Soil erosion | water erosion | Wind erosion | cause and effect of soil erosion | types of soil erosion | soil erosion causes | soil erosion and degradation | soil erosion prevention

SOIL EROSION

Soil erosion

Soil erosion is the process of detaching soil particles from the upper soil layer and transporting soil particles released by wind and / or water. The agents that cause erosion are wind and water. Release agents are falling raindrops, gutter flow and wind. The transport agents are running water, splashes of rain and wind.

Nature and extent of erosion

The problem of soil erosion exists throughout the country. Of the 329 m.ha of the geographical area of India, about 175 m.ha (53.3%) are subject to soil erosion and some types of soil degradation. About 150 m Ha are subject to wind and water erosion. It is estimated that about 5,333 Mt of soil are poured from the soil every year. Of this 29% is transported by rivers to the sea and about 10% is deposited in artificial basins, with a loss of storage capacity of 1-2% per year. The estimated annual loss of soil is 16.35 tons / ha / year.

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Types of erosion:

According to the origin: Soil erosion can be classified into two types, namely geological erosion and accelerated erosion.

Geological erosion:

in undisturbed natural conditions, a balance is established between the climate of a place and the vegetation cover that protects the soil layer. Plant cover such as trees and forests slow down the transport of soil material and act as a brake against excessive erosion. However, some erosion also occurs under the natural cover. This erosion, called geological erosion, is a slow process and is compensated for by the formation of the soil under the natural weathering process. Its effect is of little importance for agricultural land.

Accelerated erosion:

When the soil is cultivated, the natural balance between the soil, its vegetation cover and the climate is disturbed. Under such conditions, soil removal by natural agents occurs at a faster rate than can be accumulated by the soil formation process. The erosion that occurs under these conditions is called accelerated erosion. Their rates are higher than geological erosion. Accelerated erosion impoverishes soil fertility on agricultural land. According to erosion agents: Soil erosion is broadly classified into different types based on the agent that triggers the erosion activity. Listed below are the four main types of soil erosion, such as water erosion, wind erosion, glacial erosion, and gravitational erosion.

The two main types of soil erosion are mentioned below.

WATER EROSION

The loss of soil from the earth's surface to water, including runoff from melted snow and ice, is generally called water erosion. The main erosive agents of water erosion are the fall or impact of raindrops and runoff water flowing on the soil surface.

Water erosion process

The detachment of the soil particles is due to the impact of a drop of rain or running water. The single raindrops hit the ground surface at speeds of up to 9 m / s creating a very strong hydrodynamic force at the point of impact which leads to the detachment of the soil particles. Earth flow separates soil particles when their erosive hydrodynamic force exceeds the soil's resistance to erosion. Loose soil particles are carried away by splashes and the runoff of raindrops. The amount of earth carried by the runoff is more than due to the splashes of raindrops. Therefore, the falling raindrops break up the soil aggregates and separate the soil particles from each other. The finer particles (silt and clay) block the pores in the soil and increase the runoff rate and thus the loss of water and soil. Forms of water erosion Water erosion occurs in stages identified as splash erosion, laminar erosion, streams, ravines, ravines, landslides and embankment erosion.

a) Splash erosion: Splash erosion is the first stage of the erosion process and is the least noticeable, but the most extensive. It occurs when raindrops hit bare ground. The explosive impact breaks down the soil aggregates so that individual soil particles "dot" the soil surface. Splashed particles can rise up to 60 cm above the ground and travel up to 1.5 meters from the point of impact.

b) Laminar erosion: Laminar erosion is the removal of soil in thin layers by the impact of raindrops and surface flow. It occurs fairly evenly over one area. It's so thin it may not even be visible until much of the valuable nutrient-rich topsoil has already been removed. If there is a buildup of soil and crop residues at one end of the field, it could be sheet erosion. The soils most vulnerable to lamina erosion are over-exploited and cultivated soils where there is little vegetation to protect and maintain the soil.

Sheet erosion

[ Images credit by:- Flickr]

C) Rill erosion: when runoff begins, channeling begins and erosion is no longer uniform. The impact of raindrops does not directly release particles below the flow line into streams, but increases the detachment and transport capacity of the flow. Stream erosion begins when runoff exceeds 0.3-0.7mm / s. The incisions that form in the ground due to runoff and erosion are more noticeable than sheet erosion. This is the second stage of erosion. Furrows are small channels that can be removed promptly by normal tillage operations.

Rill erosion

[ Images credit by:- imaggeo]

D) Gully Erosion : it is the advanced stage of water erosion. The size of uncontrolled flows increases due to outflow. Ravines are formed when runoff channeled from vast sloping grounds is sufficient in volume and speed to cut wide and deep channels. Ravines are the spectacular symptoms of erosion. If not controlled over time, there is no margin for the production of herbaceous crops.

Gully erosion

[ Images credit by:- Geograph]

E) Ravines: these are the manifestations of a prolonged process of erosion of the ravines. They are typically found in deep alluvial soils. They are deep and wide ravines that indicate an advanced state of erosion of the ravine.

