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.
| Surface | Runoff Coefficient |
|---|---|
| Forested | 0.05 - 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 |