Storm-Water Runoff Coefficients vs. Surface

Storm-water runoff coefficients for various surfaces. Reference table showing typical runoff coefficient ranges for different surface types used in stormwater management calculations.

SurfaceRunoff Coefficient
Gardens, lawns, parks0.05 - 0.25
Pavements, inferior block0.40 - 0.50
Pavements, stone or brick0.75 - 0.80
Pavements, asphalt0.85 - 0.90
Roads, gravel0.15 - 0.30
Roadways, macadamized0.25 - 0.60
Roofs0.70 - 0.95
Walks, gravel0.15 - 0.30

Usage

Storm-water runoff coefficients are used to estimate the volume of runoff generated from a given rainfall event. The coefficient varies based on the surface type and its permeability.

Key Points:

  • Lower coefficients (lawns, gardens) indicate high infiltration and less runoff
  • Higher coefficients (asphalt, roofs) indicate low infiltration and more runoff
  • Use these values in the rational method formula: Q = C × I × A
    • Q = Peak runoff (m³/s or similar)
    • C = Runoff coefficient
    • I = Rainfall intensity
    • A = Drainage area