Principles of Soil Science1234567891.pdf

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1. Lesson 2:
Principles of Soil
Erosion
Land and Water Conservation Engineering

2. Causes of Soil
Erosion
01
Destruction of Natural
Protective Layer
loss of canopy cover as well as vegetation
cover
forest fires
exposed land surface, higher vulnerability
to erosion
overgrazing of the vegetative cover
and
Loss of canopy cover - no interception, no
dissipation of kinetic energy, higher
vulnerability to erosion
indiscriminate cutting of trees

3. Causes of Soil
Erosion
02
Improper land use
water flow along the slope - higher erosive
capacity
cultivation along the land slope
exposed land surface, higher vulnerability
to erosion
Improper cultivation or cropping
pattern
no protective cover on the surface -
higher vulnerability to erosion
barren land subject to the action of
rain and wind

4. Types of Soil
Erosion
01
Geological
Erosion
Water Erosion
Wind Erosion
Glacial Erosion
Gravitational Erosion
02
Accelerated Erosion

5. Geological
Erosion
Also referred to as
“normal” or “natural”
erosion
Relatively slow,
continuous process that
often goes unnoticed
It is a “natural” process
responsible for the
formation of and the
loss of soil
simultaneously
Responsible for the
formation of the
topographical features
such as stream
channels, valleys, etc.
01

6. Example of Geological
Erosion
One of the geologic wonders of the
world
Formed by the entrenchment of the
Colorado River
The Grand Canyon displays rock
from about 200 million to 2 billion
years old
Grand Canyon, Arizona, USA

7. Accelerated
Erosion
Also referred to as
anthropogenic or man-
induced erosion
It is activated by
human activities that
bring changes in
natural cover and soil
conditions.
Soil removal is much
faster than the natural
soil formation process
02
Leads to serious
environmental
damages

8. Accelerated Erosion
Water erodes and transports
soil particles from higher
altitude and deposits them in
low lying areas.
(i) raindrop erosion, (ii) sheet
erosion, (iii) rill erosion,
(iv)gully erosion , & (v)
stream bank erosion
Water Erosion
Glacial Erosion
Wind Erosion
Gravitational Erosion

9. Water Erosion
The first stage of the erosion
process
(i) Raindrop Erosion
the primary cause of soil
detachment and soil
disintegration
Raindrop impact on bare soil
causes splash
impact breaks up soil
aggregates and as a result
individual soil particles are
‘spalshed’
Loosens the top soil making it
vulnerable to soil erosion
the loose soil particles clog
the soil pores and result in
reduced infiltration and
increased runoff

10. Water Erosion
It is the uniform removal of
soil in thin layers during the
overland flow process
(ii) Sheet Erosion
Overland flow begins once
the infiltration capacity is
satisfied
results in loss of the most
fertile soil particles that
contain most of the available
nutrients and organic matter
in soil
It typically occurs gradually
and goes unnoticed until
most of the productive topsoil
has been lost
Overgrazed and cultivated
soils are most vulnerable to
the sheet erosion

11. Water Erosion
If the overland flow process
continues, its erosive action
results in the formation of
shallow channels, known as
“rills”
(iii) Rill Erosion
The rills can usually be
removed with primary tillage
implements
Rill erosion is the
intermediate stage between
sheet erosion and gully
erosion
The removal of soil by
concentrated water running
through rills is “Rill erosion”
It is common in bare
agricultural land, overgrazed
land, and freshly cultivated
soil

12. Water Erosion
If rills are not destroyed and
the detachment continues,
then these become wider and
deeper
(iv) Gully Erosion
Two main processes:
This results in the formation
of Gullies
The overland flow falling
into the gully at the head
end undercuts it and
results in upslope
extension of the gully
These cannot be smoothened
out by normal cultivation
Advance and last stage of
erosion
Waterfall Erosion
Water flowing through the
gully erodes the bed and
the sides causing walls
collapse and slumping of
the sidewalls
Channel Erosion

13. Water Erosion
(iv) Gully Erosion
Channel erosion by a
downward scour of the
top soil (Rill ----> Gully)
Formation Stage
Consist of U/S movement
of the gully head and
enlargement of gully in
width and depth
(Waterfall and Channel
Erosion)
Development Stage
Vegetation growth begins
in gully
Healing Stage
Vegetative cover spreads
over the gully surface
such that Gully reaches a
stable gradient, and walls
reach a stable slope
Stabilization Stage

14. Water Erosion
Classification of Gullies
U-shaped - formed where
both the topsoil and
subsoil have the same
resistance against erosion
Based on shape
Small (Depth <1m;
Drainage area < 2 ha)
Based on size
V-shaped - formed where
the subsoil has more
resistance than topsoil
against erosion
Medium (Depth 1 - 5m;
Drainage area 2 - 20 ha)
Large (Depth >5m;
Drainage area > 20 ha)

15. Water Erosion
Refers to the scouring and
undercutting of the soil below
the water surface in a stream
iv) Stream Bank Erosion
Also caused by water flowing
over the sides of the stream
It is a natural process, but the
rate at which it occurs may be
influenced by human
activities
It gets aggravated due to
removal of vegetation, over-
grazing, or cultivation on the
area close to the stream
banks

16. Water Erosion

17. Wind Erosion
Refers to the natural removal
of soil from an area due to
wind
Mostly occurs in low rainfall
areas when soil moisture
content is at wilting point or
below
It may caused by a light wind
that rolls soil particles along
the surface through to a
strong wind that lifts a large
volume of soil particles into
the air to create dust storms

18. Glacial Erosion
referred to as ice erosion,
common in cold regions at
high altitudes
When soil comes in contact
with large moving glaciers, it
sticks to the base of these
glaciers
This is eventually transported
with the glaciers, and as they
start melting it is deposited in
the course of the moving
chunks of ice

19. Gravitational Erosion
basically the mass movement
of soil due to gravitational
force
While landslides and slumps
happen within seconds,
phenomena such as soil
creep take a longer period for
occurrence
Creep is a very slow
movement of rock and soil
down a hillside that causes
trees and other structures on
the surface to tilt downhill

21. How do people
affect soil erosion?
removal of canopy covers
exposes soil to raindrop
impact or flowing
Deforestation
Residential or Commercial
Construction
Traditional Cultivation Practices
like Ploughing or Tillage

22. Thank You