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Kerby's Equation
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Kirpich's Equation
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)
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Kerby's Equation
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Kirpich's Equation