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Erosion and Sedimentation Processes

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									  Erosion and Sedimentation
Processes, Factors and Impacts
     on the Environment
                 Level IA: Fundamentals Seminar
                Education and Training Certification
  Requirements for Persons Involved with Land Disturbing Activities



                                                        Issued May 2009
                                                                          1
               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

                                                    2
EROSION - The process by which the
land surface is worn away by the action
of water, wind, ice and gravity




                                      3
Predevelopment




  Construction   4
Photograph of erosion




Water Erosion           5
Types of Water Erosion

   1. Splash Erosion
   2. Sheet Erosion
   3. Rill Erosion
   4. Gully Erosion

                         6
          Raindrop impact on bare soil



Splash                .
Erosion




                                         7
Sheet Erosion




            8
Photograph of rill erosion




   RILL EROSION              9
    Gully Erosion


Photograph of gully erosion




                              10
TYPES OF WATER EROSION



                Insert picture here
SPLASH
     SHEET



             RILL &
             GULLY


                      STREAM &
                      CHANNEL         11
 Sedimentation
The process by which the eroded
material is transported and deposited by

               • Water
               • Wind
               • Ice
               • Gravity
                                      12
Photograph of sediment




    SEDIMENTATION
                         13
      SEDIMENT TRANSPORT




GA stream following
    1/2” of rain
  June 26, 2001            14
Stages in Erosion & Sedimentation
1. Detachment   2. Transport   3. Deposition




                                               15
Natural Erosion vs. Accelerated Erosion




                                    16
Natural (Normal) Erosion

• Erosion without the interference
  of man’s activities.

• The rate is generally small except
  for stream channel and shore
  erosion.                             17
Accelerated Erosion

Erosion intensified by human activities
  – Example: Farming
  – Example: Construction




                                    18
        Expected Erosion Rates
            (Tons/Acre/Year)

1. Forest Land            1 or greater
2. Farm Land            15 or greater
3. Construction Sites   100 or greater

                                        19
 Impacts of Construction Activities

1. Removal of soil organic matter
2. Removal of vegetation
3. Reshaping of ground surface contours
4. Exposure of subsoil
5. Changing the pervious ground surface
  to impervious
                                          20
Factors Affecting Erosion
 1. Climatic (rainfall and runoff) Factors
 2. Soil Factors
 3. Topographic Factors
 4. Vegetative Factors

                                             21
RAINDROP IMPACT & SPLASH EROSION




                             22
The potential for soil erosion
varies during the year in GA




    We have more thunderstorms
          in the summer
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                                                                           Atlanta, GA




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                                                                        Rainstorm Energy




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24
     Photograph of river




VOLUME AND VELOCITY OF FLOW
                              25
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.


                                                 26
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

    1’

                   4’
                                            27
Slope Gradient




                 28
Soil Factors

• Fine sandy & silty soils are more
  erodible than clay type soil & those with
  higher percentage of organic matter.




                                              29
    Vegetative Factors

•   Absorbs raindrop impact
•   Reduces detachment
•   Roots hold soil in place
•   Slows water flow
•   Adds organic material to the soil
•   Reduces runoff
•   Increases infiltration
                                        30
31
Photograph of vegetation holding soil
              in place


                Vegetation holds
                  soil in place     32
 Photograph of vegetation slowing
   water and trapping sediment

Vegetation slows the flow of water,
  reducing erosion and trapping
            sediment                33
Photograph rate and speed of runoff




                 Rate and speed
                    of runoff         34
Photograph




             35
Vegetation provides
 organic material




                      36
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

                                        37
Increased maintenance
 costs for stormwater
 management systems




                    38
Decreased Recreational Value
                               39
Screens Out Sunlight = Decline in Plant Growth




        Biological impacts




                                           40
Sedimentation Disrupts The Ecosystem   41
42
43
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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

                                                45
 Georgia Soil and Water
Conservation Commission

      State Office
     706.542.3065
      Certification
     706.542.1840
 www.gaswcc.georgia.gov
                          46
QUESTIONS?




             47

								
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