Erosion refers to detachment and transport of soil and soil materials by water, wind, ice or gravity. No soil phenomenon is more destructive worldwide than the erosion caused by wind and water. Erosion damages the site on which it occurs and also has undesirable effects off-site in the larger environment.

1. On-site and off-site
consequences of soil erosion
Prepared by:
Santosh Pathak ( IAAS, Lamjung)

2. Soil erosion
• Erosion refers to detachment and
transport of soil and soil materials
by water, wind, ice or gravity.
• No soil phenomenon is more
destructive worldwide than the
erosion caused by wind and water.
• Erosion damages the site on which
it occurs and also has undesirable
effects off-site in the larger
environment.

3. • The loss of soil itself.
• The damage done to the soil is greater
than the amount of soil lost as the soil
material eroded away is almost always
more valuable than that left behind.
• In Nepal, the annual loss of soil from
agricultural plots ranges from 0.1 t/ha
to 105 t/ha (Chalise and Khanal)
• Erosion removes organic matters and
fine minerals particles while leaving
behind mainly relatively less active,
coarser fraction.
• O.M and N2 in the eroded materials to
be five times as high as in original top
soils.
Fig: decline in soil productivity

4. On site consequences…
• 1.8 tons of plant nutrients are removed from the soil
by crop harvest and soil erosion and only 0.3 million
mt. (16%) are replenished by organic and inorganic
fertilizers (MOEP, 2001)
• Eroded zone has lower water holding capacity and
cation exchange capacity, less biological activity, less
access to nutrients for plant.

5. • Erosion spread plant disease
organisms.
• Deterioration of soil structure
• Dense crust formation
• Reduce water infiltration
• Increases water runoff
• Seed and seedlings may be
washed downhills.
• Uprooting of trees.
• Small plants buried in sediments
Fig: Tree being uprooted
Fig: Small plants buried in sediments

6. • In the case of wind erosion :
 Fruits and foliage damaged
by the sand blasting.
 leaf incrustation causes
stomatal closening.
• Relatively large gullies make the
use of tractors impossible.
• Under cut pavements and
building foundation : unsafe
conditions and expensive repairs.
Fig: Gully erosion
Fig: Difficulty in transportation due to gullies

7. • Movements of sediments and
nutrients off the land, creates
two most widespread water
pollution.
• eutrophication caused by
excessive nitrogen and
phosphorus.
• Carry toxic metals and
organic compounds such as
pesticides, leads to bio
magnification.
Damages from sediments
 Smother crop and low
growing vegetation.
 Roadside drainage and
ditches filled creating
hazardous driving
conditions.
 Turbidity of streams
increased preventing
sunlight penetration and
reduced photosynthesis and
survival of submerged
aquatic vegetation(SAV).
Fig: Water turbidity increased due to soil erosion

8. Contd……
 The demise of SAV, in turn, degrades the fish
habitat and upsets the aquatic food chain.
 Spawning sites of the freshwater fishes buried.
 According to the WWF, a group of Brazilian Indians
reported significant decreases in fish numbers.
 Bottom sediments buildup raise the level of river
causing frequent and severe flooding.
 Koshi river of Nepal is a popularly noted for its
sediment transportation, it occurs in 6th position
with 172 million tons/annum sediment
transportation.
 The life span of kulekhani reservoir in the central
Nepal has been reduced to half of the targeted
design and one quarter of the expected life due to
soil erosion.
 Reservoir capacity is decreased.
 Very high cost of remedy operations like excavation,
filtering, and construction activities. Fig: Reservoir exceeds its capacity

9. Contd…..
• In case of wind erosion, blowing
sand may bury roads and fill
drainage ditches, necessitating
expensive maintainance.
• Sand blasting effect damage the
fruits and foliage of the field as well
as paint on vehicle and building.
• Dust storms and air pollution cause
discomforts, disease infections,
automobile accidents etc.
• Change in landforms and
topography.
Fig: Adverse effects on human
health caused by pollution
Fig: Formation of canyon due to erosion

10. • Combating soil erosion is
everybody's business.
attention must be paid to control on
site consequences which finally
reduce off site consequenses.