility and quality

Soil erosion caused the loss of a large amount of fertile topsoil, and soil fertility and plant yields were rapidly reduced. For example, in the black soil area of Jilin Province, the thickness of the lost soil layer is 0.5-3cm every year, and the fertile black soil layer is constantly thinning, and some places are even eroded, making the loess or rubble all over the ground. The earth and rocky hilly area in the middle of the Sichuan Basin has a slope of 150-200. The topsoil is eroded 2.5cm per year. The area eroded strongly on the Loess Plateau has an average annual erosion of more than 6000 tons per square kilometer and a maximum of 20,000 tons. Take the Xingguo County of Jiangxi as an example. The average annual loss is 50008000 tons / km2, up to 13500t / km2. The exposed granite weathered crust slope has a surface temperature of 70 ° C in summer. It is known as the "red desert in the south" ". The annual loss of soil in the country exceeds 500,000 tons, accounting for 20% of the world's total loss. It is equivalent to stripping 10mm thick fertile soil surface. The lost soil nutrients such as nitrogen, phosphorus, and potassium are equivalent to more than 50 million tons of fertilizer. The soil that is lost through soil and water is generally a fertile soil surface, which causes a large amount of soil organic matter and nutrients loss, soil physical and chemical properties deteriorate, soil compaction, soil quality deterioration, soil ventilation and water permeability decrease, resulting in rapid decline in soil fertility and quality.

3. Deterioration of ecological environment

Due to severe soil and water loss, severe damage to surface vegetation and imbalance of natural ecological environment

Deterioration, floods, floods, droughts, hail and other natural disasters have followed in succession, especially the threat of drought is becoming increasingly serious. According to data, 5-7 years of the Loess Plateau are dry years every 10 years. Frequent droughts seriously threaten the development of agricultural and forestry production. Due to the damage caused by wind erosion, large areas of soil are desertified, and dust storms are often formed in northwestern China, causing serious atmospheric environmental pollution.

4. Destroy facilities

A large amount of sediment carried away by soil erosion was sent to reservoirs, rivers, and natural lakes, which caused the river bed to silt up and rise, causing river flooding, which was the main reason for the occurrence of catastrophic floods in the plains. According to statistics of 20 key reservoirs built for 20 years, the sedimentation volume has reached 7.7 billion cubic meters, which is nearly 20% of the total storage capacity, which greatly shortens the service life of water conservancy facilities. At the same time, a large amount of sediment will cause secondary salinization of large areas of soil. Collapses, landslides, or mudslides caused by gravity erosion in some areas often cause traffic interruptions, road and bridge damage, and river blockages, which have caused huge economic losses.

5. Sedimentation raises river bed and aggravates flood disaster

Soil erosion has caused a large amount of sediment on the slope to be eroded and deposited in downstream rivers after transportation, which weakens the flood discharge capacity of the riverbed and exacerbates flood damage. Since the founding of the People's Republic of China, the riverbed on the lower Yellow River averages 8 to 10 cm in height every year. At present, many sections have been 4 to 10 m above the ground on both sides of the river, making it a "hanging river" on the ground. In recent decades, the Yellow River-like situation has occurred in various parts of the country, including the Yangtze River in China. With the intensification of soil erosion, the riverbeds and floods of large, medium and small rivers have become increasingly serious. The severe flood disasters that occurred in the mainstream of the Yangtze River and the Songhua River between July and August 1998 caused hundreds of millions of yuan in damage to the country, which largely explained the high river bed siltation and reduced flooding capacity caused by soil erosion. The problem of increasing flood damage.

6. Silted reservoirs and lakes affect development and utilization

Since the founding of the People's Republic of China, ^{[5] a} preliminary estimate of

Various reservoirs, mountain ponds and other reservoirs have accumulated more than 20 billion cubic meters over the years. The Dongting Lake in the middle reaches of the Yangtze River had a surface of 6,270 square kilometers during the Daoguang years of the Qing Dynasty. Due to sedimentation caused by soil erosion and reclamation along the lake, the area of the lake surface was reduced to 4,350 square kilometers in 1949, and to 4,641 square kilometers in 1993. At the same time, due to the sediment buildup at the bottom of the lake, its capacity was reduced by 40%, which seriously affected the flood mitigation capacity of Dongting Lake and the ecological environment around the lake. The major flood disasters that occurred in the mainstream of the Yangtze River in 1998 were closely related to it.

