Parameters
Flow Length – The length of the Sheet flow path.
Land Slope – The slope of the hydraulic gradient line.
Catchment Roughness – Horton’s Roughness value.
Calculation
where:
B = Const (107 metric)
S = Average catchment slope (%)
L = Length of overland flow (m)
n = Horton's roughness (similar but not identical to Manning’s n)
Paved 0.015
Bare Soil .0275
Poorly Grassed .035
Average Grass .045
Dense grass 0.06
tc = time of concentration (mins)