Soil erosion:

It is defined as the detachment, transport, and deposition of soil particles from one place to another place by the action of water and wind. It is the loss or depletion of soil both in relation to quality as well as quantity due to the impact of erosive forces such as rainfall, runoff, wind, etc.

Steps or process of soil erosion

 In soil erosion, there are three steps are involved

 a. Detachment: Detaching agents are falling raindrops, water, and wind flow

 b. Transport: Transport agents are flowing water, rain splash, and wind

 c. Deposition :

 CAUSES OF SOIL EROSION

1. Desertification: Process of turning the productive land into desert

2. over cultivation

3. Overgrazing due to livestock pressure

4. Deforestation

5. Natural hazards

• Land topography (steep slopes)

• Climatic factors (intense rain, high-velocity wind, strong leaching in humid regions & drought conditions in dry regions.)

6. Unsuitable land use & inappropriate land management practices.

7. Unbalanced fertilizer use and non-adoption of soil conservation management practices

8. Road construction

Factors of soil erosion

There are various factors responsible for causing soil erosion which are given below

a.       Rainfall

Rainfall causes both detachment and transportation of soil particles. Amount, intensity, duration, and distribution of rainfall influence runoff and erosion. High-intensity of rainfall of long duration causes severe erosion.

b.      Wind velocity

Wind velocity is directly related to soil erosion. High wind velocity has more energy to carry soil particles and thus causes higher wind erosion.

c.       Vegetation

The impact of raindrops is reduced by vegetation so it prevents the breakdown of soil aggregates. The plant root bind soil particles thus reducing soil erosion.

d.      Soil type

Generally, fine texture (clay soil) soil is subjected to more runoff although low detachments thus increasing soil loss. Sandy and sandy loam soils are easier to detach but difficult to transport as the particles are heavy.

e.       Human activity

Human activities like cultivation on sloppy land, deforestation, overgrazing, mining, etc disturb soil aggregate which increases soil erosion

Consequences of soil erosion:

1. Agriculture:

•      Removes valuable topsoil which is the most productive part of the soil profile for agricultural purposes.

•       When topsoil is gone, rills and gullies  erosion can cause 

•      Soil erosion cause flooding and flooding cause soil erosion reduce the ability to absorb water.

•       Reduced ability of the soil to store water and nutrients

•       Deposits of silt in low-lying areas

2. Pollution

    Pollution by sediment has two major dimensions:

   1. Physical dimension

   2. Chemical dimension.

    3. Reduction in crop quality

•      Crops grown under nutrient-deficient soil are of inferior quality.

•       Do not contain essential nutrients for human and animal growth and development.

•       Calcium and phosphorus occur in inadequate amounts in many parts of the world.

•       The erosion‐induced reduction in crop yields is attributed to loss of rooting depth, degradation of soil structure, decrease in plant‐available water reserves, reduction in organic matter, and nutrient imbalance.

      4. Increased demand for power

•      More power is needed to till the hard subsurface horizon due to the removal of topsoil.

 5. Loss of human value

Poor soil means poor people

6. Sedimentation on reservoir, river, and agricultural land

¨  Life span of the Kulekhani reservoir in central Nepal has been reduced to half of the targeted design.

¨  Reduced one-quarter of expected life span due to serious soil erosion.

Sediments that wash into streams make the water cloudy or turbid

¨  Sediments when deposited on agricultural fields destroy land and reduce the potentiality of crop production.

¨  Hectares of fertile land in the Terai region of Nepal are damaged by sediment deposition.

 

 

 

 Types of soil erosion (based on the agent)

Water erosion

It is the process of detachment, transport, and deposition of soil particles from one place to another place by the action of water.

 Mechanism or Process of Soil Erosion by Water

a. Detachment Impacts of the raindrops are detaching soil particles; destroying soil granulation and splashing soil particles. Raindrops loosen & detach soil granules into pieces, and disperse them.

b. Transportation The flow of water transports the detached soil particles. The ability of the moving water to transport soil varies as the fifth power of its velocity.

c. Deposition The deposition is the end of the erosion process. As the runoff speed subsides, particles deposit in reservoirs, riverbeds, flood plains, and level lands.

Types or forms of water erosion/ erosion by water

 a. Splash Erosion/raindrop erosion

 b. Sheet Erosion

 c. Rill erosion

 d. Gully Erosion

 e. Streambank Erosion

a. Splash erosion or raindrop erosion

The scattering of detached soil particles by the raindrop impact on bare soil is called splash erosion. It is the first step of water erosion that results from the direct impact of raindrops on bare soil. Raindrop acts as a miniature bomb that detaches & splashes soil particles 2m horizontally as well as 20 cm vertically. It is affected by vegetative cover and mulches, rainfall characteristics, and topography.

a.      Sheet erosion

 It is defined as the uniform removal of soil in thin layers from the surface of the soil. It is caused by a shallow/thin sheet of water moving over the soil surface with a gentle slope. It occurs at a slow rate and goes unnoticed/uncared.

d.Rill erosion

 It is the advanced stage of sheet erosion that lead to form tiny finger-like channels of few inches deep in the over field. It starts simultaneously with sheet erosion when channels are large enough to be visible. It removes topsoil i.e. organic soil, productive soil, and fertile soils. It can be smoothed by normal tillage operations.

d.Gully erosion

It is the advanced form of rill erosion that developed into a large channel with the increase in depth and width of the channel. It is the highly visible form of soil erosion If a gully is once formed, it can‘t be smoothed by normal tillage operations. It requires costly structures & practices to control further advancement.

Stages of Gulley development

 Stage 1: Formation Stage: Begins by downward scour of the topsoil.

 Stage 2: Development Stage: Upstream movement of the gully head & simultaneous enlargement of width & depth take place.

 Stage 3: Healing Stage: Vegetation begins to grow in the channel and further erosion ceases.

 Stage 4: Stabilization Stage: The gully bed & sides reach a stable slope, and sufficient vegetation grows to anchor the Slide 1

f.       Stream Channel Erosion

Stream water removes the bank (bank erosion) and bed (scour erosion). It occurs during periods of high stream flow. It is a very serious problem as the river gets widened every year results destroying huge cultivated land, settlements, and structures. Costly protection measures are required to prevent this erosion.