It can be seen that the damage caused by soil erosion is very serious, and it must be highly valued and effective measures must be taken to prevent it.

Factors affecting soil erosion

The factors affecting soil erosion are divided into natural factors and human factors.

Soil Erosion Natural factors are prerequisites for the occurrence and development of soil and water loss, or potential factors, and human factors are the main reason for aggravating soil and water loss.

1. Climate: Climate factors, especially monsoon climate, are closely related to soil erosion. The monsoon climate is characterized by heavy and concentrated rainfall and heavy rainfall, which intensifies soil erosion. The most important and direct is precipitation, especially the climatic factors that cause the most prominent soil and water loss caused by heavy rain. The so-called torrential rain refers to strong precipitation in a short period of time. A day's rainfall that can exceed 50mm or an hour's rainfall exceeding 16mm is called torrential rain. Generally speaking, the greater the intensity of the storm, the greater the amount of soil erosion.

2. Terrain: Terrain is an important factor affecting soil and water loss, and the size, length, and shape of the slope all have an effect on soil and water loss. Among them, the slope has the largest impact because the slope is the main factor determining the erosion capacity of the runoff. Sloping arable land and exposing the soil to flowing water are the driving factors for soil loss. In general, the steeper the slope, the greater the surface runoff velocity and the more serious the soil erosion.

3. Soil: Soil is the main object of erosion, so the characteristics of soil water permeability, corrosion resistance and impact resistance will also have a great impact on soil erosion. Soil water permeability is related to texture, structure, and pores. Generally, soil with sandy texture and loose structure is prone to erosion. Soil corrosion resistance refers to the ability of the soil to resist the dispersion and suspension of runoff to them. If the cementing force between soil particles is strong and the structures are not easily dispersed, the soil corrosion resistance is also strong. Soil impact resistance refers to the ability of soil to resist mechanical damage such as flowing water and wind erosion. According to research, the larger the coefficient of soil expansion, the faster the disintegration, and the weaker the impact resistance. If the roots are entangled, uniting the soil will increase the impact resistance.

4. Vegetation: Vegetation destruction causes the soil to lose its natural protective barrier and becomes a leading factor in accelerating soil erosion. According to the test results of the South China Institute of Botany of the Chinese Academy of Sciences, the annual loss of sediment by light board is 26902 kg / ha, the eucalyptus forest land is 6210 kg / ha, and the broad-leaved mixed forest land is only 3 kg / ha. Therefore, protecting vegetation and increasing the cover of surface plants are of great significance for controlling soil erosion.

5. Geology: mainly geological tectonic movements, earthquakes and rock properties. Elevation or descent of the earth's crust causes changes in the erosion datum, resulting in changes in erosion and accumulation. Earthquakes often induce a large number of landslides, collapses and even mudslides ^[1] .

Human activities are the main cause of soil loss, manifested by vegetation destruction (such as inadequate reclamation, indiscriminate logging, and excessive grazing) and sloping farmland cultivation (such as steep slope reclamation, down-slope farming, and excessive grazing), or due to mining or road construction failure. Taking necessary precautions will aggravate soil erosion.

Soil erosion control measures

Preventing soil erosion, protecting and rationally using water and soil resources is a fundamental measure to change the appearance of mountainous areas, hilly areas, and wind and sand areas, control rivers, reduce water, drought, and wind and sand disasters, establish a good ecological environment, and promote sustainable development of agricultural and forestry production. It is an important content of land remediation. Soil and water conservation is the lifeline of ecological construction in mountainous areas. Effective comprehensive measures for soil and water conservation must be adopted. Through a large number of production practices and scientific research at home and abroad, the experience of comprehensive water and soil conservation management combined with water conservancy engineering, biological engineering and agricultural technology has been summarized, and good results have been achieved through popularization and application.

Soil erosion hydraulic engineering measures

Slope treatment project

According to its function, it can be divided into terraces, slope water storage projects and interception and anti-scouring projects. Terraced fields are an effective measure for slope control projects, which can store more than 90% of soil and water loss. There are various forms of terraced fields. The horizontal level of the field surface is a horizontal terraced field, the high and low levels of the field surface are reverse sloped terraced fields, the interval between adjacent two horizontal field surfaces is a sloped terraced field, and the sloped terraced field has a certain slope. . The slope water storage project is mainly used to stop the surface runoff on the slope surface, and to solve the human and livestock and irrigation water. Generally there are dry wells, waterlogging ponds, etc. The interception and anti-scouring project mainly refers to the hillside intercepting ditch. On the sloping field, the channel constructed on the slope can block and transport surface runoff every certain distance from top to bottom. Its function is to change the length of the slope and block rainstorm. And discharge it into the water storage project, play a role in intercepting, slowing, storage, drainage and other functions to regulate runoff.

