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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. OVERVIEW. Introduction of Erosion and Sedimentation (E&S)
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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
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
EROSION- The process by which the land surface is worn away by the action of water, wind, ice and gravity
Predevelopment Construction
Photograph of erosion Water Erosion
Types of Water Erosion 1. Splash Erosion 2. Sheet Erosion 3. Rill Erosion 4. Gully Erosion
Raindropimpact on bare soil Splash Erosion .
Photograph of rill erosion RILLEROSION
Gully Erosion Photograph of gully erosion
TYPES OF WATER EROSION Insert picture here SPLASH SHEET RILL & GULLY STREAM & CHANNEL
Sedimentation The process by which the erodedmaterial istransportedanddepositedby • Water • Wind • Ice • Gravity
SEDIMENT TRANSPORT GA stream following 1/2” of rain June 26, 2001
Photograph of sediment SEDIMENTATION
Stages in Erosion & Sedimentation 1. Detachment 2. Transport 3. Deposition
Natural (Normal) Erosion Erosionwithout theinterference of man’s activities. The rate is generally small except for stream channel and shore erosion.
Accelerated Erosion Erosionintensifiedby human activities Example: Farming Example: Construction
Estimation of Average Annual Soil LossRevised Universal Soil Loss Equation(RUSLE) A = R K S L C P A:Average Annual Soil LossR:Rainfall Erosivity Factor K:Soil Erodibility FactorS:Percent Slope L:Length of Slope C:Cover Management Factor P:Conservation Practice Factor
RUSLE ExampleA = 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
RUSLE ExampleA = RKLSCP If youreduce the slope steepnessto 3:1 (LS = 4.93) … A = 75.9 tons/acre/year, a38%reduction in soil loss. or If youincrease the vegetative coverto 80% (C = 0.013) … A = 8.0 tons/acre/year, a94%reduction in soil loss.
Expected Erosion Rates(Tons/Acre/Year) 1. Forest Land 1or greater 2. Farm Land 15or greater 3. Construction Sites100or greater
Impacts of Construction Activities 1. Removal oforganic soil matter 2. Removal ofvegetation 3. Reshaping of groundsurface contours 4. Exposure ofsubsoil 5. Changing theperviousground surface toimpervious
Factors Affecting Erosion 1. Climatic (rainfall and runoff) Factors 2. Soil Factors 3. Topographic Factors 4. Vegetative Factors
The potential for soil erosion varies during the year in GA We have more thunderstorms in the summer
Photograph of river VOLUME AND VELOCITY OF FLOW
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.
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
Soil Factors • Fine sandy & silty soils are more erodible than clay type soils & those with higher percentage of organic matter.
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
Photograph of vegetation holding soil in place Vegetation holds soil in place
Photograph of vegetation slowing water and trapping sediment Vegetation slows the flow of water, reducing erosion and trapping sediment
Photograph rate and speed of runoff Rate and speed of runoff
Impacts of Erosion and Sedimentation 1. Loss ofsoil productivity 2. Adverse effects on otherwater resource facilities 3. Loss ofreservoir storagecapacity 4.Floodimpacts 5.Recreationalimpacts 6. Deterioration ofwater quality
Increased maintenance costs for stormwater management systems
Screens Out Sunlight = Decline in Plant Growth Biological impacts
ECOSYSTEM Sedimentation Disrupts The Ecosystem
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
Georgia Soil and Water Conservation Commission State Office 706.542.3065 Certification 706.542.1840 www.gaswcc.georgia.gov