Agents of Soil Erosion:

 Agents of Soil Erosion:

1.  Water erosion:

 water erosion is the removal of soil from the land’s surface by running water, including runoff from melted snow and ice. Depending upon the form of the lost soil, water erosion is subdivided into Sheet, Rill and Gully erosion.

1.  Sheet erosion: 

It is the uniform removal of soil in thin layer from sloping land. 

This results from sheet or overland flows, the runoff from the surface in thin layer .

 The beating action of raindrops combined with surface flow causes the major portion of the sheet erosion.

 From an energy stand point, raindrop erosion is far more important because raindrops have velocity of about 20 to 30 feet per second where as overland flow velocities are about 1 to 2 feet per second. 

Raindrops cause the particles to be detached and transported and the increased sediment reduces the infiltration rate by scaling the soil pores. 

 where loose, shallow topsoil over lies a tight sub soil are most susceptible to sheet erosion.

 

• Rill & Ravine erosion: 

It is the removal of soil by water from small but well-defined channel or streamlets where there is a concentration of overland flow. 

There is no sharp line of demarcation where sheet erosion ends and rill erosion begins. 

Rills are small enough to be easily removed by normal tillage operation. 

Detachability and transportability are both greater in rill erosion than in sheet erosion because of high velocities.

 Rill erosion is the most serious where intense storm occurs on soil having high runoff producing characteristics and loose, shallow topsoil.

• Gully erosion:

It produces channels larger than rills. These channels carry water during and immediately after rains and as distinguished from rills, gullies cannot be obliterated by tillage. Thus gully erosion is an advanced stage of sheet erosion. 

A gully develops by processes that may take place either simultaneously or during different periods of its growth.

 These processes are:

 (1) Water fall erosion at the gully head, 

(2) Channel erosion caused by the water flowing through the gully or by rain-drop splash,

 (3) Alternate freezing and thawing of exposed soil banks, and

 (4) Slides or mass movement of soil in the gully. 

Wind erosion:

Soil erosion by wind is common in dry (arid) regions where soil is chiefly sandy and the vegetation is very poor or even absent.

 As in water erosion, wind erosion also is triggered by the destruction of natural vegetation cover of land by over felling and over grazing.  

The high velocity winds blow away the soil particles. Depending upon the whole mechanism of the soil removal.

•  Saltation: 

In such arid regions where rainfall is low, drainage is poor and high temperatures prevail, water evaporates quickly leaving behind the salts.

 Salt accumulation occurs mainly in lowlands around the oceans. The major portion of such salty soil is carried by wind in the form of small leaps, which is caused by direct pressure of wind on small particles of soil. 

 Suspension:

 The wind throws away smallest soil particles into air, which move as fine dust with the wind. By this way soils are transported to fairly long distances.

 Surface creep:

The heavier particles of soil that are not easily thrown up by wind, are simply pushed or spread along the surface by wind. 

Landslides or Slip erosion: 

The hydraulic pressure caused by heavy rains increases the weight of the rocks at cliffs, which come under the gravitational force and finally slip or fall off. 

Sometimes entire hillock may slide down. In this type of erosion, water and gravity act together.

Stream bank erosion:

 The rivers during floods splash their water against the banks and thus cuts through them.

 Particularly at curves, water strikes with great speed and the bank caves in alongside. 

This type of erosion is also known as Riparian erosion.