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Stuart Jennings Reclamation Research Group, LLC

Sediment and Erosion Control: Field Performance of Construction Site BMPs and Optimized Designs for Enhanced Stormwater Control. Stuart Jennings Reclamation Research Group, LLC. Format of Presentation. Review of BMPs and resources Estimating erosion severity BMP strategies

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Stuart Jennings Reclamation Research Group, LLC

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  1. Sediment and Erosion Control: Field Performance of Construction Site BMPs and Optimized Designs for Enhanced Stormwater Control Stuart Jennings Reclamation Research Group, LLC

  2. Format of Presentation • Review of BMPs and resources • Estimating erosion severity • BMP strategies • Observations from construction sites

  3. Erosion • Accelerated erosion occurs at construction sites when stabilizing vegetation is removed

  4. On-site Stormwater Control • Which BMPs are appropriate to my site? • What are the unique soil and vegetation characteristics of my site? • What can I expect for precipitation? • How long will it take for stabilization by vegetation?

  5. Families of BMPs • Surface Stabilization BMPs—hydromulch, straw mulch, erosion control blankets, temporary seeding, slope roughening, others • Sediment Control BMPs—silt fence, check dams, sediment basins, lined channels, straw bales, others • Non-storm water BMPs—Equipment decon areas, stockpile management, tracking control, stabilized site entrances, others

  6. A Generic BMP Gameplan

  7. Examples of BMPs—straw mulch

  8. Examples of BMPs—rock check dams

  9. Examples of BMPs—erosion control fabric

  10. Revisiting the Construction BMP Palette Using EPA and Montana Department of Transportation Guidance • http://cfpub.epa.gov/npdes/stormwater/menuofbmps/ • http://www.mdt.mt.gov/research/projects/env/erosion.shtml

  11. MDT Menu of BMPs • Section 3 - Best Management Practices • Section 3a - Soil Stabilization BMPs • Section 3b - Sediment Control BMPs • Section 3c - Wind Erosion Control • Section 3d - Snow Management • Section 3e - Stabilized Construction Entrance/Exit • Section 3f - Water Conservation Practices • Section 3g - Material Delivery and Storage 50 page .pdf, 15 BMPs 41 page .pdf, 11 BMPs 3 page .pdf, 1 BMP 7 page .pdf, 3 BMPs

  12. Developing a site specific strategy • Soil type • Slope steepness • Potential rainfall • Adjacent water resources • Seasonality of work • Construction sequencing • BMP selection, installation, monitoring, maintenance • Emphasis on surface stabilization or sediment control BMPs, or both

  13. Erosion Prediction using the Universal Soil Loss Equation A=RKLSCP • A = Average Annual Soil Loss (tons) • R = Rainfall Amount • K = Soil Erodibility • L = Slope Length • S = Slope steepness • C = Cover Factor • P = Conservation Practices RUSLE Computer Program: http://www.techtransfer.osmre.gov/NTTMainSite/Library/hbmanual/rusle.htm

  14. Rainfall Factor (R) • Rainfall intensity and duration • Built in database for rainfall intensity • As rainfall intensity increases, erosion increases • As rainfall duration increases, erosion increases A=RKLSCP

  15. NRCS TR-55 Storm Types

  16. Soil Erodibility Factor (K) • Relates to soil texture and rock content • Silty soils are typically most erodible • Sandy soils have better infiltration, larger particles • Clay soils have better cohesion A=RKLSCP

  17. Slope Factors • L = Length of Flow Path • Longer flow paths have more erosive power • S = Slope steepness • Steep slopes have higher runoff velocities A=RKLSCP

  18. Cover Management Factor (C) • Erosion rate directly proportional to the amount of vegetation cover protecting the soil surface • Vegetation reduces rainfall impact energy • Vegetation promotes infiltration • Vegetation reduces runoff velocity • Vegetation traps sediment • Have control over this factor A=RKLSCP

  19. Conservation Practices Factor (P) • Manipulation of the soil surface to discourage erosion • Provides slope storage • Surface roughening • Pitting • Implemented on the contour A=RKLSCP

  20. Example 1, Consider a 1 acre area • In an area that receives 12 in of annual precipitation, 1 acre-ft of water is applied to the soil surface annually as rain and snow • 1 acre-ft = 325,000 gallons per acre per year • Therefore a 1 inch rainstorm = 27,000 gal water • 27,000 gal water or 112 tons of water • Question: How much erosion will occur? • Answer: It all depends

  21. Example 2, consider 1 acre of bare soil • Apply 1 in of rain over a 1-hour period • Sandy loam texture • 90% infiltration, 3,000 gal runoff • Silt loam texture • 40% infiltration, 16,000 gal runoff • Clay loam texture • 20% infiltration, 22,000 gal runoff

  22. Model example This example uses an 18.2 acre watershed and the Colstrip 16-18 climate record

  23. Bare soil, no BMPs

  24. Bare soil, no BMPs

  25. Bare soil, no BMPs

  26. BMP= soil rough, broadcast seeded, woodfiber mulch

  27. BMP= soil rough, broadcast seeded, woodfiber mulch

  28. Erosion Control by Dense Grass

  29. Sediment Yield Example

  30. Runoff Curve Numbers • NRCS National Engineering Handbook • Runoff Curve Number • Dependent on soil characteristics and cover • Simpler planning tool for runoff outcome expressing the percentage of rainfall that is likely to runoff • Four soil types with increasing runoff potential compared to typical land uses

  31. Runoff Coefficients

  32. Example • How much runoff would result from a 0.4 inch rainstorm falling on a 2.5 acre construction site with the following characteristics: • Type B soil • 25% undisturbed pasture • 17% paved parking • 10% gravel roads • 48% newly graded areas

  33. Calculation • 0.41 inch rainstorm across 2.5 acres= • 0.41”/12 x 2.5 acres x 43,560 ft2 x 7.48 gal/ft3= 27,831 gallons of rainfall on site • 22, 734 gallons runoff • 5,096 gallons infiltration

  34. Review • Erosion is a naturally occurring process that is greatly accelerated on construction sites when bare soil is exposed • There are many types of BMPs that may be used to control erosion (Internet guides) • Erosion can be predicted by computer models and vast amounts of sediment can be eroded from small areas

  35. How do we control erosion? • Limit the extent of disturbance • Rapidly reestablish stabilizing plant cover • Promote infiltration and prevent runoff • Provide for capture of sediment if runoff occurs

  36. Mass Balance • Bozeman receives ~19 inches of annual precipitation, or 516,000 gallons of water per acre per year • What happens to all that water? • Mass balance is required: P-ET+D±RO=∆S P=Precipitation ET=Evapotranspiration D=Drainage RO=Run-off/Run-on ∆S=Change is soil storage

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