“The removal of soil and rock material by water, wind, or frost.” _ BCFT
Erosion is defined as the removal and redistribution of material from the land surface by weathering and abrasion processes.
It is the process in which soil and minerals are detached and transported by water, wind or gravity.
“The detachment, transportation, and deposition of land surface by water, wind, gravity and other biological activities are called soil erosion”.
The power or force of flowing water to cause erosion is called Erosivity.
Resistance/ vulnerability/ Sustainability of the soil to erosive force is called its Erodibility.
TYPES/ KINDS OF EROSION:
There are two main types of soil erosion;
- Geological / Natural /Normal
- Accelerated erosion.
The erosion which occurs naturally is called geological / Natural or normal erosion.
It occurs under normal undisturbed conditions balance with the process of soil formation from rocks weathering and organic matter. It is a natural process depending on climate and other condition beyond human influence.
As it occurs naturally so it is also called natural erosion or normal erosion.
The erosion which is caused by different human activities is called accelerated erosion.
The erosion which is caused by different factors of human concern
Man affects or helps erosion by ploughing, building, dams, canals construction also the construction of roads and by deforestation.
PHASES OF EROSION:
There are generally three phases of erosion.
The removal of the upper soil surface by water is called detachment.
When rainwater strikes the soil, it weakens the adhesive forces of water molecules are responsible for the weakening of adhesive forces of soil particles due to which soil particles are detached from each other and erosion starts.
The detached particles are taken away by water, wind or by other agents from one place to another; this is called transportation of soil particles.
When the transported soil particles come down, these are deposited or accumulated into streams, reservoirs and other places. This process is known as a deposition. Due to the accumulation of soil particles, the lifespan of our reservoirs decreases. In the deposition process, soil particles are deposited in places where it is not needed.
AGENTS OR CAUSES OF EROSION:-
Following are the main Agents of erosion
Water, Wind, Gravity, Ice, Soil frost, Glaciers, Water and Gravity, Biological activities
Water: – The runoff water first detaches the soil particles and then take them with its flow from one place to another thus causing hydric / water erosion.
Wind: – Wind is also an important agent of erosion; it carries away the soil particles from surface soil from one place to another and thus causes wind erosion
Gravity: –Big pieces of rock and soil move down the hill due to the force of gravity. The movement of runoff water is also due to the force of gravity. So gravitational force is also one of the agents of erosion.
Ice: Ice is active in soil freezing whereby soil particles may be loosened and lifted and soil creeps may be initiated.
Soil Frost: It also affects adversely the natural water regime of the soil and includes excessive surface runoff, hence erosion.
Glaciers: These causes mechanical erosion simply by their weight and movement whereby great masses of debris are being stirred up ground to pieces and transported.
Water and gravity: Water and gravity are both involved in masses movement of soil such as soil creep, mudflow, landslides,
Living Organisms or Biological activities: Many living organisms such as lichens, mosses, insects, earthworms, rodents and roots of plants etc have an important role in soil erosion.
FACTORS WHICH AFFECT SOIL EROSION: –
Following are some factors which affect erosion.
The variation in temperature during day and night, summer and winter are responsible for the cracking of soil surface and rocks. By increasing the cracking in the soil, temperature helps in erosion.
The slope is also an important factor, which affects erosion. If the slope of a mountain is steep, so, there is less chance of infiltration while surface runoff will of erosion and vice Versa.
The intensity of Rainfall: –
If the intensity of rainfall is greater then automatically erosion will be more. As we know that the raindrop falls towards the surface of the earth with kinetic energy (1/2 mv2). So greater intense means with high-velocity rain drop strike the surface soil and there will be more erosion.
Size of drop also plays an important role in erosion. Greater the size droplet more will be splash erosion.
This also plays an important role in soil erosion. If the soil is sandy or silty then there will be more chances of erosion. But if the soil is clayey then there will be less chance of soil erosion as compared to salty/sandy soils.
Vegetation Cover: –
Vegetation cover reduces soil erosion by following ways.
- By interception
- By reducing the velocity of runoff
- Increasing infiltration
- By root binding. So, by increasing vegetation cover we can reduce the soil erosion and vice versa.
Due to gazing the vegetation i-e grasses on the soil surface decreases and raindrops directly fall on the soil without being intercepted .so there are more chances of splash erosion.
Fire damages the vegetation as well as the soil due to which there are more chances of erosion.
Man activities: –
Man activities also play a very important role in increasing or decreasing soil erosion. If man afforested an area or constructing different engineering structure such as cheek dam will decrease erosion, while construction of roads, deforestation and plugging etc increases.
EFFECT OF VEGETATION ON EROSION: –
Following are the effects of vegetation on erosion.
- Reduce the velocity of runoff.
- Increasing infiltration.
- Root binding:- Roots of the plants can bind the soil particles and rocks together and provide protection to them from erosion.
- Effect on wind erosion: – The effect of vegetation on wind erosion is largely mechanical by covering the soil and protecting it from being blowing or by reducing wind velocity.
