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 Retardance
Retardance coefficient.
Calculation
Where:
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
tc = time of concentration (mins)
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Bransby Williams Method
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Kerby's Equation