Parameters
Flow Length – The length of the Sheet flow path.
Land Slope – The slope of the hydraulic gradient 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
Gravelled 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)