Soil loss generated from gentle and moderate slopes subject to sheet and rill erosion can be determined using the USLE model. Steep slopes and areas of concentrated flows, such as swales, cannot be modeled using the USLE methodology, and instead, are subject to prescriptive compliance.

Prescriptive compliance should be established by designing and including appropriate measures in the erosion control plan. Compliance with the soil loss standard can be assumed at prescriptive compliance locations where appropriate measures are used.

Specific areas where prescriptive compliance should be followed are:

• Slopes exceeding 33% (Note difference from DNR guidance of 20%)
• Areas of concentrated flows
  • Swales
  • Pipe outfalls
  • Street grading
• Soil stockpiles
• Utility trench excavations

Once areas identified as needing prescriptive compliance are identified and clearly defined in the plan, appropriate measures need be designed.

For slopes exceeding 33%, the soil loss standard is assumed to be met if all the following measures are followed:

1. Provide stable diversion of off-site runoff around slope.
2. Provide slope interruption devices in accordance with DNR Slope Interruption Standard.
3. Design and implement stabilization measures in accordance with DNR Non-Channel Erosion Mat Standard.
4. Schedule land disturbance activities to limit exposure of bare soil in accordance with Table 1.

Table 1: Maximum length of soil exposure on slopes >33%