Permaculture Earthworks

Rainfall Runoff Calculator

The volume of runoff is given by the fomula

VRunoff = A × R × C

where A is the area of the catchment in m2,

R is the rainfall in mm, and

C is the runoff coefficient.

Runoff Coefficients
SurfaceRunoff Coefficient
Forested0.05 - 0.25
Sandy (bare)0.20 - 0.40
Sandy (with crop)0.10 - 0.25
Sandy (grass covered, flat to 1.15º)0.05 - 0.10
Sandy (grass covered, 1.15º to 4º)0.10 - 0.15
Sandy (grass covered, 4º+)0.15 - 0.20
Heavy soil (bare)0.30 - 0.60
Heavy soil (with crop)0.20 - 0.50
Heavy soil (grass covered, flat to 1.15º)0.13 - 0.17
Heavy soil (grass covered, 1.15º to 4º)0.18 - 0.22
Heavy soil (grass covered, 4º+)0.25 - 0.35
Input numbers only.
See table below for coefficients.