Soil Erosion by Water

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Soil Erosion by Water

• AST 324
• Carl E. Anderson

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Chapter 6 Soil Erosion by Water Learning
Objectives

• Understand the factors effecting the erosive
  force of flowing water
• Understand the factors effecting the forces
  resisting soil erosion
• Understand the basic procedures available for
  controlling soil erosion

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Soil Erosion

• The gradual wearing away of the land surface by
  running water, wind, ice, or other geological
  agents.
• Erosion is a natural process which cant be
  stopped completely.
• Some natural ecosystems depend on a natural rate
  of erosion.

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NATURAL EROSION
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Accelerated ErosionCAUSED BY

• Overgrazing range and pasture
• Cultivation
• Construction
• Heavy traffic on bare slopes
• Maximum when bare soil is exposed during periods
  of maximum rainfall.

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SOIL EROSION PROCESSES

• DETACHMENT
• TRANSPORT

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Soil Properties Affecting Erosion
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Forces Tending to Cause Soil Particle Detachment

• Raindrop impact
• Forces of flowing water
• Abrasive action of other moving particles
• Weathering
• Animal and human actions
• Burrowing
• Tillage
• Excavation

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Soil Properties Tending to Resist Detachment

• Adhesion
• Cohesion
• Binding forces of plant root systems
• Protective coverings such as plant material

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Forces Tending to Transport Soil Particles

• Raindrop splash
• Forces of flowing water
• Wind movement
• Gravity

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Soil Properties Tending to Resist Transport

• Inertia
• High density
• Large particle size

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EFFECTS OF RAINDROPS ON SOIL EROSION

• Break up soil aggregates into small particles
• Compact the soil surface and thus increase
  surface runoff
• Splash small soil particles down the slope
• Increase the turbulence of overland flow and thus
  increase the transport capacity of the flow.

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Raindrop Erosion
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Erosion Control Methods

• Reduce Forces of Fluid
• Reduce Flow Velocity
• Increase Forces Holding Soil
• Increase Adhesion
• Increase Plant Root Structure
• Separate Soil From Flow
• Pavement
• Mulch
• Residue

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TYPES OF SOIL EROSION BY WATER

• SHEET OR INTERRILL
• RILL
• GULLY
• STREAMBANK

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Sheet Erosion
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Sheet and Rill Erosion
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Rill Erosion
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Gully Erosion
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Soil Loss Tolerance

• The maximum level of soil erosion that will
  permit a high level of crop productivity to be
  maintained both economically and indefinitely.

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SOIL EROSION UNITS

• MASS PER UNIT AREA PER UNIT TIME
• TONS PER ACRE PER YEAR
• METRIC TONS PER HECTARE PER YEAR

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NATURAL EROSION RATE

• 1 TO 5 TONS / ACRE / YEAR
• Erosion Rates in this Range are Sustainable
  Indefinitely.
• 1 ton / ac / year 163 years / inch soil loss

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MAJOR FACTORS AFFECTING SOIL EROSION

• Climate R
• Soil K
• Topography LS
• Vegetation C
• Conservation Practices P