2. trench management project

There are mainly trench protection projects, Gufang, trench storage projects and silt dams. The ditch head protection project is a water conservation project to prevent the ditch head from advancing, the undercut of the ditch and the expansion of the ditch bank caused by runoff erosion, and to protect the slope from erosion. First, strengthen the slope management at the head of the ditch so that the water will not go down the ditch. The second is to consolidate the ditch heads and ditch slopes, repair fish scale pits, horizontal ditches, and horizontal steps on both sides of the ditch slope, plant trees and forests, prevent erosion, and reduce surface runoff to the bottom of the ditch. At the bottom of the ditch from Maogou to Zhigou to Gangou, according to different conditions, various projects such as repairing valleys, silt dams, small reservoirs, and pond dams were adopted to intercept flood cement and sand and prevent flash flood damage.

3. Small water conservancy projects

Mainly to stop the surface runoff and sediment during heavy rain, small water conservancy projects can be built, which are closely integrated with soil and water conservation, such as reservoirs, diversion tunnels, flood diversion floodlands, etc.

Biological engineering measures for soil erosion

Bioengineering measures refer to afforestation and grass planting, greening of barren hills, and integrated management of agriculture, forestry, and animal husbandry, in order to prevent soil erosion, maintain and rationally use water and soil resources, to increase ground coverage, improve soil, improve land productivity, develop production, and prosper the economy. Soil and water conservation measures, also known as soil and water conservation forest and grass measures. In addition to the role of water conservation and soil and water conservation, forest and grass measures can improve soil fertility, provide fuel, feed, fertilizer, and wood, promote the comprehensive development of agriculture, forestry, animal husbandry, and sideline industries, and improve and regulate the ecological environment. Significant economic, social and ecological benefits. Biological protection measures can be divided into two types: one is for the purpose of protection, such as the management of biological protection fields in the loess area, sloping field forests, hilly slope forests, ditch protection forests, ditch slope protection forests, and ditch bottom erosion forests. , Bank protection forest, mountain water source forest, sand fixation forest, etc. The other is a variety of forestry management types for the purpose of forest production, including grassland rotation, forest and grain intercropping, fruit forests, oil forests, timber forests, grazing forests, and charcoal forests.

Soil erosion agricultural technical measures

Technical measures for soil and water conservation agriculture, mainly farming methods for soil and water conservation, are the basic measures for soil and water conservation. It covers a wide range and can be divided into three main categories according to its role:

1. Agricultural technical measures for soil and water conservation focusing on changing the tiny terrain on the ground and increasing the roughness of the ground: intercepting surface water and reducing soil erosion, mainly including high-slope cultivation such as cross-slope farming, ditch ridge planting, horizontal furrows, and ridge planting High yield ditch etc.

2. Agricultural technical measures for soil and water conservation focusing on increasing ground cover: its role is to protect the ground, slow down runoff, and enhance soil corrosion resistance. It mainly includes intercropping, crop rotation, strip intercropping in grass fields, wide-row dense planting, and the use of stalks. Grass, etc. for biological cover, no-till or less-till.

3. Agricultural technical measures mainly to increase soil infiltration: loosen soil, improve soil physical and chemical properties, increase soil corrosion, infiltration, and water storage capacity, mainly including increasing application of organic fertilizers, deep farming and soil improvement, rainwater storage, And cooperate with raking, shallow tillage, etc. to reduce precipitation loss and control soil erosion.

In order to prevent and control soil erosion, necessary specific measures must be taken in accordance with the movement law of soil erosion and its conditions. However, it is difficult to obtain the desired results by adopting any single control measure. According to the purpose and characteristics of different measures, the following comprehensive management principles must be followed: combining mountain and water management, combining trench and slope management, and integrating engineering measures with biological measures. In combination, field engineering is combined with water conservation and soil conservation farming measures, governance and utilization are combined, and current interests are combined with long-term interests. Only by adopting a centralized and comprehensive management policy that uses small watersheds as a unit, slope and ditch governance, and slope management, and combines engineering measures, biological measures, and agricultural measures, can it achieve lasting and stable results.