Parameters
Flowpath Length – The length of the Sheet flow path.
Land Slope – The slope of the hydraulic gradient line.
Average Runoff Coefficient – The proportion of the rainfall that runs off the area.
Calculation
where:
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)