EROSION CONTROL AND ASSESSMENT

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EROSION CONTROLAND ASSESSMENT

• Dr. Stephan A. Schroeder, CPSS
• Environmental Scientist
• ND Public Service Commission
• Presented at the 2007 ND Solid
• Waste and Recycling Symposium

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OBJECTIVES

• 1. To very briefly show how to control erosion
  and increase stability, and
• 2. To develop alternative methodology through
  empirical comparisons

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EROSION CONTROL

• 1. Establishment of vegetative cover
• a. Permanent, self sustaining
• b. Not detrimental to land use (no noxious
  weeds, etc.)
• c. Diverse species and seasonality
• d. Sod formers vs bunch grasses

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EROSION CONTROL (cont.)

• 2. Best management practices
• a. Mulching
• b. Erosion matting
• c. Strawbale dikes, silt fences,
• rock check dams
• d. Terraces, diversions, etc.

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EROSION ASSESSMENT

• Emperical models
• RUSLE 1.06
• RUSLE2

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What are RUSLE 1.06 and RUSLE2?

• They are empirical models for estimating
  soil loss from hillslopes caused by raindrop
  impact and overland flow based on earlier
  versions of RUSLE and the Universal Soil Loss
  Equation
• RUSLE 1.06 is DOS based developed in the
  late 1990s while RUSLE2
• is Windows based developed in the early
  2000s
• Both run on Window systems up through XP
• RUSLE 1.06 is especially designed to be
  used on mined lands,
• construction sites, and reclaimed lands

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What are RUSLE 1.06 and RUSLE2?

• Limitations
• Neither estimate gully or stream-channel
• erosion, only soil loss only from rill and
  
• interrill erosion
• Soil losses are long term average amounts,
• not specific rainfall event estimates
• Estimated accuracy of soil loss estimates
• 1ltAlt4 tons/ac/year 50
• 4ltAlt30 tons/ac/year 25
• 30ltAlt50 tons/ac/year 50
• Least accurate when Alt1 or Agt50 tons/ac/year

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What are RUSLE 1.06 and RUSLE2? (cont.)

• - Provides soil loss estimates, not soil
  loss absolutes, and are the best technology
  available at this time
• - Limits have been established for which
  hillslope length and gradient have been
  verified
• - Neither produce watershed-scale sediment
  yields and

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RUSLE Model s

• RUSLE models consists of many mathematical
  equations derived from erosion research data to
  estimate soil loss
• The models retain the same structure of that of
  the USLE, namely
• A R K L S C P
  
• Where A Average annual soil loss
  (tons/acre/year)
• R Rainfall/runoff erosivity
  factor
• K Soil erodibility factor
• L Hillslope length
• S Hillslope steepness
• C Cover management factor
• P Support practice factor

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RUSLE Models

• R factor - ranges from about 70 in the very
  southeastern part of North Dakota to about 30 in
  the very northwestern part
• K factor based upon soil texture, soil
  structure, organic matter, and soil permeability
  and generally ranges from 0.2 to 0.4
• Neither factor can be manipulated as easily as
  the other factors

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Hillslope Length and Gradient Factor (LS)

• General Comments
• - The greatest potential soil loss in the
  field is usually the
• area where the hillslope gradient is the
  largest
• - This factor is combined with hillslope
  length into a single
• topographic factor, LS, to define the
  ratio of soil loss
• from a given hillslope compared to a
  unit plot
• - This factor is more sensitive to gradient
  values than
• slope length

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Hillslope Length and Gradient Factor (LS) (cont.)

• Slope
  Length (ft)
• Gradient () 50 100 200
  300
• 1 0.127 0.148
  0.172 0.187
• 5 0.470 0.670
  0.954 1.174
• 10 0.925 1.427
  2.200 2.840
• 20 2.113 3.462
  5.674 7.574
• 25 2.659 4.422
  7.357 9.908

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Hillslope Length and Gradient Factor (LS) (cont.)

