Permaculture Earthworks

Swale Calculator

This calculator originally appeared at Permaculture Reflections. A more detailed explanation of the calculator is available there.

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

Distance from the bottom to the top of the hill (m).

Volume of rainfall in large event (mm).

Length of swale (m)

Estimated slope above swale in degrees.

Note: No slopes over 20º for safety and efficacy.

Select estimated percent of runoff.


Swale spacing