This equation is declared in Hydraulic Engineering Circular No. 22 (HEC-22) Urban Drainage Design Manual for computing the travel time of sheet flow.
| Tc |
Time of concentration (min) |
| L |
Flow length (ft) |
| i |
Rainfall intensity (in/hr) |
| S |
Slope (ft/ft) |
| n |
Manning's Roughness |
