Natural vs. Accelerated Soil Erosion

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Natural vs. Accelerated Soil Erosion

• Natural geologic erosion has occurred at a
  relatively slow rate since the earth was formed.
  Natural erosion produces about 30 of all
  sediment in the U. S.
• Accelerated erosion is the increased rate of
  erosion caused primarily by the removal of
  vegetation or the alteration of ground contours.
  This type of erosion accounts for 70 of
  sediment in the country.

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The Three Processes of Soil Erosion

• Detachment
• Transport
• Deposition

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Erosion

• Erosion is the process in which, by the actions
  of wind or water, soil particles are detached and
  transported.

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Detachment
Raindrop impact energy is enough to dislodge
surface sediments.
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Transport
Detached soil particles are transported by the
energy of water flowing over ground and in
channels. Additionally, soil particles in
fluid systems (like watercourses and ditches) may
also detach unprotected soil particles by
physical action.
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Sediment

• Sediment is eroded material suspended in wind or
  water.

Sedimentation
Sedimentation is the deposition of eroded
material.
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The Erosion Process
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Rill Erosion
As flow concentrates, small channels begin to
form in the soil surface.
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Rill Erosion to Gully Erosion
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Gully Erosion
Gullies are formed when Runoff cuts rills deeper
and wider or when flows from several rills come
together and form a large channel.
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Slope Failure
Left unattended, erosion can cause catastrophic
failure of roads or other facilities.
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What can accelerateerosion problems?

• Unrestricted development
• Removal of surface cover
• Increased imperviousness (i.e., paving) that
  increases runoff
• Poor stewardship

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Construction-relatederosion can...

• Cause problems for down slope property owners
• Create nuisance problems on adjacent streets
• Clog streams and storm drains

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Construction-relatederosion can...

• Result in turbidity plumes in downstream water
  bodies
• Cover sensitive habitat areas with sediment

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Pollutant Export During Construction

• Clearing and grading exposes soils
• Eroded sediment can be transported
• Also transports nutrients, pesticides, bacteria,
  organic matter, and toxic substances
• Uncontrolled construction site sediment loads can
  be 35 to 45 tons/acre/year

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In-stream Damages

• May include
• destruction of spawning areas, food sources,
  habitat
• direct toxicity to wildlife
• lake degradation
• filling of navigation channels
• impacts to commercial fisheries
• reduction of water storage capacities

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Suspended Material
Sediment can affect light penetration, channel
stability, fisheries habitat.
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Off-stream Damages

• May include
• Increased flood hazards
• Increased water treatment costs
• Decreased capacity in conveyance facilities
• Higher infrastructure maintenance costs

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Before...
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and After
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Before...
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and After
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Questions