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)