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Soil Erosion • Detachment, Transportation and deposition of soil material Types of Erosion 1. Geological erosion 2. Accelerated erosion
Geological Erosion • It is also called natural erosion or normal erosion • The erosion which is undisturbed by human activity Types • Water erosion • Wind erosion
Water Erosion Removal of soil mass by running water from snow and ice melt, and transporting it usually downhill Forms of water Erosion • Sheet erosion • Rill erosion • Gully erosion
Sheet Erosion Uniform removal of soil in thin layers resulting from sheet or over land flow of water occuring in thin layers • It causes the color of land to chang gradually from dark to light, usually this change in color is accompnied by progressive decline in yield
Rill Erosion • It is the advanced satge of sheet erosion • When sheet erosion continues for sometime and the land is neglected rills start deepning and widening so tht runoff concetrates through them. These rills then go on developing with the passage of time and prove fore runners of gullies. this stage of erosion is called rill erosion
Gully Erosion • It is the advanced stage of rill erosion Stages of gully development • Formation of rills by sheet washing • Deepning and cutting of rills • Start of under cutting of rocks • Eating of backwards and uphill by gullies
Process of Water Erosion • Detachment • Transportation • Deposition
Damages of Water Erosion • Washing of soil • Loss of fertile soil • Increase runoff • Top soil removal • Decrease infiltration capacity • Stones will be left • Effect on wild life
Wind Erosion which is caused by wind is called wind erosion • In Pakistan, 40 % area is affected by wind erosion e. g Thal, Cholistan and D. G. Khan It occurs in • Dry lands • In arid and semi arid areas
Process of Wind Erosion 1. Initiation of soil movement • The turbulance of wind, together with its velocity is responsible for starting the movement of soil in wind erosion process • Minimum velocity of wind required to initiate soil movement is called threshhold velocity of wind. It greatly depends upon the size of soil grain • There is a range of threshold velocities for any soil depending upon previous history of field
2. Transportation of Soil • Transportability of soil depends upon the size of soil particles • Fine dust once lifted, may be carried to great distances from the eroding areas
3. Deposition of Atmospheric Load • Material carried either in suspension or saltation is deposited primarly when the wind velocity decrease • The process of picking up and depositing material is continuous is due to variable character of wind and to the nature and process of saltation
Modes of Sand Transport Depending upon wind force, sand particle’s and mass a. Saltation • Progression of particles in succesive jumps • Size of particles 0. 1 to 0. 5 in diameter most susceptible
b. Surface Creep • The soil particles with diameter 0. 5 -1 mm are too heavy to be moved by saltation but are pushed along the surface by the impact of particles to surface creep.
c. Suspension • Very fine dust particles less than 0. 05 mm in diameter are carried in true suspension, • The amount of sand transported in suspension is only a very small portion of total.
Damages • • Loss of fertility Accumulation of materials Uprooting of seedlings Weed seed transportation Covering of roads and railway tracks Air pollution Damage of agri. machinery
2. Accelerated Erosion • The deterioration of soil as a result of man’s activities is called accelerated erosion. • It is also called abnormal erosion • It is associated with changes in natural vegetation and soil conditions.
Kinds of intensities of soil erosion Kind of erosion Water erosion (11. 18 mha) • Sheet &rill erosion • Rill &gully erosion • Gully erosion Intensity of Affected hazard area (mha) Slight Moderate Severe Very severe 0. 40 3. 58 3. 75 3. 45
Kinds of intensities of soil erosion Kind of erosion Intensity of Affected hazard area (mha) Wind erosion (4. 73 mha) • Light wind erosion Slight • Moderate wind erosion Moderate • Severe wind erosion Severe 2. 56 0. 50 1. 67