SCS Equation
This is the classic SCS velocity equation for sheet flow.
Where
- L is the distance to the hydraulically most remote point
- V is an overland flow velocity for specific type of ground surface
The following equations are taken from the SCS velocity chart.
Where s is average slope in direction of flow and a & b are coefficients. The coefficients are:
| Description | a | b |
|---|
| Forest and fallow | 2.5 | 0.5 |
|---|
| Minimum tillage cultivation | 4.7 | 0.5 |
|---|
| Short pasture and lawn | 7.0 | 0.5 |
|---|
| nearly bare ground | 10.1 | 0.5 |
|---|
| Grassed waterway | 15.0 | 0.5 |
|---|
| Paved surface | 20.0 | 0.5 |
|---|
The following figure is representative of the equations given above. The Figure was taken
from Modern Sewer Design, 1995 and includes additional land use types.
Figure 4: Average Velocities for Estimating Travel Time for Overland Flow.