- Evapotranspiration: – when there is more water in the soil the chances of evaporation increases water flows as runoff on it, so, it causes erosion. But due to the presence of vegetation waster is continuously checked by the plants and released to the atmosphere by transpiration.
- Snow melting effect: – The area where trees are absent the snow-melting rate is very high and it causes erosion while areas where vegetation is present. Snow melting rate is lass due to shade cover and hence low speed and less erosion.
WATER / HYDRIC EROSION:-
The detachment, transportation, and depositions of soil particles by water are called water erosion.
The erosion which occurs due to water is called water or hydric erosion.
TYPES OF WATER EROSION:-
Water erosion is of following types
Surface erosion is the detachment and transportation of surface soil particles or aggregates from unchanged areas, and can be classified as:
Splash erosion: –
Raindrop splash erosion results from the impact of water drops. Falling directly on exposed soil particle with some energy (1/2mv2) due to which soil particle splashed into the air and erosion occur called splash erosion. Here soil particles can be thrown off as far as 3 feet.
Sheet erosion: –
The removal of soil particles uniformly in thin layers or sheets from a watershed area is called sheet erosion.
This erosion occurs in the area has uniform soil texture and structure and where the rate of rainfall is greater than the infiltration capacity. In this type of erosion, the whole watershed area is uniformly eroded.
Channel erosion: –
It is usually the stream or river bank or bed erosion. Cutting of channel or stream may channel erosion depends on the credibility of channel surfaces and proclivity of water. Channel erosion exists as i) Rill erosion ii) Gully erosion
Rill erosion is the removal of soil by water from very small but well defined, visible channels or rill. But no deeper than 5 to 10 feet. In this type of erosion, small channels can be eliminated or removed by normal cultural methods.
Gully erosion: –
In this type, the channels are so large & well established that these cannot be removed by cultural methods. This is a modified form of rill erosion, in this case, first rill erosion stats which increases in-depth with so converted into gully erosion.
It is the movement of a mass of consolidated or unconsolidated material down gradient due to the force of gravity .e.g. rock fall landslides mudflow and debris flow.
“The detachment, transportation, and deposition of soil particles by wind are called wind erosion.” OR;
“The erosion or removal of soil by the action of the wind is called wind erosion.”
It depends upon.
- Wind velocity
- Dryness of soil and
- The texture of the soil.
TYPES OF WIND EROSION:-
Detrusion / Suspension Erosion: –
This type of erosion occurs due to the high pressure of winds. These winds are parallel to the ground surface and maybe a few yards above the soil surface. The wind moves such a speed that it can even move rocks. Thus breaking them and producing soil particle. As the wind carries these particles in the form of suspension so, this is also called suspension erosion.
EFFECTS OF EROSION: –
Economic implications of soil erosion
- Decrease the fertility of the soil.
- Decrease the lifespan of our reservoirs. (due to satiation)
- Decrease the vegetation.
- Decrease the depth or thickness of soil.
- Decrease the water holding capacity of the soil.
- Due to erosion, there are depositional sediments in stream channels and reservoirs.
- Irrigation systems also affected.
- Frequent flood
- Loss of crops
- Erosion increases the pollution mainly water and air pollution.
- Decrease the quality of water.
- Other effects
- Dust storm causes death from prolonged dust inhalation
- Dust pneumonia and inflamed eyes
- Roads are blocked by drift sand
- A decrease in quality of water
- Dangerous for wildlife, esp marine, and submarine
PREVENTION OF WATER EROSION:
Water erosion can be condoled up to some extent.
- Biological control
- Engineering structures
- Modification of land surface.
1) Biological Control:-
Biological control includes the control of erosion through vegetation, and the effect of vegetation on erosion is already, expanded above. Besides those affects different vegetative practices also reduce. Or minimize erosion, which is.
- Crop rotation
- Contour cultivation
- Strip cropping
- Mulching etc.
2) Engineering Structures: –
Engineering Structure includes.
- Contour bunds.
- Dyke in channels.
- Gabion structures.
- Retaining walls _ for control of landslides
- Riprapping _ ground is pitched with stones to avoid sedimentation
- Check dams etc.
Modification of land surface;-to minimize the effect of erosion and slope, the land surface is modified as a result of this modification the land surface is protected from the effect of erosion.
The following are some modification of the land surface.
- Division banks/ channels
- Contour ridges or absorption banks
- Gradoney Trenches.
- Graded terraces.
PREVENTION OR CONTROL OF WIND EROSION:-
- Vegetation cover _ most effective method
- By Cover crops
- By Crop rotation
- By Mulching
- By Contour cropping
- Windbreaks / Shelterbelts _ in the direction of the wind (a shelter book is lingering than windbreak)
- Cultivation of land.
- Using chemicals and oil etc like bitumen.
WHAT IS THE DIFFERENCE B/W SEDIMENTATION AND SILTATION?
Sedimentation is the transport of Sediments soil deposits.
Siltation is sedimentation in a valuable reservoir eg in Mangla Dam.
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