Flow Length

The length of the Sheet flow path.

Land Slope

The slope of the hydraulic grade line.

Event Intensity

The intensity of the rainfall.

Catchment Retardance

Retardance coefficient.



L  = Length of overland flow (ft)

S = Average catchment slope (ft/ft)

i  = Rainfall Intensity (in/hr)

Cr  = Retardance Coefficient

Very smooth asphalt 0.007

Tar and sand pavement 0.0075

Concrete 0.012

Tar and gravel pavement 0.017

Short grass 0.046

Dense grass 0.06

 t= time of concentration (mins)