Download Calculating Sedimentation Loads from Unpaved/Logging Roads

Calculating Sedimentation Loads from Unpaved/Logging Roads
Tom Ballestero
University of New Hampshire
1 May 2013
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Fundamental Causes of Erosion
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Climate
Land Use
Soil Type
Land Cover
Topography
Groundwater
Surface water
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Climate
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Wind
Precipitation
Waves
Glaciers
Freeze/thaw
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Land Use
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Grazing
Construction
Deforestation/logging
Forested
Urban
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Soil Type
• For gravel roads, this is going to be gravel
• Most erodible materials are fine sands to silts
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Land Cover
• Vegetation
• Pavement
• Bare soil
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Topography
• Slope (gravity)
• Slope length
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Groundwater
• Submerged soils have less ability to resist erosion (soil strength)
• Groundwater places a pressure on the soil against gravity
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Surface Water
• Velocity
• Depth of flow
Shear stress related to
depth times slope
– Sheet flow
– Shallow concentrated
– Rills
– Gullies
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Fundamentally
• Sediment is available
• Something can move the sediment
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Erosion Control
• Minimize sediment available to move (protect) –
prevent erosion
• Eliminate what moves the sediment (drain)
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After Erosion Occurred
• Now in management mode – how best to remove the sediment before it gets to the receiving water?
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Reid and Dunne, 1984
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Methods to Estimate Erosion on Unpaved Roads
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Universal Soil Loss Equation (USDA)
• Developed from erosion plot and rainfall simulator experiments
• Sheet and rill erosion
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USLE
A = R x K x LS x C x P = RKLSCP
• A = long‐term average annual soil loss [ton/(acre/year)] • R = rainfall erosivity factor [hundreds of ft.tonsf.in/acre.hr.year]
• K = the soil erodibility factor [tons per acre per unit R]
• L and S = topographic factors [‐]
• C and P = the cropping management factors [‐]
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Road Gravel Particle Sizes
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• 38 mm
• 19 mm
• 4.75 mm
• 2 mm
• 0.075 mm
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LS Values for Freshly Prepared Construction and other Highly Disturbed
Soil, with Little, or no Cover (Renard, et al. 1987)
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Wait, There’s More!
• MUSLE
• RUSLE
I don’t always compute soil loss, but when I do I start with the USLE
Stay uneroded my friend
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Water Erosion Prediction Project (USDA)
• Process based erosion model that can be used to simulate low volume road erosion
• Database of erosion estimates for 72,900 different road configurations, locations, and soil types
• Database was then used to derive equations for low volume road erosion and runoff (+/‐ 20%)
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WEPP Road Soil Loss
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Equation Reference Table 3
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Equation Reference Table 4
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WEPP Predictive Power
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WEPP Reference
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Imhoff, et al, 2010
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Imhoff, et al, 2010
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SEDMODL (WEPP with GIS)
GIS‐based road erosion and delivery model designed to identify road segments with high potential for delivering sediment to streams. The model uses an elevation grid combined with road and stream information layers to produce what is essentially a computer‐generated version of the Washington surface road erosion model. It estimates background sediment, generation of sediment for individual road segments, finds road/stream intersections, and estimates delivery of road sediment to streams.
http://www.ncasi.org/support/downloads/Detail.aspx?id
=5
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Effects of Grading
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Tread (Road) Sediment Delivery
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Geologic Factor
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Road Tread Surfacing Factor
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Road Width and Traffic Factors (1)
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Road Width and Traffic Factors (2)
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Road Slope Factor
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Cut Slope Sediment Delivery
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Cut Slope Height
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Data Base for Cut Slope Height
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Cut Slope Cover Factor
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Rainfall Factor
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Road Delivery Factor
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Road Age Factor
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Segment Length/Road Drainage Configuration
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Segment Lengths Used for Each Configuration
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Spreadsheet Tool for Estimating Pollutant Load (STEPL)
• Region 5 Model
• http://it.tetratech‐ffx.com/steplweb/
• Spreadsheet model based on the USLE
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Simple Method
• Planning tool
• Assess different best management practices at the watershed and subwatershed scale
• estimates contaminant loads based on:
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land use, annual runoff, drainage area, and system performance
• does not factor in volume reductions for infiltration
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Simple Method with BMPs
L = 0.226 * R * C * A * RE
• L = Annual load (lbs)
• R = Annual runoff (inches)
• C = Pollutant concentration (mg/l)
• A = Area (acres)
• 0.226 = Unit conversion factor
• RE=Best Management Practice removal efficiency (%)
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BMP Sediment Removal
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Brackett Road Case Study
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Many Bad Examples
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Predominant Pollutant Concentrations
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Sediment From Each Site
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Estimated Unpaved Sediment
4.6 Tons/acre/year
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Ranking of Alternatives
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Simple Reference
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Rates
• TN – 25 tons/acre/year
• NC – 100 tons/acre/year
• CA – 2 to 480 tons/acre/year
For a 15‐ft wide gravel road, 1 ton/acre/year
~ 0.083 inches/year
Range of loss = 1/6 in to 3.3 in/yr
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Northeast Regional Climate Center
• Home Page
http://precip.eas.cornell.edu/
• Extreme Precipitation
http://precip.eas.cornell.edu/
• Map Tool
http://precip.eas.cornell.edu/
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Map Tool
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StreamStats
• Home Page
http://streamstats.usgs.gov/
• State Application
http://streamstats.usgs.gov/ssonline.html
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