Parameters

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.

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

 t= time of concentration (mins)