Lecture 2. Accelerated Erosion.pptx

Accelerated erosion and different types

1. Course: ENGG-121 Course teacher, Prof. P. R. Kowe Dept. of Agricultural Engineering Lecture 2. Accelerated soil erosion - water and wind erosion definitions, Types of water erosion Prof. P. R. Kowe , Department of Agril. Engg.

2. Accelerated erosion (Abnormal erosion) It i s due t o ma n mad e activitie s , whic h h av e b r oug h t ab o ut cha n g e s in natural cover and soil conditions. The activities includes; Land preparation for raising crops Land use p a tt ern s f or b u il d i n g h ous e s, i n f r a s tr u ctu r es , i n d us tr i es , h i ll cu t t i n g , deforestation, lack of soil conservation and watershed management The removal of surface soil takes place at a much faster rate than the soil forming processes. Erosion on cultivated land is of accelerated type. It is also referred as anthropogenic or man-induced erosion. The various forces involved in accelerated erosion are as follows: Destabilizing force of water or wind , which removes and transports the soil particles from one place to another R e s t oring ( r e t a r d ing) f o r ce s whic h r esi s t the e r osion. , Normal l y sur f ace characteristics offer resistance to the erosion. .

3. Types of accelerated Erosion i. Wind Erosion Water erosion Raindrop/Splash erosion Sheet erosion Rill erosion Gully erosion Stream bank erosion Prof. P. R. Kowe , Department of Agril . Engg .

4. Wind Erosion Definition: Wind erosion is the process deposit i on o f s o il p articles by o f d e t achm e n t, t r a n spor t a t i on and the action of wind. A r a r e o r a b se n t v e g e t a t i v e co v e r , a lo o se, d r y and s m o o th s o il sur f ac e , la r g e field s and s t r ong wi n ds all increase the risk of wind erosion. Winds with velocities of less than 12- 19 km/hr rarely gives sufficient energy at the soil surface to dislodge and put into motion sand-sized particles. Prof. P. R. Kowe , Department of Agril . Engg .

5. Process of Wind Erosion Prof. P. R. Kowe , Department of Agril . Engg . i) Saltation: Saltation occurs when the wind lifts larger particles off the ground for short distances , leading to sand drifts. Fine and medium sand-sized particles are lifted a short distance into the air, dislodging more soil as they fall back to the ground. ii) Suspension: Suspension occurs when the wind lifts finer particles into the air l eading to dust storms. Very fine soil particles are lifted from the surface by the impact of saltation and carried high into the air, remaining suspended in air for long distances. (iii) Surface Creep: The movement of large soil particles along the surface of the soil after being loosened by the impact of saltating particles.

6. Water Erosion Prof. P. R. Kowe , Department of Agril . Engg . Definition: It is the removal of soil from the exposed surface of land by the impact of raindrops and running water including runoff from rainfall, melted snow & ice. It is affected by land slope, soil type, density of vegetative cover, amount of intensity of rainfall. A) Raindrop/Splash Erosion: Raindrop erosion or splash erosion results from the soil splash caused by the impact of falling raindrops. Factors affecting raindrop erosion are : Climate - Heavy rainfall and temperature Soil - its inherent resistance to dispersion and its infiltration rate Topography - steepness and length of slope Plant cover – either living or the residue

7. The falling raindrops break down soil aggregates and detach soil particles from the soil mass. Raindrop splash gradually removes the fine materials from the soil. The impact of raindrops per unit area is determined by the number and size of the drops, and the velocity of the drops . Large drops may increase the sediment carrying capacity as much as 12 times . A single raindrop may splash wet soil as much as 60 cm high and 150 cm away from the spot. The factor affecting the direction and distance of soil splash are wind, land slope, soil surface conditions. Prof. P. R. Kowe , Department of Agril . Engg .

8. Prof. P. R. Kowe , Department of Agril . Engg . B) Sheet Erosion Def. - Sheet erosion is the removal of a fairly uniform layer of soil from the land surface by the action of rainfall and runoff. In sheet erosion soil is removed from the surface in a thin layer or sheet of relatively uniform thickness. This type of erosion is extremely harmful to the land. It is common on lands having a gentle slope. It results in the uniform “ skimming off the cream ” of the top soil with every hard rain. Areas where loose, shallow top soil overlies light subsoil are most susceptible to sheet erosion.

9. Prof. P. R. Kowe , Department of Agril . Engg . C) Rill Erosion Def: It is the removal of soil by running water with the formation of a series of small shallow branching channels. There is no sharp line of demarcation where sheet erosion ends and rill erosion begins. Rill erosion is more readily apparent than sheet erosion. Rills develop when there is a concentration of runoff water. If rill erosion is neglected it grows into large gullies. Ril l e r osion i s m o r e s e r i ous in s oils h a vin g loo s e shallow top soil . It m a y b e r e g a r d e d a s a i n t e r medi a t e s t a g e between sheet erosion and gully erosion. Rill s o f s m a ll de p th ca n b e s m o o thed out by ordinary farm tillage.

10. Prof. P. R. Kowe , Department of Agril . Engg . D) Gully Erosion Def: It is the removal of soil by excessive concentration of running water, resulting in the formation of channels ranging in size from 30 cm to 10 m or more. Gully erosion is an advanced stage of rill erosion. If the rills are not destroyed and detachment continues, then it becomes wider and deeper which forms gullies. Unattended rills get deepened and widened every year and begin to attain the form of gullies. During every rain, the rainwater rushes down these gullies, increasing their width, depth and length. Advanced and Last stage of erosion.

11. Prof. P. R. Kowe , Department of Agril . Engg . E) Stream Bank Erosion Def: It is the scouring of material from the side and bottom of the stream or water and the cutting of bank by running water. It is mainly due to removal of vegetation, over glazing or cultivation on the area near to the stream bank. Also caused by water flowing over the sides of the stream.