Discharges eligible for Rainfall Erosivity Waiver must occur during periods when the rainfall erosivity factor is less than what value?

• A. 3
• B. 5
• C. 7
• D. 10

Answer: (B)

Discharges eligible for a Rainfall Erosivity Waiver occur only during periods when the rainfall erosivity factor is below five. The rainfall erosivity factor, part of the USLE/RUSLE framework, represents the potential of rainfall to cause erosion by combining rainfall intensity and amount for a storm. When this erosivity is low, the energy available to mobilize sediment is minimal, so regulatory agencies allow these small events to bypass certain permit requirements. Thus the threshold is five, and any event with a rainfall erosivity below five qualifies.