Erosion Control Toolbox: Duff

Introduction

Duff consists of vegetation removed from the project site that is chipped, stockpiled, and then reapplied to disturbed soil areas after completion of earthwork. Duff does NOT include topsoil - other than soil attached to roots of plants removed by clearing and grubbing operations. Use Local Topsoil to specify the removal, stockpiling and replacement of the organic topsoil layer.

When to Use This Treatment

Typically applied on slopes 1.5:1 (H:V) and flatter. The following application rates are suggested:

• Slopes 1.5:1 (H:V) - 2" maximum thickness
• Slopes 2:1 (H:V) - 3" maximum thickness
• Slopes 3:1 (H:V) - 4" maximum thickness
• Slopes ≤ 4:1 (H:V) - 6" maximum thickness

Benefits

• Improved protection from raindrop splash erosion
• Reduced stormwater runoff volume and velocity
• Improved infiltration rate
• Conserves soil moisture
• Improved soil biology - activity by bacteria, mycorrhizal fungi, nematodes, protozoa, microarthropod and earthworms
• Improved soil nutrient levels and nutrient cycling
• Improved sustainable vegetation coverage

Limitations

• More costly and effective than surficial treatments such as Erosion Control (Hydroseed)
• May increase the cost of earthwork activities
• May require temporary storage space within the project limits to stockpile materials
• Requires removal of noxious weed species prior to harvesting of materials from the project site
• Requires site accessibility by earthwork equipment

How to Specify This Treatment

• Identify duff collection and placement areas on the plans using callouts, bubbles or tables on quantity plan sheets
• Exclude known areas of noxious or invasive weed species from duff collection
• Temporary cover of duff stockpiles is likely not required by stormwater regulations because duff stockpiles are primarily chipped plant material
• If temporary cover of duff stockpiles is required, use Caltrans standard temporary erosion control products and specifications

Specifications

• Refer to Standard Specifications - Section 21 Erosion Control

Plans and Details

• Click here to see examples of how to specify Duff on the project plans

Example of how to specify Duff on the project plans:

Estimate Information

• Use Bid Item Codes:
  • 210120 Duff (SQFT)
  • 210121 Duff (ACRE)

References

• Caltrans Stormwater Quality Handbook - Project Planning and Design Guide, See Appendix A, Section A.5 Slope/Surface Protection Systems (PDF)
• David Steinfield, Scott Riley, Kim Wilkinson, Thomas D. Landis, Lee Riley, et al. 2017. "Roadside Revegetation, An Integrated Approach to Establishing Native Plants and Pollinator Habitat"

Updated: February 8, 2019