Ravines

F) Landslides: Landslides occur on mountain slopes, when the slope exceeds 20% and the width is 6 m. In general, landslides cause traffic to stop on ghat roads.

Landslides

[ Images credit by:- Flickr]

G) Erosion of streams' banks: Small streams, streams, streams (hill streams) are subject to erosion of the banks of streams due to the obstruction of their flow. Vegetation sprouts as streams dry up and obstruct flow causing levee cuts or flow changes.

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Factors affecting water erosion

a) Climate: Water erosion is a direct function of precipitation and runoff. The amount, duration and distribution of precipitation influence runoff and erosion. Longer and more intense rains cause severe erosion. The greater the intensity, the larger the size of the raindrop. Rain intensity above 5cm / h is considered severe. The total energy of the raindrops falling on one hectare of land with a rain intensity of 5 cm / h is equal to 625 H.P. This energy can raise the soil surface by 17.5 cm 89 times from one hectare to a height of 3 feet. Two thirds of the above energy is used to seal the pores in the soil. Runoff can occur without erosion, but there is no water erosion without runoff. The raindrop thus breaks up the soil aggregates, separates the soil particles and transports rainwater with fine particles. These fine particles seal the pores of the soil surface and increase runoff causing erosion.

b) Topography: the degree, length and curvature of the slope determine the amount of runoff and the extent of erosion. Water flows slowly on a gentle slope, while at a higher speed on a steeper slope. As the water flows down the slope, it accelerates under the forces of gravity. When the runoff reaches a speed of about 1 m / s, it is capable of eroding the soil. If the slope percentage increases by 4 times, the speed of the water flowing down doubles. Doubling the speed quadruples the erosive power and increases the amount of soil that can be transported by about 32 times and the size of the particles that can be transported by about 64 times.

c) Vegetation: vegetation intercepts rain and reduces the impact of raindrops. It also slows down the flow by obstructing the flow of water. Fibrous roots are also effective in forming stable soil aggregates, increasing infiltration and reducing erosion.

d) Soil properties: Soil properties that influence soil erosion by water can be grouped into two types. I. Those properties that affect the infiltration rate and permeability. ii. Those properties that resist dispersion, splashes, abrasion and the transport forces of rain and runoff. The structure, texture, organic matter and moisture content of the upper layers determine the degree of erosion. Sandy soils are easily removable but not easy to transport. Soils with medium to high clay content have a low infiltration capacity and are easily transported by water after dispersion, but their release capacity is generally low.

WIND EROSION

Soil erosion by wind is known as wind erosion. It is a serious problem in soils that are devoid of vegetation. It is more common in arid and semi-arid regions. It is essentially a phenomenon of dry climate stimulated by the lack of soil moisture. The wind erosion process consists of three phases: initiation of movement, transport and deposition. About 33 million hectares in India are affected by wind erosion. This includes 23.49m. It has desert and about 6.5 m. It has coastal sands. The Thar Desert is mainly made up of sand shots.

Wind erosion mechanism

Wind erosion

[ Images credit by:- Geograph]

The lifting and abrasive action of the wind causes the detachment of small particles of soil from the granules or clods. The impact of these rapidly moving particles removes other particles from the lumps and aggregates. These detached particles are ready to move. The movement of soil particles in wind erosion begins when the wind pressure against the surface soil grains exceeds the force of gravity on the grains. The minimum wind speed required to initiate the movement of most of the erodible soil particles (about 0.1 mm in diameter) is about 16 km / h at a height of 30.5 cm. The most practical limit in field conditions, where a mix of sizes of single-grain material present is about 21 km / h at a height of 30.5 cm. In general, the movement of soil particles by the wind occurs in three phases: salting, surface sliding and suspension.

a. Salting: is the first phase of the movement of soil particles in a short series of bounces or jumps along the surface of the soil. After being blown away by the wind, the soil particles suddenly jump almost vertically to form the initial stage of the jumping movement. The size of the soil particles moved by the salting is between 0.1 and 0.5 mm in diameter. This process can account for 50 to 70% of the total movement due to wind erosion.

Flying particles cause wear. Wear occurs when bouncing and jumping particles collide with each other in flight and break apart. This wear can continue until the particles become fine or dust particles.

B. Surface creep: The creep and flow of soil particles along the soil surface due to the impact of the particles that descend and strike during salting is called surface creep. The movement of the particles by surface creep causes an abrasive action of the soil surface which leads to the decomposition of the non-erodible soil aggregates. Coarse particles larger than 0.5-2.0mm in diameter are displaced by surface sliding. This process can account for 5 to 25% of the total movement.

C. Suspension: The movement of fine dust particles less than 0.1mm in diameter while floating in the air is known as suspension. Soil particles transported in suspension are deposited when the sedimentation force is greater than the force that holds them in suspension. This occurs with decreasing wind speed. Generally the suspension cannot represent more than 15% of the total movement.

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