• Slope shape effects
• Scenario
• Silt loam soil
• Disturbed fill, w/ topsoil, no rock cover
• 200 feet in length, equal 20-ft lengths
• LS factor values
• Linear ?
• Concave ?
• Convex ?

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Hillslope Length and Gradient Factor (LS) (cont.)

• Slope shape effects
• Scenario
• Silt loam soil
• Disturbed fill, w/ topsoil, no rock cover
• 200 feet in length, equal 20-ft lengths
• LS factor values
• Linear 2.200
• Concave 0.823
• Convex 1.380

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Cover-Management (C)

• Definition this factor represents vegetative,
  management and erosion-control practice effects
  that primarily affect the process of detachment
  on soil loss
• Similar to the other factors, the calculated C
  factor is the ratio of soil loss comparing the
  defined, existing surface conditions to that of a
  
• unit plot
• Has the greatest possible range of all factors

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Cover-Management (C) (cont.)

• Is based upon several factors including
• Prior land use
• Canopy cover
• Surface cover
• Surface roughness
• Soil moisture
• Can be based on single disturbances or rotations
• Can be base under stripcropping or buffer strips

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Cover-Management (C) (cont.)

• For example
• Straw Mulch Equivalent Cover Operational C
• (t/ac) ()
  Value _
• 0.25 26
  0.345
• 1.00 70
  0.084
• 2.00 91
  0.043

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Support Practice (P)

• This factor takes into consideration the effect
  of specific support practices on soil loss
• The support practices generally affect soil loss
  through their influence by reductions in the
  amount and rate of runoff, and/or changing the
  flow pattern or direction of the surface flow
• P subfactors include contouring, barrier strips
  or concave hillslope shape, terracing, sediment
  basins, and subsurface drainage

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Support Practice (P) (cont.)

• Contouring Effects
• - Contouring causes runoff to flow around
  the
• slope thus reducing sediment transport
  more
• than runoff amounts
• - Effects are dependent upon ridge height
  and
• slope gradient, for example assuming a
  6-inch
• high ridge
• P subfactor 1 for 1ltslope gradientgt25
  
• 0.5-0.6 for 2-7
  slope gradient

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Support Practice (P) (cont.)

• Terracing
• - Terraces divide the hillslope length into
  
• shorter segments and RUSLE hillslope
• profiles since water from upper terraces
  
• never runs down onto the lower terraces
• - Effectiveness depends upon climate,
• hillslope length and gradient between
• terraces, soil type, cover, terrace
  grade, and
• soil loss from inter-terrace space

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Support Practice (P) (cont.)

• Terrace P-subfactors values
• 
  Open outlet grades
• Hor. Terrace Closed
  ()
• Interval (ft) Outlets 0.1-0.3
  0.4-0.7 gt0.8
• lt110 0.5 0.6
  0.7 1.0
• 110-140 0.6 0.7
  0.8 1.0
• 140-180 0.7 0.8
  0.9 1.0
• Must be multiplied by other P-subfactors to
  obtain
• composite P-factor value

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Support Practice (P) (cont.)

• Sediment Control Barrier or Structures
• - Common ones used on mining, reclaimed
  lands, and construction sites include vegetative
  buffer strips, strawbale dikes, and silt fences
• - RUSLE assumes that these features are
  installed on the contour and are properly
  designed, installed, and maintained
• - P-subfactor values vary due to design,
  etc.

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For more information on RUSLE 1.06 including
downloads of the software, instruction manual,
and tutorials, go to

• http//www.ott.wrcc.osmre.gov/elearning/rusle1
  06b.htm

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Conclusions

• Control
• - Establish cover
• - Use BMPs
• i.e. Contouring, silt fences, terracing,
  etc.
• Assessment
• - Use empirical erosion equations like RUSLE
• 1.06 or RUSLE2 to compare various erosion
• rates under various construction scenarios