Erosivity and erodibility pptx

Erosivity and Erodibility ppt [Soil and water conservation engeneering]

1. Erosivity & E r odibility Submitted By; Rajendra Kumar Rajak Roll no-35, Sec-B B.Sc. Agriculture,2 nd semester MIPS , Rayagada Submitted To, J wel Bhuiya Assistant professor [Soil and water conservation engeneering ] [AT-121] MIPS , Rayagada

2. Erosivity & Erodibility Erosivity: Ability of rain (characteristic of erosion) to detach the soil particles. Erodibility: Susceptibility of soil (characteristic of erodibility) to with stand against the raindrop impact. Soil occurs when rainfall erosivity exceeds the soil erodibility. When erosivity is increase then the erodibility means soil erosion take place.

3. E r os i vi t y Erosivity is the potential ability of rain to cause erosion. Function of physical characteristics. Energy is required to break the soil, splashing them and carrying with run-off. Depend on the following factor: Rainfall intensity Drop size distribution Terminal velocity (depend upon the size-higher the velocity more will be the kinetic energy) Wind velocity Direction of slope

4. Estimation of erosivity from rainfall data: EI 30 Index method KE > 25 Index method EI 30 Index method It was introduced by wishmeier in 1965. R= KE*I 30 = EI 30 (E & KE are equivalent/same) It is computed by the product of kinetic energy of storm and 30-min maxi rainfall intensity. The greatest average intensity experienced in any 30 mint. max. intensity during the strom

5. Relation b/w KE and rainfall intensity by Wischmeir and Smith, 1958 E=0.119 - 0.0873 log 10 I where, E= Kinetic energy, MJ/ha-mm I = Rainfall intensity, mm/h (I ≤ 76 ) Both KE and I 30 are obtained for a rainfall event Rainfall is identified from rain-gauge (which comes from recording type rain-gauge). There are various type of rain-gauge Recording type:- 1. Tipping type bucket, 2. Weighing bucket, 3. Float/Siphon Non Recording type .

6. EI 30 Index method T i m e Showing magnitude of rainfall No rainfall occurring 6 10

7. Limitations EI 30 index developed under American cond n . Not very accurate for tropical and sub-tropical. An alternate method is developed. KE > 25 Index method Threshold value for rainfall intensity is 25 mm/h determined on the basis of experiments. This is based on - low intensity rainfall - no erosion. It assumed that rainfall < 25 mm/h do not yield a significant soil erosion.5 Procedure - similar to EI 30 . Difference - KE is calculated only if I ≥ 25mm/h.

8. Erodibility Erodibility is the soil’s inherent susceptibility to erosion Physical property of soil type, land and crop management. Varies with – Soil texture Aggregate stability Infiltration Capacity Organic matter Acc. to the Bouyouces, 1935 Soil depends upon mechanical composition Proportional to the ratio of = %Sand + %Silt % C l ay

9. It is estimated by using Runoff Plots Soil properties Runoff Plots The runoff from the runoff plots is collected in a tank and measure its volume. Estimating Soil loss, the water in the tank. A sample of 500-1000 cc is drawn. The samples separated in the lab and amt. of soil is measured to get soil loss (g/l). Soil loss = (g/l)*runoff vol (l)*10 -6 tonne soil loss/ha(tonne/ha) = soil loss in tonne Area of plot in ha

10. Adjusted soil loss = Soil loss/ha (topography factor) Adjusted soil loss K= Rainfall Erosivity Index where, K = Soil Erodibility value .

11. Thank You