natural vs. accelerated soil erosion natural geologic erosion has occurred at a relatively slow rate...
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Natural vs. Accelerated Soil Natural vs. Accelerated Soil ErosionErosion
Natural geologic erosion has occurred at a Natural geologic erosion has occurred at a relatively slow rate since the earth was relatively slow rate since the earth was formed. Natural erosion produces about formed. Natural erosion produces about 30% of all sediment in the U. S.30% of all sediment in the U. S.
Accelerated erosion is the increased rate Accelerated erosion is the increased rate of erosion caused primarily by the removal of erosion caused primarily by the removal of vegetation or the alteration of ground of vegetation or the alteration of ground contours. This type of erosion accounts contours. This type of erosion accounts for 70 % of sediment in the country.for 70 % of sediment in the country.
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The Three Processes of Soil The Three Processes of Soil ErosionErosion
DetachmentDetachment
Transport Transport
DepositionDeposition
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ErosionErosion
Erosion is the process in which, by the
actions of wind or water, soil particles are detached and
transported.
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DetachmenDetachmentt
Raindrop impact energy is enough to
dislodge surface
sediments.
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TransportTransport
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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SedimentSedimentSediment is eroded material suspended
in wind or water.
Sedimentation is the deposition of eroded material.
SedimentationSedimentation
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The Erosion ProcessThe Erosion Process
Rain hitting the land Rain hitting the land surface can dislodge surface can dislodge significant amounts of significant amounts of pollutantspollutants
Sheet flow overland can erode slopes
Unchecked erosion will commonly lead to formation of channels
The receiving water bears the impact of quantity and quality degradation
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Rill ErosionRill Erosion
As flow concentrates, small channels begin to form in the soil surface.
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Rill Erosion to Gully Rill Erosion to Gully ErosionErosion
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Gully Gully ErosionErosion
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 FailureSlope Failure
Left unattended, erosion can cause catastrophic failure of roads or other
facilities.
Left unattended, erosion can cause catastrophic failure of roads or other
facilities.
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What can accelerateWhat can accelerateerosion problems?erosion problems?
Unrestricted development
Removal of surface cover
Increased imperviousness (i.e., paving) that increases runoff
Poor stewardship
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Construction-relatedConstruction-relatederosion can...erosion can...
Cause problems for down slope property owners
Create nuisance problems on adjacent streets
Clog streams and storm drains
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Construction-relatedConstruction-relatederosion can...erosion can...
Result in turbidity plumes in downstream water bodies
Cover sensitive habitat areas with sediment
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Pollutant Export Pollutant Export During ConstructionDuring Construction
Clearing and grading exposes soilsClearing and grading exposes soils Eroded sediment can be transportedEroded sediment can be transported Also transports nutrients, pesticides, Also transports nutrients, pesticides,
bacteria, organic matter, and toxic bacteria, organic matter, and toxic substancessubstances
Uncontrolled construction site Uncontrolled construction site sediment loads can be 35 to 45 sediment loads can be 35 to 45 tons/acre/yeartons/acre/year
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In-stream DamagesIn-stream Damages
May include:May include:
• destruction of spawning areas, food destruction of spawning areas, food sources, habitatsources, habitat
• direct toxicity to wildlifedirect toxicity to wildlife
• lake degradationlake degradation
• filling of navigation channelsfilling of navigation channels
• impacts to commercial fisheriesimpacts to commercial fisheries
• reduction of water storage capacitiesreduction of water storage capacities
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Suspended MaterialSuspended Material
Sediment can affect light penetration, channel stability, fisheries & habitat.
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Off-stream DamagesOff-stream Damages
May include:May include:
• Increased flood hazardsIncreased flood hazards
• Increased water treatment costsIncreased water treatment costs
• Decreased capacity in conveyance facilitiesDecreased capacity in conveyance facilities
• Higher infrastructure maintenance costsHigher infrastructure maintenance costs
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Before...Before...
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……and Afterand After
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Before...Before...
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……and Afterand After
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QuestionsQuestions