factors that influence erosion...thermal degradation / freeze thaw erosion •freezing & thawing...
TRANSCRIPT
Factors that Influence Erosion
• Soils • Precipitation • Vegetation • Surface Area • Slope Length • Slope Gradient • Surface Texture Grayling
Most Sites Have Various Soils
How Deep will you be Digging? How will the Soil Change?
Differing Soil Types
Sand
Gravel
Loamy sand
Clay Loam
Clay
Clay
Soil Surveys: Ministry of Environment
http://sis.agr.gc.ca/cansis/taxa/landscape/slc_bcsouth.html
Most sites have specific Geotechnical reports and Bore Logs available
My Next Job Site
Woeisme Acres
This report indicates that
80% of the soil is .01mm
or smaller
200 Sieve
Sandy Soils Erode & Settle Quickly
Compacted Soils
Slow infiltration rates, impedes downward movement of water.
Clay Soils
Low Erosion Potential, but… Once Suspended it’s Very Difficult to Settle!
Organic Matter
Root Zone
Sub Grade
Graphic by USDA, NRCS
Soil Horizons
Erodibility Increases as the % of Silt & Sand Increases
Erodibility Decreases
as the % of Clay & Organic Material
Increases
Soil Texture & Erodibility
Surface Texture
Track Walking Increases Roughness
Imprinting Slopes Increases Texture & Assists Vegetation
Composition of a Compacted Soil
SolidAirWater
Note the reduced air space in a compacted soil.
Before After
70% 50%
Courtesy Dwayne Stenlund CPESC MNDOT
Soil Ripping
Reduces Compaction Increases Infiltration
Thermal Degradation / Freeze Thaw Erosion
•Freezing & Thawing detaches soil particles and causes down-slope movement •Frost loosened soil is more susceptible to erosion by rain and snowmelt •Eroded soil can become saturated with spring breakup resulting in mass movement
Precipitation
Climate
Rainfall factors that influence erosion
http://atlas.nrcan.gc.ca/site/english/maps/environment/climate/precipitation/precip
Mean Annual precip mm per year
Rainfall Data On
the Internet
www.climate.weatheroffice.gc.ca
Benefits of Vegetation
Reduces Runoff Volume
Reduces Flow Velocity
Sediment Filtration
Energy Absorption
Pollution Reduction
Soil Retention
Photo by USDA - NRCS
Trees
Shrubs
Moss
Duff
Roots
http://plants.alaska.gov/
Soil Rehabilitation Handbook Forest Practices Code
DFO Guidance
Revegetation Guidance
TOPOGRAPHY
Doubling the slope length increases erosion potential by 4 times.
Doubling the slope gradient increases erosion potential by 5 times.
Slope Length & Gradient
Surface Area
Larger bare areas contribute larger volumes & greater velocities of runoff
Soil Characterization
Slope Length & Gradient
Surface Texture
Vegetation
Precipitation Basin Area
= Erosion Losses
Factors that Influence Erosion
Revised Universal Soil Loss Equation A=R x K x LS x C x P
R= Rainfall Runoff Erosivity K= Soil Erodibility L= Length of Slope S= Slope Steepness C= Cover Practice P= Support Practice
A= Soil Loss In
Tons / Acre / Year
Soil loss equations can assist contractors in quantifying soil loss and the effects of BMP’s for risk management decisions.
Location
Location
Location
Erosion Risk Assessment
How much risk does your site pose? Consider: • Soil type- above and below the surface • Climate- frequency, intensity, and duration of rainfall • Vegetation • Surface Area • Slope Length & Gradient • Surface Texture