Flowpath Length - The length of the Sheet flow path.
Land Slope - The slope of the hydraulic grade line.
Average Runoff Coefficient - The proportion of the rainfall that runs off of the area.
L = Length of overland flow (ft)
A = Catchment area (ha)
S = Slope (%)
C = Runoff coefficient (0 - 1)
Business district 0.70 - 0.95
Single family residential 0.30 - 0.50
Asphalt/Concrete 0.70 - 0.95
Sandy soil lawn 0.05 - 0.20
Heavy soil lawn 0.13 - 0.35
Brick 0.70 - 0.85
tc = time of concentration (mins)