Parameters
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 Roughness - Horton’s Roughness value.
Calculation
where:
L = Length of overland flow (m)
S = Average catchment slope (m/m)
i = Rainfall Intensity (mm/hr)
n = Surface roughness (similar but not identical to Manning’s n)
Concrete or Asphalt 0.010 - 0.013
Bare Sand 0.010 - 0.016
Graveled Surface 0.012 - 0.030
Bare Clay-Loam Soil (eroded) 0.012 - 0.033
Sparse Vegetation 0.053 - 0.130
Short Grass Prairie 0.100 - 0.200
Lawns 0.170 - 0.480
tc = time of concentration (hrs)