Transcript Erosion and Sedimentation Processes, Factors and Impacts on the Environment Level IB: Advanced Fundamentals Seminar Education and Training Requirements for Individuals Involved in Land Disturbing.

Erosion and Sedimentation
Processes, Factors and Impacts
on the Environment
Level IB: Advanced Fundamentals Seminar
Education and Training Requirements for Individuals Involved in Land
Disturbing Activities
Issued May 2009
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OVERVIEW
• Introduction of Erosion and Sedimentation (E&S)
– Definitions and general stages of E&S
– Basic processes and factors governing E&S
– Natural erosion vs. accelerated erosion
• Impacts of Erosion and Sedimentation (E&S)
– Environmental impacts
– Economic impacts
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EROSION - The process by which the
land surface is worn away by the action
of water, wind, ice and gravity
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Predevelopment
Construction
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Photograph of erosion
Water Erosion
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Types of Water Erosion
1. Splash Erosion
2. Sheet Erosion
3. Rill Erosion
4. Gully Erosion
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Raindrop impact on bare soil
Splash
Erosion
.
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Sheet Erosion
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Photograph of rill erosion
RILL EROSION
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Gully Erosion
Photograph of gully erosion
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TYPES OF WATER EROSION
Insert picture here
SPLASH
SHEET
RILL &
GULLY
STREAM &
CHANNEL
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Sedimentation
The process by which the eroded
material is transported and deposited by
• Water
• Wind
• Ice
• Gravity
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SEDIMENT TRANSPORT
GA stream following
1/2” of rain
June 26, 2001
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Photograph of sediment
SEDIMENTATION
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Stages in Erosion & Sedimentation
1. Detachment
2. Transport
3. Deposition
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Natural Erosion vs. Accelerated Erosion
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Natural (Normal) Erosion
• Erosion without the interference of
man’s activities.
• The rate is generally small except for
stream channel and shore erosion.
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Accelerated Erosion
Erosion intensified by human activities
– Example: Farming
– Example: Construction
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Estimation of Average Annual Soil Loss
Revised Universal Soil Loss Equation
(RUSLE)
A=RKSLCP
A: Average Annual Soil Loss
R: Rainfall Erosivity Factor
K: Soil Erodibility Factor
S: Percent Slope
L: Length of Slope
C: Cover Management Factor
P: Conservation Practice Factor
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RUSLE Example
A = RKLSCP
Given:
Clarke County (R = 275) Table B-2.1
Cecil sandy loam (K = 0.28) Soil Survey
2:1 slope, 20 feet long (LS = 7.97) Table B-2.2
20% grass cover (C = 0.2) Table B-2.5
No other conservation practices (P = 1.00)
Find:
Soil loss for the given conditions.
A = 122.7 tons per acre per year
*Information taken from the Manual for Erosion and
Sediment Control in GA
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RUSLE Example
A = RKLSCP
If you reduce the slope steepness to 3:1 (LS = 4.93) …
A = 75.9 tons/acre/year, a 38% reduction in soil loss.
or
If you increase the vegetative cover to 80% (C = 0.013) …
A = 8.0 tons/acre/year, a 94% reduction in soil loss.
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Expected Erosion Rates
(Tons/Acre/Year)
1. Forest Land
2. Farm Land
3. Construction Sites
1 or greater
15 or greater
100 or greater
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Impacts of Construction Activities
1. Removal of organic soil matter
2. Removal of vegetation
3. Reshaping of ground surface contours
4. Exposure of subsoil
5. Changing the pervious ground surface
to impervious
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Factors Affecting Erosion
1. Climatic (rainfall and runoff) Factors
2. Soil Factors
3. Topographic Factors
4. Vegetative Factors
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RAINDROP IMPACT & SPLASH EROSION
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The potential for soil erosion
varies during the year in GA
We have more thunderstorms
in the summer
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Rainstorm Energy
Atlanta, GA
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Photograph of river
VOLUME AND VELOCITY OF FLOW
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Topography
SLOPE GRADIENT
SLOPE LENGTH
Gradient is expressed as number of horizontal
units per unit vertical such as 3 to 1 or 4 to 1 or
in percentage as 33 percent or 25 percent.
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Slope Gradient
• 4 to 1 or 4:1 means that four feet of
horizontal length are required for each
foot of vertical change in elevation
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4
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Slope Gradient
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Soil Factors
• Fine sandy & silty soils are more
erodible than clay type soils & those
with higher percentage of organic
matter.
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Vegetative Factors
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Absorbs raindrop impact
Reduces detachment
Roots hold soil in place
Slows water flow
Adds organic material to the soil
Reduces runoff
Increases infiltration
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Photograph of vegetation holding soil
in place
Vegetation holds
soil in place
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Photograph of vegetation slowing
water and trapping sediment
Vegetation slows the flow of water,
reducing erosion and trapping
sediment
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Photograph rate and speed of runoff
Rate and speed
of runoff
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Photograph
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Vegetation provides
organic material
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Impacts of Erosion and Sedimentation
1. Loss of soil productivity
2. Adverse effects on other water
resource facilities
3. Loss of reservoir storage capacity
4. Flood impacts
5. Recreational impacts
6. Deterioration of water quality
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Increased maintenance
costs for stormwater
management systems
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Decreased Recreational Value
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Screens Out Sunlight = Decline in Plant Growth
Biological impacts
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Sedimentation Disrupts The Ecosystem
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SUMMARY
• Many processes and factors are involved in
erosion and sedimentation
• Erosion is a natural process, but it can be
accelerated by human activities. KEEP BARE
SOIL TO AN ABSOLUTE MINIMUM!
• Impacts of erosion and sedimentation can be
devastating to both the environment and the
economy
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Georgia Soil and Water
Conservation Commission
State Office
706.542.3065
Certification
706.542.1840
www.gaswcc.georgia.gov
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QUESTIONS?
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