Erosivity and Erodibility ppt [Soil and water conservation engeneering]

1. Erosivity
&
Erodibility
Submitted By;
Rajendra Kumar Rajak
Roll no-35, Sec-B
B.Sc. Agriculture,2nd semester
MIPS , Rayagada
Submitted To,
Jwel 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. Erosivity
• 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:
EI30 Index method
KE > 25 Index method
• EI30 Index method
• It was introduced by wishmeier in 1965.
R= KE*I30 =EI30 (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 log10 I
where, E= Kinetic energy, MJ/ha-mm
I = Rainfall intensity, mm/h (I ≤ 76)
• Both KE and I30 are obtained for a rainfallevent
• 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. EI30 Indexmethod
Time
Showing magnitude
of rainfall
No rainfall occurring
6
10

7. • Limitations
• EI30 index developed under American condn .
• 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 EI30 .
• 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
%Clay

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