Primary Mechanical Processes of Erosion both wind and water

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Primary Mechanical Processes of Erosion (both
wind and water)

• Detachment particles are detached from soil
  surface
• Transportation particles are moved in the fluid
  stream
• Deposition particles drop out of the fluid
  stream

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Agents of Erosion

• Wind
• Water
• Both wind and water are fluids and have similar
  physics of operation
• Energy of the moving fluid is a function of mass
  and velocity
• KE 1/2 m v2
• Deposition occurs when energy decreases

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Water

• Falling raindrops
• Detach particles
• Destroy aggregates
• Transport soil
• Flowing water
• Detaches particles
• Transports soil

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Types of Water Erosion

• Sheet - uniform soil layer
• Rill - channel flow
• Gully - channels that cannot be removed with
  tillage

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Factors that determine soil losses from water
erosion

• There are 5 primary factors (one a combination of
  two others) that affect soil loss.
• Take a minute to brainstorm factors you might
  expect to affect soil erosion.
• These factors are based on the Universal Soil
  Loss Equation used to estimate average annual
  soil loss by water erosion
• The first diagram is a blank, the second lists
  the USLE factors, and the third shows the same
  diagram with the factors listed

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Water Erosion Prediction

• Models predict sheet and rill (not gully)
• Universal Soil Loss Equation
• A R K LS C P, where
• A total soil loss, tons/acre/year
• R local rainfall erosive potential
• K soil erodibility factor
• LS slope length and gradient
• C vegetative cover or management
• P erosion control practice

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USLE Water Erosion Factors
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Water Erosion Prediction

• R climatic factor
• Precipitation timing Is cropland covered or
  bare?
• Precipitation intensity Gentle rains or violent
  thunderstorms with high winds?
• Precipitation quantity How much total?
• Precipitation distribution Does it come
  throughout the year, or in a short period?

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Water Erosion Prediction

• K soil erodibility
• Primarily a function of soil texture and soil
  organic carbon (SOC) content, which determine
  aggregate stability
• LS slope length and gradient
• Combination of how long and steep a slope is,
  which determines the energy that can be attained
  by flowing water

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Water Erosion Prediction

• C vegetative cover or management
• Does the soil have actively growing vegetation or
  residues to protect it from raindrop impact and
  to slow flowing water
• Vegetated or residue covered surfaces have little
  erosion potential
• P erosion control practice
• Tillage practices like contour tillage, strip
  tillage
• Cultural practices like rotations

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Wind

• Detaches particles
• Abrades aggregates
• Transports particles

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Wind Erosion Prediction

• Wind Erosion Equation
• E f( I C K L V ), where
• E total soil loss, tons/acre/year
• I soil erodibility factor
• C climate erosive potential
• K soil roughness
• L length of unobstructed wind run
• V vegetative cover or management

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Wind Erosion Equation Factors
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Wind Erosion Prediction

• Wind Erosion Equation
• I soil erodibility factor
• As with water erosion, a function of texture and
  SOC
• C climate erosive potential
• How much wind?
• When does the wind blow?
• What is the surface/cover condition when the wind
  blows?

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Wind Erosion Prediction

• Wind Erosion Equation
• K soil roughness
• Soil surface configuration changes the wind speed
  at the surface. Smooth surfaces blow more readily
  than rough ones
• Oriented beds and ridges
• Random sand fighter, etc., Though emergency
  tillage is a common practice, it shows the battle
  has already been lost

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Wind Erosion Prediction

• Wind Erosion Equation
• V vegetative cover or management
• This is the best way to avoid the need for
  emergency tillage.
• This is where the battle against erosion is won,
  protecting the soil surface from forces that
  destroy aggregates (abrading sand particles) and
  dislodge particles

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Wind Transport

• Saltation
• 50 to 70 of soil movement
• near ground (
• Soil creep
• 5 to 25 of soil movement
• particles
• Suspension
• Small percentage of soil movement
• Dust clouds several m to km above surface
• Deposited km to hundreds of km away

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• Though the suspension component of wind erosion
  is the most impressive, it is not the most
  destructive. Suspension movement of fine soil
  particles and SOC from Africa actually provide
  fertility for islands in the Atlantic, and for
  the tropical rain forest in South America
• If the sand particles were not coming loose and
  abrading others, the fine particles would never
  enter suspension.

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Focus

• Contemplate the similarities between the wind and
  water erosion prediction equations
• Articulate the methods required to limit soil
  losses by wind and water Think in terms of
  general principles that are applicable across all
  levels of technology