Parameters

Flow Length - The length of the Sheet flow path.

Land Slope - The slope of the hydraulic grade line.

Catchment Roughness - Horton’s Roughness value.

Calculation



where:

 B = Const (107 metric)

 S = Average catchment slope (m/m)

 L  = Length of overland flow (m)

 n  = Horton's roughness (similar but not identical to Manning’s n)

 Paved 0.015

 Bare Soil .0275

 Poorly Grassed .035

 Average Grass .045

Dense grass 0.06

  t= time of concentration (mins)